Optical Engineering

Optical Engineering

  • Felipe Beltran-Mejia added an answer:
    How can I calculate cladding line (cladding effective index) for a photonic bandgap fiber?

    I need to calculate the cladding line (referred as cladding effective index) for a photonic bandgap fiber. How may it be done?

    Felipe Beltran-Mejia · Instituto Nacional de Telecomunicações

    From my point of view there are two ways you can do that:

    1) Calculate a cell of your PCF and by using periodic boundary conditions you will be simulating an infinite crystal without any defect. In that way your fundamental mode will be the cladding effective index.

    2) Eliminate the defect in your PCF (for example by putting an air-hole in the core of a conventional PCF). Then calculate the fundamental mode of that structure. I must say this  is a simpler approach, although less accurate. But not much though.

  • S. Selvendran added an answer:
    Is there any relationship between data rate and mach zehnder modulator losses?

    I am working on Passive Optical Network. I have designed the two transmitter one with data rate of 10 gbps and other with 1gbps. I have used mach zehnder modulator. I have set the laser power of both transmitters to 0 dbm. It is found that the losses are less in case of 10 gbps as compared to 1gps. Is there any relationship between data rate and mach zehnder modulator losses?

    S. Selvendran · Alagappa Chettiar College of Engineering and Technology

    optisystem  simulation tool is exactly suitable for you requirement... you can download this tool for 30day evaluation (full latest version) from the optiwave website....  

  • Alan Robinson added an answer:
    How many optical cycles does it take for Rayleigh scattering to occur?

    I am trying to detect Rayleigh scattering from a liquid and am concerned that my optical pulses are too short. I am using a 13 fs, 80 MHz Ti:Sapphire laser. So, there are about 3 optical cycles per pulse.

    In an old experiment where we had pulses of 150 fs, 1KHz, we did not have any trouble finding it. 

    How many optical cycles does it take for Rayleigh Scattering to occur?

    Alan Robinson · 4D Optics


    "I am using a photodiode, chopper, and lock-in for my detection. In our old set-up we used a PMT. In the current set-up, from classical Rayleigh scattering cross-section estimates, we should be detecting significantly more signal."

    Are you using a mechanical chopper at a low frequency (e.g. 1 Hz to 1 kHz) compared with the pulse rate?  In the classical case, the scattered signal should depend only on the mean laser input power, the path length of liquid, and the solid angle over which the light is collected. In this limit your signal should be independent of pulse width for the same average input power and wavelength.

    Can you estimate the absolute signal power detected in the old experiment?

    Are the wavelengths and average laser powers comparable?  Are you collecting a similar proportion of the scattered light?

    One significant difference is your use of a photodiode rather than PMT.  A decent large area silicon photodiode will have a noise effective power (NEP) around 10-14 W/sqrt(Hz).  A photomultiplier could easily have a noise floor 100 times smaller.

    Could higher noise  from the photodiode explain your problems?  What kind of amplifier do you use between photodiode and lock-in?  What is the chopper frequency?  Noise will increase with frequency when using a large area photodiode with a relatively high junction capacitance ~1 nF.

  • Alan Robinson added an answer:
    Please suggest suitable laser diode to convert up to 20 volt input signal into optical signal?

    Dear all

    I have to make a transmitter  which will convert electrical signal to optical signal and transmit over fiber up to 5 meter distance the range of input signal will be 10 mvolt to 20 Volt. pls suggest suitable laser diode for this range.

    Alan Robinson · 4D Optics

    The voltage response of diode lasers is highly non-linear.  Converting the input voltage to current, as suggested by David, will greatly improve linearity (and reduce the likelihood of destroying the laser).  However, although the optical intensity increases more linearly with current than voltage, laser diodes typically exhibit a lasing threshold current below which the output is very weak.  This can be offset in the driver, but the threshold is sensitive to laser junction temperature, so with a constant current drive the output will drift with time as the ambient and laser temperatures change.

    David's advice to use a voltage to frequency converter is sound.

    If an output with reproducible optical intensity is essential, then some kind of feedback control is highly desirable.  Many lasers are provided with a monitor photodiode which delivers a current proportional to the optical output from the laser cavity.  Alternatively, a fibre tap coupler and a separate photodiode offers the same functionality.  Many commercial laser driver modules support these configurations.

