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Optical methods of measurement do not require contact of a probe and the object under study, and thus have found use in a broad range of applications such as nondestructive testing (NDT), where noninvasive measurement is crucial. Measuring the refractive index of a material can give a valuable insight into its composition. Low‑coherence radiation sources enable measurement of the sample’s properties across a wide spectrum, while simultaneously measuring the absolute value of optical path difference between interfering waves, which is necessary to calculate the refractive index. The measurement setup used in this study consists of a fiber‑based Fabry‑Perot interferometer, illuminated by a low‑coherence infrared source. The samples under measurement are located in the cavity of the interferometer, and their transmission spectra are recorded using an optical spectrum analyzer. Additional reference measurements are performed with the cavity filled with air, in order to precisely measure the geometrical length of the cavity. The purpose of the study was to develop a digital signal processing algorithm to improve the resolution of analysis of the spectra of radiation measured at the output of the interferometer. This goal was achieved by decreasing the broadening of the signal in the Fourier domain caused by dispersion of the medium filling the cavity. The Fractional Fourier Transform is a generalization of the Fourier transform allowing arbitrary rotation of the signal in the time-frequency domain, allowing more precise analysis of signals with variable frequency. This property makes this transformation a valuable tool for the analysis of interferometric signals obtained from measurements of dispersive media, as the variable rate of change of the optical path length with respect to wavenumber in such media results in varying frequency of the modulation of measured spectra. The optical path difference inside the material under measurement is used together with the geometrical length obtained from the reference measurement in order to determine the refractive index. The parameters of the transformation are found by iterative adjustment to the signal under analysis. The developed algorithm was tested using both real measured spectra and simulated signals based on a theoretical model of the interferometric setup, and its effectiveness was compared to previously used methods of analysis. It was found to increase the resolution of analysis up to the Fourier limit that occurs in signals with no dispersion.

The paper presents a relatively simple though effective approach to fringe field processing for variable wavelengthinterferometry- related techniques including a detailed analysis of noise influence on the accuracy of fringe parameters extraction.

In digital holographic interferometry (DHI), coherent noise degrades accuracy of phase information. We present multi-beam polarization DHI in which two cross polarized interferograms are recorded. Fourier analysis of interferograms reduces coherent noise and increases accuracy.

Digital shearography is a well-established technique for non-destructive testing of composite structures. Furthermore the application for defect detection on artwork could also be successfully proven. While in general the location of a defect in the object plane works very well, no depth information is obtained. To overcome this issue, similar to thermography, the lock-in-technique can be applied to shearography. Due to different modulation frequencies the penetration depth of the thermal wave can be controlled. This enables the determination of depth information. In this paper we investigate the potential of the lock-in-technique for the use in non-destructive testing of artwork. Therefore we do simulations on a wooden panel with different defect-depth. We describe the basic concept and compare the results with lock-in thermography. Finally, we show that the blind-frequency is suitable for quantitative depth information in lock-inshearography and discuss limits, to be overcome.

Our study focuses on an analysis of the original method of investigation biological tissues in the spectral OCT (optical coherence tomography) with usage hyperchromatic lenses. Using hyperchromatic lens, i.e. the lens with uncorrected longitudinal color allows scanning in the depth of the object by changing the wavelength of the emitter. In this case, the depth of the scan will be determined not by the microlens depth of field, but the value of axial color. In our study, we demonstrated the advantages of this method of research on biological tissues existing. Spectral OCT schemes with the hyperchromatic lens could increase the depth of spectral scanning, eliminate the use of multi-channel systems with a set of microscope objectives, reduce the time of measurement. In our paper, we show the developed method of calculation of hyperchromatic lenses and hybrid hyperchromatic lens consisting of a diffractive and refractive component in spectral OCT systems. We also demonstrate the results of aberration calculation designed microscope lenses. We show examples of developed hyperchromatic lenses with the diffractive element and without it.

