Optical Fibers - Science topic

Regards,

Sorry I can't help you but I don't have that information. I work with traditional materials.

Dear Muhamed A. Sewidan ,

each type of fiber has its own transmission window characteristics according to the material composition of the fibre;

See for example Fig. 6 of:

Even at the spectral sections, which are not labelled as window, you are able guide light, but you will experience a lot of losses here.

Attaching a lense will not change the fiber attenuation but you will be able to increase the light intensity at the input port of the fiber.

Best regards

G.M.

Thank you very much for your good answer

Fiber attenuation, which is also called signal loss or fiber loss, is the consequence of the intrinsic properties of an optical fiber (multimode and single mode fiber). Apart from the intrinsic fiber losses, there are some other types of losses in the optical fiber that contribute to the link loss, such as splicing, patch connections, bending, etc.

a)Absorption losses in optical fiber are the major cause of optical fiber losses during the transmission.

b)Dispersion losses are the results of the distortion of optical signal when traveling along the fiber.

c)Scattering losses in optical fiber are due to microscopic variations in the material density, compositional fluctuations, structural inhomogeneities and manufacturing defects.

You need to consider the cable type ( Single mode / Multimode) and the wavelength of transmission for the calculation of losses which is expressed in

dB/ Km also given in the EIA/TIA-568 standards for reference on fibre losses for different fibre types.

Please refer to FS.com website for more details.

Hi, this is a straight-forward calculation. The nonlinear phase shift is given as,

ΔφNL(t) = ϒ* Leff* P(t)

Where, ϒ is the fiber nonlinear coefficient,

Leff= (1- e-α*L)/α, is the effective nonlinear length of the fiber, and

P(t) is the optical power.

There are several ways to coat the optical fibers. Our research group tried a block copolymer templating method. If you are interested, please refer to our work (DOI:

"Optical Fiber Communications" By: JOHN M. SENIOR

According to my studies in these few days and review of articles, I came to this conclusion. Can we calculate the transmission in the structure of fiber sensors using the following two formulas?

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.

Thank You

1) Yes, I have set PML layer.

2) Yes, you got the problem. I will try.

3) Ok I will explore the comsol application gallery and please help me if I need any further support from your side.

@Mickey Ken : Thanks for your answer. I want to view it when the fiber ( after coating is stripped ) is inside a capillary tube ( silica glass ). We are using UV camera and UV LED to view it. But the contrast is not very good at the moment.

I'm going to buck the trend here and suggest you do not use such high NA fibres, regardless of your light source. The problem is that any increase in NA makes the light coming out the end scatter more, decreasing your effective stimulation distance. With a higher NA fibre you need ridiculously high light output to maintain your effective stimulation depth.

For example, in a typical experiment with a 200um fibre and requiring an irradiance of 1mW/mm^2 to activate ChR2, if you wanted to have effective stimulation for 1 mm from the end of your fibre, you would need approximately 4.6 mW from a 0.22 NA fibre. But if you used a 0.65 NA fibre, you would need 27.4 mW. I ran these calculations based on the Aravanis model, and using my online optogenetics power calculator at: https://nicneuro.net/power-calculator/

My experience, using both Plexon and Prizmatix LED's, is that increasing the NA of your fibre only gives a small increase in light power. For example, I recently tested 0.22 NA and 0.50 NA fibres with a Plexbright blue LED and achieved 7.4 and 11.0 mW, respectively. In this case, increasing the NA produced a 50 % increase in light output, but due to the massive increase in light divergence gave an approximate 30 % DECREASE in effective stimulation distance in the mouse brain.

Hello,

You can check the following website. It is a french company

If the parameters of the original fiber are somewhat different, a null coupler may result, where light launched into one fiber will emerge only from the corresponding end, and coupling occurs only e.g. under the influence of a sound wave propagating in the taper region. That way, one obtain an unusual kind of acousto-optic modulator.

Thank you very much for your answer, i have much clear idea on how to do it now !

Sol Photonics offers an easy to use program to simulate many different kinds of FBGs. Uniform, chirped, apodized, etc.