    What type of fibre are you using?  What is the core size, numerical aperture and operating wavelength?  Is it single mode or multi-mode?  A collimated laser output may not be the best option.  Additional optical components could be needed to couple power efficiently into the fibre core if the core is not comparable in diameter or larger than the laser beam width.  Depending on the type of fibre, laser diodes should be available with matching or compatible pigtail fibres, and this may be a simpler option, especially if you can use a splice or fibre connector.

  • Kate Peters added an answer:
    How can i make a microelectrode wiht closure in glass?

    when i used a lot of gluse to enclose the glass in order to get plane microelectrode. how can i get help from the experiments

    Kate Peters · University of Leicester

    If you want to fabricate carbon fibre electrodes you can use glass tubing and an electrode puller to get a tight seal no need for glue, or you can use Clark et al's (attached) method of encasing the carbon fibre in glass capillary with epoxy glue. But it depends on what materials you are using for the sensor. The Clark type electrodes are suitable for both in vitro and in vivo use in cyclic voltammetry and other applications.  

  • Stefano Penna added an answer:
    What has the highest priority in the design of a slot waveguide EO modulator between the effective area and the optical confinement factor ?

    I'm having a long discussion with my boss concerning with the optimal design of a slot waveguide EO modulator. He considers that the maxmization of the optical confinement factor into the slot has the highest priority with respect to the minimization of the optical mode effective area, as the final aim is to maximise the overlap with the RF field into the slot, whereas the minimum effective area impacts mainly in devices based on light-to-light interactions, such as in all-optical modulators. Nevertheless, almost all the publications on this topic reports on efforts to minimize the effective area. What's your opinion about it ?

    Stefano Penna · National Institute of Information and Communications Technology

    I had a deeper reading and some calculations starting from your replies. As Patrick said, the aim with Kerr effect materials is to minimize the mode effective area Aeff,  as the non linear interaction factor is maximized by minimized Aeff. This is true as Kerr materials are never used for standard EO modulators but only for all-optical non linearities, as frequency combs or FWM. Checking better the publications from the Karlsruhe KIT  group, they use standard Pockels effect polymers for modulators and Kerr effect small molecules for all-optical interaction based devices.
    Indeed, if we used a Kerr effect material into EO modulators and we derived the half wave voltage, we'd have a linear dependence on the inverse of the confinement factor (as we need anyway to overlap the driving RF electric field to the optical field) and only a square root dependence on the effective area (square root as Kerr is a quadratic effect). So this would mean that the half wave voltage would be improved more by the maximization of the optical confinement  rather than by the minimization of the effective area.

  • Mostafa El-Aasser added an answer:
    Can anybody explain the d{ln(αhν)}/d(hν) versus hν plot ? And also, how can I calculate it if I have data between absorbance and wavelength?

    For optical studies the terms many a times I have come across this term please help ?

    Mostafa El-Aasser · Ain Shams University

    I think Stewart covered everything and mentioned all details.

  • Alexander B. Missyul’ added an answer:
    How can I study the optical property of Mn-doped TiO2 if Mn2O3 impurities are present?

    I have made some black powder sample, which is confirmed by PXRD to be a mixture of rutile TiO2 and a-Mn2O3 . There is possibly also some Mn-doped TiO2 inside, as the XRD peaks for TiO2 shift a bit. 

    Now I would like to know the optical properties of the Mn-doped TiO2, but it seems to be completely masked by the black a-Mn2O3 impurties.

    So is there any method that I can isolate and study Mn-doped TiO2 alone? Is it possible that I can dissolve the mixture in some solution with properly tuned pH which can specifically remove Mn2O3 and leave TiO2 intact?

    Thanks a lot.  

    Alexander B. Missyul’ · Samsung

    I would try to dissolve Mn2O3 carefully in the acidic solution of the Mohr's salt (the procedure similar to what is used for the determination of the mean oxidation state of the transition metals by titration). But it will probably require very accurate tuning of the experimental conditions in order to avoid reduction of the Mn+4 in TiO2.

    Anyway, it is unlikely that you will be able to dissolve Mn2O3 simply by tuning of pH. Mn3+ easily disproportionates to Mn2+ and MnO2 in the water solutions and selective removal of the solid MnO2 will be much more complicated.

  • Sridhar Iyer added an answer:
    In MLR WDM Networks, there is trade-off between spectral & energy efficiency. Is this true only for fixed BER or can this be applied to varied BER?

    In MLR optical WDM Networks

    Trade off between spectral & energy efficiency is established for fixed signal quality (BER). Can this be applied to varied signal quality (BER) requirement also?

