UC Santa Barbara

Semiconductor tunable diode lasers have applications in various fields such as spectroscopy, remote sensing, and fiber optic communications. They are used as the sources in wavelength division multiplexing (WDM) systems, as local oscillators in coherent detection schemes, and as a key component in various photonic integrated circuits (PIC). In recent years there has been increasing interest in hybrid silicon-III/V as a platform for photonics. Silicon processing has been well defined in CMOS fabrication facilities, has low waveguide loss at telecommunications wavelengths, and has the capability of being integrated closely with electronics. Combining silicon with active III/V materials, such as InP, allows a higher level of integration on a single chip. Additionally, new types of tunable lasers can be created that utilize the strengths of both materials. This work explores the design, fabrication and measurement of several ring-based tunable lasers and their application in two photonic integrated circuits.

The first PIC is the first fully integrated two-dimensional beam-steering chip. The tunable wavelength from the laser is utilized to change the angle of emission from an output surface grating array. The second dimension of tuning is controlled by an optical phased array. Coherent light is split into multiple channels with individually tuned phases which are emitted from an array of surface gratings. By proper tuning of the phases an arbitrary beam angle can be formed from the interfering outputs of the array. Beam-steering from a fully-integrated chip is demonstrated over 23˚ x 3.6˚ with respective beam widths of 1˚ x 0.6˚, allowing for 138 resolvable points.

The second PIC is a tunable photonic microwave signal generator. This is created by heterodyning the output from two lasers on a fast photodetector and reading the beat tone at the frequency difference between them. The output frequency of the device can be shifted by tuning one of the laser sources relative to the other laser thus creating a tunable microwave source. The photodiode exhibits 65 GHz 3 dB bandwidth. Microwave signals from 1 to 112 GHz are demonstrated from a fully integrated PIC.