Sebastian Zaske

Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band

We report on single photon frequency downconversion from the red part of the spectrum (738 nm) to the telecommunications C-band. By mixing attenuated laser pulses with an average photon number per pulse < 1 with a strong continuous light field at 1403 nm in a periodically poled Zn:LiNbO3 ridge waveguide an internal conversion efficiency of ∼ 73% is achieved. We further investigate the noise properties of the process by measuring the output spectrum. Our results indicate that by narrow spectral filtering a quantum interface should be feasible which bridges the wavelength gap between quantum emitters like color centers in diamond emitting in the red part of the spectrum and low-loss fiber-optic telecommunications wavelengths.

Frequency down-conversion of single photons into the telecom band

We propose a practical implementation for single-photon down conversion based on difference frequency generation by a nonlinear crystal. A theoretical model is presented, where the quantum noise sources, relevant to the process, are identified.

Green-pumped CW singly resonant optical parametric oscillator based on MgO:PPLN with frequency stabilization

In recent years the development of green-pumped, cw singly resonant optical parametric oscillators (cw SROs) based on undoped periodically poled LiNbO 3 (PPLN) has been impeded by the effects of photorefractive damage and green-induced infrared absorption (GRIIRA) [1,2]. It has been demonstrated that both effects are eliminated or at least significantly reduced for MgO doped LiNbO 3 [3,4]. Nevertheless MgO doped stoichiometric periodically poled LiTaO 3 (MgO:sPPLT) was the preferred nonlinear material for green-pumped cw SROs in recent works [2,5,6]. We here show that it is possible to build a stable cw SRO from (5 mol%) MgO doped PPLN pumped at 532 nm by a single-mode DPSS laser. The device features a low threshold which is reduced by a factor of more than 2.3 compared to similar devices made of MgO:sPPLT. The experimental setup is depicted in Fig. 1(a). The ring cavity is resonant for the signal wave and one mirror (M3) is mounted on a piezo-actuator for scanning and controlling the cavity length. The temperature controlled, 40 mm-long MgO:PPLN crystal (grating period Λ = 7.3 µm) is placed between the mirrors M1 and M2. An uncoated glass etalon inside the resonator allows for frequency fine tuning. As shown in Fig. 1(b) parametric oscillation occurs at P pump ≥ 1.2 W. At a pump power of 2 W we yield a maximum idler power of 310 mW at an idler wavelength of 1416 nm (conversion efficiency 41%). Single-mode signal operation is confirmed by monitoring the transmission of a scanning FPI (FSR = 1 GHz). The SRO is operated at temperatures from 40.0°C to 80.0°C giving access to an idler wavelength range of 1406–1451 nm (corresponding signal wavelength range: 840–;856 nm).

Lock-in detection of single photons after two-step frequency conversion.

We report on cascaded frequency conversion at the single-photon level, consisting of a downconversion from the red (738 nm) to a telecom band (1403 nm) and the reverse upconversion process in the same nonlinear crystal. Detecting the converted single photons suffers from a large noise floor. We were able to recover the signal by implementing a lock-in analyzer technique in the data postprocessing.

Quantum frequency conversion of visible single photons from a quantum dot to a telecom band

The work demonstrates frequency downconversion of single photons from a quantum dot and prove the preservation of the single photon character. The authors were able to translate the frequency of single photons of a semiconductor quantum dot from the red spectral range to the telecom O-band. It was proven that this conversion process leaves the quantum properties of the photons untouched. The high over-all efficiency of 32% for this conversion interface makes it well suited for an application in long-range quantum transmission links.

Highly efficient frequency downconversion at the single photon level

Much recent progress has been achieved in the fabrication of single photon emitters based on color centers in diamond, e.g., silicon-vacancy (SiV) centers emitting at λ<inf>s</inf> = 738nm [1]. However, efficient single photon transmission in future quantum networks requires wavelengths in the telecom bands around λ<inf>0</inf> = 1310nm or λ<inf>c</inf> = 1550nm. In order to bridge this wavelength gap we investigate frequency downconversion according to λ<inf>s</inf>⁻¹ − λ<inf>p</inf>⁻¹ ≈ λ<inf>c</inf>⁻¹, where λ<inf>p</inf> denotes the wavelength of a strong pump field. We here report on work achieving a conversion efficiency that is at least 40 times higher compared to similar experiments that have used optical powers at the single photon level [2,3]. Our setup is shown in Fig. 1(a). To emulate the single photon source at λ<inf>s</inf> an attenuated continuous wave Ti:Sapphire laser (Ti:Sa) together with a pulse picker is used. A home-built tunable continuous wave optical parametric oscillator generates the pump light at λ<inf>p</inf> = 1403nm. The two fields are coupled into a temperature controlled ridge waveguide (WG) made of periodically poled ZnO:LiNbO<inf>3</inf>. It is possible to excite only the fundamental WG mode at λ<inf>s</inf> (see inset in Fig. 1(a)) which in combination with the strong confinement in the WG provides a good spatial overlap between the interacting modes. Using a spectral filtering stage (prism, pinhole, bandpass filters) one of the three beams can be selected at the waveguide output and coupled into an optical fiber for further analysis using a single photon avalanche diode (SPAD) or a grating spectrometer, respectively.

Efficient Frequency Downconversion at the Single Photon Level from 738 nm to 1557 nm

We report on quantum frequency downconversion using a ZnO:PPLN ridge waveguide. An internal conversion efficiency of 73% is achieved. We identify Raman scattering to be the dominant noise source in the frequency converter.

Continuous-wave 532 nm pumped ingly-resonant optical parametric oscillator based on MgO-doped PPLN

We present a continuous-wave (CW) optical parametric oscillator (OPO) based on quasi-phase-matching in a MgO-doped periodically-poled LiNbO3 (PPLN) crystal. We report and discuss our observation of different charactarisics between the signal and idler output power.