Non-Uniform Sub-Nyquist Optical Sampling by Acousto-Optic Delay Modulation

Abstract

This paper presents an optical sampler based on the combination of a mode-locked laser and external acousto-optic delay modulator, and demonstrates its use in a non-uniformly subsampled photonic link. Delay modulation of the laser's uniformly spaced pulse sequence produces a non-uniformly spaced optical pulse train, which subsequently sub-samples the microwave input of the photonic link. Using this non-uniform sub-sampler, microwave frequencies spanning a range exceeding 200 Nyquist zones are aliased to a single zone, with modulation sidebands added that uniquely identify the input frequency. This enables wideband spectral folding and frequency disambiguation, using a single sampler that is based on a high-stability pulsed laser.

A 1550nm passively mode-locked fiber laser with the repetition rate of 800MHz

“…A 1550 nm femtosecond (fs) fiber laser with a high repetition rate more than 500 MHz, has been widely used in laser spectroscopy, precision measurement, microwave photonic signal processing, optical sampling, analog-to-digital converter etc. [1][2][3][4][5][6]. A passively mode-locked fiber laser is an effective way to realize a high repetition rate fiber laser with fs pulses, at a wavelength around 1550 nm, in turnkey operation [7; 8].…”