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Fiber Optics - Science topic

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The fiber optic interferometer has effectively proven that Special Relativity is incorrect! The propagation of light requires the ether, and the ether is completely dragged by the Earth. We hope that our research will bring new perspectives to our peers and actively promote the research and application of optical theories.
Special Relativity has been erroneously in existence for 100 years, starting from MMX and ending at Sagnac. Although this is difficult to accept, we must confront it.
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I believe that Fizeau's experiment is the key to the universe.
Einstein's special theory of relativity provides an approximate proof under the restriction "v<<c". When v cannot be ignored, the proof based on SR is no longer valid.
We have given a proof that does not require any restrictions.
SR starts with MMX and ends with Sagnac.
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The spot diameter of the signal light is 1.3mm, and the collimating lens is a flat convex lens with a focal length of 11mm. The spot is measured by a spot quality analyzer, and the spot is measured 10cm away from the collimator. It is found that the spot is concentric circle type and the spot diameter is about 15μm after the collimating lens is focused. The large-mode optical fiber is liekki passive 30/250 dc pm with core NA of 0.07. Cut both ends of the optical fiber by 8°.
In the experiment, the collimated light beam is deflected through the half-wave plate and PBS, and then the optical fiber axis is used after passing through the second half-wave plate. The passive fiber is placed on the five-dimensional adjusting frame, and the output end of the passive fiber is collimated through a flat-convex lens with a focal length of 15mm. The output light spot can obviously see the panda eye spot, and there is no obvious bright spot in the center of the light spot, indicating that most of the signal light has entered the cladding, and the extinction ratio is only 1dB.
I have three questions:
1. If the signal is a fundamental mode Gaussian beam (actually a concentric ring type), it can be fully coupled into the core according to the formula, but the coupling effect is very poor at present, why?
2. How to measure the result of coupling? Is the output light spot periphery has entered the envelope of the diaphragm filter, and then measure the coupling efficiency, so that the extinction ratio is not taken into account. The goal of coupling is to get as much signal light into the core as possible with high coupling efficiency while maintaining a high extinction ratio for the output. The current experiments are sometimes more efficient, but the extinction ratio is worse.
3. If the passive fiber is replaced by a gain fiber, model liekki y1200 30/250 dc pm, how should the coupling result be measured? At this time, the signal light will have higher absorption in the core and less absorption in the cladding, and the coupling efficiency seems to be inappropriate.
I hope you can answer. If there are skills and experiences about spatial optical coupling into large mode field polarization-maintaining fibers, I also hope to share them.
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Oluşan halkalardan kuvvetli olan halka üzerinde işlem yapılır. Çok sayıda ve gereksiz halka oluşmasını önlemek için fiber optik kaynağın gücü ayarlanmalı veya başka bir kaynak kullanılmalı.
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I'm having a bubbling error while splicing 100/350 um optical fiber (core/cladding) on ​​the Fujikura FSM100P+. I have tried some ways such as changing Prefuse power and Prefuse time but to no avail. Is there any way to handle this error? I put specific images in the file below.
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Malzemenin özelliği değişmiş olur.
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a) Design a scalable and robust network architecture that can handle the increasing data traffic and support various communication technologies.
b) Recommend suitable transmission technologies, such as fiber optics, microwave of satellite, based on factors like bandwidth requirements, distance coverage and reliability.
c) Incorporate robust security measures to protect the network against cyber threats and ensure high reliability through redundancy and backup systems.
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Arun Yadav Current solutions to achieve flexible, secure, scalable, highly available and economical networks are based on SDN technology and in the case of distant multisite links, SDN-WAN with layer 2 Overlay technologies over the Internet.
These solutions make it possible to have different concurrent Internet access technologies or (WAN) and different operators simultaneously and offer a private layer 2 (Ethernet) plane independent of transport networks and operators. They offer ring redundancy utilities with DualHoming over the internet, bandwidth aggregation and NVF redundancy such as VirtualSwitch.
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Hi all,
Recently I've been setting up Doric's ilFMC4 (3rd gen) cube for fiber photometry experiments. It says that in the cube itself there is an isobestic excitation (IE) port, a regular excitation (E) port of our wavelength needed, and a fluorescence (F) port that has a built in detector and amplifier. I had wired up the cube to a NI DAQ and everything was working fine two days ago. I removed the BNC cables connecting the E and F ports to the DAQ in order to use an oscilloscope to test for AC/DC current (maybe not the best idea?).
When I reconnected them and tested the system, I found that I had no light coming out of the the fiber optic patch cord that is connected to my sample port, where it's supposed to shine from. Usually I get about 40-50uW from the end of that cable that then goes into a fiber optic rotary joint (at this point I will get about 30-40uW) that is then used to shine light onto a mouse's implanted fiber (this final output has about 25-30uW of light at max). I could not get light to come out of even the first step, where it would usually be about 40-50uW.
I maxed out the LEDs to see if I got anything, and it looks like only the IE might be on. I saw absolutely no blue light at all. Any ideas what could have gone wrong? The cube was turned off between two days ago and when I switched it on today, and the only thing I fiddled around with was the E and F BNC cables to attempt to measure voltage on the oscilloscope. It runs on a power cord, not battery.
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Ortama ölçüm cihazı yerleştirip kayıplar ölçülmelidir. Ortamda radyasyon olabilir veya kızılötesi ışın yaymış olabilir.
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Dear community members,
I need to study the fluorescence of certain analytes in an aqueous solution. Currently, I am investigating fluorescence in a physiological solution. To conduct this study, I am using an Avantes spectrophotometer.
My goal is to obtain calibration curves for specific analytes in water at different concentrations.
The experimental setup consists of a peristaltic pump drawing the aqueous solution from a beaker containing the analyte. The solution flows through a plastic tubing. A small section of the plastic tubing consists of a circular plastic cuvette housed inside a light-shielded box. Inside this box, there are two LEDs and the entrance of the optical fiber that captures the light from the LEDs and the fluorescence of the solution excited by the LED light. Once crossed the box containing the LEDs, the liquid through the plastic tube returns to the beaker where the solution is recirculated for the experiment.
As mentioned, there is an optical fiber that captures the light from the LEDs and the fluorescence of the analytes dissolved in the water. The captured light travels through the fiber and goes into the box where the conversion of the light signal to an electrical signal takes place, along with all subsequent electronic processing. The spectrophotometer is connected via Ethernet to a Raspberry Pi, and I see the software interface on the screen to manage the spectrophotometer parameters. We have two LEDs: LED 1 emits light at 445 nm, and LED 2 emits light at 340 nm. One analyte absorbs at 445 nm and emits fluorescence between 500 and 600 nm, with a peak at 523 nm. Another analyte absorbs at 340 nm and emits fluorescence between 400 nm and 600 nm with a peak at 461 nm.
Now that I have explained the operation, let me describe the optical problem I am encountering.
