High-visibility Interference Research Articles

Ultra-fast quantum randomness generation by accelerated phase diffusion in a pulsed laser diode

We demonstrate a high bit-rate quantum random number generator by interferometric detection of phase diffusion in a gain-switched DFB laser diode. Gain switching at few-GHz frequencies produces a train of bright pulses with nearly equal amplitudes and random phases. An unbalanced Mach-Zehnder interferometer is used to interfere subsequent pulses and thereby generate strong random-amplitude pulses, which are detected and digitized to produce a high-rate random bit string. Using established models of semiconductor laser field dynamics, we predict a regime of high visibility interference and nearly complete vacuum-fluctuation-induced phase diffusion between pulses. These are confirmed by measurement of pulse power statistics at the output of the interferometer. Using a 5.825 GHz excitation rate and 14-bit digitization, we observe 43 Gbps quantum randomness generation.

Nonclassical two-photon interference between independent telecommunication light pulses converted by difference-frequency generation

We experimentally demonstrated the Hong-Ou-Mandel (HOM) interference between two photons after visible-to-telecommunication wavelength conversion. In the experiment, we prepared a heralded single photon by using spontaneous parametric down-conversion and the other photon from a weak laser source at 780 nm. We converted the wavelength of both photons to the telecommunication wavelength of 1522 nm by using difference-frequency generation in a periodically-poled lithium niobate, and then observed the HOM interference between the photons. The observed visibility is $0.76\pm 0.12$ which clearly shows the non-classical interference of the two photons. The high-visibility interference is an important step for fiber-based quantum communications of photons generated from visible photon emitters.

High-Visibility Photonic Crystal Fiber Interferometer as Multifunctional Sensor

A photonic crystal fiber (PCF) interferometer that exhibits record fringe contrast (∼40 dB) is demonstrated along with its sensing applications. The device operates in reflection mode and consists of a centimeter-long segment of properly selected PCF fusion spliced to single mode optical fibers. Two identical collapsed zones in the PCF combined with its modal properties allow high-visibility interference patterns. The interferometer is suitable for refractometric and liquid level sensing. The measuring refractive index range goes from 1.33 to 1.43 and the maximum resolution is ∼1.6 × 10−5.

134-W phase locking of two-dimensional four-fiber lasers with improved self-imaging resonator

We experimentally demonstrate the phase locking of a two-dimensional (2D) array of four fiber lasers using an improved self-imaging resonator with a spatial filter. The high visibility interference round stripes of the coherent beam profile are observed. The coherent output power of the fiber array exceeds 134 W. The entire system operates quite stably, and no thermal effects observe in the spatial filter, indicating that the coherent output power can be increased using this method.

High-visibility interference fringes with femtosecond laser radiation

We propose and experimentally demonstrate an interferometer for femtosecond pulses with spectral bandwidth about 100 nm. The scheme is based on a Michelson interferometer with a dispersion compensating module. A diffractive lens serves the purpose of equalizing the optical-path-length difference for a wide range of frequencies. In this way, it is possible to register high-contrast interference fringes with micrometric resolution over the whole area of a commercial CCD sensor for broadband femtosecond pulses.

Coherence properties of two fiber lasers coupled by mutual injection

Phase locking of two fiber lasers is obtained by mutual injection. The coherence properties of this composite laser are analyzed. In the most general case, the radiations at the two output mirrors of the laser are not mutually coherent. The cross-correlation of the two emitted beams shows that an extra-cavity delay line is required to get stable and high visibility interference fringes. Such a laser configuration is attractive for coherent beam combining in the far field provided the multiple output beams are properly time delayed.

Spectral interference of frequency-shifted solitons in a photonic-crystal fiber

Frequency-shifted solitons in a highly nonlinear photonic-crystal fiber (PCF) are shown to give rise to high-visibility interference fringes in PCF output spectra, indicating flat spectral phase profiles of individual solitons in the PCF output. This experimental finding, supported by numerical simulations, suggests a promising method of fiber-format pulse shaping and an attractive technology for few-cycle pulse synthesis through a coherent addition of frequency-shifted solitons generated in a highly nonlinear fiber.

High-visibility intensity interference and ghost imaging with pseudo-thermal light

We consider higher-order intensity correlations in thermal light and show that they can be used for observing high-visibility interference of the Hanbury Brown–Twiss-type as well as high-visibility ghost imaging. Experimental results are obtained for third- and fourth-order intensity interference, by processing images made with a digital photographic camera.

Erratum: High-visibility multiphoton interference of Hanbury Brown–Twiss type for classical light [Phys. Rev. A77, 053801 (2008)

Erratum: High-visibility multiphoton interference of Hanbury Brown–Twiss type for classical light [Phys. Rev. A<b>77</b>, 053801 (2008)

Interference of Multimode Photon Echoes Generated in Spatially Separated Solid-State Atomic Ensembles

High-visibility interference of photon echoes generated in spatially separated solid-state atomic ensembles is demonstrated. The solid-state ensembles were LiNbO(3) waveguides doped with erbium ions absorbing at 1.53 microm. Bright coherent states of light in several temporal modes (up to 3) are stored and retrieved from the optical memories using two-pulse photon echoes. The stored and retrieved optical pulses, when combined at a beam splitter, show almost perfect interference, which demonstrates both phase preserving storage and indistinguishability of photon echoes from separate optical memories. By measuring interference fringes for different storage times, we also show explicitly that the visibility is not limited by atomic decoherence. These results are relevant for novel quantum-repeater architectures with photon-echo based multimode quantum memories.

