THORLABS PDA50B2 User manual

PDA50B2
Ge Switchable Gain
Detector
User Guide

Ge 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
8.1. Waste Treatment is Your Own Responsibility ............... 12
8.2. Ecological Background................................................. 12
Chapter 9 Thorlabs Worldwide Contacts....................................... 13

Ge Switchable Gain Detector Chapter 1: Warning Symbol Definitions
Rev D, May 29, 2019 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

Ge Switchable Gain Detector Chapter 2: Description
Page 2 TTN135074-D02
Chapter 2 Description
The PDA50B2 is an amplified, switchable-gain, Germanium (Ge) detector
designed for detection of light signals ranging from 800 to 1800 nm. An eight-
position rotary switch allows the user to vary the gain in 10 dB steps. A buffered
output drives 50 Ωload impedances up to 5 V. The PDA50B2 housing includes a
removable threaded coupler (SM1T1) and retainerring (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.

Ge Switchable Gain Detector Chapter 3: Setup
Rev D, May 29, 2019 Page 3
Chapter 3 Setup
The detector can be set up in many different ways using our extensive line of
adapters. However, the detector should always be mounted and secured for best
operation.
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
PDA50B2.
3. Plug the power supply into a 50 to 60Hz, 100 V / 120 V / 230 V power
outlet.
4. Attach a 50 Ωcoax 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 Ωresistor (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 Ωterminator. The combined loads will equal 25 Ωwhich
could allow ~135 mA of output current. This will damage the output driver
of the PDA50B2.
5. Power the PDA50B2 on using the power switch located on the top side
of the unit.
Caution!
The PDA50B2 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.

Ge Switchable Gain Detector Chapter 4: Operation
Page 4 TTN135074-D02
Chapter 4 Operation
4.1. Theory of Operation
Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.
The PDA50B2 includes a Ge photodiode mated to a switchable gain
transimpedance amplifier and is 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.

Ge Switchable Gain Detector Chapter 4: Operation
Rev D, May 29, 2019 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 PDA50B2 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 PDA50B2 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 PDA50B2 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 are8 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.

Ge Switchable Gain Detector Chapter 5: Troubleshooting
Page 6 TTN135074-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.
Detector Output is skewed.
Check to make sure the detector is not saturated.
Refer to the Output Voltage spec. in the
Specifications table.
Install a 1" Lens Tube (SM1L10) to the thread
coulpler (SM1T1) to baffle any external light
sources to see if this improves the response.

Ge Switchable Gain Detector Chapter 6: Specifications
Rev D, May 29, 2019 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.
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
510 kHz
Bandwidth3
6.3 kHz
Noise (RMS)
220 μV
Noise (RMS)
220 μV
NEP (@ p)
1.76 x 10-10 W/Hz
NEP (@ p)
4.63 x 10-12 W/Hz
Offset
±15 mV (Typ.)
±20 mV (Max)
Offset
±15 mV (Typ.)
±20 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
270 kHz
Bandwidth3
2 kHz
Noise (RMS)
233 μV
Noise (RMS)
231 μV
NEP (@ p)
8.77 x 10-11 W/Hz
NEP (@ p)
4.83 x 10-11 W/Hz
Offset
±15 mV (Typ.)
±20 mV (Max)
Offset
±15 mV (Typ.)
±20 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
85 kHz
Bandwidth3
630 Hz
Noise (RMS)
223 μV
Noise (RMS)
247 μV
NEP (@ p)
1.95 x 10-11 W/Hz
NEP (@ p)
6.73 x 10-12 W/Hz
Offset
±15 mV (Typ.)
±20 mV (Max)
Offset:
±15 mV (Typ.)
±20 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
22 kHz
Bandwidth3
210 Hz
Noise (RMS)
230 μV
Noise (RMS)
333 μV
NEP (@ p)
6.41 x 10-12 W/Hz
NEP (@ p)
1.04 x 10-11 W/Hz
Offset
±15 mV (Typ.)
±20 mV (Max)
Offset
±15 mV (Typ.)
±20 mV (Max)
2
The PDA50B2 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.

Ge Switchable Gain Detector Chapter 6: Specifications
Page 8 TTN135074-D02
Electrical Specifications
Detector
-
Ge
Active Area
-
Ø5.0 mm (19.6 mm2)
Wavelength Range
λ
800 to 1800 nm
Peak Wavelength
λp
1550 nm (Typ.)
Peak Response
( λ p)
0.85 A/W (Typ.)
Amplifier GBP
-
25 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.

Ge Switchable Gain Detector Chapter 6: Specifications
Rev D, May 29, 2019 Page 9
6.1. Response Curve
800 1000 1200 1400 1600 1800
0.0
0.2
0.4
0.6
0.8
1.0
PDA50B2 Responsivity
Responsivity (A/W)
Wavelength (nm)

Ge Switchable Gain Detector Chapter 6: Specifications
Page 10 TTN135074-D02
6.2. Mechanical Drawing

Ge Switchable Gain Detector Chapter 7: Certificate of Conformance
Rev D, May 29, 2019 Page 11
Chapter 7 Certificate of Conformance

Ge Switchable Gain Detector Chapter 8: Regulatory
Page 12 TTN135074-D02
Chapter 8 Regulatory
As required by the WEEE (Waste Electrical and Electronic Equipment Directive)
of the European Community and the corresponding national laws, Thorlabs offers
all end users in the EC the possibility to return “end of life” units without incurring
disposal charges.
This offer is valid for Thorlabs electrical and electronic equipment:
Sold after August 13, 2005
Marked correspondingly with the crossed out
“wheelie bin” logo (see right)
Sold to a company or institute within the EC
Currently owned by a company or institute within the
EC
Still complete, not disassembled and not
contaminated
As the WEEE directive applies to self contained operational electrical and
electronic products, this end of life take back service does not refer to other
Thorlabs products, such as:
Pure OEM products, that means assemblies to be built into a unit by the
user (e.g. OEM laser driver cards)
Components
Mechanics and optics
Left over parts of units disassembled by the user (PCB’s, housings etc.).
If you wish to return a Thorlabs unit for waste recovery, please contact Thorlabs or
your nearest dealer for further information.
Waste Treatment is Your Own Responsibility
If you do not return an “end of life” unit to Thorlabs, you must hand it to a company
specialized in waste recovery. Do not dispose of the unit in a litter bin or at a public
waste disposal site.
Ecological Background
It is well known that WEEE pollutes the environment by releasing toxic products
during decomposition. The aim of the European RoHS directive is to reduce the
content of toxic substances in electronic products in the future.
The intent of the WEEE directive is to enforce the recycling of WEEE. A controlled
recycling of end of life products will thereby avoid negative impacts on the
environment.
Wheelie Bin Logo

Ge Switchable Gain Detector Chapter 9: Thorlabs Worldwide Contacts
Rev D, May 29, 2019 Page 13
Chapter 9 Thorlabs Worldwide Contacts
For technical support or sales inquiries, please visit us at
www.thorlabs.com/contact for our most up-to-date contact information.
USA, Canada, and South America
Thorlabs, Inc.
sal[email protected]
[email protected]
Europe
Thorlabs GmbH
[email protected]
France
Thorlabs SAS
[email protected]
Japan
Thorlabs Japan, Inc.
[email protected]
UK and Ireland
Thorlabs Ltd.
[email protected]
[email protected]
Scandinavia
Thorlabs Sweden AB
[email protected]
Brazil
Thorlabs Vendas de Fotônicos Ltda.
[email protected]
China
Thorlabs China
[email protected]

www.thorlabs.com