In short, I observe a problem of "drift" in the light intensity detected by the light-to-electric signal converter. Let me explain it better. The LEDs (unless proven otherwise) always absorb the same amount of current (the voltage across the resistor is always the same over time, and they operate in the linear region), so they always emit the same light intensity. I observe that depending on how I bend the optical fiber and how it is touched and moved, the optical fiber affects the detected light signal, accentuating or attenuating a constant increase in detected light. If the optical fiber remains bent with very pronounced curves, I observe the drift phenomenon, i.e., a weak but constant linear increase over time in the light intensity of the LEDs or the fluorescence of the analytes, as shown in the plot attached. Let me explain it better. If the fluorescence peak of an analyte at 523 nm is, for example, 250 counts at a certain concentration, if no additional concentration of the analyte is added, and the circulating solution is always the same, then the fluorescence of the analyte at that constant concentration should remain constant. Instead, I observe a linear, weak but persistent increase in the fluorescence of the analytes at all emission wavelengths. So, if at time t, I observe fluorescence at 523 nm equal to 250 counts, after, for example, t + Dt, now the entire spectrum has grown, and, for example, the peak is at 1000 counts. Obviously, this "drift" in light intensity is not due to the LEDs because I believe their light intensity remains constant over time since the current they receive remains the same. At most, the LED intensity should decrease over time. It is not due to the auto-fluorescence of the analyte from ambient light because this phenomenon is observed even when the room is completely dark. There are no chemical reactions or degradation of the analytes (I would observe a decrease in fluorescence, not an increase because the degradation products of these substances do not absorb at 445 or 340 nm). Also, this positive drift phenomenon is observed even with plain water or air. It is not due to problems with the light-to-electric signal conversion electronics or due to bugs present in the source code.
I attribute it to the optical fiber, which, if it is straight, this problem is attenuated, but if it is very bent, this effect of increasing the detected light manifests. Attached, you will also find photo and plot files showing the abnormal trend over time of the fluorescence of the analytes or the light captured by the LEDs. I do not believe this anomalous trend depends on the light source.
I'm using a FT600EMT - 0.39 NA, Ø600 µm Core Multimode Optical Fiber
In your opinion, what could this uncommon phenomenon in the optical fiber be due to? And how could it be resolved?
I would appreciate any suggestions. Thank you for your patience and the time you've taken to read my question.
Best regards,
Lorenzo
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Dear.
the fakt, that the electronic board does not overheat does not mean that there is no temperature dependence with respect to the LEDs.
The temperature dependence may be due to 2 effects
a) change of intensity and intensity distribution as Nikolay Pavlov meant,
b) change of light coupling into the fiber port due to temperature dependent relative mechanical movement of fiber and fiber inputport due to thermal expansion...
So in consequence: fixing the fibers and waiting for thermal equilibrium.
I admit, that waiting for that equilibrium is a boring job. Once before I were participating in an x-ray experiment, the X-ray source of which achieved a stable intensity output at about 1,5 hours after swithing on...
Best regards
G.M.
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optical crystal fibers
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To me, the best software for designing photonic crystal fiber is "COMSOL". Also, you can try Lumerical as it is faster and more user-friendly.
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In one of our fiber photometry rigs, there is a pigtailed rotary joint connected to an FC-FC mating adapter (flange 11mm) that is then connected to our fiber optic patch cord. The problem is, the light transmission out of the pigtail is around 90 uW, and the adapter is pretty much the same, but then when we measure light transmission out of the fiber optic patch cord its around 20-30 uW. Is there any way to better optimize this region to get a higher light output?
Thanks!
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Assuming that you have matched NA's, core diameters, fibers (polarization characteristics, for example) and have compatible end-faces (angled/angled or straight/straight), in other words, that you have the right fibers and connectors, then you might suffer the problem that plagues all fiber connections -- dirt stuck to one of the end-faces or damage to one or more end-faces. You can check under a low-powered microscope. (Please take no offense at this low-tech suggestion -- it happens in all photonics labs.)
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Is the attenuation of light intensity at the outgoing end of a fiber related to the angle of the polarization plane after linearly polarized light has propagated within a single-mode fiber?
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After linearly polarized light is emitted in a single-mode fiber, the attenuation of light intensity at the output end of the fiber is related to the angle of the polarization plane. This phenomenon is related to the structure of the fiber and how polarization is affected by the direction of light travel.
Light in fiber optics typically has two fundamental planes of polarization: light linearly polarized with respect to the x and y axes. This polarization orientation can change along the fiber if the polarization plane of the incident light changes with the internal structure of the fiber or external factors that cause it to bend as it travels along the fiber.
As a result, the light intensity at the output end of the fiber can vary along the fiber with the polarization plane of the incident light, and this change can cause light attenuation at the output. This phenomenon is a factor that must be taken into account when designing and implementing fiber optics and must be managed correctly.
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There are different approaches to diffuse reflectance modeling, most of them based on the solution of the radiative transport equation by the diffusion-based approximation. However, a set of fiber optic probes measure only a part of the diffuse reflectance leaving the tissue surface, and therefore there is inherent scale invariance in the measurement.
Then, how could I consider the numerical aperture and the refractive index of the fibers to remove scale invariance in the measurements?
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Dağınık yansıma yarıçapla ters orantılıdır. Kaynağa yakın olan merceğin ışığı dağıtma oranı daha fazladır. En uzak merceğe yaklaştıkça bu oran azalır. Işık ışınları yakın olunca simetri ekseninde daha dağınık uzak olunca bir eksende toplanmaya başlar. Bu durumda en yakındaki mercek ince kenarlı mercek özelliği gösterirken, en uzaktaki mercek kalın kenarlı mercek özelliği gösterir. Bu özellik ve kayma simetrik ve asimetrik özelliklerden kaynaklanır.
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By converting AC to DC then to light signals,then is it possible to transmit the light signals through optic fibre cables?  
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The Tesla principle can be used. In stead of wireless power transmission, that power which is converted in to electromagnetic field, can be oriented in to the Modulator (transform in to electric field in the modulator), than transmitted through the optical cable to the destination and demodulated and transformed in to adequate used power.
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I am recently new in trying my hand at fiber photometry, but recently implanted fiber optics as well as viruses to monitor both dopamine and serotonin neurotransmission. I successfully implanted two fiber optics, injected the virus bilaterally, and added screws in the skull to reinforce their placement. The screws were placed deep enough to hold in the skull, but not so deep as to be flush against the surface of the skull. Three screws were put into place (one approximately 5 mm posterior from the injections), two screws ~1 mm anterior from the injections. After implanting the screws and optics, I briefly scoured the skull with a drill bit to provide a rough surface and applied the dental cement. These dental cement caps were secure 2 months following surgeries until I attempted to record from these animals.
My problem is, when I went to attach the optic cables to the implanted fibers, the caps popped off. It was also difficult to secure the plastic sleeves that are designed to cover half of the optic cable, and half of the fiber optic to prevent bleed-through of light onto the implanted optics. (I'm wondering if an excess build-up of dental cement surrounding the fiber optic made this difficult). However, the caps still should not have popped off as I attempted to attach these cables.
Does anyone have any advice for successfully ensuring that these "caps" remain attached to keep the fibers in place while attaching the optics?
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Hi Kimberley,
This is a common problem with implanting optic fibres. I’ll try to give some possible ideas for troubleshooting, and it’s great how much info you‘ve provided.
