Si Fiber-Coupled Avalanche Photodetector

Wavelength Range from 400 - 1000 nm
Temperature Compensated and Variable Gain
Integrated Flange Enables Direct Fiber Coupling Using Adapters
FC/APC, FC/PC, LC/PC, and SC/PC Adapters Available

APDA2-A

FC/APC Fiber Connector Adapter, 350 - 700 nm

APDF2-B

FC/PC Fiber Connector Adapter, 600 - 1050 nm

APDL-A

LC/PC Fiber Connector Adapter, 350 - 700 nm

APD431A

Si Fiber-Coupled
Avalanche Photodetector

Related Items

Free-Space Silicon APDs

Single Photon Detectors

Fiber Optic Detectors

Response-Flattening Filters

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Overview
Specs
Graphs
Pin Diagrams
Pulse Calculations
Selection Guide
Feedback

Avalanche Photodiode Selection Guide^a
Free-Space Si APDs
Fiber-Coupled Si APDs
Free-Space InGaAs APDs
Fiber-Coupled InGaAs APDs

Please see the Selection Guide tab for a complete list of all of our avalanche photodetectors.

Click to Enlarge
The APD431A photodetector is connected to an optical fiber (sold separately) using the APDA2-A fiber connector adapter.

Features

Wavelength Range from 400 to 1000 nm
Temperature Compensated to Provide M Factor Stability of ≤±3% Over 18 to 28 °C
Continuously Variable Gain with M Factor from 10 to 100
Robust Fiber Coupling Using M12 x 0.5-Threaded Fiber Connector Adapters (Sold Below)
Post Mountable in Three Orientations Using Universal 8-32 / M4 x 0.7 Taps
LDS12B Power Supply Included

Thorlabs offers a Fiber-Coupled Silicon Avalanche Photodetector (APD) that is sensitive to light from 400 to 1000 nm. This temperature compensated photodetector features a variable gain and large usable bandwidth of DC to 400 MHz. It also features an externally M12 x 0.5-threaded flange for robust fiber coupling when used with our Fiber Connector Adapters sold below. With increased sensitivity and lower noise compared to standard PIN detectors, it is ideal for applications with low optical power levels.

In general, avalanche photodiodes use an internal gain mechanism to increase sensitivity. A high reverse bias voltage is applied to the diodes to create a strong electric field. When an incident photon generates an electron-hole pair, the electric field accelerates the electrons, leading to the production of secondary electrons by impact ionization. The resulting electron avalanche can produce a gain factor of several hundred times, described by a multiplication factor, M, that is a function of both the reverse bias voltage and temperature. In general, the M factor increases with lower temperatures and decreases with higher temperatures. Similarly, the M factor will increase when the reverse bias voltage is raised and decrease when the reverse bias voltage is lowered.

The APD431A photodetector offers a large usable bandwidth of DC to 400 MHz. It features an integrated thermistor that maintains an M factor stability of ±3% or better over 23 ± 5 °C by adjusting the bias voltage across the avalanche photodiode. It also features a variable gain that can be controlled by a knob on the right side of the housing, which varies the M factor from 10 to 100.

The orientation of the mechanical and electrical connections, combined with the compact design, ensures that the APD431A detector can fit into tight spaces. Three universal 8-32 / M4 x 0.7 mounting holes further ensure easy integration into complicated mechanical setups.

Fiber-Coupling and Mechanical Adapters
The APD431A photodetector is designed to offer robust fiber-coupling capabilities to our existing APD430A free-space avalanche photodetector. It features an externally M12 x 0.5-threaded flange that is compatible with our M12 x 0.5-threaded fiber connector adapters (sold below), allowing for quick fiber coupling with high reproducibility. The adapters are optimized for single mode fibers, and for multimode fibers with a 200 μm core and NA = 0.22; however, they can be used with all optical fibers with some loss of coupling efficiency. Options are available for FC/APC, FC/PC, LC/PC, or SC/PC fiber connections, and with coatings for 350 - 700 nm or 600 - 1050 nm.

Click to Enlarge
The back plate of the APD431A photodetector is engraved with the detector's specifications.

