Interferometer Configuration Research Articles

Analysis of interferometric configuration for optical devices

Abstract With the exponential growth in information related applications and the continuous increase in voice over IP (VoIP) applications, the carriers are expanding their networks to provide improved services to their end users. In such cases, the synchronous optical network/synchronous digital hierarchy model is not suitable. In this work, we are going to investigate the electro optic switch with the help of a VB script to simulate the device for various parameters. Further, we will then scan the central electrode voltages and take account of the overlap integral taking place at the output port with the help of waveguide mode. The best switching for switches at different voltages so as to have negligible coupling loss for different input signals is investigated. We aim to evaluate the MZI switches with the Li-Tn channel profile wave guiding structure and confirm their performance as compared to the existing MZI switches.

Phase-Shifting Common-Path Polarization Self-Interferometry for Evaluating the Reconstruction of Holograms Displayed on a Phase-Only Display

In this work we apply a phase-shifting interferometry (PSI) to evaluate the reconstruction of complex-valued holograms displayed onto a phase-only spatial light modulator (SLM). The interferometer is vibration-free since it uses a common-path polarization arrangement based on the SLM itself, which is used simultaneously to display the hologram and to apply the phase-shifting values. The change from the hologram display configuration to the interferometer configuration involves only a rotation of a polarizer. The continuous phase modulation provided by the SLM allows using PSI with arbitrary phase bias values. Several examples are demonstrated by generating different combinations of modes with an efficient on-axis hologram encoding technique.

Performance of the KAGRA detector during the first joint observation with GEO 600 (O3GK)

Abstract KAGRA, the kilometer-scale underground gravitational-wave detector, is located at Kamioka, Japan. In April 2020, an astrophysics observation was performed at the KAGRA detector in combination with the GEO 600 detector; this observation operation is called O3GK. The optical configuration in O3GK is based on a power-recycled Fabry–Pérot–Michelson interferometer; all the mirrors were set at room temperature. The duty factor of the operation was approximately 53%, and the displacement sensitivity was approximately 1 × 10−18 ${\rm m}/\sqrt{\rm {Hz}}$ at 250 Hz. The binary-neutron-star (BNS) inspiral range was about 0.6 Mpc. The contributions of various noise sources to the sensitivity of O3GK were investigated to understand how the observation range could be improved; this study is called a “noise budget”. According to our noise budget, the measured sensitivity could be approximated by adding up the effect of each noise. The sensitivity was dominated by noise from the sensors used for local controls of the vibration isolation systems, acoustic noise, shot noise, and laser frequency noise. Further, other noise sources that did not limit the sensitivity were investigated. This paper provides a detailed account of the KAGRA detector in O3GK, including interferometer configuration, status, and noise budget. In addition, strategies for future sensitivity improvements, such as hardware upgrades, are discussed.

Active multi-mode interferometer semiconductor optical amplifier on quantum dots toward high saturated output power under high temperature

A semiconductor optical amplifier (SOA) is wildly used as gain media in a photonic integrated circuit, as it is integrable with various devices, including wavelength filter, on the same wafer. Quantum dots (QD) have been known to realize high-temperature operation without using a thermo-cooler, the saturated output power was not high due to the limited density of state in QD. To realize high saturated output power under high temperatures, we have exploited the active multi-mode interferometer (active-MMI) configuration on QD SOA. We fabricated active-MMI SOA using a 1.31 μm InAs/GaAs QD active layer with the design of approximately 5 times larger footprint compared to a single stripe, whereas it holds regular single transverse mode output. As a result, a significant improvement of 15 dB saturated output power at 75 °C was substantiated successfully.

Photonic crystal based interferometric design for label-free all-optical sensing applications.

