Interferometer Configuration Research Articles

High-Linearity Dual-Parallel Mach–Zehnder Modulators in Thin-Film Lithium Niobate

Microwave photonic (MWP) systems are inseparable from conversions of microwave electrical signals into optical signals, and their performances highly depend on the linearity of electro-optic modulators. Thin-film lithium niobate (TFLN) is expected to be an ideal platform for future microwave photonic systems due to its compact size, low optical loss, linear electro-optic effect, and high bandwidth. In this paper, we propose a TFLN modulator with a low voltage–length product (VπL) of 1.97 V·cm and an ultra-high-linearity carrier-to-distortion ratio (CDR) of 112.33 dB, using a dual-parallel Mach–Zehnder interferometer configuration. It provides an effective approach to fully suppress the third-order intermodulation distortions (IMD3), leading to 76 dB improvement over a single Mach–Zehnder modulator (MZM) in TFLN. The proposed TFLN modulator would enable a wide variety of applications in integrated MWP systems with large-scale integration, low power consumption, low optical loss, and high bandwidth.

On-axis full-field swept-source optical coherence tomography for murine retinal imaging

A full-field swept-source optical coherence tomography (FF-SS-OCT) for in vivo murine retinal imaging is demonstrated. The on-axis FF-SS-OCT system was built in a Mach–Zehnder interferometer configuration employing a tunable laser source with an adjustable sweep rate and sweep range in conjunction with a fast 2D-CMOS camera. A large field retinal (coherent) illumination was accomplished using an imaging interface comprised of a short-focal length imaging lens and a contact lens. The magnification between the camera and retina (spatial sampling) was appropriately chosen to record the microscopic structural features of the retina in the image. A pupil stop was employed in the detection path to reject unwanted backscattering from the mouse eye and other sources and limit aberrations distorting the retinal images. In vivo mouse retinal imaging was performed at a sweep rate of 150 Hz to acquire volumes unaffected by the system vibrations, which predominated at lower frequencies. Operating the FF-SS-OCT at this speed yielded an effective axial scan rate of 20 million A-scans/s and a field of view of 820 × 410 µm (24.12° × 12.06°). High-quality retinal B-scans and enface images of the retina were obtained with the SS-FF-OCT, revealing all major retinal layers and vascular plexuses.

Nanophotonic Bragg grating assisted Mach–Zehnder interferometers for O-band add-drop filters

Spectral filters are fundamental building blocks in integrated photonics. Bragg grating filters have been demonstrated in silicon waveguides with a wide range of spectral responses and are suitable for wavelength division multiplexing applications. However, retrieving Bragg grating reflections typically requires external components such as fiber optic circulators. In this work, we develop fully integrated add-drop filters based on cladding-modulated Bragg gratings incorporated in a Mach–Zehnder interferometer configuration. We design complex spectral filtering devices with single and dual-band flat-top responses for the specified bandwidth. Additionally, we propose a novel design methodology which aims to minimize phase errors within the filters. We experimentally demonstrate add-drop filters with single-band and two-band rejection spectra at the datacom O-band, fabricated on a 220-nm thick silicon-on-insulator platform. Our results show an insertion loss below 1 dB and a crosstalk of around −20 dB at the channel center for a 4.5-nm wavelength grid and 3-nm wide channels.

Tapered fiber optic sensor for arterial pulse wave monitoring

Arterial pulse wave monitoring has been recognized as an effective medical diagnostic tool for various cardiovascular diseases. To overcome the barriers in traditional, complex, and expensive detection configurations, new electronic and optical sensors have been developed with their unique advantages. Particularly, various configurations of fiber-optic sensors have been proposed. This paper demonstrates the use of a tapered optical fiber structure to create a sensitive sensor that can detect carotid arterial pulse waves on the skin surface. The demonstrated fiber sensor probe utilizes an in-line Mach-Zehnder interferometer configuration and liquid-gold film coating on the sensor tip to enhance its sensitivity and demonstrate its use by encapsulating the sensor with a flexible elastomer material for detecting arterial pulse waves with a simple testing configuration. Considering the simple fabrication and high sensitivity without a complex demodulation scheme, the proposed sensor has broad implementation in biomedical health monitoring systems.

