Frank J. Effenberger

Monolithic InGaAs-on-silicon detector with a CMOS-switched capacitor integrator

We have successfully grown InGaAs detectors on the silicon substrate using the special technique of selective epitaxy. Small diameter (50 micrometers ) selective area depositions of In0.5Ga0.5As on silicon have exhibited a lower dislocation density, and hence, better electrical performance. These InGaAs detectors are grown by Molecular Beam Epitaxy (MBE). The final goal is to monolithically integrate InGaAs detectors with a silicon CMOS switched capacitor integrator. We have designed a CMOS switched-capacitor integrator (SCI) to realize a linear current-to-voltage conversion over a wide voltage range (-5 to +5 V) with low noise characteristics. The SCI circuit consists of an operational amplifier with a feedback capacitor and a reset switch. The SCI circuit uses +/- 5 V dual power supply and one -5 to +5 V voltage pulse generator. The circuit was simulated using PSPICE and the chip layout was done with the Mentor Graphics.

Space Division Multiplexing in Access Networks

Space division multiplexing (SDM) has received a lot of attention in the past years, as it is seen as the final frontier of fiber optic capacity improvement for long haul transmission. Its use in access networks is even more interesting, due to the different design optimization goals in access versus transport. This paper explores some of the applications of SDM in access that have the potential for early adoption.

Ultrafast InGaAs pin detector for eye-safe lidar

Eyesafe LIDAR systems require detectors that operate in the 1.55 micron band with high bandwidth and large area. This paper describes the three design methods used in developing such detectors. First, a thick dual-depletion width pin structure is optimized for low capacitance and transit time. This enables the detector itself to have the best intrinsic speed. Second a extra-low input impedance preamplifier is designed. This preamplifier improves the performance of the already fast pin by lowering the electrical time-constants of the readout. Third, a novel partitioned detector layout is developed. This technique allows the connection of a large number of small, high-speed segments in parallel to form a single large detector. When used in combination, these design methods can produce a new class of detectors with diameters greater than 1 mm and bandwidths greater than 4 GHz.

Modal analysis of transport processes in SPRITE detectors

Carrier transport in signal-processing-in-the-element (SPRITE) detectors is an important phenomenon because it determines properties such as the responsivity and the modulation transfer function (MTF). The previous literature has presented approximate solutions to the transport problem that neglect boundary effects, which have long been thought to play a major role in SPRITE behavior. We present a new solution to the problem through the use of modal analysis. This method intrinsically includes boundary conditions and thus is more complete than the previous analysis. Furthermore we use this solution to derive expressions for the MTF. The effects of the boundary conditions on the MTF are studied to determine their optimum values.

Dual-carrier transport model of SPRITE detectors

Abstract A numerical model for signal-processing-in-the-element (SPRITE) detectors is developed that incorporates both hole and electron motion, the effects of space charge and varying field, and boundary conditions. The model is used to generate a spatial-frequency response for a rectangular SPRITE structure. Further, we use this model to investigate two improved SPRITE structures: the tapered detector and the modulation-doped detector.

Modal analysis of noise in signal-processing-in-the-element detectors.

Detector noise limits the performance of signal-processing-in-the-element detectors. For detectors to be optimized, an expression for the signal and noise must be found. The results of the eigenmode solution to the charge transport problem are used to derive the power spectral density of the noise in analytic form. This result is then coordinated with a similarly obtained modulation transfer function to yield a frequency-dependent signal-to-noise ratio (SNR). The SNR is used to reveal performance trends over several ranges of detector parameters. The most important result is that the contact boundary velocity strongly controls the SNR. The optimum SNR condition occurs when the contacts are not perfectly ohmic but exhibit a partially blocking behavior.

Modal analysis of SPRITE noise spectra

The detector noise is the key limit to any imaging system. The unique design of signal processing in the element (SPRITE) detectors provides measurable signal to noise improvement over ordinary detectors. The analysis and description of the noise in this type of detector is complicated by the fact that transport phenomena filter the noise spectra prior to readout. Previous analyses of the noise behavior used an approximate solution to the charge transport problem to produce expressions for the noise PSD, and yield predictions of a flat PSD at low frequencies. Measurements of real devices show a large 1/f behavior at low frequencies, but this has always been attributed to contact effects. In this paper, we use the results of the eigenmode solution to the transport problem to derive the PSD of the noise. We show that this analysis produces noise PSDs that have a 1/f dependence caused simply by the operation of the transport processes. The result is then coordinated with the similarly obtained signal response MTF to produce the frequency dependent signal to noise ratio. These are computed over several ranges of detector parameters with the intent of revealing their optimum values.

Modal analysis of SPRITE transport processes

Carrier transport in signal processing in the element (SPRITE) detectors is an important phenomenon because it determines properties such as the responsivity and the modulation transfer function (MTF). The previous literature has presented approximate solutions to the transport problem that neglect boundary effects, which have long been thought to play a major role in SPRITE behavior. In this paper we present a new solution to the problem through the use of modal analysis. This method intrinsically includes the three dimensional boundary conditions, and thus is more complete than the previous analysis. Through the analysis, certain dimensionless numbers arise which can be used to characterize SPRITE structure parameters and clarify how these parameters impact device performance. Further, we use this solution to derive an expression for the MTF. The effects of the boundary conditions and the device geometry on MTF are investigated using the new theory. Our results show that the quality of the passivated surfaces has a weak influence on the MTF; however, the device width affects the MTF performance more strongly when the passivation is poor. The effect of blocking at the contacts is investigated. It is found that while marginal improvements in MTF roll-off could be achieved by making the contacts highly ohmic, the maximum signal amplitude is obtained with partially blocking contacts.

Resonant optical detection

Monochromatic optical detection is often desired. One technique to accomplish this is to place the detector within an optical resonator. The authors consider the theoretical description of resonant optical detection using an intrinsic semiconductor detector layer placed within a monolithic vertical cavity. The effects of wavelength-dependent index and absorption are included in the analysis. It is found that, unlike passive Fabry-Perot filters, the resonant detector can have a single resonant peak and thus strong suppression of out-of-band light.

Gradient-index-mirror solid-state lasers

The properties of diode-pumped lasers with gradient-index (GRIN)-mirror resonators are described. The total loss of typical GRIN elements is measured and is found to be comparable with conventional mirrors. The efficiency, threshold, and modal quality of GRIN-mirror Nd:YAG lasers are shown to compare favorably with conventional designs. In addition, a polarized single-frequency laser that uses GRIN elements in conjunction with metal-film étalons is constructed and is shown to deliver output powers comparable with those of more complicated single-frequency designs.