MKS Ophir FPD-IG-175 User manual

www.ophiropt.com/photonics
Fasr Photodiode Detectors
Fast Photodiode Detectors
FPD-IG-175, FPD-UV-3000, FPD-VIS-300
Ophir Optronics Solutions Ltd.
Temporal Sensors
Temporal Sensors
User Manual

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 2
Ophir Fast Photodiode Detector User’s Manual
Thank you for purchasing your Fast Photodiode Detector from Ophir. This user’s manual will help answer any
questions you may have regarding the safe use and optimal operation of your Fast Photodiode Detector.
Table of Contents
I. Fast Photodiode Detector Overview................................................................................................................. 2
II. Operation of your Ophir Fast Photodiode Detector.......................................................................................... 3
III. Batteries............................................................................................................................................................ 3
IV. Accessories....................................................................................................................................................... 4
V. Troubleshooting................................................................................................................................................ 4
VI. Specifications: Fast Photodiode Detectors ....................................................................................................... 6
VII. Drawings: Fast Photodiode Detectors .............................................................................................................. 7
VIII. Schematic: Fast Photodiode Detectors............................................................................................................. 8
IX. Glossary of Terms ............................................................................................................................................ 8
I. Fast Photodiode Detector Overview
Ophir’s Fast Photodiode Detectors contain PIN photodiodes that utilize the photovoltaic effect to
convert optical power into an electrical current for measurement. Internal circuitry provides a reverse
bias voltage to improve the photodiode’s response time. For optimal performance, the output
should be connected to a 50Ω load resistance. Figure 1 below identifies the main elements of your
Fast Photodiode Detector.
Figure 1: Ophir Fast Photodiode Detector
When terminated into the 50Ω input of an oscilloscope, the pulse width of a laser can be measured. When
terminated into a spectrum analyzer, the frequency response of a laser can be measured.

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 3
II. Operation of your Ophir Fast Photodiode Detector
A. Caution: Eye safety precautions must be followed with any equipment used in the vicinity of laser
beams. Laser beams may reflect from the surface of the detector or the optical mount and caution
must be exercised.
B. Mount the detector to an optical stand using the mounting holes on the bottom of the detector housing.
Each detector is provided with an 8-32 threaded nylon standoff. If the detector is mounted to a metal
post, it is recommended to insert the standoff between the detector and the post in order to minimize
the potential for electrical noise pickup.
C. Adjust the voltage scale of the oscilloscope to 100mV/division before connecting the detector. On
models with >3V bias supply, the signal may be large enough to damage the oscilloscope if this is
not done.
D. Connect the detector to the oscilloscope using a 50Ω coaxial cable that is one meter or less in length.
E. Use the 50Ω impedance input of the oscilloscope or other measurement instrument. If the
oscilloscope does not have a 50Ω input, connect a 50Ω terminator between the coax cable and
the oscilloscope’s high impedance input.
Note: Current will be drawn from the batteries whenever a load is present at the output. In
order to avoid draining the batteries, the output connection should be disconnected
whenever the product is not in use.
F. Verify that the laser power density is below the maximum recommended signal level and place
the detector in the laser beam. However, it is not necessary for the detector to be located directly
in the laser beam to measure properly. If the laser beam is too powerful and it saturates the
detector, the beam can be scattered from a white surface and the detector can be placed at a
distance from the beam to look at a small fraction of the beam intensity. The distance from the
scattering surface and the detector can be varied to get a good but not saturated signal. If the
intensity is still too high, or it is not convenient to measure scattered light, filters are available to
lower the laser intensity. See the Accessories section below.
III. Batteries
Batteries will typically operate for several years, but operation with CW or high rep rate lasers can drain the
batteries much faster. Leaving the detector output connected to a load for long periods of time can also
drain the batteries. It is recommended to disconnect the output whenever the detector will not be in use for
long periods of time.
As the batteries become depleted, the bias voltage on the photodiode will decrease. This will increase the
rise and falls times of the detector and also reduce its saturation level. The ability of the battery to supply
current quickly will also be reduced which is manifested as saturation effects in the output signal.
The batteries can be accessed for checking their voltage and replacement by removing the top plate of the
housing. If necessary, replace with type CR2430 lithium cells. Check the specifications below for the
number of batteries required for each model. Install batteries with positive side down.

