Sagnac Research Articles

Ultrafast laser-enabled optoacoustic characterization of Three-dimensional, nanoscopic interior features of microchips

The recent advances in micromanufacturing have been pushing boundaries of the new generation of semiconductor devices, which, in the meantime, brings new challenges in the material and structural characterization – a key step to ensure the device quality through the micromanufacturing process. An ultrafast laser-enable optoacoustic characterization methodology is developed, targeting in situ calibration and delineation of the three-dimensional (3-D), nanoscopic interior features of opaque semiconductor chips. With the guidance of ultrafast electron–phonon coupling effect and velocity-perturbated optical interference, a femtosecond-laser pump–probe set-up based on Sagnac interferometer is configured to generate and acquire picosecond ultrasonic bulk waves (P-UBWs) traversing the microchips. The interior features of the microchips shift the phase of acquired P-UBW signals, reflected in the perturbed probe laser beam. The phase shifts are calibrated to compute signal correlation of P-UBW signals between different acquiring positions, whereby to delineate the interior features in an intuitive manner. The approach is experimentally validated by characterizing nanoscopic, invisible interior aurum(Au)-gratings with periodically varied depths in typical microchips. Results highlight that the 3-D nanoscopic features of the microchips can be revealed with a microscopic and a nanoscopic spatial resolution, respectively along the transverse and depth directions of the chip, where the Au-gratings become “visible” with a depth variance of a few tens of nanometers only. This proposed approach has provided a fast, nondestructive approach to “see” through an opaque microchip with a nanoscopic resolution.

Use of a rugged mid-infrared spectrometer for in situ process analysis of liquids

The widespread application of mid-infrared (MIR) spectroscopy for process monitoring is currently limited by the poor transmission of MIR light through fibre optics. In this work, the performance of a novel and robust MIR spectrometer has been evaluated for practical deployment in a pilot plant or production environment. The spectrometer utilises a Sagnac interferometer design containing no moving parts and is directly attached to an attenuated total reflectance probe, eliminating the need for fibre optics. The quantitative performance of the spectrometer for the in situ analysis of ternary solvent mixtures was assessed. The predictions obtained by partial least squares were accurate (root mean square error of prediction of < 1% w/w) and comparable to those of a benchmark Michelson-based spectrometer with a fibre-coupled probe, which is more amenable to process development in a laboratory or pilot plant. Calibration transfer between the two spectrometers was performed using the spectral space transformation method to mimic the scenario of the scale-up of a process from the laboratory to pilot scale or from a pilot plant to production scale, where the two different MIR instruments might be deployed. The ability to perform in situ reaction monitoring with the robust Sagnac-based spectrometer was then demonstrated. Spectra acquired during an esterification reaction were resolved using multivariate curve resolution, to produce concentration profiles of each component. These results demonstrate the suitability of this rugged spectrometer for quantitative in situ monitoring of liquid processes, opening up new opportunities for process monitoring in the MIR region.

Signal-to-noise-ratio amplification based on symmetry breaking induced by the Sagnac effect

Signal-to-noise-ratio amplification based on symmetry breaking induced by the Sagnac effect

Temperature and Lateral Pressure Sensing Using a Sagnac Sensor Based on Cascaded Tilted Grating and Polarization-Maintaining Fibers

This study introduces a Sagnac Interferometer (SI) fiber sensor that integrates Polarization-Maintaining Fibers (PMFs) with a Tilted Fiber Bragg Grating (TFBG) for the dual-parameter measurement of strain and lateral pressure. By incorporating a 6° TFBG with PMFs into the SI sensor, its sensitivity is significantly enhanced, enabling advanced multi-parameter sensing capabilities. The sensor demonstrates a temperature sensitivity of −1.413 nm/°C and a lateral pressure sensitivity of −4.264 dB/kPa, as validated by repeated experiments. The results exhibit excellent repeatability and high precision, underscoring the sensor’s potential for robust and accurate multi-parameter sensing applications.

Sagnac-witnessed laser deflection is an ultra-sensitive acoustic detector

Laser-deflection-based acoustic sensing is known for high bandwidth but low sensitivity. By embedding the sensing laser within a Sagnac interferometer and incorporating split-beam detection—originally developed for optical trapping microscopy—we demonstrate sensitive acoustic detection in air with a 2 MHz bandwidth. In a direct comparison, our method far-exceeds performance metrics of a state-of-the-art, commercially-available, high-bandwidth microphone. In upcoming large-volume-bubble-chamber searches for dark matter, our method could replace traditional acoustic sensors confined to the chamber’s exterior where signals are weakest.

