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Experimental scheme: (single) photons at 1550 nm are combined with a tunable (see text) laser at 980 nm in a fiber WDM before entering a nonlinear PPLN W/G for upconversion to 600 nm. This output is filtered using a prism and an interference filter before detection with a Si APD. Signal and pump intensities and wavelengths are monitored after a fiber beamsplitter.
The efficiency-noise characteristics for the upconversion detector showing a peak efficiency of nearly 12%. In the inset we see the low noise efficiency response in detail.
The detection efficiency as a function of the signal wavelength for three different pump wavelengths. The peak efficiency corresponds to a noise level of 50 kHz in each case. We see the normal acceptance bandwidth of can be extended tenfold to around 5 nm as illustrated by the envelope—this is to guide the eye and is not a fit.
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