1. On a general note, this does happen sometimes, regardless of how experienced you are, so you need to do more than 2 animals.
2. Why did you leave them 2 months? The longer you leave them, the more likely they will loosen. If you’re using AAV’s to insert you sensors, they usually have good expression after a couple of weeks (in my experience).
3. It’s good that you scoured the surface with a drill bit. I would do that before putting screws in so that you can be sure to clear the entire surface. And be thorough, this is an important step. FYI I only ever put in a single screw, and have minimal problems. Also, some of my colleagues would dab superglue round the edge of the cement to “seal” the edge. I didn’t do that, but it‘s worth a try if you’re still having issues.
4. What kind of cement did you use? I had real issues with the old powdered dental cement we had. Then we switched to a more modern light-cured cement and my problems all but disappeared.
5. What fibres did you use? I had real issues with ceramic fibres gripping the mating sleeve too tight and being ripped out. I would suggest using steel cannulae.
I hope some of these suggestions might be useful. Feel free to message me if you want to discuss further.
Best of luck!
Nic
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Now i'm researching the size of photon....The silicon atoms size typical is 1.2 angstrom. is it possible can replaced the hardware by transfer current within transistor using photon instead of silicon atoms, If the photon size much smaller than silicon atom, it can minimize the IC feature size.
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I found the photon cross-section to be [ alpha/(2 pi ^2) lambda^2]
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Generally, in coupler when light goes through one input port of Y coupler it divides into two output. But my doubt is that , will they produce entangled photons as well in the output.
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If a single photon were incident on an ideal 50/50 Y coupler, the output would be 1/sqrt(2)*[|0>|1> +|1>|0>] where the first ket indicates the number of photons in the upper branch and the second ket represents the lower branch. This is a spatially entangled Bell state.
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I want to proceed the experiment using optical fiber. However, there is a problem. In one of the processes, the temperature reaches almost 600 degrees(Celsius). I know that the glass transition temperature of the soda lime glass is around 600 degrees.
In addition, the commercial glass optical fiber is consisting of 3 parts, core(pure silica) cladding(doped silica),and buffer layer(polyimide). The company says that this fiber can endure even at 400 degrees because of the polyimide, which is heat-resisting polymer. But, I think that it can endure up to 600 degrees if there is no polymer. Is it true? I will use the fiber as just a substrate, so I don't need any other layer except the core.
After I etch the polymer, what is the limit temperature for the glass optical fiber? 
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the commercial glass optical fiber is comsist of core and cladding, core is doped with GeO2, cladding is pure solica. the pure silica can be used under 1600C but the dopant can't. If you want to monitor the temperature base on the optical fiber, I suggest you use FBG sensor. After writing FBG on the commercial optical fiber and then you can regenerate the FBG, then the FBG sensor can be used under 1000C. There is another option is to use the PCF which is made from pure silica.
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It is generally accepted that the fringe shift produced in a fiber optic Sagnac interferometer is independent of the refractive index of the fiber. In fact, the waveguide aspect of the fiber is not of any consequence, the counter propagating beams may propagate in any dielectric medium. Does anybody know a physical explanation for this effect, other than the special relativistic (M von Laue: On the Experiment of F. Harress) or general relativistic (Post, E.J: Sagnac Effect) explanations? It has been reported that(Wang, R: Modified Sagnac experiment for measuring travel-time difference between counter-propagating light beams in a uniformly moving fiber) the Sagnac effect is produced even when the moving path is effectively a straight line. This later configuration approximates an inertial frame, and with in an inertial frame one should not be able to measure one's state of motion!
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Just wanted to share you with some observations from an amateur's viewpoint.
My understanding about the LAW of conservation of angular momentum is ... it manifests itself that "ROTATION" is an "ABSOLUTE" motion (e.g. the spinning of any fermions) with respect to anyone on the inertial reference frames.
The fringe differences in FOG (Fiber Optic Gyro or Sagnac Interferometer) is indeed dependent of the refractive index of the fiber. A larger refractive index will cause the larger fringe phase shift. While having normalized light speed and wavelength in accordance the refractive index of the media, we shall still get the same and a designated angular (rotation) speed of that particular "encircled" system.
Sagnac effect is produced even when "PART" of the moving path is effectively a straight line along with a "encircled" system. Once considering a "encircled" system, such a "Partial-linear" ROG configuration CANNOT approximate with any inertial frames.
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For applications in visible and NIR ranges.
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Dear Ricardo,
You can contact the supplier they can provide the design according to your requirements. Here you have the flexibility to select the fiber features (core diameter, NA, type of fibers, and so on).
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I am heating a tube to a very high temperature. i want to collect thermal radiation from the internal tube surface through a small hole I made. i have a fiber optics and various kinds of lens. Can anyone suggest a lens combination/arrangement so that I can collect maximum amount of radiation from the internal tube surface?
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What wavelengths are of interest?
* What's the angular acceptance angle of the sensor?
* Can you support lenses freely some distance from the tube?
* This is all happening in air or a vacuum, right?
I've used ZnSe lenses to focus four micron IR quite nicely in the past.
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There are some interesting challenges for DAS systems in fields of agri-biophotonics and/or biophotonics - from vibration impact studies on the roots of growing plants to sea fauna acoustics monitoring, but researchers usually prefer array of single sensors or quasi-distributed sensors. Or maybe you know the examples with the DAS application? Thank you!
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There were two related talks that presented very promising results at the 2022 DCLDE workshop (see https://www.soest.hawaii.edu/ore/dclde/program/ )
Léa Bouffaut- Listening at the speed of light: baleen whale monitoring using distributed acoustic sensing
William Wilcock- A Community Test of Distributed Acoustic Sensing on the Ocean Observatories Initiative Regional Cabled Array Offshore Central Oregon
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As we know, when we get a type of fiber from a company, we can get a few dispersion parameter D at corresponding wavelengths( lambda).so we can also get the dispersion slope dD/d_lambda.
Then how can we get the value of 4th disperison beta_4 with the value of D and dispersion slope dD/d_lambda?
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i am also comfuse about the beta valume, how can we calculate the beta2, beta 3...
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I am simulating an Octagonal Photonic Crystal Fiber by Comsol. It is desired to extract some properties such as Dispersion, Confinement Loss and Effective Area vs. wavelength. For this purpose, I should obtain the Effective Refractive Index and Field Distribution for the Fundamental Mode. The Structure is a Solid-Core PCF (silica core n=1.45 and air holes n=1).
How I can reach to the Fundamental Mode?
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By means of modeling the solid mono-core optical crystal fibers by Comsol Multiphysics Software.
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I am wondering if it is possible to measure mode-locked laser stability (timing jitter, Noise) with an oscilloscope if the pulse duration is in the femtoseconds regime (lets say 150fs). If so, what type of measurement on an oscilloscope would quantify laser stability. What should be the bandwidth of the photodetector and oscilloscope?