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 4
IV. Accessories
The following types of accessories are available for use with Ophir Fast Photodiode Detectors:
1. Fiber optic cable connectors
2. Adapters for attachment to IS6 integrating spheres
3. ND filters for attenuating the laser signal level
Fiber Adapters
SC type
7Z08227
ST type
7Z08226
FC type
7Z08229
SMA type
1G01236A
ND Attenuators
ND1 nom. X10 attenuator
7Z08200
ND2 nom. X50 attenuator
7Z08201
IS6 Integrating Sphere
Adapter
For FPD detectors
7Z08350
V. Troubleshooting
A. No signal is seen the first time the detector is used.
1. Be certain that the signal is not too high for the scale set on the oscilloscope.
2. Is the wavelength of the laser within the spectral range of the detector?
3. Is the coaxial signal cable terminated into a 50Ω connection?
4. Try moving the detector within the laser beam. The detector’s small active area may make
alignment somewhat difficult.
5. Is the light level (see sensitivity spec on the data sheet) incident on the detector sufficient to
generate a measurable signal?
SC fiber adapter ST fiber adapter FC fiber adapter SMA fiber adapter
ND Attenuators IS6 Integrating
Sphere Adapter

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 5
B. A signal has been detected previously obtained, but is currently lost.
1. Try steps listed under A.
2. Inspect the active area of the photodiode for any signs of damage.
3. Try a higher input termination on the oscilloscope, but remember to return to 50Ω if this does not
work.
4. Test the power supply:
a. Units with internal batteries will typically operate for several years, but operation with CW
or high rep rate lasers can drain the batteries much faster. If a load is present at the output,
current will be drawn from the batteries, so disconnect the BNC when not in use.
Remove top cover to replace the 3V lithium cells with Duracell Model DL2430, positive side
down.
b. Units with an external power supply should at least receive the voltage that is printed on the
plug.
5. You can terminate the detector in 1MΩ input of an oscilloscope to obtain a higher output
voltage signal but this will decrease the detector’s bandwidth by a factor of 5x105.
C. Increasing the power incident on the detector does not result in a higher voltage signal on
the oscilloscope:
1. The detector is probably saturated. You should lower the power incident on the detector
to a level below the saturation point.
2. Check that the photodiode bias voltage is correct. Check the power supply voltage is
correct and connected or check the battery voltage.
D. The measured pulse shape is not as expected. The rise and fall times are too long or the
area around the peak is distorted and/or attenuated:
1. Check that the photodiode bias voltage is correct. Check the power supply voltage is
correct and connected or check the battery voltage.

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 6
VI. Specifications: Fast Photodiode Detectors
Model (a)
FPD-UV-3000
FPD-VIS-300
FPD-IG-175
Detector Type
UV-Si
Si
InGaAs
Rise Time/Fall Time nsec
3
<0.3
<0.175
Spectral Range nm (see graph below)
193-1100
320-1100
900-1700
Active Area Diameter mm
2.55
0.4
0.1
Detector Area mm2
5.11
0.13
0.0079
Wavelength of Peak Sensitivity nm
890
850
1600
Responsivity at Peak Wavelength A/W
0.58
0.5
1.1
Responsivity (Irradiance) at Peak
Wavelength V/(W/cm2)
1.5
31 x 10-3
4.3 x 10-3
Bias Voltage VDC
24
9
6
Bias Voltage Source
External
Batteries
Batteries
Battery Type
NA
CR2430 x3
CR2430 x2
Bandwidth
>118 MHz
>1.2 GHz
>2 GHz
Dark Current nA
<10
<0.1
<2
Noise Equivalent Power(b) pW/√Hz
<0.10
<0.01
<0.03
Maximum Average Power Input (b), (c) mW
15
25
10
Mounting (Tapped Holes)
8-32 & M4
8-32 & M4
8-32 & M4
Output Connector
BNC
BNC
BNC
Accessory Threads
M20x1
M20x1
M20x1
Version
Part Number
7Z02506
7Z02507
7Z02509
Notes: (a) All specs are with 50 load
Notes: (b) At wavelength of peak sensitivity
Notes: (c) Maximum peak power is twice the
average power for 10 nsec pulses
0.0
0.2
0.4
0.6
0.8
1.0
1.2
200 400 600 800 1000 1200 1400 1600 1800
Responsivity [A/W]
Wavelength [nm]
Spectral Response
FPD-VIS-300
FPD-UV-3000
FPD-IG-175