Optical sensing devices has a great potential in both industrial and biomedical applications for the detection of biochemicals, toxic substances or hazardous gases thanks to their sustainability and high-selectivity characteristics. Among different kinds of optical sensors based on such as fibers, surface plasmons and resonators; photonic crystal (PC) based optical sensors enable the realization of more compact and highly efficient on-chip sensing platforms due to their intriguing dispersive relations. Interferometric devices based on PCs render possible the creation of biochemical sensors with high sensitivity since a slight change of sensor path length caused by the captured biochemicals could be detected at the output of the interferometer via the interferences of separated beams. In this study, a new type of Mach-Zehnder Interferometer (MZI) using low-symmetric Si PCs is proposed, which is compatible with available CMOS technology. Intended optical path difference between the two MZI channels is provided by the periodic alignments of symmetry-reduced PC unit cells in the MZI arms. Unlike the conventional symmetrical PC based MZIs, Fano resonances exist for the proposed MZI design, i.e. transmission dips and peaks appear in the output spectrum, and the location of dip and peak frequencies in transmission spectra can be efficiently controlled by utilizing interference phenomenon. Exploiting this effect, any refractive index change at the surrounding medium could be distinctly observed at the transmission spectra. In the view of such results, it is convenient to say that the proposed MZI configuration is suitable for efficient optical sensing of toxic gases as well as liquids. The designed all-dielectric MZI system is numerically investigated in both spectral and spatial domains to analyze its interferometric tunability: an optical sensitivity of about 300 nm/RIU is calculated for gaseous analytes whereas that sensitivity value is around 263.2 nm/RIU in the case of liquid analytes. Furthermore, high quality factor of Q > 45000 is obtained at Fano resonances with Figure-of-Merit (FoM) value of FoM ∼ 8950 RIU-1(7690 RIU-1) in the case of gas analytes (liquid analytes), which is the indication of enhanced optical sensing performance of the proposed MZI design. Considering all the above-mentioned advantages, the proposed interferometric configurations based on low-symmetric PCs could be utilized for efficient photonic sensor applications that require controllable output power or sensing of gaseous and liquid substances.

Electrical control of surface acoustic waves

Acoustic waves at microwave frequencies are widely used in wireless communication and are potential information carriers in quantum applications. However, most acoustic devices are passive components, and the development of phononic integrated circuits is limited by the inability to control acoustic waves in a low-loss, scalable manner. Here we report the electrical control of gigahertz travelling acoustic waves at room temperature and millikelvin temperatures. We achieve phase modulation by tuning the elasticity of a lithium niobate acoustic waveguide via the electro-acoustic effect. This phase modulator is then used to build an acoustic frequency shifter based on serrodyne phase modulation, and phase modulators in a Mach–Zehnder interferometer configuration are used to create an electro-acoustic amplitude modulator. By tailoring the phase matching between acoustic and quasi-travelling electric fields, we achieve reconfigurable non-reciprocal modulation with a non-reciprocity of over 40 dB. To illustrate the potential of the approach in quantum applications, we show that our electro-acoustic modulator can provide coherent modulation of single-phonon-level acoustic waves at 50 mK. The electro-acoustic effect can be used to electrically control the phase velocity of travelling acoustic waves in a lithium niobate waveguide, and to construct devices that can modulate the phase, frequency and amplitude of acoustic waves, even at the limit of single phonons.

Detectability of a spatial correlation between stellar mass black hole mergers and active galactic nuclei in the local Universe

ABSTRACT The origin of the binary black hole (BBH) mergers detected through gravitational waves (GWs) by the LIGO-Virgo-KAGRA (LVK) collaboration remains debated. One fundamental reason is our ignorance of their host environment, as the typical size of an event’s localization volume can easily contain thousands of galaxies. A strategy around this is to exploit statistical approaches to assess the spatial correlation between these mergers and astrophysically motivated host galaxy types, such as active galactic nuclei (AGNs). We use a likelihood ratio method to infer the degree of GW–AGN connection out to z = 0.2. We simulate BBH mergers whose components’ masses are sampled from a realistic distribution of the underlying population of black holes (BHs). Localization volumes for these events are calculated assuming two different interferometric network configurations. These correspond to the configuration of the third (O3) and of the upcoming fourth (O4) LVK observing runs. We conclude that the 13 BBH mergers detected during the third observing run at z ≤ 0.2 are not enough to reject with a 3σ significance the hypothesis according to which there is no connection between GW and AGNs more luminous than $\approx 10^{44.3}\rm {erg}\ \rm {s}^{-1}$, that have number density higher than 10−4.75 Mpc−3. However, 13 detections are enough to reject this no-connection hypothesis when rarer categories of AGNs are considered, with bolometric luminosities greater than $\approx 10^{45.5}\rm {erg}\ \rm {s}^{-1}$. We estimate that O4 results will potentially allow us to test fractional contributions to the total BBH merger population from AGNs of any luminosity higher than $80{{\ \rm per\ cent}}$.

