The generation of interband photon pairs with wavelengths near 0.5 and 1.6 μm in a photonic-crystal fiber under low-power cw optical pumping by a diode laser with a central wavelength of 0.8 μm has been experimentally demonstrated. It has been found that the generation rate of entangled photons under cw pumping is comparable with values obtained with pulsed pumping by a femtosecond Ti:sapphire laser if the average cw pump power is an order of magnitude higher than the average pulsed pump power. The reached rates of photon generation are ensured by the used photonic-crystal fiber with a small effective mode area and a special dispersion profile. The reached low noise in the output signal is ensured by the separation of carrier frequencies of generated photons into different spectral bands.
The generation of interband photon pairs with wavelengths near 0.5 and 1.6 μm in a photonic-crystal fiber under low-power cw optical pumping by a diode laser with a central wavelength of 0.8 μm has been experimentally demonstrated. It has been found that the generation rate of entangled photons under cw pumping is comparable with values obtained with pulsed pumping by a femtosecond Ti:sapphire laser if the average cw pump power is an order of magnitude higher than the average pulsed pump power. The reached rates of photon generation are ensured by the used photonic-crystal fiber with a small effective mode area and a special dispersion profile. The reached low noise in the output signal is ensured by the separation of carrier frequencies of generated photons into different spectral bands.
Entangled photon sources have applications in such fields as quantum communications, quantum sensing and quantum computing. Of particular interest are pulsed entangled photon sources, as they provide an additional degree of freedom – the temporal degree of freedom – to manipulate entanglement properties, hence increasing the information capacity of the entangled photons they produce. An entangled photon source in the telecom wavelength typically requires a 780 nm pump laser. So far, in most cases, pulsed entangled photon sources are pumped by the Ti:Sapph mode-locked laser, which, due to its bulky size and high cost, has limited the widescale adoption of pulsed entangled photon sources. In this thesis, I demonstrate a simple, cost-effective, pulsed laser diode capable of competing with the Ti:Sapph for the purposes of entangled photon generation. The diode and driver are capable of pulsing at up to 60 MHz , with peak power exceeding 1 W and pulse energy in excess of 1 nJ , and with a spectral width narrower than 0.1 nm. I also demonstrate a pulsed, fully fiber-based, entangled photon source, with high entanglement quality (maximum concurrence of 0.985) and a high pair generation rate (0.15 pairs/pulse). The source is to our knowledge the first of its kind.
An actual task of quantum communications over long distances is the creation of a bright source of photon pairs operating at standard wavelengths of fiber optic communication lines. In this work, we experimentally investigated the spectral and correlation characteristics of photon pairs generated on the phenomenon of spontaneous four-wave mixing in a highly nonlinear photonic-crystal fiber with a wavelength of one of the photons near 1.5 μm. The demonstrated source can be used as an efficient single photon generator at a telecommunications wavelength with prediction and tuning over a wide spectral range.
We demonstrate an efficient generation of frequency anti-correlated entangled photon pairs at telecom wavelength. The fundamental laser is a continuous-wave high-power fiber laser at 1560 nm, through an extracavity frequency doubling system, a 780-nm pump with a power as high as 742 mW is realized. After single-passing through a periodically poled KTiOPO4 (PPKTP) crystal, degenerate down-converted photon pairs are generated. With an overall detection efficiency of 14.8 %, the count rates of the single photons and coincidence of the photon pairs are measured to be 370 kHz and 22 kHz, respectively. The spectra of the signal and idler photons are centered at 1560.23 and 1560.04 nm, while their 3-dB bandwidths being 3.22 nm both. The joint spectrum of the photon pair is observed to be frequency anti-correlated and have a spectral bandwidth of 0.52 nm. According to the ratio of the single-photon spectral bandwidth to the joint spectral bandwidth of the photon pairs, the degree of frequency entanglement is quantified to be 6.19. Based on a Hong–Ou–Mandel interferometric coincidence measurement, a frequency indistinguishability of 95 % is demonstrated. The good agreements with the theoretical estimations show that the inherent extra intensity noise in fiber lasers has little influence on frequency entanglement of the generated photon pairs.
Photon pair sources are fundamental building blocks for quantum entanglement and quantum communication. Recent studies in silicon photonics have documented promising characteristics for photon pair sources within the telecommunications band, including sub-milliwatt optical pump power, high spectral brightness, and high photon purity. However, most quantum systems suitable for local operation (e.g., storage/computation) support optical transitions in the visible or short nearinfrared bands. In comparison to telecommunications wavelengths, the significantly higher optical attenuation in silica at such wavelengths limits the length scale over which optical-fiber-based quantum communication between such local nodes can take place. One approach to connect such systems over fiber is through a photon pair source that can bridge the visible and telecom bands, but an appropriate source, which should produce narrow-band photon pairs with a high signal-to-noise ratio, has not yet been developed in an integrated platform. Here, we demonstrate a nanophotonic visible-telecom photon pair source for the first time, using high quality factor silicon nitride resonators to generate narrow-band photon pairs with unprecedented purity and brightness, with coincidence-toaccidental ratio (CAR) up to 3,780 ± 140 and detected photon-pair flux up to (18,400 ± 1,000) pairs/s. We further demonstrate visible-telecom time-energy entanglement and its distribution over a 20 km fiber, far exceeding the fiber length over which purely visible wavelength quantum light sources can be transmitted. Finally, we show how dispersion engineering of the microresonators enables the connections of different species of trapped atoms/ions, defect centers, and quantum dots to the telecommunications bands for future quantum communication systems.
Efficient on-chip entangled photon pair generation at telecom wavelengths is an integral aspect of emerging quantum optical technologies, particularly for quantum communication and computing. However, moving to shorter wavelengths enables the use of more accessible silicon detector technology, and opens up applications in imaging and spectroscopy. Here, we present high brightness ((1.6 ± 0.3) × 10 9 pairs/s/mW/nm) visible–near-IR photon pair generation in a periodically poled lithium niobate nanophotonic waveguide. The degenerate spectrum of the photon pairs is centered at 811 nm with a bandwidth of 117 nm when pumped with a spectrally multimode laser diode. The measured on-chip source efficiency of (2.3 ± 0.5) × 10 11 pairs/s/mW is on par with source efficiencies at telecom wavelengths and is also orders of magnitude higher than the efficiencies of other visible sources implemented in bulk crystal or diffused waveguide-based technologies. Further improvements in the brightness and efficiencies are possible by pumping the device with a single-frequency laser, which would also shrink the pair bandwidth. These results represent the shortest wavelength of photon pairs generated in a nanophotonic waveguide reported to date by nearly an octave.
The generation of single photons in the near-infrared range with a wavelength of 1533 nm is demonstrated. The generation is performed in an optical fiber using continuous-wave laser excitation and a heralding photon in the visible range with a wavelength of 520 nm. Despite relatively high pump powers and a significant contribution of noise photons, the presented source provides a high degree of single-photon generation purity ( gc(2)(0)=0.04) . This work reveals the potential for creating compact fiber-optic sources of single infrared photons using continuous-wave laser sources.