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InGaAs Transimpedance Amplified Photodetectors
Detector with Ø1" Lens
380 MHz Bandwidth
Thorlabs' Indium Gallium Arsenide (InGaAs) Transimpedance Amplified Photodetectors provide low-noise amplified signals from InGaAs photodetectors, which are sensitive to light in the NIR wavelength range. Our selection of PDA series amplified photodetectors are designed to meet a range of requirements, with offerings that include the 380 MHz PDA015C with an impulse response of 1 ns, the high-sensitivity PDF10C with a noise equivalent power (NEP) of 7.5 fW/Hz1/2, and the switchable-gain PDA10CS with eight switchable maximum gain (bandwidth) combinations from 1.15 kV/A (17 MHz) to 4.75 MV/A (12 kHz).
The PDF10C with femtowatt sensitivity is a low-frequency device that should only be terminated into high impedance (Hi-Z) loads, while all other of our InGaAs amplified photodetectors are capable of driving loads from 50 Ω to Hi-Z.
Each of Thorlabs' amplified photodetectors has a frequency response extending to DC. Switchable-gain versions include 8 gain settings, in which each gain setting also adjusts the maximum bandwidth. Bandwidth varies inversely with gain. Fixed-gain versions possess a fixed maximum bandwidth and total transimpedance gain. Across the PDA series, amplification is provided by either a low-noise transimpedance amplifier (TIA) or a low-noise TIA followed by a voltage amplifier. Signal output is via a BNC connector.
Each unit's housing features 8-32 tapped holes (M4 for -EC and /M models) that enable the amplified photodetector to be vertically or horizontally post mounted. For more information about the location of these mounting points and mounting these units, please see the Housing Features and Mounting Options tabs. The housings also feature internal SM05 (0.535"-40) threading and external SM1 (1.035"-40) threading, as shown in the image to the right. An SM1T1 internally SM1-threaded adapter is included with each detector. The PDA015C, PDA10CF, PDA10D, PDA10CS, and PDA20CS also each include an SM1RR retaining ring. A TRE(/M) electrically isolated TR post adapter is included with the PDF10C.
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The power supply is included with all of the detectors on this page and replacements are sold below.
Included with each amplified photodetector is a ±12 V power supply, which features a switch that is toggled to select for either 115 or 230 VAC input voltage. Always use the power switch on the housing or on the power supply to power on the amplified photodetector . Hot plugging is not recommended, as this may result in an oscillating or negative output signal. Thorlabs recommends centering the incident light on the active area of the photodetector and not overfilling the detector area. Failing to do so may result in undesirable capacitance and resistance effects, arising from inhomogeneities at the edges of the active area of the detector, that distort the frequency response.
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Housings feature internal SM05 and external SM1 threads. An SM1T1 SM1 Adapter with internal threads is included with each amplified photodetector, and an SM1RR Retaining Ring is included with the PDA015C, PDA10CF, PDA10D, PDA10CS, and PDA20CS.
The SM1 threading on the housing is ideally suited for mounting a Ø1" focusing lens or pinhole in front of the detector element. In addition, these photodetectors pair well with Thorlabs' passive low-pass filters, which have a 50 Ω input and a high-impedance output that allows them to be directly attached to high-impedance measurement devices such as an oscilloscope. Thorlabs offers a wide variety of BNC, BNC-to-SMA, and SMC cables, as well as a variety of BNC, SMA, and SMC adapters.
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Figure 2: Housings feature internal SM05 and external SM1 threads. An SM1T1 SM1 Adapter with internal threads is included with each amplified photodetector, and an SM1RR Retaining Ring is included with the PDA015C, PDA10CF, PDA10D, PDA10CS, and PDA20CS.
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Figure 1: Connectors and LED Located at Top of Housing
As a convenience, the back panel of the PDA015C is engraved with the responsivity curve of the silicon photodiode. The equation written above the responsivity curve can be used to calculate the conversion gain (C.G.) for a given operating wavelength.
Housing Features of the PDA Series Amplified InGaAs Photodetectors
Thorlabs' Amplified Photodiode series feature a slim design and many common elements.
Connectors: The Power In connector, Output BNC connector, and power indicator LED are located at the top of the housing, as is shown in Figure 1.
SM1 and SM05 Threading: As shown in Figure 2, the housings feature external SM1 (1.035"-40) threading, and an SM1T1 internally SM1-threaded adapter is included with each detector. The PDA015C, PDA10CF, PDA10D, PDA10CS, and PDA20CS each additionally include an SM1RR retaining ring. Most SM1-threaded fiber adapters are compatible with these detectors. Externally SM1-threaded adapters can be mated to the included internally SM1-threaded adapter, while internally SM1-threaded adapters can be mated directly to the housing. The S120-FC internally SM1-threaded fiber adapter is not compatible with these detectors.
