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Schematic of the experimental setup used for single photon adiabatic wavelength conversion. Ti:Sapphire laser (76 MHz repetition rate, 100 fs pulses, λ = 830 nm) produces pump pulses (using a BiBO second-harmonic-generation crystal) and probe pulses using an OPO. A fiber based Fabry-perot tunable etalon (Δλ = 0.14 nm) filters the probe pulses. The pulses are attenuated to the single photon level using a calibrated variable attenuator. The probe pulses are converted to a new wavelength using the refractive index change induced by the pump that is focused on the ring resonator (inset shows the measured transmission of the ring resonator). The resulting signal is measured either using an OSA or SSPD.
Adiabatic wavelength conversion at the single photon level and with coherent (bright) light for comparison. The three plots are for wavelength changes of (a) 0.25 nm, (b) 0.3 nm, and (c) 0.45 nm. The original probe signal, without wavelength conversion, is shown at ¼ scale (black dashes), the coherent (blue dash-dot), and single photon (red solid) signals are normalized to the original signal. The single photon signal is broader due to the use of a wider bandwidth filter.
(a) Relative reduction in conversion efficiencys due to free-carrier absorption vs. wavelength change. (b) Wavelength conversion efficiency as a function of time offset between the pump and the probe, where negative delays correspond to the probe pulse coming earlier than the pump pulse. The data are averaged from multiple wavelength changes. The original λ (blue circles) and new λ (red triangles) data points are obtained by integrating the spectral signal at the respective wavelengths. The loss due to free carrires, part (a) of the figure, was removed in order to normalize the overall efficiency regardless of wavelength change. The total signal (black squares) is the sum of the New λ and Original λ data. The solid lines are from a coupled mode theory model.19
Measured spectra as the relative delay between the pump and probe pulse are varied (negative delays correspond to the probe coming earlier than the pump). The left panel is when the probe is at the original wavelength of the cavity. The right panel is when the probe is at the new wavelength of the cavity.
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