White Paper CWDM components for 40 G and 100 G Transceivers D-5006 Introduction In this White paper the principals of Cube’s Thin Film Filter design and their performance with regard to construction tolerances and filter performance will be explained. We will look at 3 areas that are key to explaining Cubes core technology. These areas are the construction tolerances of the demux device with regard to loss, the optical pass band performance of the demux with regard to angle and the third is to look at the overall performance of a 25 G link. Loss performance as a function Angle of Incidence (AOI) The basic construction of the device uses the principals of thin film filters in a “zig zag or multiple bounce” construction. The basic 4 channel would look like the figure below: Construction of simple 4-channel demux with input and output fibers. The 4 channels on the left show the output fibers, where individual wavelengths are selected and passed through the filter. The fiber on the right contains all 4 wavelengths with each of the colored blocks representing a specific thin film filter. The development of the part has some basic constraints that can be described in the following: 1. The key design challenge for thin film filter multiplexing is the routing of the collimated optical beam through the ‘zig zag’ as shown above. 2. To achieve this high angular alignment accuracy are required (filters are essentially mirrors) The angular tolerance is the ability to guide the light through this structure with the least amount of loss. The light leaving the structure needs to be confined to a specific area. The enabling technology here is to keep the filters in a well-defined fixed position with regard to angle; this would enable the lowest insertion loss through the device. The variation of angular tolerance with regard to insertion loss can be seen in the figure below. This data is for a standard 4 channel demux with a nominal 10° incident angle. IL [dB] 25 20 15 10 5 0 9 9,2 9,4 9,6 9,8 10 10,2 10,4 10,6 10,8 11 AOI [deg] Document: D-5006 On the vertical axis is the insertion loss in dB, with the angle of incidence (AOI) on the horizontal axis. Page 1/4
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