THORLABS DET08CFC User manual

DET08CFC(/M)
Fiber Input
InGaAs Biased Detector
User Guide

DET08CFC(/M)
Page 1 Rev B, April 29, 2015
Table of Contents
Chapter 1 Warning Symbol Definitions ...........................................2
Chapter 2 Description........................................................................3
Chapter 3 Setup.................................................................................. 4
Chapter 4 Operation...........................................................................5
4.1. Theory of Operation....................................................... 5
4.2. Responsivity .................................................................. 5
4.3. Modes of Operation....................................................... 5
4.3.1. Photoconductive ..........................................................................6
4.3.2. Photovoltaic .................................................................................6
4.4. Dark Current.................................................................. 6
4.5. Junction Capacitance ..................................................... 7
4.6. Bandwidth and Response............................................... 7
4.7. Terminating Resistance.................................................. 8
4.8. Shunt Resistance............................................................ 8
4.9. Series Resistance ........................................................... 8
4.10. Damage Threshold......................................................... 8
4.11. Battery Replacement ..................................................... 9
Chapter 5 Common Operating Circuits ......................................... 10
Chapter 6 Specifications .................................................................12
6.1. Response Curve............................................................ 13
6.2. Typical Response ......................................................... 13
6.3. Mechanical Drawing.................................................... 14
Chapter 7 Troubleshooting .............................................................15
Chapter 8 Certificate of Conformance ...........................................16
Chapter 9 Regulatory.......................................................................17
Chapter 10 Thorlabs Worldwide Contacts....................................... 18

DET08CFC(/M) Chapter 1: Warning Symbol Definitions
TTN020103-D02 Page 2
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: Spinning Blades May Cause Harm

DET08CFC(/M)
Page 3 Rev B, April 29, 2015
Chapter 2 Description
The DET08CFC(/M) 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 5 GHz and
will operate over the spectral range of 800 - 1700 nm. A visible version, the
DET025AFC(/M), is also available for operation in the 400 - 1100 nm spectral
range.

DET08CFC(/M) Chapter 3: Setup
TTN020103-D02 Page 4
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 ∅1/2″post into
one of the #8-32 (M4 on the /M version) tapped holes, located on the
bottom and side of the housing, and mount into a PH-series post holder.
2. Attach a 50 ΩSMA to Coax cable (i.e., CA28xx) to the output of the
detector. Select and provide a terminating resistor to the remaining end
of the cable. See Chapter 4, page 5, to determine resistor values.
Thorlabs sells a 50 Ωterminator (T4119) for best frequency
performance and a variable terminator (VT1) 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
Note: For fastest response, terminate with 50 Ω.
3. Apply a light source to the detector.

DET08CFC(/M)
Page 5 Rev B, April 29, 2015
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 expected level of the output
current 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
(IPD) 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 speed
requirements of, and the amount of tolerable dark current (leakage current)
within, each individual application.
Photodetector
Diode Junction
Capacitance
Shunt
Resistance
Series
Resistance
External
Load
Resistance
I
PD
I
D
I
OUT

DET08CFC(/M) Chapter 4: Operation
TTN020103-D02 Page 6
4.3.1. 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 and a decrease in junction
capacitance: a linear response. Operating under these conditions tends to
produce a larger dark current, but this can be limited by selecting an appropriate
photodiode material. (Note: This detector is reverse biased and cannot be
operated under a forward bias.)
4.3.2. Photovoltaic
In photovoltaic mode, the photodiode is zero biased. The flow of current out of
the device is restricted causing a build up of voltage. 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 a bias voltage is applied to a photodiode, a leakage current, called dark
current, is produced. Photoconductive mode tends to generate a higher dark
current that varies directly with temperature. Dark current approximately doubles
every 10 °C increase in temperature, and shunt resistance doubles every 6 °C
rise. Applying a higher bias will decrease the junction capacitance but will also
increase the amount of dark current present.
The photodiode material, and the size of the active area, also affect the amount
of dark current present. Silicon devices generally produce low dark current
compared to germanium devices, which have high dark currents. The table on
the next page lists several photodiode materials and their relative dark currents,
speeds, sensitivities, and costs.

DET08CFC(/M)
Page 7 Rev B, April 29, 2015
The table below compares five common types of detector materials.
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 it can have
a profound impact on the photodiode’s bandwidth and response. 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 (CJ) and the
load resistance (RLOAD):
 =1
(2×
=0.35

aApproximate values, actual wavelength values will vary from unit to unit.