The internal SM05 (0.535"-40) threading on the housing is suitable for mating to an externally threaded SM05 lens tube. Please note that other SM05 components, such as fiber adapters, cannot be threaded onto the SM05 threading.
Other Features: Threaded holes on the housing allow the unit to be mounted in a horizontal or vertical orientation, which gives the user the option to route the power and BNC cables from above or alongside the beam path. For more information on mounting these units, please see the Mounting Options tab.
PDA10CS and PDA20CS Switchable-Gain Amplified Photodetectors: Figure 3 shows the key housing features. Mounting points are located at the bottom and left side of the units, which are 8-32 threaded holes on the imperial and M4 threaded holes on the metric versions. The power switch and an eight-position rotary gain switch are located on the right side of the housing. The location of the gain switch enables easy access while the amplified detector is mounted.
PDA015C, PDA10CF, and PDA10D Fixed-Gain Amplified Photodetectors: Figure 4 shows the key housing features. Mounting points are located at the bottom and left side of the units, which are 8-32 threaded holes on the imperial and M4 threaded holes on the metric versions. The power switch is located on the right side of the housing.
PDA20C and PDF10C Fixed-Gain Amplified Photodetectors: Figure 5 shows the key housing features. Mounting holes, 8-32 for the imperial versions and M4 for the metric, feature surfaces flush with the housing and located on the right side beneath the power switch, on the left side, and on the bottom of the housing. A TRE(/M) electrically isolated TR post adapter is included with the PDF10C. The power switch is located on the right side of the housing.
Switchable-Gain Amplified Detectors
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Figure 3: Power Switch, Gain Switch, and Mounting Options
Fixed-Gain Amplified Detectors
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Figure 4: Power Switch and Mounting Options
Fixed-Gain Amplified Detectors
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Figure 5: Power Switch and Mounting Options
PDA Series Mounting Options
The PDA series of amplified photodetectors are compatible with our entire line of lens tubes, TR series posts, and cage mounting systems. Because of the wide range of mounting options, the best method for mounting the housing in a given optical setup is not always obvious. The pictures and text in this tab will discuss some of the common mounting solutions. As always, our technical support staff is available for individual consultation.
TR Series Post (Ø1/2" Posts) System
The PDA housing can be mounted vertically or horizontally on a TR Series Post using the 8-32 (M4) threaded holes.
Lens Tube System
Each PDA housing includes a detachable Ø1" Optic Mount (SM1T1) that allows for Ø1" (Ø25.4 mm) optical components, such as optical filters and lenses, to be mounted along the axis perpendicular to the center of the photosensitive region. The maximum thickness of an optic that can be mounted in the SM1T1 is 0.1" (2.8 mm). For thicker Ø1" (Ø25.4 mm) optics or for any thickness of Ø0.5" (Ø12.7 mm) optics, remove the SM1T1 from the front of the detector and place (must be purchased separately) an SM1 or SM05 series lens tube, respectively, on the front of the detector.
The SM1 and SM05 threadings on the PDA photodetector housing make it compatible with our SM lens tube system and accessories. Two particularly useful accessories include the SM-threaded irises and the SM-compatible IR and visible alignment tools. Also available are fiber optic adapters for use with connectorized fibers.
The simplest method for attaching the PDA photodetector housing to a cage plate is to remove the SM1T1 that is attached to the front of the PDA when it is shipped. This will expose external SM1 threading that is deep enough to thread the photodetector directly to a CP02 30 mm cage plate. When the CP02 cage plate is tightened down onto the PDA photodetector housing, the cage plate will not necessarily be square with the detector. To fix this, back off the cage plate until it is square with the photodetector and then use the retaining ring included with the SM1T1 to lock the PDA photodetector into the desired location.
This method for attaching the PDA photodetector housing to a cage plate does not allow much freedom in determining the orientation of the photodetector; however, it has the benefit of not needing an adapter piece, and it allows the diode to be as close as possible to the cage plate, which can be important in setups where the light is divergent. As a side note, Thorlabs sells the SM05PD and SM1PD series of photodiodes that can be threaded into a cage plate so that the diode is flush with the front surface of the cage plate; however, the photodiode is unbiased.
For more freedom in choosing the orientation of the PDA photodetector housing when attaching it, a SM1T2 lens tube coupler can be purchased. In this configuration the SM1T1 is left on the detector and the SM1T2 is threaded into it. The exposed external SM1 threading is now deep enough to secure the detector to a CP02 cage plate in any orientation and lock it into place using one of the two locking rings on the ST1T2.
