ABSTRACT

Optical tap is used for monitoring the signal transmitted in the busline to control certain characteristics of the transmission line such as the polarization. Some amount of light power transmitted in the transmission line is dropped to the drop port and the rest of the input power is transmitted to the through port. Therefore, this device must have at least one input port and two output ports, that is, the through port and the drop port. In the in situ measurement, an optical tap is needed to detect the signal transmitted from the transmission line or from an optical device. To measure the reflected signal from the transmission line or a device, an optical circulator is used. For stable and accurate monitoring and measurement, the tap coefficient, which is defined by power ratio of input power to the drop power, must be polarization independent and wavelength independent. In addition, the tap coefficient must be stable against time and ambient temperature.