Low-loss semiconductor waveguide bends.

An experimental comparison is made between the losses of waveguide bends in disorder-delineated waveguides in semiconductor superlattices composed of GaAs and AlAs layers for simple abrupt bends and abrupt bends with an additional half-angle guiding wall proposed by Shiina et al. [Opt. Lett. 11, 736 (1986)]. For light above the band gap of bulk GaAs, the abrupt and Shiina bends were found to have to 3-dB loss angles of 3 and 7 deg, respectively. This improved performance suggests that the specific geometry of the bends is yet another degree of freedom in designing guiding structure for planar routing.

Losses in semiconductor waveguide S bends fabricated by impurity-induced layer disordering.

An experimental comparison is made between the losses of S bends fabricated by impurity-induced layer disordering in GaAs-AlAs superlattices. For parallel waveguides offset by 100 microm, transition lengths corresponding to 3-dB excess loss were found to be approximately 290 microm for approximately single-mode S bends in the form of a raised cosine and approximately 335 microm for bends in the form of two constant-radius-of-curvature sections. These buried-channel bends appear to have losses that compare favorably with those formed from rib waveguides.

Optimum emission polarization and power enhancement in circularly polarized optically pumped lasers.

Two-wave-coupling coefficients are presented in the high-J limit for all combinations of linearly and circularly polarized waves and all dipole-allowed transition branches. The results are used to predict the optimum state of emission polarization and the anticipated output-power change under the influence of a circularly polarized pump in optically pumped lasers.

Far-IR optical properties of freestanding and dielectrically backed metal meshes.

The optical properties of freestanding and dielectrically backed inductive metal meshes are investigated in the far IR spectral regime. The most pronounced effect of the substrate is to cause a shift in the diffraction edge to longer wavelengths by a factor equal to the substrate index of refraction. Various theoretical models are reviewed and tested with the main result being that only the microwave based waveguide-array model successfully predicts the freestanding and dielectrically back optical features in and around the diffraction edge. A simplified version of this model is presented and shown to be adequate for describing the majority of the spectral features. The backed meshes are then characterized in terms of mirror quality for use in optically pumped far IR lasers.

Some considerations in the design of a high power, pulsed n(2) laser.

Pulsed, megawatt laser power levels at 3371 A from nitrogen gas require the formation of a high density plasma of high electron temperature in the first few nanoseconds of gaseous breakdown. This has been obtained from a laser tube powered by a pulse forming network in the form of a low impedance, parallel plate transmission line. Another low impedance, parallel plate transmission line, charged to 30 kV is used to pulse charge the pulse forming line by means of a synchronized, multiple spark gap switch. The pulse forming transmission line terminates in a continuous high voltage electrode which runs parallel to the axis of the tube, i.e., in the direction of the light beam. The finite, nonzero time required for the gas in the laser tube to break down, permits (a) pulse charging this line to voltages many times larger than the dc breakdown voltage of the nitrogen in the laser tube, and (b) the placement of the switch in the circuit where its impedance does not limit the rate of rise of current during the laser excitation process. Furthermore, it is shown that decreasing the impedance of the pulse forming line increases the laser output power, when the current in the laser circuit is not limited by circuit inductance.