THORLABS DET01CFC User manual

DET01CFC(/M)
Fiber Input
InGaAs Biased Detector
User Guide

InGaAs Biased 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.ModesofOperation....................................................4
4.4.DarkCurrent...............................................................5
4.5.JunctionCapacitance..................................................6
4.6.BandwidthandResponse............................................6
4.7.TerminatingResistance..............................................7
4.8.ShuntResistance.........................................................7
4.9.SeriesResistance........................................................7
4.10.DamageThreshold......................................................7
4.11.BatteryReplacement..................................................8
Chapter 5Common Operating Circuits ............................................. 9
Chapter 6Troubleshooting...............................................................11
Chapter 7Specifications................................................................... 12
7.1.ResponseCurve........................................................13
7.2.MechanicalDrawing.................................................14
Chapter 8Certificate of Conformance............................................. 15
Chapter 9Regulatory ........................................................................16
Chapter 10Thorlabs Worldwide Contacts ........................................ 17

InGaAs Biased Detector Chapter 1: Warning Symbol Definitions
Rev G, April 17, 2017 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 Biased Detector Chapter 2: Description
Page 2 15830-D02
Chapter 2 Description
The DET01CFC is a ready-to-use, high-speed InGaAs photodetector for use with
FC/PC connectorized fiber optic cables in NIR optical systems. The unit comes
with an FC/PC bulkhead connector, detector, and 12 V bias battery enclosed in a
compact aluminum housing. The FC/PC connector provides easy coupling to
fiber-based light sources. The output uses an SMA jack to minimize size and
maximize frequency response. The maximum bandwidth is 1.2 GHz and the
detector will operate over the 800-1700 nm spectral range. A visible version, the
DET02AFC, is also available and operates in the 400-1100 nm spectral range.
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 Biased Detector Chapter 3: Setup
Rev G, April 17, 2017 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. Step 1 in the setup instructions below outline how to mount the
detector onto a post.
1. Unpack the optical head, install a Thorlabs TR-series ½" diameter post into
one of the #8-32 (M4 on /M version) tapped hole, located on the bottom and
side of the sensor, and mount into a PH-series post holder.
2. Attach a 50 SMA to Coax cable (i.e. CA28xx) to the output of the DET.
Select and install a terminating resistor to the remaining end of the cable
(BNC Side), and connect to a voltage measurement device. See Chapter 4,
page 7 to determine resistor values. Thorlabs sells a 50 terminator
(T4119) for best frequency performance and a variable terminator (VT2) for
output voltage flexibility. Note the input impedance of your measurement
device since this will act as a terminating resistor. A load resistor is not
necessary when using current measurement devices.
3. 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.
4. Apply a light source to the detector.

InGaAs Biased Detector Chapter 4: Operation
Page 4 15830-D02
Chapter 4 Operation
4.1. Theory of Operation
A junction photodiode is an intrinsic device, which 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, linear
device that exhibits high quantum efficiency based upon the application used in a
variety of different applications.
It is necessary to be able to determine correctly 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. 





Figure 1 Photodiode Model
4.2. Responsivity
The definition of photodiode responsivity is the ratio of generated photocurrent
(I
PD
) to the incident light power (P) at a given wavelength:
󰇛󰇜


4.3. Modes of Operation
The photodiode can operate in one of two modes: photoconductive (reverse bias)
or photovoltaic (zero-bias). Mode selection depends upon the applications speed
requirements and the amount of tolerable dark current (leakage current).

InGaAs Biased Detector Chapter 4: Operation
Rev G, April 17, 2017 Page 5
Photoconductive
In photoconductive mode a reverse external 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 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: The DET detectors are reverse
biased and cannot be operated under a forward bias.)
Note
The DET detectors are reverse biased and cannot be operated under
forward bias conditions.
Photovoltaic
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. When operating in
photovoltaic mode the amount of dark current is at a minimum setting.
4.4. Dark Current
When we apply bias voltage to a photodiode, produces a leakage current called
dark current. Photoconductive mode tends to generate a higher dark current that
varies directly with temperature. It infers that, dark current can approximately
double for every 10 °C increase in temperature, and shunt resistance can 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 photodiode material and the size of the active area also affect the dark
current present. 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.

InGaAs Biased Detector Chapter 4: Operation
Page 6 15830-D02
The table below gives some advantages to each common type of detector
material.
Material
Dark
Current Speed
Sensitivitya
(nm) Cost
Silicon (Si) Low High 400 – 1000 Low
Germanium (Ge) High Low 900 – 1600 Low
Gallium Phosphide (GaP) Low High 150 – 550 Med
Indium Gallium Arsenide
(InGaAs)
Low High 800 – 1800 Med
Extended Range: Indium
Gallium Arsenide (InGaAs)
High High 1200 – 2600 High
4.5. Junction Capacitance
Junction capacitance (CJ) is an important property of a photodiode as this can
have a profound impact on the bandwidth and the response of a photodiode. It
reaffirms that larger diode areas encompass a greater junction volume with
increased charge capacity. In a reverse bias application, the depletion width of
the junction increases, thus effectively reducing the junction capacitance and
increasing the response speed.
4.6. Bandwidth and Response
A load resistor will react with the photodetector junction capacitance to limit the
bandwidth. For best frequency response, a 50 terminator should be used in
conjunction with a 50 coaxial cable. The bandwidth (fBW) and the rise time
response (tr) can be approximated using the junction capacitance and the load
resistance (RLOAD):
 1
󰇛2󰇜
0.35

aApproximate values, actual wavelength values will vary from unit to unit.

