Low-drift AM–PM based optical single-sideband modulator without 2nd-order sideband with adjustable optical carrier-to-sideband ratio

Abstract We propose and theoretically investigated a novel scheme to implement optical single-sideband (OSSB) modulator without 2nd-order sideband with adjustable optical carrier-to-sideband ratio (OCSR). The proposed structure is based on a hybrid concatenated electro-optic amplitude (or intensity) modulator (AM) and phase modulator (PM). The AM consists of a bidirectional PM inside a Sagnac loop (SL). Bias-drift associated problems do not present in the proposed structure because it uses PMs which are bias-free. Furthermore, clockwise (CW) and counter clockwise (CCW) optical signals propagate in the same optical fiber inside the SL, so its robustness against environmental changes increases. The structure is fed by three microwave signals with equal amplitudes and proper phases. The OCSR of the generated OSSB modulated signal can be adjusted by tuning the optical and/or microwave phase shifters and/or the PM modulation indices. The 3rd-order sidebands can also be suppressed by setting the proper optical and microwave phase shifts and adjusting the PM modulation indices.