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I think RF Spectrum Analyser is much more suitable and easier for estimating time jitter. The Allan deviation and phase noise could be measured by RF spectrum analyser, and these two parameters are always used to analyze the short/long time period stability of modelocked lasers. I recommend you to read this paper, maybe it will help you.(10 GHz regeneratively mode-locked thulium fiber laser with a stabilized repetition rate)
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Hi, I am looking forward for collaborators (academic and research work) who are interested to work in the following area:
Quantum Attacks
Quantum Computing
Quantum Artificial Intelligence
Post-quantum Cryptography
Internet of Drones
Blockchain and Quantum Computing
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Hello Sir,
I am interested in the suggested topics. My domain is cloud computing security using cryptographic techniques. I have few publications in this domain. Please have a look.
Regards
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Can anyone recommend any papers/studies regarding the relationship of the core diameter of photonic bandgap (PBG) and/or inhibited coupling (IC)/Kagome fibers and signal propagation? I cannot seem to find a discussion in comparing core sizes and efficacy in transmission, although I imagine there must be some influence.
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I think you are referring to hollow-core fibers here. Regardless of the exact structure, researchers in this field typically heavily rely on numerical simulations, mostly with finite-element methods. Such simulations are certainly useful to compute the guiding properties of a given fiber, but it is difficult to understand the physics or the scaling behavior from these simulations. For your question, it is probably best to look into the pre-computer literature, namely, the Marcatili & Schmeltzer method. There is an excellent paper by Morten Bache about this, and he calls it the poor man's method, but I think this may actually sometimes more useful than the rich man's comsol: https://arxiv.org/pdf/1806.10416.pdf
I also recommend reading the original Ref. 6. There is a relatively simple equation for the scaling behavior of the losses with diameter.
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How would the spectrometer signal change if the target molecule was well dispersed in a solution and placed on the fiber optic SPR cable VS the target molecule concentrated at a specific region on the fiber optic cable?
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The effect can be very strong. If the concentration change is e.g. aggregation, then not only shielding effect blocks light from reaching molecules inside an aggregate, but also spectra might be changed by interactions between the molecules in the aggregate. In some cases, addition of 0.1% of a solvent which prevents aggregation transforms a clear (for eyes) solution into a deeply colored one, even when no precipitation was seen in the original suspension.
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I've been playing with a code for simulation of FBG properties. Code is using CMT and TMM implemented in matlab. Can anyone tell me why are there those sudden "drops/falls" in calculated dispersion? Am I missing something?
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Unless you are sure that there is a good reason for you to have calculated half the angle, you need to look at whether you need to use the tan2 function. Do you know what the tan2 funtion is? Look it up.
If you just multiply by 2 with no good reason you will get twice the dispersion you should have.
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Can anyone tell what is the reason of these sharp frequency modulation in SPM broadened power spectrum. This is the spectrum of mode-locked laser with 0.4nm initial bandwidth at 1064nm. After amplification to 400mW (in YDF) and propagating through 6m length of PM-980, such spectrum appeared. I am wondering how to get rid of these modulations to enable efficient pulse compression.
Pls see the attached picture.
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As far as I can see, you are showing the spectrum on a log scale, but these oscillations are essentially a hallmark of the SPM, and you can estimate the total accumulated nonlinear phase from the number of the spectral oscillations. This was observed for the first time by Roger Stolen in the 1970s:
Self-phase-modulation in silica optical fibers
R. H. Stolen and Chinlon Lin
Phys. Rev. A 17, 1448 – Published 1 April 1978
A more detailed discussion can be found in the textbook by Govind Agrawal, Nonlinear Fiber Optics. I would estimate the total nonlinear phase in your fiber as about 3.5 \pi.
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Two years ago, during my PhD defense one of the members of the committee asked me what diffuse reflectance is. I said diffuse reflectance is a type of surface reflectance (the other is specular reflectance) whose angle of reflection is independent on the angle of incident radiation. Diffuse reflectance is often observed with radiation incident on a mat or dull surface such as paper, tissues whereas specular reflectance is observed with radiation incident on a polished surface such as a mirror. This is a perfect text book definition
(ref Optical thermal response of laser irradiated tissue, A J Welch or Modern techniques in applied molecular spectroscopy by F. Mirabella)
However, my answer did not sit well with the committee, especially the “surface” part. They argued if diffuse reflectance is a surface reflectance than why diffuse reflectance spectroscopy (DRS) is used to detect tissue abnormality 300-400 micron underneath the surface? They came to agree that diffuse reflectance is “radiation that undergoes scattering and absorption events in tissue and comes back to the surface to be detected by detector”
I disagreed.
Just a few days ago, the same question is asked: what is diffuse reflectance? My answer is the same. Once again, there was lots of confusion.
Today, to put my mind to rest I am posting my explanation here. Again, diffuse reflectance is a type of surface reflectance (nobody can change that definition). The name diffuse reflectance spectroscopy (DRS) itself is quite confusing.
DRS collects not only the diffuse reflectance but also the remission. In clinical application of DRS, remission is frankly much more important because it tells us how light propagates within the tissue, and thus help us draw a picture of tissue components (scatterer, absorber). By the textbook, remission is the process in which light is scattered within the tissue, leaving tissue and propagating toward the detector. Therefore, remission is the result of complicated light propagation within the tissue.
This is, partially, why fiber optics DRS with fiber tip in contact with tissue plays an important role. The math is complicated. Principally, contact point of measurement DRS reduces chances to collect surface reflectance and increases chance to collect remission. DRS gave out-standing spectral resolution but not so much spatial information. So, there comes bundle of fibers in an optical probe that likely give enough spatial information to detect tumor margin.
Two tissue samples with different optical properties but same surface structure will have similar diffuse reflectance but different remission. As the results, different DRS signal is collected.
Next topic: Raw fluorescence signal that was not corrected for tissue attenuation is useless.
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Thank you for good discussion, is there any paper pointing out these information you mentioned V. N. Du Le ?
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We are trying to run fiber photometry experiments for long time scales, but we get these sinusoidal artifacts that come up. We think they may be caused by twisting of the fiber optic subject cable. We tried using a rotatory joint to alleviate this, but the attenuation it causes is way too high (it attenuates the light coming back from the animal). Another rotatory joint we tried causes too much motion artifact and defeats the purpose of using it. Does anyone know a solution to minimize this type of artifact, or know of a good rotatory joint for photometry?
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you might explain a bit more in detail the set up and the animal(s) you are dealing with.
Such a curve reminds me on results when I dealt with fiber optic heartbeat and respiration motion detection.
What about respriation motion which causes 'periodic' coupling losses?
Mice and rabbits as animals?
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What is the reason of the received optical signal to be slimmed down in multi-mode fiber?
I have 4 km multi-mode fiber
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Dear Egalon,
Thank you for your reply
I have attached a picture of transmitting and receiving optical signal in MMF optical fiber.
There is no spectral shift
Best regards
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Hello everyone, I would like some collective brainstorming on my setup.
I have a laser providing a collimated, randomly polarized beam at 1064 nm and I run it at about 150 mW of power. I focus the beam with an aspheric lens onto the SMF-28-100 fiber. The fiber is fixed in an FC/PC holder mounted on an XYZ translational stage with 2 rotational knobs. I struggle to obtain a stable Gaussian output.