Research Facilities for Europe’s Next Generation Gravitational-Wave Detector Einstein Telescope

The Einstein Telescope is Europe’s next generation gravitational-wave detector. To develop all necessary technology, four research facilities have emerged across Europe: The Amaldi Research Center (ARC) in Rome (Italy), ETpathfinder in Maastricht (The Netherlands), SarGrav in the Sos Enattos mines on Sardinia (Italy) and E-TEST in Liége (Belgium) and its surroundings. The ARC pursues the investigation of a large cryostat, equipped with dedicated low-vibration cooling lines, to test full-scale cryogenic payloads. The installation will be gradual and interlaced with the payload development. ETpathfinder aims to provide a low-noise facility that allows the testing of full interferometer configurations and the interplay of their subsystems in an ET-like environment. ETpathfinder will focus amongst others on cryogenic technologies, silicon mirrors, lasers and optics at 1550 and 2090 nm and advanced quantum noise reduction schemes. The SarGrav laboratory has a surface lab and an underground operation. On the surface, the Archimedes experiment investigates the interaction of vacuum fluctuations with gravity and is developing (tilt) sensor technology for the Einstein Telescope. In an underground laboratory, seismic characterisation campaigns are undertaken for the Sardinian site characterisation. Lastly, the Einstein Telecope Euregio meuse-rhine Site & Technology (E-TEST) is a single cryogenic suspension of an ET-sized silicon mirror. Additionally, E-TEST investigates the Belgian–Dutch–German border region that is the other candidate site for Einstein Telescope using boreholes and seismic arrays and hydrogeological characterisation. In this article, we describe the Einstein Telescope, the low-frequency part of its science case and the four research facilities.

Generation of A Space-Variant Vector Beam with Catenary-Shaped Polarization States.

We demonstrate the generation of a space-variant vector beam with catenary-shaped polarization states based on the polarization interferometry. With a spatial light modulator and a common path interferometric configuration, two orthogonally circularly polarized beams with different phase modulation overlap each other, yielding the vector beams. In addition, the polarization states of this vector beam are scalable to the arbitrary spatial distribution because of its great flexibility and universal applicability. It is expected that this vector beam may have many potential and intriguing applications in the micro/nano material processing, liquid crystal elements fabrication and optical micro-manipulation, and so on.

Design and development of integrated TIRF and common-path quantitative phase microscopic health care system with high stability

We demonstrate a compact microscopy system that enables simultaneous cell imaging in both digital holographic and fluorescence mode thus providing valuable multi-modal information for biosciences applications. The digital holographic imaging system uses a speckle free illumination by employing a rotating diffuser. Further a compact shear plate based interferometer arrangement is used to significantly reduce the system size and increase its robustness when compared with Michelson or Mach-Zehnder interferometer configurations. The overall reduction in form factor of the system is achieved since we employ the shear plate configuration additionally as a beam-splitter for the fluorescence imaging part of the system. We have fabricated a compact total internal reflection fluorescence (TIRF) unit which is combined with the common path sheared interferometer for this purpose. Our experiments with this compact system show excellent temporal phase stability. The working of the system is illustrated with imaging of polystyrene beads and MG63 osteosarcoma cell line sample. The fluorescence image of MG63 cell shows high expression of vinculin protein around the nuclei when compared with the expression in the cell's filopodia. These proteins are among the major molecular markers for cell adhesion and play a vital role in sensing the mechanical stimulus of the microenvironment. Further the quantitative phase information about the cell also provides its optical thickness information that is spatially aligned with the fluorescence signal. The proposed system can find applications in bioscience laboratories as well as in diagnostics.

Temperature sensor based on an erbium-doped fiber Sagnac interferometer.

