THORLABS PDA20CS2 User manual

PDA20CS2
InGaAs Switchable Gain
Detector
User Guide

InGaAs Switchable Gain Detector
Table of Contents
Chapter 1 Warning Symbol Definitions ..............................1
Chapter 2 Description...........................................................2
Chapter 3 Setup.....................................................................3
Chapter 4 Operation..............................................................4
4.1. Theory of Operation..........................................4
4.2. Responsivity .....................................................4
4.3. Dark Current.....................................................4
4.4. Bandwidth and Response ..................................5
4.5. Terminating Resistance.....................................5
4.6. Gain Adjustment...............................................5
Chapter 5 Troubleshooting..................................................6
Chapter 6 Specifications......................................................7
6.1. Response Curve.................................................9
6.2. Mechanical Drawing .......................................10
Chapter 7 Certificate of Conformance ..............................11
Chapter 8 Regulatory..........................................................12
Chapter 9 Thorlabs Worldwide Contacts..........................13

InGaAs Switchable Gain Detector Chapter 1: Warning Symbol Definitions
Rev D, April 21, 2020 Page 1
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your
device.
Symbol
Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or Chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution: Risk of Electric Shock
Caution: Hot Surface
Caution: Risk of Danger
Warning: Laser Radiation
Caution: ESD Sensitive Components

InGaAs Switchable Gain Detector Chapter 2: Description
Page 2 TTN135000-D02
Chapter 2 Description
The PDA20CS2 is an amplified, switchable-gain, Indium Gallium Arsenide
(InGaAs) detector designed for detection of light signals ranging from 800 to
1700 nm. An eight-position rotary switch allows the user to vary the gain in 10 dB
steps. A buffered output drives 50 Ω load impedances up to 5 V. The PDA20CS2
housing includes a removable threaded coupler (SM1T1) and retainer ring
(SM1RR) that is compatible with any number of Thorlabs 1” threaded
accessories. This allows convenient mounting of external optics, light filters,
apertures, as well as providing an easy mounting mechanism using Thorlabs’
cage assembly accessories.
ESD Caution
The components inside this instrument are ESD sensitive. Take all
appropriate precautions to discharge personnel and equipment before
making any electrical connections to the unit.

InGaAs Switchable Gain Detector Chapter 3: Setup
Rev D, April 21, 2020 Page 3
Chapter 3 Setup
The detector can be set up in many different ways using our extensive line of
adapters. For best operation, the detector should be mounted and secured.
1. Unpack the optical head, install either an imperial or metric optical post
into one of the mounting holes located on the bottom and side of the
sensor, and mount using a post holder. Note that these detectors
feature tapped holes that accept both 8-32 and M4 threads, so using
either imperial or metric TR posts is possible.
2. Connect the power supply 3-pin plug into the power receptacle on the
PDA20CS2.
3. Plug the power supply into a 50 to 60Hz, 100 V / 120 V / 230 V power
outlet.
4. Attach a 50 Ω coax cable (i.e. RG-58U) to the output of the PDA. When
running cable lengths longer than 12" we recommend terminating the
opposite end of the coax with a 50 Ω resistor (Thorlabs p/n T4119) for
maximum performance. Connect the remaining end to a measurement
device such as an oscilloscope or high speed DAQ card. Caution: Many
high speed oscilloscopes have input impedances of 50 Ω. In this case,
do not install a 50 Ω terminator. The combined loads will equal 25 Ω
which could allow ~135 mA of output current. This will damage the
output driver of the PDA20CS2.
5. Power the PDA20CS2 on using the power switch located on the top
side of the unit.
Caution!
The PDA20CS2 was designed to allow maximum accessibility to the
photodetector by having the active area surface of the diode flush with the
outside of the PDA housing. When using fiber adapters, make sure that the fiber
ferrule does not crash into the detector. Failure to do so may cause damage to
the diode and/or the fiber.
6. Install any desired filters, optics, adapters, or fiber adapters to the input
aperture.
7. During alignment, take appropriate precautions, such as using reduced
radiation power, or other precautions, and use proper eye and/or skin
protection as recommended by the radiation source manufacturer.
8. Apply a light source to the detector. Adjust the gain to the desired
setting.