Peculiarities of optical design for optical coherence tomography (OCT) system with illumination by a swept-source in the spectral range 1.26-1.36 μm are considered. In the OCT system, an object is illuminated by light intensity distribution in the form of line providing high power efficiency of the light source when evaluating micro structure of objects. A linearray photo detector with the frame acquisition rate of a few tens of kilohertz is utilized that allows obtaining B-scans without mechanical lateral scanning. The illumination power density at each point of investigated object is much less with respect to conventional "flying spot" methods that is important when studying biological objects not resistant to intensive light. Results of experimental investigations utilizing the Linnik micro interferometer optical scheme are given. Experimental tomograms of different objects are presented.

Holographic techniques have been used to measure the shape and the radial deformation of a blood vessel model and a real sheep aorta. Measurements are obtained from several holograms recorded for different object states. For each object state, two holograms with two different wavelengths are multiplexed in the same digital recording. Thus both holograms are simultaneously recorded but the information from each of them is separately obtained. The shape analysis gives a wrapped phase map whose fringes are related to a synthetic wavelength. After a filtering and unwrapping process, the 3D shape can be obtained. The shape data for each line are fitted to a circumference in order to determine the local vessel radius and center. The deformation analysis also results in a wrapped phase map, but the fringes are related to the laser wavelength used in the corresponding hologram. After the filtering and unwrapping process, a 2D map of the deformation in an out-of-plane direction is reconstructed. The radial deformation is then calculated by using the shape information.

Here we introduce a compact holographic microscope embedded onboard a Lab-on-a-Chip (LoC) platform. A wavefront division interferometer is realized by writing a polymer grating onto the channel to extract a reference wave from the object wave impinging the LoC. A portion of the beam reaches the samples flowing along the channel path, carrying their information content to the recording device, while one of the diffraction orders from the grating acts as an off-axis reference wave. Polymeric micro-lenses are delivered forward the chip by Pyro-ElectroHydroDynamic (Pyro-EHD) inkjet printing techniques. Thus, all the required optical components are embedded onboard a pocket device, and fast, non-iterative, reconstruction algorithms can be used. We use our device in combination with a novel high-throughput technique, named Space-Time Digital Holography (STDH). STDH exploits the samples motion inside microfluidic channels to obtain a synthetic hologram, mapped in a hybrid space-time domain, and with intrinsic useful features. Indeed, a single Linear Sensor Array (LSA) is sufficient to build up a synthetic representation of the entire experiment (i.e. the STDH) with unlimited Field of View (FoV) along the scanning direction, independently from the magnification factor. The throughput of the imaging system is dramatically increased as STDH provides unlimited FoV, refocusable imaging of samples inside the liquid volume with no need for hologram stitching. To test our embedded STDH microscopy module, we counted, imaged and tracked in 3D with high-throughput red blood cells moving inside the channel volume under non ideal flow conditions.

The complete phase and amplitude information of biological specimens can be easily determined by phase-shifting digital holography. Spatial light modulators (SLMs) based on liquid crystal technology, with a frame-rate around 60 Hz, have been employed in digital holography. In contrast, digital micro-mirror devices (DMDs) can reach frame rates up to 22 kHz. A method proposed by Lee to design computer generated holograms (CGHs) permits the use of such binary amplitude modulators as phase-modulation devices. Single-pixel imaging techniques record images by sampling the object with a sequence of micro-structured light patterns and using a simple photodetector. Our group has reported some approaches combining single-pixel imaging and phase-shifting digital holography. In this communication, we review these techniques and present the possibility of a high-speed single-pixel phase-shifting digital holography system with phase-encoded illumination. This system is based on a Mach-Zehnder interferometer, with a DMD acting as the modulator for projecting the sampling patterns on the object and also being used for phase-shifting. The proposed sampling functions are phaseencoded Hadamard patterns generated through a Lee hologram approach. The method allows the recording of the complex amplitude distribution of an object at high speed on account of the high frame rates of the DMD. Reconstruction may take just a few seconds. Besides, the optical setup is envisaged as a true adaptive system, which is able to measure the aberration induced by the optical system in the absence of a sample object, and then to compensate the wavefront in the phasemodulation stage.

