Electro-Optics Technology, Inc.
3340 Parkland Ct. Traverse City, MI 49686 USA
Traverse City, MI 46986 USA
EOT reserves the right to inspect photodetectors returned under warranty to assess if the problem was
caused by a manufacturer defect. If EOT determines the problem is not due to a manufacturer defect,
repairs will be done at the customer’s expense. EOT will always provide a written quote for repair prior
to performing repairs at the customer’s expense.
VIII. Glossary of Terms
Bandwidth: The range of frequencies from 0Hz (DC) to the frequency at which the amplitude 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 causes the photodiode to have a faster
response.
BNC Connector: Used to connect the customer’s coaxial cable.
Dark Current: When a termination is present, a dark current (nA range) will flow if the photodiode is
biased. Disconnecting the coaxial cable will prevent this current from flowing.
Decoupling Capacitor: Maintains bias voltage when fast pulses cause the battery voltage to reduce (this
would slow the response time of the photodiode); the capacitor allows the battery to recover to its initial
voltage. It also acts as a low-pass filter for external power supplies.
Noise Equivalent Power (NEP): A function of responsivity and dark current and is the minimum
optical power needed for an output signal to noise ratio of 1. Dark current is the current that flows
through a reverse biased photodiode even when light is not present, and is typically on the order of nA.
Shot noise (Ishot) is a source of noise generated in part by dark current; in the case of reversed biased
diodes it is the dominant contributor. NEP is calculated from shot noise and responsivity. For example,
for an ET-2040: dark current <20nA, responsivity @ 830nm = 0.5 A/W:
q = charge on an electron
Photodiode: Converts photons into a photocurrent.
Resistor: Part of the low-pass filter at the photodiode cathode.
Responsivity: In amps per watt (A/W), responsivity is the current output of the photodiode for a given
input power, and is determined by the diode structure. Responsivity varies with wavelength and diode
material.
Rise Time/Fall Time: Rise Time is the time taken by a signal to change from a specified low value to a
specified high value. Fall Time is the time taken for the amplitude of a pulse to decrease from a