Additionally, Thorlabs offers the SM1A610 mechanical adapter (sold below), which features internal M12 x 0.5 threads to connect directly to the APD431A photodetector, and external SM1 threads for compatibility with SM1-threaded components. This adapter allows the APD431A photodetector to be used as a free-space detector with standard optomechanical components; however, if space is a concern, the APD430A photodetector provides a more compact design as a free-space Si APD.

Please note that our free-space Si APDs can also support fiber coupling through the use of a fiber collimation package, focusing lens, and X-Y translator (please see the Fiber Coupling tab here for more information). However, the externally M12 x 0.5-threaded flange featured on the APD431A photodetector provides a more stable and compact means for fiber coupling. This M12 x 0.5-threaded flange can be added to any of Thorlabs' Avalanche Photodetectors to provide robust fiber-coupling capabilities. Please contact Tech Support for more information

Power Supply
An LDS12B ±12 V linear power supply is included with the amplified photodetector; replacement power supplies are available below. The power supply features a three-way switch and can be plugged into any 50 to 60 Hz, 100 V / 120 V / 230 V power outlet. Before connecting the power supply to an outlet or to the detector, make sure that the power switches on both the power supply and the detector are in the off position. Hot-plugging is not recommended.

A complete list of all of our APDs can be found on the Selection Guide tab. Please note that our Single Photon Detectors are the only avalanche photodetectors suitable for single photon counting.

All technical data are valid at 23 ± 5 °C and 45% ± 15% relative humidity (non-condensing).

Item #	APD431A
Detector Type	Silicon APD
Wavelength Range	400 - 1000 nm
Output Bandwidth (3 dB)^a	DC - 400 MHz
Threading	External M12 x 0.5
Active Area Diameter	0.5 mm
Max Responsivity	53 A/W @ 800 nm (M = 100)
M Factor	10 - 100 (Continuous)
M Factor Temperature Stability	±2% (Typical); ±3% (Max)
Transimpedance Gain^b	5 kV/A (50 Ω Termination) 10 kV/A (High-Z Termination)
Max Conversion Gain^c	5.3 × 10⁵ V/W
CW Saturation Power^d	8.0 µW @ 800 nm, M = 100 80 µW @ 800 nm, M = 10
Max Input Power^e	1 mW
Minimum NEP^f	0.14 pW/√Hz (DC - 100 MHz)
Integrated Noise	5.5 nW (RMS, DC - 400 MHz)
Electrical Output, Impedance	BNC, 50 Ω
Max Output Voltage Swing^b	2.0 V (50 Ω Termination) 4.1 V (High-Z Termination)
DC Offset Electrical Output	<±3 mV
Included Power Supply^g	LDS12B, ±12 V @ 250 mA (100/120/230 VAC, 50 - 60 Hz, Switchable)
General
Operating Temperature Range	0 to 40 °C (Non-Condensing)
Storage Temperature Range	-40 to 70 °C
Dimensions (H x W x D)	2.93" x 2.20" x 1.33" (74.5 mm x 55.8 mm x 33.7 mm)
Weight	0.122 kg

At Maximum Gain Setting
50 Ω termination is recommended for the best performance.
At the Peak Responsivity Wavelength
For Free-Space Input
This value is the damage threshold for the photodiode.
For more information on how NEP is calculated, please see Thorlabs' Noise Equivalent Power White Paper.
A replacement power supply is available below.

Click to Enlarge
Click Here for Raw Data
Typical responsivity curve for the APD431A photodetector.

Click to Enlarge
Click Here for Raw Data
Typical output frequency response curve for the APD431A photodetector.

Click to Enlarge
Click Here for Raw Data
Typical spectral noise for the APD431A photodetector.

BNC Female Output (Photodetector)

APD Male (Power Cables)

APD Female (Photodetector)

Pinout for PDA Power Connector

Pulsed Laser Emission: Power and Energy Calculations

Click above to download the full report.

