Showing papers on "Mach–Zehnder interferometer published in 1992"

Practical quantum cryptography based on two-photon interferometry.

Abstract: We propose an experimental realization of cryptographic-key-sharing scheme exploiting quantum correlations between pair photons. Our experimental setup consists of an external source of correlated photon pairs which propagate to two widely separated unbalanced Mach-Zehnder interferometers. The probability of detection of photon pairs in any two outputs of the interferometers can be fully modulated by phase plates in either interferometer.

High-sensitivity magnetometer based on index-enhanced media

Abstract: The large dispersion of a phase-coherent medium, at a point of vanishing absorption, is applied to interferometric measurements of detuning between atomic and radiation frequencies. It is shown that, under certain conditions, the interferometer quantum-limited operation is determined by vacuum-fluctuation shot noise while the noise introduced by the interaction of the probe field with the phase-coherent atoms can be made negligible. As a possible application, an optical magnetometer is analyzed whose sensitivity is shown to be potentially superior to the present state-of-the-art devices.

Fundamental phase noise limit in optical fibres due to temperature fluctuations

Abstract: Theoretical results are presented for the power and RMS amplitude spectra of phase noise in optical fibres due to thermodynamic temperature fluctuations, including the effects of finite fibre outside diameter and retardation. For a fibre optic Mach–Zehnder interferometer with 20m of 125μm diameter fibre in each arm, the (0–25) kHz phase noise is (5.1–1.3) × 10−7rad RMS/√(Hz) at 1300nm.

A gas sensor based on an integrated optical Mach-Zehnder interferometer

Abstract: In this paper we demonstrate a sensor system for measuring gaseous compounds using an integrated optical Mach-Zehnder interferometer (IO-MZ chip). One of the surface waveguide arms of the IO device is covered with a polysiloxane layer, sensitive to organic solvents. The refractive index of the polymer layer changes continuously when exposed to the vapours of such solvents. The influence on the evanescent field of the guided mode causes a change in the optical pathlength in the covered arm. Incoupled light of a semiconductor laser diode results in an interference pattern at the output of the IO-MZ chip. The phase shift of the signal is dependent on the gas concentration and the solvent type. We have determined the values for some hydrocarbons, chlorohydrocarbons and aromatic compounds. The extremely short response time of the system allows it to be used like a gas chromatographic detector. The applicationn of Maxwell's equations for the propagation of light in waveguides offers a simulation of the interference signals. By this means, the experimental signal obtained can be correlated to changes in refractive index of the polymer layer. The dependence of the interference patterns on wavelength is explained. White light interference is obtained by use of a xenon lamp.

The magnesium ramsey interferometer: Applications and prospects

Abstract: In this paper it will be shown that an atom interferometer, based on the coherent splitting of the atomic wavefunction by four travelling waves (Ramsey interferometer), may be explained by a purely mechanical interpretation. As our first application of this Ramsey interferometer we have measured the phase shifts respectively optical length changes in a magnesium atomic beam caused by the acceleration of the partial atomic wave in one arm of the interferometer. This acceleration was achieved by the dipole force exerted by an off-resonant crossing laser beam which interacted with the ground state part of the wavefunction only. Further applications of this interferometer and improvements due to laser cooling will be discussed.

Ultrafast all-optical switching in GaAlAs integrated interferometer in 1.55 mu m spectral region

Abstract: The first observation is reported of ultrafast all-optical switching in an integrated asymmetric Mach-Zehnder inter-ferometer, using the nonresonant nonlinearity in Ga0.82Al0.18As below half the bandgap. A relative switching fraction of more than 80% has been achieved using 330 fs pulses at around 1.55 μm from a coupled-cavity mode-locked colour centre laser.

