InGaAs SPAD The InGaAs Single-Photon Counter is based on InGaAs/InP SPAD for the detection of Near-Infrared single photons up to 1700 nm. The module includes a pulse generator for gating the detector, a frontend circuit for avalanche sensing, a fast circuitry for detector quenching and resetting, and some subcircuits for signal conditioning High Photon Detection Efficiency Higher than 30% from 920nm to 1550nm, reaching more than 40% from 950nm to 1400nm Best-in class Timing Accuracy < 150ps FWHM (focused light) 133 MHz gate frequency & fine adjustable gate width Fully programmable module i.e. gate width, gate repetition frequency, hold-off MODULE FEATURES Based on InGaAs/InP SPAD 25µm active sensing area diameter Free Space and SMF-28 Fiber Pigtailed version Sensitivity from 900nm to 1700nm Available in different Grade depending on Dark Counts specifications Adjustable PDE and hold-off time Gate width from 1 ns to 500 ns Int. or Ext. trigger up to 133 MHz Labview interface via USB BIOMEDICAL INDUSTRIAL QUANTUM ASTRONOMY Confocal Microscopy Single Molecule Spectroscopy Ultra-Sensitive Fluorescence Time-correlated single photon counting Optical Testing of integrated circuits Metrology by Time of Flight measurements Fiber optics characterization Quantum Cryptography Quantum Optics Single-photon source characterisation Optical Range Finding, LIDAR & LADAR Astronomy Observations & Adaptive Optics Single Molecule Detection
Overview The InGaAs Single-Photon Counter is a photon counting module based on an InGaAs/InP Single- Photon Avalanche Diode (SPAD) for the detection of near-infrared single photons up to 1700 nm. The module includes the pulse generator for gating the detector, the front-end circuit for avalanche sensing, a fast circuitry for detector quenching and resetting and some sub-circuits for signal conditioning. All the main gate parameters (gate width, and gate frequency) and SPAD settings (excess bias, holdoff time and temperature) are user adjustable, by means of a PC interface, for matching the requirements of the different applications. The system can be conveniently used both for counting and timing measurements, since the high performance electronics guarantees a clean temporal response even with fast gate transitions. The module is composed by two parts connected together through a 2m wide-bandwidth cable: A Detection Head (DH) which comprises of an InGaAs/InP SPAD detector and the related fast electronics. Its small dimension allows easy integration in all experimental setups. A Control Unit (CU) which contains the pulse generator, Peltier controller, communication system and power supplies of the entire module. Principle of operation Normally single photon detectors are operated in the so-called free-running mode, where the devices are enabled immediately after the quenching of each avalanche current. Usually this is true for Silicon SPADs but for InGaAs SPADs the DCR would be so high that the use of these detectors would be almost impossible. As a consequence, for further reducing these unwanted counts, the InGaAs SPADs are operated in gated regime: the detector is periodically enabled for a short time window called Gate, of duration Gate-Width, whereas it is usually held off at a bias slightly below the breakdown voltage. The gate repetition rate (frequency) is set by a reference signal, the Gate Sync, whose ON time corresponds to the Gate-Width. The actual signal applied to the SPAD is instead the Gate. Initially Gate and Gate Sync are the same. When a photon is absorbed, it triggers the avalanche current which is marked by the raising edge of Photon Output pulse. Once the avalanche is detected, it is immediately quenched: the system does not wait for the end of the Gate window to bias below breakdown the SPAD. Now Gate and Gate Sync begin to differ due to the hold-off time. The hold-off time is the time during which a detector is kept-off after every avalanche ignition. During the hold-off time, Gate Sync pulses are ignored, and the Gate remains low, keeping the photodetector OFF. The SPAD is enabled again only at the first rising edge of the Gate Sync signal after the end of the hold-off time. The Gate signal, which thus represents the true, non-masked, applied Gate, is also called Valid Gate. Module Output: pulse generator (GATE SYNC), pulses at the SPAD detector (GATE) and photon output signal (PHOTON OUTPUT).
