Itay Shtrichman

Picoseconds time resolved photoinduced absorption by infrared active vibrations as a probe for charge photogeneration in MEH-PPV/C60 composites

Abstract We have applied a visible pump mid-infrared probe picosecond time resolved technique, in order to study the photogeneration of charges in MEH-PPV/C 60 composites. The photoinduced infrared active vibrations on the polymer chains have been used as a direct measure for the photogenerated charges. We have found that, within our time resolution of ⋍60 ps, polarons are photogenerated on the MEH-PPV chains with a quantum yield of the order of 5%.

Adiabatic mode multiplexer for evanescent-coupling-insensitive optical switching

A novel adiabatic mode multiplexer enables a 2 x 2 optical switch whose operation does not depend on accumulated phase due to evanescent coupling between waveguides. The adiabatic mode multiplexer has a negligible insertion loss over C+L bands and modal cross talk better than -40 dB for any polarization state. Mode multiplexing is achieved by adiabatic transition from the fundamental mode of the single-mode waveguide to the higher mode of the multimode waveguide. Experimental measurement results for a device realized in silica-on-silicon technology are presented. By directly measuring the nonadiabatic transition probability, we show that the adiabatic mode multiplexer operates in the Landau-Zener regime.

Spatial resolution of SCD's InSb 2D detector arrays

The two-dimensional spatial response of a pixel in SCDs back-side illuminated InSb Focal Plane Array (FPA) is measured directly for arrays with a small pitch, namely 30, 20 and 15&mgr;m. The characterization method uses a spot-scan measurement and de-convolution algorithm to obtain the net spatial response of a pixel. Two independent methods are used to measure the detector spatial response: a) direct spot-scan of a pixel with a focused beam; b) uniform illumination upon back-side evaporated thin gold coating, in which sub-pixel apertures are distributed in precise positions across the array. The experimental results are compared to a 3D numerical simulation with excellent agreement for all pitch dimensions. The spatial response is used to calculate the crosstalk and the Modulation Transfer Function (MTF) of the pixel. We find that for all three pixel dimensions, the net spatial response width (FWHM) is equal to the pitch, and the MTF width is inversely proportional to the pitch. Thus, the spatial resolution of the detector improves with decreasing pixel size as expected. Moreover, for a given optics and smaller array pitch, the overall system spatial resolution is limited more by the optical diffraction than by the detector. We show actual improved spatial resolution in an imaging system with a detector of smaller array pitch.

3D simulation of detector parameters for backside illuminated InSb 2D arrays

Accurate and reliable numerical simulation tools are necessary for the development of advanced semiconductor devices. SCD is using the Silvaco Atlas simulation tool to simultaneously solve the Poisson, Continuity and transport equations for 3D detector structures. In this work we describe a set of systematic experiments performed in order to calibrate the Atlas simulation to SCDs backside illuminated InSb focal plane arrays (FPA) realized with planar technology. From these experiments we extract physical parameters such as diffusion length, surface recombination velocity, and SRH lifetime. The actual and predicted performance (e.g. dark-current and MTF) of present and future detectors is presented. We have studied arrays with pitch in the range of 15 to 30 μm. We find that the MTF width is inversely proportional to the pitch. Thus, the spatial resolution of the detector improves with decreasing pixel size as expected. Using the Atlas simulation we predict the performance of planar InSb arrays with smaller pixel dimensions, e.g., 12 and 10 μm.

Controlled mode interaction based wide-band and robust optical switching unit in silica-on-silicon

We present a novel wide band and robust planar lightwave circuit (PLC) switching unit having two switching states with low cross talk. The CMI based SU does not require post fabrication trimming and can be used as a normally dark VOA.

Optical switching based on the adiabatic temperature induced mode localization

We present optical switching device that combines two ideas: thermally induced waveguides and adiabatic mode transition in a slowly widening taper. We explain conditions for the optimal operation and present experimental results for 1 /spl times/ 2 switch.

Dynamics of carriers in resonantly excited quantum-well lasers studied by intersubband absorption

Using infrared picosecond pulses to probe the intersubband absorption of GaAs/AlGaAs quantum-well lasers following their optical excitation, we directly measure the dynamics of carriers in these devices. We find no evidence for excitonic gain even at cryogenic temperatures and resonant excitonic excitation.

Time-resolved intersubband optical transitions in resonantly optically pumped semiconductor lasers

Abstract Using picosecond visible-pump mid-infrared-probe technique, we directly measured the photoexcited electron dynamics in the first conduction subband of a GaAs/AlGaAs quantum well laser, below and above its threshold. Our results clearly show that even at low temperatures, under optical excitation into the lowest heavy hole exciton resonance, GaAs/GaAlAs quantum well lasers lase in accordance with the common two-plasma model and not from an excitonic phase.

Spatial and spectral filtering on focal plane arrays

This article describes new imaging capabilities and technologies developed for infrared focal plane arrays (FPAs) at SCD. One of the new technologies is the patterning of the back surface of the FPA, whose front surface is bonded to a silicon readout integrated circuit (ROIC). Another is the hybridization of a spectral filter to the same back surface. Increased image resolution has been achieved by using an opaque mask on the backside of the FPA with small central apertures. The reduced fill factor of the sensor leads to lower crosstalk between neighboring pixels and a higher Nyquist frequency. A highly detailed multi-mega pixel image is obtained when the sensor is micro-scanned relative to the imaging optics. Spectral filtering was achieved by hybridization of a designated filter to the backside of the FPA. The filter was glued to the FPA with high accuracy achieving single pixel resolution. System implementation of these SWIR sensor cameras has been demonstrated at imec and is reported in this paper. First results are reported for a continuously varying monolithic filter deposited onto the FPA, which has a high spectral dispersion. We report electro-optical measurements on several different sensors and describe some of their key parameters.

Tapping light from waveguides by high-order mode excitation and demultiplexing

A novel high-performance optical tap with low wavelength-dependent loss(WDL), polarization-dependent loss (PDL), and excess loss is described. The tap is based on exciting a high-order mode by an abrupt change in the waveguide profile, and then tapping the optical power in the high-order mode by using a modal-demultiplexer. The tap can be designed to give a tapping ratio in the range of -30 to -10 dB over a wavelength range of 1510-1640 nm. In addition, it is shown that the tapping ratio is tolerant to process variations, repeatable and predictable, enabling the design to be implemented in a single process run, with no need for additional fine-tuning iterations, while achieving a high process yield. We show that measurements are in good agreement with simulated results. In the tap channel we measured 0.3 dB WDL and 0.2-dB PDL over the C- and L- bands, while the signal in the main channel was virtually uncontaminated relative to a plain single-mode reference waveguide.