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Calibrated Photodiodes

  • Si, Ge, and InGaAs Photodiodes Available
  • NIST Traceable
  • Photodiodes Shipped with Calibration Curves




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Mounted and Unmounted Detectors
Unmounted Photodiodes (150 - 2600 nm)
Calibrated Photodiodes (350 - 1800 nm)
Mounted Photodiodes (150 - 1800 nm)
Thermopile Detectors (0.2 - 15 µm)
Photoconductors (1 - 4.8 µm)
Photovoltaic Detectors (2.0 - 10.6 µm)
Pigtailed Photodiodes (320 - 1000 nm)

Thorlabs offers four photodiodes, with NIST traceable calibration, that ship from stock. These include one Indium Gallium Arsenide (InGaAs), two Silicon (Si), and one Germanium (Ge) photodiodes.

Calibration Features:

  • Responsivity Measured Every 10 nm Over the Spectral Range of the Photodiode
  • Measurement Uncertainty ±5%
  • NIST Traceable

Each photodiode comes with its own data table and graph of the responsivity vs wavelength.

The responsivity of a particular photodiode varies from lot to lot. Due to this, the photodiode you receive may have a slightly different response than what is represented in the graphs in the info icons below, but will include calibration data. To the right, a graph for the FDS1010 photodiode shows how significantly you can expect the response to vary. Data was collected from 104 photodiodes. Minimum, Average, and Maximum responsivity was calculated at each data point and has been plotted.

Please note that inhomogeneities at the edges of the active area of the detector can generate unwanted capacitance and resistance effects that distort the time-domain response of the photodiode output. Thorlabs therefore recommends that the incident light on the photodiode is well centered on the active area. This can be accomplished by placing a focusing lens or pinhole in front of the detector element.

These photodiodes are calibrated with zero bias. We do not recommend reverse voltage biasing these photodiodes; doing so will increase the responsivity and void the calibration. For more information on voltage biasing as well as the noise floor, please see the Lab Facts tab.

Photodiode Tutorial

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.

Equation 1
Photodiode Circuit Diagram
Figure 1: Photodiode Model

Photodiode Terminology

The responsivity of a photodiode can be defined as a ratio of generated photocurrent (IPD) to the incident light power (P) at a given wavelength:

Equation 2

Modes of Operation (Photoconductive vs. Photovoltaic)
A photodiode can be operated in one of two modes: photoconductive (reverse bias) or photovoltaic (zero-bias). Mode selection depends upon the application's speed requirements and the amount of tolerable dark current (leakage current).

In photoconductive mode, an external reverse bias is applied, which is the basis for our DET series detectors. The current measured through the circuit indicates illumination of the device; the measured output current is linearly proportional to the input optical power. Applying a reverse bias increases the width of the depletion junction producing an increased responsivity with a decrease in junction capacitance and produces a very linear response. Operating under these conditions does tend to produce a larger dark current, but this can be limited based upon the photodiode material. (Note: Our DET detectors are reverse biased and cannot be operated under a forward bias.)

In photovoltaic mode the photodiode is zero biased. The flow of current out of the device is restricted and a voltage builds up. This mode of operation exploits the photovoltaic effect, which is the basis for solar cells. The amount of dark current is kept at a minimum when operating in photovoltaic mode.

Dark Current
Dark current is leakage current that flows when a bias voltage is applied to a photodiode. When operating in a photoconductive mode, there tends to be a higher dark current that varies directly with temperature. Dark current approximately doubles for every 10 °C increase in temperature, and shunt resistance tends to double for every 6 °C rise. Of course, applying a higher bias will decrease the junction capacitance but will increase the amount of dark current present.

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.

MaterialDark CurrentSpeedSpectral RangeCost
Silicon (Si) Low High Speed Visible to NIR Low
Germanium (Ge) High Low Speed NIR Low
Gallium Phosphide (GaP) Low High Speed UV to Visible Moderate
Indium Gallium Arsenide (InGaAs) Low High Speed NIR Moderate
Indium Arsenide Antimonide (InAsSb) High Low Speed NIR to MIR High
Extended Range Indium Gallium Arsenide (InGaAs) High High Speed NIR High
Mercury Cadmium Telluride (MCT, HgCdTe) High Low Speed NIR to MIR High

Junction Capacitance
Junction capacitance (Cj) is an important property of a photodiode as this can have a profound impact on the photodiode's bandwidth and response. It should be noted that larger diode areas encompass a greater junction volume with increased charge capacity. In a reverse bias application, the depletion width of the junction is increased, thus effectively reducing the junction capacitance and increasing the response speed.

