Simple Interferometer Research Articles

Simple heterodyne interferometer using a polarizing beam displacer.

A novel, to the best of our knowledge, and simple heterodyne interferometer that uses spatially separated input beams to minimize the influence of the periodic nonlinearity is constructed. A custom designed polarizing beam displacer is used to split the input beams to parallel outputs with orthogonal polarizations, which provides a balanced path and completely symmetric structure for the interferometer. This novel optical setup suppresses the nonlinearity caused by the frequency and polarization mixing, and the very simple optical structure makes the interferometer less susceptible to environmental turbulence with potential use in many sensor applications. Experiments have confirmed that the interferometer maintains sub-nanometer nonlinearities in the laboratory environment.

No-core fiber interferometry pH sensor based on a polyvinyl alcohol/polyacrylic acid and silica/polyvinyl alcohol/polyacrylic acid hydrogel coating.

In this paper, we present an investigation on the sensing performance of a pH sensor based on a modal interferometer formed by a simple NO-core fiber interferometer (NCFI) that operates in transmission mode. The fundamental configuration of this sensor encompasses a single-mode-no-core-single-mode fiber (SMF-NCF-SMF "SNCS") segment chain. The chemical etching method has been used with hydrofluoric (HF) acid to prepare diverse NCF diameters. This was proposed to expand the evanescent fields and enhance sensor sensitivity. Then, the two diverse segments of etched NCF were cladded with polymeric composite fabricated by polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel and pure silica nanoparticles embedded in polyvinyl alcohol/polyacrylic acid (SiO2@PVA/PAA) hydrogel, respectively, for more sensing enhancement. Our results reveal that the PAA/PVA coating is a candidate coating material for acidic sensing, while SiO2@PVA/PAA is more appropriate for the base sensing, in which these coating materials show enhancement in the sensitivity above the NCF structure before an uncoated sensor due to greater enhancement of the evanescent field affected by the coating layer. The experimental results demonstrate a high average sensitivity of 3.42 nm/pH unit for the 11 w.t.% PVA/PAA coated sensor in the pH range from 1 to 7 and 3.2 nm/pH unit in the pH range from 8 to 14. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. The simple fabrication and high sensitivity of this sensor may prompt many potential applications in the fields of biology and chemistry.

Programmable RF Receiver Related On-Chip Photonic Processor

This study reports and experimentally demonstrates a programmable on-chip photonic processor towards different RF receiver configurations. The Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> processor is built by interconnecting independent subunits such as simple and complex Mach-Zehnder interferometers and Ring resonators. The design, fabrication, and characterization of a dedicated chip are described. As a proof of concept, it can be used as a reconfigurable filter with distinct frequency response. More importantly, a thorough RF receiver related passive processor including out-of-band suppression, carrier-sideband routing, channelization filtering, as well as I-Q mixing prior to an optical detection stage. This is effective proof of a programmable integrated processor encompassing most passive filtering and routing subunits for broadband photonic RF receiver.

Improved optical fiber Mach-Zehnder high-sensitivity refractive index sensor

A simple, highly sensitive, and all-fiber four-tapered Mach-Zehnder interferometer (FTMZI) refractive index (RI) sensor was proposed and experimentally demonstrated, which was fabricated by simply and repeatedly discharging a small section of single-mode fiber (SMF). Multiple tapers excite the high-order mode of the fiber cladding, making it sensitive to changes of external RI. The sensor shows a high sensitivity of 987.9 nm/RIU when the external RI changes from 1.330 to 1.346. Furthermore, the thermal response experimental results show that the temperature sensitivity of the sensor is 19.2 pm/°C, and the temperature crosstalk is only 0.00002 RIU/°C, making it a suitable candidate for temperature independent RI sensing.

Calibration of liquid crystal variable retarders using a common-path interferometer and fit of a closed-form expression for the retardance curve.

A liquid crystal variable retarder (LCVR) enables fast, automated control of retardance that can be used as a variable waveplate in polarimetric instruments. However, precise control of the polarization state requires calibration of the LCVR. A manufacturer calibration curve is typically supplied for a single specific wavelength and temperature, but for applications under different conditions, additional calibration is needed. Calibration is typically performed with crossed polarizers to generate an intensity curve that is converted to retardance, but this method is prone to noise when retardance is close to zero. Here, we demonstrate a simple common-path Sagnac interferometer to measure retardance and provide open source software for automated generation of calibration curves for retardance as a function of wavelength and voltage. We also provide a curve fitting method and closed-form functional representation that outputs the voltage needed to achieve a desired retardance given a specified wavelength.