Determining whether emission from a pulsed laser is compatible with a device or application can require referencing parameters that are not supplied by the laser's manufacturer. When this is the case, the necessary parameters can typically be calculated from the available information. Calculating peak pulse power, average power, pulse energy, and related parameters can be necessary to achieve desired outcomes including:

Protecting biological samples from harm.
Measuring the pulsed laser emission without damaging photodetectors and other sensors.
Exciting fluorescence and non-linear effects in materials.

Pulsed laser radiation parameters are illustrated in Figure 1 and described in the table. For quick reference, a list of equations is provided below. The document available for download provides this information, as well as an introduction to pulsed laser emission, an overview of relationships among the different parameters, and guidance for applying the calculations.

Equations:
Period and repetition rate are reciprocal:		and
Pulse energy calculated from average power:
Average power calculated from pulse energy:
Peak pulse power estimated from pulse energy:
Peak power and average power calculated from each other:
	and
Peak power calculated from average power and duty cycle*:
	*Duty cycle () is the fraction of time during which there is laser pulse emission.

Click to Enlarge

Figure 1: Parameters used to describe pulsed laser emission are indicated in the plot (above) and described in the table (below). Pulse energy (E) is the shaded area under the pulse curve. Pulse energy is, equivalently, the area of the diagonally hashed region.

Parameter	Symbol	Units
Pulse Energy	E	Joules [J]	A measure of one pulse's total emission, which is the only light emitted by the laser over the entire period. The pulse energy equals the shaded area, which is equivalent to the area covered by diagonal hash marks.
Period	Δt	Seconds [s]	The amount of time between the start of one pulse and the start of the next.
Average Power	P_avg	Watts [W]	The height on the optical power axis, if the energy emitted by the pulse were uniformly spread over the entire period.
Instantaneous Power	P	Watts [W]	The optical power at a single, specific point in time.
Peak Power	P_peak	Watts [W]	The maximum instantaneous optical power output by the laser.
Pulse Width		Seconds [s]	A measure of the time between the beginning and end of the pulse, typically based on the full width half maximum (FWHM) of the pulse shape. Also called pulse duration.
Repetition Rate	f_rep	Hertz [Hz]	The frequency with which pulses are emitted. Equal to the reciprocal of the period.

Example Calculation:

Is it safe to use a detector with a specified maximum peak optical input power of 75 mW to measure the following pulsed laser emission?

Average Power: 1 mW
Repetition Rate: 85 MHz
Pulse Width: 10 fs

The energy per pulse:

seems low, but the peak pulse power is:

It is not safe to use the detector to measure this pulsed laser emission, since the peak power of the pulses is >5 orders of magnitude higher than the detector's maximum peak optical input power.