In this work we consider a microscopic optical system in which the beam with an optical vortex illuminates the sample. The sample modifies the geometry of the vortex beam wavefront and the information about it is transferred into the detection plane. It is shown that the beam at the detection plane can be represented by two parts: non-disturbed vortex part and sample part. We propose and test a scheme for recovering the phase changes caused by sample inserted into the vortex beam. The numerical simulations are supported by the experimental work.

In this paper, we have employed the L 2 waveguides in order to guide the light into two different arms constructed by the inclusion of an engineered obstacle in front of the input optical port. The light which travels inside the core liquid is coupled into these two arms experiencing different optical paths due to the asymmetric geometry of the obstacle and also the different used cladding liquids. We have used several sets of coupled hydrodynamic-electromagnetic simulations to characterize the interferometer based on the output intensity of the waveguide. The simulation results indicate that this technique has a maximum sensitivity of 595%/RIU and a maximum resolution of 3.3×10 -6 RIU which depends on the range of flow rate.

In this work we have measured the group-delay dispersion of an empty Michelson interferometer for s- and p-polarized light beams applying two different non-polarizing beam splitter cubes. The interference pattern appearing at the output of the interferometer was resolved with two different spectrometers. It was found that the group-delay dispersion of the empty interferometer depended on the polarization directions in case of both beam splitter cubes. The results were checked by inserting a glass plate in the sample arm of the interferometer and similar difference was obtained for the two polarization directions. These results show that to reach high precision, linearly polarized white light beam should be used and the residual dispersion of the empty interferometer should be measured at both polarization directions.

Dynamic metrology holds the key to overcoming several challenging limitations of conventional optical metrology, especially with regards to precision freeform optical elements. We present two dynamic metrology systems: 1) adaptive interferometric null testing; and 2) instantaneous phase shifting deflectometry, along with an overview of a gradient data processing and surface reconstruction technique. The adaptive null testing method, utilizing a deformable mirror, adopts a stochastic parallel gradient descent search algorithm in order to dynamically create a null testing condition for unknown freeform optics. The single-shot deflectometry system implemented on an iPhone uses a multiplexed display pattern to enable dynamic measurements of time-varying optical components or optics in vibration. Experimental data, measurement accuracy / precision, and data processing algorithms are discussed.

A Fizeau interferometer is significantly less sensitive to vibrations and air turbulence than other types of interferometers. This is due to the common path of the reference wave front and the object wave front. A common path arrangement offers the opportunity to reduce systematic errors of the measured phase of the surface under test (SUT). That is why Fizeau type interferometers are most commonly used to test e.g. plane surfaces, spheres or aspheres. A reduced uncertainty of the measured phase distribution can be obtained if the reference surface is placed close to the SUT. Multiple beam reflections will produce interference fringes, which are not sinusoidal. Furthermore, the discrete intensity distribution depends on the reflectance of the reference surface and the reflectance of the SUT. Some surfaces to be tested show significant variations of the local reflectance, e.g. lithographic masks with 0.05 ≤ r(x,y) ≤ 0.95. Thus, the inherent potential of phase shifting algorithms cannot be used. A modification of the reference surface can be applied. An on-axis polarization beam splitter, which is placed in the plane of the reference surface, separates the two surfaces, which are imaged onto the detector. Thus, true two beam interference can be obtained. The potential of phase shifting algorithms can be used. The interference contrast is high, even if large local variations of r(x,y) are present. In addition, high speed operation is enabled. The embodiment of a modified Fizeau type interferometer will be described.

