Optiwave Systems Inc.
Product Manager – OptiBPM, OptiFiber and OptiGrating
Forum Replies Created
It would be interesting to see an example. Can you attach one to your post?
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.
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.
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.
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.
This is a frequently asked question. So much so that I did a webinar on it. I have attached the written material from the webinar. I hope that helps.
I’m afraid that OptiGrating was not designed for sweeping parameters. As you can see, it has a facility for presenting a single spectrum, not many spectra. Even if the parameter could be scanned/sweeped, OptiGrating would not be able to properly present the results. As it is, it can present the spectrum for a specified temperature or temperature distribution over the fibre length, but that is all.
It appears that OptiFDTD can export DFT data from Observation Area and Observation Lines. It can also export time series data from Observation Points. However, the function of export of DFT data from Observation Points seems to be missing. Sorry about that. 🙁
OptiBPM Designer can display the Z axis on a different scale from the X or Y. Go to View >> Layout Options. The Display ratio panel in the Options dialog box will let you dial any Z to X ratio you want.
The interface suggests the dimensions to be microns. However, the simulator scales everything to whatever was specified to be the optical wavelength in the Simulation Parameters dialog box. Again, the interface suggests to enter this wavelength in microns. However, you could enter the wavelength in nm, cm, m, or even inches, if you like. In that case, all other dimensions would be in whatever units were used for the specification of wavelength. If you specify the wavelength in cubits, the dimensions in the layout will be interpreted as cubits too. 😀
I believe the point of the 8° inclined cleave is to reduce the amplitude of the backwards travelling optical fibre mode reflected from the end of the fibre. The Beam Propagation Method will not shed any light on this (no pun intended), as the BP method cannot simulate reflections. On the other hand, I don’t think the inclined facet will change the far field pattern significantly, except for the change in the direction of optical axis that could be anticipated from Snell’s law.
This text file begins with some data about the size of the window and the number of points in the X axis (NX) and the number in Y (NY). The optical data follows one mesh point at a time as
Z1 complex number z data point with coordinates (xmin, ymin)
Z2 complex number z data point with coordinates (xmin+dx, ymin)
Z3 complex number z data point with coordinates (xmin+2dx, ymin)
ZNX complex number z data point with coordinates (xmax, ymin)
ZNX+1 complex number z data point with coordinates (xmin, ymin+dy)
ZN last complex number z data point with coordinates (xmax, ymax),
There are two images, in one there is a honeycomb photonic crystal fibre, in the other there is the same image but with fewer points in the discretization of the image. One of the images comes from an .rid file with Nx = Ny = 651. The other image must be from the ref. index view in an OptiBPM project. The discretization of the OptiBPM project will follow the settings found in the 3D tab of the Simulation Parameters dialog box. There is a panel called Mesh Size for the number of points to be used in X and Y. Could the OptiBPM project have smaller mesh parameters? Nx appears smaller than 651, Ny also appears smaller than 651.
In the Export Profile… / Import Profile feature, the profile data is arranged as a sequence of concentric layers of specified width and refractive index. The first column has the widths (annuli) in microns. The second column has the refractive index found in each layer (annulus). The first column is not a coordinate value of the radius. For example, a step index fibre with core diameter 8.3 and cladding outer diameter 125 µm will appear as
and not as it would be in coordinate form
If the data is presented in coordinate form, the radii will be interpreted as widths and the fibre will appear somewhat larger than expected!