User`s guide

Optical Interface Theory of Operation
The OE-2 consists of a high-performance optical-to-electrical converter followed by wide-bandwidth signal
processing devices. Dual-channel models include two identical signal paths. The block diagram below
shows the structure of a single-channel OE-2.
The optical input signal is converted to an electrical current using a low-noise, temperature-stabilized
photoreceiver.
The electrical signal is amplified by a wideband transimpedance amplifier (TIA) that is integrated with the
photoreceiver.
Because optical signals may have high levels of wideband noise, they are often filtered to improve the
signal-to-noise ratio. Communications standards require a fourth-order Bessel-Thomson low-pass filter
characteristic with a cut-off frequency of 75% of the data rate. Each channel of the OE-2 has four
filters—for different communications protocols—selectable by electronic switches. In addition, a fifth
setting bypasses the filters for full-bandwidth operation.
Filter settings can be selected independently for each channel with a front panel control or through the
GPIB interface.
A bank of wideband electronic amplifiers follows the filters. These amplifiers, also electronically
switched, amplify the electrical signal by 10 dB, 20 dB, 30 dB, or 40 dB. The amplifier setting can be
selected independently for each channel either with a front panel control or through the GPIB interface.
The average current in the photoreceiver is measured to determine the average optical power of the
input signal. This average power value is available only through the GPIB interface.
The signal gain in every filter path and every amplifier path in the OE-2 is measured and stored locally
in the OE-2. These calibration values are used by Wavecrest
GigaView software to display accurate
optical signal power levels.
All OE-2 functions are controlled by a central processor. The processor also handles communications with
the GPIB interface port.
Section 4 - GigaView © WAVECREST Corporation 2005
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