There is a free evaluation version you can download: https://www.solphotonics.nl/fbg-simulation

Hmmm …. That’s interesting. Its hard to see with such a small difference, but it looks to me like the extra counts are uniform across the whole spectrum. The whole sensor is counting higher. You could subtract to be sure. If so, that suggests to me that the extra counts aren‘t from light. Oh, it could be light leaking into the box from somewhere other than the entrance, but, frankly, that almost never happens. You could double check by doing it again with the room lights off. If it doesn’t change, it’s not light.

The only thing I can think of that would cause this is temperature. Could it be that when you cover it you are preventing the room circulation from reaching the sensor, and perhaps also trapping heat? The sensor does produce a small but non negligible amount of heat, and, even though the visible spectrometers don’t have fans, they do rely on conduction through the case and room convection to shed that heat.

The dark rate is a combination of read noise (what you get at zero integration time) and dark noise (the part that is proportional to integration time). It is impossible for me to tell how much of the ~ 3700 counts is dark noise, but I assume most of it. Dark noise is a strong function of temperature and it would only take a very small temperature increase to raise the dark noise 5 or 10 counts out of 3700.

By the way, you can be confident that the black cloth isn’t necessary. Spectrometer housings don’t leak light. If it doesn’t enter through the fiber connector it doesn’t enter. (Unless someone has taken it apart and put it back together poorly). Again, you can verify by comparing the counts with the room lights on and with them off.

Using COMSOL or MATLAB or other simulation softwares it is easy to calculate the MFD. You need consider the change of wave-guiding difference as the tapering diameter decreasing: initially silica/(silica+Ge) and then air/silica. I believe you cannot use a simple formula to get the accurate result

Well, one way would be to consider the transcendental modal equations for the LP modes and compute the propagation constants for LP01 and LP02 for different values of the core radius. Infact, as long as the fiber is an FMF, you could find the propagation constants of all the LP modes allowed by the structure. Then you could use the equation given above to check if the criteria is met or not.

The criterion will be slightly modified for structures with more than two modes. For eaxmple, if your structure has LP02 mode as well, then you must check the above criteria more for coupling between LP01 and LP11 modes rather than LP02 mode.

The modified criteron will contain the computation of the minimum of (\beta_a - \beta_b) for different pairs of \beta.

Let me also add that this critereon of only considering the Eigenvalues is not very efficient. The adiabaticity theorem is often extended the photonics context to consider both the eigenvalue (propagation constant) and the eigen function (the modal profile) for a better adiabaticity criteria. You could find many paper to this regard. Some of my PhD work also might be useful.

Thank you

Problem solved : The reel was getting pinched and deflected at the bare fiber adapter to the detector causing a huge drop in power.

Vincent Lecoeuche Thanks for your thoughts as well.

Yes, you can say both polarizations get rotated. Taking each component separately, they both would get rotated by the same amount, and superposition applies, so together they do the sum of what each of the pieces would do.

However, if it helps, that is not the only way to think of it. We like to think in terms of linear polarization. We like to think of arbitrary polarization as a superposition of two orthogonal linear polarizations. It’s easy to make the diagrams. It also makes sense for linear polarizers and linear retarders. However, that is not the only choice. You can just as easily express an arbitrary polarization as the superposition of left and right circular polarizations. In the basis of right and left circular polarization a Faraday rotator is in fact a phase retarder. if the two components have equal amplitude the result is linear polarization. The relative phase determines the orientation of the linear polarization, so retarding the phase rotates the linear polarization. If the two components have different amplitude, you get an ellipse where the major and minor axes are the sum and difference of the amplitudes. Again, if you retard the phase, the whole ellipse just rotates.

As to why your experiment is producing answers that don’t quite seem right, I think this measurement has several things that can confuse the result. Although I don’t see why you wouldn’t put a polarizer on the entrance, I doubt the entering ellipticity is really the problem. That should just reduce your modulation amplitude making the signal a little weaker, but it shouldn’t impact the phase. A much more likely culprit is linear birefringence in the fiber. Fibers can have significant residual birefringence from the manufacturing, but also bending through the fiber acts as a retardation. For example, sequential coils of fiber called fiber paddles are sold as polarization manipulators.

i am also comfuse about the beta valume, how can we calculate the beta2, beta 3...

Nirmal,

Apply a grating coupler on the clad layer of the fiber. Regards, Shigeo.

Hi Felipe Beltran-Mejia,

If you are unsure of the exact fibre type, and not too concerned about accuracy, a reasonable assumption is that the fibre is single mode, and emits an ideal Gaussian beam.

