Wideband RF photonic in-phase and quadrature-phase generation

Abstract

A photonic implementation of a practical broadband RF Hilbert transformer is demonstrated by using a four-tap transversal system. An almost ideal 90 degrees phase shift with less than 3 dB of amplitude ripple has been achieved from 2.4 to 17.6 GHz. An efficient method to realize both transformed (quadrature-phase) and reference (in-phase) signal has been achieved by using a coarse wavelength division multiplexing coupler. Extension of the transformer bandwidth and further improvements of its implementation are discussed.

Integrated frequency comb source based Hilbert transformer for wideband microwave photonic phase analysis

“…1(a)] is a continuous hyperbolic function 1/(πt) that extends to infinity in time. In order to realize this impulse response using transversal filtering, the hyperbolic function is truncated and sampled in time by discrete taps [12]. The theoretical RF transfer function of the filter is the Fourier transform of the impulse response.…”

“…The time delay between filter taps (wavelengths) can be achieved by using a dispersive medium such as a long optical fiber [12] or a chirped grating [15]. In previous demonstrations of a Hilbert transformer using photonic transversal filtering, discrete filter taps were realized by employing an array of discrete continuous-wave laser sources.…”

“…The number of filter taps that could be achieved was actually limited by the bandwidth of the waveshaper and the gain bandwidth of the optical amplifier (EDFA2). If desired, it would also be possible to reduce the amplitude ripple within the pass-band by apodizing the tap coefficients from the ideal hyperbolic function [12]. To assess the stability of the system, the RF response was measured at different times.…”

“…Microwave Photonic transversal filters have been reported by several groups [11], including a broadband photonic Hilbert transformer for in-phase and quadrature-phase generation [12,13] that exhibited low amplitude ripple and very low phase error over a multioctave bandwidth [12]. The application of this transformer to instantaneous frequency measurement (IFM) has been reported [14][15][16].…”

Reconfigurable broadband microwave photonic intensity differentiator based on an integrated optical frequency comb source

“…[30][31][32] The transfer function of a typical transversal filter can be described as where M is the number of taps, a n is the tap coefficient of the nth tap, and T is the time delay between adjacent taps. It should be noted that differentiators based on Eq.…”