A broadly tunable MQW laser utilizing a combined impurity-free vacancy disordering and beam steering techniques is
proposed and investigated experimentally. The device consists of a beam-steering section and an optical amplifier
section fabricated on a GaAs/AlGaAs MQW p-i-n hetrostructure substrate. The beam steering section forms a
reconfigurable single mode waveguide that can be positioned laterally by applying electrical currents to two parallel
contact stripes. The active core of the gain section contains a GaAs/AlGaAs MQW that is progressively disordered such
that an optical beam steered through the selected region experience a peak in the gain spectrum that is determined by the
degree of disordering of the MQWs. Furthermore the MQW in the beam-steering section is disordered to the largest
extent to minimize optical beam attenuation. The MQW structure was intermixed using an impurity-free vacancy
induced disordering technique. The MQW sample is encapsulated with a SiO2 film grown by plasma enhanced chemical
vapor deposition (PECVD). The beam steering region is coated with a 400nm thick SiO2 film whereas in the gain
section, the SiO2 film is selectively etched such that the thickness grades linearly ranging from 0 to 325nm. The
disordering of the entire slab region is then induced by a single rapid thermal annealing step at 975°C for a 20s.
Experimental results showed a controllable 10 to 60 nm wavelength blue shift of the peak of the photoluminescence
spectrum corresponding to the change in SiO2 caps thickness and a lateral beam steering range up to 20 μm over the slab
An integrated 2 x 2 multimode interference switching device was fabricated with InAs/In0.15Ga0.85As quantum dots as the
active medium. The device, when probed with a 1.31 μm wavelength laser beam, showed similar responses for TE and
TM polarization with initial power splitting ratios of 1:29 (TE) and 1:52 (TM) that were continuously adjustable to 49:1
(TE) and 38:1 (TM) when a change in current of 24 mA was applied through one of the electrodes. This is equivalent to
achieving channel-to-channel crosstalk values of better than -15 dB for both polarizations. A 50:50 split ratio was
reached at a current of 17 mA. We also present the preliminary results from an integrated variable power splitter that is
based on a half-length multimode interference structure.
We demonstrate an integrated 1x3 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells. The core of the switch relies on a beam-steering concept which allows us to steer the optical beam to any of three output waveguides. The device is relatively simple, since current is only applied to two electrodes for complete operational control. The device integration is achieved using an area-selective zinc in-diffusion process that is used to channel the currents into the multiple quantum wells, thereby enhancing the efficiency of the carrier-induced effects. This results in a low electrical power consumption, allowing the switch to be operated uncooled and under d.c. current conditions. The crosstalk between channels is better than -17 dB over a range of 50 nm centered at 1565 nm.
We propose a robust, multi-mode interferometer-based, 2x2 photonic switch, which demonstrates high tolerance to typical fabrication errors and material non-uniformity. This tolerance margin is dependent upon the properties inherent to the MMI design and benefits from the high symmetry of the switch. The key design parameter of the device is to form a pair of well defined self-images from the injected light in the exact center of the switch. In allowing the index modulated regions to precisely overlap these positions, and by creating identical contact features there, any refractive index change induced in the material due to electrical isolation will be duplicated in both self-images. Since the phase relation will remain unchanged between the images, the off-state output will be unaltered. Similarly, offset and dimension errors are reflected symmetrically onto both self-images and, as a result, do not seriously impact the imaging. We investigate the characteristics of the switch under different scenarios using the finite difference beam propagation method. Crosstalk levels better than -20 dB are achievable over a wavelength range of 100 nm when utilizing this configuration. Polarization independence is maintained during device operation.
We report on an integrated 1 x 4 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells. The device is very simple, requiring only the currents applied to two electrodes for complete operational control. An area-selective zinc in-diffusion process is used to channel the current into the multiple quantum wells, thereby enhancing the efficiency of the carrier based effects. As a result, the electrical power consumption of the device is significantly reduced, allowing the switch to be operated uncooled and under d.c. current conditions. Our initial 1 x 4 switch exhibits a -8 dB crosstalk between channels. However, improvements on the switch design and better control during the device fabrication process will significantly enhance this value.
We report an optical switch that is based on the beam steering of an optical waveguide formed by injection of electrons in a p-i-n slab waveguide structure. The structure consists of an undoped InGaAsP multiple quantum well (MQW) layer, with a total thickness of 0.28 μm that is sandwiched between n-doped InP cladding layers. Zinc is diffused into the top cladding layer through a silicon nitride mask to form the p-regions on top of which a pair of 10 um wide parallel titanium-zinc-gold contact stripes are deposited by evaporation and lift-off. The gap between the stripes is 20 μm wide and the device is cleaved to a length of 800 um. Electrical currents are injected through the electrodes and a laser beam is launched into the middle of the gap region. The injected electrons accumulate in the MQW layer and spread sideways by diffusion. The regions that are saturated with electrons experience a decrease in refractive index and surround a narrow high index region effectively forming a channel waveguide. By carefully controlling the current ratio through the two parallel stripes, the waveguide can be shifted, thereby steering the guided laser beam.