The basic physical measurement principle in DaOS is the vignettation of a quasi-parallel light beam emitted by an expanded light source in auto collimation arrangement. The beam is reflected by the surface under test, using invariant deflection by a moving and scanning pentaprism. Thereby nearly any curvature of the specimen is measurable. Resolution, systematic errors and random errors will be shown and explicitly discussed for the profile determination error. Measurements for a “plano-double-sombrero” device will be analyzed and reconstructed to find out the limit of resolution and errors of the reconstruction model and algorithms. These measurements are compared critically to reference results that are recorded by interferometry and Deflectometric Flatness Reference (DFR) method using a scanning penta device.

High precision optical components with large numerical aperture are widely used in industrial products. The stitching interferometry system was designed to measure high-numerical-aperture sphericity and extended the measurement range of interferometry. Firstly, sub-aperture stitching model and experimental system were analyzed. Adjustment mechanism with seven degrees of freedom was built to keep spherical surface in the null position. Then, optical path difference caused by adjustment errors was described by mathematical model. The misalignment aberrations in measurement result were removed after fitted by the Zernike polynomial and the accurate surface shape of single aperture is gained. Finally, a high-numerical-aperture sphericity was measured by the error homogenization algorithm. The PV and RMS are consistent with the results of full aperture testing.

Due to its multi properties, including excellent stiffness-to-weight and strength-to-weight ratios, closed-cell aluminum and its alloy foams become candidate materials for use in many high-technology industries, such as the automotive and aerospace industries. For the efficient use of closed-cell foams in structural applications, it is necessary and important to detailly understand their mechanical characteristics. In this paper, the nonlinear vibration responses of the cantilever beams of closed-cell aluminum foams were investigated by use of electronic speckle pattern interferometry (ESPI). The nonlinear resonant mode shapes of testing specimens under harmonic excitation were measured. It is first time to obtain from the experimental results that there exist super-harmonic responses when the cantilever beams of closed-cell aluminum foam were forced to vibrate, which was caused by its specific cellular structures.

A method to directly pattern nanoscale periodic features within optically transparent solid materials by means of a configurable multi-beam femtosecond laser interference is proposed. While femtosecond micromachining of optically transparent solid materials has been explored in great detail in the recent past, research in direct interference patterning on such materials has not been well established. Therefore, different design considerations such as complete void formation and flexibility of the patterned substrate are investigated as part of this study. The relationship between intensity distributions and actual void formation in optically transparent materials is also investigated to establish critical parameters for pattern formation. It is envisaged that this proposed method and data obtained may enable to explore the untapped domains of developing substrates for solid-state 3D microbattery applications. Published version

The work is devoted to the method of mounting and surface shape measurement of the primary mirror of ARCA telescope, intended for the Sun observation in EUV wavelength range. Calculation of mirror’s deformation due to weight is carried out and a method of its experimental determination in interferometer is proposed. The method of deformation-free installation of mirror into the telescope is proposed. Impact shocks and vibrations, arising during missile launch, is analyzed, and an optimal size of bridges in the rim is determined. Calculations of the mirror deformation due to temperature difference in the telescope on the Earth's orbit and its influence on the resolution of the telescope are conducted. The stresses arising in epoxy adhesive due to temperature changes and due to starting shocks are simulated.

Interference, where the superposition of two or more waves resulting in a new wave pattern, has been considered as one of the most important and fundamental physical phenomenon. In optics, the statistical properties of light play an important role in determining the outcome of most optical experiments and the cross correlation between the fluctuating fields at different space time points, known as the optical coherence functions, is a quantity of great interest. Due to the fact that the wave equations govern propagation of optical coherence, it can be envisaged that the interference phenomena also appear in the format of the optical coherence function. Meanwhile, the study of propagation and superposition of optical coherence function also provides theoretical and experimental foundations for coherence holography. In this paper, we have given the mathematical expression of interference of the optical coherence functions, and have proposed a full-field coherence visualization system for coherence holographic interferometry. The interference of two optical coherence functions has been experimentally investigated which can be regarded as an extension of Young’s double-slit interferometer for optical waves. Some interesting phenomena, such as missing class of the coherence function and multiple-coherence function interference are demonstrated for the first time.