I would expect one or more of the simulation packages you mention to support free space propagation of Gaussian beams, but there is a lot you can do with pencil, paper and a pocket calculator. https://en.wikipedia.org/wiki/Gaussian_beam

For SMF 28e+ fibre, the nominal mode field diameter is 9.2 µm at 1310 nm and 10.4 µm at 1550 nm. https://www.corning.com/content/dam/corning/media/worldwide/coc/documents/Fiber/PI-1463-AEN.pdf

So at 1550 nm, the radiant exitance at the fibre exit facet falls to 1/e² of the peak value at a radius, w₀ = 5.2 µm.

At distances much greater than the Rayleigh range (0.055 mm), the angle at which the radiant intensity falls to 1/e² of the peak is θ₀ = λ/(π w₀) = 0.095 radian. Note that the numerical aperture of 0.14 specified in the Corning data sheet is measured at 1% intensity, corresponding to a wider divergence and a lower intensity.

At a distance of 14 mm from the fibre tip, the 1/e² radius of the irradiance is 1.33 mm, so most of the light from the fibre will pass through a 3.5 mm aperture.

(The half-angle subtended by a 3.5 mm circular aperture at a distance of 14 mm corresponds to a numerical aperture of 0.125 - which is why I mentioned that value).

More generally, for a Gaussian beam of radius w, the fraction of the total power transmitted through a circular aperture of radius R is [1 - exp(-2 R²/ w²)].

Peak irradiance is 2 P₀ / (π w²) where P₀ is the total power.

Specifically, if your technician holds the fibre 14 mm from his eye, 97% of the 500 mW power will fall inside a 3.5 mm circle aligned with the centre of the beam, so 497 mW. Peak irradiance of 18 W/cm² is significantly higher than the 4 W/cm² threshold for thermal corneal damage.

Note that at 1550 nm, most of the power will be absorbed in the cornea, and will not reach the retina of a human eye.

At 1310 nm, transmission is higher, but there is significant absorption in the lens of the eye.

At 850 nm, 980 nm or 1060 nm, transmission to the retina will be much higher.

The effective focal length of the human eye is approximately 17 mm, so light from a fibre only 14 mm from the subject will not be focused onto the retina. The retinal damage threshold will be reached much sooner with the fibre at a greater distance from the eye, such that the radiation converges to a smaller retinal spot. Is this one of the factors you intend to address in your model?

If you have not seen it already, this paper may be of interest:

D. Sliney et. al, "Adjustment of guidelines for exposure of the eye to optical radiation from ocular instruments: statement from a task group of the International Commission on Non-Ionizing Radiation Protection (ICNIRP)", Applied Optics, vol. 44, np 11, 2005.

Also: https://en.wikipedia.org/wiki/Laser_safety has some useful links.

Dera Mustafa Hammood ,

you may ahve a look at equation 1a and 1b for a description of the gap and wavelength dependence of the coupling loss/ transmission in a butt joint SM-fiber connection:

But, sorry, no experimental data yet...

Best regards

G.M.t

(200-micron core Yb-doped fiber for high pulse energy applications)

Taynara Oliveira - regarding the Lumerical article, as far as I can tell, they are calculating a 2-D overlap integral over the waveguide cross-section.

I believe there are some errors in the web page, for example using S rather than dS in the first overlap integral. Their approach using both E and H fields looks similar to an integral over contributions to the Poynting vector which I had not seen before. Google found references to its use with waveguides which are birefringent or chiral, and these may give you more background.

Lumerical reference A. W. Snyder and J. D. Love, "Optical Waveguide Theory". London: Kluwer Academic Publishers (1983).

Snyder and Love describe both vector treatments and scalar wave approximations for waveguide propagation. Chapter 20 begins with the vector results, but mostly deals in the weakly guiding limit, where it is sufficient to consider only the electric field components. They consider various Gaussian approximations (as suggested by David A. Ackerman) in some detail.

As I pointed out in my first response, and as David also states, with radial symmetry, it is possible to reduce the 2D overlap to 1-dimensional integrals, but it is essential to include the appropriate radial weighting.

Not including a radial weighting factor is a likely reason for your 20% discrepancy.

Attatched is a comparison of 1D and 2D overlap integrals for a Gaussian mode field, and a "top hat" illumination field.

