Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE
Degenerate parametric down-conversion at 1570 nm by periodically poled lithium niobate waveguide: a route to single photon source and photon entanglement
Stefania Castelletto, Ivo Pietro Degiovanni, Valentina Schettini, Leonardo Papi, Tommaso Del Rosso, Giancarlo Margheri, Stefano Sottini
In this paper we measure the efficiency of photon pair production from parametric downconversion at the photon counting level, generated in a laboratory prototype of PPLN waveguide at 1572 nm. The aim is to enhance the brightness of an heralded single photon source and to improve compactness for quantum communication applications, namely quantum key distribution. We observed a maximum of the conversion efficiency corresponding to 7.9 106 photon pairs/s for a pump power of 28 μW. This value is compared with the measured pairs production in a classical experiment of difference frequency generation, realized with the same sample by analogue classical detection. We highlight the advantages of using the waveguide versus a bulk PPLN for such applications and we foresee further possible improvements by adopting waveguide in a single photon level experimental setup.
In this paper we measure the efficiency of photon pair production from parametric downconversion at the photon counting level, generated in a laboratory prototype of PPLN waveguide at 1572 nm. The aim is to enhance the brightness of an heralded single photon source and to improve compactness for quantum communication applications, namely quantum key distribution. We observed a maximum of the conversion efficiency corresponding to 7.9 106 photon pairs/s for a pump power of 28 μW. This value is compared with the measured pairs production in a classical experiment of difference frequency generation, realized with the same sample by analogue classical detection. We highlight the advantages of using the waveguide versus a bulk PPLN for such applications and we foresee further possible improvements by adopting waveguide in a single photon level experimental setup.
The frequency entangled photon pairs generated by spontaneous parametric down-conversion (SPDC) possess wide applications in quantum optics and relevant fields.To facilitate the practical quantum information technologies,particularly in optical fiber links,a frequency entangled source at telecommunication wavelength with features of compactness,portability,high efficiency and miniaturization is highly desired.In this paper,we report the experimental generation of a miniaturized frequency entangled source in telecommunication band from a 10 mm-long type-Ⅱ periodically poled lithium niobate (PPLN) waveguide pumped by a 780 nm distributed Bragg reflector (DBR) laser diode.The frequency entangled photon pairs generated by SPDC possess wide applications in quantum optics and relevant fields.When the DBR laser diode is driven by a current of 170 mA at a temperature controlled to 20℃,the output power is measured to be 70.4 mW with a central wavelength of 780.585 nm.Under this pump,the orthogonally-polarized photon pairs are generated and output from the PPLN waveguide.After filtering out the remaining pump by three high-performance long-pass filters mounted on an adjustable U-type fiber bench,the photon-pair generation rate,spectral and temporal properties of the generated frequency entangled source are measured.The results show that the generation rate of the photon pairs,after being corrected for the detection efficiencies of the single photon detectors and the optical losses,is achieved to be 1.86×107 s-1 at a pump power of 44.9 mW (coupled into the waveguide).Optimizing the working temperature of the waveguide and fixing it at 46.5℃,the frequency degeneracy of the SPDC generated photon pairs is realized.Based on the coincidence measurement setup together with two infrared spectrometers,the spectra of the signal and idler photons are obtained with their center wavelengths of 1561.43 nm and 1561.45 nm,and their 3-dB bandwidths of 3.62 nm and 3.60 nm respectively.The joint spectrum of the photon pair is observed,showing a joint spectrum bandwidth of 3.18 nm.The degree of frequency entanglement is quantified to be 1.13 according to the bandwidth ratio between the single photon spectrum and the joint spectrum.Furthermore,based on the Hong-Ou-Mandel (HOM) interferometric coincidence measurement setup,a visibility of about 96.1% is observed,which indicates the very good frequency indistinguishibility of the down-converted biphotons.The measured 3-dB width of the HOM dip is 1.47 ps and shows good agreement with the measured single-photon spectral bandwidth.The experimental results lay a solid foundation for developing portable,miniaturized frequency entangled sources at telecommunication band for the further applications in quantum information areas,such as quantum time synchronization.
We report on a new kind of correlated photon-pair source based on a waveguide integrated on a Periodically Poled Lithium Niobate substrate. Using a pump laser of a few micro-Watts at 657 nm, we generate degenerate photon-pairs at 1314 nm. Detecting about 1500 coincidences per second, we can infer a conversion rate of 10-6 pairs per pump photon, which is four orders of magnitude higher than that obtained with previous bulk sources. These results are very promising for the realization of sources for quantum communication and quantum metrology experiments requiring a high signal-to-noise ratio or working with more than one photon-pair at a time.
A new kind of correlated photon-pair source based on a waveguide integrated on a periodically poled lithium niobate substrate is reported. Using a pump laser of a few µW at 657 nm, photon-pairs are generated/degenerated at 1314 nm. Detecting ~1500 coincidences per second, a conversion rate of 10-6 pairs per pump photon can be inferred, which is four orders of magnitude higher than that obtained with previous bulk sources. These results are very promising for the realisation of sources for quantum communication and quantum metrology experiments requiring a high signal-to-noise ratio or working with more than one photon-pair at a time.
We present two independent measurements of the photon pairs production efficiency (PPPE) at 1572 nm, generated in a noncommercial periodically poled lithium-niobate waveguide fabricated in our laboratory. The first measurement, referred to as "direct" measurement, is performed at the photon-counting level (light power at the level of a few picowatts), exploiting a typical coincidence detection technique and a dedicated statistical model. In this case the measured PPPE is (4.1±1.1)1011 pairs/(s W). The same parameter was estimated independently by a well-established "indirect" measurement, based on a difference frequency generation experiment (typical light power level of a few microwatts). This other measurement yields (5.0±2.4)1011 pairs/(s W). Despite the large uncertainty of this second measurement, we observe that the two results are in good agreement even considering only the lower uncertainty value. To our knowledge, it is the first realization of a comparison between these two measurement techniques, working at so different light levels.
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.