Since it's first generation more than 30 years ago, squeezed light has developed towards a tool for high precision measurements as well as a tool for quantum information tasks like quantum key distribution. Miniaturization of sensors is an active field of research with the prospect of many applications. The precision of optical sensors based on interferometric measurements is often limited by the fundamental shot noise. While shot noise can be reduced by increasing the employed light power, integrated sensors pose limitations on the maximum possible amount due to damaging effects of high intensity as well as power consumption. Bright quadrature squeezed light produced by the optical Kerr effect in a nonlinear medium offers an opportunity to overcome these limitations. Here, we present first steps towards a bright quadrature squeezed light source produced by the optical Kerr effect in race-track resonators in silicon nitride by presenting characterizations of the chip. Using standard fabrication techniques this source will have the potential of seamless integration into on-chip optical sensors.

We propose the novel structure of an interferometric biosensor based on multimode interference (MMI) waveguides. We present the design of the biosensor using eigenmode expansion (EME) method in accordance with the requirements and standards of today's photonic technology. The MMI structures with a 90 nm Si3N4 core are used as power splitters with 5 outputs. The 5 high-resolution images at the end of the multimode region show high power balance. We analyze the coupling efficiency of the laser source with the structure, the excess loss and power imbalance for different compact MMI waveguides with widths ranging from 45 μm to 15 μm. For a laser source with a tolerance of ±1mm in linearization we could achieve a coupling efficiency of 52%. MMI waveguides with tapered channels show excess loss values under 0.5 dB and power imbalance values under 0.08 dB. In addition, we show that for a 10 nm deviation of the source wavelength from its optimal value and for a 10 μm deviation of the MMI length from its optimal value, the performance of the MMI waveguides remains acceptable. Finally, we analyze the power budget of the whole biosensor structure and show that it is sufficient for the proper operation of this device.

Integrated optics has the potential to play a transformative role in astronomical instrumentation. It has already made a significant impact in the field of optical interferometry, through the use of planar waveguide arrays for beam combination and phase-shifting. Additionally, the potential benefits of micro-spectrographs based on array waveguide gratings have also been demonstrated. Here we examine a new application of integrated optics, using ring resonators as notch filters to remove the signal from atmospheric OH emission lines from astronomical spectra. We also briefly discuss their use as frequency combs for wavelength calibration and as drop filters for Doppler planet searches. We discuss the theoretical requirements for ring resonators for OH suppression. We find that small radius (< 10 μm), high index contrast (Si or Si3N4) rings are necessary to provide an adequate free spectral range. The suppression depth, resolving power, and throughput for efficient OH suppression can be realised with critically coupled rings with high self-coupling coefficients. We report on preliminary laboratory tests of our Si and Si3N4 rings and give details of their fabrication. We demonstrate high self-coupling coefficients (> 0:9) and good control over the free spectral range and wavelength separation of multi-ring devices. Current devices have Q ≈ 4000 and ≈ 10 dB suppression, which should be improved through further optimisation of the coupling coefficients. The overall prospects for the use of ring resonators in astronomical instruments is promising, provided efficient fibre-chip coupling can be achieved.

Long-range surface plasmon waveguides, and their application to various transducer architectures for amplitude- or phase-sensitive biosensing, are discussed. Straight and Y-junction waveguides are used for direct intensity-based detection, whereas Bragg gratings and single-, dual- and triple-output Mach Zehnder interferometers are used for phasebased detection. In either case, multiple-output biosensors which provide means for referencing are very useful to eliminate common perturbations and drift. Application of the biosensors to disease detection in complex fluids is discussed. Application to biomolecular interaction analysis and kinetics extraction is also discussed.

