Shih-Yuan Wang

Gaussian beam profile and single transverse mode emission from previously multimode gain-guided VCSEL using novel etch

A simple model is used to design and optimize masks that when etched onto the aperture of a normally multi-mode gain guided vertical-cavity surface-emitting laser, VCSEL, cause the device to lase in a single transverse mode. After etching, Gaussian beam profiles for the LP01 mode are achieved over the entire operating current range with greater than 16 dB modal suppression. To date single mode emission at 2 mW has been achieved with pinning of the nearfield width. The modelling shows that the etching introduces a spatial filter on the higher order modes. The power in the fundamental mode remains constant before and after etching.

Gain-switching of GaInN MQW laser diodes

A study of the gain-switching process in GaInN MQW laser diodes is reported. Single peak gain-switched optical pulses with pulse widths less than or equal to 40 ps and optical powers equal to 100 mW are observed when electrical pulses with duration of 800 ps are applied. Sub-nanosecond optical pulses with peak powers in excess of 450 mW are also obtained and degradation mechanisms are analyzed. The transient response characteristics of the laser diodes are studied in both the time and spectral domains.

Analysis of polarisation pinning in vertical cavity surface emitting lasers using etched trenches

Recent work has shown that the etching of deep trenches in close proximity to GaAs VCSEL apertures consistently causes the linear TE polarization of the emission to be pinned in a direction parallel to the line etch. Further enhancement of this polarization pinning has been achieved by post- annealing after etching. Initial studies have been carried out using photoluminescence and Raman measurements of the VCSEL wafer before and after etching as well as after annealing. Modeling the observed shift in the optical cavity (longitudinal) mode has indicated that etching introduces strain perpendicular to the etch in the active region of the VCSEL of 4 X 108 dyn/cm2. The strain causes the cavity mode to shift to longer wavelength and reduces the spontaneous emission in the direction perpendicular to the etched trenches. The strain introduced by etching is believed to be the origin of this polarization pinning effect. Measurements of the spontaneous emission profile across the VCSEL facet after etching give valuable information on the mechanisms involved.