Showing papers on "Mach–Zehnder interferometer published in 1999"

Remote opto-chemical sensing with extreme sensitivity: design, fabrication and performance of a pigtailed integrated optical phase-modulated Mach-Zehnder interferometer system

Abstract: This paper describes the design, fabrication and testing of a pigtailed integrated optical (IO) phase-modulated Mach–Zehnder interferometer (MZI) including both the optical chip and the electronics. The optical chip is realised in SiON technology. The IO components (the sensing function, the straight waveguiding channels, the phase modulator, the polariser, the splitter, the combiner and the fibre-to-chip connection unit) are individually optimised and interconnected by using transversal adiabatic tapers. To obtain a high waveguide evanescent field sensitivity, the sensor is designed for — but not limited to — a wavelength of 632.8 nm. The integrated MZI is actively phase-modulated by virtue of the electro-optic effect of the incorporated material zinc oxide (ZnO). The electro-optical voltage–length product Vπ is 16 V cm at frequencies above 10 Hz. The polariser is a distributed function, that effectively filters TM-polarised light (TE/TM polarising ratio >30 dB). The fibre pigtail, affording remote optical sensing, is based on a cheap, easy-to-use fibre-to-chip connection with a typical coupling efficiency of 50%, while the device throughput (“insertion loss”) is −20 dB. The drive- and demodulation electronics enable a phase resolution 5×10−5×2π, corresponding to a refractive index resolution of 2×10−8. The sensing system as has been realised up to now shows a phase resolution of 1×10−4×2π, its long-term stability (hours) being ≤3×10−4×2π. This corresponds to a refractive index resolution of 5×10−8, and a long-term stability of 10−7.

Optimal interferometer designs for optical coherence tomography

Abstract: We introduce a family of power-conserving fiber-optic interferometer designs for low-coherence reflectometry that use optical circulators, unbalanced couplers, and (or) balanced heterodyne detection. Simple design equations for optimization of the signal-to-noise ratio of the interferometers are expressed in terms of relevant signal and noise sources and measurable system parameters. We use the equations to evaluate the expected performance of the new configurations compared with that of the standard Michelson interferometer that is commonly used in optical coherence tomography (OCT) systems. The analysis indicates that improved sensitivity is expected for all the new interferometer designs, compared with the sensitivity of the standard OCT interferometer, under high-speed imaging conditions.

Generation of optical macroscopic quantum superposition states via state reduction with a mach-zehnder interferometer containing a kerr medium

Abstract: A method for producing macroscopic quantum superposition states (generally known as Schr\"odinger cat) states for optical fields is presented. The proposed method involves two modes of the field interacting dispersively in a Kerr medium where one of the modes is an arm of a Mach-Zehnder interferometer and the other mode is external to it. If the external mode initially contains a macroscopic quantum state, such as a coherent state, and the vacuum and a single photon state are the inputs to the interferometer, the external field state becomes entangled with the number states associated with the two paths of the interferometer. Selective measurement at the output ports of the interferometer project the external mode into the desired cat states. It is pointed out that the method can also be used to generate cat states out of multimode states initially containing correlations.

Broad-band linearization of a Mach-Zehnder electrooptic modulator

Abstract: Analog optical-link dynamic range in excess of 75 dB in a 1-MHz band has been achieved using specially designed electrooptic modulators that minimize one or more orders of harmonic and intermodulation distortion. To date, however, such "linearized" modulators have only enabled improved link dynamic ranges at frequencies below 1 GHz. Additionally, linearization across more than an octave bandwidth has required precise balancing of the signal voltage levels on multiple electrodes in a custom modulator, which represents a significant implementation challenge. In this paper, a link linearization technique that uses a standard Mach-Zehnder lithium-niobate modulator with only one RF and one dc-bias electrode to achieve broad-band linearization is discussed, resulting in a dynamic range of 74 dB in 1 MHz across greater than an octave bandwidth (800-2500 MHz). Instead of balancing the voltages on two RF electrodes, the modulator in this new link architecture simultaneously modulates optical carriers at two wavelengths, and it is the ratio of these optical carrier powers that is adjusted for optimum distortion canceling. The paper concludes by describing a second analogous link architecture in which it is the ratio of optical power at two modulated polarizations that is adjusted in order to achieve broad-band linearization.

Passive, light intensity-independent interferometric method for fibre Bragg grating interrogation

Abstract: The authors describe a passive technique for sensing the strain-induced wavelength shift of a fibre Bragg grating (FBG) using a Mach-Zehnder interferometer that utilises a 3/spl times/3 coupler. Laboratory data show that a resolution of /spl sim/10 n/spl epsiv///spl radic/(Hz) RMS is achievable with inherent insensitivity to source intensity variations.

