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The SPM Overview |
The sensor is housed in a hermetically sealed TO8 can and cooled to -30C. The SPM Series sensors are supplied with an integrated power supply and can be mounted on optical posts via a tapped hole located on the bottom of the housing. The output is a 0 – 2V signal supplied via an SMA connector.
A number of variants of the SPM Sensor are available
- Two sizes, (1mm diameter or 3mm x 3mm)
- Two types of silicon (Dynamic Range Optimized or Quantum Efficiency Optimized)
- Transimpedance Preamplifier Circuit |
The Silicon Photomultipliers (SPM or SiPM) Technology |
The SPM detection area consists of an array of Geiger mode APDs, or microcells, each individually coupled to integrated quench electronics, and is a type of detector commonly referred to as a Silicon Photomultiplier (SPM or SiPM). These microcells have extremely high internal amplification that allows single photon sensitivity at room temperature. The output of each microcell is an identical, fixed charge or current pulse for each single photon detected. The SPM connects this array of microcells in parallel and the summed output is proportional to the number of Geiger mode pulses and hence proportional to the incident photon flux. The uniform high gain across the array allows the single photoelectron peaks to be clearly resolved permitting both single photon detection and accurate calibration of the photon number. |
Comparison with a typical PMT and APD |
Below is a table that compares key specifications of the SPM series detector, a typical PMT, and a typical APD. It is easy to see why researchers should evaluate SPM technology. |
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Typical PMT |
Typical APD |
SPM |
| Sensor Area (mm2) |
> 50 |
< 10 |
1 or 9 |
| Operating Voltage (V) |
1000s |
100s |
30 |
| Ambient/excess Light |
Damaged |
Damaged |
No Impact |
| Magnetic Field |
Distorted |
No Impact |
No Impact |
| Dynamic Range (Orders) |
4 to 5 |
4 to 5 |
3 to 4 (SPM1)
4 to 5 (SPM3) |
| Spectral Response (nm) |
300 - 600 |
400 - 950 |
450 - 850 |
| Gain |
1 to 5 x 106 |
100 |
>1.5 x 106 |
| Rise Time (nsec) |
1 |
Varies |
5 - 10 |
| Cost |
High |
Low |
Medium |
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Quantum Efficiency (QE) vs. Dynamic Range (DR) Optimization |
Two Geiger mode microcell sizes are offered, 35 µm to optimize the quantum efficiency by enhancing the probability of detecting a photon with the larger size, and 20 µm to optimize the dynamic range requirements of your application by fitting more detectors in a single device with a given active area. |
Transimpedance Amplifier |
Given the high gain inherent in the SPM, it is possible to use a low gain pre-amplifier board.
The transimpedance preamplifier can convert the raw current from the SPM into a voltage. The typical gain for the transimpedance amplifier option is 470V/A for 3mm device and 2,200 for the 1mm device. This board is ideal for applications that require detection of continuous signals where integration of the signal is done over time. One application is cell imaging or DNA micro-arrays where it is desired to integrate the optical signal from a sample for periods from 1µs to 1ms in time. |
Signal to Noise (S/N) |
Signal to Noise as a function of Optical Power for PMT, Si Photodiode and SPM 1mm series. The graph shows that the PMT is a more sensitive detector at low signal levels but in the region above 10pW the SPM has a better signal to noise ratio than the PMT. This is due to the lower excess noise factor of the SPM. |
SNR and Photon Detection Efficiency |
The Signal-to-Noise ratio of the SPM is better than a PMT and Photodiode for many applications, due to the superior excess noise of the SPM technology.
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Single Photoelectron Spectrum |
A histogram of an ADC output in response to repeated fast pulses of low-level light incident on the SPM results in a photoelectron spectrum with well-resolved peaks. Such a spectrum is indicative of the low noise and uniform, stable gain of the Geiger-mode APDs. The first peak in the spectrum, often called the pedestal, is a measure of the noise in the system (detector + electronics) and corresponds to instances when no pulses were recorded during the gate time. The second peak of the spectrum or the first photo-electron peak corresponds to instances when a single pixel red and this peak is well-separated from the pedestal peak. |
Bandwidth |
The bandwidth is a measurement of the SPM 1mm series detector response (peak output voltage) to a relatively large frequency modulated optical signal. The detector response was recorded as a function of the frequency of the optical signal. A high bandwidth amplifier was used so that the amplifier did not influence the measurement. The results show that the detector has a bandwidth of some tens of MHz. |
SPM's Photon Detection Efficiency vs. Wavelength
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Transimpedance Amplifier Response to Small Optical Signal
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Transimpedance Amplifier Response to Large Optical Signal
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In situations where the signal is a pulse input, such as ranging applications or scintillation experiments, the pulse amplification preamplifier option is the best choice. This allows the fast rise time of the detector to be exploited and provides the simplest way to accurately bring pulse information to the user. The SPM is coupled to a high-speed pulse preamplifier that uses an internal gain of 20. This signal is then output to the user via a DC blocking capacitor to convey pulse information originating in the SPM. |
Pulse Amplifier Response to Small Optical Signal
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Pulse Amplifier Response to Large Optical Signal
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C Mount Adapter Option |
A C Mount Adapter option is available that attaches to the collar around the T08 can and facilitates the attachment of various standard C Mount fittings, including filters and lenses. This is an ideal solution for attaching light collection lenses. |
Fiber Coupler Option |
Newport offers a pigtail lens style photodiode to multimode (MM) fiber coupler to couple light signals from a source via MM glass fiber to all modules.
A universal receptacle is mounted onto the collar of the SPM module which allows different fiber types and specifications depending on the application requirements. The fiber output facet to the detector is tipped with a focusing lens for optimal coupling onto detector. This approach offers a “plug and play” solution for any fiber type, which can be specified when placing your order. Details of current fiber specifications are avail-able on our website under product options. |
Fiber Specifications: |
Pigtail lens style photodiode to MM fiber coupler (22mm OD) optimized for 532nm.
0.50 meter long, 3mm OD armor cabled 400/440µm NA=0.22 GI MM fiber, with a -25dB return loss.
Fiber connector type: Flat FC/PC connector. (NTT/FC compatible connector)
Lens (Fiber tip): A lens focuser is used with spot size of 900um +/-30um to underfill beam on the detector active area.
Pigtail coupler: Pigtail collimator with flange not permanently locked. Customer can remove and adjust using tilt alignment provided.
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The complete line of SPM Series High Gain Avalanche Photodiodes were developed for Newport by SensL, "The Low Light Sensing Company", Cork, Ireland. SensL is dedicated to developing low light detectors and imaging systems based on Geiger Mode Photodiode technology. |
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