Optically efficient high dynamic range electro-optic modulator

Abstract

An electro-optic modulator and a method for its use, in which an optical carrier is effectively suppressed for transmission of a radio-frequency (rf) modulating signal over an optical communication link, to provide improved demodulator performance. A carrier component is recovered from the modulator, amplified, and reused, to minimize the effect of optical carrier losses. In one embodiment of the invention, a modulator (10) with complementary output ports (20 and 22) generates a carrier-suppressed output (FIG. 2B) containing rf sidebands from one port (20) and a strong carrier component (FIG. 2C) from the other output port (22). The carrier component is filtered in a residual sideband filter (14), amplified in an optical amplifying medium (12) and returned to the modulator (10) as its carrier input. In a second embodiment of the invention, a modulator (30) with a single output port produces rf sidebands and a suppressed carrier component (FIG. 4A), all of which are amplified in an optical amplifying medium (32) and coupled to an optical circulator (34), which, in cooperation with a narrowband filter (36), separates the rf sidebands from the amplified carrier component, the latter being returned to the modulator (30) as the carrier input. In both embodiments, a suppressed-carrier optical signal is obtained for transmission over a communication link, but carrier losses are minimized by recovery and recirculation of the carrier. In an alternate embodiment of the invention (FIG. 5), a second modulator (40) removes any residual rf components and avoids any unwanted cavity resonance.