Forum Replies Created

    #50085
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    Steve Dods
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    To make a layer composed of graded index in OptiFiber:

    1) In the Fiber Profile dialog box, select a layer. Some data for this layer will appear in the Region name panel.
    2) In the Profile combo box select “function” (Default is “constant”)

    3) In the Function combo box box select “linear, or parabolic, alpha peak, dip, exponential, Gaussian…etc.

    4) click on Refr. Index Define button inRegion name panel to specify details of your refractive index.

    5) Adjust Steps as required for sufficient precision.

    #50076
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    Steve Dods
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    I could not open 1800.bpd. I get the error message “Unrecognised format in file 1800.bpd”.
    Was this project file made by a recent version of the OptiBPM designer?

    #50056
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    Steve Dods
    Participant

    Before a BPM simulation can begin, the optical field must be known for every point on the input plane. This usually requires a mode solver. OptiBPM will call one if set that way. The above message is sent when that modesolving fails, either because of incorrect settings in the modesolver or because the mode does not exist. Using Gaussian fields for the input plane will help, but you’ll have to supply a value for the reference index – OptiBPM will call the mode solver to find that parameter if you don’t specify it.

    #49401
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    Steve Dods
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    FBG2.ifo

    Attachments:
    1. FBG2.ifo
    #49399
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    Steve Dods
    Participant

    FBG1.ifo

    Attachments:
    1. fbg1.ifo
    #49398
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    Steve Dods
    Participant

    I got the results of OptiGrating Section (Fig. 1, Fig. 2, and Fig. 3) in these two OptiGrating projects attached.

    #49341
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    Steve Dods
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    Yes, that’s right. Segment is not the same as period. Segment means only that within the segment the grating is taken to be uniform – same period, same amplitude. OptiGrating calculates non-uniform gratings by connecting many short uniform ones.

    #49339
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    Steve Dods
    Participant

    Profile0 is a plot of the grating shape: the refractive index variation with Z over one grating period. That explains why 0 < z < .5338 for that plot. OptiGrating will display that curve in its own interface if you right click on the Profile tab and select Shape…

    Plots 1, 2, and 3 display local period, apodization, and average refractive index. Those are defined over the length of the grating, 0 < z < 50,000. The number of points for display comes from the number of segments specified in the Grating Definition dialog box. The file will show the value at the beginning and the end of each segment: two values per segment. Therefore if there are 100 segments, there will be 200 points.

    #49338
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    Steve Dods
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    Unfortunately User Function Profile returns only real numbers. There is no way to add loss as a calculated imaginary part of refractive index. On the other hand, putting an additive User Function Profile on a lossy dielectric is a clever trick. That should be a good workaround for most cases.

    #48910
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    Steve Dods
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    It would be interesting to see an example. Can you attach one to your post?

    #48857
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    Steve Dods
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    OptiBPM can calculate the power in the fundamental mode at the end of the propagation. Those results can indicate the level of coupling efficiency in the simulation.

    +1
    #48770
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    Steve Dods
    Participant

    Hello Jawad,
    In the usual case, modes in a waveguide are independent, meaning that the light in one mode will propagate without affecting the light in another mode. The case where light goes from propagation in one mode to propagation in another is exceptional, usually due to some special circumstances, such as a periodic disturbance or possibly an environmental influence. Therefore mode conversion is sometimes the basis for a sensor, making it interesting for practical applications.

    #48464
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    Steve Dods
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    I’m afraid OptiFiber will not help with this simulation. OptiFiber uses modal analysis, but this method won’t work well for this sample. Your sample fibre has a radius of 980 µm, wavelength .65 µm, core and cladding refractive index 1.49 and .13725. The V number is therefore 5,494. The number of modes for high V number is estimated from 0.5*V^2, which is more than 15 million. I’m afraid that is too many modes! OptiFiber can perform multimode analysis. It will work reliably even if there are dozens of modes, but 15 million is just too many!

    You can probably get meaningful results from a propagation kind of simulation, like BPM, but modal analysis is simply the wrong method for this problem.

    #48422
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    Steve Dods
    Participant

    The Beam Propagation Method (BPM) is a paraxial method. This means it applies only in the case where there is an optical axis. The U bend is not such a case. On the other hand, accurate results have been demonstrated when BPM is used together with a conformal mapping. (see, for example, IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 43, NO. 10, pg 899-909 OCTOBER 2007)

    OptiBPM has a conformal mapping region. Please use the conformal mapping region of OptiBPM to calculate the details of optical propagation in a U bend.

    #48200
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    Steve Dods
    Participant

    SymmetricCombiner.pdf