    Sridhar Iyer · Christ University, Bangalore

    Yes, agree with you view. The switching will play a crucial role. I am thinking of how to model a network that can provide high spectral efficiency and low power consumption (both at the same time) for varied BER which will depend on the demands that come into the network. 

  • Stefano Penna added an answer:
    What is the proper area to refer for the Optical Confinement Factor in Slot Waveguide Modulators ?

    In order to optimize the design of an EO modulator the maximum overlap of the RF electric field to the optical field must be achieved. In a Slot waveguide it implies the overlap must be achieved mostly into the slot region. Therefore, limiting to the optical field, the design must induce the highest confinement of the lightwave into the slot. Typical vaues reported for the optical confinement factor are in the order of 20%-30%. Nevertheless, some papers (e.g. Koos and Leuthold works) report also other optical confinement factors referring for instance to all the EO cladding in the case of EO polymer modulators. Which is the benefit of having light confined out of the slot ? In my opinion, even if the optical propagating wave spread out of the slot, with part of the power guided into the EO cladding or the Silicon arms, the "useful" light confinement to be addressed concerns with the slot. What is your opinion on that ?

    Stefano Penna · National Institute of Information and Communications Technology

    I thank you guys for the enlightening discussion.
    Martin is right as I provided not enough details on my device assuming too much as given. When I said "in terms of final application" I meant the typical condition of a strip-loaded slot waveguided photonic modulator where usually the RF electrical field is strongly concentrated into the slot, so that one should aim to increase as much as possible the optical confinement into the slot to maximise the overlap of the RF and optical fields.
    Martin is also right that typically we focus more on numbers, such as gamma in this case, without considering that it resumes a distributed physical quantity such as the optical field. This is a quite typical mistake for engineers :)

  • Mohammad Kazem Moravvej-Farshi added an answer:
    Which software is most suitable for Photonic Crystal Fiber analysis?
    Dispersion vs wavelength, MD vs lambda.
    Mohammad Kazem Moravvej-Farshi · Tarbiat Modares University

    COMSOL or Lumerical

  • Steve Zein added an answer:
    How can the relation between stimulated Brillouin scattering gain and the acoustic waves' damping time be explained physically?

    The same for the relation between acoustic-phonon lifetime and the spatial resolution.

    Steve Zein · Isfahan University of Technology

    Thank you very much, it was very helpful

    Best regards.

  • Dan Borza added an answer:
    Which methods can you recommend for a speckle noise reduction in acquisition stage in the holography?

    I am interested in the methods to reduce the speckle noise in acquisition stage, but I am also interested in the speckle noise reduction in post-processing stage. Do you have any references?

    Dan Borza

    You might also see the full reference text  "Chapter: Vibration Measurement by Speckle Interferometry between High Spatial and High Temporal Resolution" on my researchgate page.

  • Dan Borza added an answer:
    What lasers could be used for Holographic interferometry (HI) and for speckle-interferometry (ESPI)?
    For ESPI application should we use the lasers which are suitable for HI or we can take a laser with lower quality requirements?
    Dan Borza

    One thing more, which I forgot with my first answer:

    With high-power lasers (usually from a few hundred mW up) and high rate cameras (ans small sensitivity) which usually require a rather large exposure, you also have to be careful in case you study very small objects (a few mm for example) - especially if the object beam has a very small divergence. The concentrated laser beam may heat or even destroy the objects under study.

  • Stefano Penna added an answer:
    Why does the Silicon doping rate impact on the optical field in a waveguiding photonic device ?

    The doping rate of a Silicon base waveguide is known to be effective on the optical field propagating through the waveguide. In particular, the highest the doping the highest the optical loss. Nevertheless in active devices, higher doping rates of Silicon are preferred to increase the conductivity of the material and allow for lower power supply.
    I am having several BPM simulations of the device I designed, taking into account the effect of different Silicon doping rates on the real refractive index of Silicon. I am wondering if the effect of the doping rate for my simulations is just all into the refractivity or if the optical loss can be related to some other effects that i am not considering.

    Stefano Penna · National Institute of Information and Communications Technology

    Dear Martijn I really thank you. The doping profile in my slot waveguide is uniform both in the arms and in the strip-loads. I read in similar publications that they use uniform doping, as well, and just say loss to be negligible. Nevertheless, I should demonstrate it. So if I understand, given the profile to be uniform, I just need to consider the impact of the Silicon doping concentration in the values of and k into the material profile settings, before simulating. I usually use the Rsoft FemSIM, that is a quite generalized Mode Solver.
    Thanks again for you precious help.