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 7
VII. Drawings: Fast Photodiode Detectors

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 8
VIII. Schematic: Fast Photodiode Detectors
IX. Glossary of Terms
Bandwidth: The range of frequencies from 0 Hz (DC) to the frequency at which the responsivity
decreases by 3dB. Bandwidth and rise time can be approximately related by the equation:
Bandwidth ≈ 0.35/rise time for a Gaussian pulse input.
Bias Voltage: The photodiode’s junction capacitance can be modified by applying a reverse voltage. The
bias voltage reduces the junction capacitance, which improves the photodiode’s temporal response. The
bias voltage also induces a dark current. When a photodiode is used with reverse bias, the shot noise of the
dark current is usually the dominant contributor to the NEP.
Dark Current (Idark): When a photodiode is connected in a circuit and operated in reverse bias mode, a
small DC current (typically nanoamps) will flow, even without the presence of an optical signal.
Disconnecting the coaxial cable will prevent this current from flowing. If operated without a reverse bias
(photovoltaic mode) the dark current will be comprised of thermally generated noise without any DC
component. This thermal noise will typically be orders of magnitude lower than the shot noise of the dark
current in the same device when it is reverse biased.
Decoupling Capacitor: A capacitor is connected in parallel with the bias voltage source. Its purpose is
twofold: 1) It maintains the bias voltage when fast signal pulses would otherwise cause the battery voltage
to droop (this would slow the response time of the photodiode) and 2) It also acts as a low-pass filter for
external power supplies.

FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual 9
Noise Equivalent Power (NEP): NEP refers to the amount of optical input power that would generate an
electric signal that is equal in magnitude to the electrical noise (in the dark). It is a function of the device
responsivity and the dark current. Shot noise (Ishot) is a source of noise generated by current; in the case
of reversed biased diodes operating at high speeds and low signal levels, it is the dominant contributor to
the total noise. NEP can be calculated from the shot noise and responsivity. For example, for the FPD-
UV-3000 with a dark current of <10nA and responsivity of 0.58 A/W at 890 nm, the shot noise will be:
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    at 890 nm
q = electron charge =   
Photodiode: A semiconductor device that converts photons into an electrical current.
Responsivity: In amps per watt (A/W), responsivity is the current output of the photodiode per input
power, and is determined by the diode structure. Responsivity varies with wavelength and diode
material.
Responsivity (Irradiance): In V per W/cm2is the voltage output as a function of the light input
irradiance. This is equal to the responsivity in units of A/W multiplied by the photodiode sensitive area
and the effective impedance load seen by the photodiode.
Rise Time & Fall Time: Rise Time is the time required by a signal to change from a specified low value
to a specified high value (typically 10% to 90%). Fall Time is the time taken for the amplitude of a pulse
to decrease from the specified high value to the specified low value. In photodiodes, the junction
capacitance is a major factor contributing to the rise time and fall times. Reverse biasing of the
photodiode is a method used to decrease the junction capacitance and improve the rise and fall times.
FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual
18 June 2020
Rev 1.2-2
For the latest version, please visit our website: www.ophiropt.com/photonics.