Analysis of generalized Mach-Zehnder interferometers for variable-ratio power splitting and optimized switching

Abstract: The nonideal integrated optical N/spl times/N generalized Mach-Zehnder interferometer (GMZI) employing multimode interference (MMI) couplers is analyzed using transfer matrix techniques. Deviations in the phase relations and the power splitting ratio of the MMI couplers are included in the theory, along with the effects of phase errors in the interferometer arms. The predictions of the theory are compared to the response of a 4/spl times/4 GMZI which has been fabricated. The device is operated as both a variable-ratio power splitter and a switch by compensating for the phase errors in the interferometer arms, but the performance is ultimately limited by the nonideal imaging in the MMI couplers. The practicality of these applications is investigated by performing a tolerance analysis for the operation of 1/spl times/N power splitters and switches for N up to 10.

Imbalanced Mach-Zehnder interferometer integrated in micromachined silicon substrate for pressure sensor

Abstract: This paper describes an interferometric pressure sensor designed to work as a remote sensor in a coherence modulation scheme, allowing a linear phase read-out of the signal. The sensor is realized from a silicon nitride waveguide Mach-Zehnder interferometer integrated on a (100) silicon substrate, and includes a micromachined membrane below a branch of the Mach-Zehnder. The characterization is achieved by a spectral analysis and shows a nonlinear relationship between the static pressure applied to the membrane and the phase variation thus obtained. The analytical description takes into account the induced deflection of the membrane and the resulting mechanical elongation of the waveguide.

Push-pull poled polymer Mach-Zehnder modulators with a single microstrip line electrode

Abstract: A push-pull structure has been realized for integrated Mach-Zehnder modulators based on a thermoset electrooptic polymer. The two modulator waveguide arms were poled in the opposite directions and covered by a single microstrip line electrode. This device structure can reduce the half-wave voltage by 50% without compromising wide-band frequency response. Efficient poling was achieved by using a compatible cladding material to lower the poling voltage, and by using a top cover piece and an inert gas to suppress air breakdown between the poling electrodes. Our fabricated devices exhibited the predicted 50% half-wave voltage reduction compared with non-push-pull devices fabricated on the same chip.

Analysis of polarization independent Mach-Zehnder-type integrated optical isolator

Abstract: This paper proposes, for the first time, an integrated optical isolator independent of light polarization. A Mach-Zehnder interferometer (MZI) with two nonreciprocal phase shifters, one for transverse electric (TE) modes and another one for transverse magnetic (TM) modes can be adjusted so that it blocks the fundamental modes of the waveguides constituting the interferometer propagating in one direction and is transparent for the modes propagating in the opposite direction. If the interferometer branch waveguides are in single mode regime, the performance of the device will not depend on the polarization of incoming light. The nonreciprocal phase shifters can be realized on structures with magnetization tangential to the propagation direction. Three geometries of nonreciprocal phase shifters are discussed and tolerances are estimated.

Broadband linearization of a Mach-Zehnder electro-optic modulator

Abstract: A new analog fiber-optic link architecture uses a standard Mach-Zehnder electro-optic modulator in lithium niobate with a single RF traveling-wave electrode to achieve linearization across greater than an octave bandwidth. A broadband (800-2500 MHz) link with this new architecture has a measured dynamic range of 74 dB (in an instantaneous bandwidth of 1 MHz).

All-optical Mach-Zehnder interferometer wavelength converters and switches with integrated data- and control-signal separation scheme

Abstract: All-optical Mach-Zehnder interferometer (MZI) wavelength converters and switches with monolithically integrated data- and control-signal separation schemes are reported. Two schemes to separate the data from the strong control signals are discussed. A first dual-order mode configuration uses modes of different symmetry for the data and control signals. A second configuration uses additional MZIs to separate the two signals. The control-signal separation permits to operate the devices with copropagating data and control signal without distortion of the control signal in the data-signal output. Copropagative operation allows for shorter switching windows compared to the counterpropagative operation. Further, this concept enables cascading of several devices since the control signal is filtered out and does not disturb the signal processing in a next cascade of devices. The all-optical switches are characterized under static and dynamic 10 GHz conditions.

A novel fiber-optic sensor array based on the Sagnac interferometer

Abstract: We propose a novel design for a fiber-optic acoustic sensor array that is based on the Sagnac interferometer. The performance of this Sagnac sensor array (SSA) design is analyzed and compared to acoustic sensor arrays based on the Mach-Zehnder (MZ) interferometer. It is found that the SSA exhibits several decisive advantages, including a stable bias point, a reduced conversion of source phase noise into intensity noise, and a frequency response that matches the ambient ocean noise. It is also shown that the SSA can be easily designed to have a much larger dynamic range than an MZ-based sensor array. Potential noise sources are analyzed and shown to be manageable. A means for eliminating polarization-induced signal fading is presented. The applicability of time-division, frequency-division, and code-division multiplexing schemes for the proposed design is presented.

