1. Field
The invention is related to an apparatus for measuring the power levels of an operating optical communications system, and more particularly to an apparatus for measuring the power levels in a passive optical network (PON), like those used in fiber to the ‘X’ (X: H=home, C=curb, N=node, P=premises, etc.) or CWDM (coarse wavelength division multiplexing) systems.
2. Related Art
Measuring the power levels of an operating optical communications system, specifically a passive optical network (PON), like those used in fiber to the ‘X’ (X: H=home, C=curb, N=node, P=premises, etc.) or CWDM (coarse wavelength division multiplexing) systems, requires the use of an inline power meter capable of sampling and measuring a small portion of the total optical power of each wavelength present in the optical fiber. (The fiber in an FTTx PON carries bidirectional traffic, with one or two wavelengths transmitted one direction, and a third wavelength transmitted in the reverse direction.) A number of methods already exist that use optical couplers with a 95:5, 90:10 or 80:20 split ratio to tap a portion of the desired signals from the fiber, split out the individual wavelengths of interest, detect and measure them. Such existing configurations may make use of a 2×2 coupler (see for example, U.S. Pat. No. 7,187,861) or a pair of 1×2 couplers (see for example, U.S. Pat. No. 7,756,418) to perform this function.
However, each stage needed to perform the steps just described contributes to the complexity of the optical assemblies required to tap and split out the optical signals while adding loss of signal level at each stage before detection and measurement, limiting the dynamic range of the measurement circuits. Also, these configurations can take up a considerable amount of space inside the instrument designed to measure the optical power levels, adding to the cost of those instruments.