Optical Engineering

Optical Engineering

  • Stefano Penna asked a question:
    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 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.

  • Qijin Chi 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

    Qijin Chi · Technical University of Denmark

    What is material of microelectrodes you used? Depending on material types, you can use different ways to seal a microwire (such as carbon fibre, metal wires) in a glass tube.  

  • 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 · Institut National des Sciences Appliquées de Rouen

    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 · Institut National des Sciences Appliquées de Rouen

    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.

  • Karar Abdali 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.

    Karar Abdali · University of Babylon

    Dear, this is may be happen according to change the crystal structure that led to change the optical density, furthermore must be doing FTIR spectrum after and before melt to certain from the chemical structure. I ask does the color of wax change after melt?  see my paper on research gate.

  • 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.

  • Rakesh kumar Naik added an answer:
    Which software can be used for simulation of raman spectroscopy other than optisystem?

    I tried with optisystem, but sample is an issue. I can't find any component which is a good substitute for a sample. Please provide me with a solution!

    Rakesh kumar Naik · Indian Institute of Technology Bhubaneswar

    you can use COMSOL multiphysics


    or you can go through the link below



    but optiFDTD is more recommended

  • Sridhar Iyer added an answer:
    Most research on mixed line rate optical networks restricts the highest rate to 100 Gbps? Is it possible to have a rate much higher than that?

    Most research on mixed line rate optical networks restricts the highest rate to 100 Gbps. Is it possible to have a rate much higher than that. Of course non-linear effects have to be minimized as usual. If that can be done, can we achieve a much higher rate.

    Sridhar Iyer · Christ University, Bangalore

    The only hitch, as I see right now, is the accumulation of non-linear effects. In this regard, it will be interesting to see if XPM still is the dominant effect, as it is till 100 Gbps. O-OFDM ofcourse will have a major role to play for very high rates. Thanks for the comments.

  • Erick Reyes Vera added an answer:
    Best sructure for high effective area in a PCF?

    What is the best structure to achieving high effective area in a solid-core silica-air hole photonic crystal fiber?

    Erick Reyes Vera · Instituto Tecnológico Metropolitano

    Hello Bijan,

    This parameter is influenced by the shape of your fiber. Hence you have a simulation by a shape with variations in period and diameter of holes to optimize this.

  • Florian Bryce Soulard added an answer:
    How should I simulate a digital holographic image with polarized reference and object light?

    I am going to simulate a holographic image that is recorded by polarized light. Could you please let me know how I should do it?

    Florian Bryce Soulard · Durham University


    There is a PhD thesis about polarization imaging for digital holographic microscopy. I haven't studied the polarization part in depth, but it may give you some hints about how to simulate it.
    Simulating a linearly polarized object beam with a linearly polarized reference beam shouldn't be too difficult. Create a 2D complex field with two components (parallel and orthogonal) for the object beam. Add them together with different ratios to simulate a rotation of the polarization direction on the reference beam. Then add to the 2D complex reference distribution and calculate the intensity.

    Good luck.


  • Elwira Czerska added an answer:
    How can I prevent bubbles from occuring in PMMA?

    I'm manufacturing PMMA cladding on glass fiber. I have tried vacuum, water bath and ultrasonic but it didn't help. I need to obtain smooth layer.

    Elwira Czerska · Silesian University of Technology


    I'm using two-component methacrylate resin which composition is:
    powder: copolymer MMA + MA
    liquid: methylmethacrylate, dimethyl-paratoluidine, ethylene glycoldimethacrylate.
    I used room temperature and I tried also water bath of 80oC but after mixing and covering the fiber.


  • Daniel Poitras added an answer:
    Can any explain how to make a rugate broad band design in visible region?

    Thin film optics

    Daniel Poitras · National Research Council Canada

    The bandwidth of the rugate, as for quarterwave stacks, is mostly set by the refractive indices contrast (nH/nL) in the design; the largest the contrast, the largest the reflection band. If you need sharp edges to the reflection band, the thickness required for doing that will be larger for rugate filters than for equivalent quarterwave stack, and even more if you use an apodization envelop with your rugate design.

    If you need to extend the band further, then you probably need to design a filter that will have 2 or more adjacent reflectance bands on the wavelength scale.  We have published a paper on that topic (see attachment), and I am sure that you could find other similar papers.  The resulting design profile will seem complex, but not necessarily complicated to make (some of these designs are not too sensitive to errors I believe).

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