Performance analysis of an optical single sideband modulation approach with tunable optical carrier-to-sideband ratio

In this work, we report an all-optical approach to tune the optical carrier-to-sideband ratio (OCSR) of the typical optical single sideband (OSSB) modulation signals. The key component is a broadband polarization-maintaining fiber Bragg grating (PMF-FBG), which can be fabricated using a chirped grating phase mask. Firstly, we employed this PMF-FBG to reflect two subcarriers (carrier and sideband) of the typical OSSB modulation signals with orthogonal polarization, simultaneously. Since chirped fiber gratings have broadband reflection bandwidth, it will be easy to align the target subcarriers to the grating's reflection bandwidth. Then, a linear polarizer is connected with its principal axes aligned at 45° relative to the fast axis of the PMF-FBG. By doing this, the OCSR is strictly dependent on the injected polarization direction at the PMF-FBG. In other words, the OCSR's tunablity can be realized by tuning a polarization controller placed in front of the grating. Thus continuous tunability of the OCSR can be done. To investigate this technique, a more normal case is considered, with multi tones as the RF source (N denotes the number of RF tones). It is found that when OCSR=N (in value) is satisfied, best receiver sensitivity can be predicted.

► An all-optical approach is proposed to tune the OCSR.
► It is characterized by OCSR tunability continuously and also low attenuation.
► A broadband PMF-FBG is employed, which is cheap and easy to fabricate.
► Multi RF tones modulation is considered. The optimum OCSR is found as OCSR=N.