User`s guide

How the OE-2 Works
The OE-2 consists of a high-performance optical-to-electrical converter followed by wide-
bandwidth, signal processing devices. Dual-channel models incorporate two identical channels.
The block diagram below shows the structure of one OE-2 channel.
Figure 2 – Block diagram of an OE-2 channel
The optical input signal is converted to an electrical current using a low-noise, temperature-
stabilized photo receiver. The electrical signal is then amplified by a wideband transimpedance
amplifier (TIA) integrated within the photo receiver.
Because optical signals may have high levels of wideband noise, filters are often used 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 independently selected for each channel using front panel controls or
through the GPIB interface.
A bank of wideband electronic amplifiers follows the filters. These electronically switched
amplifiers amplify the electrical signal by approximately 10 dB, 20 dB, 30 dB or 40 dB. The
amplifier setting can be independently selected for each channel using front panel controls or
through the GPIB interface.
The average current in the photo receiver is measured to determine the average optical power of
the input signal and is available only through the GPIB interface.
The signal gain in every filter and amplifier path in the OE-2 is measured and stored locally in
the OE-2. These calibration values are used by
WAVECREST’s VISI software to display accurate
optical signal power levels.
A central processor controls all OE-2 functions. The processor also handles communication with
the GPIB interface port.
| Section 1 | Introduction
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