Mach-Zehnder Research Articles

Gain sensitivity of the Mach–Zehnder interferometer by photon subtraction

Abstract The phase sensitivity of a Mach–Zehnder (MZ) interferometer with a two-mode squeezed vacuum (TMSV) probe state is studied. At the initial stage, the TMSV state is deterministically converted into two single-mode squeezed vacuum (SMSV) states, from each of which photons are subtracted via photon-number resolving measurement in auxiliary measurement modes. The new probe state can already demonstrate gain sensitivity of more than 20 dB with input squeezing of 5 dB and follow Heisenberg scaling. The phase sensitivity of the MZ interferometer, estimated by measuring the intensity difference of two measurement-induced continuous variable states, can surpass the ultimate one with SMSV probe states, at least, with squeezing less than 5 dB. In general, the strategy with preliminary subtraction of photons significantly increases the estimate potential of weakly squeezed states as the probe in MZ phase-dependent interferometry; in particular, it is more effective compared to generating highly squeezed TMSV states or SMSV states.

Design and Demonstration of a Novel Interferometric Polarimeter for Quantitative Determination of Sugars in a Solution

Accurate quantification of sugar in food and pharmaceutical products is important to achieve the desired levels of sweetness, texture, flavor and nutritional content. This article introduces a novel polarization-sensitive interferometric method for measuring the concentration of sugar in solutions. The impact of sugar concentration is investigated by analyzing the visibility of the interference pattern using a Mach-Zehnder interferometer with an interference pattern scanning and recording system. The visibility of the interference fringes is determined by cross-sectional scanning of the fringe pattern from its center over the photodetector, followed by cut-profile analysis. As the concentration of sucrose, glucose and fructose increases, a gradual decrease in interference pattern visibility is observed, following a parabolic trend within the broader detection range of 0–14 g/50 ml. The sensor’s performance is divided into two linear regions: region-1 (0–6 g/50 ml) and region-2 (6–14 g/50 ml). In region-1, fructose exhibited the highest sensitivity of 0.0195 (g/50 ml)-1, which is 6.09 times and 1.89 times higher than glucose and sucrose, respectively. Similarly, in region-2, fructose showed a sensitivity of 0.077 (g/50 ml)-1, surpassing glucose by 3.56 times and sucrose by 2.41 times. However, sucrose achieved the lowest limit of detection of 0.0021 g/ml, which is 2.76 times and 1.71 times better than glucose and fructose, respectively. The decreasing trend in interference pattern visibility is further validated through irradiance and optical rotation measurements of the laser beam passing through the sugar solutions relative to the reference laser beam. Results from both optical techniques demonstrated good agreement, with average deviations of 1.75%, 1.72%, and 4.24% for sucrose, glucose and fructose, respectively. The proposed technique is universally applicable for measuring the concentration of transparent, optically active solutions and has the potential to be a valuable tool for quality control and optimization in the food and pharmaceutical industries.

Wavelength Locking and Calibration of Fiber-Optic Ultrasonic Sensors Using Single-Sideband-Modulated Laser

Implementation of edge-filter detection for interrogating optical interferometric ultrasonic sensors is often hindered by the lack of cost-effective laser sources with agile wavelength tunability and good noise performance. The detected signal can also be affected by optical power variations and locking-point drift, negatively affecting the sensor accuracy. Here, we report the use of laser single-sideband generation with a dual-parallel Mach–Zehnder interferometer (DP-MZI) for laser wavelength tuning and locking in edge-filter detection of fiber-optic ultrasonic sensors. We also demonstrate real-time in situ calibration of the sensor response to ultrasound-induced wavelength shift tuning. The DP-MZI is employed to generate a known wavelength modulation of the laser, whose response is used to gauge the sensor response to the ultrasound-induced wavelength shifts in real time and in situ. Experiments were performed on a fiber-optic ultrasonic sensor based on a high-finesse Fabry–Perot interferometer formed by two fiber Bragg gratings. The results demonstrated the effectiveness of the laser locking against laser wavelength drift and temperature variations and the effectiveness of the calibration method against optical power variations and locking-point drift. These techniques can enhance the operational robustness and increase the measurement accuracy of optical ultrasonic sensors.

