Optical SSB modulator/frequency shifter with ultralow spurious sidebands

Abstract

In this paper, we report and theoretically investigate an optical single-sideband suppressed-carrier (OSSB-SC) modulator/frequency shifter with ultralow spurious sidebands. The novel, to the best of our knowledge, structure is based on three Sagnac interferometers (SIs) and two bidirectional phase modulators (PMs). The two bidirectional PMs are driven by four radio frequency (RF) signals with equal powers and appropriate phases. An OSSB-SC signal with only ( 4 n + 1 ) th-order sidebands, where n is an integer number, is generated. Besides, by applying appropriate RF phase shifts, an OSSB with carrier ( O S S B + C ) modulator can be obtained whose optical carrier-to-sideband ratio (OCSR) can be tuned by controlling the PMs modulation indices. Also, by using the proposed OSSB-SC modulator in another SI, its OCSR can be tuned by controlling the state of polarization in addition to the modulation indices of the PMs. Since the proposed structure is based on SI and no direct current (DC) bias is required for the PMs, it is robust against environmental perturbations and decreases problems associated with DC bias-drift. In addition, performance of the proposed structure under the power and phase imbalances due to the external non-ideal RF hybrid couplers and the phase imbalance of practical non-ideal nonreciprocal optical phase shifters are investigated. Simulation results using commercial software are also presented which are in good agreement with analytical results.

A Microwave Photonic Frequency-Doubling Phase Shifter Based on Dual-Parallel Mach–Zehnder Modulators

“…The RF signals are modulated onto an optical carrier and processed in the optical domain [4]. Thanks to the advantages of the small volume, lightweight, low loss, large bandwidth, and anti-electromagnetic interference, photonic techniques are widely used to create broadband phase shifters with a 360-degree shifting range [5][6][7][8][9][10][11][12].…”

“…Furthermore, magnitude deviations resulting from the notch-magnitude response of the MRR should be noted in the design of MRR-based phase shifters. Another approach to implementing phase shifting is using electro-optic modulators (OEMs), such as dual-polarization dual-parallel Mach-Zehnder modulators (MZMs) [9], dual-polarization MZMs [10], bidirectional phase modulators [11], or dual-drive dual-parallel MZMs [12]. In OEM-based phase shifters, the phase shifts are usually implemented by adjusting the bias voltage.…”