Experimental demonstration of the time-dependent source side-channel and countermeasures in polarization-based BB84 QKD systems

High-speed is one development tendency of the practical and commercial quantum key distribution (QKD) systems, and the gain-switched semiconductor laser (GSSL) and Sagnac interferometer have been popular components for high-speed commercial polarization-based BB84 QKD systems thanks to their stability, compactness and low cost. However, due to the finite extinction ratio (ER) of the GSSL, the time-dependent source side-channel, which is theoretically presented in [Phys. Rev. A 106(6): 062618 (2022)10.1103/PhysRevA.106.062618], also exists in these QKD systems. In this article, we experimentally investigate this side-channel in the polarization-based BB84 QKD system. The results show an obvious correlation in the output polarization states between the weak leakage light and its adjacent pulses, which will cause information to leak. More importantly, we have proposed several countermeasures, retested the side channel, and developed a mathematical framework to quantitatively assess the impact of the time-dependent side channel and these countermeasures on the secure key rate. Finally, we offer a trade-off analysis that considers defense effectiveness, pulse impact, and cost for various countermeasures in QKD. This provides a practical recommendation for improving the security of QKD systems.

Experimental Study of Fiber-Optic Temperature Sensor Based on Dual FSIs

To improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaining fibers (PMFs) with lengths of 13.62 m and 15.05 m respectively is used to achieve the basic Vernier effect. Then by changing the length of one PMF to approximately i times that of the others, the FSI composed of two PMFs of 7.1 m and 15.05 m is used to achieve the first-order harmonic Vernier effect. Afterward, temperature sensing tests are conducted to observe the wavelength drift during temperature changes and ultimately achieve high sensitivity. The experimental results show that the temperature sensitivity of the sensor based on the first-order harmonic Vernier effect is −28.89 nm/°C, which is 17.09 times that of a single FSI structure (−1.69 nm/°C) and 1.84 times that of the sensitivity generated by the structure based on the basic Vernier effect (−15.69 nm/°C). The experimental results are consistent with the theoretical analysis. The structure proposed in this paper achieves drift measurement of 0.1 °C variation based on 1 °C drift, making the fiber optic temperature sensor applicable to related fields that require high precision temperature. The proposed temperature sensor has the simple structure, low production cost, high sensitivity, and broad application prospects.

A Study on Sensitivity Improvement of the Fiber Optic Acoustic Sensing System Based on Sagnac Interference.

A new pickup structure was introduced and modified to improve the resolution of the linear Sagnac optical fiber acoustic sensing system. The maximum strains corresponding to the material, diameter, wall thickness, and height of the pickups were analyzed by simulation. An aluminum cylinder with a diameter of 110 mm, a wall thickness of 3 mm, and a height of 120 mm was chosen as the basic pickup. A four-groove pickup with a vertical width of 80 mm and a horizontal width of 20 mm was introduced to improve the sensitivity of the system. The experiments showed that the average peak-to-peak sensitivity of the four-groove pickup increased by 215.54% to 106.806 mV/Pa. The improved pickup can be applied in areas to monitor the situation of invasion of the Sagnac optical fiber acoustic sensing system.

Single-shot picosecond interferometry for the characterization of laser-driven shock waves

In conventional laser-driven shock experiments, an out-of-plane shock wave is launched and is typically detected interferometrically after it propagates through the sample. In such experiments, the target materials are unavoidably optically damaged at each laser shot. This necessitates changing targets after laser exposure, lowering the shot-to-shot reproducibility and data quality. Here we present a Sagnac interferometer combined with an echelon that can split a single femtosecond probe into many beams, very well adapted for single-shot interferometric characterization of laser-induced shock waves. The echelon provides a 10 ps time resolution and a full time window of about 150 ps. The simplicity, stability, and sensitivity of the single-shot Sagnac interferometer technique ease the thorough characterization of picosecond to nanosecond shock waves, specifically for samples available in limited quantities or for samples that are not uniform from one region to the next.

Sagnac effect in a rotating ring with Dirac fermions

Sagnac effect in a rotating ring with Dirac fermions

Real-Time Optical Fiber Salinity Interrogator Based on Time-Domain Demodulation and TPMF Incorporated Sagnac Interferometer.

