Nonuniformly Spaced Photonic Microwave Delay-Line Filters and Applications

Abstract

A finite impulse response (FIR) filter for microwave signal processing implemented based on an optical delay-line structure with uniformly spaced taps has been extensively investigated, but the realization of such a filter with negative or complex tap coefficients to provide an arbitrary frequency response is still a challenge. In this paper, an overview of photonic microwave delay-line filters with nonuniformly spaced taps, by which an arbitrary bandpass frequency response can be achieved with all-positive tap coefficients, is presented. We show that the nonuniform time delays provide equivalent phase shifts to the tap coefficients, while the all-positive-coefficient nature simplifies greatly the filter realization. Based on the theory, a 50-tap flat-top bandpass filter with a quadratic phase response is designed and analyzed. A seven-tap nonuniformly spaced photonic microwave filter with a flat-top and chirp-free bandpass response is then demonstrated. The use of the proposed technique for advanced microwave signal processing is then discussed. The generation of a chirped microwave signal and a phase-coded microwave signal are discussed and demonstrated. The use of the proposed technique to design a FIR filter for microwave matched filtering is also discussed and experimentally demonstrated.Index Terms-Finite impulse response (FIR), microwave photonics, nonuniformly spaced sampling, optical processing of microwave signals.

Microwave Photonic Filter: A Systematic Literature Review

“…Non-uniformly speed taps for complex coefficient by introducing additional delay to taps [12]. Impulse response h R (T) given by…”

“…Phase term introduced into specific coefficient by adding an additional time delay know as time-delay based on phase shift [12] As the tunablity of a filters increases it is essential that the bandwidth of the filter remains unchanged thus the complex coefficient filters came into picture, the phase component of coefficients helps the filter to maintain the bandwidth of filter even of the filter is tuned to other frequency as well. The filter with complex coefficient in frequency domain can expressed as:…”

Sistemas ópticos incoherentes para la generación de señales arbitrarias basados en filtros fotónicos de microondas

“…En la literatura podemos encontrar un gran número de estructuras basadas en filtros fotónicos de microondas adaptadas para la generación de señales [61][62][63][64][65][66][67][68][69][70][71][72][73][74][75]. La generación de señales eléctricas sin componente continua ha centrado gran parte del interés de las propuestas [76].…”

“…Por otra parte, en la literatura también se pueden encontrar estructuras que sintetizan coeficientes complejos para poder modificar características de la fase de la señal generada [74,75]. En ese caso, se hace uso de un elemento dispersivo para introducir el retardo entre muestras y se asocia cada una de ellas a un láser sintonizable de forma que no se encuentren equiespaciados.…”

“…En ese caso, se hace uso de un elemento dispersivo para introducir el retardo entre muestras y se asocia cada una de ellas a un láser sintonizable de forma que no se encuentren equiespaciados. De este modo, es posible generar pulsos con chirp [74] o codificar señales en fase [75].…”