DET08CFC(/M) Chapter 4: Operation
TTN020103-D02 Page 8
4.7. Terminating Resistance
A load resistance is used to convert the generated photocurrent into a voltage
(VOUT) for viewing on an oscilloscope:
 =×
Depending on the type of photodiode, the 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, we recommend
the cable length to be as short as possible.
4.8. Shunt Resistance
Shunt resistance represents the resistance of the zero-biased photodiode
junction. An ideal photodiode has an infinite shunt resistance, but actual values
may range from the order of 10 to thousands of M, and is dependent on the
photodiode material. For example, and InGaAs detector has a shunt resistance
on 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 can be ignored.
4.9. Series Resistance
Series resistance models the resistance of the semiconductor material. This
resistance is typically very low and can be ignored. The series resistance arises
from the contacts and the wire bonds of the photodiode. It 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.  =∗
=
ℎ

DET08CFC(/M)
Page 9 Rev B, April 29, 2015
4.11. Battery Replacement
Thorlabs delivers each detector with an A23 12 V battery installed. This battery is
readily available at most retail stores, as well as through Thorlabs. The supplied
battery will deliver about 40 hours of operation with a 1 mA load, which is roughly
equivalent to a continuous 1.5 mW light source at peak wavelength. When no
light is applied, the supply current is 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 the cap back into the detector. Be careful not to cross thread the cap into
the housing. This detector does not include a protection diode to prevent
damage if the battery is installed backwards. The correct battery direction is also
indicated on the housing.

DET08CFC(/M) Chapter 5: Common Operating Circuits
TTN020103-D02 Page 10
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 its
wavelength and can be viewed on an oscilloscope by attaching a load resistance
on the output of the detector. The RC Filter removes all high frequency noise
from the input supply, which otherwise 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

DET08CFC(/M)
Page 11 Rev B, April 29, 2015
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 maintained 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: The photodiode is reverse biased 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:
(−3󰇜=
4×,
Where GBP is the amplifier product gain-bandwidth and CDis the sum
of the junction capacitance, amplifier capacitance, and feedback
capacitance.

DET08CFC(/M) Chapter 6: Specifications
TTN020103-D02 Page 12
Chapter 6 Specifications
All measurements are performed with a 50 load unless stated otherwise.
Electrical Specifications
Detector InGaAs PIN
Active Area Diameter Ø80 um
Wavelength Range 800 to 1700 nm
Peak Wavelength p 1550 nm
Peak Responsebℜ( p) 0.90 A/W (Typ.)
Diode Capacitance CJ0.3 pF
Bandwidth (-3 dB)b5 GHz
Rise Time (20/80%) @1538 nm <70 ps
Rise Time (20/80%) @1538 nm <70 ps
NEP (λp) @ 1550 nm 2 x 10-15 W/Hz1/2
Recommended Maximum Output (50 Ω)d1 V
After-Pulse Ringing <20% of Maximum
Bias Voltage VR12 V
Dark Currentb ID1.5 nA
Output Voltage VOUT 0 to 1 V (50 )c
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)
Ball Lens Clear Aperture ∅0.8 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
Bandwidth and Cutoff Frequency is a defined as boundary at which the output of
the circuit is 3 dB below the nominal output.
bMeasured with specified bias voltage of 12 V
cCalculated based upon peak responsivity and damage threshold.
dOutputs higher than this will degrade bandwidth.

DET08CFC(/M)
Page 13 Rev B, April 29, 2015
6.1. Response Curve
6.2. Typical Response
Figure 4 Tr= 55 ps, Tf = 52 ps@ 20/80%, Tp= 110 ps

DET08CFC(/M) Chapter 6: Specifications
TTN020103-D02 Page 14
6.3. Mechanical Drawing
1.40"
(35.6 mm) 0.95"
(24.1 mm)
2.23"
(56.6 mm)
0.80"
(20.3 mm)
0.95"
(25.1 mm)
0.40"
(10.2 mm)
0.35"
(8.9 mm)
0.40"
(10.2 mm)
0.40"
(10.2 mm)
1.50"
(38.1 mm)
0.40"
(10.2 mm)
Mounting Hole
8-32 (M4) x 0.25"
SMA (Female)
Output Connector
Battery Tube
(Use Only A23
12 V Batteries)
FC/PC Fiber
Input Connector
InGaAs Photodetector

DET08CFC(/M)
Page 15 Rev B, April 29, 2015
Chapter 7 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 (>9 V)
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 detector to an oscilloscope without a
terminating resistor installed. Most general
purpose oscilloscopes will have a 10 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 9 V or
greater. Make sure you are not saturating the
detector as this can lead to permanent damage.

DET08CFC(/M) Chapter 8: Certificate of Conformance
TTN020103-D02 Page 16
Chapter 8 Certificate of Conformance

DET08CFC(/M)
Page 17 Rev B, April 29, 2015
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

DET08CFC(/M) Chapter 10: Thorlabs Worldwide Contacts
TTN020103-D02 Page 18
Chapter 10 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
Cambridgeshire 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
Germany
Tel: [phone]
Fax: [phone]
www.thorlabs.de
Email: [email protected]
Scandinavia
Thorlabs Sweden AB
Mölndalsvägen 3
412 63 Göteborg
Sweden
Tel: [phone]
Fax: [phone]
www.thorlabs.com
Email: [e-mail]
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.
Higashi-Ikebukuro Q Building 1F
2-23-2, Higashi-Ikebukuro,
Toshima-ku, Tokyo 170-0013
Japan
Tel: [phone]
Fax: [phone]
www.thorlabs.jp
Email: [email protected]
China
Thorlabs China
Room A101, No. 100
Lane 2891, South Qilianshan Road
Putuo District
Shanghai
China
Tel: [phone]
Fax: [phone]
www.thorlabschina.cn
Email: [email protected]om

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