Bandwidth and Response
A load resistor will react with the photodetector junction capacitance to limit the bandwidth. For best frequency response, a 50 Ω terminator should be used in conjunction with a 50 Ω coaxial cable. The bandwidth (fBW) and the rise time response (tr) can be approximated using the junction capacitance (Cj) and the load resistance (RLOAD):

Equation 3

Noise Equivalent Power
The noise equivalent power (NEP) is the generated RMS signal voltage generated when the signal to noise ratio is equal to one. This is useful, as the NEP determines the ability of the detector to detect low level light. In general, the NEP increases with the active area of the detector and is given by the following equation:

Photoconductor NEP

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.

Terminating Resistance
A load resistance is used to convert the generated photocurrent into a voltage (VOUT) for viewing on an oscilloscope:

Equation 4

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.

Shunt Resistance
Shunt resistance represents the resistance of the zero-biased photodiode junction. An ideal photodiode will have an infinite shunt resistance, but actual values may range from the order of ten Ω to thousands of MΩ and is dependent on the photodiode material. For example, and InGaAs detector has a shunt resistance on the order of 10 MΩ while a Ge detector is in the kΩ range. This can significantly impact the noise current on the photodiode. For most applications, however, the high resistance produces little effect and can be ignored.

Series Resistance
Series resistance is the resistance of the semiconductor material, and this low resistance can generally be ignored. The series resistance arises from the contacts and the wire bonds of the photodiode and is used to mainly determine the linearity of the photodiode under zero bias conditions.

Common Operating Circuits

Reverse Biased DET Circuit
Figure 2: Reverse-Biased Circuit (DET Series Detectors)

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.

Reverse Biased DET Circuit
Figure 3: Amplified Detector Circuit

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:

  • Photovoltaic mode: The circuit is held at zero volts across the photodiode, since point A is held at the same potential as point B by the operational amplifier. This eliminates the possibility of dark current.
  • Photoconductive mode: The photodiode is reversed biased, thus improving the bandwidth while lowering the junction capacitance. The gain of the detector is dependent on the feedback element (Rf). The bandwidth of the detector can be calculated using the following:

Equation 5

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

Photoconductor Chopper Equation

This tab contains a collection of experiments performed at Thorlabs regarding the performance of photodiodes we offer. Each section is its own independent experiment, which can be viewed by clicking in the appropriate box below. Photodiode Saturation Limit and Noise Floor explores how different conditions, including temperature, resistivity, reverse-bias voltage, responsivity, and system bandwidth, can affect noise in a photodiode's output. Photodiode Spatial Uniformity explores how spatial uniformity changes when varying the material of a photodiode or the wavelength of light incident on the diode; this section also includes spatial uniformity variance across multiple samples in a single product line. Dark Current as a Function of Temperature and Noise Equivalent Power (NEP) as a Function of Temperature describe how dark current and NEP, respectively, vary with temperature and how measurements are affected. Beam Size and Photodiode Saturation shows how the photodiode saturation point changes with the incident beam size and investigates several models to explain the results. Bias Voltage examines the effects of incident power on the effective reverse bias voltage of a photodiode circuit and verifies a reliable model for predicting those changes.

About Our Lab Facts
Our application engineers live the experience of our customers by conducting experiments in Alex’s personal lab. Here, they gain a greater understanding of our products’ performance across a range of application spaces. Their results can be found throughout our website on associated product pages in Lab Facts tabs. Experiments are used to compare performance with theory and look at the benefits and drawbacks of using similar products in unique setups, in an attempt to understand the intricacies and practical limitations of our products. In all cases, the theory, procedure, and results are provided to assist with your buying decisions.