1. Are there any fibers with cut-off wavelength close to 1064 nm? It looks like at least Throlabs and Newport have cut-off wavelengths at 970-980 nm and then at 1300-1500 nm.
2. How much effect would alignment have? The stage is a little bit unstable and may move when I turn one of the knob, so I have to use the rotational knobs until the power is maximized. I am even thinking of ordering a custom metal holder to mount both lens and the FC/PC connector ring on it.
3. The fiber is about 1 m long and mostly covered with the acrylate coating so I don't think I should worry about the cladding modes.
4. How efficient would be folding the fiber into '8's to achieve mode mixing and more of a flat beam profile?
Thank you in advance!
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Elena Renzhiglova - I agree that LP01 will couple from a Gaussian beam with highest efficiency into the available modes. In fact, if the beam has a circularly symmetric Gaussian profile, there will be minimal excitation of the LP11 modes when the launch spot is accurately centred onto the fibre core.
My concern was that a small offset of the launch spot would decrease the LP01 power, but would increase the proportion of LP11 modes, so that simply looking at total launch power may not be the most accurate way to assess mode purity.
How did you calculate the V-number? Corning specify a nominal core diameter of 8.2 µm for SM28 Ultra, and a numerical aperture of 0.14 (measured as 1% far field intensity in a 1-D scan). V=3.39 at 1064 nm, so V²/2 = 5.7.
Strictly speaking, we should specify NA in terms of refractive index difference between core and cladding, rather than radiation angle (which varies with wavelength). For their earlier SMF 28e+ fibre, Corning specified nominal relative index difference, Δ=0.0036, so NA=0.124 and V=3 at 1064 nm.
In any case, the formula for the number of bound modes, V²/2, is an approximation which is most useful for larger V. At low V, it is simpler to count the number of modes directly.
  • We have two orthogonally polarised fundamental modes.
  • In addition there are four LP11 modes - two polarisations for each of the sine and cosine azimuthal variants. More accurately, we have TE01, TM01 and 2x HE21 hybrid modes, but in the weakly guided approximation, the LP11 modes are a linear combinations of the 4 vector modes. The LP modes are usually a more convenient description when the launch spot is linearly polarised, or has a uniform elliptical polarisation state.
If we ignore cladding modes, then the theoretical number of bound modes in a step index fibre is 6 for V numbers between 2.405 and 3.832. At shorter wavelengths (V>3.83), the four LP21 (HE31, EH11) modes are also supported.
We can ignore most of this if you decide to use a fibre such as HI1060, which is single mode at 1064 nm. This would be my preferred solution.
I do not anticipate significant cladding mode propagation over 1 m of acrylate coated fibre. As Vincent Lecoeuche suggests, if cladding light is present, then a few loose bends in the fibre should couple to higher order cladding modes so they are more effectively absorbed by the cladding, without perturbing the bound modes (unless they are close to cut-off).
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Hello! Colleagues, what resource do you use to monitor conferences on fiber optics and photonics?
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There's a conference in 2021 that is good when it starts telling you
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BER analyzer parameters meaning.
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The reliability of data transmission characterizes the probability of getting a distortion for the transmitted data bit. This indicator is often referred to as the Bit Error Rate (BER). The BER value for communication channels without additional means of error protection is 10-4 — 10-6, in optical fiber — 10-9. A ber value of 10-4 indicates that on average, one bit is distorted out of 10,000 bits. The q-factor of the receiving system Q is determined from the expression:
Q = GA/TC,
or, in logarithmic form:
Q[dB] = GA[dB] - 10lgTC[x].
It is the q-factor of the receiving system that determines the signal-to-noise ratio (C/N) at the output of the low-noise Converter (LNC or LNB). It is important to note that the final C/N value does not depend on the LNC gain.
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Based on Faraday effect, If a piece of glass is exposed to a magnetic field, it optically activates.As the linearly polarized light passes parallel to the applied magnetic field, the plane of light polarization rotates.
1- can we pass light through fiber optic and fiber optic works as glass?
2- in some sources I see the linearly polarized light should be circularly polarized,because left and right circular polarized light waves have different speeds in magnetic field, I dont know to use linear or circular polarized light?
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Shabnam Jamshidi Please check out the following work:
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In recent research perspective this is very important field. Parity operation is reversal of co-ordinate (x->-x, p->-p)and time reversal operation is reversal of time (x->x,p->-p, i->-i).
But talking about this combined PT-symmetry in any field of science and engineering, what it implies?
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Dear Prof. Samit Kumar Gupta,
In superconductors, a PT symmetry invariance broken state could be the main manifestation of anionic superconductivity. There are not agreements so far on the subject.
Please see this external reference:
Selected Topics in Superconductivity by L. C. Gupta, M. S. Multani
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I was wondering if anyone has looked into the use of Far UVC light as a way of treating Covid-19. Far UVC light has a strong antiviral effect but has minimal effect on mammalian cells compared to UVC light. By use of a Thoracosopy technique a fiber optic Far UVC light source could be introduced into a patients lungs and target the Covid-19 cells. Combining this with Ultraviolet Blood Irradiation (UBI) may be a therapeutic treatment that in some critical cases could be applied until such time as a true drug therapy can be applied.
Please let me know your thoughts
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Through a Thoracosopy technique a fiber optic Far UVC light source could be introduced into a patients lungs. This would be done to illuminate the lungs to the Far UVC Light for a brief time period to kill the virus while not killing the lung tissue. Also through UBI the patients blood would be passed through a device that exposes the plasma to Far UVC light before it is reentered into the patients body.
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I'm interested in directing as much light as possible from the LED into the SMA-terminated optical fibre. What sort of adaptor or bushing would I need to be able to connect the LED to the fibre? I am using Osram SFH 4725S for the NIR LED and a lab-grade patch cord from Ocean Optics.
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Unfortunately, the "etendue" of LED's prevents efficient coupling into fibers. A large portion of the light generated is contained in very high angle rays that simply cannot be coupled into the fiber. Optics wont help this case as conservation of irradiance says that as the apparent source size is reduced (demag) the NA is increased. Making the source spot small to match the fiber mode size increase the source NA and ends up not being guided in the fiber. Laser diodes have a much smaller NA in both axis and fiber designs have been tailored (or maybe both) to work with each other.
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Can thin glass (thickness of 50μm or less) creep under high pressure and high temperature (754 mmHg, 80°C or 60°C) over long period of time (e.g. 40 days)? If the pressure on the thin glass is applied by submerging it in heated water (80°C or 60°C)?
If anyone knows about any research paper or literature on this topic, it will be really helpful.
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Strictly speaking, glass will always be subject to creep. However, the whole thing is on a scale. Different kinds of glass have different softening temperatures and, therefore, different creep under given conditions. For example, I would not expect creep from quartz glass under the described conditions, however, such creep is possible for sodium or potassium glasses with a low softening temperature.
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Tight buffered fibers or bare fibers in a loose tube? If loose tube, with or without gel? Does a corrugated steel armor attenuate the accustic energy?