Estimation of orbital parameters from [formula omitted]-coverage for a space radio interferometer

Searching for a suitable very long baseline (VLBI) interferometer geometry is a key task in planning observations, especially imaging sessions. VLBI image quality is characterized by (u,v)-coverage. With one or more radio telescopes located in space, such a task becomes more complex. This paper presents a method of recovering the optimal orbital parameters for space radio telescopes having a given desired (u,v)-coverage. In turn, this task can be called the inverse of the task of searching for the optimal geometry and orbital configurations of space-ground and pure space VLBI interferometers.

Designing an Optical Router Based on a Multimode-Interference Silicon-On-Insulator Coupler with Tunable Power Transmittance

The demand on fast and high-bandwidth data transmission is in continuous increase. These demands are highly dependent on optical signal manipulation, including switching, modulation, and routing. We demonstrate a two-port silicon optical router based on the multimode interferometer (MMI) configuration. The same MMI structure was used for both inward and backward waveguiding to reduce the total length of the device. A phase shifter consisting of two ring-like waveguides made of silicon p-n junctions was used to introduce the phase shift needed for optical routing upon voltage application. Two designs for the MMI optical router were studied: Firstly, a conventional MMI with a crosstalk ratio of 15.1 dB was investigated. Finally, an angled MMI reaching a crosstalk ratio of 18.2 dB at a wavelength of 1.55 μm was investigated.

Photo‐Induced Electric Field Effects on Water Droplets Generated in a LiNbO3 Opto‐Microfluidic Platform

AbstractIn this work, droplets elongation as a result of the photo‐induced photovoltaic electric field is presented and modeled. Moving water droplets are generated in microfluidics channels by means of a droplet‐based opto‐microfluidic platform integrated in lithium niobate (LN). A cross‐junction is engraved on the substrate as droplets generator, on top of which a z‐cut iron‐doped lithium niobate (Fe:LN) crystal is placed in order to build up photo‐induced electric field as a result of photovoltaic effect promoted upon suitable illumination. Droplets detection is realized by optical waveguides, designed in a Mach‐Zehnder Interferometer (MZI) configuration on the same substrate. The dynamics of droplet elongation is investigated, highlighting the impact of the photovoltaic electric field on the droplet dimension and surface tension.

Self-mixing Interferometer: Frequency Modulation Noise Dependence on Laser Source

The acquisition of frequency modulation in self-mixing interferometry opens the way to a new generation of instruments, with significantly superior performance compared to traditional self-mixing interferometers. In this work, we experimentally confirm the noise limit dependence of this kind of interferometer on the laser source linewidth. The obtained results confirm the theoretical prediction, opening the way for a deeper improvement in sensitivity, by employing narrow-line lasers in this interferometric configuration.

Cepstrum-based interferometric microscopy (CIM) for quantitative phase imaging

A universal methodology for coding-decoding the complex amplitude field of an imaged sample in coherent microscopy is presented, where no restrictions on any of the two interferometric beams are required. Thus, the imaging beam can be overlapped with, in general, any other complex amplitude distribution and, in particular, with a coherent and shifted version of itself considering two orthogonal directions. The complex field values are retrieved by a novel Cepstrum-based algorithm, named as Spatial-Shifting Cepstrum (SSC), based on a weighted subtraction of the Cepstrum transform in the cross-correlation term of the object field spectrum in addition with the generation of a complex pupil from the combination of the information retrieved from different holographic recordings (one in horizontal and one in vertical direction) where one of the interferometric beams is shifted 1 pixel. As a result, the field of view is tripled since the complex amplitudes of the three interferometric fields involved in the process are retrieved. Proof-of-concept validation of this methodology, named as Cepstrum-based Interferometric Microscopy (CIM), is provided considering an off-axis holographic configuration for retrieving the cross-correlation of the two interferometric complex amplitude fields in a compact quasi-common path Michelson interferometric configuration. Experimental results for different types of phase samples (resolution test targets for step-by-step calibration and demonstration as well as fixed biosamples) are included.