Avalanche Photodetector Selection Guide

Item #	Detector Type	Wavelength Range	3 dB Bandwidth	Active Area Diameter	M Factor	Typical Max Responsivity	Max Conversion Gain^a	Variable Gain	Fiber-Coupled^b
APD440A2	UV Enhanced Silicon APD	200 - 1000 nm	DC - 0.1 MHz	1 mm	5 - 50	25 A/W @ 600 nm (M = 50)	1.25 x 10⁹ V/W		-
APD410A2			DC - 10 MHz	0.5 mm	5 - 50	25 A/W @ 600 nm (M = 50)	12.5 x 10⁶ V/W		-
APD130A2			DC - 50 MHz	1 mm	50	25 A/W @ 600 nm (M = 50)	2.5 x 10⁶ V/W	-	-
APD430A2			DC - 400 MHz	0.2 mm	10 - 100	50 A/W @ 600 nm (M = 100)	5.0 x 10⁵ V/W		-
APD410			5 - 900 MHz^c	0.2 mm	50	22 A/W @ 650 nm (M = 50)	4.5 x 10⁴ V/W^d		-
APD440A	Silicon APD	400 - 1000 nm	DC - 0.1 MHz	1 mm	10 - 100	53 A/W @ 800 nm (M = 100)	2.65 x 10⁹ V/W		-
APD410A			DC - 10 MHz	1.0 mm	10 - 100	53 A/W @ 800 nm (M=100)	26.5 x 10⁶ V/W		-
APD130A			DC - 50 MHz	1 mm	50	25 A/W @ 800 nm (M = 50)	2.5 x 10⁶ V/W	-	-
APD430A			DC - 400 MHz	0.5 mm	10 - 100	53 A/W @ 800 nm (M = 100)	5.3 x 10⁵ V/W		-
APD431A			DC - 400 MHz^e	0.5 mm	10 - 100	53 A/W @ 800 nm (M = 100)	5.3 x 105 V/W
APD210			5 - 1000 MHz^c	0.5 mm	100	50 A/W @ 800 nm (M = 100)	2.5 x 10⁵ V/W^f		-
APD130C	InGaAs APD	900 - 1700 nm	DC - 50 MHz	0.2 mm	10	9 A/W @ 1500 nm (M = 10)	0.9 x 10⁶ V/W	-	-
APD410C			DC - 10 MHz	0.2 mm	4 - 20	18 A/W @ 1550 nm (M = 20)	9.0 x 10⁶ V/W		-
APD430C			DC - 400 MHz	0.2 mm	4 - 20	18 A/W @ 1550 nm (M = 20)	1.8 x 10⁵ V/W		-
APD431C			DC - 400 MHz^e	0.2 mm	4 - 20	18 A/W @ 1550 nm (M = 20)	1.8 x 10⁵ V/W
APD450C		1260 - 1620 nm	0.3 - 1600 MHz	1.5 mm^g	2 - 10	9 A/W @ 1550 nm (M = 10)	45 × 10³ V/W		-
APD310		850 - 1650 nm	5 - 1000 MHz^c	0.04 mm	30	0.9 A/W @ 1550 nm (M = 30)	2.5 x 10⁴ V/W^h		-

At Peak Responsivity Wavelength Unless Otherwise Stated
Fiber-coupled APDs have an external M12 x 0.5-threaded flange that is directly compatible with our APD fiber connector adapters. This M12 x 0.5-threaded flange can be added to any of Thorlabs' Avalanche Photodetectors. Please contact Tech Support for more information.
The max frequency range is 1 MHz - 1600 MHz.
At 1 GHz and 650 nm
At Maximum Gain Setting
At 1 GHz and 800 nm
75 µm Detector with Ø1.5 mm Ball Lens
At 1 GHz and 1500 nm

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Si Fiber-Coupled Avalanche Photodetector

Item #^a,b	Housing Features^c	Wavelength Range	Output Bandwidth (3 dB)^d	Threading^e	Active Area Diameter	Max Responsivity	Typical Performance Graph	Max Conversion Gain^f	M Factor Adjustment Range	Minimum NEP^g,h	Power Supply Included
APD431A		400 - 1000 nm	DC - 400 MHz	External M12 x 0.5	0.5 mm	53 A/W @ 800 nm (M = 100)	Click Here for Raw Data	5.3 × 10⁵ V/W	10 - 100 (Continuous)	0.14 pW/√Hz	Yesⁱ

For a complete list of specification, please see the Specs tab above. Data are valid at 23 ± 5 °C and 45% ± 15% relative humidity (non-condensing).
Click on the link to view a photo of the item.
Click the icon for details of the housing.
At Maximum Gain Setting
Compatible with M12 x 0.5-threaded fiber and mechanical adapters (sold below).
At the Peak Responsivity Wavelength
DC - 100 MHz
For more information on how NEP is calculated, please see Thorlabs' Noise Equivalent Power White Paper.
The LDS12B power supply is included with each photodetector. Replacement power supplies are sold below.

Fiber Connector Adapters for Fiber-Coupled Avalanche Photodetector

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Click to Enlarge
The APDF2-A Fiber Connector Adapter Mounted to the APD431A Photodetector

Enable Fiber-Coupling to the APD431A Avalanche Photodetector (Sold Above)
Compatible with Single Mode and Multimode Fibers
Four Fiber Connection Options Available
Two Coating Options Available for Visible Light Detection

Thorlabs offers Fiber Connector Adapters that enable single-mode and multi-mode fibers to connect to our APD431A photodetector. These robust adapters allow for easy fiber coupling with high reproduciblity. Each adapter has a small footprint and can be directly mounted to the APD via M12 x 0.5 threading. They feature a built-in Molded Glass Aspheric Lens and are optimized for single mode fibers, and for multimode fibers with a 200 μm core and NA = 0.22; however, they can be used with all optical fibers with some loss of coupling efficiency. Options are available for FC/APC, FC/PC, LC/PC, and SC/PC fiber connections, and with coatings for 350 - 700 nm and 600 - 1050 nm. For adapters with coatings for infrared light detection, please see our InGaAs APD fiber connector adapters.