Seven-Core Fiber Composite Structures-Based Mach-Zehnder Interferometer for Bending and Temperature Measurement

AbstractIn the paper, an optical fiber sensor based on a seven-core fiber composite structure is presented, which enables dual-parameter sensing of bending and temperature. The proposed structure is fabricated by combining the strongly-coupled seven-core fibers (SC-SCFs) and a weakly-coupled seven-core fiber (WC-SCF). The SC-SCF acts as a beam coupler and enhances the Mach-Zehnder interference, while the WC-SCF serves as the enhanced section of another Mach-Zehnder interference. Therefore, the spectrum response of the fiber structure mentioned above exhibits a superposition effect of two Mach-Zehnder interferometers (MZIs). Among them, two dips corresponding to different MZIs are used to measure bending and temperature. The experimental results show the bending sensitivity and temperature sensitivity of the two MZIs are −4.238 nm/m−1, −2.263 nm/m−1, 0.047 nm/°C, and 0.064 nm/°C, respectively. It proves that our sensor is very sensitive to bending. Through the dual-wavelength matrix method, the bending and temperature can be measured simultaneously. With the benefit of the composite structure, low cost, and ease of fabrication, the proposed sensor can be used in harsh environments.

Quantum computation with photochromic films in a Mach–Zehnder interferometer

Photochromic materials are of great interest because they enable the fabrication of photo-activated switches. In this study, an experiment is proposed in which two chromene-based photochromic layers were inserted into the arms of a Mach–Zehnder interferometer. The chromene was studied from the perspective of optical absorption to determine the wavelength-dependent complex refractive index. Impinging ultraviolet light on one of the chromene layers induces a transition from the closed to the open form of the chromene, resulting in different phase shifts in the two arms of the interferometer. This results in a change in the probability of detecting a photon by the two detectors after the second mirror of the Mach–Zehnder interferometer. The experiment may be of interest to researchers working in the fields of quantum information and quantum communications.

Optimization of InP-based traveling-wave Mach-Zehnder modulator design using artificial neural network and heuristic algorithms

In this study, we report an innovative multi-parameter artificial neural network (ANN) based optimization approach for designing InP-based capacitive loading traveling wave Mach-Zehnder modulators (CL-MZMs). Our ANN-based heuristic algorithm optimization method surpasses traditional manual optical device design in efficiently searching for the optimal solution, based on user-defined figure of merit (FOM) in a large multi-parameter design space, while also providing statistical data-based insight into the underlying complex device physics involved. We achieved an optimized 1 mm InP MZM design, with an anticipated 112 GHz 3-dB electro-optic bandwidth and 5.8 V half-wave voltage, making it a promising candidate for next-generation data center high-speed optical link applications at 400 Gb/s and beyond.

High-Extinction Photonic Filters by Cascaded Mach–Zehnder Interferometer-Coupled Resonators

In this study, we demonstrate high-extinction stop-band photonic filters based on Mach–Zehnder interferometer (MZI)-coupled silicon nitride (Si3N4) resonators fabricated using I-line lithography technology. Leveraging the low-loss silicon nitride waveguide, our approach enables the creation of stable, high-performance filters suitable for applications in quantum and nonlinear photonics. With destructive interference at the feedback loop, photonic filters with an extinction ratio of 35 dB are demonstrated with four cascaded MZI-coupled resonators. This cascading design not only enhances the filter’s extinction but also improves its spectral sharpness, providing a more selective stop-band profile. Experimental results agree well with the theoretical results, showing linear scaling of extinction ratios with the number of cascaded MZI-coupled resonators. The scalability of this architecture opens the possibility for further integration and optimization in complex photonic circuits, where high extinction ratios and precise wavelength selectivity are critical for advanced signal processing and quantum information applications.

