Auto-Balanced Detector with Avalanche Photodiodes

Designed for Low-Power Applications Between 1200 and 1700 nm
DC - 400 MHz Bandwidth
>35 dB Common Mode Rejection Ratio (Typical)
Fiber-Coupled FC/APC Inputs

PDB570C

Right View of
PDB570C

SMA Connectors
for Output Signal

Input for
Power Cord

Please Wait

Overview
Specs
Detector Operation
Pin Diagrams
Feedback

Balanced Detector Selection Guide
Balanced Detectors with Fast Monitor Output
Large-Area Balanced Amplified Detectors
Suitable for OCT
Compact Balanced Amplified Detectors
Compact 5 GHz Balanced Detectors
OCT Balanced Detectors with Fast Monitor Output
Auto-Balanced Detector with Avalanche Photodiodes
Polarization-Dependent Balanced Detector

Selected Specifications^a
Operating Wavelength Range	1200 - 1700 nm (Optimized for 1300 nm)
Typical Responsivity^b	0.9 A/W @ 1300 nm
Bandwidth (3 dB; Balanced/Auto-Balanced)	DC to 400 MHz
Min NEP (DC to 100 MHz)^c	1.0 pW/√Hz
Common Mode Rejection Ratio	>25 dB (>35 dB Typical)
Transimpedance Gain, High Z^d	2 x 10³ V/A
Detector Type	InGaAs APD
Internal Coupling Fiber	SMF-28e+
Optical Inputs	FC/APC

For the complete specifications, please see the Specs tab.
At optical gain M = 1. This value is a general specification for the bare APDs. As used inside the PDB570C, the gain of the APDs can be varied between M = 2.5 and M = 10.
At maximum optical gain (M = 10).
Values for transimpedance gain are lossless gain values, i.e., losses introduced by FC/APC connectors (typically 0.15 to 0.25 dB) are not considered.

Features

Optical Gain Control and Auto-Balance Function
Avalanche Photodiodes (APDs) Excellent for Low-Input-Power Applications
Optimized for 1300 nm
Operating Wavelength Range: 1200 - 1700 nm
Wide DC to 400 MHz Bandwidth
Exceptionally Low NEP: 1.0 pW/√Hz (DC - 100 MHz)
>35 dB Common Mode Rejection Ratio (Typical)
<0.4 mV_RMS Output Voltage Noise
Fiber-Coupled FC/APC Inputs
Switchable Universal Power Supply Included

Thorlabs' PDB570C Avalanche-Photodiode-Based Balanced Detector is a balanced receiver that subtracts the two input signals from each other, resulting in the cancellation of common mode noise. The balanced detector, which uses two well-matched avalanche photodiodes (APDs) and an ultra-low-noise, ultra-low-distortion, high-speed transimpedance amplifier, is optimized for applications with low optical input powers (minimum NEP of 1.0 pW/√Hz). Each avalanche photodiode is fiber coupled to the FC/APC outputs via length-matched SMF-28e+ fibers so as not to introduce optical path differences between the input and the active area of the photodiode. Compared to our other balanced detectors that use Si or InGaAs PIN photodiodes, the PDB570C offers unique features such as exceptionally low NEP, optical gain control, and an auto-balancing function with a variable closed-loop control velocity.

Click to Enlarge
The mating sleeve can be removed to access the FC/APC ferrules for cleaning.

This balanced detector features an adjustable gain and three different detection modes: single detector, balanced (BAL), and auto-balanced (AUTO-BAL). The single detector mode allows the output of each photodiode to be measured individually. In the BAL mode, the PDB570C functions as a standard balanced detector while allowing the optical gain of both photodiodes to be simultaneously adjusted. In the AUTO-BAL mode, the balanced detector compensates for power differences between the two optical input signals that vary at a slower rate than a cutoff frequency set via the CONTROL VELOCITY knob. This power difference can be monitored via the CONTROL OUTPUT and will not contribute to the voltage generated by the balanced detector at the RF output. For details on how to operate the PDB570C, please see the Detector Operation tab.

The included post-mounting adapter plate has both 8-32 and M4 taps and can be attached to either the bottom or back of the PDB570C's shielded aluminum housing with the included M2 x 8 screws. The PDB570C's compact housing is 95 mm x 80 mm x 44.3 mm (3.74" x 3.15" x 1.74"), including the depth of the control knobs. Each detector is shipped with a ±12 V DC power supply with an input voltage of 115 V or 230 V that can be selected by a switch. A replacement power supply that supports input voltages of 100, 120, and 230 V is available below.

