Electronic – How to model an optical filter using python

band passfiltermodelopticspython

Say I have an RGB LED which transmit intensity modulated signals, at one symbol transmission I want to send a symbol with all three chips.. Can I just model three bandpass optical filters like RF filters to filter out the individual intensities impinging the PD? I can't seem to find any design procedure on optical filters.

Basically I want to use color shift keying (CSK) to modulate the data symbols into the LED chips and be able to detect the CSK data symbols on the receiver side (as defined by the IEEE 802.15.7-2018 standard). On the transmitter side I am able to modulate (using python) the symbols but however I do not know how to model the RGB filter and I don't really understand the optical filter design process. Some details regarding CSK can be found at [ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7482661]

Any direction to relevant literature is appreciated.

Best Answer

Yes, you can.

There are a great number of parallels between (certain) microwave filters and (certain) optical filters based on impedance concepts. This section of a video can illustrate this: https://youtu.be/pLl3q6WKtxw?t=2346

Both optical and RF signals and filters can be modeled with complex amplitude/phase responses VS frequency, and so you can use all the same mathematical ideas to model the impact of both in the same way.

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Ti has it's own SPICE tool much like LTSpice is for LT. It is called Tina and it might even have the macro models for your device.

Electronic – Laplace transform on simple low pass filter in Python

You're trying to plot in the time domain (ie. the x-axis is in seconds) but your formula is in the frequency domain (s is a complex frequency variable). You would need to perform the inverse Laplace transform to get back to the time domain.

This cannot be done unless you have a s-domain expression for Vin, which is tricky given that you just created it with random time domain values. Generally when doing this sort of s-domain stuff the output is only calculated for very simple (but very useful) inputs like step functions, impulses or single frequency sine waves.

There are many ways to go about what you're doing, and many of them require years of study. As suggested by @sstobbe, I think time domain simulation is probably your best route. Fortunately Python (via the SciPy library) has an equivalent lsim function. You just have to construct a system transfer function using lti. Something like this:

import matplotlib.pyplot as plt
from scipy import signal

sys = signal.lti(1,[1*0.1E-6,1])
t = np.linspace(0, 5, 150)
v_in = np.random.uniform(-0.005,0.005,150)+5
tout, y, x = signal.lsim(sys, v_in, t)

plt.plot(t, y)

Best Answer

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