For detection there are many factors: the geometry for retrieving the signal, the sensitivity of the detector, the resolution of the spectrometer, and how well you can filter out the Raman signal from the high level scattered laser signal. All this aspects need optimization, and any one of them may be giving you problems,

At any way statistically standard deviation can be used to refer for the root mean square value, of signal, then separate information signal from noisy signal by the means of signal processing to calculate SNR.

many factors determine the amount of loss you are going to encounter.

coating refractive index is a very important parameter for guiding the wave in the core, but this index may lead to a weakly guided wave or guided wave.

losses depend on waveguide structure and class of materials used

I would recommend the following textbook to expand your knowledge

Optical Fiber Communications 4th by Gerd Keiser

You can try a scalpel to scrape the epoxy off the sides of the ferrule. This is effective, but you can accidentally break the fiber off during the scraping process. Improperly cleaved / scribed fibers can result in fiber break / crack defects.

The total spectrum/wavelengths has the same intensity dependence with the distance of your fiber tip. So, in a real aplication, it is quite difficult to analyze the total intensity reflectance values, but you can analyze spectrum changes (intra-).

Try to use a wavelenght, that you are prety sure is not related with a characteristic of your plant analyzed, as reference, allowing you to check the intensity fluctuations (due to sun-light variation intensity or experimental changes, etc..) Now, use other spectral region related with the plant characteristic, divided by the intensity of the wavelength reference. Therefore, the spectral analysis is not more sentitive to sun-light fluctuations.

I found this, i hope it can help you Marcos Túlio Antunes Bezerra Segundo Matteo Perazzini https://www.ijsr.net/archive/v6i5/ART20173865.pdf

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.

What field of view you will get depends on the core size of your fiber. 3 degrees is a capability of the lens, not an indication of what you will get. What they are saying is that the lens will focus well onto the focal plane at field angles of up to 3 degrees off axis, but you won't actually have anything to catch the light 3 degrees off axis at the focal plane. The full-angle field of view you will actually get is 2*arctan(fiber core diameter/(2*focal length))

The flip side which is probably equally important to you is that the reduced field of view comes with a larger collection area (and so sensitivity to signal). The aperture diameter is increased from the core size in the case of the bare fiber to 2*tan(arcsin(fiber NA))*focal length

This all assumes a multi-mode fiber which is almost certainly your case.

Data rates are mostly affected by the noise level on the detector side. The ultimate limit is shot noise, which scales with the square root of the number of photons detected. Doubling the intensity should therefore enable about 40% higher data rates at best. If you are working near 1.5 microns, there is virtually no absorption in the core of the fiber, at least as far as heating is concerned. However, the cladding is typically coated with an absorptive material. If you are launching light into the fiber and you do not exactly match your mode, you will see a lot of absorption in this coating, and the fiber will start to burn. This will limit the power that you can launch into the fiber. I recall that I managed to launch more than a watt into a single-mode fiber, but this is probably far beyond practical levels as you would immediately destroy your receiver with such elevated power levels.

There could be multiple ways. However, if the transverse and the longitudinal extent of the device is large, then its will be a computationally intensive problem while using FEM. This is especially the case for low contrast devices. However, here is a possibility which could be extended.

You could use COMSOL to compute the modes of the composite structure. Then by exciting a certain core and propagating the field, you are essentially propagating a superposition of those modes each acquiring a different phase during propagation. The propagated field could be analyzed to compute the coupling coefficients.

It looks as if you designed it in sequential mode. That means ray interaction with surfaces is only checked in the exact order you define the surfaces. If you want to simulate interactions where the order is not known beforehand you must design it in non-sequential mode. Then a model of a multimode waveguide will work, but not a singlemode waveguide, which is poorly described by rays.

Hi Abdul Aziz Khan: - Can you explain in more detail how my answer differs from the established view of DWDM performance? In particular:

A useful resource is the Handbook of Optical Fiber, Cables and Systems, published by the International Telecommunications Union in 2009. By now, this is a little dated and does not cover recent developments in QAM modulation formats and coherent systems. Having said this, the basic information remains valid.

In particular, you may find the following sections may of interest

My previous answer reflects my understanding of the state of the art around 2011. At that time I had been involved in developing commercial WDM transmission systems for 18 years. My responsibilities included analysis of non-linear propagation impairments and establishing robust and efficient link budgeting techniques. Since then I have not followed developments in detail, but I am not aware of any technical developments or changes to our understanding of the underlying physics which would change my conclusions.