The exceptionally low noise of the PDB570C APD-based auto-balanced detector makes it suitable for OCT applications. The full range of our PIN photodiode-based balanced detectors that can be used for OCT applications are found here. Thorlabs also offers Fiber-Based Interferometers, which feature an integrated balanced detector.

While the PDB570C is intended for fiber-coupled applications, a free-space beam can be coupled into the FC/APC inputs via a pigtailed aspheric collimator. Care should be taken to length-match the fibers between the collimator and the inputs in an attempt to avoid introducing unwanted path length differences into the system. Thorlabs also offers balanced detectors designed for free-space applications. Additionally, some of our fiber-coupled balanced detectors with fast monitor outputs have removable FC/APC detectors for easy integration into free-space applications.

Specifications
Detector
Detector Type	InGaAs APD
Optical Inputs	FC/APC
Internal Coupling Fiber	SMF-28e+
Coupling Loss	<0.5 dB (<0.3 dB Typical)
Operating Wavelength	Optimized for 1300 nm (1200 to 1700 nm Operating Range)
Max Responsivity (Typical)^a	0.9 A/W @ 1300 nm
Optical Back Reflection (at the Detector Surface)	<-40 dB
Max Input Power (Damage Threshold)^b	200 µW
RF Output
Bandwidth (3 dB; Balanced/Auto-Balanced)	DC to 400 MHz
Bandwidth (3 dB; INPUT+/INPUT -)	DC to 300 MHz
Common Mode Rejection Ratio	>25 dB (>35 dB Typical)
Transimpedance Gain, High Z^c	2 x 10³ V/A
Optical Gain Factor	2.5 to 10, Adjustable
Conversion Gain at 1300 nm^c	4.5 x 10³ to 18.0 x 10³ V/W
CW Saturation Power^b	200 µW @ 1300 nm
RF Output Coupling	DC Coupling Only
RF Output Impedance	50 Ω
Max RF OUTPUT Voltage Swing	±4.2 V (High Z Load) ±2.1 V (50 Ω Load)
Min NEP (DC to 100 MHz)^b,d	1.0 pW/√Hz
Overall Output Voltage Noise	<0.4 mV_RMS
Typical DC Offset	±3 mV
Control Output
Impedance	1 kΩ
Voltage Swing, High Z Load	±4.7 V (Max)
General
Electrical Outputs	SMA
Included Power Supply^e	±12 V @ 250 mA (100/120/230 VAC, 50 - 60 Hz, Switchable)
Operating Temperature Range (Non-Condensing)	0 to 40 °C
Storage Temperature Range	-40 to 70 °C
Dimensions without Connectors (W x H x D)^f	95 mm x 80 mm x 44.3 mm (3.74" x 3.15" x 1.74")
Weight	0.37 kg (0.82 lbs)

At optical gain M = 1. This value is a general specification for the bare APDs. As used inside the PDB570C, the gain of the APDs can be varied between M = 2.5 and M = 10.
At maximum optical gain (M = 10)..
Values for transimpedance gain and conversion gain are lossless gain values, i.e., losses introduced by FC/APC connectors (typically 0.15 to 0.25 dB) are not considered.
For more information on NEP, please see Thorlabs' Noise Equivalent Power White Paper
A replacement power supply is available below.
These dimensions include the depth of the control knobs on the front of the housing.

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

Click to Enlarge
The blue-shaded regions indicate the specified 1200 - 1700 nm operating wavelength range of the PDB570C APD balanced detector. Optimal performance is obtained for wavelengths between 1260 nm and 1625 nm, which is denoted by the darker blue shaded region; this optimized region is narrower due to the optical properties of the SMF-28e+ fiber used to couple the photodiodes to the inputs. The fiber pigtails may introduce additional insertion loss outside of this range and transmit multi-modal light below the fiber's 1240 nm cutoff wavelength. The 900 to 1700 nm range of the graph indicates the full operating range of the APDs. This photodiode has been optimized for use at 1300 nm, which is indicated with a vertical blue line.

Click for Details
Simplified Mechanical Drawing of the PDB570C

Click to Enlarge
A functional diagram of the PDB570C. The transimpedance amplifier generates an output voltage proportional to the difference between the photocurrents of the two photodiodes. The gain of the detector and cut-off frequency for the auto-balance feature can be set by the user.