Quantum Interference of Electromagnetic Fields from Remote Quantum Memories

We observe quantum, Hong-Ou-Mandel, interference of fields produced by two remote atomic memories. High-visibility interference is obtained by utilizing the finite atomic memory time in four-photon delayed coincidence measurements. Interference of fields from remote atomic memories is a crucial element in protocols for scalable entanglement distribution.

Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks.

Highly correlated photons or, accordingly, high-fidelity single-photon states are a prerequisite for closing detection loopholes in experimental tests of local realism and implementing scalable linear optical quantum computation. We demonstrate a parametric down-conversion source exhibiting a conditional detection efficiency of 51% (with corresponding preparation efficiency of 85%) and extraordinarily high detection rates of up to 8.5 x 10(5) coincidences/(s mW). We exploit a novel type-II phase matching configuration in a microstructured waveguide in conjunction with an ultrashort pump.

Generation of a variable linear array of phase-coherent supercontinuum sources

We investigate the coherence properties of a linear array of white-light sources produced in bulk media by ultrashort laser pulses. The array is generated out of the spatial interference pattern between two laser pump pulses, so that the number of supercontinuum sources and their separations can be easily manipulated by varying the geometry of the laser beam interaction. We find that all the secondary white-light sources which arise from the generation of filaments in the optical medium are well phase-locked and are thus able to generate stable and high-visibility multiple-beam interference patterns in the far-field. Observations are compared to the results of a simple model which takes into account a clamping of the peak laser intensity inside the filaments and includes intensity-dependent phase shifts among the different sources.

Photon engineering for quantum information processing

We study distinguishing information in the context of quantum interference involving more than one parametric downconversion (PDC) source and in the context of generating polarization-entangled photon pairs based on PDC. We arrive at specific design criteria for two-photon sources so that when used as part of complex optical systems, such as photon-based quantum information processing schemes, distinguishing information between the photons is eliminated guaranteeing high visibility interference. We propose practical techniques which lead to suitably engineered two-photon states that can be realistically implemented with available technology. Finally, we study an implementation of the nonlinear-sign shift (NS) logic gate with PDC sources and show the effect of distinguishing information on the performance of the gate.

Spatial Interference Effect of Two-Photon in Femtosecond-PulsePumped Spontaneous Parametric Down-Conversion

We have used the transverse correlated properties of the entangledphoton pairs generated in the process of spontaneous parametricdown-conversion, which is pumped by a femtosecond pulse laser, to performYoung's interference experiment. Unlike the case of a continuouswave laser pump, a broadband pulse laser pump can submerge an interferencepattern. In order to obtain a high visibility interference pattern,we used a lens with a tunable focal length and two interferencefilters to eliminate the effects of the broadband pump laser. Itis proven that the process of two-photon direct interferenceis a post-selection process.

High-visibility interference in a Bell-inequality experiment for energy and time.

We report on a two-photon interference experiment proposed by Franson [Phys. Rev. Lett. 62, 2205 (1989)], in which sinusoidal fringes with visibilities greater than 70.7%, such as those predicted by quantum mechanics, violate a Bell inequality. We observe visibility of 80.4\ifmmode\pm\else\textpm\fi{}0.6%, implying a violation of the inequality by 16 standard deviations. Here the elements of reality under consideration are energy and time rather than spin components. Any classical field models describing separate beams in a Franson interferometer are limited to visibilities less than 50%, and hence ruled out as well, without the need for any supplementary assumptions.

Pulsed holographic vibration analysis on high-speed rotating objects: fringe formation, recording techniques, and practical applications

The pulsed laser holographic vibration analysis on high-speed rotating structures presents several difficulties due to the rotational movement of the object between the two laser pulses recording the holographic interferogram. Apart from the vibrational motion, the recorded holographic fringes can be additionally modulated due to the object's rotary motion. Beyond small angles of rotation, a decorrelation of the recorded object waves occurs, preventing the formation of high-visibility interference fringes. To overcome these effects, different holographic recording techniques were used, including an interferometer in which both the reference wave and the holographic recording plate are rotated simultaneously in relation to the object and an interferometer incorporating an image derotator. Conditions for the practical application of these experiments are outlined, and examples of vibrational studies of high-speed rotating components, i.e. , cantilever beams, disks, cooling fans, and radial impellers, are presented. The radial impeller vibration investigation was done on a compressor test facility up to object speeds of more than 13,000 rpm, corresponding to a circumferential speed of approximately 200 m/s.

Novel achromatic distributed feedback dye laser for subpicosecond operation

The optical pump arrangement of distributed feedback dye lasers (DFDLs) having a grating beam splitter is analyzed in detail. The upper limit of the pump spectral bandwidth and beam divergence are given as a function of the length of the excited volume. A novel achromatic pump arrangement is reported which is capable of producing a short, high visibility interference pattern even if a divergent pump source of several nm bandwidth is used. The DFDL pulse duration has an estimated lower limit of 200 fs.