Consider that Google is a search engine and advertising platform. The links it returns reflect accessibility and some measure of popularity. Judging technical merit is a more difficult task for an automated system.

Out of interest, I did search Google for differences between G652 and G655 fibres, and near the top of the hits found several blog sites of questionable reliability. Is this where you found your opinions?

Note that fosn.com, fs.com, medium.com, thefoa.com, mefiberoptic.com and mjadom.com, typically display very similar graphics, and most include a table indicating that G652 fibre is unsuitable for long haul DWDM or data rates. This suggests to me that they may be more closely linked than is apparent, rather than expressing independent opinions.

The graph common to several, showing positive and negative dispersion fibres is highly incongruous to anyone familiar with single mode fibre design. Although there was a short period in the mid-1990s where negative dispersion fibres were investigated for their insensitivity to modulation instability, these fibres had positive dispersion slope, not negative as shown in the graph.

Sylvie Liu on https://medium.com/@sylvieliu66/single-mode-fiber-type-g652-vs-g655-fiber-fbbcc6db67ee is more specific. She states "G655 is an enhanced single mode fiber with the characteristic of elimination of FWM and low dispersion value". It absolutely does NOT eliminate FWM. This is not a matter of opinion or debate. Low dispersion is well known to greatly increase the magnitude of four wave mixing,

I note that the post is dated 9 May 2018, but states that G.655 has A, B and C subcategories. She does not mention the G.655.D and G.655.E versions from the 2006 release of the standard, or that the A and B subcategories were dropped. Such lack of attention to detail does not inspire confidence, and she reveals little understanding of non-linear Kerr effect crosstalk in WDM systems.

A more focused Google search found a more recent publication. I have not downloaded the full paper, but the abstract indicates a much more realistic understanding of DWDM propagation. It reports a mixed line rate comparison of G.652, G.652D, G.653, G.654, G.655 and LEAF fibres, with G.652 showing best performance.

Bajpai, R., Sengar, S., Iyer, S. et al. Performance investigation of MLR optical WDM network based on ITU-T conforming fibers in the presence of SRS, XPM and FWM. Int. j. inf. tecnol. 11, 213–227 (2019). https://doi.org/10.1007/s41870-018-0212-2

The benefits of high chromatic dispersion in suppressing WDM non-linearity was understood from the earliest demonstrations of FWM in optical fibres.

K.O.Hill et. al, "CW three-wave mixing in single mode optical fibers", J. Appl Phys 49, p 5098, 1979. https://aip.scitation.org/doi/abs/10.1063/1.324456

The impact of low dispersion on FWM was explored in more detail in the paper by N. Shibata, R. Braun & R. Waarts, "Phase-mismatch dependence of efficiency of wave generation through four-wave mixing in a single-mode optical fiber" IEEE JQE vol 23, #7, pp1205-1210, (1987), https://ieeexplore.ieee.org/document/1073489/

The analysis was extended to multi-span systems when erbium-doped fibre amplifiers were introduced. https://www.researchgate.net/publication/26861221_Phase-mismatching_characteristic_of_four-wave_mixing_in_fiber_lines_with_multistage_optical_amplifiers

As modulation rates increased from 2.5 to 10 Gb/s, cross phase modulation became the dominant WDM penalty for many systems. There is a rather more complex relationship between fibre dispersion, channel spacing, and dispersion compensation strategy for XPM impairments, discussed by Rongqing Hui, K.R. Demarest, & C.T. Allen, "Cross-phase modulation in multispan WDM optical fiber systems", JLT, 17, #6, pp 1018-1026, 1999.

In spite of their poorer DWDM performance, there can be valid reasons to deploy near-zero dispersion-shifted fibres to reduce the need and expense of dispersion compensation modules. Typically, this will be where cost of terminal equipment is more important than maximising capacity and the potential for future enhancements. However, stating that G652 fibre is unsuitable for 10 Gbit/s DWDM is demonstrably untrue.