Diverging cyclic radial shearing interferometry for single-shot wavefront sensing.

In this investigation, we describe a simple cyclic radial shearing interferometer for single-shot wavefront sensing. Instead of using the telescope lens system used in typical radial shearing interferometry, a single lens is used to generate two diverging radial shearing beams. This simple modification leads to the advantages of conveniently adjusting the radial shearing ratio, compactness of the system, and practical ease of alignment. With the aid of a polarization pixelated CMOS camera, the spatial phase-shifting technique is used to extract the phase with a single image. The most important feature is the fringe contrast enhancement by reducing the aberrations caused by the complicated optical system even though an incoherent light is used. The experimental results show the fringe contrast enhancement is at least 0.1 better than that of the conventional method, and the wavefronts are properly reconstructed with less than 0.071λ root-mean-squared wavefront error regardless of the coherence of the light.

Characterization of Temperature Response of Asymmetric Tapered-Plastic Optical Fiber-Mach Zehnder Interferometer

Temperature measurement is important in various applications; therefore, various temperature sensors have been developed. Due to its advantages, many optical fiber-based temperature sensors have been proposed. The wavelength modulation-based optical sensor is interesting due to high accuracy. However, the complex fabrication process and high cost limit the advantages of the sensors. Therefore, we proposed a simple and low-cost Mach Zehnder interferometer (MZI) sensor using step-index plastic optical fiber (SI-POF). Performance characterization of the sensor to temperature variation is presented. The sensor consists of two tapers at several distances, forming an interferometer. The first taper was designed to be steep to allow excitation of cladding modes, while the second taper was gradual to suppress power loss. Characterizations were done in terms of sensitivity, hysteresis, and repeatability by analyzing the output spectrums recorded by the spectrometer at various environment temperatures, 35oC to 85oC, with an increment of 10oC. The results showed that the sensor has a sensitivity of 0.0431 nm/oC and a correlation coefficient of 0.9965. Hysteresis of 6.9×10-3 was observed. In terms of repeatability, the sensor shows a maximum deviation, ±3oC, which was mainly resulted from the fluctuation of the oven temperature. Despite its high deviation, the sensor has advantages of simple fabrication, low cost, robust, and low power loss, which make it a good candidate for temperature sensors.

Operational resource theory of nonclassicality via quantum metrology

The nonclassical properties of quantum states are of tremendous interest due to their potential applications in future technologies. It has recently been realized that the concept of a "resource theory" is a powerful approach to quantifying and understanding nonclassicality. To realize the potential of this approach one must first find resource theoretic measures of nonclassicality that are "operational", meaning that they also quantify the ability of quantum states to provide enhanced performance for specific tasks, such as precision sensing. Here we achieve a significant milestone in this endeavor by presenting the first such operational resource theoretic measure. In addition to satisfying the requirements of a resource measure, it has the closest possible relationship to the quantum-enhancement provided by a non-classical state for measuring phase-space displacement: it is equal to this enhancement for pure states, and is a tight upper bound on it for mixed states. We also show that a lower-bound on this measure can be obtained experimentally using a simple Mach-Zehnder interferometer.

Temperature and strain response of in-fiber air-cavity Fabry-Perot interferometer under extreme temperature condition

In this work, a simple fiber Fabry-Perot air-cavity interferometer (FPI) is formed by splicing a 246 μm long hollow core silica tube (HCST) between two single mode fibers (SMFs). In the thermal characterization test, the FPI exhibits limited linear range up to 700 °C in the first cycle of isochronal annealing treatment from room temperature up to 1000 °C. However, after a series of repeated isochronal thermal annealing, the temperature response of the proposed FPI is extended further to 1000 °C with a good thermal repeatability. Meanwhile, the annealed FPI has linear axial strain sensitivities up to 1000 με from room temperature up to 800 °C. The proposed fiber structure is a potential sensor for high-temperature or stress measurement in aeronautical or metallurgical fields.

