Scheme for the generation of entangled solitons for quantum communication

Abstract

Quantum-communication needs a source of entanglement which is accessible to non-local measurements. It is shown that an entangled pair of light beams may be generated from two bright amplitude squeezed beams. This is applicable to light pulses and to optical solitons in fibres. A possible experimental scheme for stroboscopic quantum teleportation is discussed.     

CdS-GaN heterostructure photodetector with switching and memory

A photodetector having two stable states is fabricated. Switching is effected by a light pulse from an external source. The states are stored until a voltage is supplied to the photodetector. The design and properties of the photodetector are presented. The basic device is an M-i-n-GaN light-emitting diode structure. Pis’ma Zh. Tekh. Fiz. 23, 75–78 (October 26, 1997)     

Fiber-optic gyroscope with suppression of excess noise from the radiation source

A new optical system is proposed and investigated experimentally for a Sagnac fiber interferometer in which the excess noise of the wide-band radiation source is suppressed. A tenfold improvement in the sensitivity of a fiber-optic gyroscope with an erbium/ytterbium fiber superfluorescent light source was achieved experimentally. It is shown that the identity of the polarization characteristics of the interferometer channels plays an important role. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (September 26, 1998)     

Call for Papers

Abstract

An expression is found for the propagation of the radiance function for light in any state of coherence through a concentrator which can be represented by a linear, stationary optical system. For light from a quasi-homogeneous source this expression can be somewhat simplified by an approximation. It is shown that the radiance function is invariant for a large class of optical systems. Finally it is shown that fundamental limitations for the concentration of light follow from the uncertainty principle and the second law of thermodynamics, which apply quite generally. These relations show why quasi-homogeneous light (i.e. light from thermal sources) cannot be concentrated as well as light from some other sources (such as light from a laser).     

1x8 fiber-optic switch based on an innovative waveguide converter and a micro torsion mirror

This paper reports a 1x8 fiber-optic switch based on an innovative waveguide converter and a micro torsion mirror. A compact 9-fiber collimator is implemented with the waveguide converter. With the micro torsion mirror aligned to the 9-fiber collimator, light from the central fiber can be steered to any of the other 8 fibers. The introduction of the waveguide converter enables a smaller and faster micro torsion mirror. The switch shows good performance, insertion loss, nonuniformity, and cross talk is <3.02 dB, <0.4 dB, and <-35 dB respectively. Improvements of performance are expected after further optimization.     

The Optical Signal Generator and Phase-locked Loop Based on a Triangularly Phase-modulated Fibre-optic Gyroscope

Abstract

A novel optical signal generator with purely sinusoidal waveform output has been demonstrated by applying a triangular phase modulation waveform to a fibre-optic gyroscope (FOG). A frequency-multiplied output in the format of an optical signal could be generated. An optical-type electrical phase-locked-loop system based on the intensity-modulated light source and this triangularly phase-modulated FOG has also been demonstrated.     

Transient response of a cold atomic beam in the presence of a far-off resonance light guide

Abstract

A low velocity intense source (LVIS) of cold rubidium atoms is guided along a co-propagating far-off resonance light guide. An 8% enhancement of the guided atomic flux is observed in the steady state. Data are presented for the transient response of the LVIS to the guide beam observing a non-adiabatic kick and a transient 25% enhancement of the guided flux. A characteristic decay time of 0.45 s is recorded for the return to the steady state flux.     

Resonance ring interferometry with incoherent light

A new method of measuring the phase nonreciprocity in a passive ring resonator using a light source of low coherence is described. The method provides effective suppression of noise from the backscattering of light in the ring resonator and insensitivity of the interferometer to excursions of the resonance frequencies of the resonator due to reciprocal effects (e.g., thermal expansion) and also permits modulation and compensation of the phase nonreciprocity by using a device outside the resonator to shift the frequency of the light. One version of a low-coherent resonance ring interferometer is examined, viz., a two-transit asymmetric interferometer with a rotating mirror. Pis’ma Zh. Tekh. Fiz. 24, 24–29 (September 12, 1998)     

Time-domain intermodal interference including higherorder dispersion effects

Abstract

The intermodal interference is analysed theoretically at the output of both a few-mode optical fibre alone and a tandem configuration of a Michelson interferometer with an optical fibre when higher-order intermodal dispersion effects are taken into account. It is revealed theoretically that in a special case of a two-mode optical fibre with a quadratic spectral dependence of the difference of propagation constants, which includes the equalization frequency with zero intermodal group delay, and fibre excitation by a broad-band light source, the time-domain visibility functions differ substantially from those corresponding to fibre excitation by a low-coherence light source. Moreover, measuring a two-mode optical fibre using time-domain and spectral-domain white-light interferometric techniques, some theoretical results are confirmed experimentally.     

Optical Fourier Transforms of Birefringent Fibres

Abstract

A cylindrical birefringent fibre orientated diagonally between two crossed polarizers can be regarded as a single-, double- or multiple-slit source of light, depending on the refractive index of the medium which surrounds the fibre. When normally trans-illuminated by monochromatic light and observed through a polarizing microscope fitted with a condenser-slit diaphragm, the fibre produces specific interference patterns in the exit pupil of the microscope objective. These patterns manifest themselves as optical Fourier transforms. Their properties and possible applications are discussed. The experiments were performed using polymeric textile fibres.     

