Bruce Nyman

Gain and noise in ytterbium-sensitized erbium-doped fiber amplifiers: measurements and simulations

The fiber gain and noise figure in erbium (Er)-ytterbium (Yb) codoped fiber amplifiers are experimentally studied and theoretically modeled. The different fiber parameters for the model are found in separate characterization measurements. The comparison between the measured and calculated data show excellent agreement. In addition, we demonstrate the design process for a specific cladding-pumped fiber to find the optimum fiber length.

InP-based Negative Feedback Avalanche Diodes

The operation of InP-based single photon avalanche diodes (SPADs) in Geiger mode provides great utility for the detection of single photons at near-infrared wavelengths between 1.0 and 1.6 um. However, SPADs have performance limitations with respect to photon counting rate and the absence of photon number resolution that, at the most fundamental level, can be traced back to the positive feedback inherent in the impact ionization-driven avalanche process. In this paper, we describe the inclusion of negative feedback with best-in-class InP-based single photon avalanche diode (SPAD) structures to form negative feedback avalanche diodes (NFADs) in which many of the present limitations of SPAD operation can be overcome. The use of thin film resistors as monolithic passive negative feedback elements ensures rapid self-quenching with very low parasitic effects and wafer-level integration for creating multi-element NFAD arrays. To our knowledge, this is the first demonstration of this approach with InP-based avalanche diode structures. We present NFAD device properties, including pulse response, quenching dynamics, and photon counting performance parameters such as photon detection efficiency.

Afterpulsing in InGaAs/InP single photon avalanche photodetectors

The effect of short gating pulses on after-pulsing in a single photon avalanche photodetector operating at a telecom wavelength of 1.5 mum is characterized and discussed. Comparison between short and longer overbias gate pulses shows that the number of carriers created with a 1 ns (short) gating pulse is lower than that of a 20 ns pulse, when the avalanche is dark-count generated

Negative feedback avalanche diodes for near-infrared single-photon detection

In recent years significant progress has been made in near-infrared single photon detection using Geiger-mode InP-based single photon avalanche diodes (SPADs). A more detailed understanding of these detectors with regard to device design, material growth and device fabrication has led to continual performance improvements. A variety of circuits for enabling SPAD Geiger-mode operation have been proposed and demonstrated as well. However, due to the inherent positive feedback nature of the avalanche process, Geiger-mode SPADs are constrained by certain performance limitations, particularly with regard to counting rate and the absence of photon number resolution. These limitations hinder the use of SPADs in certain applications. By incorporating a negative feedback mechanism into InP-based SPADs, these SPAD performance limitations can be overcome. In this paper, we present a negative feedback avalanche diode (NFAD), which is formed by monolithically integrating a passive negative feedback element with a high-performance InP-based SPAD. We describe the design and operation of the NFAD device, along with basic characteristics such as pulse response and quenching dynamics, as well as the dependence of these characteristics on excess bias voltage and input photon number. We will also review the results of near-infrared single photon counting performance for fundamental performance parameters such as photon detection efficiency, dark count rate, and afterpulsing.

The modified beam propagation method

A method is presented for the analysis of waveguide structures with abrupt index changes in both the transverse and axial directions. The method accurately includes the reflected fields and the Goos-Hanchen shift. The method can be extended to three-dimensional and graded index structures, and to include diffraction effects. For a graded index structure with no abrupt index changes the method reduces to the standard beam propagation method. >

Geiger-Mode APD Single Photon Detectors

We present experimental and modeling results for InP-based avalanche photodiodes designed for single photon counting in the wavelength range of 0.95-1.65 μm. We describe performance trade-offs and underlying mechanisms governing key device characteristics.

Single photon avalanche photodiodes for near-infrared photon counting

InP-based single photon avalanche diodes (SPADs) have proven to be the most practical solution currently available for many applications requiring high-performance photon counting at near-infrared wavelengths between 1.0 and 1.6 µm. We describe recent progress in the design, characterization, and modeling of InP-based SPADs, particularly with respect to the dark count rate vs. photon detection efficiency metric of devices optimized for use at both 1.55 μm and 1.06 μm. In this context, we report for the first time dark count probabilities as low as 7 x 10-7 ns-1 for fiber-coupled 1.55 μm SPADs operated at 20% detection efficiency and 215 K. Additionally, because of the critical role played by afterpulsing in limiting photon counting rates, we describe recent characterization of the dependence of afterpulsing effects on SPAD operating conditions such as photon detection efficiency, repetition rate, and bias gate length.

InP-based single photon avalanche diodes

We describe recent results for the performance and modeling of InP-based single photon avalanche diodes. At 1.55 mum, dark count probabilities < 2 times 10-7 ns-1 have been achieved at 220 K for a photon detection efficiency of 15%.

Afterpulsing Effects in 1.5 μm Single Photon Avalanche Photodetectors

The effects of short (~1 ns) gating pulses and blanking on afterpulsing in an InGaAs/InP single photon detector are characterized at 1.5μm. Afterpulse mitigation using gate pulse blanking immediately following detection events is studied, and temporal effects are discussed

Study of afterpulsing in InP-based single photon avalanche diodes for 1.5 μm and 1.06 μm photon counting applications

Afterpulsing effects in InP-based single photon avalanche diodes have been studied both experimentally and theoretically. Characterization methods include both gated and free- running operation, and afterpulsing dependence on count rate is reported for both methods.