Tapered Optical Fiber Sensor for Discrimination of Strain and Temperature

A simple Mach-Zehnder interferometer (MZI) based on a standard single-mode fiber for simultaneous strain and temperature sensing was proposed and demonstrated experimentally. The interferometer was fabricated by electrical arc discharge method in which a portion of the standard single-mode fiber was heated and stretched. Any special type of fiber or a particular splicer was not required to form the MZI and it indicated high resolution. To find the modes that contributed to the interference spectrum, Fourier analysis was done and the spatial frequency versus normalized intensity plot showed that LP02 was the excited dominant higher order cladding mode. Coefficient matrix was realized for simultaneous measurement of strain and temperature ability of such an MZI. For discrete measurements, a resolution of 0.79 °C in temperature and 1.18 micro-strain can be achieved for 10 pm wavelength resolution. This extremely simple, low-cost sensor easily fabricated with good repeatability is a good candidate in diverse sensing applications.

Compact fiber optical interferometer technique to measure picometer displacements in biological piezoelectric materials

A simple and robust fiber optical interferometer was developed to non-invasively study the weak piezoelectric effect from thin samples. A biological sample from inter-molt dactyl clubs obtained from the mantis shrimp was used as the test sample. The non-contact technique can measure displacements better than 0.5 pm for samples subjected to large electric fields. The approach utilizes a simple visible diode laser, commercial optical fibers and, the phase dependent detection of an oscillating cavity at different frequencies from 0.5 kHz to 2.0 kHz. The piezoelectric constant of the biological samples was calculated from the optical interference fringes and determined to be in the range of 0.3–0.5 pm V−1. The noise of 20 fm Hz−0.5 in the setup is primarily due to thermally associated strains from current flow to the sample electrodes during the measurement.

Single Grating Reflective Digital Holography With Double Field of View

Since 1960s, digital holography (DH) has been developed significantly as an exquisite optical sensing technique with its computational interpretation. Recent advances in the image sensor and the coherent light source have suggested the possibility of using DH in portable form that can be utilized in industrial fields. Field of view (FOV) should be sufficiently wide and the system be simple for successful landing of DH on the industrial market. To embody the possibility, in this paper, we present a method for implementing off-axis reflective DH using a single diffraction grating. Beam splitter and mirror in the conventional off-axis DH are replaced with a single diffraction grating. This replacement enables the implementation of simple interferometer while maintaining the performance of the holography. In addition, we apply the multiplexed illumination method to enhance space-bandwidth product of off-axis hologram. Using the wavelength dependence of the diffraction grating, the FOV can be doubled without additional optical element. We demonstrate the proposed method by three holographic imaging experiments with two laser diodes. The prototype provides lateral resolution of 19.69 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m with the FOV of 6.85 mm × 8.72 mm. The FOV is 1.9 times wider than the image sensor area of 6.85 mm × 4.59 mm. Overall size of the prototype is 12 cm × 17 cm × 5 cm, showing the suitability of implementation to the various industrial fields.

Size measurement of Daphnia pulex using low-coherence Gabor digital holography

We measured the size of Daphnia pulex (D. pulex), which is an indicator organism used for examining toxicity, under freely-swimming and stress-free conditions, made possible by the post-focusing ability of digital holography (DH). This environmental measurement is a new application of DH. This implementation, which is a key point of this research, should be applicable to real on-site use in non-sterile and unstable mechanical situations. Through trial and error, we arrived at the simplest interferometer configuration using a single beam line that can withstand vibrations, a low-coherence light source for reducing coherent noise, and single-shot image capturing. Automatic size measurement based on DH with image processing was performed. The originality of this research is the quantitative size measurement and performance estimation achieved by comparing the results with those from conventional manual eye measurement using ordinary optical microscope observation and image processing software. The estimation also allowed us to determine the proper parameters in the image processing for DH measurement.

Cylindrical vector beam generator using a two-element interferometer

We realize a robust and compact cylindrical vector beam generator that consists of a simple two-element interferometer composed of a beam displacer and a cube beamsplitter. The interferometer operates on the higher-order Poincaré sphere transforming a homogeneously polarized vortex into a cylindrical vector (CV) beam. We experimentally demonstrate the transformation of a single vortex beam into all the well-known CV beams and show the operations on the higher-order Poincaré sphere according to the control parameters. Our method offers an alternative to the Pancharatnam-Berry phase optical elements and has the potential to be implemented as a monolithic device.

Practical reflective birefringent fiber interferometer sensor.