A wide-band Ti:LiNbO/sub 3/ optical modulator with a conventional coplanar waveguide type electrode

Abstract: The design and fabrication parameters needed to obtain a low-loss coplanar waveguide structure were determined. A large optical bandwidth (more than 23 GHz) and low driving voltage (5 V) Ti:LiNbO/sub 3/ Mach-Zehnder interferometer type optical modulator at a wavelength of 1.52 mu m, using a conventional and thick coplanar waveguide type electrode structure. >

Optical frequency discriminator using two mach-zehnder interferometer arrangement

Abstract: An optical frequency discriminator having enhanced linearity is provided, which discriminator may be utilized in FM communications systems or in other applications. The discriminator has two interferometers with the optical path length difference for the first interferometer being ΔL and for the second interferometer being mΔL where m>1. The optical FM signal is applied in parallel to both optical interferometers with approximately m 3 times as much of the signal being applied to the first interferometer as to the second interferometer. Each interferometer has an output signal versus frequency characteristic with a substantially linear region about a center frequency, which center frequency is approximately equal to the center frequency of the input optical signal. The outputs from the interferometers are combined in a manner such as the difference in absolute value of the linear region characteristic slopes is obtained, the resulting output being a discriminated output which is substantially linear over an enhanced FM range.

Cutting optical fibers to equal lengths for broadband stellar interferometry.

Abstract: Six fibers of length 1.5 m are cut with a mean difference in length of 10.8 μm. The pigtailed ends of the couplers are also cut to this accuracy.

Achromatic self-referencing interferometer

Abstract: A self-referencing Mach-Zehnder interferometer for accurately measuring laser wavefronts over a broad wavelength range (for example, 600 nm to 900 nm). The apparatus directs a reference portion of an input beam to a reference arm and a measurement portion of the input beam to a measurement arm, recombines the output beams from the reference and measurement arms, and registers the resulting interference pattern ("first" interferogram) at a first detector. Optionally, subportions of the measurement portion are diverted to second and third detectors, which respectively register intensity and interferogram signals which can be processed to reduce the first interferogram's sensitivity to input noise. The reference arm includes a spatial filter producing a high quality spherical beam from the reference portion, a tilted wedge plate compensating for off-axis aberrations in the spatial filter output, and mirror collimating the radiation transmitted through the tilted wedge plate. The apparatus includes a thermally and mechanically stable baseplate which supports all reference arm optics, or at least the spatial filter, tilted wedge plate, and the collimator. The tilted wedge plate is mounted adjustably with respect to the spatial filter and collimator, so that it can be maintained in an orientation in which it does not introduce significant wave front errors into the beam propagating through the reference arm. The apparatus is polarization insensitive and has an equal path length configuration enabling measurement of radiation from broadband as well as closely spaced laser line sources.

Thin-film thermo-optic Ge(x)Si(1-x) Mach-Zehnder interferometer.

Abstract: We report on the design and fabrication of Ge(x)Si(1-x) Mach-Zehnder interferometers based on the thermo-optic effect. The modulators exhibit 8 dB of extinction with a pi-phase-shift power requirement, P(pi), of 245 mW. The 3-dB bandwidth of these thermo-optic devices is 88 kHz. Finally, we present calculations indicating the effect of various parameters on the modulation of the Mach-Zehnder interferometer.

Mach-zehnder optical modulator with monitoring function of output light

Abstract: A Mach-Zehnder optical modulator with an output light monitoring function whereby emitted light from the modulator is monitored for controlling a DC bias voltage applied between a first and a second electrode provided on a first and a second branch optical waveguide. The end face of the waveguide substrate on the output side is obliquely formed and an optical waveguide is provided on the waveguide substrate for taking out reflected light from the output end face as monitor light. A photodetector for detecting the monitor light is attached to the side face of the waveguide substrate. By such arrangement, the length of the waveguide substrate can be made shorter than that in the prior art. As an alternative, such an arrangement may be made that a double refraction crystal for separating monitor light is attached to the end face on the output side of the waveguide substrate and a prism for correcting optical path is attached to the double refraction crystal.