Item #	APDA2-A	APDA2-B	APDF2-A	APDF2-B	APDL-A	APDL-B	APDS-A	APDS-B
Fiber Connector Type^a	FC/APC Narrow-Key (2.0 mm)		FC/PC Narrow-Key (2.0 mm)		LC/PC		SC/PC
Built-In Lens	355440-A	355440-B	355440-A	355440-B	355440-A	355440-B	355440-A	355440-B
AR Coating Range^b	350 - 700 nm (-A Coating)^c	600 - 1050 nm (-B Coating)^d	350 - 700 nm (-A Coating)^c	600 - 1050 nm (-B Coating)^d	350 - 700 nm (-A Coating)^c	600 - 1050 nm (-B Coating)^d	350 - 700 nm (-A Coating)^c	600 - 1050 nm (-B Coating)^d

Click on the link to view a photo of the connector.
Average Reflectance <0.5% at 0° AOI
Click Here for Raw Data
Click Here for Raw Data

Based on your currency / country selection, your order will ship from Newton, New Jersey

+1 Qty Docs Part Number - Universal Price Available

APDA2-A FC/APC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 350 - 700 nm

$332.75

3-5 Days

APDA2-B FC/APC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 600 - 1050 nm

$332.75

Lead Time

APDF2-A FC/PC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 350 - 700 nm

$289.50

3-5 Days

APDF2-B FC/PC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 600 - 1050 nm

$289.50

Lead Time

APDL-A LC/PC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 350 - 700 nm

$358.75

3-5 Days

APDL-B LC/PC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 600 - 1050 nm

$358.75

3-5 Days

APDS-A SC/PC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 350 - 700 nm

$358.75

3-5 Days

APDS-B SC/PC Avalanche Photodetector Fiber Connector Adapter, AR Coating: 600 - 1050 nm

$358.75

3-5 Days

Adapter with External SM1 (1.035"-40) Threads and Internal M12 x 0.5 Threads

Adapter with External SM1 (1.035in-40) Threads and Internal M12 x 0.5 Threads

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Click to Enlarge
An SM1M10 lens tube is connected to the APD431A photodetector using the SM1A610 adapter.

Compatible with the APD431A Avalanche Photodetector (Sold Above) and Other Externally M12 x 0.5-Threaded Components
Compatible with SM1-Threaded Components

The SM1A610 adapter allows the APD431A photodetector to be used as a free-space detector with standard optomechanics. This robust adapter connects directly to the APD431A photodetector via internal M12 x 0.5 threading and features external SM1 (1.035"-40) threads for use with standard SM1-threaded components.

±12 VDC Regulated Linear Power Supply

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LDS12B Male Power Cable

Replacement Power Supply for APD431A Avalanche Photodetector (Sold Above)
±12 VDC Power Output
Current Limit Enabling Short Circuit and Overload Protection
On/Off Switch with LED Indicator
Switchable AC Input Voltage (100, 120, or 230 VAC)
2 m (6.6') Cable with LUMBERG RSMV3 Male Connector
UL and CE Compliant

The LDS12B ±12 VDC Regulated Linear Power Supply is intended as a replacement for the supply included with our APD431A avalanche photodetector sold above. The cord has three pins: one for ground, one for +12 V, and one for -12 V (see diagram to the right). A region-specific power cord is shipped with the unit based on your location. This power supply can also be used with the PDA series of amplified photodetectors, PDB series of balanced photodetectors, PMM series of photomultiplier modules, and the FSAC autocorrelator for femtosecond lasers.