Analysis of SiNx Waveguide-Integrated Liquid Crystal Platform for Wideband Optical Phase Shifters and Modulators

In this study, the potential of employing SiNx (silicon nitride) waveguide platforms to enable the use of liquid-crystal-based phase shifters for on-chip optical modulators was thoroughly investigated using 3D-FDTD (3D finite-difference time-domain) simulations. The entire structure of liquid-crystal-based Mach–Zehnder interferometer (MZI) optical modulators, consisting of multi-mode interferometer splitters, different tapering sections, and liquid-crystal-based phase shifters, was systematically and holistically investigated with a view to developing a compact, wideband, and CMOS-compatible (complementary metal-oxide semiconductor) bias voltage optical modulator with competitive modulation efficiency, good fabrication tolerance, and single-mode operation using the same SiNx waveguide layer for the entire device. The trade-off between several important parameters is critically discussed in order to reach a conclusion on the possible optimized parameter sets. Contrary to previous demonstrations, this investigation focused on the potential of achieving such an optical device using the same SiNx waveguide layer for the entire device, including both the passive and active regions. Significantly, we show that it is necessary to carefully select the phase shifter length of the LC-based (liquid crystal) MZI optical modulator, as the phase shifter length required to obtain a π phase shift could be as low as a few tens of microns; therefore, a phase shifter length that is too long can contradictorily worsen the optical modulation.

Simple three-stage control scheme achieving interrupt-free integrated polarization stabilization

It is a long-outstanding challenge to achieve low-complexity interrupt-free integrated polarization stabilization of infinitely changing light. Integrated phase shifters have finite tuning range and experience abrupt switching or reset when reaching the limits of their tuning ranges during the polarization stabilization process. We propose a three-stage interrupt-free integrated polarization stabilization scheme with nested electronic-photonic loops (NEPL) and dimensionality reduction (DR) method. Based on the NEPL structure, only three Mach-Zehnder interferometer (MZI) stages are needed to achieve interrupt-free polarization stabilization scheme. The input state is first constrained into a predetermined range using a nested loops with the first MZI stage and then processed by regular two-stage scheme. Throughout the entire operation, all phase shifters are tuned continuously without any pause, abrupt switching or reset. Furthermore, a DR method is introduced to reduce the control complexity and enhance control speed and accuracy of the regular two-stage scheme. A detailed analysis of the proposed design is provided, and its effectiveness is verified using electronic-photonic co-simulation in the Cadence platform. This scheme consists of only phase shifters, couplers and photodiodes (PDs) with simple electronic controllers, and can be implemented in various material systems and process platforms. To the best of our knowledge, this is the first three-stage interrupt-free polarization stabilization scheme reported in the literature.

Interferometric analysis of the opto‐mechanical properties for polyamide‐6 antimicrobial fibers

AbstractPolyamide‐6 fibers were modified for use as antimicrobial fibers using two complementary methods: grafting with polyacrylic acid and silver nanoparticle treatment. The grafted samples exhibited different grafting yields of 7%, 8.8%, 10%, and 20.7%. Subsequently, two grafted samples (7% and 20.7% yields) were treated with silver nanoparticles (Ag NPs). The grafting process and the silver nanotreament were successfully confirmed using FTIR spectroscopy and SEM microscopy. Shake‐ flask method was used to study the cell viability of nanotreated samples. A two‐beam Mach–Zehnder interferometer was used to characterize the opto‐mechnaical and structural properties of the modified samples. For this purpose, a mechanical drawing device was equipped with the interferometer. The results indicated that with increasing grafting yield, optical properties decreased in both directions of light vibration. A fitting method was employed to calculate intrinsic optical properties that help to determine structural properties. Mechanical properties, including tensile strength and elongation at break, were also examined. Treatment of the grafted samples with silver nanoparticles improved their optical, mechanical, and antimicrobial properties. These findings confirmed that the PA‐6‐g‐PAA 20.7%‐t‐Ag NPs sample is suitable for various medical applications. Figures and tables are provided for illustration.Highlights PA‐6 fiber has been modified for medical applications by complementary processes. Grafting process introduced additional functional groups and enhanced ductility. Ag nano‐treatment gives the grafted PA‐6 fiber good antimicrobial activity. Interferometry precisely characterizes structural and opto‐mechanical properties. PA‐6‐g‐PAA20.7%‐t‐Ag NPs sample has good mechanical and antimicrobial properties.