Although not pictured here, the PDA photodetector housing can be connected to a 16 mm cage system by purchasing an SM05T2. It can be used to connect the PDA photodetector housing to an SP02 cage plate.
The image below shows a Michelson Interferometer built entirely from parts available from Thorlabs. This application demonstrates the ease with which an optical system can be constructed using our lens tube, TR series post, and cage systems. A PDA series photodetector is interchangable with the DET series photodetector shown in the picture.
The table below contains a part list for the Michelson Interferometer for use in the visible range. Follow the links to the pages for more information about the individual parts.
BNC Female 0 - 10 V Output (Photodetector)
0 - 10 V Output
PDA Male (Power Cables)
PDA Female Power IN (Photodetector)
Theory of Operation
A junction photodiode is an intrinsic device that behaves similarly to an ordinary signal diode, but it generates a photocurrent when light is absorbed in the depleted region of the junction semiconductor. A photodiode is a fast, highly linear device that exhibits high quantum efficiency based upon the application and may be used in a variety of different applications.
It is necessary to be able to correctly determine the level of the output current to expect and the responsivity based upon the incident light. Depicted in Figure 1 is a junction photodiode model with basic discrete components to help visualize the main characteristics and gain a better understanding of the operation of Thorlabs' photodiodes.
Modes of Operation (Photoconductive vs. Photovoltaic)
The dark current present is also affected by the photodiode material and the size of the active area. Silicon devices generally produce low dark current compared to germanium devices which have high dark currents. The table below lists several photodiode materials and their relative dark currents, speeds, sensitivity, and costs.
Bandwidth and Response
Noise Equivalent Power
Here, S/N is the Signal to Noise Ratio, Δf is the Noise Bandwidth, and Incident Energy has units of W/cm2. For more information on NEP, please see Thorlabs' Noise Equivalent Power White Paper.
Depending on the type of the photodiode, load resistance can affect the response speed. For maximum bandwidth, we recommend using a 50 Ω coaxial cable with a 50 Ω terminating resistor at the opposite end of the cable. This will minimize ringing by matching the cable with its characteristic impedance. If bandwidth is not important, you may increase the amount of voltage for a given light level by increasing RLOAD. In an unmatched termination, the length of the coaxial cable can have a profound impact on the response, so it is recommended to keep the cable as short as possible.
Common Operating Circuits
The DET series detectors are modeled with the circuit depicted above. The detector is reverse biased to produce a linear response to the applied input light. The amount of photocurrent generated is based upon the incident light and wavelength and can be viewed on an oscilloscope by attaching a load resistance on the output. The function of the RC filter is to filter any high-frequency noise from the input supply that may contribute to a noisy output.
One can also use a photodetector with an amplifier for the purpose of achieving high gain. The user can choose whether to operate in Photovoltaic of Photoconductive modes. There are a few benefits of choosing this active circuit:
where GBP is the amplifier gain bandwidth product and CD is the sum of the junction capacitance and amplifier capacitance.
Effects of Chopping Frequency
The photoconductor signal will remain constant up to the time constant response limit. Many detectors, including PbS, PbSe, HgCdTe (MCT), and InAsSb, have a typical 1/f noise spectrum (i.e., the noise decreases as chopping frequency increases), which has a profound impact on the time constant at lower frequencies.
The detector will exhibit lower responsivity at lower chopping frequencies. Frequency response and detectivity are maximized for
The following table lists Thorlabs' selection of photodiodes and photoconductive detectors. Item numbers in the same row contain the same detector element.
The PDA-C-72 is a power cord for the PDA line of amplified photodetectors. The cord has tinned leads on one end and a PDA-compatible 3-pin connector on the other end. It can be used to power the PDA series of amplified photodetectors with any power supply that provides a DC voltage. The pin descriptions are shown to the right.
The LDS1212 ±12 VDC Regulated Linear Power Supply is intended as a replacement for the supply that comes with our PDA line of amplified 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 and the voltage switch is set to the proper setting for your location before it is shipped. This power supply can also be used with our PDB series of balanced photodetectors, our PMM series of photomultiplier modules, our APD series of avalanche photodetectors, and our dichroic atomic vapor spectroscopy systems.
These internally SM1-threaded (1.035"-40) adapters mate connectorized fiber to any of our externally SM1-threaded components, including our photodiode power sensors, our thermal power sensors, and our photodetectors. These adapters are compatible with the housing of the photodetectors on this page.
Each disk has four dimples, two in the front surface and two in the back surface, that allow it to be tightened from either side with the SPW909 or SPW801 spanner wrench. The dimples do not go all the way through the disk so that the adapters can be used in light-tight applications when paired with SM1 lens tubes. Once the adapter is at the desired position, use an SM1RR retaining ring to secure it in place.