  • Udo Bünting added an answer:
    What is the physical limit of the edge steepness of a flat top beam profile?

    What is the physical limit of the edge steepness of a flat top beam Profile?

    We image the output (IR ns pulses) of a multimode fiber to our target in order to drill holes. But the low steepness of the flat top causes flaking on the edges of the hole. The material is a mulilayer structure.

    I like to know the physical relation between the steepness of the beam profile edges with respect to the fiber core diameter, NA and wavelength.

    Udo Bünting · LPKF AG

    Thanks for your prompt answers - it helped!

    We added a phase plate into the TEM00 beam and got a soft flat top. That was coupled into a multimode fiber whitch is some 10m long and coiled in order to mix to modes. At the output we use a 4f transformation with a spatial filter (pin hole) and a high performance optic to focus to the target. All this together gives us a nice and sharp flat top – and as you mentioned – it correlates with the number of modes one can create in the fiber. Hence, as bigger the fiber core as better the result. Off cores all is limited by the aperture of the following optics.

  • Gerson Flavio Mendes de Lima added an answer:
    How is bpm(bi phae modulation) scheme done in optisystem?

    How is bpm(bi phae modulation) scheme done in optisystem?

    Gerson Flavio Mendes de Lima · CGW USA LLC

    may be this paper can help you


  • Juan Marcos Sanz added an answer:
    Why do we have a blue shift when we increase the degree of truncation for Ag nanoprism?

    by simulation, we notice that if we truncate the corner of Ag nanoprisms we have a blue shift and also by increasing the degree of truncation causes increasing in the blue shift in the resonant wavelength of Ag triangular prism structure. please if any one can give any article that explain why do we have blue shift??? Thank you  

    Juan Marcos Sanz · Textil Santanderina, S.A.

    Although I'm not really sure about it, I think that this is a confinement effect. For instance, there is an example in Bohren and Huffman's book for ellipsoids (pg. 141) that can also be related to the 'lightening rod effect' (see S. Maier book on Plasmonics pg. 162, https://books.google.es/books?id=yT2ux7TmDc8C&pg=PA162&lpg=PA162&dq=lightning+rod+effect&source=bl&ots=uevafn1J5z&sig=Ic3sTTZvblUaweiHjd-6WIu5L0s&hl=es&sa=X&ei=8r8rVdrNLoirOtfHgKgD&ved=0CHYQ6AEwDQ#v=onepage&q=lightning%20rod%20effect&f=false). Obviously, without taking into account other effects, if your prism dimension is smaller after the truncation the LSPR will be blue shifted.

  • Benjamin D Snow added an answer:
    How would index of refraction of paraffin change when it melt from solid to liquid?

    I designed an experiment about sensing the phase change of the wax. It start to melt at 40 to 45 degree. I don't know how would the RI change when I heat the wax and the change of the RI is very important to my simulation. If you know please let me know.

    Benjamin D Snow · Merck Group

    Paraffin wax seems to have a refractive index of 1.45, whereas liquid paraffin has an index of 1.48. So to answer your question, the refractive index would increase during the phase change. You may also want to consider a light scattering method if the phase transition temperature is of interest to you.

  • M. F. Sanya added an answer:
    What are the current reaches and capacities of LAN, MAN and WAN networks?

    I would like to draw a diagram of the performances of the known LAN, MAN and WAN networks based on the technologies used, the standards, the distance reached and the capacities. I know someone could answer about the wireless context. Is it possible to give me more informations in the context of optical fiber also? Please help ! Thank you all :)

    M. F. Sanya · University of Limoges/ University of Abomey-Calavi, Benin

    Great and very interesting ;-) ! Thank you dear Francisco Taitingfong

  • Sridhar Iyer added an answer:
    In an OFDM-optical network, how will spectrum overlapping between connections (served at their requested transmission rate) affect the RMLSA problem?

    In an OFDM-based optical network, how will spectrum overlapping between connections (which are served at their requested transmission rate) affect the Routing, Modulation Level, and Spectrum Allocation (RMLSA) problem?

    Sridhar Iyer · Christ University, Bangalore

    Thanks Gerson. That text answers the questions.

