An electronically controlled semiconductor laser phased array

Abstract

A two-element laser phased array is implemented where two commercially available DFB lasers are phase locked to a reference laser using two heterodyne Electro-Optical Phase Locked Loops (EOPLL) with integrated CMOS electronics. Integrated frequency aided acquisition system increases the acquisition range of EOPLLs from 8 MHz to 980 MHz, improving the phase locking performance in presence of environment fluctuations. The phase of each laser is controlled by phase shifting of the radio frequency signal outside the PLLs, eliminating optical phase shifters. An external feedback loop using a voltage controlled oscillator is realized to compensate for the relative phase fluctuations between the output of locked lasers at the point of beam combining. By electronically adjusting the relative phase between lasers, beam steering over more than 1 mrad at the far field (corresponding to 1 mm beam spot displacement at one meter away from the phased array emitters) has been demonstrated. Use of integrated electronics enables realization of laser phased arrays with large number of elements.