Quantum optics has become a key field of development for investigations of quantum physics principles, leading to novel quantum technologies. In this view Integrated Optics allows implementing complex quantum circuits that can give rise to significant outcomes, difficult to reach using traditional approaches based on discrete components. In this framework, a non-linear Mach-Zehnder Interferometer (MZI) was implemented by using two commercial 50:50 directional fibre couplers. One of the MZI arms was equipped with a single mode Er:LiNbO3 optical waveguide, acting as non-linear component whereas the other MZI arm was provided with an undoped LiNbO3 single mode optical waveguide, used to obtain a phase shift through the application of a controlled voltage ramp. The injection in the MZI of a 980nm wavelength laser radiation allowed to collect structured interferogrammes, that could be ascribed exclusively to the pump photons, as all frequency conversion events are localized only in one arm of the Interferometer. The Fourier Transform elaboration of such interferogrammes, produces multiple peak spectra that tightly match the typical transition spectrograms of Er:LiNbO3 when excited by a 980nm radiation. Thus it is possible to perform a spectrometry of the noninterfering converted photons only by using the interfering pump photons. In this work, the experimental apparatus and the most interesting results, obtained in different experimental conditions, are described. Finally, a possible interpretation is outlined.

The method of amplification of hologram was applied to the so-called Rozhdestvenskiy hooks, that were obtained in the Rozhdestvenskiy interferometer (Michelson interferometer, combined with a grating spectrograph). In such a device the absorption lines reveal themselves as specific “hooks”, whose curvature provides the information about the atomic oscillator force. The holographic amplification “smoothes” the hooks and thus makes their analysis much simpler.

We present a method for holographic imaging through a volume scattering material, which is based on selfreference and light with good spatial but limited temporal coherence. In contrast to existing techniques, we do not require a separate reference wave, thus our approach provides great advantages towards the flexibility of the measurement system. The main applications are remote sensing and investigation of moving objects through gaseous streams, bubbles or foggy water for example. Furthermore, due to the common path nature, the system is also insensitive to mechanical disturbances. The measurement result is a complex amplitude which is comparable to a phase shifted digital hologramm and therefore allows 3D imaging, numerical refocusing and quantitative phase contrast imaging. As an example of application, we present measurements of the quantitative phase contrast of the epidermis of an onion through a volume scattering material.

The expansion dynamics of laser-induced plasma (LIP) at front and rear surface of fused silica under 1064 nm nanosecond laser irradiation was investigated with fast photography, shadowgraphy and interferometry. Self-emission images of LIP show that the rear surface plasma (RSP) splits into a fast and a slow component at tens of nanoseconds delay after laser irradiation while the front surface plasma (FSP) does not split. Moreover, the FSP is identified to mainly contain free electrons while the RSP includes ejected neutrals. Thermal emission of superheated neutrals is suggested to be responsible for the generation of slow component.

One of the main problems faced by the Space Situational Awareness community is the detection and characterization of faint objects around geosats. Independent of the origin of these objects, whether they are debris or controlled spacecraft, they can potentially harm these assets and contaminate the geobelt environment. The challenge of detecting these companion objects comes from their proximity and brightness ratio relative to geosats. Here we present a novel interferometric fringe nulling technique, aimed at solving these issues. This technique takes advantage of the fact that the presence of companions introduces large phase fluctuations in the fringe phase observed by an interferometer, when the interferometer is observing a target at spatial frequencies where the fringe amplitude is near zero. We describe the ongoing development of this technique at the Navy Precision Optical Interferometer, and the results of simulations of interferometric observations of satellites with companions. We also present the current state of the NPOI and related SSA work being done with this interferometer, as well as undergoing upgrades to the system.

With the aim to prevent the oceans ecosystems degradation, there is an urgent need to develop portable sensing tools able to operate directly in the environment, avoiding the transportation of the ocean samples to analytical laboratories. To achieve this long-term objective, we describe here the work carried out to develop and characterize a multiplexed photonic immunosensor for the direct analysis of toxic chemical targets in marine samples. We have employed immunosensors based on photonic Bimodal Waveguide (BiMW) interferometric devices fabricated in silicon technologies combined with specific receptors and antibodies for the targeted chemical targets. Several procedures for the functionalization of the S₃iN₄ sensor surfaces have been evaluated based on wet silanization methods and further covalent receptor immobilization. The developed immunosensors, based on competitive inhibition assays, show LODs at μg/L or ng/L levels, depending on the analyzed chemical target.