A spatial carrier dynamic quantitative differential phase imaging method

Differential interference contrast (DIC) microscopy is an important method for quantitative phase imaging (QPI) due to its high compatibility regarding to partial coherent light illumination and excellent optical sectioning ability. However, limited by the on-axis interferometric configuration of Nomarski DIC microscopic imaging system, it is difficult to achieve single-shot phase retrieval. Here, we propose a simple and efficient method for dynamic quantitative differential phase imaging (QDPI) by introducing a spatial carrier device into DIC microscope. A Wollaston prism (WP) is placed on the imaging plane of DIC microscope and then projected by a 4f imaging system, so two orthogonally polarized imaging beams with a certain shearing amount will interfere on the conjugate plane of the 4f imaging system and form a spatial carrier DIC image, thus the QDPI can be conveniently realized. Importantly, the system not only possesses high temporal phase stability provided by the common-path geometries and low spatial phase noise due to partially coherent light illumination, but also the advantages of simple optical implementation, no additional phase distortion, high light energy utilization efficiency, and high signal-to-noise ratio. The experimental result demonstrates that using the proposed method, the phase measurement sensitivity reaches 0.003 rad, the corresponding applicability is verified by a polystyrene microsphere crown and biological cells.

Fast reconstruction of programmable interferometers with intensity-only measurements

Programmable linear optical interferometers are promising for classical and quantum applications. Their integrated design makes it possible to create more scalable and stable devices. To use them in practice, one has to reconstruct the whole device model taking the manufacturing errors into account. The inability to address individual interferometer elements complicates the reconstruction problem. A naive approach is to train the model via some complex optimization procedure. A faster optimization-free algorithm has been recently proposed (Bantysh et al 2023 Opt. Express 31 16729–42). However, it requires the full transfer matrix tomography while a more practical setup measures only the fields intensities at the interferometer output. In this paper, we propose the modification of the fast algorithm, which uses additional set of interferometer configurations in order to reconstruct the model in the case of intensity-only measurements. We show that it performs slightly worse than the original fast algorithm but it is more practical and still does not require intensive numerical optimization.

Loss and revival of coherence in the interaction between a positron beam and a photon field

We study the interaction between a positron beam in the single-particle regime in an interferometric configuration and a microwave electromagnetic field. We discuss the conditions under which quantum interference can be affected by the field and we outline its possible experimental study in the framework of QUantum interferometry and gravitation with Positrons and LASers (QUPLAS) experiment.

Reconfigurable all-optical logic device based on cross-phase modulation across highly non-linear fiber

All-optical logic gates are the basic building blocks of photonic integrated circuits to be used for signal processing, to ensure high speed signal processing and decreasing complexity of network. In this paper, reconfigurable all-optical logic gate has been proposed and numerical simulations are analysed at a bit rate of 120 Gb/s. Wavelength Converter, NOT, NOR, AND, XOR, XNOR, A¯.B and OR are the all-optical logic gates that has been designed and implemented using single circuit and has minimum quality factor of 27 dB. All the signal processing operations have been implemented by the exploitation of cross-phase modulation in two parallelly placed (Mach-Zehnder Interferometric configuration) highly nonlinear fibers (HNLF). The influence of variation in input power, at different length of HNLF determines that the quality factor increases for increase in power or length of highly nonlinear fiber up to a certain limit. Quality factor increases for decrease in effective area of the highly nonlinear fiber for a certain range of input power and saturates for further increase in input power. Also, the quality factor is not directly affected with increase in bit rate but adversely affected by increase in dispersion.

One-step jones matrix polarization holography for polarization-sensitive materials using angular-multiplexing

A polarization digital holography (DH) using angular multiplexing was developed for extracting the Jones matrix of anisotropy materials in one step. This technique is implemented by adopting an off-axis interferometric configuration connecting two identical CCD cameras. The combined orthogonal 45° beams is split using a nonpolarizing beam splitter to produce the sample and reference beams. Our method yields two angular-multiplexing polarization interferograms simultaneously, in which the orthogonal fringe directions for each interferogram are modulated by two self-installed retro-reflector mirrors. In this case, the spatially resolved Jones matrix parameters of the polarization-sensitive materials can be determined in one step. The basic feasibility of the scheme is verified by measuring the Jones matrices of polarizing optics, a transmitted spatial light modulator, and synthetic mica plates.

Design and analysis of SOA-MZI based optical digital circuits for high speed optical networks

This paper explores using Semiconductor Optical Amplifier assisted Mach-Zehnder Interferometer (SOA-MZI) configuration for designing various all-optical digital circuits. A specific focus on the design and analysis of all-optical inverters, decimal-to-binary code converters, and hexa decimal-to-binary code converters operating at a speed of 10 Gbps is given. These circuits employ OR, XOR, and NOR gates. The SOA-MZI configuration capitalizes on the nonlinear properties of the SOA to achieve all-optical logic functions. Phase modulation can be transformed into intensity modulation by incorporating the SOA within an interferometer setup and using 3-dB couplers. The Cross-Phase Modulation (XPM) technique, which offers superior performance compared to other types of SOA non-linearity, is employed to make the incoming signal insensitive to polarization. The system was analyzed using an optisystem. The performance achieved was 0.0109 in terms of Eye height, 3.45 e−70 in terms of Bit Error Rate (BER), and 17.66 in terms of Q-factor.

