FastGated-SPAD
The Fast-Gated Single-Photon Avalanche Diode (SPAD) module is a compact detection module capable of gating a silicon SPAD for wide dynamic range optical measurement. The module includes a fast pulse generator, with gating transitions below 200 ps at repetition rates up to 80 MHz, with fully programmable ON time and excess bias. The differential front-end electronics picks up the avalanche pulse with low timing jitter.
High Photon Detection Efficiency
Up to 48% at 5 V excess bias (VEX)
Best-in class Timing Accuracy
< 50 ps FWHM
80 MHz gate frequency
fine adjustable gate width
Fully programmable module
gate width, gate repetition frequency, hold-off time SPAD excess bias and temperature
MODULE FEATURES
• Gate rise-time: < 200 ps • Gate repetition frequency: up to 80 MHz • Free-running mode available
• Timing jitter: < 50 ps • Detector active area diameter: 20 µm - 100 µm • Detection efficiency: 50% @ 400 nm, 5% @ 800 nm
BIOMEDICAL APPLICATION
• Time resolved spectroscopy
• Functional brain imaging
• Optical molecular imaging
• Gated STED
• FLIM - Fluorescence Lifetime IMaging
• FCS - Fluorescence Correlation Spectroscopy
• DOT - Diffuse Optical Tomography
INDUSTRIAL APPLICATION
• Optical Testing of integrated circuits
• Metrology by Time of Flight measurements
• Fibre optics characterization
• OTDR – Optical Time-Domain Reflectometry
• LIDAR and ranging
QUANTUM APPLICATION
• Quantum Cryptography
• Quantum Optics
• Single-photon source characterisation
Overview
The FastGatedSPAD module is a compact detection module capable of gating a silicon SPAD for wide dynamic range optical measurement. The module includes a fast pulse generator, with gating transitions below 200 ps at repetition rates up to 80 MHz, with fully programmable ON time and excess bias. The differential front-end electronics picks up the avalanche pulse with low timing jitter. The module can be operated also in free-running mode, with the SPAD always ON. The main feature of the module is the possibility to increase the Dynamic Range of TCSPC systems thanks to a fast OFF-ON transition. Thus, weak signals can be extracted out of a huge background by enabling the detector only in well-defined time-windows. The good photon detection efficiency and timing resolution are obtained through both the use of epitaxial SPAD and the microwave layout optimized to reduce the effect of voltage oscillations following the fast gate transitions. The FastGatedSPAD module is controlled through a PC software interface where 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.
Principle of gated operation
Gated mode operation: 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. 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. Pulse’s falling edge marks 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.
Module composition and Mechanical Dimensions
The module is composed by two parts connected together through a 2m wide-bandwidth cable: a Detection Head (DH) which comprises of a CMOS SPAD detector and the related fast electronics, and a Control Unit (CU) which contains the pulse generator, the Peltier controller, communication system and power supplies for the entire module.
Specifications1
Parameter
Notes
Min
Typ
Max
Units
Active area diameter
50
µm
Photon Detection Efficiency
@ 400 nm
50
%
@ 600 nm
20
%
@ 800 nm
5
%
DCR
Single photon timing jitter (FWHM)
At VEX = 4 V
< 50
ps
At VEX = 6 V
< 50
ps
Excess Bias range
2.5
7
V
SPAD temperature
SW selectable
TBD
TBD
K
Hold-off time
SW selectable @ 24 ns step
24
1500
ns
Accuracy
TBD
ns
Gate rise time
(20% - 80%)
100
200
ps
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
80
MHz
Internal trigger
0.0002
80
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 Fiber connectorised
System Requirements
USB1.1 or 2.0 and Microsoft
Windows OS
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).
Ordering Information
A standard FastGatedSPAD module 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