Integrated AlGaAs waveguide components for optical phase difference measurement and correction

A Y-junction interferometer phase measurement technique has been developed that is independent of the power or power ratio in the input arms. This technique was incorporated into a proof-of-concept AlGaAs guided-wave Mach-Zehnder interferometer to demonstrate the measurement and correction of a phase difference between the arms. In the first part of this paper, we describe the design, fabrication, and characterization of the individual AlGaAs dielectric-loaded rib waveguide components that were chosen to fabricate the proof-of-concept interferometer. These components include passive waveguides, bends and Y-junctions, and reverse-biased phase modulators. The composition of the waveguide layer was chosen so that these modulators would have low loss at the applied voltage required for maximum phase correction. The choice was based on electroabsorption measurements on test modulators as a function of the energy difference between the bandgap of the waveguide layer and the operating wavelength. The average propagation loss at 862 nm of the passive single-mode guides used was 1.1 dB/cm. The abrupt bend insertion loss was ~0.20 dB/bend for a 0.5° bend angle, and the Y-junction insertion loss was ~0.37 dB for 1.0° full angle. Two-mm-long p⁺ -n^--n⁺ phase modulators typically had V_π voltages of ~6.8 V. On a slightly modified structure, V _π voltages as low as 2.65 V were measured. In the last part of the paper, the proof-of-concept interferometer and test setup are described and recent phase difference measurement and correction data with intentional power imbalances greater than 90% between the interferometer arms are presented. These results demonstrate conclusively that the phase difference measurement and correction performance of the Y-junction interferometer technique are independent of the power ratio in the interferometer input arms for power ratios >10:1