A large-momentum-transfer matter-wave interferometer to measure the effect of gravity on positronium

This paper reports the study of a new interferometric configuration to measure the effect of gravity on positronium. A Mach–Zehnder matter-wave interferometer has been designed to operate with single-photon transitions and to transfer high momentum to a 200 eV positronium beam. The work shows the results and methods used to simulate the interferometer and estimate the operating parameters and the time needed to perform the experiment. It has been estimated that within less than 1 year, the acquisition time is sufficient to achieve a 10% accuracy level in measuring positronium gravitational acceleration, even with a poorly collimated beam, which is significant for theoretical models describing matter–antimatter symmetry. These results pave the way for single photon transition large momentum transfer interferometry with fast atomic beams, which is particularly useful for studies with antimatter and unstable atoms.

Orbital configurations of spaceborne interferometers for studying photon rings of supermassive black holes

Recent advances in technology coupled with the progress of observational radio astronomy methods resulted in achieving a major milestone of astrophysics - a direct image of the shadow of a supermassive black hole, taken by the Earth-based Event Horizon Telescope (EHT). The EHT was able to achieve a resolution of ∼20μas, enabling it to resolve the shadows of the black holes in the centres of two celestial objects: the supergiant elliptical galaxy M87 and the Milky Way Galaxy. The EHT results mark the start of a new round of development of next generation Very Long Baseline Interferometers (VLBI) which will be able to operate at millimetre and sub-millimetre wavelengths. The inclusion of baselines exceeding the diameter of the Earth and observation at as short a wavelength as possible is imperative for further development of high resolution astronomical observations. This can be achieved by a spaceborne VLBI system. We consider the preliminary mission design of such a system, specifically focused on the detection and analysis of photon rings, an intrinsic feature of supermassive black holes. Optimised Earth, Sun–Earth L2 and Earth–Moon L2 orbit configurations for the space interferometer system are presented, all of which provide an order of magnitude improvement in resolution compared to the EHT. Such a space-borne interferometer would be able to conduct a comprehensive survey of supermassive black holes in active galactic nuclei and enable uniquely robust and accurate tests of strong gravity, through detection of the photon ring features.

All optical 4 bit digital to analog converter based on carrier reservoir SOA-Mach Zehnder Interferometer (MZI) configuration

All optical 4 bit digital to analog converter based on carrier reservoir SOA-Mach Zehnder Interferometer (MZI) configuration

Simultaneous thickness and phase index measurements with a motion-free actively tunable Twyman-Green interferometer.

In this paper, we present a scheme to simultaneously measure the thickness and refractive index of parallel plate samples, involving no bulk mechanical motion, by deploying an electronically tunable Twyman-Green interferometer configuration. The active electronic control with no bulk mechanical motion is realized via the introduction of a tunable focus lens within the classical motion-based Twyman-Green interferometer configuration. The resulting interferometer is repeatable and delivers accurate estimates of the thickness and refractive index of a sample under test. Elimination of bulk motion also promises a potential for miniaturization. We develop a theoretical model for estimating sample thickness and index values using this reconfigurable interferometer setup and present detailed experimental results that demonstrate the working principle of the proposed interferometer.

Star shape interferometer with reduced vibration sensitivity

An optical interferometer has a high sensitivity to displacements of the mirrors and other optical elements, something that becomes a source of fluctuations in situations where one is only interested in the phase change due to a sample inserted in one of the paths. A Sagnac interferometer minimizes this sensitivity by having the two beams follow opposite trajectories, so that a mirror displacement gives a similar phase change for both paths, but makes it impossible to insert an element that affects only one path. We present a new kind of interferometer, the Star interferometer, where the two beams still interact with all the optical elements while having different trajectories. We obtain a common phase change in both trajectories by having a different number of turns for each path. Having independent access to both trajectories makes it possible to determine the phase change due to a sample inserted in one of the paths, opening new possibilities for interferometric configurations that maintain a reduced sensitivity to displacements of the optical elements.