The perimeter length is 40Km and the required spatial resolution is 10 meters. Does the answer depend on the sensing method (e.g. Rayleigh coherent back scattering, Brillouin scattering etc.)?
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Hi, David! Yes, a tight buffer is better. Metal tubes and steel armor degrade the sensitivity of the cable to acoustic vibrations. In addition, the sound propagates along metal along the cable and this must be taken into account. Therefore, it is better to use a dielectric cable with Kevlar filaments and with tight packaging. It is advisable to choose the right materials. If you need to bury the cable, you need to understand that high frequencies are cut off a lot. I think that there is a difference in cable design for different methods.
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For a single mode optical fiber having a step-index refractive index profile, the
relative refractive index difference Δ between the core (refractive index n1 )
and cladding (refractive index n2) is defined as Δ=( n1- n2)/n1.
What happens with the following parameters if Δ increases)s(n2 approaches n1) ?
1.The mode field radius
2The zero dispersion wavelength
3. The cut-off wavelength
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what the value of the clad in optical fiber@
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Hi
Does someone know how we can calculate absorption coefficient in optical fiber at different wavelengths (such as 1117 nm).
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Asavela Sigonya In general, the saturable absorption coefficient in erbium-doped fibres depends on:
  • The absorption cross-section at the wavelength of interest, σ(λ)
  • The erbium-ion concentration and the radial distribution of ions within the core and cladding ρ(r)
  • The mode field distribution of the fibre mode ψ(r, λ)
Absorption coefficient α = ∫∫ ψ2(r,φ) ρ(r,φ) σ r dr dφ / ∫∫ ψ2(r,φ) r dr dφ
where the integrals are with respect to area over the the fibre cross-section, here expressed in cylindrical coordinates (r,φ).
If the Er doping is confined to a cylindrical cross-section, concentric with the core, and doping concentration ρ0 is constant within this region then:
α(λ) = ρ0 σ(λ) Γ(λ)
If the uniformly doped region also coincides with the core of a step-index fibre, then the overlap integral, Γ(λ), is simply the fraction of power within the core. It depends only on the normalised frequency (V-number) of the fibre via the wavelength.
More generally you need to know both dopant profile and mode field distributions.
The erbium cross-section varies with both wavelength and with the composition of the host glass. Alumina-doped silica fibres have a different absorption spectrum to germania-doped fibres. Desurvire (1994) cites peak values for absorption cross-section near 1530 nm of 4.7∙10-25 m2 for Ge-Al doped silica and 8∙10-25 m2 for germania-silica fibres.
Given the overlap integral, average concentration: ρ0 = α(λ) / σ(λ) Γ(λ)
Conversion from number density to ppm-wt is straightforward, given appropriate attention to whether you require ppm-wt Er3+, or ppm-wt Er2O3.
There is a useful discussion in Giles & Desurvire, "Modeling erbium-doped fiber amplifiers", J. Lightwave Tech., vol 9, no 2, p 271, Feb 1991.
More details in "Erbium-doped fiber amplifiers", Emmanuel Desurvire, Wiley, 1994.
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I am trying to build a fiber laser based on multimode interference in SMF-GIMF-SMF (GIMF spliced between two SMFs) leading to saturable absorber phenomena in the design. I am using Er fiber as a gain median and pumping it by 980nm source. I observe Q-switching or sometimes unstable or weak mode-locking. What can I improve or add in this setup to achieve better modelocking.
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Aktham Tashtush Its a ring laser. Thanks for suggestion , I'll definitely consider it.
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Hello, i'm having a project where I must implement ofdm simulation with mmse estimator for the rayleigh channel. Although the estimation seems tolerant, i'm getting no improve with ber, even for simulation of 10000 symbols.
I have attached the paper i'm trying to implement, with the matlab code and some representative figures to see exactly what i'm doing
I can't understand if i'm missing something very important when estimating the channel or when using specific pilot symbols or in somewhere else..
Thanks in advance,
Anastasia
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Hello Tesla;
I have same question.
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To change the path of Vehicle pushed at the speed of light by wavefront of Electromagnetic wave
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I suggest you to study the photonic crystal based structures. Using these structure, one can guide the waves at the desired path or ring.
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What is the function of line traps other than communication?
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If power line carrier communication is used for signal transmission through the power conductor itself then only wave trap is required to filter out the noises.
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I'am a specialist in fiber optic sensor development and already worked in a R&D project to detect and measure bacterial contamination on hospital environment using fiber optic properly modified.
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It is interesting : interractions photons with nuclons (neutrons + protons), what is axion?
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Plastic core fiber optic sensor gives a sensing spectra with y axis variation i.e intensity variation with constant wavelength of 690 nm. Spectral shifting with x axis i.e. wavelength variation is not happening. Do i need to change the fiber or any spectroscopy setting can give x axis variations?
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Hello,
Please go through the article
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I am simulation one fiber optic liquid level sensor where I am taking 1cm long multimode fiber. The cladding of the multimode fiber is removed by chemical etching process. For, measuring the liquid level, some portion of the fiber is immersed in the liquid and the remaining portion in in the air. Thus, the guided mode beam profile in the air-cladding section and that in the fluid-cladding section should be different. So there should be mode conversion loss.
Is there any theoretical formula to calculate such mode conversion loss.
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Iwould like to defined fiber optics in communication systems
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Nice to know that you are about to start in fiber optics in Pspice. Regarding books which might be helpful for your project, I can suggest
Power Electronics Handbook: Devices, Circuits and Applications by M. Rashidi. Another book that may be also useful is Optical Fibers, cables and systems. Hope, it will help you.
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When I cut the optical fiber, due to the large diameter of the fiber, cracks are formed on the surface.
By polishing the fiber, the fiber surface becomes angular.
This phenomenon greatly affects the scattering of photons.
Is there information about the best way to polish high-diameter optical fibers?
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You may also want to try using Hydrofluoric acid. I once got very interesting results with that. But you have to be truly very careful with the acid, particularly if you don't have the necessary equipment such as protection, hood, etc. It is a very dangerous acid in several respects.
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Dear All, I request the experts to provide me with some references about the use of nanotechnology to improve the fiber optics specifications in the Distributed Temperature Sensing DTS for temperature measuring and detection. I wish to study the effect of Nanomaterials (or nanoparticles) on the Raman Scattering in fiber optics ?
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Q-factor= 20*log10(sqrt(2)*(erfcinv(2*(BER))));
I have searched a lot but unfortunately I only found the equation above that calculate the Q from BER ,but the Q will be infinity when the BER is 0. Also,when we need to calculate the Q for each individual subcarrier , the Q will be infinity for some of them.
In addition, is it applicable for all the M-size QAM and all the O-OFDM systems like DDO-OFDM or CO-OFDM?
So,is there any other way to find the Q-factor for optical QAM-OFDM ? may be for the Eb/No or others?
Thanks and best regards ....
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You can use that equation to calculate Q-factor,
But, I want to understand how you got BER=0; this result is experimental!
if Not,you may increase iteration, using Monte Carlo Methods, so, BER will be different from 0, and then you can calculate Q-Factor!
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how to measure DFB-LD frequency deviation per unit drive current change (in mA).