Dual wavelength fibre interferometer with wavelength selection via fibre Bragg grating elements

Abstract: The use of intra-core fibre gratings to provide the selection of two stable, closely spaced wavelength-components at the output of a fibre interferometer is reported. An unambiguous sensing range in the optical path difference of an interferometer of +or-0.49 mm is demonstrated using two gratings spaced by 2.5 nm. >

Fabrication of integrated-optic polarization controller using Z-propagating Ti-LiNbO/sub 3/ waveguides

Abstract: The fabrication and performance of a LiNbO/sub 3/-based waveguide-type polarization controller with a Ti-indiffused waveguide along the z axis is reported. The device, designed for use at 1.55- mu m wavelength and consisting of a TE/TM mode converter and a phase shifter in series, exhibited the half-wave voltages of 25 and 20 V for the TE/TM mode converter and the phase shifter, respectively. The modal birefringence and the behavior of the respective elements under applied fields are described in some detail. In addition, a preliminary performance test of the device was conducted by placing the device in a Mach-Zehnder interferometer. >

Integrated optical device adjustable as a polarization splitter by means of a Mach-Zehnder interferometer

Abstract: The invention relates to an integrated optical device which comprises an adjustable Mach-Zehnder interferometer. The waveguide structure of the device is fabricated on the basis of polable unpoled material, the material in one (2) of the branches (2, 3) of the MZ interferometer being poled in a certain area (7). In the case of maximum poling in advance, the degree of poling of the poled material can subsequently be adjusted under conditions of accelerated thermal relaxation. Advantage: the device can first be fabricated, as far as its structure is concerned, using fabrication techniques which are standard for the selected material without additional attention to correct sizing, after which the interferometer section can then be adjusted in a simple manner to the optical pathlength differences required for the specific function of the device. As an example, a passive polarisation splitter is described.

New integrated optical ring resonator in glass

Abstract: A new integrated optical ring resonator using a four-port nonsymmetric Mach-Zehnder interferometer as an input/output coupler is demonstrated. The device is fabricated in glass substrate by the double-ion-exchange process. A finesse of 5 at λ = 1.523 μm is measured. Propagation losses of 0.17 dB/cm in the ring waveguide are estimated.

Multimode quantum analysis of an interferometer with moving mirrors.

Abstract: A multimode quantum analysis of noise reduction in interferometric measurements is presented. A unitary transformation relating the output modes with the input ones for a Michelson interferometer with moving mirrors is given. The evaluation of the noise spectrum shows that with a proper choice of the input states, the sensitivity of the interferometer can be pushed beyond the standard quantum limit. The results are compared with a semiclassical analysis.

Quantum Limits to All-Optical Switching in the Nonlinear Mach-Zehnder Interferometer

Abstract: A Mach–Zehnder interferometer with a nonlinear medium in each arm is treated as an all-optical switching device. In a classical treatment, the interferometer can, in principle, operate as an ideal switch, but quantization of the electromagnetic fields limits the switching capability. In this treatment we illustrate the fundamental quantum limits that apply to switching in all-optical devices by studying the nonlinear Mach–Zehnder interferometer. In particular the input states are assumed to be coherent states and the reduction in the quality of the switching device is discussed.

Interferometric quantum well modulators with gain

Abstract: Details on the design, fabrication and properties of the first interferometric intensity modulators with monolithically integrated optical gain are presented. These guided-wave devices make use of two sets of InP-based quantum well heterostructures that are contained in a single base wafer and individually designed for enhanced electrorefraction and amplification at 1.55 mu m. The unique quantum well electrooptic properties as well as the fabrication techniques and waveguide design issues that determine final device performance are discussed. >

Waveguide optical pick-up head using mach-zehnder interferometer wavefront sensor apparatus and method

Abstract: An integrated optic head contains a planar and a channel waveguide, a waveguide condensing lens, and integrated waveguide photodetectors. The main portion of the beam returning from the disk is focused by the lens onto an integrated waveguide photodetector to provide the data signal. A smaller portion of the beam is sampled by channel waveguide Mach-Zehnder (MZ) interferometers that measure the beam wavefront curvature to provide the focus error signal (FES). Additional channel waveguides provide reference signals for the interferometers and provide a means of measuring the tracking error signal (TES). The TES method includes subtracting light detected by one channel waveguide detector from light detected by another, which difference is the tracking error. The FES method includes obtaining the difference in the ratios of the light emanating from two interferometers divided by the light emanating from their respective channel waveguides, which difference in ratios is the focus error.

Four‐port guided‐wave nonsymmetric Mach–Zehnder interferometer

Abstract: A four‐port guided‐wave nonsymmetric Mach–Zehnder interferometer based on two hybrid optical couplers is proposed. A potential application of the device is a 0.98 μm/1.55 μm wavelength multiplexer in connection with an optical ring resonator. The proposed device is designed by using the effective indices of the guided modes in a silver ion‐exchanged waveguide. The device is fabricated in glass substrate by a two‐step ion‐exchange process, and it is characterized using a continuous source as well as lasers at λ=1.06, 1.3, and 1.523 μm.

