Optimum modulator bias systems and methods in coherent optical transmitters

摘要

A modulator bias selection method, a coherent optical transmitter, and optical modulator solve the problem of generating a correct constellation using the bias points with the minimum phase adjustment range. The optimum modulator bias systems and methods include a coherent optical transmitter with control of four (XI, XQ, YI, YQ) quadrature data signals via a transmitter (Tx) application specific integrated circuit (ASIC), with a modulator bias controller which implements an algorithm to find the optimum bias points. The optimum bias points yield a correct constellation with minimum phase/bias adjustment. An algorithm is used to find the optimum bias solution using fast, simple method, adjusting only one quadrature at a time and exploiting a control feature of the Tx ASIC. This algorithm is significantly simpler than a generalized search, is a local algorithm, and uses only DC power measurement at the transmitter.

主权项

1. A modulator bias selection method for setting bias values in an optical modulator system of an optical transmitter, comprising:
for a pair of inner phase adjusters of an optical modulator, selecting a minimum bias point by sweeping a left phase adjuster and a right phase adjuster of each of the inner phase adjusters and measuring a resulting bias point in the optical modulator system until the minimum bias point is found; for a pair of outer phase adjusters, selecting a half-power bias point by sweeping a left phase adjuster and a right phase adjuster of each of the outer phase adjusters and measuring a resulting bias point in the optical modular system until the half-power bias point is found; and setting bias values for the pair of inner phase adjusters and the pair of outer phase adjusters based on the selected minimum bias point and the selected half-power bias point, wherein the modulator bias selection method is performed locally at the optical modulator system.