Output Of Interferometer Research Articles

Simple phase shifting by polarizer rotations in a cube beam-splitter interferometer.

A simple and low-cost method for phase-shifting interferometry by the rotation of a polarizer is presented. This proposal takes advantage of the polarization aberration in a cube beam splitter due to its geometry, to the angular dependence with the coating, and to the polarization angle of the input beam. The interferometric setup performs as a two-window common-path interferometer in which the added phase shifting is achieved by simply rotating a polarizer at the interferometer output. The viability of the proposal is sustained with experimental results in which the phase-shift value and the resulting wavefront are calculated with Farrel's technique and the three-step PSI algorithm, respectively.

Fourier Transform Spectrometry with Fourier Analysis of the Interferogram as Just an Optional Tool.

Fourier transform spectrometers replace the traditional dispersive frequency analyzer by a Michelson interferometer. The spectrum is the Fourier transform of the interferogram constituting the raw output. The method is a primary tool for chemical analysis because it has decisive advantages over the dispersive one for analyzing infrared electromagnetic radiation (Fourier transform infrared, FTIR). A new procedure for dealing with the raw interferometric output of the instrument, not needing Fourier transformation and having additional advantages, is put forward here. It rests on recent advances in the theory of the interaction of matter with electromagnetic radiation yielding first principles analytic expressions for the Fourier transform of the spectral lineshapes, which can be fitted directly to the experimentally measured interferogram. The relevant physical information, as the integrated intensities of the electronic transitions and their net energy release, not affected by Stokes shifts, is readily obtained in the fitting procedure. Ulterior analysis of the spectra, introducing phenomenological standard interpolation functions to deconvolute and integrate peaks, becomes unnecessary. Both methods, standard FTIR and the one outlined here, demand little computer time and can be used simultaneously with synergistic effects.

Numerical modeling of nominal and stray waves in birefringent interferometers: application to large-field-of-view imaging Fourier transform spectrometers.

Birefringent interferometers are often used for compact static Fourier transform spectrometers. In such devices, several uniaxial birefringent parallel or prismatic plates are stacked, with their optical axes set so that there is an efficient coupling from ordinary to extraordinary and extraordinary to ordinary eigenmodes of two successive plates. Such coupling, aside from few particular cases, is, however, not perfect, an effect that may adversely affect performance. In order to help the design and the tolerancing of these interferometers, we have developed a numerical modeling based on the propagation of plane waves inside and through the interface of birefringent media. This tool evaluates the traveled optical path length and the amplitude of the different polarization modes, enabling prediction of both the optical path differences on the interferometer outputs and the unwanted coupling strengths and related stray wave amplitudes. The tool behavior is illustrated on Savart and double-Wollaston interferometers and compared with experimental characterization of a calcite double-Wollaston prism.

Recovering distance information in spectral domain interferometry

This work evaluates the performance of the Complex Master Slave (CMS) method, that processes the spectra at the interferometer output of a spectral domain interferometry device without involving Fourier transforms (FT) after data acquisition. Reliability and performance of CMS are compared side by side with the conventional method based on FT, phase calibration with dispersion compensation (PCDC). We demonstrate that both methods provide similar results in terms of resolution and sensitivity drop-off. The mathematical operations required to produce CMS results are highly parallelizable, allowing real-time, simultaneous delivery of data from several points of different optical path differences in the interferometer, not possible via PCDC.

Multichannel IR Fourier transform spectrometer

The authors propose to implement a multi-channel continuous scan Fourier spectrometer for simultaneous recording and analysis of the spectral characteristics of several objects. To implement such a scheme is used multiprobe fiber in which several optical fibers, at one end, are connected in one optical connector and fixed in the output of interferometer. In this scheme, the Fourier spectrometer is used as a modulator. On the other hand, each fiber individually mated with the test sample and its own radiation detector. The spectral resolution of the proposed system is 1 cm-1. For the system the aperture of the spectrometer from the condition of minimum spectral resolution and optical fibers parameters is calculated. Using the proposed scheme emission spectra of helium neon lamp have been registered for each single fiber with diameter of 1 mm and a numerical aperture NA = 0,22.