Thorlabs' PDB570C Balanced Detector with Avalanche Photodiodes features an adjustable gain and three different detection modes: single detector, balanced (BAL), and auto-balanced (AUTO-BAL). The single detector mode allows the output of each photodiode to be measured individually. In this mode, sources can be connected to both INPUT+ and INPUT-, while the RF OUTPUT knob can be used to select which input you wish to monitor. The optical gain control allows the RF OUTPUT signal level to be adjusted. This feature is helpful when setting your experiment to provide equal input power levels to each APD prior to continuing with measurements in the balanced or auto-balanced detection modes.

Click to Enlarge
Front View of the PDB570C APD-Based Balanced Detector

In the BAL mode, the PDB570C functions as a standard balanced detector while allowing the optical gain of both photodiodes to be simultaneously adjusted. The output signal generated by the difference between the two input signals can then be measured via the RF OUTPUT connector.

In the AUTO-BAL mode, the optical gain control only affects INPUT-, while the gain for INPUT+ is automatically adjusted via a power-balance control loop to match the current generated by INPUT- (see the figure to the right). This circuit will compensate for power differences between the two optical input signals that vary at a slower rate than a cutoff frequency set via the CONTROL VELOCITY knob. Differences between the two input signals that vary slower than this frequency will not contribute to the voltage generated at RF OUTPUT. The CONTROL OUTPUT in auto-balance mode provides a measure of this rejected signal (i.e., the constant or slowly varying power imbalance between the two input optical signals). Therefore, the control circuit effectively functions as a lowpass filter for the CONTROL OUTPUT.

A second lowpass filter serves to remove noise from the output of the transimpedance amplifier before it is read out at RF OUTPUT. The CONTROL VELOCITY knob is not marked with graduated bandwidth values, as the control loop is affected by several factors including the optical gain, ratio of input power levels, absolute input power level, and the modulation depth of the disturbance signal.

Pin Diagrams for Auto-Balanced Detectors

Control Output

SMA Female

BNC Female

RF Output

SMA Female

BNC Female

PDB Male (Power Cables)

PDB Female (Photodetector)

Pinout for PDA Power Connector

Posted Comments:

Michael Slocum (posted 2021-02-12 17:11:20.363)

Following up on the comment from cbrideau, if you can't find a Si APD that can tolerate the high voltage bias, would it be possible to use a GaAs APD to achieve visible detection and the higher bandwidth?

dpossin (posted 2021-02-17 05:18:06.0)

Dear Michael, Thank you for your feedback. In general it is possible to offer APD in the VIS based on GaAs within our low voltage PCB design. I will reach out to you in order to discuss the technical details.

hoju1301 (posted 2017-07-02 13:45:10.157)

Hello! How does this perform compared to the Newport/New Focus Nirvana series auto balance detector?

swick (posted 2017-07-05 03:27:45.0)

This is a response from Sebastian at Thorlabs. Thank you for the inquiry. I have contacted you directly for detailed comparison of the specifications.

spiros.mikroulis (posted 2016-09-23 09:20:02.27)

I would like to have more info for the PDB570C. First what can be the maximum input power level? I see the max input power is 200 μW but can this be increased using low gain? Spiros Mikroulis

swick (posted 2016-09-28 06:43:45.0)

This is a response from Sebastian at Thorlabs. Thank you for the inquiry. The optical damage threshold of PDB570C is 200µW. Applying optical power of more than 200µW to the PDB570C would result in damage.

cbrideau (posted 2015-01-16 15:12:38.04)

Are there any plans to make these available with Si photodiodes like the APD120 or APD210 for use in the visible? This could be useful for a correlation project I have on the back burner for visible fluorescence.

shallwig (posted 2015-01-19 04:26:47.0)

This is a response from Stefan at Thorlabs. Thank you very much for your inquiry. We are checking the market for APDs in the visible range which match with the layout of our PDB570C in terms of bias voltage. Unfortunately there are no APDs available which fit with our low voltage layout. The APDs which are available so far need about 150V while the InGaAs APDs only need 50V. We will go on checking the market for solutions and keep you informed.

Auto-Balanced Detector with Avalanche Photodiodes

±12 VDC Regulated Linear Power Supply

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Replacement Power Supply for the Balanced Amplified Photodetectors 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 ft) 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 PDB line of balanced photodetectors sold on this page. The cord has three pins: one for ground, one for +12 V, and one for -12 V (see diagram above). This power supply ships with a location-specific power cord. This power supply can also be used with the PDA series of amplified photodetectors, PMM series of photomultiplier modules, APD series of avalanche photodetectors, and the FSAC autocorrelator for femtosecond lasers.