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Abstract
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In this paper a novel optical intensity modulator with tunable optical carrier-to-sideband ratio (OCSR) and
adjustable chirp parameter is proposed and theoretically investigated. It is based on a bidirectional phase
modulator (PM) and a tunable nonreciprocal optical phase shifter in a Sagnac interferometer (SI). Because no
bias is necessary for a PM, the bias-drift problems are automatically removed. Besides, clockwise (CW) and
counter clockwise (CCW) propagating lights travel in the same path so enhances robustness against environmental
perturbations. In this modulator two radio frequency (RF) signals with opposite phases and tunable
power ratio are applied to the bidirectional PM. Chirp parameter and OCSR of the modulator can be tuned by
tuning the phase shift of the optical phase shifter and RF power ratio. Besides, this modulator can have two
complementary balanced outputs. So common-mode noises such as relative intensity noise (RIN) of the laser can
be suppressed in a microwave photonic link (MWPL) based on this modulator and using a balanced receiver. This
novel modulator can also operate bidirectionally. An intensity modulated optical signal with tunable OCSR and
chirp parameter is achieved by adjusting the optical phase shifter and the RF power ratio. The effect of the lossy
SI and finite optical extinction ratio on the performance of the proposed modulator is theoretically investigated.
In addition applications of the proposed chirp-adjustable modulator to overcome fiber dispersion-induced power
penalty in a MWPL is investigated It is shown that by adjusting the chirp parameter, link distance for a given
frequency (or bandwidth for a given link distance) doubles.
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