Posted Comments:
s.krause  (posted 2017-07-31 09:45:28.43)
We bought a FDS1010-CAL to measure light intensities without applying bias voltage, just connecting the diode to an Pico-Amperemeter. I wonder how linear the response is to incident light level? Do you have any numbers, until which current output it is linear (within 1%)? Best, Sascha
tfrisch  (posted 2017-07-31 03:36:54.0)
Hello, thank you for contacting Thorlabs. We have some information on the theory of saturation in the below lab facts. It will depend on a number of factors including the bias voltage, built-in voltage, responsivity, load resistance and series resistance, but likely the detector would be completely saturated at a few mW with no bias voltage, and non-linear performance would begin before that. For the built in voltage of a silicon diode, 0.6V is a fair estimate, but you can get a more accurate measurement by finding the output voltage at saturation with a large load resistor.
hakan.pettersson  (posted 2017-03-21 19:34:14.967)
I wonder at which bias the provided responsivity data for the FDS100-CAL is recorded at. Also, can the responsivity simply be scaled with bias according to a simply relation? All the best HåkanP
swick  (posted 2017-03-22 06:15:53.0)
This is a response from Sebastian at Thorlabs. Thank you for the inquiry. The calibration is performed without bias voltage. Unfortunately, there is no simple relation between responsivity and bias. The calibration data is only valid without bias.
Jeff.Wheeldon  (posted 2016-06-08 16:01:31.357)
Could you tell me the highest measurable power using FDG05-CAL. We regularly measure total powers of 45 mW is this within the specification for this product?
besembeson  (posted 2016-06-09 09:18:53.0)
Response from Bweh at Thorlabs USA: That may be too high. At peak responsivity (1550nm) for example with 45mW, you will be around 38mA of output generated current, and you will be saturating the detector. Depending on your wavelength, you want to keep optical power level such that output current is under 1mA to stay in the linear regime for the detector.
dojin78  (posted 2014-03-18 10:49:01.103)
Could you tell me the difference FGA21-CAL and FGA21?
alexandru.serb05  (posted 2013-09-03 11:01:18.603)
Do we know what the optical damage threshold for this product is (and for that matter for all of them)? In other words beyond what sort of irradiance will I start frying the device? I suspect this will be wavelength dependent so ideally there will be some sort of plot showing damage threshold in W/M^2 vs wavelength, but if not, some rough figure would also be very helpful. Thanks
jlow  (posted 2013-09-04 09:36:00.0)
Response from Jeremy at Thorlabs: The photodiode will start to saturate well before damage would occur. In general, I would recommend keeping the current output from the photodiode to be <1mA to avoid saturating the photodiode. I will get in contact with you to discuss about your application further.
bdada  (posted 2011-11-17 15:29:00.0)
Response from Buki at Thorlabs: Thank you for your feedback. We can provide the calibrated version of the SM05PD1A. We will contact you regarding a quote.
gert  (posted 2011-11-17 15:09:23.0)
Can you give us a price for a calibrated and mounted FDS100 Si photodiode, type SM05PD1A ? Thank you, Gert Raskin
jjurado  (posted 2011-02-24 14:33:00.0)
Response from Javier at Thorlabs to rjaculbia: Thank you for contacting us with your request. We currently do not offer mounts or adapters for easily mounting the calibrated photodiodes. However, we can offer these already mounted in SM05 and SM1 compatible tubes with SMA or BNC output connectors as special items. Please visit the link below: I will contact you directly to get information about your selection.
rbjaculbia  (posted 2011-02-24 01:04:07.0)
hi, how do we mount these diodes in a setup? can this be mounted using the s1lm9? Thanks
apalmentieri  (posted 2010-01-20 15:33:04.0)
A response from Adam at Thorlabs: The calibration data is in the form of an excel data table with a wavelength resolution of 10nm. When calibrating these diodes, we do not use fiber coupling methods. We use a monochromator with an output beam diameter of 1.7mm so not to overfill the aperture. The accuracy of +/-5% is a tolerance that includes any measurement errors, for instance shot noise and johnson noise from the detector, that must be taken into account while calibrating the diode to NIST traceable standards.
markus.blaser  (posted 2010-01-20 11:05:25.0)
Few questions with respect to FGA21-CAL: In which form is the calibration data availabe: Data Table ? Wavelength resolution ? What is the optical coupling method used for the calibration procedure: Butt Fiber / Angled Fiber or other coupling technique ? Why is the accuracy only +/- 5%, when the detector is calibrated against a NIST traceable reference detector ?

The following table lists Thorlabs' selection of photodiodes and photoconductive detectors. Item numbers in the same row contain the same detector element.

Photodetector Cross Reference
Wavelength Material Unmounted
150 - 550 nm GaP FGAP71 - SM05PD7A DET25K2 PDA25K2
200 - 1100 nm Si FDS010 - SM05PD2A
Si - - SM1PD2A - -
320 - 1000 nm Si - - - - PDA8A(/M)
320 - 1100 nm Si FD11A - SM05PD3A - PDF10A(/M)
Si - - - DET100A2 PDA100A2
340 - 1100 nm Si FDS10X10 - - - -
350 - 1100 nm Si FDS100
FDS100-CAL a
- SM05PD1A
Si FDS1010
FDS1010-CAL a
- -
400 - 1000 nm Si - - - - PDA015A(/M)
400 - 1100 nm Si FDS015 b - - - -
Si FDS025 b
FDS02 c
- - DET02AFC(/M)
400 - 1700 nm Si & InGaAs DSD2 - - - -
500 - 1700 nm InGaAs - - - DET10N2 -
750 - 1650 nm InGaAs - - - - PDA8GS
800 - 1700 nm InGaAs FGA015 - - - PDA015C(/M)
InGaAs FGA21
- SM05PD5A DET20C2 PDA20C(/M)
InGaAs FGA01 b
- - DET01CFC(/M) -
InGaAs FDGA05 b - - - PDA05CF2
InGaAs - - - DET08CFC(/M)
800 - 1800 nm Ge FDG03
- SM05PD6A DET30B2 PDA30B2
Ge FDG50 - - DET50B2 PDA50B2
Ge FDG05 - - - -
900 - 1700 nm InGaAs FGA10 - SM05PD4A DET10C2 PDA10CS2
900 - 2600 nm InGaAs FD05D - - - -
FD10D - - - -
- - - DET05D2
950 - 1650 nm InGaAs - - - - FPD310-FC-NIR
1.0 - 2.9 µm PbS - FDPS3X3 - - PDA30G(-EC)
1.0 - 5.8 µm InAsSb - - - - PDA10PT(-EC)
1.5 - 4.8 µm PbSe - FDPSE2X2 - - PDA20H(-EC)
2.0 - 5.4 µm HgCdTe (MCT) - - - - PDA10JT(-EC)
2.0 - 8.0 µm HgCdTe (MCT) VML8T0
VML8T4 d
- - - PDAVJ8
2.0 - 10.6 µm HgCdTe (MCT) VML10T0
VML10T4 d
- - - PDAVJ10
2.7 - 5.0 µm HgCdTe (MCT) VL5T0 - - - -
  • Calibrated Unmounted Photodiode
  • Unmounted TO-46 Can Photodiode
  • Unmounted TO-46 Can Photodiode with FC/PC Bulkhead
  • Photovoltaic Detector with Thermoelectric Cooler