A novel demodulation scheme for a point-type fiber sensor is designed for salinity concentration monitoring based on a Sagnac interferometer (SI) composed of a tapered polarization-maintaining fiber (TPMF) and optical time stretching technology. The SI, constructed using a PMF with a taper region of 5.92 μm and an overall length of 30 cm, demonstrated a notable enhancement in the evanescent field, which intensifies the interaction between the light field and external salinity. This enhancement allows for a direct assessment of salinity concentration changes by analyzing the variations in the SI reflection spectra and the experimental results indicate that the sensitivity of the sensor is 0.151 nm/‱. In contrast to traditional fiber optic sensors that depend on spectral demodulation with slower response rates, this work introduces a new approach where the spectral shift is translated to the time domain, utilizing a dispersion compensation fiber (DCF) with the demodulation rate reaching up to 50 MHz. The experimental outcomes reveal that the sensor exhibits a sensitivity of -0.15 ns/‱ in the time domain. The designed sensor is anticipated to play a pivotal role in remote, real-time monitoring of ocean salinity.

Enhancement of Nonreciprocal Entanglement and Transmission via Phase‐Dependent Unidirectional Coupling

AbstractThe nonreciprocal property of quantum systems is crucial for chiral quantum networks. In this study, a phase‐controlled scheme is proposed to enhance the nonreciprocal quantum entanglement and optical transmission in a cavity optomechanical system by introducing a phase‐dependent unidirectional coupling between two whispering‐gallery‐mode (WGM) resonators. The Sagnac effect induced by the spinning resonator generates nonreciprocity, while the interference effect between direct evanescent coupling and indirect phase‐dependent unidirectional coupling significantly enhances entanglement under the anti‐Stokes sideband. For specific coupling phases, ideal nonreciprocity can be achieved in both entanglement and transmission. The proposed phase‐controlled nonreciprocity presented offers an effective strategy for constructing a unidirectional quantum channel and implementing an optical diode in chiral quantum networks, thereby opening up new possibilities for applications in quantum technologies.

Non-reciprocal optical phase shifter based on the Sagnac effect and its implementation as an optical isolator

This work describes the operation of a non-reciprocal optical phase shifter (NRPS) based on the Sagnac effect and provides examples of its usage through integration into various optical circuits. The origin of the occurrence of the phase shift was discussed and experimentally validated. The scheme of a non-magnetic optical isolator with NRPS embedded in a Sagnac interferometer was experimentally demonstrated. A ratio of 110:1 in light transmittance between the forward and backward directions was obtained.

Determination of temperature coefficient of change half-wave voltage phase modulator on LiNbO3.

Measurements of the half-wave voltage of the integrated-optical phase modulator on LiNbO3 were carried out in the temperature range from –40 to +60 °C. The measurements were carried out by two methods using the Sagnac and Mach-Zehnder interferometers. The temperature coefficients of the half-wave voltage change obtained in the experiments agree with the theoretical ones.

Design and analysis of glucose sensor based on Sagnac interferometer utilizing photonic crystal fiber with micro-holes

Design and analysis of glucose sensor based on Sagnac interferometer utilizing photonic crystal fiber with micro-holes

Ultra-sensitive strain sensor based on Sagnac interferometer with different length panda fiber

A high-sensitivity harmonic Vernier effect (HVE) strain sensor is fabricated by cascading Sagnac interferometer (SI) and Fabry-Perot interferometer (FPI). SI is fabricated by the panda fiber (PF). PF is a typical polarization maintaining fiber (PMF) that has two pressure zones, making it particularly sensitive to strain. SI1, SI2, and SI3 are constructed using PF with lengths of 20 cm, 50 cm, and 80 cm, respectively. They have interference spectra similar to sine waves in the wavelength range of 1250 nm to 1650 nm. Research has found that the sensitivity of SI is directly proportional to the effective PF length under strain action. In addition, if the strain acts on the entire length of the PF, the strain sensitivities of SI1, SI2, and SI3 are 30.4 pm/με, 28.4 pm/με, and 30.1 pm/με, respectively, which are relatively close. Then, FPI is fabricated by splicing single mode fiber (SMF) and quartz capillary, and it is an “SMF-Capillary-SMF” sandwich structure, and the free spectral range (FSR) of FPI is approximately half of that of SI2. FPI and SI2 are cascaded to produce a first-order HVE sensor, further amplifying the strain sensitivity of SI2. The intersection point of the internal envelope based on the HVE sensor spectrum can provide accurate spectral wavelength position and drift, and the strain sensitivity of the HVE sensor reaches 293.0 pm/με, improving the strain sensitivity of SI2 by 10.3 times. The detection limit of the HVE sensor is 0.5 µε as the strain varies from 0 to 700 µε. This HVE strain sensor is relatively easy to manufacture, low-cost, linear and reliable, and can achieve high sensitivity strain measurement. It has certain application value in the field of strain measurement.

