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Optics Express

Spatially single mode photon pair source at 800 nm in periodically poled Rubidium exchanged KTP waveguides

Christof Eigner, Laura Padberg, Matteo Santandrea, Harald Herrmann, Benjamin Brecht, Christine Silberhorn

Published Sep 24, 2020• 12 citations
Publisher

Abstract

Photon pair sources in the visible to NIR wavelength region play a key role in quantum optics. The wavelength range around 800 nm provides an opportunity for using low cost detectors, which makes it highly interesting for practical, large scale quantum applications. Here, we report on the realization of single mode Rubidium (Rb) exchanged waveguides in periodically poled (PP) Potassium Titanyl Phosphate (Rb:KTiOPO4 or Rb:KTP) for frequency-non-degenerate type II parametric down-conversion pumped at 400 nm and generating pairs of photons at around 800 nm. The source exhibits a nonlinear conversion efficiency of 2.0%/(Wcm2), estimated from SHG measurements. Characterisation of the generated two-photon state confirms nonclassical photon-number correlations, characterized by g(1,1). The high nonlinear conversion efficiency and low temperature sensitivity make this source a promising candidate for operations in both classical and quantum integrated network applications.

DOI
10.1364/oe.399483

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Photon pair sources in the visible to NIR wavelength region play a key role in quantum optics. The wavelength range around 800 nm provides an opportunity for using low cost detectors, which makes it highly interesting for practical, large scale quantum applications. Here, we report on the realization of single mode Rubidium (Rb) exchanged waveguides in periodically poled (PP) Potassium Titanyl Phosphate (Rb:KTiOPO4 or Rb:KTP) for frequency-non-degenerate type II parametric down-conversion pumped at 400 nm and generating pairs of photons at around 800 nm. The source exhibits a nonlinear conversion efficiency of 2.0%/(Wcm2), estimated from SHG measurements. Characterisation of the generated two-photon state confirms nonclassical photon-number correlations, characterized by g(1,1). The high nonlinear conversion efficiency and low temperature sensitivity make this source a promising candidate for operations in both classical and quantum integrated network applications.
We present a systematic study of a correlated photon-pair source based on a periodically-poled KTiOPO4 (PPKTP) waveguide. The waveguide was fabricated on a KTiOPO4 crystal supporting type-II parametric down-conversion. In addition, periodic poling was applied along the waveguide to quasi-phase-match the type-0 down-conversion process. The design pump wavelength is 532 nm, and the wavelengths of the down-converted, correlated photons are around 900 nm and 1300 nm. We examine the two-photon correlation spectra and singlephoton spectra at a variety of temperature and power settings for both type-0 and type II down-conversion processes. Our study shows that the waveguide source has a number of advantages compared to its bulk-crystal counterpart, including higher spectral brightness, narrower emission bandwidth and single spatial-mode output. With greatly simplified engineering, this compact, highly efficient, low photon-loss, and cost-effective waveguide source of correlated photon pairs is promising for future chip-scale quantum information processing applications.
A high generation rate photon-pair source using a dual element periodically-poled potassium titanyl phosphate (PP KTP) waveguide is described. The fully integrated photon-pair source consists of a 1064-nm pump diode laser, fiber-coupled to a dual element waveguide within which a pair of 1064-nm photons are up-converted to a single 532-nm photon in the first stage. In the second stage, the 532-nm photon is down-converted to an entangled photon-pair at 800 nm and 1600 nm which are fiber-coupled at the waveguide output. The photon-pair source features a high pair generation rate, a compact power-efficient package, and continuous wave (CW) or pulsed operation. This is a significant step towards the long term goal of developing sources for high-rate Quantum Key Distribution (QKD) to enable Earth-space secure communications. Characterization and test results are presented. Details and preliminary results of a laboratory free space QKD experiment with the B92 protocol are also presented.
We have experimentally implemented a non-degenerate sequential time-bin entangled photon-pair source using a periodically poled potassium titanyl phosphate waveguide at a clock rate of 1 GHz. The wavelengths of the signal and idler are 895 nm and 1310 nm, which are suitable for local and long distance optical communications, respectively and the 895 nm signal is also suitable for quantum memory research. A silicon avalanche photodiode is used to detect the photons at 895 nm while a periodically poled lithium niobate waveguide based up-conversion detector is used to detect the photons at 1310 nm. The measured entangled-photon-pair flux rate is 650 Hz and the fringe visibility for two-photon interference is 79.4% without noise subtraction.
A scheme to generate multi-channel photon pairs is presented,based on a periodically poled(PP) Potassium Titanyl Phosphate(KTP) waveguide via spontaneous parametric downconversion(SPDC).Type-II and type-I phase matching cases with a pulsed and a cw pump laser are discussed respectively.It is analytically shown that several photon pairs could be generated in a single type-II PPKTP waveguide,and the wavelengths of all photon pairs are in the telecom band.In type-I case,several photon pairs can be prepared,but one photon of each pair is not in telecom band.And,a multi-channel photon pairs source could be realized.
We report the realization of a bright ultrafast type II parametric down-conversion source of twin beams free of any spatiotemporal correlations in a periodically poled KTiOPO4 (PP-KTP) waveguide. From a robust, single-pass setup it emits pulsed two-mode squeezed vacuum states: photon-number entangled pairs of single-mode pulses or, in terms of continuous variables quantum optics, pulsed Einstein-Podolsky-Rosen states in the telecom wavelength regime. We verify the single-mode character of our source by measuring Glauber correlation functions g(2) and demonstrate with a pump energy as low as 75 pJ per pump pulse a mean photon number of 2.5.
We report on the generation of a bright photon source at telecom wavelengths using spontaneous parametric down-conversion in a type II periodically poled potassium titanyl phosphate crystal. Simultaneous resonances of the pump and the two down-converted fields are achieved with a properly designed optical cavity. This triple-resonance optical parametric oscillator operates far below threshold, generating photon pairs at 1560 nm wavelength with a bandwidth of 8 MHz. Time correlation measurements produce an estimate of 27.7 ns for the coherence time, and production rate of 134±25 s−1 MHz−1 mW−1 for photon pairs. As photon pairs in the telecom regime are suitable for long-distance transmission, this source may find application in quantum communications.