THORLABS PDB440A, Руководство по эксплуатации, Страница: 8 / 29

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PDB440x and PDB450x detectors
The PDB440x and PDB450x detectors is powered by an external linear power supply ( ± 12 V,
250 mA - included) via a PICO M8 power connector.
Below is a functional block diagram of the PDB440x and PDB450x detectors Balanced Ampli-
fied Photodetectors:
3.2 Optical Inputs
For all models the fiber inputs are coupled to the photodiodes using two removable FC adap-
ters. These FC receptacles accommodate either single-mode or multi-mode fiber with FC/PC or
FC/APC connectors.
Attention
Be very careful when connecting the fibers to the optical inputs! The photodiodes are mounted
in such that the gap between the protective diode glass and the fiber tip is as small as possible.
For this reason, be very careful when tightening the fiber connector, in order to avoid damages
to the glass window that protects the photodiode.
For all PDB4xxC models the FC adapters are aligned for Corning SMF28
TM
single mode fibers
with PC connectors. When using FC/APC connectors, minimal alignment errors may occur due
to the small detector size, this may result in reduced output signal. In this case, the FC recept-
acle can be rotated from its original position in steps of 90° to check for an improved alignment.
For this process use optical input power below the saturation level while observing the RF
OUTPUT voltage on a digital voltmeter or other low-frequency measurement device. If you
have an AC-coupled version, use either MONITOR output (CW signal) or RF OUTPUT (modu-
lated optical signal) with a connected oscilloscope for measurement.
In general, a multi-mode fiber can be used. However, please be aware that the light beam spot
diameter exceeds the detector’s active area which results in a reduced output signal.
For free-space beam applications it is recommended to remove the FC adapter (receptacle) to
have direct access to the photodiodes as shown below on a drawing of the PDB410C. This is
identical to PDB440 and PDB450. Please be aware the INPUT+ and INPUT- are reversed in
PDB440x versus PDB450x.