The introduction of electronic dispersion compensation eliminated much of any potential cost benefit for reduced dispersion fibre in high capacity long-haul transmission, avoiding the need for fibre dispersion compensation modules. For example: Doug McGhan, Charles Laperle, Alexander Savchenko, Chuandong Li, Gary Mak, and Maurice O’Sullivan, "5120-km RZ-DPSK Transmission Over G.652 Fiber at 10 Gb/s Without Optical Dispersion Compensation", IEEE Photonics Technology Letters, Vol. 18, No. 2, January 15, 2006

Coherent detection and digital signal processing at the receiver gave further improvements in performance, even on legacy fibre with relatively poor polarisation mode dispersion.

C.Laperle, "WDM performance and PMD tolerance of a coherent 40-Gbit/s dual-polarization QPSK transceiver" JLT Feb 2008.

Note that the papers above used G652 fibre. This is not only because G652 fibre is very widely deployed, but also because it delivers significantly better WDM performance for this type of system.

Here is more recent work using ULA fibre with an even higher chromatic dispersion than G652 to improve the WDM performance

I have no plans at present to publish a more detailed justification. As I hope I have shown, there is a huge volume of work published in peer-reviewed journals supporting much of what I stated. Have you identified an audience who are unable to access such information, or do they simply need to know what questions to ask?

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

Good question

I think that

May be

to couple a image to a fiber is focusing the image on the surface of the fiber end by convergent lens is placed after the image and before the fiber

Jörn Bonse provides a very clear explanation of speckle motion in MM fiber resulting from fiber flexion. The next question is how to move the fiber to reduce the speckles adequately to meet you needs. Presumably, your aim is to create a smooth illumination field for your endoscope. So, how to vibrate the fiber, in terms of direction of motion, amplitude, frequency, etc? Some of these questions can be answered through experiment -- you will be time averaging (integrating) the moving speckle field over the frame time or exposure of your camera. Therefore, the vibration period must be less than 1/10 of the exposure and preferably much shorter to enable speckle patterns to average out. The amplitude of the vibration only needs to be enough to 'shake' the speckle pattern by a few characteristic speckle dimensions or so. Once you have a mechanism to vibrate the fiber, you can ensure that the amplitude of vibration is large enough. Finally, you need to create a diverse set of speckle patterns during an exposure time. Some schemes use two vibrators in orthogonal directions at different frequencies (that are not low integer multiples). It is probably best to build up your system with vibration frequency set first, then experiment to ensure that the speckle pattern averages out enough for your purposes. Add complexity if it is needed. Finally, there are other ways to smooth speckle patterns that use spinning diffusers in the light path. However, in your endoscope, your idea of vibration seems practical. Here is an interesting reference: https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-9-13662&id=431120.

The simplest way is to use a fiber fusion splicer. By playing with the parameters of splicing such as charging time, strength as well as the distance between the two fibers, you can get the structure as you want.

speckle patters arise whenever lights from a variety of directions hit a scree, When the number of different directions is large (≈>50) the one sees the "normal" speckle pattern (BTW each fo the black spec is actually a phase singularly, or optical vortex). A multimode fibre typical supports >1000 fibre modes so their addition/interference is what creates the speckle.

within a ray optical picture, the rays associated with different fibre modes zig-zag down the fibre at different angles from each other 8every mode having ≈ its own zig zag). the higher order modes zig zag more tightly. remember that the wavevector has x, y, and z components (kx^2+ky^2 +kz^2 = k0^2). if the ray has non zero kx and ky then kz must be reduced below k0. the more tight the zig zag the more kz is reduced. phase velocity in z-direction is omega/kz, smaller kz gives larger Vphase.

Fibercore

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.

I can give a link to the work where such high-temperature optical fibers were studied "high-temperature optical FIBERS WITH a COPPER coating" Approximate characteristics of the Type of optical fibers: Single-mode (G. 652), multimode.(G. 651), “quartz-quartz”

Type of coating: copper, aluminum and alloys based on Them

Operating temperature: 500 °C (aluminum coating),

800 °C (copper-based coating)

Length: up to 5 km (continuous)

Optical losses: minimal (depends on the design of the light guide and operating conditions) 1-4 dB/km (at 20 °C) at λ=1310, 1550 nm

2-4 dB/km (at 700 °C) at λ=1310, 1550 nm

Strength: 8-10 GPa

Diameter of the light guide: 125-1000 microns.

essentially, you have to match the collection angle of the your collecting lens to the NA numerical aperture of the optical fiber as well as the image size should be matched to the core diameter of the optical fiber.

