Photodiode
CAUTION
ELECTROSTATIC SENSITIVE DEVICE
DO NOT HANDLE EXCEPT
WITH AN ESD WRIST STRAP AT A
STATIC-FREE WORKSTATION
FDS100
Description
The Thorlabs FDS100 photodiode is ideal for measuring both pulsed and CW fiber light sources, by
converting the optical power to an electrical current. The detector is housed in a TO-5 package with an
anode, cathode, and case connection. The photodiode anode produces a current, which is a function of
the incident light power and the wavelength. The responsivity ℜ(λ), can be read from the responsivity
graph to estimate the amount of photocurrent to expect. This can be converted to a voltage by placing
a load resistor (RL) from the photodiode anode to the circuit ground. The output voltage is derived as:
=
×ℜ
×
The bandwidth, fBW, and the rise time response, tR, are determined from the diode capacitance, CJ,
and the load resistance, RL, as shown below. Placing a bias voltage from the photo diode cathode to
the circuit ground can lower the photo diode capacitance.
=
1
2
,
=
0.35
Specifications
FDS100
Wavelength Range
Active Area
Rise/Fall Time (RL=50 Ω, 20 V)
Bandwidth (RL=50 Ω, -3 dB, 20 V)
NEP (900 nm, 20 V)
Dark Current, Max (20 V)
Capacitance, Typical
Package
Sensor Material
Max Ratings
Damage Threshold, CW
Damage Threshold, 10 ns Pulse
Max Bias (Reverse) Voltage
Operating Temperature
Storage Temperature
Reverse Current
350 - 1100 nm
3.6 mm x 3.6 mm (13 mm2)
10 ns
35 MHz
1.2 x 10-14 W/Hz½
20 nA
40 pF @ 10 V
TO-5, 0.36" can
Si PIN
n/a
n/a
25 V
-40 to 100 °C
-55 to 125 °C
5 mA
February 10, 2012
0637-S01, Rev I
Recommended Circuit Diagram
Application of a reverse bias can greatly improve the response speed and linearity of the device. This is
due to increase in the depletion region width and, consequently, decrease in junction capacitance.
However, the dark current and noise will increase.
Noise Filter
+
Bias
Voltage
-
PD
R1 = 1 kΩ
+
RL
C1 = 0.1 μF
Vo
*
* Case ground for PD with a third lead.
Graphs
The responsivity of a photodiode is a measure of its sensitivity to light, and it is defined as the ratio of the
photocurrent IP to the incident light power P at a given wavelength:
=
In other words, it is a measure of the effectiveness of the conversion of light power into electrical current.
Responsivity varies from lot to lot and with the wavelength of the incident light, applied reverse bias, and
temperature. It increases slightly with applied reverse bias due to improved charge collection efficiency in the
photodiode. The change in temperature increases or decreases the width of the band gap and varies inversely
with the temperature.
February 10, 2012
0637-S01, Rev I
FDS Series Photodiode Responsivity
0.7
Responsivity (A/W)
0.6
0.5
FDS02
FDS010
FDS100
FDS1010
0.4
0.3
0.2
0.1
0.0
200
400
600
800
1200
1000
Wavelength (nm)
Drawings
2
Ø0.36"
(Ø9.14 mm)
0.08"
(2.03 mm)
Ø0.0.18"
(Ø0.46 mm)
3
Ø0.23"
Ø0.32"
(Ø5.84 mm) (Ø8.13 mm)
45°
2
Ø0.40"
(Ø10.16 mm)
1
3
Pin
1
2
3
1
Description
Anode
Cathode
Case
1.50"
(38.1 mm)
0.06"
(1.52 mm)
Ø0.20"
(Ø5.08 mm)
Bottom View
February 10, 2012
0637-S01, Rev I