Abstract: A control method and apparatus used for a bias controller of automatic bias correction on an optical modulator of optical emitter of external modulation type is a close-loop control system, composed of a base signal generator, an optical receiver, a second-order harmonic signal generator, a second-order harmonic signal detector, a DC amplifier, and a temperature automatic correction device. The bias voltage point of the optical modulator can remain a constant, whereby the optical power can be exported in stable level and distortion of transmission is reduced. It can be avoided about the effect of the environmental temperature, resulting in the change of optical output and the additional signal distortion of the transmission signal.

Abstract: An optical fiber transmitter, which consists of a modulated optical source, a pre-distortion circuit, a chirped-fiber grating, an optical circulator or a coupler, is designed to transport subcarrier multiplexed (SCM) signals over a long transmission distance. Here the SCM signals include: analog amplitude-modulated vestigial-sideband (AM-VSB) cable television signals, digital quadrature-amplitude-modulated (QAM) signals, or orthogonal-frequency-division-multiplexed (OFDM) signals, or quadrature-phase-shift-keyed (QPSK) signals, etc. on radio-frequency (RF) or microwave carriers, and/or digital wireless signals on RF, microwave or millimeter wave carriers. The modulated light source can be a directly modulated laser diode, or an external LiNbO3 modulator with a continuous wave (CW) laser diode as the source, or an external electro-absorption modulator with an integrated CW laser diode.

Abstract: The invention provide an optical fiber transmitter by both suppressing stimulated Brillouin scattering (SBS) effect and composite second-order (CSO) distortions at an optimized condition. The optical fiber transmitter includes a frequency modulator generating a first tone microwave with frequency f1 coupled to a laser source, and a phase modulator generating a second tone microwave with frequency f2 coupled to an external phase modulator, so as to broaden the modulated light spectrum. The first tone microwave with frequency f1 is set to be greater than 2 to 3 times of the highest frequency content in the modulating signals. The second tone microwave with frequency f2 is designed to be close to a harmonic frequency of f1 and no less than three times of f1. The first tone microwave with frequency f1 and a second frequency f2 are inputted to two power amplifiers, respectively, and then are respectively inputted to a laser source and an external phase modulator.

Abstract: A distortion-compensation circuit for use on a wideband optical-fiber communication system is provided. This distortion-compensation circuit can compensate for the CSO/CTB (composite second order and composite third beat) distortions in the transmitted signals that are caused due to the intermodulation of undesired harmonics that are caused by nonlinear devices in the system. The distortion-compensation circuit includes splitting means, such as a directional coupler, for splitting the input signal into a first signal and a second signal. The first signal is directed to a first path, while the second signal is directed to a second path. A featured CSO/CTB generator is coupled on the second path to receive the second signal for selectively generating a compensating CSO/CTB output from the second signal. Further, combining means, such as another directional coupler, is arranged at the end of the first and second paths, for combining the compensating CSO/CTB output of the CSO/CTB generator with the first signal.