Polarization-insensitive optical coherence tomography using pseudo-depolarized reference light for mitigating birefringence-related image artifacts.

Optical coherence tomography (OCT) images are prone to image artifacts due to the birefringence of the sample or the optical system when a polarized light source is used for imaging. These artifacts can lead to degraded image quality and diagnostic information. We aim to mitigate these birefringence-related artifacts in OCT images by adding a depolarizer module in the reference arm of the interferometer. We investigated different configurations of liquid crystal patterned retarders as pseudo-depolarizers in the reference arm of OCT setups. We identified the most effective depolarization module layout for polarization artifact suppression for a spectral-domain OCT system based on a Michelson and a Mach-Zehnder interferometer. The performance of our approach was demonstrated in an achromatic quarter-wave plate allowing the selection of a variety of sample polarization states. A substantial improvement of the OCT signal magnitude was observed after placing the optimal depolarizer configuration, reducing the cross-polarization artifact from 5.7 to 1.8dB and from 8.0 to 1.0dB below the co-polarized signal for the fiber-based Michelson and Mach-Zehnder setup, respectively. An imaging experiment in the birefringent scleral tissue of a post-mortem alpine marmot eye and a mouse tail specimen further showcased a significant improvement in the detected signal intensity and an enhanced OCT image quality followed by a drastic elimination of the birefringence-related artifacts. Our study presents a simple yet cost-effective technique to mitigate birefringence-related artifacts in OCT imaging. This method can be readily implemented in existing OCT technology and improve the effectiveness of various OCT imaging applications in biomedicine.

Femtosecond laser-inscribed in-fiber Mach-Zehnder interferometer for ultra-sensitive small-angle torsion measurement

We propose and demonstrate a novel in-fiber Mach-Zehnder interferometer (MZI), using a femtosecond (FS) laser to inscribe two parallel straight waveguides along both sides of the core-cladding boundary of an optical fiber. Both simulations and experiments demonstrated that constructing a second straight waveguide (WG2) on the opposite side of the fiber core significantly enhances the mode coupling efficiency in fiber, resulting in ultra-sensitive small twist-angle torsion measurement by intensity interrogation. By finely adjusting the waveguide spacing between the WG2 and the fiber core during the FS fabrication process, a large tuning range of ∼ 200 nm for the designable interference wavelength with maximal fringe contrast has been achieved. Through comparative experiments, the proposed in-fiber MZI performs ultra-sensitivity with 17417.92 dB/(rad/mm) over small twist angles from −10° to 0° for the sample “WG1-4/WG2-4” and 19480.57 dB/(rad/mm) over small twist angles from 0° to 10° for the sample “WG1-4/WG2-6”. Besides, the device is insensitive to temperature and strain. The exhibited advantages of high sensitivity, high reproducibility, and low crosstalks promote the proposed in-fiber MZI to be applied in future industrial engineering monitoring and intelligent health monitoring.