Let`s make simple estimation: Angular diameter of sun is about 10 mrad. Maximum diameter of custom fiber bundle (available at the market) is ~2 cm. So maximum focal length of ideal concentrator is 2: 0.01 = 200 cm. Supposing maximum available NA (full acceptance angle) = 0.5, we obtain maximum diameter of concentrator 100 cm. So, available sun light power from one module "concentrator + fiber bundle" at the input is ~ 800 W. To get 1000x1000 W you need to use ~1250 modules (in the best case).

May be better to concentrate the light by spherical mirror instead Fresnel lens ?

Don`t worry about losses in fiber, main losses you will get before the input.

Standard fiber bundles have a length <2 m. But I suppose there are military systems with much longer bundles, the technology allowes to make longer bundles. Look for the supplier by yourselves. Standard bundles will not satisfy you.

At the fiber input the maximum power density is ~ 250 W/cm2. It is not very high. Also you can reject UV and IR before input and obtain much less than 200 W/cm2.

So, in total your idea seems real, but not good. To my opinion, free space transportation of sun light is more resonable.

In our last experiment, we used PMMA as a coating for the FBG sensor. However, the low thickness of the PMMA layer did not affect the principle of operation of our sensor:

https://www.mdpi.com/1424-8220/20/19/5468

Yes, after a long search I was able to find the product.

It was the EH-600 from ASI ( https://asi-instruments.com/stereotaxic-instruments/)

Dear Viet Nguyen ,

nice idea.

You should have a look at the planes perpendicular to the fibers. I assume you think on circular fibers . So the net area when picking up the light in the case of fibers is much smaller than the real area which is exposed to light. So you will pick up only about 2/3 of the light. At the planes where you will transfer the light from one fiber system to the next you will have additional areal losses.

Have you taken all these losses into account?

From that point of view, I think, any lense( e.g. a Fresnel lense) will have a better efficiency than your system.

Please check the areal coupling losses.

Good luck

By the way: In your drawing you have presented one of the very few rays which successfully end up at your output port. There are a lot of rays which will not end up there, even for perpendicular incidence at your entrance port.

Slope of the initial linear portion should be used to be absolutely sure that you are truly in the elastic region. Perhaps you need more data points at low stress/strain regions

Dear Rajib Biswas Sir, the 2nd and 3rd links are not open. Can you please resend it.

You can design a code by matlab to analyze the optical beam profile or used a CCD.

Your question Dear Xiaojing Xia, is akin to asking what the end values are if one knows the birefringence of a given unknown mineral particle. If that is correct then I completely agree with those who say you can not pin down the RI of core and/or cladding. On the other hand, if an optical microscope is available you could grind some up and examine it to discover the RI of both materials ... if it makes sense to snip off a sample of a given fiber.

Your question may well be addressed by applying my specialty, about which you can learn more by visiting at least these four (4) files,

1. Preprint#4: https://tinyurl.com/y76yba6n

(Click Download to get 4 May 2020 PREPRINT#4)

2. Raw data: https://tinyurl.com/v9u4hkf

3. Video: https://tinyurl.com/uajcnxx (open in a video player)

4. 20200512 1325 Final E% COORDINATES & MORE .pdf, https://tinyurl.com/y9lrmnec

and maybe also by paying a visit to some of the other Supplemental Materials in folder https://tinyurl.com/to8tsbt .

I hope that this helps and that you will, in turn, share with me any thoughts you may have about how I could improve any aspect of my work.

With all best wishes for your own continuing successes! :-)

Sincerely, -Steve- gambist@gmail.com

you can use the bidirectional fiber in Optisystem tool which include the SBS effect. Have a look at this article

Simulation and experimental validation of gain saturation in raman fiber amplifier

So, as I understand you right, you are asking the following question:

What is the effect of changing the length of a uniform fiber Bragg grating (https://en.wikipedia.org/wiki/Fiber_Bragg_grating)?

So, I try to answer this question:

When light is send through the fiber with fiber Bragg grating (FBG), it reflects a specific wavelength, which is determined by the refractive index and the grating period. So in the spectrum of the reflected light you will observe a peak.

Changing the FBG length will change the reflected peak of the FBG. The Full-Width-Half-Maximum (FWHM) for example, is influenced by the FBG length.