Metrology of freeform shapes has traditionally been difficult, especially at the sub-micron level. Sub-aperture polishing techniques and diamond turning allow optical designers to incorporate freeform surfaces into their systems. Contact measuring systems typically lack the accuracy or resolution required for optical qualification and can potentially damage the surfaces. Interferometric systems are unable to handle high spherical departures and may require complicated lateral calibration to generate feedback for deterministic grinding and polishing. OptiPro has developed UltraSurf, a noncontact coordinate measuring machine to determine the form, figure, and thickness of freeform optics. We integrated several non-contact sensors that acquire surface information through different optical principles. Each probe has strength and weaknesses relative to an optic’s material properties, surface finish, and figure error. The measuring probe is scanned over the optical surface while maintaining perpendicularity and a constant focal offset. Incorporating datums from mechanical prints into the non-contact measuring method is especially important for freeform surfaces. UltraSurf has the ability to measure a wide range of surface roughness and has the degrees of freeform needed to scan datums and surfaces. The metrology method of UltraSurf and the non-contact probes will be presented. Form, figure, and thickness data will highlight the capabilities of UltraSurf to measure freeform surfaces.

We characterize an efficient and nearly-noiseless parametric frequency upconverter. The ultra-low noise regime is reached by the wide spectral separation between the input and pump frequencies and the low pump frequency relative to the input photons. The background of only ≈100 photons per hour is demonstrated. We demonstrate phase preservation in a frequency upconversion process at the single-photon level. We summarize our efforts to measure this ultra-low noise level, and discuss both single-photon avalanche photodiode measurements and a photon-counting transition edge sensor (TES) measurements. To reach the required accuracy, we supplemented our TES with a dark count reduction algorithm. The preservation of the coherence was demonstrated by simultaneously upconverting the input of each arm of a Mach-Zehnder interferometer through high interference fringe contrast. We observe fringe visibilities of ≥0.97 with faint coherent input.

We propose a large aperture static imaging spectrometer (LASIS) based on planar lightwave circuit (PLC) MZI array. The imaging spectrometer works in the push-broom mode with the spectrum performed by interferometry. While the satellite/aircraft is orbiting, the same source, seen from the satellite/aircraft, moves across the aperture and enters different MZIs, while adjacent sources enter adjacent MZIs at the same time. The on-chip spectrometer consists of 256 input mode converters, followed by 256 MZIs with linearly increasing optical path delays and a detector array. Multiple chips are stick together to form the 2D image surface and receive light from the imaging lens. Two MZI arrays are proposed, one works in wavelength ranging from 500nm to 900nm with SiON(refractive index 1.6) waveguides and another ranging from 1100nm to 1700nm with SOI platform. To meet the requirements of imaging spectrometer applications, we choose large cross-section ridge waveguide to achieve polarization insensitive, maintain single mode propagation in broad spectrum and increase production tolerance. The SiON on-chip spectrometer has a spectral resolution of 80cm -1 with a footprint of 17×15mm 2 and the SOI based on-chip spectrometer has a resolution of 38cm -1 with a size of 22×19mm 2 . The spectral and space resolution of the imaging spectrometer can be further improved by simply adding more MZIs. The on-chip waveguide MZI array based Fourier transform imaging spectrometer can provide a highly compact solution for remote sensing on unmanned aerial vehicles or satellites with advantages of small size, light weight, no moving parts and large input aperture.

In this study, a method for reducing the atmospheric effects on SAR interferometric products is proposed. The method exploits MODIS data, as well as the Saastamoinen model for the estimation of the atmospheric component and the generation of spatially continuous data for this component. Then it recovers the interferometric signal from delays caused by the atmospheric component, through the appropriate modelling of the interferometric phase. Performance of the method depends on MODIS data resolution; however, it always improves results. Experiments showed that the accuracy of DEMs that are produced by interferometry is improved when the proposed method is applied.

