C Xiong

Nonclassical 2-photon interference with separate intrinsically narrowband fibre sources

In this paper, we demonstrate a source of photon pairs based on four-wave-mixing in photonic crystal fibres. Careful engineering of the phase matching conditions in the fibres enables us to create photon pairs at 597 nm and 860 nm in an intrinsically factorable state showing no spectral correlations. This allows for heralding one photon in a pure state and hence renders narrow band filtering obsolete. The source is narrow band, bright and achieves an overall detection efficiency of up to 21% per photon. For the first time, a Hong-Ou-Mandel interference with unfiltered photons from separate fibre sources is presented.

Generation of correlated photon pairs in a chalcogenide As2S3 waveguide

We demonstrate a 1550 nm correlated photon-pair source in an integrated glass platform—a chalcogenide As2S3 waveguide. A measured pair coincidence rate of 80u2004s−1 was achieved using 57 mW of continuous-wave pump. The coincidence to accidental ratio was shown to be limited by spontaneous Raman scattering effects that are expected to be mitigated by using a pulsed pump source.

Polarized supercontinuum in birefringent photonic crystal fibre pumped at 1064 nm and application to tuneable visible/UV generation

We generate a flat, polarized and single mode supercontinuum (SC) spanning 450-1750 nm in a highly birefringent photonic crystal fibre (PCF) pumped by a 1064 nm microchip laser. More than 99% of the total power is kept in a single linear polarization. The measured power coupling penalty due to the elliptical core is less than 6% (0.25 dB). As one of its applications, we demonstrate tuneable visible/UV generation in the nonlinear crystal BIBO pumped by this polarized SC source. A tuneable range of 400-525 nm is obtained by critical phase matching in BIBO. We also show the results of visible/UV generation in BIBO pumped by the signal wavelength of polarized four-wave mixing (FWM) in PCF.

Narrowband high-fidelity all-fibre source of heralded single photons at 1570 nm.

An all-fibre heralded single photon source operating at 1570 nm has been demonstrated. The device generates correlated photon pairs, widely spaced in frequency, through four-wave mixing in a photonic crystal fibre. Separation of the pair photons and narrowband filtering is all achieved in fibre. The output heralded single photon rate was 9.2 x 10(4) per second, with a counts-to-accidentals ratio of 10.4 and a heralding fidelity of 52 %. Furthermore, narrowband filtering ensured that the output single photon state was near time-bandwidth limited with a coherence length of 4 ps. Such a source is well suited to quantum information processing applications.

Enhanced visible continuum generation from a microchip 1064nm laser.

We demonstrate a cascaded nonlinear process using pump conversion to 742 nm by four-wave mixing in the normal dispersion regime then continuum generation by modulation instability to generate bright single-mode visible continuum with an average power up to -20 dBm/nm, from a compact 1064 nm infrared source in a monolithic single-mode photonic crystal fibre with a tapered section in one end.

Intrinsically narrowband pair photon generation in microstructured fibres

In this paper, we study the tailoring of photon spectral properties generated by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is to produce intrinsically narrow-band photons and hence to achieve high non-classical interference visibility and generate high-fidelity entanglement without any requirement for spectral filtering, leading to high effective detection efficiencies. We show unfiltered Hong-Ou-Mandel interference visibilities of 77% between photons from the same PCF and 80% between separate sources. We compare results from modelling the PCF to these experiments and analyse photon purities.

Characteristics of Correlated Photon Pairs Generated in Ultracompact Silicon Slow-Light Photonic Crystal Waveguides

We report the characterization of correlated photon pairs generated in dispersion-engineered silicon slow-light photonic crystal waveguides pumped by picosecond pulses. We found that taking advantage of the 15-nm flat-band slow-light window (vg ~ c/30), the bandwidth for correlated photon-pair generation in 96- and 196-μm-long waveguides was at least 11.2 nm, while a 396-μm-long waveguide reduced the bandwidth to 8 nm (only half of the slow-light bandwidth due to the increased impact of phase matching in a longer waveguide). The key metrics for a photon-pair source: coincidence to accidental ratio (CAR) and pair brightness were measured to be a maximum 33 at a pair generation rate of 0.004 pair per pulse in a 196- μm-long waveguide. Within the measurement errors, the maximum CAR achieved in 96-, 196-, and 396-μm-long waveguides is constant. The noise analysis shows that detector dark counts, leaked pump light, linear and nonlinear losses, multiple pair generation, and detector jitter are the limiting factors to the CAR performance of the sources.

Dual-Wavelength-Pumped Supercontinuum Generation in an All-Fiber Device

We demonstrate supercontinuum generation with a novel dual-wavelength pumping scheme. The dual-wavelength pump source and supercontinuum generation were realized one after another in a fusion spliced all-fibre device. The spectrum extends to 370 nm.

More than threefold expansion of highly nonlinear photonic crystal fiber cores for low-loss fusion splicing

We have formed low-loss fusion splices from highly nonlinear (HNL) photonic crystal fibers (PCFs) with small cores and high air-filling fractions to fibers with much larger mode field diameters (MFDs). The PCF core was locally enlarged by the controlled collapse of holes around the core while keeping other holes open. The fiber was then cleaved at the enlarged core and spliced to the large MFD fiber with a conventional electric arc fusion splicer. Splice losses as low as 0.36 dB were achieved between a PCF and a standard single-mode fiber (SMF) with MFDs of 1.8 microm and 5.9 microm, respectively.

Near-zero anomalous dispersion Ge11.5As24Se64.5 glass nanowires for correlated photon pair generation: design and analysis.

We show that highly nonlinear chalcogenide glass nanowire waveguides with near-zero anomalous dispersion should be capable of generating correlated photon-pairs by spontaneous four-wave mixing at frequencies detuned by over 17 THz from the pump where Raman noise is absent. In this region we predict a photon pair correlation of >100, a figure of merit >10 and brightness of ~8×10(8) pairs/s over a bandwidth of >15 THz in nanowires with group velocity dispersion of <5 ps∙km(-1) nm(-1). We present designs for double-clad Ge(11.5)As(24)Se(64.5) glass nanowires with realistic tolerance to fabrication errors that achieve near-zero anomalous dispersion at a 1420 nm pump wavelength. This structure has a fabrication tolerance of 80-170 nm in the waveguide width and utilizes a SiO(2)/Al(2)O(3) layer deposited by atomic layer deposition to compensate the fabrication errors in the film thickness.