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Hello Abbas,
Vincent's solution is the best way to do this.
Another way you could do this if you don't have access to either a wavemeter or stable reference laser is to scan the laser across an interferometer with a known free spectral range with several peaks in the tuning range. Finding the frequency deviation is then just a matter of counting the number of fringes that go by as you tune the laser, then multiplying by the free spectral range to get frequency change. This solution won't give you the center frequency of the laser, just the relative change. One nice aspect of this approach is that it can be done both slowly or at high rate with a current chirp. At high rate, you can use this approach measure the dynamic response of the laser (ie, see it tune faster/slower during a linear current ramp) and calibrate accordingly.
If you lack an interferometer with a short enough FSR, you can build a Fabry-Perot with two optical half-mirrored flats or wedges and a detector. That way you can make the FSR as short as you like, though you'll need ~1.5 m for a 100 MHz FSR, and alignment will be a fun exercise.
Good Luck,
Aaron
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After amplification in optic fiber amplifier pulse autocorrelation (red line in the attached picture) width  decrease as compared to initial pulse autocorrelation (black line). Fiber amplifier dispertion is normal, pulse chirp is positive. Pulse amplified spectrum width about 12 nm, output averaged power 2 W. What possible reason of pulse width shrinkage ?
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Biao Sun "Is there a trend of the pulse width with the increased power?"
There is a potentially complex interaction between non-linear phase shift and chromatic dispersion.
In the absence of chromatic dispersion or wavelength-selective attenuation, the pulse shape is unchanged by phase modulation.
Kerr effect non-linearity typically broadens the spectrum of an input pulse, so that the pulse width is more sensitive to chromatic dispersion.  One approach to create narrow pulses uses self-phase modulation (SPM) to induce chirp in a smooth un-chirped pulse, and combines this with anomalous dispersion to reduce chirp and compress the pulse.
SPM combined with anomalous dispersion (i.e. phase velocity slower for low optical frequencies than for high frequencies) is responsible for modulation instability.  MI selectively amplifies some envelope perturbations at moderate powers, and leads to chaotic instability and break-up of pulses at high signal powers.
Single channel MI gain is not usually a concern in fibre with normal dispersion.  Spectral broadening can still occur and increase the sensitivity to linear chromatic dispersion, so that pulse broadening or narrowing is more pronounced.
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I need this at wavelength 1550nm and 850nm. I have LED source already, but it is with SMA connector. I tried using SMA/FC converter, but it did not work. 
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Fabio:  Is this to couple into single mode fibre too?  You should have few problems aligning the 1 mm2 LEDs from Thorlabs, M1550L3, M590L3, but coupling efficiency will be very low.
The 31 mW M1550L3 has an approximately Lambertian radiation pattern, with radiance on-axis of order   L ~ 10 mW mm-2 sr-1.
Power coupled into a single mode fibre will depend on the mode field distribution.  We can make a very approximate estimate using the étendue of the core in the geometric optics limit  https://en.wikipedia.org/wiki/Etendue
Core area for standard single mode fibre ~ π a2 where core radius a ~ 0.004 mm.
Numerical aperture of standard single mode fibre NA ~ 0.12
Power coupled from extended Lambertian source ~ L π2a2NA2 ~ 23 nW.
The 590 nm LED has higher output power and a narrower radiation pattern.  On-axis radiance could be 10x higher, but this will be offset in part by the lower étendue (smaller core diameter) of fibre which is single mode at 590 nm.
Hope this helps.
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 How can be use the  CW diode laser  with sample from fiber optics part to obtained laser fiber?
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My dear Yariv Shamir, 
I am very happy for  
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How can I get the waveguide and material dispersion of a step-index single-mode fiber at the operating wavelength if I know its core size and NA? 
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What accuracy do you need?
For material dispersion, you need to make some assumptions about the composition of the fibre core and cladding.
J. W. Fleming, “Material dispersion in lightguide glasses”, Electron. Lett., vol. 14, pp. 326-328, (1978) reports refractive index measurements for pure silica, GeO2, P2O5 and Fluorine-doped glasses.  For a binary glass (SiO2-GeO2) you can estimate the composition by linear interpolation from Fleming's values if you know the core/clad refractive index difference at a particular wavelength, then use his Sellmeier coefficients to calculate the refractive index and its derivative at any other wavelength.  With more than one dopant, if you don't know the ratios, then some guesswork is required.  For the same index difference, material dispersion depends on the exact chemical composition of the glass.
For an ideal step-index fibre there are good analytic approximations for waveguide dispersion in the weakly guiding limit, which apply to typical single mode fibres.  Allan W. Snyder & J. D. Love, “Optical Waveguide Theory”, Chapman Hall, 1983, ISBN 0 412 09950 0, present a decent overview with analytic, graphical and tabular results for step (and other) profiles.
Strictly speaking, you can't simply add the material and waveguide dispersion components together.  The field distribution changes as the normalised frequency (V-number) varies, and there may be second order terms, for instance associated with the change of index difference with wavelength (referred to as profile dispersion).  These effects may be small enough to ignore, but I don't recall how small for typical single mode fibres.  I do know that profile dispersion can be significant for multimode graded index fibre dispersion.
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In order to get highest coupling of the laser and fiber,  who can  promises the simple set up  for this goal?
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I think the simplest way to couple light into a fiber is to use a mating sleeve between a fiber connected to a laser source and another fiber on which we couple this laser. I note that a mating sleeve presents only an insertion loss of 0.3 dB.
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I was thinking about 2 m YB single mode-double clad
HR FBG  100%
OC FBG -Fresnel Loss 4%
Pump Power 6W
Can someone give me a little feedback on this design?
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Dear Ronnie,
You need a bit patience, little more than others. Good Luck!
Faramarz
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...
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The question states no amplifier or repeater. If the intention was to mean "in-line" then this allows the use of Raman scattering to provide end pumped amplification.
Kumar's formula is for a purely loss limited transmission with a direct detection receiver. In practice there may be penalties from dispersion which can be compensated for either optically before the receiver or electrically using coherent receivers (for which Kumar's formula does not apply).
Anwar's answer of 100km is typical for unamplified and uncompensated systems of bit rate around 10Gb/s.
Demonstrations of systems involving end pumping have achieved results of around 400km.
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I need an answer on that question
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Dear Sowedi,
please have a look at the diagram of the link.
This is just the one you look for.
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I am trying to couple NIR light from a high power LED to a multimode optical fiber. Ideally only a few (five) modes would be coupled but I am concerned about how it affects time coherence if compared to original time coherence (from LED). 
The LED is 850nm/30nm and 1W power. 
I am aware of power loss but I expect a few mW in the fiber output.
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Henrique,
I have not studied the Imai & Ohtsuka paper in detail, but it seems to address the reduction of spatial coherence in a fibre excited by a narrow line laser source with high spatial coherence.  Figures 1-3 (page 333-4) show the complex coherence falling after excitation by a laser source with linewidth less than 1 GHz for mode group delay differences of 1 ns.