InGaAs Switchable Gain Detector Chapter 4: Operation
Page 4 TTN135000-D02
Chapter 4 Operation
4.1. Theory of Operation
Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.
The PDA20CS2 includes a reverse-biased PIN photo diode, mated to a
switchable gain transimpedance amplifier, and packaged in a rugged housing.
4.2. Responsivity
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:
󰇛󰇜

4.3. Dark Current
Dark current is leakage current which flows when a bias voltage is applied to a
photodiode. The PDA with Transimpedance Amplifier does control the dark
current flowing out. Looking at the figure above, it can be noted that Point B is
held at ground and the amplifier will try to hold point A to “Virtual Ground”. This
minimizes the effects of dark current present in the system.
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. Please note that sensitivity values in the table are typical values;
Thorlabs offers photodetectors with sensitivity ranges that vary from those shown
below.

InGaAs Switchable Gain Detector Chapter 4: Operation
Rev D, April 21, 2020 Page 5
Material
Dark Current
Speed
Sensitivity1
Cost
Silicon (Si)
Low
High
400 - 1000 nm
Low
Germanium (Ge)
High
Low
900 - 1600 nm
Low
Gallium Phosphide (GaP)
Low
High
150 - 550 nm
Med
Indium Gallium Arsenide
(InGaAs)
Low
High
800 - 1800 nm
Med
Extended Range: Indium
Gallium Arsenide (InGaAs)
High
High
1200 - 2600 nm
High
4.4. Bandwidth and Response
For the PDA detectors, the gain of the detector is dependent on the feedback
element (Rf). The bandwidth of the detector can be calculated using the
following:
󰇛󰇜

Where GBP is the amplifier gain bandwidth product and CDis the sum of the
photodiode junction capacitance and the amplifier capacitance.
4.5. Terminating Resistance
The maximum output of the PDA20CS2 is 10 V for high impedance loads (i.e.
RLoad > 5 kΩ) and 5 V for 50 Ω loads. Adjust the gain so that the measured signal
level out of the PDA20CS2 is below 10 V (5 V with a 50 Ω load) to avoid
saturation.
For low terminating resistors, <5 kΩ or 1% error, an additional factor needs to be
considered. The output of the PDA includes a 50 Ω series resistor (Rs). The
output load creates a voltage divider with the 50 Ω series resistor as follows:
 

 
󰇛󰇜󰇛󰇜
Note that we already include the scale factor in our specification for the gain at
50 Ω. Refer to the table in Chapter 6 for additional performance specifications.
4.6. Gain Adjustment
The PDA20CS2 includes a low noise, low offset, high gain transimpedance
amplifier that allows gain adjustment over a 70 dB range. The gain is adjusted by
rotating the gain control knob, located on the top side of the unit. There are 8
gain positions incremented in 10 dB steps. It is important to note that the
bandwidth will decrease as the gain increases. See the specifications table on
page 7 to choose the best gain verse bandwidth for a given input signal.
1
Approximate values; actual wavelength values will vary.

InGaAs Switchable Gain Detector Chapter 5: Troubleshooting
Page 6 TTN135000-D02
Chapter 5 Troubleshooting
Problem
Suggested Solutions
There is no signal response.
Verify that the power is switched on and all
connections are secure.
Verify the proper terminating resistor is installed if
using a Voltage measurement device.
Verify that the optical signal wavelength is within
the specified wavelength range.
Verify that the optical signal is illuminating the
detector active area.
Output voltage will not
increase or detector output is
skewed.
Check to make sure the detector is not saturated.
Refer to the Output Voltage spec in Chapter 6.
Install a 1" Lens Tube (SM1L10) to the thread
coulpler (SM1T1) to baffle any external light
sources to see if this improves the response.