This paper proposes a simple and practical reflective birefringent fiber interferometer sensor that consists of a polarization beam splitter, a polarization-maintaining transmission fiber, and a sensor unit comprising two segments of birefringent fibers and a thin-film reflector. This sensor could be used for dual parameter sensing. Experiments with different temperatures and lateral loads applied to the sensor unit demonstrated temperature and load sensitivity of ∼0.0010 nm/°C and 0.298nm/N, respectively. Further study showed that temperature-insensitive lateral load measurement can be achieved by using equal length of birefringent fibers and performing differential wavelength measurement. The sensor is robust against environmental disturbance on the transmission fiber, making it potentially attractive for practical field applications.

Compact picometer-scale interferometer using twisted light.

We propose a simple compact interferometer using twisted light to detect picometer displacement on a solid or liquid surface. The heart of the interferometer lies in producing a daisy petal pattern formed by interference between two oppositely charged twisted beams. The sample being probed is an active component of the interferometer. By analyzing the rotation of the petal pattern, caused by the relative displacement between the cylindrical lens (CL) and solid/liquid surface, we exhibit picometer resolution in displacement measurements. Remarkably, we explore the significance of a radial quantum number in the measurement of surface displacement and surface tilt angle. We also investigate the arbitrary surface deformation profile with similar precision by modifying the set-up. We perform simulations in realistic experimental settings and show that they are in excellent agreement with the predictions of analytic expressions. The proposed set-up can be further miniaturized by a small focal length CL and will open routes for tremendous applications in picometer-scale displacement measurement of a solid or liquid interface by various excitations.

Radial Shearing Interferometer Based on a Cosinusoidal Zone Plate

A simple and compact radial shearing interferometer (RSI) based on a cosinusoidal zone plate (CZP) is proposed. The CZP can modulate both phase and amplitude, it has two foci, so as the nominal plane beam under test passes through the CZP, it is diffracted into two parts, i.e., a converging beam and a diverging beam. Then, the two beams can be considered as the compressed beam and the expanded beam in the RSI, respectively. A charge-coupled device detector located in the vicinity of the CZP records the interference pattern. This RSI needs only a single zone plate and therefore can be made very compact. The experiment validates the correctness of the proposed method. With the compactness and stability, the presented interferometer is expected to be used in the detection of moving objects and dynamic processes.

Detection of Bell correlations at finite temperature from matter-wave interference fringes

We show that matter-wave interference fringes formed by two overlapping atomic clouds can yield information about the non-local Bell correlations. To this end, we consider a simple atomic interferometer, where the clouds are released from the double-well potential and the relative phase is estimated from the density fit to this interference pattern. The Bell correlations can be deduced from the sensitivity of the phase obtained in this way. We examine the relation between these two quantities for a wide range of ground states of the double-well, scanning through the attractive and the repulsive interactions. The presented analysis includes the effects of finite temperature, when excited states are thermally occupied. We also consider the impact of the spatial resolution of the single-atom detectors and the fluctuations of the energy mismatch between the wells. These results establish a link between the fundamental (non-locality) and application-oriented (quantum metrology) aspects of entanglement.

Measurement of refractive index and temperature using balloon-shaped Mach-Zehnder interferometer

In this paper, a simple balloon-shaped fiber interferometer is proposed and demonstrated for measurement of refractive index and temperature. The interferometer has a very simple structure including a standard SMF with a bare fiber bent into balloon shape with two ends of the fiber passed through one silica capillary adhered side by side. The wavelengths of two dips are both sensitive to the external refractive index and temperature. The dips exhibit obvious nonlinear response with the increase of the environment RI. The sensitivities have been retrieved experimentally by fitting the experimental data. The proposed device has the advantages of easy fabrication, robust structure, and low cost.

Three-wave radial shearing interferometer.

We propose a simple and compact three-wave radial shearing interferometer (TWRSI). This interferometer is constructed by a Gabor zone plate (GZP) and a charge-coupled device (CCD). The nominal plane wavefront under test is diffracted by the GZP into three orders (i.e., a parallel beam, a converging spherical beam, and a diverging spherical beam) leading to an interference pattern. In the imaging plane, three beams can be considered as being the copies of the incident beam, the compressed beam, and the expanded beam, respectively. A CCD detector located in the vicinity of the GZP records this interference pattern. Wavefront can be reconstructed by a single interferogram. The experiment result shows that the proposed method is correct and accurate. This TWRSI is compact, vibration insensitive, suitable for measurement of continuous and transient wavefront.