Multifunction interferometry using the electron mobility visibility and mean free path relationship.

A conventional Michelson interferometer is modified and used to form the various types of interferometers. The basic system consists of a conventional Michelson interferometer with silicon-graphene-gold embedded between layers on the ports. When light from the monochromatic source is input into the system via the input port (silicon waveguide), the change in optical path difference (OPD) of light traveling in the stacked layers introduces the change in the optical phase, which affects to the electron mean free path within the gold layer, induces the change in the overall electron mobility can be seen by the interferometer output visibility. Further plasmonic waves are introduced on the graphene thin film and the electron mobility occurred within the gold layer, in which the light-electron energy conversion in terms of the electron mobility can be observed, the gold layer length is 100 nm. The measurement resolution in terms of the OPD of 50 nm is achieved. In applications, the outputs of the drop port device of the modified Michelson interferometer can be arranged by the different detectors, where the polarized light outputs, the photon outputs, the electron spin outputs can be obtained by the interference fringe visibility, mobility visibility and the spin up-down splitting output energies. The modified Michelson interferometer theory and the detection schemes are given in details.

A Study of All-fiber Different Bandwidth Interleaver Based on Linear Chirped Fiber Grating

To improve the utilization efficiency of interleaver bandwidth in 10Gbit/s plus 40Gbit/s mixed system, an all-fiber MZI different bandwidth optical interleaver based on linear chirped fiber grating is proposed and discussed in this paper. The same two linear chirped fiber gratings are written at the output of conventional Mach-Zehnder interferometer (MZI), which constitute a reflective cascaded MZI filter. Based on its structure, the output spectrum expression is established and described by using the principle of fiber transmission, reflex theory of fiber grating and the matrix transfer function. Influences on its transmission characteristics by such factors as the coupling coefficients of the couplers, structure parameters of fiber grating and the length differences of the interferometer arms are numerically analyzed and optimized. The results of numerical simulation indicate that when the above parameters are some certain values, 50GHz input single of device is separated into channel spacing of 100GHz odd-even two output signals. Their spectrum bandwidth are 64.67GHz and 36.98GHz at 3dB, they satisfy the requirement of different transmission rates on bandwidth in 10Gbit/s plus 40Gbit/s mixed system and implements different bandwidth transmission. The device has a certain ability to resist the deviation. Compared with the ordinary cascaded MZI interleaver, the advantage of the new interleaver is that reduced numbers of coupler. It has higher bandwidth utilization that compared with the equal bandwidth interleaver, and achieves different bandwidth transmission within 100GHz.

Electrical Double Layer-Induced Ion Surface Accumulation for Ultrasensitive Refractive Index Sensing with Nanostructured Porous Silicon Interferometers.

Herein, we provide the first experimental evidence on the use of electrical double layer (EDL)-induced accumulation of charged ions (using both Na+ and K+ ions in water as the model) onto a negatively charged nanostructured surface (e.g., thermally growth SiO2)-Ion Surface Accumulation, ISA-as a means of improving performance of nanostructured porous silicon (PSi) interferometers for optical refractometric applications. Nanostructured PSi interferometers are very promising optical platforms for refractive index sensing due to PSi huge specific surface (hundreds of m2 per gram) and low preparation cost (less than $0.01 per 8 in. silicon wafer), though they have shown poor resolution ( R) and detection limit (DL) (on the order of 10-4-10-5 RIU) compared to other plasmonic and photonic platforms ( R and DL on the order of 10-7-10-8 RIU). This can be ascribed to both low sensitivity and high noise floor of PSi interferometers when bulk refractive index variation of the solution infiltrating the nanopores either approaches or is below 10-4 RIU. Electrical double layer-induced ion surface accumulation (EDL-ISA) on oxidized PSi interferometers allows the interferometer output signal (spectral interferogram) to be impressively amplified at bulk refractive index variation below 10-4 RIU, increasing, in turn, sensitivity up to 2 orders of magnitude and allowing reliable measurement of refractive index variations to be carried out with both DL and R of 10-7 RIU. This represents a 250-fold-improvement (at least) with respect to the state-of-the-art literature on PSi refractometers and pushes PSi interferometer performance to that of state-of-the-art ultrasensitive photonics/plasmonics refractive index platforms.

