Operating Instruction; Operating Principle - THORLABS PDB48*C-AC series Operation Manual

3 Operating Instruction

Turn the power switch of the power supply to I. The green LED next to the DC input con-
·
nector indicates correct power supply.
· Connect the optical source(s) to the optical input(s). Please note that the PDB48xC-AC is
designed for FC/APC connectors!
MONITOR outputs can be used for convenient alignment of a coarse input power balance.
·
The maximum output voltage swing of the MONITOR outputs is 10V for high impedance
loads. Saturation of the MONITOR outputs will occur at optical input power greater than
1 mW.
· The RF output signal must not exceed the maximum RF OUTPUT power at 1 dB com-
pression (see Technical Data
For balanced operation illuminate both photodetectors simultaneously and use the
·
MONITOR outputs to fine-tune the optical power balance by observing voltage on a digital
voltmeter or other low-frequency measurement device.
After finishing measurements, turn power off.
·
Attention
The damage threshold of the photo diodes is 10 mW (PDB480C-AC) resp. 5 mW (PDB481C-
AC)! Exceeding this value will permanently destroy the detector!

3.1 Operating Principle

Thorlabs PDB48xC-AC Balanced Amplified Photodetectors consist of two well-matched, pig-
tailed photodiodes and an ultra-low noise, ultra-low distortion high-speed transimpedance amp-
lifier that generates an output voltage (RF OUTPUT) proportional to the difference between the
photo currents of the two photodiodes, i.e. the difference between the two optical input signals.
Additionally, the unit has two monitor outputs (MONITOR+ and MONITOR-) to observe the op-
tical input power level on each photodiode separately. Due to their increased cut-off frequency,
these outputs can also be used to measure low frequency modulated signals on each detector
separately. This allows a signal normalization up to 3 MHz.
The PDB48xC-AC is powered by an external linear power supply (±12 V, 250 mA - included)
via a PICO M8 power connector.
© 2019 Thorlabs
) to avoid saturation.
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3 Operating Instruction
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