Bandpass filter with flat-top transmission using multistage Fabry-Perot with unequal cavity lengths

Faiza Iftikhar; Imran Cheema

doi:10.1117/12.2578189

5 March 2021 Bandpass filter with flat-top transmission using multistage Fabry-Perot with unequal cavity lengths

Faiza Iftikhar, Imran Cheema

Proceedings Volume 11713, Next-Generation Optical Communication: Components, Sub-Systems, and Systems X; 117130N (2021) https://doi.org/10.1117/12.2578189
Event: SPIE OPTO, 2021, Online Only

Abstract

A bandpass filter with a flat-top transmission is highly essential for various applications in optical communications. Previously, bandpass filters are designed by optimizing reflectivities of multistage Faby-Perot with equal length cavities. In these prior cases, at least the same number of equal length cavities are required as the filter’s designed order. Here, we present a novel digital synthesis technique to achieve a ripple-free passband transmission by optimizing the multistage etalons’ unequal cavity lengths. We find that the number of cavities is less than half of the designed filter order with our approach. As an example, we design a Chebyshev bandpass optical filter with ripples less than 0.0001 dB in the passband, stopband peak rejection of less than -50dB, and isolation among the neighboring channels greater than 60 dB. The desired filter is designed and estimated its transfer function in the z-domain. It is then refined by changing the denominator and numerator polynomials’ powers in a set pattern iteratively and compared the response with the desired one using predictive-error-method to get the transfer function of unequal cavity multistage Fabry-Perot with least mean-square-error. Using our proposed procedure, we realize the filter by determining the required number of cavities and their respective lengths by assuming fixed reflectivities of reflectors. This work is easily generalizable to ring resonators and Fiber-Bragg-grating based cavities.

Conference Presentation

Citation Download Citation

Faiza Iftikhar and Imran Cheema "Bandpass filter with flat-top transmission using multistage Fabry-Perot with unequal cavity lengths", Proc. SPIE 11713, Next-Generation Optical Communication: Components, Sub-Systems, and Systems X, 117130N (5 March 2021); https://doi.org/10.1117/12.2578189

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