Detection module control The InGaAs module is controlled through a PC software interface. With this software it is possible to set all the relevant gate parameters (int./ext. trigger, gate frequency, gate width) and all the detector s parameters: temperature, excess bias and hold-off time. In this way it is possible to adjust the detector performances in terms of DCR, hold-off time and photon detection efficiency, in order to properly match the requirements of the user application. The PC interface also offers four different pre-set configurations, which lead to different detector performance configurations: Low Noise: it presents the lowest achievable DCR at the expense of detection efficiency; High Efficiency: offers high detection efficiency but also high DCR; Clean Timing: trade-off between low noise and high efficiency, with a good temporal response of the detector; High Count Rate: gives high photon counts at the expense of a stronger afterpulsing contribution. Hardware connections PHOTON OUT : output, SMA connector; a digital pulse is generated for each detected photon; the output is a NIM pulse. The falling edge of the pulse marks, with very low jitter, the photon arrival time; VALID GATE : output, SMA connector; outputs which Gate pulses effectively enabled the SPAD (nonmasked gate pulses). The pulses are LVTTL standard; TRIGGER OUT : output, SMA connector; outputs the internal trigger reference signal used to periodically enable the SPAD. The pulses are LVTTL standard; TRIGGER IN : input, SMA connector; if an external trigger is needed, then the signal must be connected to this input. The external trigger signal can be positive or negative up to ±5V and the internal comparator allows for a programmable threshold.
Specifications Parameter Notes Min Typ Max Units Active area diameter 25 µm Photon Detection Efficiency At 2.5V excess bias, λ= 1550 nm, T=230K 15 20 % Single photon timing jitter (FWHM) At V EX = 6.5 V (free space) < 150 ps At V EX = 6.5 V (fiber pigtailed) < 100 ps Gate rise time (20% - 80%) 700 1500 ps SPAD temperature SW selectable @ 0.1 K 230 290 K Hold-off time Gate width Gate repetition frequency SW selectable @ 24 ns step 1 3000 µs Accuracy ± 3.5 ns SW selectable @ 40 ps step 0.2 10 ns SW selectable @ 2 ns step 10 500 ns External trigger DC 133 MHz Internal trigger 0.2E-3 133 MHz Photon output NIM output -800 0 mv Trigger input Supply voltage Optical input Amplitude -2 2.5 V Threshold (SW selectable 18 mv step) -2 2.5 V 100-240 VAC @ 50-60 Hz Free space or FC/PC fiber coupled (SMF-28) Designed and built compliant with the European Union Directive 2011/65/CE (also known as RoHS 2) Grades Specifications Active Area Diameter 25m Free space Grade Dark Counts (c/s) TE Cooled @ 230 K and 2.5V excess bias C B A < 10 kc/s (available upon request) < 20 kc/s < 40 kc/s SMF-28 Fiber coupled < 10 kc/s N/A < 40 kc/s (available upon request) Very low dark counts modules can be selected in order to meet customer requirements System requirements USB 1.1 or 2.0 interface Microsoft Windows XP, Vista,7,8 32 or 64 bit versions
Ordering Information The InGaAs module can be purchased as a KIT, which includes the Detection Head (either free space or fiber coupled), the Control Unit and the interconnection cable, or as individual components; in this latter case the user shall already have a KIT from a previous purchase. A standard InGaAs KIT is usually shipped with the following parts: Control Unit; Detection Head (either fiber-pigtailed or windowed); Orange wide-bandwidth Cable for Control Unit to Detection Head connection; USB key containing the installation software and the user manual in PDF format; SPAD test report. Optical table Universal adaptor Products can be ordered directly from Micro Photon Devices or its representatives. For a complete list of representatives, visit our website at www.micro-photon-devices.com. Custom designed products are available upon request. Kit Ordering Components Ordering
Mechanical Dimensions Warranty A standard 24-month warranty following shipment applies. Any warranty is null and void if the module case has been opened or if the absolute maximum ratings are exceeded.