GHz-bandwidth upconversion detector using a unidirectional ring cavity to reduce multilongitudinal mode pump effects

Abstract

We demonstrate efficient upconversion of modulated infrared (IR) signals over a wide bandwidth (up to frequencies in excess of 1 GHz) via cavity-enhanced sum-frequency generation (SFG) in a periodically poled LiNbO. Intensity modulated IR signal is produced by combining beams from two 1547 nm narrow-linewidth lasers in a fiber coupler while tuning their wavelength difference down to 10 pm or less. The SFG crystal is placed inside an Nd:YVO ring cavity that provides 1064 nm circulating pump powers of up to 150 W in unidirectional operation. Measured Fabry-Pérot spectrum at 1064 nm confirms the enhanced spectral stability from multiple to single longitudinal mode pumping condition. We describe analytically and demonstrate experimentally the deleterious effects of using a multimode pump to the high-bandwidth RF spectrum of the 630 nm SFG output. Offering enhanced sensitivity without the need for cooling, the GHz-bandwidth upconverter can readily be extended to the mid-IR (2 - 5 μm) as an alternative to cooled low-bandgap semiconductor detectors for applications such as high-speed free-space optical communications.

Parametric upconversion imaging and its applications

“…Additionally, a single longitudinal mode for the pump ensures better spectral purity. In that case, a ring cavity might be a better choice than a linear cavity [83], [157]. Furthermore, it offers higher damage threshold as the pump laser propagates through the nonlinear material in a unidirectional manner.…”

Upconversion detector for range-resolved DIAL measurement of atmospheric CH4

“…Figure 2 shows the photo and the schematic diagram of the UCD. Its design is similar to the upconversion module in [18], but some components and parameters are changed in order to suit our CH 4 DIAL application. The poling period of the PPLN crystal is 12.45 µm and the temperature of the crystal is precisely maintained at 129.9 °C (optimal for the chosen combination of on-and off-line DIAL wavelengths) in a temperature controlled oven (Covesion Ltd. PV40 and OC1).…”

“…At high pump power levels, single mode operation of the ring laser improves upconversion efficiency [19]. Furthermore, unwanted noise due to multimode pumping [18] is avoided. Second, we improve the overall QE of the new UCD by employing a longer PPLN crystal (25 mm versus 20 mm), a larger intracavity pump power (150 W versus 50 W), and a larger pump beam waist w 0 (200 µm versus 100 µm).…”

Enhancing the detectivity of an upconversion single-photon detector by spatial filtering of upconverted parametric fluorescence

“…Figure 1 shows the experimental setup where the ring pattern of USPDC noise from a shortwavelength-pumped UCD was first discovered. More details of the UCD can be found in our previous work [10]. It is worth mentioning that the USPDC noise locates in the transmission window of the bandpass (BP) filter set in front of the EM-CCD camera (Luca S 658M, Andor).…”