A Wavefront Division Polarimeter for the Measurements of Solute Concentrations in Solutions.

Polarimeters are useful instruments that measure concentrations of optically active substances in a given solution. The conventional polarimetric principle consists of measuring the rotation angle of linearly polarized light. Here, we present a novel polarimeter based on the study of interference patterns. A Mach–Zehnder interferometer with linearly polarized light at the input is used. One beam passes through the liquid sample and the other is a reference beam. As the linearly polarized sample beam propagates through the optically active solution the vibration plane of the electric field will rotate. As a result, the visibility of the interference pattern at the interferometer output will decrease. Fringe contrast will be maximum when both beams present a polarization perpendicular to the plane of incidence. However, minimum visibility is obtained when, after propagation through the sample the polarization of the sample beam is oriented parallel to the plane of incidence. By using different solute concentrations, a calibration plot is obtained showing the behavior of visibility.

Quantum-enhanced interferometry with cavity QED-generated non-classical light

We propose an enhanced optical interferometer based on tailored non-classical light generated by nonlinear dynamics and projective measurements in a three-level atom cavity QED system. A coherent state in the cavity becomes dynamically entangled with two ground states of the atom and is transformed to a macroscopic superposition state via a projective measurement on the atom. We show that the resulting highly non-classical state can improve interferometric precision measurements well beyond the shot-noise limit once combined with a classical laser pulse at the input of a Mach–Zehnder interferometer. For a practical implementation, we identify an efficient phase shift estimation scheme based on the counting of photons at the interferometer output. Photon losses and photon-counting errors deteriorate the interferometer sensitivity, but we demonstrate that it still can be significantly better than the shot-noise limit under realistic conditions.Graphical abstract

A data-acquisition and control system for spectral-domain optical coherence tomography with a speed of 91 912 A-scans/s based on a USB 3.0 interface

We describe a system of optical spectrum registration at the output of an interferometer with controlled phase shifts for an experimental device intended for visualizing the internal structure of an optically turbid specimen, using the method of spectral domain optical coherence tomography. A device for spectral domain optical coherence tomography based on a common-path optical scheme with a USB 3.0 interface for inputting data into a computer has been developed. An imaging speed of 91 912 A-scans/s has been attained. At the achieved speed, a series of live experiments were carried out to visualize the internal structure of skin tissues from a finger and front segments of an eye.

Supersensitive ancilla-based adaptive quantum phase estimation

The super-sensitivity attained in quantum phase estimation is known to be compromised in the presence of decoherence. This is particularly patent at blind spots -- phase values at which sensitivity is totally lost. One remedy is to use a precisely known reference phase to shift the operation point of the sensor to a less vulnerable phase value. We present here an alternative approach based on combining the probe with an ancillary degree of freedom containing adjustable parameters to create an entangled quantum state of higher dimension. We validate this concept by simulating a configuration of a Mach-Zehnder interferometer with a two-photon probe and a polarization ancilla of adjustable parameters, entangled at a polarizing beam splitter. At the interferometer output, the photons are measured after an adjustable unitary transformation in the polarization subspace. Through calculation of the Fisher information and simulation of an adaptive estimation procedure, we show that optimizing the adjustable polarization parameters using an adaptive measurement process provides globally super-sensitive unbiased phase estimates for a range of decoherence levels, without prior information or a reference phase.