InGaAs Switchable Gain Detector Chapter 6: Specifications
Rev D, April 21, 2020 Page 7
Chapter 6 Specifications
All performance specifications are typical, performed at 25 °C ambient temperature,
and assume a 50 Ω load, unless stated otherwise.
2
The PDA20CS2 has a 50 Ω series terminator resistor (i.e. in series with amplifier output). This
forms a voltage divider with any load impedance (e.g. 50 Ω load divides signal in half).
3
Tested at 1550 nm wavelength.
Performance Specifications2
0 dB Setting
40 dB Setting
Gain (Hi-Z)
1.51 x 103V/A ±2%
Gain (Hi-Z)
1.51 x 105V/A ±2%
Gain(50 Ω)
0.75 x 103V/A ±2%
Gain(50 Ω)
0.75 x 105V/A ±2%
Bandwidth3
11 MHz
Bandwidth3
90 kHz
Noise (RMS)
286 μV
Noise (RMS)
240 μV
NEP
6.1 x 10-11 W/Hz
NEP
1.95 x 10-12 W/Hz
Offset
±8 mV (Typ.)
±12 mV (Max)
Offset
±8 mV (Typ.)
±12 mV (Max)
10 dB Setting
50 dB Setting
Gain (Hi-Z)
4.75 x 103V/A ±2%
Gain (Hi-Z)
4.75 x 105V/A ±2%
Gain(50 Ω)
2.38 x 103V/A ±2%
Gain(50 Ω)
2.38 x 105V/A ±2%
Bandwidth3
1.5 MHz
Bandwidth3
28 kHz
Noise (RMS)
201 μV
Noise (RMS)
260 μV
NEP
5.7 x 10-12 W/Hz
NEP
2.24 x 10-12 W/Hz
Offset
±8 mV (Typ.)
±12 mV (Max)
Offset
±8 mV (Typ.)
±12 mV (Max)
20 dB Setting
60 dB Setting
Gain (Hi-Z)
1.5 x 104V/A ±2%
Gain (Hi-Z)
1.5 x 106V/A ±5%
Gain(50 Ω)
0.75 x 104V/A ±2%
Gain(50 Ω)
0.75 x 106V/A ±5%
Bandwidth3
1 MHz
Bandwidth3
9 kHz
Noise (RMS)
236 μV
Noise (RMS)
300 μV
NEP
2.93 x 10-12 W/Hz
NEP
2.25 x 10-12 W/Hz
Offset
±8 mV (Typ.)
±12 mV (Max)
Offset:
±8 mV (Typ.)
±12 mV (Max)
30 dB Setting
70 dB Setting
Gain (Hi-Z)
4.75 x 104V/A ±2%
Gain (Hi-Z)
4.75 x 106V/A ±5%
Gain (50 Ω)
2.38 x 104V/A ±2%
Gain(50 Ω)
2.38 x 106V/A ±5%
Bandwidth3
260 kHz
Bandwidth3
3 kHz
Noise (RMS)
234 μV
Noise (RMS)
396 μV
NEP
2.19 x 10-12 W/Hz
NEP
2.28 x 10-12 W/Hz
Offset
±8 mV (Typ.)
±12 mV (Max)
Offset
±8 mV (Typ.)
±12 mV (Max)

InGaAs Switchable Gain Detector Chapter 6: Specifications
Page 8 TTN135000-D02
Electrical Specifications
Detector
-
InGaAs
Active Area
-
Ø2.0 mm (3.14 mm2)
Wavelength Range
λ
800 to 1700 nm
Peak Wavelength
λp
1590 nm (Typ.)
Peak Response
( λ p)
1.04 A/W (Typ.)
Amplifier GBP
-
600 MHz
Output Impedance
-
50 Ω
Max Ouput Current
IOUT
100 mA
Load Impedance
-
50 Ωto Hi-Z
Gain Adjustment Range
-
0 dB to 70 dB
Gain Steps
-
8 x 10 dB Steps
Output Voltage
VOUT
0 to 5 V (50 Ω)
0 to 10 V (Hi-Z)
General
On/Off Switch
Slide
Gain Switch
8 Position Rotary
Output
BNC (DC Coupled)
Package Size
2.79" x 2.07" x 0.89"
(70.9 mm x 52.5 mm x 22.5 mm)
PD Surface Depth4
0.09" (2.2 mm)
Weight, Detector Only
0.10 kg
Accessories
SM1T1 Coupler
SM1RR Retainer Ring
Operating Temp
10 to 40 °C
Storage Temp
-20 to 70 °C
AC Power Supply
AC –DC Converter
Input Power5
6 W
100 V / 120 V / 230 V, 50 –60 Hz
4
Measured from the active area to the start of the threads on the housing body. The detector
active area surface is flush with the front of the housing body.
5
Although the power supply is rated for 6 W, the detector’s actual usage is <5 W over the full
operating range.