Open area ratio - MCP

The ratio of the open area to the total effective area of a MCP.

Open circuit voltage (Voc)

The open circuit voltage is a photovoltaic voltage developed when the load resistance is infinite and exhibits a constant value independent of the device's photosensitive area.

Open-loop gain

This is the gain of an operational amplifier with no feedback applied, and represents the ratio of the output voltage to the input voltage. Units are in dB.

Optical return loss (ORL)

The ratio of the reflected return light to the incident light. If the reflected return light level is high, the laser diode oscillation on the transmit side will become unstable causing relative intensity noise to increase. The reflected return light level must therefore be minimized. As solutions for this problem in receptacle type modules, an optical isolator, or a ferrule called a “stub”(component with the fiber insertion side polished for physical contact and the device side polished slantwise) is often inserted in the optical path to minimize the optical return loss.


This is the maximum light input power of a photosensor device. When more than a given amount of light enters a photosensor device, the photodiode or amplifier becomes saturated. This disturbs the output waveform, making it impossible to receive optical signal correctly.