Development of a Free Space, LED Illuminated Spectral-domain Optical Coherence Tomography Setup

Free-space spectral domain optical coherence tomography has been demonstrated using an 8 mW ultra-bright 850 nm light-emitting diode with a 40 nm spectral width. The system detects longitudinal reflectivity of surface and sub-surface layers of optical elements to depths of a millimetre with high fidelity. Development stages included mathematical analysis of light interference by superposition of electric field phasors of reference and sample arms of a Michelson interferometer. A method by which depth-resolved reflectivity is acquired is described. A locally assembled Czerny Turner monochromator was aligned such that the interferometer output beam is dispersed into its spectral components before image re-construction. Calibration of the 2048-pixel detecting charge-coupled device line camera was performed using a Mercury vapour lamp with 8 spectral lines spanning from the ultra-violet to yellow region of the electromagnetic spectrum. Processing of interference fringe signals from spectral domain data is described and an analysis of variations in frequency of the interference fringe signal and threshold illumination with depth into the sample presented. A test of sensitivity of the depth imaging algorithm to low-amplitude signals is also reported.

Adaptive phase estimation with two-mode squeezed vacuum and parity measurement

A proposed phase-estimation protocol based on measuring the parity of a two-mode squeezed-vacuum state at the output of a Mach-Zehnder interferometer shows that the Cram\'{e}r-Rao sensitivity is sub-Heisenberg [Phys.\ Rev.\ Lett.\ {\bf104}, 103602 (2010)]. However, these measurements are problematic, making it unclear if this sensitivity can be obtained with a finite number of measurements. This sensitivity is only for phase near zero, and in this region there is a problem with ambiguity because measurements cannot distinguish the sign of the phase. Here, we consider a finite number of parity measurements, and show that an adaptive technique gives a highly accurate phase estimate regardless of the phase. We show that the Heisenberg limit is reachable, where the number of trials needed for mean photon number $\bar{n}=1$ is approximately one hundred. We show that the Cram\'{e}r-Rao sensitivity can be achieved approximately, and the estimation is unambiguous in the interval ($-\pi/2, \pi/2$).

Single-shot areal profilometry using hyperspectral interferometry with a microlens array.

We describe a single-shot technique to measure areal profiles on optically smooth and stepped surfaces for applications where rapid data acquisition in non-cooperative environments is essential. It is based on hyperspectral interferometry (HSI), a technique in which the output of a white-light interferometer provides the input to a hyperspectral imaging system. Previous HSI implementations suffered from inefficient utilisation of the available pixels which limited the number of measured coordinates and/or unambiguous depth range. In the current paper a >20-fold increase in pixel utilisation is achieved through the use of a 2-D microlens array, that leads to a 35 × 35 channel system with an unambiguous depth range of 0.88 mm.

Combined Use of C- and X-Band SAR Data for Subsidence Monitoring in an Urban Area

In this study, we present the detection and characterization of ground displacements in the urban area of Pisa (Central Italy) using Interferometric Synthetic Aperture Radar (InSAR) products. Thirty RADARSAT-2 and twenty-nine COSMO-SkyMed images have been analyzed with the Small BAseline Subset (SBAS) algorithm, in order to quantify the ground subsidence and its temporal evolution in the three-year time interval from 2011 to 2014. A borehole database was reclassified in stratigraphical and geotechnical homogeneous units, providing the geological background needed for the local scale analysis of the recorded displacements. Moreover, the interferometric outputs were compared with the last 30 years’ urban evolution of selected parts of the city. Two deformation patterns were recorded by the InSAR data: very slow vertical movements within the defined stability threshold (±2.5 mm/yr) and areas with subsidence rates down to −5 to −7 mm/yr, associated with high peak velocities (−15 to −20 mm/yr) registered by single buildings or small groups of buildings. Some of these structures are used to demonstrate that the high subsidence rates are related to the recent urbanization, which is the trigger for the accelerated consolidation process of highly compressible layers. Finally, this urban area was a valuable test site for demonstrating the different results of the C- and X-band data processing, in terms of the density of points and the quality of the time series of deformation.