Moreover, the FBG length also influences the reflectivity.

You find more information here:

Welding glasses sound appropriate. Maybe it would be helpful to use a high dynamic range camera with log response and monitor or video goggles. This would bridge the stark contrast between the brightly illuminated center and the surrounding.

Just some example from the web:

https://www.ims-chips.de/home.php?id=a3b15c1en&adm=

https://axiomoptics.com/llc/magic-wdr/

Hi. You should take a look at these books:

- Computational Fourier Optics a MATLAB tutorial (2010)

- Computational Photonics An Introduction with MATLAB by: Marek S. Wartak (2013)

- Fundamentals of Electromagnetics with Matlab, By: Karl E. Lonngren, Sava V. Savov (2005)

- Guided Wave Photonics _ Fundamentals and Applications with MATLAB (2012)

Thank you very much @Seyed Hadi Badri for your solution. I was also busy in solving this. I would like to share that the error was due to defining the cylindrical waveguide. COMSOL takes propagation direction in x-axis while I was defining it in z-axis. Now, it is working.

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.

Gordon Yiu

Thanks a lot

You can cut the fiber end at 45°.. If the fiber is in air, you should probably have a total reflection on the end face fiber (it is the case for standard optical fibers). If not, you can coat this cut end face with some metallic coating depending on the wavelength you intend to work. That will minimize your space at the maximum, and will have your 90° reflection quite easily.

Mohammadreza Maleki: by "without dissipation" I assume you mean with minimal coupling losses.

Manuel Gómez' answer is appropriate if you have a well-collimated beam from your laser diode source. Note that he suggested using a microscope objective lens, not an entire compound microscope instrument.

Having said that, if the core diameter of your fibre is 1.5 mm, and the numerical aperture reasonably large (say 0.2 or greater), I see little need for tilt adjustment on the fibre mount. For industrial applications, a singlet lens is probably good enough. An aspheric lens, or a plano-convex lens with the planar side towards the fibre, and the convex side facing the collimated beam, will have lower aberrations than a bi-convex lens.

On the other hand, if you are attempting to couple light directly from the exit facet of a laser diode into the fibre, you need to consider the size of the active area and the far-field radiation pattern.

What is the numerical aperture of your fibre? Does it have a graded refractive index profile or (more likely) a step refractive index profile?

For efficiency reasons, the active volume of a diode laser is usually a thin stripe, with a far-field radiation pattern which is highly divergent out of the plane of the stripe. https://www.newport.com/t/laser-diode-technology

It is not uncommon for the divergence angle (half-width at 1/e² intensity) to exceed 30°, with significant power at angles as high as 50 degrees.

If this is the case, a high numerical aperture lens is essential. A decent quality aspherical lens may be more cost-effective than a microscope objective, and could offer comparable efficiency. Precision machined and polished aspheres offer near diffraction-limited performance, but a moulded lens is probably good-enough to couple to your a 1.5 mm core diameter fibre.

In the case of a broad stripe laser such as that described in the paper by Lee, Mawst, & Botez linked above, the laser cannot be treated as a point source, and there will be some increase in aberrations at the outer edges of the active area of the laser facet. This will be more pronounced for shorter focal length lenses, but I doubt this will have a significant impact with focal lengths of 8 mm or larger. Shorter focal lengths could be acceptable, but I am guessing here as I don't have direct experience.

You appear to be aiming for 100% efficiency which will not be possible. 99% will be very difficult to achieve, with perhaps 85%-95% more likely. At normal incidence you lose 4% of light from each uncoated air-glass interface, so anti-reflection coatings with good performance at the laser wavelength are essential. Are you able to AR coat the fibre entrance and exit facets to avoid Fresnel losses here?

You can improve the collection of high angle light by combining a high NA aspheric with a longer focal length best form, plano-convex or achromat secondary lens. Mount with each lens' with most strongly curved surface facing the other lens. With a 100 μm stripe laser, I suggest a secondary lens directing light to the fibre with a focal length 5x to 10x larger than that of the asphere collecting light from the laser.

Magnification = focal length of secondary / focal length of primary asphere

Choose magnification > Aspheric lens NA / Fibre NA

Choose magnification < Fibre core diameter / laser stripe width

A ray tracing package such as Zemax will allow more precise optimisation if the highest possible efficiency is essential.