High-Sensitivity Liquid-Level Sensor Based on Mach-Zehnder Interferometer With a Side-Polished Structure

High-Sensitivity Liquid-Level Sensor Based on Mach-Zehnder Interferometer With a Side-Polished Structure

An Mach-Zehnder Interferometer Refractive Index Sensor Based on Self-phase Modulation Effect in a Tapered Double-cladding Highly Nonlinear Fiber

An Mach-Zehnder interferometer (MZI) sensor based on self-phase modulation (SPM) effect in a tapered double-cladding highly nonlinear fiber (DCHNLF) was proposed and experimentally verified for refractive index (RI) measurement. The DCHNLF was tapered and the SPM spectrum generated in its untapered region acted as the broadband light source for the sensor. The integration of the SPM effect and the RI detection not only simplified the structure of the sensor, but also enhanced its long-term stability and reliability. Since the effective RI of the outer cladding mode of the tapered DCHNLF was affected by the RI variation, a spectral shift would occur in interference spectrum between the core mode and the outer cladding mode. The tapering treatment enhanced the evanescent wave on the surface of DCHNLF, making the sensor more sensitive to external RI. In the external RI range of 1.3333 ~ 1.3972, the sensor achieved an excellent sensitivity of 238.51nm/RIU. In addition, the effect of average pump power and pump wavelength on the sensor performance were experimentally discussed. The results showed that the sensitivity was not affected by the pump condition. This MZI RI sensor has advantages of excellent performance, simple structure and easy fabrication, demonstrating broad application prospects in biomedical research, marine environment monitoring, and human health detection.

Integrated all-fiber-optic sensor based on FPI and MZI composite structures for temperature and strain measurement

In this paper, a temperature and strain sensor based on fiber-optic Mach-Zehnder interferometer (MZI) cascaded with Fabry-Perot interferometer (FPI) is designed and fabricated. The integrated sensor structure consists of no-core fiber (NCF) sandwiched by two sections of multi-mode fiber (MMF), hollow-core fiber (HCF), and two single-mode fibers (SMF) which are cascaded at the ends of the MMF and the HCF. Due to the thermal expansion effect, thermo-optic and elasto-optic effects of fiber material, the increase of the temperature and strain will make the change of the transmission mode, which will cause the spectral fringes wavelength shifting with strain, and the intensity of the spectral fringes varying with temperature but not strain variations in multiple temperature ranges. The series experiments valid show that the sensor with integrated structure realizes the strain and temperature measurements in multiple temperature ranges, and the minimum and maximum temperature sensitivities are -0.278dBm/°C and -0.670dBm/°C in the temperature range of 68-86 °C and 123-141 °C, respectively. The strain sensitivity is 2.17pm/με all over the measured range. The integrated sensor structure has the advantages of high sensitivity, multiple measuring ranges, simple manufacturing, and low cost, which has the potential to be applied in the field of the internal strain and temperature measurements of different structures.

High-fold optical subdivision blazed grating interferometer based on Mach-Zehnder interferometer

A blazed grating interferometer with high-fold optical subdivision is proposed based on the optical path design of Mach-Zehnder interferometer. In the designed measurement system, multiple diffractions are achieved on the blazed grating surface, fully leveraging the high diffraction efficiency of the blazed grating and avoiding the presence of non-coplanar beams. Furthermore, in order to avoid beam deformation resulting from multiple diffractions, the light path structure returning along the same path is constructed, and this design doubles the optical subdivision fold factor. The experimental results show that 14-fold optical subdivision can be realized in this measurement system, and the maximum calibration difference can reach 34.47 nm within a 0.2 mm travel and 101.07 nm within a 2 mm travel. The designed blazed grating interferometer has the characteristics of a simple structural layout, high-fold optical subdivision and high measurement performance, which lay the groundwork for actual product development.

Foundry fabricated compact slow-light Mach-Zehnder modulator and photodetector for on-chip analog photonic computing