Sagnac Interferometer-Assisted Microwave Photonic Link With Improved Dynamic Range

In this paper, we propose a simple method to improve the spurious-free dynamic range (SFDR) of a microwave photonic link (MPL). The proposed method is based on a Sagnac interferometer structure; signal output of the Sagnac interferometer consists of two kinds of optical components: the clockwise (CW) modulated optical signal and the counter clockwise (CCW) unmodulated optical carrier. An appropriate situation is then created to satisfy the phase and power ratio condition of the two counter propagating light waves. Eventually, in photodiode, part of the third-order intermodulation distortion (IMD3) component is generated by the CW light wave and another part is generated by the CW sidebands beating with the CCW optical carrier. Under appropriate circumstances, these two kinds of IMD3s have same amplitude but opposing phase; hence, the IMD3 can be cancelled, and an enhanced SFDR is achieved. An experiment is conducted, and results show that, as compared with a conventional MPL, the SFDR of the proposed link is improved by 10.3 dB, and for a 16-quadrature amplitude modulation (QAM) 10-MSym/s signal centered at 15 GHz, the error vector magnitude is reduced by 5.9%.

High quality of logic gates from the return arm of a Sagnac fiber interferometer

In this paper, we analyze the characteristics of obtaining logic functions and logic gates in the reflected output of the Sagnac interferometer by unbalancing the interferometer through the effects of group velocity dispersion and self-phase modulation, mapped by the influence of the extinction ratio (XR) and also analyze the logic gates of better quality by proposing accuracy precision ratio (PR) defined. We studied the phase variation in the phase inserted to the input and we analyzed the related parameters of modulation. We investigated intrinsic features of reflection of the Sagnac interferometer and obtained the logic gates AND, OR, and XOR, and the logical functions ZERO, ONE, and . A specific situation happens when ρ = 0.3 and , where we find the logic gates AND, OR, and XOR. Of all results, the XOR logic gate was obtained in a greater phase variation interval. The XR had the highest contrast when ρ = 0.2 and |ɛ| = 0.028 W1/2. The proposed reconfigurable theoretical set-up gives a contribution to the design of optical networks by the analysis of the obtained logic gates and logic functions in an all-optical environment. The best quality logic gate is the AND gate presenting the |PRTOTAL| = 34.99 when .

Absolute rotation detection by Coriolis force measurement using optomechanics

In this article, we present an application of the optomechanical cavities for absolute rotation detection. Two optomechanical cavities, one in each arm, are placed in a Michelson interferometer. The interferometer is placed on a rotating table and is moved with a uniform velocity of with respect to the rotating table. The Coriolis force acting on the interferometer changes the length of the optomechanical cavity in one arm, while the length of the optomechanical cavity in the other arm is not changed. The phase shift corresponding to the change in the optomechanical cavity length is measured at the interferometer output to estimate the angular velocity of the absolute rotation. An analytic expression for the minimum detectable rotation rate corresponding to the standard quantum limit of measurable Coriolis force in the interferometer is derived. Squeezing technique is discussed to improve the rotation detection sensitivity by a factor of at 0 K temperature, where and are the damping rate and angular frequency of the mechanical oscillator. The temperature dependence of the rotation detection sensitivity is studied.

Integrated nonlinear interferometer with wavelength multicasting functionality.

Nonlinear interference based on four wave mixing (FWM) is extremely attractive due to its phase sensitivity. On the other hand, wavelength multicasting, which supports data point-to-multipoint connections, is a key functionality to increase the network efficiency and simplify the transmitter and receiver in the wavelength-division multiplexing systems. We propose and experimentally demonstrate a nonlinear interferometer with wavelength multicasting functionality based on single-stage FWM in an integrated silicon waveguide. With a three-pump and dual-signal input, four phase sensitive idlers are obtained at the interferometer output. For a proof-of-concept application, we further theoretically demonstrate the multicasting logic exclusive-OR (XOR) gate for both intensity and phase modulated signals. The proposed scheme would be potentially applied in various on-chip applications for future optical communication system.