InGaAs Biased Detector Chapter 4: Operation
Rev G, April 17, 2017 Page 7
4.7. Terminating Resistance
We use a load resistance convert the generated photocurrent into a voltage
(VOUT) for viewing on an oscilloscope:

Depending on the type of the photodiode, load resistance can affect the
response speed. For maximum bandwidth, we recommend using a 50 coaxial
cable with a 50 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, thus is
recommendable to keep the cable as short as possible.
4.8. 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 to thousands of Mand is dependent
on the photodiode material. For example, and InGaAs detector has a shunt
resistance in the order of 10 Mwhile a Ge detector is in the krange. This can
significantly affect the noise current on the photodiode. For most applications,
however, the high resistance produces little effect and most of the time ignored.
4.9. Series Resistance
Series resistance models the resistance of the semiconductor material, and we
ignore this low resistance. The series resistance arises from the contacts and the
wire bonds of the photodiode; this mainly determines the linearity of the
photodiode under zero bias conditions.
4.10. Damage Threshold
Exposure to an intense light source can easily damage a photodiode. One of the
main characteristics of a damaged photodiode is the presence of increased dark
current, along with burn spots on the detector active area. The damage threshold
may vary from photodiode to photodiode, as this is generally dependent on
material. Silicon devices tend to be more durable than InGaAs and can handle
higher energy levels.
The formula below calculates the energy of each pulse, using the average power
and the repetition rate. If the pulse width is given, the peak power can also be
determined. 󰇛󰇜󰇛󰇜∗󰇛󰇜
󰇛󰇜󰇛󰇜
󰇛󰇜

InGaAs Biased Detector Chapter 4: Operation
Page 8 15830-D02
4.11. Battery Replacement
Thorlabs delivers each DET with an A23 12 V battery
installed. This battery is readily available at most retail
stores, as well as through Thorlabs. The battery supplied
will deliver about 40 hours with a 1 mA load, roughly
equivalent to a continuous 1.5 mW light source at peak
wavelength. When not light is applied, the supply current
turns out to be very small and the battery hardly
degrades.
Locate the battery cap directly above the output BNC.
Unthread the cap and remove the battery. Install the new
battery into the cap, negative side in, and thread back
into the DET. Be careful not to cross thread the cap into
the housing.
CAUTION: The DET does not include a protection diode
to prevent damage if the installation of the battery is
backwards. The battery direction is located on the
housing.
Detector
Body
A23 Battery
Positive
Negative
Cap

InGaAs Biased Detector Chapter 5: Common Operating Circuits
Rev G, April 17, 2017 Page 9
Chapter 5 Common Operating Circuits
Figure 2 Basic DET Circuit
The DET Series Detectors are designed according the circuit depicted above.
The detector is reverse biased to produce a linear response with applied input
light. The generated photocurrent is based upon the incident light and
wavelength and can be viewed on the 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, which may contribute to a noisy output.
Figure 3 Amplified Detector
On/Off
Switch
Protection Diode Photodetector
VBAT
RC Filter External
Resistor
1 kΩ
Capacitor 0.1 µF
V Bias
BNC
GND
GND
Battery
Voltage
Regulator
5V
RLOAD
Photodetector
Transimpedance Amp
Out
Feedback
R
F
A
B
-V
BNC
GND
GND GND
R
LOAD

InGaAs Biased Detector Chapter 5: Common Operating Circuits
Page 10 15830-D02
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: We maintain the circuit at zero volts across the
photodiode, holding point A at the same potential as point B by the
operational amplifier. This eliminates the possibility of dark current.
Photoconductive mode: We reverse bias the photodiode; it improves 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:
󰇛3󰇜
4,
Where GBP is the amplifier product gain-bandwidth and CDis the sum
of the junction capacitance, amplifier capacitance, and feedback
capacitance.

InGaAs Biased Detector Chapter 6: Troubleshooting
Rev G, April 17, 2017 Page 11
Chapter 6 Troubleshooting
Problem Suggested Solutions
There is no signal response or
response is slower than
expected.
Verify that the battery is inserted and has sufficient
power (>9V)
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.
Connect the DET to an oscilloscope without a
terminating resistor installed. Most general purpose
oscilloscopes will have a 1 Minput impedance.
Point the detector toward a fluorescent light and
verify that a 60 Hz (50 Hz outside the US) signal
appears on the scope. If so the device should be
operating properly and the problem may be with the
light source or alignment.
There is an AC signal present
when the unit is turned off.
The detector has an AC path to ground even with
the switch in the OFF position. It is normal to see an
output response to an AC signal with the switch in
this state. However, because the detector is
unbiased, operation in this mode is not
recommended.
The output appears AC coupled
with long rise times and the
power switch ON.
This is usually an indication that the battery level is
low and needs to be changed. See Battery
Replacement Section for more details.
Skewed Rise and Fall Times Check to see if the battery voltage is 9V or greater.
Make sure you are not saturating the detector as this
can lead to permanent damage.

