Optical SSB modulator/frequency shifter with ultralow spurious sidebands

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.