InGaAs SPAD - gated

The InGaAs Single-Photon Counter is based on a 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 front-end circuit for avalanche sensing and a fast circuitry for detector quenching and resetting.

BIOMEDICAL APPLICATION • Confocal Microscopy • Single Molecule

Spectroscopy • Ultra-Sensitive

Fluorescence • Time-correlated single

photon counting • Single Molecule Detection

INDUSTRIAL APPLICATION • Optical Testing of

integrated circuits • Metrology by Time of Flight

measurements • Fiber optics

characterization

QUANTUM APPLICATION • Quantum Cryptography • Quantum Optics • Single-photon source

characterisation

ASTRONOMY APPLICATION • Optical Range Finding,

LIDAR & LADAR • Astronomy Observations &

Adaptive Optics

High Photon Detection Efficiency Up to 40% at 5V excess bias (VEX)

Best-in class Timing Accuracy < 100ps FWHM (focused light)

133 MHz gate frequency fine adjustable gate width

Fully programmable module gate width, gate repetition frequency, hold-off SPAD excess bias and temperature

MODULE FEATURES • 25µm active-area diameter InGaAs/InP SPAD • Free Space and SMF-28 Fibre Pigtailed version  • Sensitivity from 900nm to 1700nm  • Available in different Grade depending on Dark

Counts specifications  • Adjustable PDE and DCR  • Gate width from 1.5 ns to 500 ns  • Int. or Ext. trigger up to 133 MHz  • PC control interface via USB  

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 and a fast circuitry for detector quenching and resetting. All gate parameters (gate width, gate frequency and trigger reference) and SPAD settings (excess bias, hold-off time and temperature) are user adjustable, by means of a PC interface. This enables the user to configure the module with optimal parameters in order to match the requirements of the different applications. Typical SPAD Photon Detection Efficiency (PDE) as a function of wavelength and excess bias is shown on the front page. Typical PDE @ 1550 nm as a function of the excess bias for fibre pigtailed modules and typical SPAD dark-counting rates (DCR) as a function of the applied excess bias and hold-off time are shown here below. 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 for the entire module.

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 five different preset configurations in order to speed up the module configuration and help the user in exploiting its intrinsic performances: ü Lowest Noise sets almost the lowest achievable

DCR at the expense of detection efficiency and timing resolution;

ü Low Noise offers higher detection efficiency and still low DCR;

ü Better Timing allows to obtain high efficiency and a good temporal response (low jitter) with moderate DCR;

ü Best Timing gives you almost the best possible efficiency and timing jitter of the module at the expense of high DCR but still not the highest;

ü Advanced allows to set any SPAD or gate parameter as desired for reaching the optimum module configuration.

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 (in the example below) 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 buffered and replicated at the control unit front panel: the VALID GATE output.

 Module  Signals:  pulse  generator  (GATE  SYNC),  pulses  at  the  SPAD  detector  (GATE)  and  photon  output  signal  (PHOTON  OUTPUT).  

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 (non-masked 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 and the internal comparator allows for a programmable threshold.

Specifications1 Parameter Notes Min Typ Max Units

Active area diameter 25 µm Photon Detection Efficiency

Vex = 2.5V, λ=1550nm, T=233K (fibre pigtailed) 12 % Vex = 2.5V, λ=1550nm, T=233K (free space) 15 %

Single photon timing jitter (FWHM)

At VEX = 7 V (free space - unfocused) < 150 ps At VEX = 7 V (fibre pigtailed) < 100 ps

Gate rise time (20% - 80%) 700 1500 ps Excess Bias range 2 7 V SPAD temperature SW selectable @ 0.1 K 228 290 K

Hold-off time SW selectable @ 24 ns step 1 3000 µs Accuracy ± 3.5 ns

Gate width SW selectable @ 40 ps step 1.5 10 ns SW selectable @ 2 ns step 10 500 ns

Gate repetition frequency

External trigger DC 133 MHz Internal trigger 0.2E-3 133 MHz

PHOTON OUT NIM output -800 0 mV Required Load (DC) 50 Ω

TRIGGER IN

Amplitude -2 2.5 V Threshold (SW selectable 18 mV step) -2 2.5 V Load Impedance (DC) 50 Ω Impulse width 2 ns

TRIGGER OUT VALID GATE

Output levels 0 3.3 V Required Load (DC) 50 Ω

Supply voltage 100 - 240 VAC @ 50 - 60 Hz

Optical input Free space or FC/PC fibre pigtailed (SMF-28)

1See the user-manual Specifications paragraph for the full list of module’s specifications. Module designed and built compliant with the European Union Directive 2011/65/CE (also known as RoHS 2).

Grades Specifications Dark Counts (c/s) TE Cooled @ 233°K and 2.5V excess bias

Module Type Grade C Grade B Grade A

Free space - 25µm active area ∅ < 10 kc/s < 20 kc/s (call MPD for availability)

< 40 kc/s (call MPD for availability)

Single Fibre coupled – SMF-28 < 10 kc/s < 20 kc/s (call MPD for availability)

< 40 kc/s (call MPD for availability)

Very low dark counts modules can be selected in order to meet customer’s requirements

System requirements (software) • USB 1.1 or 2.0 interface • Microsoft Windows XP, Vista,7,8 32 or 64 bit versions • The SW is the same for both free-running or gated modules. It is also able to control both type of

modules at the same time.

Mechanical Dimensions

Ordering Information The InGaAs module can be purchased as a KIT, which includes the Detection Head (either free space or fibre 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 fibre-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. The ordering codes for the kit and for the single components are respectively:

Warranty A standard legal warranty according to local legislation applies following shipment. Any warranty is null and void if the module case has been opened or if the absolute maximum ratings are exceeded. Specifications are subject to change without any notice. Document version v2.1.1 – June 2014

Contacts Micro Photon Devices S.r.l, Via Stradivari 4, I-39100 Bolzano, Italy T: +39 0471 051212 F: +39 0471 501524 www.micro-photon-devices.com