This work presents a scaling pathway of on-chip analog photonic computing using foundry-fabricated silicon electro-optic (EO) slow-light Mach-Zehnder modulators (SL-MZMs) and compact Ge photodetectors (PDs) to construct a computing unit. Two SL-MZMs with phase shifter (PS) lengths of 500 μm and 150 μm are studied in this work. The bit resolution, nonlinearity, clock frequency, and power consumption of the photonic computing link, including an RF amplifier, on-chip SL-MZM, and a PD, are thoroughly investigated. The computing link using the SL-MZM with 500 μm has demonstrated a low normalized mean square error (NMSE) of 0.0305 at 8-bit resolution under 3.2 GHz clock frequency. Under the setting of 6-bit resolution at a clock frequency of 800 MHz, high computing accuracy was achieved with a measured NMSE of 0.0018 using the SL-MZM with 150 μm PS length. Using the Google Speed Commands dataset to run a voice keyword spotting task, we determine that 6-bit resolution operating at 3.2 GHz achieves the optimal power-accuracy trade-off. We show a 20× improvement in energy efficiency and a 3.35× improvement in area efficiency compared to NVIDIA V100 GPU [“Volta: Performance and programmability,” IEEE Micro 38(2), 42 (2018)10.1109/MM.2018.022071134 ]. These results show that our compact SL-MZMs and PDs promise to scale up photonic computing for practical machine-learning applications.

Fermion and boson pairs in beamsplitters and MZIs

Abstract In this short Topical Review, we look at something typically considered trivial, but not given formally elsewhere---the behaviour of first multiple fermions, then multiple bosons, at a beamsplitter. Extending from this, {we then describe} the behaviour of multiple fermions and multiple bosons in Mach-Zehnder interferometers (MZIs). We hope that by showing how to go from mathematically-simple but unintuitive quantum field theory to a phenomenological description, this Review will help {both} researchers and students build a stronger intuition for the behaviour of quantum particles.

Photonics-assisted self-interference cancellation for in-band full-duplex integrated sensing and communication transceiver

In-band full-duplex (IBFD) operation is essential for both sensing-centric and communication-centric integrated sensing and communications (ISAC) systems. Both types require the monostatic transceiver to overcome the technical challenge of self-interference (SI). To address this challenge, a photonics-assisted self-interference cancellation (SIC) scheme for an IBFD ISAC transceiver is proposed and experimentally demonstrated. By utilizing wavelength division multiplexing, the SI is cancelled by a cancellation reference with matched amplitude and time delay, using two counter-biased Mach-Zehnder modulators. In proof-of-concept experiments, the proposed IBFD ISAC transceiver is tested using a 10 GHz quadrature amplitude modulation (QAM) constant envelope linear frequency modulation orthogonal frequency division multiplexing (CE-LFM-OFDM) ISAC signal with a carrier frequency and a bandwidth of 10 GHz and 2 GHz, respectively. Experimental results show that cancellation depths of 35.29 dB and 32.59 dB are achieved with bandwidths of 1 GHz and 2 GHz, respectively, in the communication receiver. The corresponding weak signal of interest is successfully recovered after effective SIC in the wireless link. The ranging and imaging functions are also experimentally verified. The experimental results show that the cancellation depth of the SI after de-chirping is 23.6 dB when the center frequency and bandwidth of the CE-LFM-OFDM RF signal are 10 GHz and 2 GHz, respectively. A dynamic range increase of 23.84 dB is achieved in imaging function. The corresponding radar ranging resolution of 10 cm is also achieved for radar function. The proposed scheme cancels the SI in both communication and radar receivers, demonstrating excellent performance in the IBFD ISAC transceiver system.

Silicon-on-insulator wavelength-selective filter with integrated detectors at the 2 µm wave band.

The short-wave infrared range is highly significant for spectroscopic sensing and upcoming optical communication applications. Integrating active and passive photonic components is essential to achieve compact optical solutions. In this paper, we show, for the first time to our knowledge, a wavelength-selective detection system based on the heterogeneous integration of two grating-coupled InGaAs photodetectors operating at the 2µm wave band, with a wavelength selectivity provided by a dual-channel Mach-Zehnder interferometer fabricated using a silicon-on-insulator (SOI) wafer. A full system responsivity of 0.1 A/W is measured together with >9.5 dB rejection ratio at two wavelengths. To our knowledge, we achieve the lowest measured dark current density (7.6 × 10-4 A/cm2 at -2 V) with micro-transfer printed integrated detectors.