InGaAs Biased Detector Chapter 7: Specifications
Page 12 15830-D02
Chapter 7 Specifications
All measurements performed at 25 °C unless stated otherwise.
Electrical Specifications
Parameter Symbol Value
Detector - InGaAs PIN
Active Area Diameter - Ø0.12 mm
Wavelength Range 800 to 1700 nm
Peak Wavelength p 1550 nm
Peak Responsea( p) 0.95 A/W (Typ.)
Diode Capacitance (12V) CJ2.4 pF
Bandwidtha,b,c (-3 dB) - 1.2 GHz
Rise Timea,b,c @1310 nm - <1.0 ns
Fall Timea,b,c @1310 nm - <1.0 ns
NEP (λp) - 4.50 x 10-15 W/Hz1/2
Saturation Power (CW)b - 5.5 mW (1550 nm)
Damage Threshold - 70 mW
Bias Voltage VR12 V
Dark Currenta,d ID0.235 nA
Output Voltage VOUT 0 to 3.5 V (50 )e
0 to 10 V (Hi-Z)
General
Input FC/PC Fiber Connector
Output SMA (DC Coupled)
Package Size 2.21" x 1.40" x 0.80"
(56.1 mm x 35.6 mm x 20.3 mm)
Ball Lens Diameter 0.059" (1.50 mm)
Weight 0.18 kg
Storage Temp 0 to 40 °C
Operating Temp 0 to 40 °C
Battery A23, 12 VDC, 40 mAh
Replacement Battery Energizer No. A23
The Rise Time specification is theoretical and is derived from formulas found in
Section 4.6 above. Measured specifications are tested and guaranteed in our
aMeasured with specified bias voltage of 12V.
bFor a 50 ΩLoad
cLow battery voltage will result in slower rise times and decreased bandwidth.
dFor a 1 MΩLoad
eCalculated based upon peak responsivity and damage threshold.

InGaAs Biased Detector Chapter 7: Specifications
Rev G, April 17, 2017 Page 13
production units. Bandwidth is defined as the boundary at which the output of the
circuit is 3 dB below the nominal output.
7.1. Response Curve
0
0.2
0.4
0.6
0.8
1
1.2
800 900 1000 1100 1200 1300 1400 1500 1600 1700
Responsivity (A/W)
Wavelength (nm)
Spectral Response

InGaAs Biased Detector Chapter 7: Specifications
Page 14 15830-D02
7.2. Mechanical Drawing
Visit the web for a more detailed mechanical drawing.

InGaAs Biased Detector Chapter 8: Certificate of Conformance
Rev G, April 17, 2017 Page 15
Chapter 8 Certificate of Conformance

InGaAs Biased Detector Chapter 9: Regulatory
Page 16 15830-D02
Chapter 9 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.
9.1. 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.
9.2. 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

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Chapter  Thorlabs Worldwide Contacts
USA, Canada, and South America
Thorlabs, Inc.
56 Sparta Avenue
Newton, NJ 07860
USA
Tel: [phone]
Fax: [phone]
www.thorlabs.com
www.thorlabs.us (West Coast)
Email: [email protected]
Support: [email protected]
UK and Ireland
Thorlabs Ltd.
1 Saint Thomas Place
Ely CB7 4EX
Great Britain
Tel: [phone]
Fax: [phone]
www.thorlabs.com
Email: [email protected]
Support: [email protected]
Europe
Thorlabs GmbH
Hans-Böckler-Str. 6
85221 Dachau / Munich
Germany
Tel: [phone]
Fax: [phone]
www.thorlabs.de
Email: [email protected]
Scandinavia
Thorlabs Sweden AB
Bergfotsgatan 7
431 35 Mölndal
Sweden
Tel: [phone]
Fax: [phone]
www.thorlabs.com
Email: [email protected]
France
Thorlabs SAS
109, rue des Côtes
78600 Maisons-Laffitte
France
Tel: [phone]
Fax: [phone]
www.thorlabs.com
Email: [email protected]
Brazil
Thorlabs Vendas de Fotônicos Ltda.
Rua Riachuelo, 171
São Carlos, SP 13560-110
Brazil
Tel: [phone]
Fax: [phone]
www.thorlabs.com
Email: [email protected]
Japan
Thorlabs Japan, Inc.
3-6-3, Kitamachi,
Nerima-ku, Tokyo 179-0081
Japan
Tel: [phone]
Fax: [phone]
www.thorlabs.co.jp
Email: [email protected]
China
Thorlabs China
Room A101, No. 100, Lane 2891,
South Qilianshan Road
Putuo District
Shanghai 200331
China
Tel: [phone]
Fax: [phone]
www.thorlabschina.cn
Email: [email protected]

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