Abstract: A complex spectrum related to a carrier signal that is modulated with random data is measured as a function of the data clock so that the randomness that is contributed by the modulation of random data can be ignored. In one embodiment, the complex spectrum that is expressed in terms of both spectral amplitude and spectral phase is sampled only at the carrier frequency and at the frequencies that are away from the carrier signal by integral multiples of the clock frequency. This sampling approach reduces the complex spectrum to only those data points that are needed to characterize the average pulse shape of the modulated carrier signal.

Abstract: A receiver and method for using the same to process optical signals is disclosed. The receiver includes an optical coupler and a polarization dependent beam splitter. The optical coupler combines an input signal and a local oscillator signal into a first combined signal. The optical coupler includes a polarization filter that operates on the local oscillator to provide a linearly polarized signal having a predetermined LO polarization direction.

Abstract: In one embodiment, a method determines the spectral content of an optical signal. Specifically, the optical signal and an optical local oscillator (LO) signal are provided to inputs of an optical hybrid (e.g., an N×N optical coupler where N is greater than two). The phase-diverse components from the optical hybrid are photodetected allowing for mixing of the optical signal and the optical local oscillator. Bandpass filtering is performed to eliminate or reduce relative intensity noise (RIN). The filtered signals are mixed with an electrical LO signal. A quadrature representation of a phase-diverse heterodyne signal is generated from signals from the mixing. The negative image and the positive image from the quadrature representation are separated. The spectral content of the optical signal is determined from the images.