Si Photodiodes with NIST Traceable Calibration

Two NIST traceable calibrated Si photodiodes are available from stock. Si photodiodes are sensitive across the visible and into the near infrared spectrum. The FDS100-CAL and FDS1010-CAL are both large area Si photodiodes and are packaged in a can and on a square ceramic substrate respectively. For detailed information about their specifications and to view responsivity, dark current, and capacitance graphs, please click on the info icons in the table below.

Thorlabs offers response-flattening filters that are designed to improve the response uniformity of these silicon photodiodes. Click here for more information.

Item # Info Wavelength Active
Capacitance Package Vbias,max Compatible
FDS100-CAL info 350 - 1100 nm 13 mm2 10 ns
@ 632 nm, 20 V
@ 900 nm, 20 V
1.0 nA
@ 20 V
24 pF
@ 20 V (Typ.)
TO-5 Can
25 V STO5S
FDS1010-CAL info 350 - 1100 nm 100 mm2 65 ns
@ 632 nm, 5 V
@ 970 nm, 5 V
600 nA
@ 5 V
375 pF
@ 5 V (Typ.)
0.45" x 0.52"
25 V Not Available
  • Typical Values; RL = 50 Ω. The photodiode will be slower at NIR wavelengths.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
FDS100-CAL Support Documentation
FDS100-CALCalibrated Si Photodiode, 350 - 1100 nm, 3.6 x 3.6 mm Active Area
FDS1010-CAL Support Documentation
FDS1010-CALCalibrated Si Photodiode, 350 - 1100 nm, 10 x 10 mm Active Area

Ge Photodiode with NIST Traceable Calibration

One NIST traceable calibrated Ge photodiode is available from stock. Ge photodiodes are sensitive in the near infrared spectrum from 800 - 1800 nm. The FDG03-CAL is AR Coated for 1300 to 1550 nm and is packaged in a can. For detailed information about its specifications and to view responsivity, dark current, and capacitance graphs, please click on the info icon in the table below.

Item # Info Wavelength Active
Capacitance Package Vbias,max Compatible
FDG03-CAL info 800 - 1800 nm 7.1 mm2 600 ns
@ 3 V
@ 1500 nm, 1 V
4.0 µA
@ 1 V
6 nF @ 1 V (Typ.)
4.5 nF @ 3 V (Typ.)
TO-5 Can
  • Typical Values; RL = 50 Ω.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
FDG03-CAL Support Documentation
FDG03-CALCalibrated Ge Photodiode, 800 - 1800 nm, Ø3.0 mm Active Area

InGaAs Photodiode with NIST Traceable Calibration

One NIST traceable calibrated InGaAs photodiode is available from stock. InGaAs photodiodes are sensitive in the near infrared spectrum from 800 to 1700 nm. The FGA21-CAL has a PIN structure that results in fast zero bias Rise / Fall times. For detailed information about its specifications and to view responsivity, dark current, and capacitance graphs, please click on the info icon in the table below.

Item # Info Wavelength Active Area Rise/Fall
Dark Current Capacitance Package Vbias,max Compatible
FGA21-CAL info 800 - 1700 nm 3.1 mm2 14 ns
@ 3 V
@ 1550 nm
50 nA @ 1 V
100 pF @ 3 V
TO-5 Can
  • Typical Values; RL = 50 Ω.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
FGA21-CAL Support Documentation
FGA21-CALCalibrated InGaAs Photodiode, 800 - 1700 nm, Ø2.0 mm Active Area
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