Compare this with your launch from a surface-emitting LED - which is unlikely to be spatially coherent to begin with, and has a line width of 12 THz.  With a group delay dispersion of 10 ps/m, you will be well to the right of the diagrams after propagating through less than 1 m of 0.1 NA fibre.  This is the region where the effects of mode coupling addressed in the paper can be ignored.
They do not address temporal coherence directly - temporal coherence is inversely proportional to their linewidth δω which is an input parameter for their model.
Their analysis shows that if you launch into few moded fibre from a spatially coherent source, the spatial coherence will be degraded during propagation.
Conversely, if the LP01 and LP11 modes are largely uncorrelated at launch - as expected for excitation by a large area surface-emitting LED - they will remain uncorrelated after transmission through the fibre.
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What is the best way of calculating or measuring the fraction of power from a seed leaser that is coupled into a semiconductor optical amplifier by a series of free space optics? Any help or references to relevant papers is much appreciated. Thanks.
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If you  have a  B. Sc. student and if you like to do research in laser practices with fibers (laser application) it will be my pressure to work supervision together ?
regard
Raad
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currently, I am working with nanosecond pulse laser for material processing. Including the synthesis of Fluorescent nanoparticles for bioimaging (in a medical application). It is one of the emerging fields.
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Hello,
We are looking for large core diameter graded-index silica MMF. Core diameter must be higher than standard 62.5 µm and cladding remaining at standard value of 125 µm. So far, we have found two providers : DrakaElite TM (100/125) and Leoni (85/125). The lengths we need is just a few meters.. Unfortunately Draka sells only 2.2 km minimum and is too expensive for our project. Furthermore they have a strict policy to not send samples.. Leoni they don't have it on stock..
So, is there anybody who use these fibers and could sell us a short piece ? Or maybe anyone knows alternative suppliers for that kind of fiber ?
Looking forward to your feedback.
Cheers,
Miguel
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What are the expressions for the TM02 mode of an step index optical fiber for Z, r and ϕ components?
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thanks
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How do I determine which type of dispersion is important for step index optical fiber if the group index of HE11= group index core material?
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For the HE11 mode, group index is equal to core group index at a specific V-number which is a function of the core-clad index difference.  Snyder & Love "Optical Waveguide Theory" (1983) includes approximations valid in the weakly guided limit in their table 14-3, page 313.  If you know Δ, solve for V.  Then calculate distortion parameter using their formula in the same table, and hence find waveguide component of group velocity dispersion using equation 11-58 on page 229.   Table 14-4 or figure 14-3 may be more convenient if you don't need exact values.
More generally, if you know core and clad materials, core diameter and core-clad index difference, solve the wave equation at your operating wavelength.  Calculate group velocity and dispersion - either by differentiating the propagation constant with respect to optical frequency, or by applying the mode field integrals presented by Snyder & Love in table 11-1 or 13-2.
The group index and dispersion of core and cladding materials can be calculated by interpolating between the compositions measured by Fleming "Material dispersion in waveguide glasses", IEE Electronics Letters, vol 14, no 11, pp 326-328 (1978).  Use Fleming's Sellmeier coefficients to calculate refractive index, group index and dispersion at any wavelength.
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For a single mode optical fiber having Δ= (n1- n2) /n1. What happens with the zero dispersion wavelength if Δ increases?
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This is where the answer changes from "have you tried google", to "it depends".
There are two main contributions to dispersion in single mode fibres. 
  • Material dispersion - which depends on the composition of core and gladding glasses.
  • Waveguide dispersion - which depends on the shape of the refractive index profile and on the relative index difference, Δ.
In a real optical fibre these contributions interact, and other factors such as the wavelength dependence of the relative index difference Δ must be included.
In a step index fibre (as specified in your previous question), and in the absence of material dispersion, waveguide dispersion is a minimum for normalised frequency V0 approximately 3 - just beyond the theoretical frequency for single mode operation (VC = 2.4048).  Group velocity is a minimum at V~3, so pulse delay decreases with increasing frequency further into the multimode region (anomalous dispersion), and delay increases with increasing frequency (normal dispersion) in the single mode region.
In the absence of material dispersion, if you increase Δ, and keep everything else constant, the cut-off wavelength will shift to longer wavelengths, and so will the dispersion zero wavelength:  λ0  = π d sqrt( 2 n1Δ )  /  V0  where V0 ~ 3.
If material dispersion is present, then the result depends on both normalised frequency (V = π d sqrt( 2 n1Δ ) / λ) and on Δ. 
The magnitude of waveguide component of dispersion is proportional to the the product D V Δ, where D is a dimensionless function of V, and is only weakly dependent on Δ (independent of Δ in the weak guidance limit where  Δ tends to zero).
For a step index fibre operating at V=1.9, an 11% increase in Δ will cause a 5% increase in V, and reduce D by a factor 0.79, for a net reduction in waveguide dispersion by 8%.  If the dispersion zero wavelength is in the single mode region it will be shifted to shorter wavelengths.
In contrast, if Δ is increased, but the core size is reduced to keep V-number (and cut-off wavelength) constant, then the magnitude of waveguide dispersion will increase in proportion to Δ.  Zero dispersion wavelength in the single mode region will be shifted to longer wavelengths.
Note that dispersion depends on the second derivative of the propagation constant, and waveguide dispersion is rather sensitive to details of the refractive index profile.  Diffusion of dopants during fibre manufacture makes it difficult to achieve a perfect step index profile, especially for larger values of core refractive index.
More details including results for graded profile single mode fibres in A. W. Snyder & J. D. Love "Optical Waveguide Theory" (1983)  http://www.springer.com/gb/book/9780412099502
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I merely fused two ports of the coupler together.
The coupling ratio is 99:1 and the port configuration is as below.
Besides, all the fibers are single mode fibers, no polarization-maintaining property. The whole optical system is placed into a vibration and thermo-isolator.
What can the reason be causing these non-periodic resonant dips?
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The optical path difference of 1-3 and 1-4-2-3 may be the key.  Eliminating the resonator can also be possible with the path length difference longer than the coherence length.
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Glass optical fiber is not suitable for my application and multimode plastic does not allow for the FBG inscription with required parameters. It can be done only if there are not more than several modes allowed in the fiber and that's why I'm looking for a SM POF or one, at least, close to it.
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Paradigm optics makes such fiber and may even have some in stock.  Check out http://www.paradigmoptics.com/pof/pof.html
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Nowadays, the structures of axial component are not enough to design all kinds of balance to meet different wind tunnel aerodynamic tests.
And some new strain sensors are used in balance, for example, fiber optic strain gage and semiconductor strain gage are gradually applied to strain balance.
So new concepts  need to be used in the design of axial component. 
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Yes!
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I winded a few meters of optical fibers on a PZT tube which is driven by a signal generator, then made a fiber optical resonator with direction coupler. The source which I used is a 1550nm laser and the detecor is made of InGaAs, the signal is demonstrated on a oscilloscope.
What I observed is that the resonant curve on the oscilloscope is swinging, which means the resonant dip is drifting during the modulation process.
I wonder whether there's something wrong with my PZT tube or the phenomenon is normal while modulating with PZT. If it's normal, how should I remove or suppress the drift of resonant dip?
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