Radiation characteristics of a dense cesium plasma in the visible range

Calculations are made of the radiation spectrum from a cesium plasma column. It is shown that this plasma may serve as a light source with a high proportion of visible radiation and an almost continuous spectrum. The visible spectrum is formed mainly by bright recombination 6P and 5D continua whose thresholds are shifted in the long-wavelength direction. Pis’ma Zh. Tekh. Fiz. 23, 40–45 (December 26, 1997)     

Off-axis Analysis of the Strehl Ratio Using the Wigner Distribution Function

Abstract

An approach based on the Wigner distribution function (WDF) is used for analysing the Strehl ratio behaviour for varying focus errors and object source locations. A relationship is found between the WDF of the pupil function and the WDF of the light field in the Fresnel region about the image plane. Tolerance criteria to defocus can be specified in terms of the ‘amplitude’ of the parageometrical rays that intersect a tilted optical axis defined by the locations of the object and image points.     

Three-dimensional Transfer Function Analysis of a Confocal Fluorescence Microscope With a Finite-sized Source and Detector

Abstract

The influence of a finite source and detector on the three-dimensional imaging of an incident light fluorescent confocal scanning optical microscope is investigated on the basis of its three-dimensional optical-transfer function. It is shown that the optical resolution in such set-ups remains the same as with punctiform pinholes if the source and the detecting pinhole radii are both smaller than the size of the Airy disc.     

White-light fiber-optic intermode interferometer

An interferometric system with a low-coherence light source and two multimode fiber-optic light guides operating in an intermode interference regime is considered theoretically. It is shown that the employment of fiber-optic intermode interferometers significantly expands the range of permissible mismatch between the lengths of the reference and signal interferometers. Mismatch up to a few centimeters is possible for light-emitting diodes (LED’s). The use of multimode light guides and intermode interference facilitates the construction of systems with fibers of great length and matching to an optical source. Pis’ma Zh. Tekh. Fiz. 25, 44–50 (June 26, 1999)     

Coherence Length of a Gaussian-Schell Beam and Atmospheric Turbulence

Abstract

The theoretical relationship between the coherence length and phase-front randomness is analysed using a Gaussian-Schell source and beam model for light propagating through a turbulent atmosphere. Computer results are given which show that partially coherent sources are less influenced by atmospheric turbulence than are coherent sources.     

A Self-aligning Interferometer Suitable for White or Monochromatic Light Consisting Solely of a Mirror and a Reflection Grating

Abstract

A simple interferometer constructed from a mirror and a reflection grating is described. This interferometer can operate with monochromatic or wideband light, and versions of it may be constructed to suit radiations other than light, such as sound waves or matter waves. A most unusual feature of the interferometer is its high tolerance to large misalignments of its optical elements.     

PKUNIFTY: A neutron imaging facility based on an RFQ accelerator

A neutron imaging facility, PKUNIFTY, based on a radio frequency quadrupole (RFQ) accelerator-driven compact neutron source, presently under construction at the Peking University, is described. It consists of a deuteron linear accelerator, a neutron target-moderator-reflector assembly, and a thermal neutron imaging system. Neutrons are generated via the deuteron-beryllium reaction with an expected fast-neutron yield of 3×10¹² n/s. The thermal neutron flux on the imaging plane is 5×10⁵ n/cm²/s at a nominal L/D ratio of 50, and the L/D ratio can be selectable over a range of 25-200. The corresponding n/γ ratio is close to or higher than 1×10¹⁰ n/cm²/Sv. The field of view is 20 cm×20 cm at 2 m downstream of the collimator entrance aperture where the thermal neutron flux uniformity is better than 7%. The effective Cd ratio can be tuned by using a light chopper and neutron time-of-flight technique without excessive sacrifice of the thermal neutron flux.     

Achromatic fan-out diffractive system for white-light free-space optical interconnects

Abstract

A simple and versatile white-light fan-out diffractive system based on the achromatization of the fractional Talbot effect is proposed. This achromatic configuration is able to interconnect a single polychromatic point source with a 2-D array of optoelectronic microdevices with low residual chromatic aberration even for white light. The whole broadband beamsplitter system is formed by two simple diffractive optical elements, a periodic diffractive lenslet array and a diffractive lens, that are made with a direct laser writing technique giving high light efficiency. The focal amplitude distribution corresponding to the lenslet array produces, by free-space propagation, self-replicas with different density of light points. These patterns, in conjunction with the achromatization process carried out by the additional diffractive lens, are, in short, the key to achieving a set of undistorted white-light spots at the output plane with high uniformity and variable separation between them. Experimental results are also shown.     

Faraday compensator of reciprocal optical anisotropy utilizing a polarization ring interferometer

It is shown that a polarization ring interferometer containing a Faraday cell can be used to compensate the reciprocal anisotropy in round-trip optical circuits. It is established theoretically and experimentally that, unlike the case of conventional Faraday mirrors, the quality of the restoration of the polarization in a compensator based on a polarization ring interferometer is practically independent of the Faraday rotation angle. A deviation of the Faraday rotation angle from 45° leads only to an additional power loss. The novel compensators can be used in fiber-optic circuits with a wideband light source or with several sources having different wavelengths. Pis’ma Zh. Tekh. Fiz. 25, 57–63 (May 26, 1999)     

基于变曲率透镜的四纤光纤准直器的设计

为实现一种新型的ROADM,设计了基于四纤光纤头和变曲率球面透镜的四纤光纤准直器.变曲率球面透镜包括斜柱体和变曲率球体两部分;4根尾纤在同一平面内等距排列,各尾纤出射光对应曲率不同的球面,可保证准直器出射光的出射角度满足应用要求.各尾纤出射面位于透镜的物方焦点处,从而使从光纤出射的光束获得准直.利用矩阵光学理论,设计出...