The development of a highly sensitive all-fiber temperature sensor based on a Sagnac interferometer configuration is demonstrated here. We use 10 m of an erbium-doped fiber (EDF) as a passive sensing element inside the Sagnac loop, taking advantage of the extra birefringence added by the presence of the doping elements. Using a standard interrogation method of simply tracing a interference peak, we were able to detect temperature variations with a sensitivity of up to 0.2 nm/°C and high linearity. The results demonstrate, for the first time, that the usage of an EDF as a totally passive element can be an interesting option to extend the range of parameter possibilities achievable for highly sensitive temperature sensors.

Optical modulator using ultra-thin silicon waveguide in SOI hybrid technology

We propose a detailed study of an on-chip optical modulator using a non-conventional silicon-based platform. This platform is based on the optimum design of ultra-thin silicon on insulator waveguide. This platform is characterized by low field confinement inside the core waveguide and high sensitivity to the cladding index. Accordingly, it lends itself to a wide range of applications, such as sensing and optical modulation. By employing this waveguide into the Mach–Zehnder interferometer configuration, an efficient optical modulator is reported using an organic polymer as an active material for the electro-optic effect. An extinction ratio of more than 20 dB is achieved with energy per bit of 13.21 fJ/bit for 0.5 V applied voltage. This studied platform shows promising and adequate performance for modulation applications. It is cheap and easy to fabricate.

Wheeler’s delayed-choice experiment based on Rydberg atoms

The delayed choice gedanken-experiment initially proposed by J A Wheeler reveals the nontrivial features of wave–particle duality in quantum world, that is, the choice of whether to observe the particle/wave character of a quantum system at a delayed time can affect its evolution history. In this work, the Wheeler’s delayed-choice experiment is conducted and tested in a new regime based on a Rydberg-ground level atomic Mach–Zehnder interferometer with optical coherent manipulation. Our quantum system exhibits an excellent single-excitation of the collective atomic state due to the Rydberg blockade effect, and the delayed choice of the interferometer configuration is realized by a quantum random number generator based on high-quality Rydberg single-photon source. Our experimental results demonstrate the Wheeler’s nontrivial time order inversion in this quantum system and confirm the Copenhagen interpretation of the physical reality of quantum state, which means the particle/wave character can only be ascribed to a quantum system when it was measured. This work is encouraging toward testing the foundations of quantum mechanics using the Rydberg atoms.

Study of acceleration measurement in gravitational wave detection

Position-meter and speed-meter interferometers have been analysed for detecting gravitational waves. Speed-meter is proposed to reduce the radiation pressure noise, which is dominant at low frequency. We introduce the concept of acceleration measurement in comparison with position and speed measurement. In this paper, we describe a general acceleration measurement and derive its standard quantum limit. We provide an example of an acceleration-meter interferometer configuration. We show that shot noise dominates at low frequency following a frequency dependence of 1/Ω2, while radiation pressure noise is constant. The acceleration-meter has even a stronger radiation pressure noise suppression than speed-meter.

Generation of a bright four-photon entangled state from a warm atomic ensemble via inherent polarization entanglement

We report the stable generation of a bright four-photon polarization-entangled Greenberger–Horne–Zeilinger (GHZ) state obtained by the spatial multiplexing of inherently polarization-entangled photons from a warm atomic ensemble of 87Rb. Owing to the total angular momentum conservation of the atomic state in the spontaneous four-wave mixing process of a cascade-type atomic system, the polarizations of the signal and idler photons in the two-photon decay are entangled. With a Rb vapor cell, we realize the generation of robust and bright four-photon GHZ states using two symmetrical spatial modes of inherently polarization-entangled photon pairs without applying an interferometric configuration. The four-photon average coincidence rate of the GHZ state with a fidelity of 0.88(2) is measured as 1.69(7) Hz under a weak pump power of 10 μW. The minimum Allan variance for the stability of the four-photon GHZ state is estimated as 0.92° for an average time of 10 h.

Gravitational acceleration estimation with a nonlinear Mach–Zehnder interferometer

We investigate the use of a nonlinear optical interferometer to estimate local gravitational acceleration. We study a Mach–Zehnder interferometer (MZI) in an optical fountain configuration where a Kerr nonlinear medium is placed in the arms of the interferometer. This configuration allows the parameter estimation to exceed the standard Heisenberg limit of a linear interferometer. Compared to previous studies, we argue that this interferometer configuration is better posed and achieves improved precision for similar scale and pump powers.

