Polarisation dependent all-optical nonlinearity far from the bandedge in active GaAs/AlGaAs quantum well waveguides

This paper describes a measurement on a GaAs quantum well waveguide with a high built in field across the quantum wells at a wavelength far from the bandedge. The device structure used for the measurement has been fabricated at STC Technology Ltd and is that of a standard laser ridge structure. In fabrication double heterostructure layers are grown on a [001] n + GaAs substrate, with the active region containing two intrinsic GaAs quantum wells of 10nm thickness separated by 10nm. A 4μm wide ridge is etched to provide transverse optical guiding. The experimental work has involved the use of 1.06μm wavelength light from a Q-switched Nd:YAG laser. Any induced change in refractive index is determined by measuring the change in transmission of the quantum well waveguide Fabry-Perot cavity. The waveguide is placed on a Peltier temperature controller to allow thermal tuning.

Electro-optic modulation of 1.5μm light in an active InGaAsP/InP quantum well waveguide

We report an InGaAsP/InP phase modulator operating in the 1.5μm wavelength band. Phase modulation of 7.5°/mA and 1.7°/mA of injected current have been measured for TE and TM polarised light respectively at a signal wavelength of 1.52 μm.

Demonstration of a compact InGaAsP active crosspoint switch operating at 1.5 μm using novel reflective y-coupler components

An extremely compact active optoelectronic crosspoint switch, having overall dimensions of 400 μm×200 μm, is reported. The device provides unity facet-to-facet gain for both bar and cross state operation for TE or TM input signals.

Multimode radiation from an unflanged, semi-infinite circular duct with uniform flow.

Multimode sound radiation from an unflanged, semi-infinite, rigid-walled circular duct with uniform subsonic mean flow everywhere is investigated theoretically. The multimode directivity depends on the amplitude and directivity function of each individual cut-on mode. The amplitude of each mode is expressed as a function of cut-on ratio for a uniform distribution of incoherent monopoles, a uniform distribution of incoherent axial dipoles, and for equal power per mode. The directivity function of each mode is obtained by applying a Lorentz transformation to the zero-flow directivity function, which is given by a Wiener-Hopf solution. This exact numerical result is compared to an analytic solution, valid in the high-frequency limit, for multimode directivity with uniform flow. The high-frequency asymptotic solution is derived assuming total transmission of power at the open end of the duct, and gives the multimode directivity function with flow in the forward arc for a general family of mode amplitude distribution functions. At high frequencies the agreement between the exact and asymptotic solutions is shown to be excellent.