Low-loss planar lightwave circuit OADM with high isolation and no polarization dependence

Abstract: A passive optical add-drop multiplexer with 1 dB of insertion loss and 36 dB of isolation is fabricated by writing Bragg gratings in a waveguide Mach-Zehnder interferometer using ArF excimer laser light. The spectral properties and bit-error-rate performance of the device are fully characterized using polarized light.

Design optimization of all-active Mach-Zehnder wavelength converters

Abstract: An integrated all-active Mach-Zehnder wavelength converter, optimized for 10-Gb/s counterpropagative operation, is described. The various active sections of the device were separately designed, taking into account their required functions as well as the constraints imposed by the all-active integration. The resulting optimizations are discussed, and the predicted performance parameters confirmed by experimental results.

Noise properties and phase resolution of interferometer systems interrogated by narrowband fiber ASE sources

Abstract: We present the results of a detailed theoretical and experimental study of the noise properties of various interferometer systems interrogated using narrowband spontaneous emission. The filtering effect of the interferometer is shown to introduce periodic structure in the optical noise spectrum with a period, level, and modulation depth that depends on the exact interferometer configuration and implementation, as well as the source linewidth and spectral shape. Our theoretical analysis, based on the assumption of a Gaussian random process model for the inherent source noise is in good agreement with our experimental results. Finally, using a dual Mach-Zehnder interferometer incorporating a frequency shifter, we show that minimum phase sensitivities of a few tens of /spl mu/rad//spl radic/Hz can be achieved for practical values of length mismatch by optimization of the source linewidth, heterodyne frequency, and interferometer birefringence. We believe the approach to be suitable for a broad range of sensing applications.

Effect of the detector efficiency on the phase sensitivity in a mach-zehnder interferometer

Abstract: The effect of quantum efficiencies of detectors on the phase sensitivity of a Mach-Zehnder is analyzed for the Fock state input. The phase uncertainty of two different interference experiments, the second order and the fourth order, are compared with two practical detectors with less than unit quantum efficiencies. It is found out that in the second-order interference experiment we cannot beat the classical limit in the phase sensitivity, even with ideal detectors. We show that almost ideal detectors are required to get the Heisenberg limit in the phase sensitivity of the fourth-order interference for two Fock state light inputs. There exists an optimum angle given by the efficiency of the detectors.

Guided-wave acoustooptic interaction with phase modulation in a ZnO thin-film transducer on an Si-based integrated Mach-Zehnder interferometer

Abstract: This paper presents the design and the realization of a novel integrated Mach-Zehnder interferometer (MZI) with heterodyne scheme. Well-controlled machining as well as ZnO thin-film transducer integration on the same Si substrate permits to transform an optically passive device to an active device with sinusoidal phase modulation. Theoretical and experimental results are presented, demonstrating that an efficient sensor can be designed and fabricated.

40-Gb/s OTDM to 4 x 10 Gb/s WDM conversion in monolithic InP Mach-Zehnder interferometer module

Abstract: Transformation of high bit-rate optical time-domain multiplexed (OTDM) signals into a multitude of lower bit-rate wavelength-division-multiplexed (WDM) channels is demonstrated by means of a single monolithically integrated indium phosphide Mach-Zehnder interferometer with semiconductor optical amplifiers in its arms. Full demultiplexing of 10-Gb/s OTDM signals into 4/spl times/10-Gb/s WDM channels is demonstrated. Bit-error-rate penalties are below 1.5 dB for polarization independent signal conversion throughout the 1.55-/spl mu/m wavelength range.

Wavelength-Tunable Laser-Diode Interferometer

Abstract: Laser diodes (LDs) have been applied to a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed. A two-wavelength laser-diode interferometer is demonstrated with current control of dual LDs in opposite directions. A synthetic wavelength makes it possible to extend the range of interferometric measurements. The wavelength is controlled by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. The optical output is demodulated with a phase-extraction algorithm. Systematic phase errors caused by the LD-power variation and by the difference between the beat frequency and ramp frequency are analyzed. A feedback interferometer with electronics is used to eliminate the phase error by locking the interferometer on a preset phase. Typical experimental results are shown.

Observation of optical isolation based on nonreciprocal phase shift in a Mach–Zehnder interferometer

Abstract: Measurements up to 45° nonreciprocal phase shift using the transverse magneto-optical effect have been made in a hybrid Mach–Zehnder waveguide/fiber interferometer. BiLu-IG waveguides of various thicknesses and lengths have been used to study the length and thickness dependence of the effect at λ=1.55 μm. This interferometric scheme is also employed to observe optical isolation; an extinction ratio of 11 dB is obtained for the 45° nonreciprocal phase shift, in agreement with theoretical predictions.

