Modulation characteristics of semiconductor Mach-Zehnder opticalmodulators

The transmission and chirp characteristics are described for two types of semiconductor Mach-Zehnder modulators, distinguished by the differential phase shift between the two arms of the interferometer in the unbiased state. The conventional modulator has a differential phase shift of 0 radians, while the π-shift modulator has a differential phase shift of π radians. The nonlinear dependence on the applied voltage of the attenuation and phase constants of the optical signal propagating in the p-i-n waveguide leads to different characteristics for the two modulators. The influence of the splitting ratio of the Y-junctions is considered for single-arm and dual-arm (push-pull) modulation formats. The π-shift modulator is shown to yield better transmission performance for 10 Gb/s systems compared to the conventional modulator     

Performance of optically preamplified receivers with Fabry-Perotoptical filters

A technique is presented for evaluating the probability of error for an optically preamplified receiver with a fiber Fabry-Perot optical filter of arbitrary bandwidth between the preamplifier and photodiode. The technique permits simultaneous consideration of the distortion due to modulator chirp and fiber dispersion, the optical filter and the baseband electrical filter. The optical filter is characterized by a Lorentzian passband response, and the quadrature noise processes due to the amplified spontaneous emission are represented by Karhunen-Loeve expansions. For an arbitrary optical filter bandwidth, the evaluation of the probability of error depends explicitly on the details of the Karhunen-Loeve expansion. The solution procedure is general and consequently can, in principle, be applied to other filter passband responses. The influence of the bandwidths of the optical and electrical filters on the performance of a 10 Gb/s system is assessed