W. R. Trutna

Interference-filter-tuned, alignment-stabilized, semiconductor external-cavity laser

We compared the angular alignment tolerance and the tuning range of a novel interference-filter-tuned semiconductor external-cavity laser based on a degenerate resonator with characteristics similar to those of a conventional grating-tuned external-cavity laser using a 1300-nm In GaAsP Fabry-Perot laser with an antireflection-coated facet as the gain medium. The interference-filter cavity had a 260-fold greater alignment tolerance (+/-26 versus +/-0.1 mrad) and nearly the same tuning range (90 versus 110 nm) as the grating-tuned cavity.

Unidirectional diode-laser-pumped Nd:YAG ring laser with a small magnetic field.

Single-mode operation of a monolithic semiconductor-laser-pumped unidirectional ring Nd:YAG laser has been demonstrated at 1319 and 1338 nm. The ring design optimizes the polarization eigenvalue difference between counterpropagating modes of the ring. The laser threshold is 4.5 mW, and the magnetic-field requirement for unidirectional operation is approximately 100 G.

Anomalous sidelobes and birefringence apodization in acousto-optic tunable filters.

Integrated-optic acousto-optic filters have large asymmetric sidelobes that have not been explained in previous publications. We show that this is caused by waveguide birefringence nonuniformity. For the devices described here, the dominant cause of the nonuniformity is a thermal gradient associated with the generation and absorption of the surface acoustic wave. When the thermal birefringence gradient is included in the coupled-mode model, asymmetric sidelobes in good agreement with observations are predicted. In addition, we show that waveguide inhomogeneities also lead to birefringence nonuniformity and can be used to tailor the birefringence to supress sidelobes in a two-section acousto-optic filter.

Reduced sidelobe integrated acousto-optic filter with birefringence apodization

A two-section integrated acousto-optic tunable filter with significantly reduced sidelobes has been fabricated. The sidelobe reduction was achieved with birefringence apodization in the form of variable-width Ti-stripe waveguides. The design and fabrication of the device, which includes integrated proton-exchanged TE and TM-pass polarizers, are described. Experimental tuning curves for each filter section and the overall device are presented and compared with calculated results. The largest sidelobes were found to be 24 dB below the peak transmission, which represents a 5.3-dB improvement over an ideal filter without birefringence apodization. The FWHM of the filter is 1.36 nm, which is only 16% larger than predicted for its interaction length of 17 mm/section.

Alignment-stabilized grating-tuned external-cavity semiconductor laser

We have demonstrated an alignment-stabilized cavity configuration for a grating-tuned external-cavity semiconductor laser using a cylinder lens to form a line focus on the surface of the grating. The grating in the stabilized cavity has a 350-fold greater angular misalignment tolerance than in a conventional collimated-beam cavity, while the same spectral resolution is maintained.

Photocurrent amplification in Schottky photodiodes

Up to 20 dB of photocurrent amplification with a frequency response of 2 GHz has been observed in GaAs Schottky photodiodes. The amplification may be caused by a reduction in Schottky built‐in potential under illumination. The device may find application in improving the sensitivity of optical receivers.

Two-piece, piezoelectrically tuned, single-mode Nd:YAG ring laser

A two-piece, single-mode, piezoelectrically tuned Nd:YAG ring laser has been demonstrated at 1338 nm. The laser was derived from a previously demonstrated monolithic unidirectional ring laser that has been cut in two to allow the cavity to be tuned by varying the gap between the two pieces. More than 1 mW of output power was produced when the laser was pumped by a 30-mW, 809-nm GaAlAs semiconductor laser. Continuous tuning over the 13.5-GHz longitudinal mode spacing with millisecond sweep times was demonstrated.

An Improved Alignment System For Wafer Steppers

A diffraction grating alignment system has been demonstrated on a GCA stepper. Registration of better than 0.2 microns, 3 sigma has been achieved on NMOS production wafers.