Polarisation state insensitive optical discriminator

Abstract: A polarization state insensitive optical discriminator is provided by a Mach Zehnder interferometer (21, 22, 23, 24) constructed in polarization preserving optical fibre, and two optical fibre polarization beam splitters (20, 25). Each polarization beam splitter is interconnected with the interferometer in such a way that its two orthogonally polarized outputs are launched to opposite ends of the interferometer with the same state of polarization.

Proton exchanged imbalanced Ti:LiNbO3 Mach‐Zehnder modulator

Abstract: We describe the fabrication process of a LiNbO3 integrated Mach‐Zehnder interferometer featuring a large path‐imbalance between the arms. This path‐imbalance is created by the proton exchange located on one arm. The proton exchange increases the extraordinary refractive index ne of lithium niobate and modifies the effective index of the guided mode. Path‐differences of 80 μm per mm of proton exchange length are obtained with the fabrication process reported here.

InGaAs/InAlAs MQW Mach-Zehnder optical modulator for 10-Gbit/s long-haul transmission systems

Abstract: Waveform deterioration due to frequency chirping in a modulated light source limits the maximum transmission distance in multigigabit optical transmission systems. Semiconductor MWQ external modulators are expected to overcome the problems, because of their potential for low chirp and high-speed modulation and for optoelectronic integration.1,2 The Mach-Zehnder type (MZ) modulator has been proposed as one of the most promising, since it achieves zero or negative chirping which maximizes the transmission distance.3 Recently, a highly efficient and small size MQW MZ modulator was reported,4 but its driving voltage was still too high (~10 V with only ~7 dB of extinction ratio) for practical use. Here, we demonstrate a low driving voltage InGaAs/InALAs MQW MZ modulator with high extinction ratio (>15 dB), for 10-Gbit/s long-haul transmission systems operating in the 1.55-μm) wavelength region.

Coherent coupling of radiation modes in Mach-Zehnder electrooptic modulators

Abstract: The effects of the radiation modes in Mach-Zehnder GaAs electrooptic modulators are studied using the standard beam propagation method (BPM). The radiation mode contribution to the energy transfer in the passive structure is studied as well as the performances of the active device under modulation. For compact weakly guiding structures, a good geometrical design that takes into account the propagation of the radiation modes is not only effective in loss reduction but also important for improving the design of the active structure. A 20% change of the modulator bias voltage is predicted with a shortening of the interaction length from 5 to 4.6 mm. This result is better understood when one considers the coherent coupling of the radiation modes in the structure. >

Bispectral magnitude and phase recovery using a wide bandwidth acousto-optic processor.

Abstract: A hybrid optical–digital processor has been developed that computes both the magnitude and phase of the bispectrum for wide bandwidth (10 MHz to 1 GHz) rf signals. The overall optical architecture is that of a modified Mach–Zehnder interferometer that contains three acousto-optic modulators and appropriate transforming lenses. The intensity distribution in the output plane of the interferometer contains an interference term that represents the real part of the bispectrum multiplied by a spatial carrier (the interference fringes). To isolate the bispectrum information, the output image is digitized and digitally filtered. The imaginary part of the bispectrum is obtained by Hilbert transforming the real part, and then computing the bispectrum magnitude and phase. The processor is tested with four different combinations of rf test signals. Each signal has a bandwidth of either 6 or 12 MHz. Test results that illustrate the performance of the processor in the recovery of magnitude and phase information for the bispectrum of quadratically related signals are presented.

New Development of Mach-Zehnder Interferometer for Laser Frequency Selection and Tuning

Abstract: A new design of Mach-Zehnder interferometer (MZI), efficiently suitable for stable single mode operation and laser cavity frequency tuning, is developed. This development eliminates the using of any additional etalons. The design is compact, broadband, low loss, easily adjustable in the laser cavity, and has a free spectral range (FSR) of 42·5 GHz. This design permits different uses in the field of laser spectroscopy and laser applications.