BDU-FC Fiber-coupled Beat Detection Unit
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The BDU beat detection unit generates a beat signal between the comb light and the light from an external cw laser to be measured. By overlapping them with the suitable polarization conditions on an avalanche photodetector a RF signal is generated, which can be fed into a frequency counter. As the repetition rate and the offset frequency of the comb is known, simple school mathematics is enough to calculate the laser frequency.
For all common wavelengths (e.g. 633 nm, 1064 nm) fiber-coupled beat detection units are available. Due to the enhanced opto-mechanical design no adjustment is required. The external lasers are connected to the unit with a standard (FC/APC) or user-specified connectors. The fiber-coupled design is the most advantagous when working with low power cw lasers.