Unbalanced low coherence interference microscopy

Low coherence interference microscopy (LCIM) provides high spatial phase sensitivity, i.e., speckle free and coherent noise free quantitative phase images of the test specimens. Due to low temporal coherence (TC) length of the light source, LCIM requires precise adjustment of the optical path difference (OPD) between the object and the reference arm, which is only a few micrometers. Consequently, previously demonstrated LCIM systems are implemented with the use of identical objective lenses in both the arms and also known as balanced interferometric configuration. The use of identical objective lens hinders both the use of high numerical aperture objective lens and also the swift change of the objective lens during imaging. In the present work, LCIM is implemented with non-identical objective lenses in the object and the reference arm also called unbalanced optical configuration. A range of objective lenses 10 × /0.25NA, 20 × /0.45NA and 60 × /1.2NA are employed in the object arm of the system while keeping single objective lens 10 × /0.25NA in the reference arm. To resolve the challenges associated with unbalanced configuration, advanced iterative algorithm (AIA) and principal component analysis (PCA) algorithms are integrated to recover quadratic phase error free phase images of the test specimens. The capabilities of the proposed method are exhibited on various specimens like USAF resolution, step-like test object and for the biological cells, HeLa cells. The proposed approach enables scalable magnification and resolution by simply rotating the imaging objective turret without the need of changing objective lens in the reference arm.

Novel Sensing Algorithm for Linear Read-Out of Bimodal Waveguide Interferometric Biosensors

Biosensors employing photonics integrated circuits, and specifically those that rely on interferometric evanescent wave working principles, have outstanding performances due to the extreme sensitivity exhibited in one-step and direct assay, without the need of amplification. Within the interferometric configurations, the Bimodal Waveguide (BiMW) interferometric sensor stands out due to its demonstrated sensitivity for real-life applications and the simplicity of its design. To overcome the ambiguities that arise from the periodic nature of interferometric read-outs, a new all-optical modulation and the subsequent trigonometry-based algorithm have been proposed and applied to the BiMW biosensor. This new algorithm has been successfully employed for the selective identification and quantification of the external Spike (S) protein of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Our biosensing results from this simple, quick, and user-friendly method demonstrate high sensitivity and specificity and pave the way towards a point-of-care device for general use.

Review of Fiber Optic Displacement Sensors

Displacement measurements are of significant importance in a variety of critical scientific and engineering fields such as gravitational wave detection, geophysical research, and manufacturing industries. Due to the inherent advantages such as compactness, high sensitivity, and immunity to electromagnetic interference, in recent years, fiber optic sensors have been widely used in an expansive range of sensing applications, ranging from infra-structural health monitoring to chemical and biological sensing. Of particular interest here, fiber optic displacement sensors have gained wide interest and have evolved from basic intensity modulation-based configurations to more advanced structures, such as fiber Bragg grating-based, interferometric configurations, etc. This paper reviews specifically the advanced fiber optic displacement sensing techniques that have been developed in the past two decades. Details regarding the working principle, sensor design, and performance measures of fiber Bragg gratings-based, interferometers-based (including the Fabry-Perot interferometer, the Michelson interferometer, and the multimode interferometer), microwave photonics-based, and surface plasmon resonance-based fiber optic displacement sensors are given. Challenges and perspectives on future research in the development of practical and high-temperature tolerant displacement sensors are also discussed.

Experimental evaluation of Fourier transform holograms by a self-interferometric technique

We present a technique that combines an encoding method to display complex-valued holograms onto a phase-only spatial light modulator (SLM) with a phase-shifting interferometric (PSI) technique for experimentally evaluating the generated complex-valued optical fields. We demonstrate an efficient common-path polarization interferometer based on the SLM itself, not requiring any external additional element. The same setup can be used to simultaneously display the complex hologram and to apply the phase-shifting values required to retrieve the phase distribution of the optical field. A simple rotation of a polarizer allows to change from the intensity configuration to the interferometer configuration.