Sagnac interferometer current transformer based on pulse multiplexing network structure

The monitoring of current plays an important role in accurately grasping the working status of the power system. In this paper, a Sagnac interferometer (SI) current transformer (CT) based on pulse multiplexing network structure is proposed. The network multiplexing structure can multiplex a pulsed light into multiple sensing signals, eliminating interference from light source power jitter and sudden changes in optical path loss. SI consists of a uniaxial working coupler, a 45° Faraday rotator, two quarter wave plates (QWPs), and spun fiber. The uniaxial working coupler used can achieve slow axis operation and fast axis cutoff, and convert light into linear polarization light. After passing QWPs, the forward and backward light changes from linear polarization to circular polarization, which can be used for current sensing. Experiments have shown that it has good linearity and repeatability. The proposed sensor has the advantages of low cost and simple structure, which has broad prospects in applications with not very high precision requirements.

Ultrasensitive refractive index and temperature sensor based on D-shaped photonic crystal fiber by group birefringence response in a Sagnac interferometer

In this paper, a D-shaped photonic crystal fiber (PCF) sensor based on a Sagnac interferometer is proposed, and it can achieve ultrahigh refractive index (RI) and temperature sensitivity when operating around the turning point of group birefringence (Bg). We undertake a theoretical analysis on Bg and a simulation calculation to study the sensing characteristics and obtain the optimized structure parameters of the D-shaped PCF sensor. The simulation results show that the maximum average RI sensitivities can reach 3253.33 and 15500 nm/RIU in the RI range of 1.33 to 1.35 and 1.40 to 1.42, respectively. When the temperature changes from -50 to 0 °C and 0 to 50 °C, the maximum average temperature sensitivities are up to 10.11 and 10.67 nm/°C, respectively. The proposed D-shaped PCF sensor can achieve dual-parameter sensing and has great potential for practical applications in biochemical and environmental science.

Dual-stage deep learning for sangac optical fiber sensing multi-event detection and localization

This paper introduces a dual-stage deep learning structure for multi-event detection and localization (DDMDL) for a loop-based Sagnac interferometer optical fiber sensing system to overcome the difficulties of detecting and localizing multiple events. The DDMDL approach comprises of a combination of (i) a detection stage made of a multi-class classification model that quantifies the events, and (ii) a localization stage made of separate deep-learning regression models tasked with precisely localizing the events. By addressing the multi-event localization as a combined multi-class classification and multi-regression problem, our approach enables more accurate prediction of event locations. We evaluate our DDMDL model in a broad range of test scenarios across three signal-to-noise ratio (SNR) levels: low, medium, and high, all outside the model’s training dataset. The model had high detection (i.e., classification) accuracy in simulation, with rates of 90%–99% for single-event scenarios, 94%–98% for two-event scenarios, and 82%–99% for three-event scenarios at the three SNR levels. The precision of localization (i.e., regression) was evaluated by Mean Absolute Error (MAE). The results showed that single-event scenarios could be localized within a range of 35–50 m, two-event scenarios within a range of 82–106 m, and three-event scenarios within a range of 131–151 m. These findings were consistent across different SNR levels, ranging from low to high, over a 50 km sensing fiber length. Experimental validations confirmed the DDMDL model’s practical applicability, with detection accuracy of 80% in single-event scenarios and localization accuracy with MAEs ranging between 32 and 65 m. For two-event scenarios, the model achieved an 87% success rate, with MAEs ranging between 122 m and 204 m, emphasizing the model’s potential effectiveness in different applications.

Calibration-independent bound on the unitarity of a quantum channel with application to a frequency converter

We report on a method to certify a unitary operation with the help of source and measurement apparatuses whose calibration throughout the certification process needs not be trusted. As in the device-independent paradigm our certification method relies on a Bell test and requires no assumption on the underlying Hilbert space dimension, but it removes the need for high detection efficiencies by including the single additional assumption that non-detected events are independent of the measurement settings. The relevance of the proposed method is demonstrated experimentally by bounding the unitarity of a quantum frequency converter. The experiment starts with the heralded creation of a maximally entangled two-qubit state between a single 40Ca+ ion and a 854 nm photon. Entanglement preserving frequency conversion to the telecom band is then realized with a non-linear waveguide embedded in a Sagnac interferometer. The resulting ion-telecom photon entangled state is assessed by means of a Bell-CHSH test from which the quality of the frequency conversion is quantified. We demonstrate frequency conversion with an average certified fidelity of ≥84% and an efficiency ≥3.1 × 10−6 at a confidence level of 99%. This ensures the suitability of the converter for integration in quantum networks from a trustful characterization procedure.