  • Jean-Christophe Michel Delagnes added an answer:
    Why there is a green emission or glowing from Er-doped fiber?

    I noticed green glowing from Er-doped fiber after it has been pumped by 975 nm. This Er-doped fiber used as an active gain medium in ring fiber laser. I need a clear explanation for that.

    Jean-Christophe Michel Delagnes · University of Bordeaux

    You do observe the same green light in Yb doped fiber amplifiers pumped at 976 nm. I thus don't know if it is specific to Er or the 976 nm pumping instead.

  • Wurood Khalil added an answer:
    Did anyone use before EDF (model:M5-980-125 from Thorlabs) as an active gain medium for fiber laser or fiber amplifier?

    I need to know the minimum length of this fiber to get signal gain

    Wurood Khalil · University of Baghdad/ Laser Institute for post graduate studies

    Hello Qun

    Many thanks, is the 6m length considered as the minimum or optimum length for this fiber??

  • Gerson Flavio Mendes de Lima added an answer:
    What is the power coupling coefficient and propagation powerloss coefficient based on optical ring waveguide?

    How to measure the power coupling coefficient and propagation powerloss coefficient based on optical ring waveguide?

    Gerson Flavio Mendes de Lima · CGW USA LLC
    1. Ring waveguide resonators are useful components for wavelength filtering, multiplexing, switching and modulation , the equation K= 2 π nz / λ
    2. take a look at the attached file published at Lightwave Journal...
  • Richard Epworth added an answer:
    How to couple light from an LED source to a single mode fiber? Is there LED source available with FC/PC connector at wavelengths 1550nm and 850 nm?

    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. 

    Richard Epworth · Goforich

    Thanks Alan I had forgotten about ELEDs

  • Dimpi Paul added an answer:
    Is there any method to get the mode field distribution in MATLAB?

    I need to get mode field distribution for photonic band gap structure using MATLAB.

    Dimpi Paul · Tezpur University

    Thank you very much for your help.

  • Adam Hughes added an answer:
    How to couple power in wave-guide from optical ring resonator using COMSOL?

    I am designing optical ring resonator based biosensor. So by calculating amount of power coupled in wave-guide, I can sense defect or impurity in the material. I am attaching a paper on which I am working if you want to suggest different tool to implement this problem please tell me.

    Adam Hughes · George Washington University

    I'm just curious, how does this compare in terms of useability to Lumerical MODE solutions?  I am not affiliated with Lumerical or Comsol, just generally curious about these waveguide design softwares that I can't afford...

  • Abdallah Ismail added an answer:
    In coherent optical Comm. sys. (PM-QPSK),How can you measure the effect of non-linearity on BER in case of having a phase correction(DSP) in the Rx ?

    I'm simulating the optical PMD-QPSK using optisystem,and I'm measuring the effect of Nonlinearity on BER,and the problem that I'm using a DSP for compensating the Dispersion,Polarization multiplexing and  carrier Phase Estimation.

    The problem that the effect of nonlinearity doesn't appear because it produce a phase error which is corrected or changed by the DSP component.

    When I tried to disable the carrier phase estimation in the DSP the system also produce error even if there is nonlinearity.

    How can I measure the nonlinearity effect on BER with this problem

    Abdallah Ismail · Egypt-Japan University of Science and Technology

    But +15dBm is a large value and in some papers ,I found that the nonlinearity appears at 5 dBm.

    I count the bits with errors at the receiver by comparing Tx bits with the received one.and I'm sending about 131,000 bits each bits with 4 samples..

    I'll try to test the system wit single span and using large powers as you mentioned and i'll reply with the results.

  • Sridhar Iyer added an answer:
    Energy minimization also implies cost (CapEx) minimization for SLR optical networks. Does the same apply for MLR optical networks?

    Energy minimization also implies cost (CapEx) minimization for single line rate (SLR) optical networks. Does the same apply for mixed line rate (MLR) optical networks?

    Sridhar Iyer · Christ University, Bangalore

    Thanks for the answers. Further, according to my study on till now, the following appears:

    The energy-consumption models for different architectures (transparent / translucent) may also work as the models for CapEx-minimized networks. However, the designed optimization costs would have to be changes accordingly from energy consumption to CapEx values for different components. I think intuitively that must be the case as more energy consuming components would also be more expensive. I agree, energy minimized may not always be CapEx minimized, but will be OpEx minimized.

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Optical engineering is the field of study that focuses on applications of optics.

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