All-optical 2R regeneration at 40 Gbit/s in an SOA-based Mach-Zehnder interferometer

Abstract: All-optical 2R regeneration in an SOA-based Mach-Zehnder interferometer is demonstrated at 40 Gbit/s The regenerative capabilities combined with an input power dynamic range of 16 dB demonstrate the feasibility of this technique at very high bit rates

Modified sagnac/mach–zehnder interferometer for distributed disturbance sensing

Abstract: We propose an alternative configuration for an interferometric distributed fiber optic sensor. The sensor uses a combination of Mach–Zehnder and Sagnac interferometers sharing the same fiber. The output of the Sagnac interferometer is a function of the product of the position where the disturbance was applied and the magnitude of the disturbance. The output of the Mach–Zehnder interferometer is a function of the magnitude of the disturbance only. The position and magnitude of a disturbance applied to the sensing fiber can thus be obtained from these two signals. Results obtained with a 200 m distributed fiber sensor are discussed. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 34–36, 1999.

Robust one-beam interferometer with phase-delay control.

Abstract: A robust one-beam interferometer with external phase-delay control is described. The device resembles a Mach-Zehnder interferometer in which the two arms are together in one collimated beam. However, the proposed device is not an amplitude-division interferometer but a wave-front division one. The phase-delay control occurs at the interferometer output with the help of two polarizing beam splitters, a quarter-wave plate, a Faraday rotator, and a polarizer. An additional phase delay is introduced by application of an electrical current to the Faraday rotator or by rotation of the polarizer (the latter is of topological origin), which permits the use of techniques of phase-stepping interferometry.

Fault detection system for an amplified optical transmission system

Abstract: A fault detection circuit and method of detecting catastrophic faults for example from a total line outage due to a transmission waveguide being inadvertently cut, includes tapping a sample of the amplified transmission multichannel signal light for analysis. The tapped light is then fed to a periodic filter such as a Mach Zehnder interferometer or a Fabry Perot etalon having a free spectral range and, phase at one output that coincides with the channel central wavelengths of the transmission system. Another output of the periodic filter provides an output response that is phase shifted by 180 degrees. Two output signals from the two output two output signals are then compared, in one embodiment by using a photodiode bridge. When one output of the periodic filter has a substantially different signal energy than the other, it is assumed that no faults occur. Conversely when the two outputs are substantially similar, it is assumed that a catastrophic fault has occurred.

Fringe contrast in three grating Mach-Zehnder atomic interferometers

Abstract: Several three-grating Mach-Zehnder atomic interferometers have been built and operated in recent years but no general theory of the contrast of the fringes produced by these apparatus is available. The purpose of this paper is to develop this theory, based on the Fresnel-Kirchoff approximate treatment of diffraction. Such a theory has been developed by Turchette et al. [JOSA B 9, 1601 (1992)] but because the necessary multiple integrals were evaluated in a purely numerical way, this treatment was not fully general. We show here how to reduce the computation by analytic means and we are thus able to calculate the contrast with a modest numerical effort. Moreover, we get a simple insight of the contrast reduction related to several defects of a real apparatus. We apply our calculations to existing interferometers as well as to an apparatus working with lithium which is under construction in our laboratory.

Design and demonstration of polarization-insensitive Mach-Zehnder switch using a lattice-matched InGaAlAs/InAlAs MQW and deep-etched high-mesa waveguide structure

Abstract: The authors have designed and demonstrated a 2/spl times/2 Mach-Zehnder switch in view of polarization independence as well as low propagation loss (/spl alpha/) and absorption change (/spl Delta//spl alpha/). To obtain polarization-insensitive refractive index change (/spl Delta/n), a lattice-matched InGaAlAs-InAlAs multiple quantum-well (MQW) with a large detuning wavelength was used. Moreover, to reduce the insertion loss difference between polarizations, we applied a multimode-interferometer 3-dB coupler and a deep-etched high-mesa waveguide structure. This switch, therefore, can provide polarization-independent operation about both driving voltage and insertion loss, which is indispensable to practical optical switching applications. We also paid attention to /spl Delta//spl alpha/ suppression when we decided the value of wavelength detuning and the length of the phase shift region. We also investigated the wavelength dependence of the switch. Within 1530-1560 nm, which is the erbium-doped fiber amplifier (EDFA) gain band, polarization independence in the driving voltage and the crosstalk was maintained. This result shows that the switch is also applicable in wavelength division multiplexing (WDM) applications.