The interference theory is developed for of the phase conjugate Michelson interferometer in which its ordinary mirrors are replaced by a single externally pumped phase conjugate mirror. According to the theory, it was found that for an interferometer with two equal arms, the path length difference depends solely on the initial alignment of the two input beams, and the vertical alignment readout. Small vertical misalignments in the readout beam by mrad causes a huge change in the phase difference in the phase between the two interferometer arms beam. The phase difference is proportional to the interferometer arm lengths. The overlap between the phase conjugate beams is not affected by the interferometer beam alignment. The interferometer is proposed for nondestructive testing and the design all optical logic and associated fuzzy logic for ultrafast optical pattern recognition.

The design and implementation of an electronic system to real-time capture and processing speckle interference patterns is presented. Because of the random and instability speckle patterns nature, is very useful a system wich allows obtaining and visualizing interference speckle patterns in the shortest time possible. Proposed system captures the first speckle pattern as steady image while captures subsequent patterns from the same source. Images are electronically transformed separately into value arrays and subtracted to obtain real-time interference speckle patterns, these patterns are automatically archived for later analysis. System consist of a CCD camera, a computer interface that makes capturing, a transparent object and a 4f interferometric system whose source is a laser that passes through diffuser glass in order to obtain speckle effect. Experimental results and analytic explanation is showed bellow.

In previous research we designed an interferometric quantum seismograph that uses entangled photon states to enhance sensitivity in an optomechanic device. However, a spatially-distributed array of such sensors, with each sensor measuring only nm-vibrations, may not provide sufficient sensitivity for the prediction of major earthquakes because it fails to exploit potentially critical phase information. We conjecture that relative phase information can explain the anecdotal observations that animals such as lemurs exhibit sensitivity to impending earthquakes earlier than can be done confidently with traditional seismic technology. More specifically, we propose that lemurs use their limbs as ground motion sensors and that relative phase differences are fused in the brain in a manner similar to a phased-array or synthetic-aperture radar. In this paper we will describe a lemur-inspired quantum sensor network for early warning of earthquakes. The system uses 4 interferometric quantum seismographs (e.g., analogous to a lemurs limbs) and then conducts phase and data fusion of the seismic information. Although we discuss a quantum-based technology, the principles described can also be applied to classical sensor arrays

We propose and demonstrate an interferometric sensor based on visibility modulation. In the interferometric sensor, a section of polarization maintain (PM) fiber is spliced into one arm as the sensing head. Due to the interference between the two beams in the two arms, respectively, an interferometric fringe can be obtained. The birefringence of the PM fiber splits the beam in the sensing arm, yielding a visibility envelop in the interferometric fringe. Strain applied on the PM fiber can be demodulated by measuring the visibility change in a given wavelength. Experimental result shows that the sensor can achieve resolution of up to 28 nano-strain. This demodulation scheme is immunity to the wavelength shift and power fluctuation of OSA, thus improving the accuracy of the sensor. This type of sensor can be improved by using a wavelength-swept laser or a mode-locked fiber laser.

The optical fiber accelerometer owns exceptional advantages in various industrial applications due to its high sensitivity, immunity to electromagnetic interference, small size, low cost and easy to form sensor network etc. This study aims to evaluate an optimized interferometric optical fiber accelerometer based on Michelson structure. An integral parameter S was firstly proposed to assess the general performance of the accelerometer including both the sensitivity and resonance frequency, the compliant cylinder of the accelerometer proposed in this study was optimized as the composite structure materials, two typical sensitivity enhanced elastic materials of polycarbonate and silicone rubber were selected. This new type accelerometer was capable to provide higher phase sensitivity and wider flat bandwidth with optimized proportional mixing between two materials. The comparison analysis of Young’s modulus and Poisson ratio on the promotion of integral parameter S was finally discussed.

Fiber-optic sensors are one of the dynamically developing areas of photonics, which is today one of the key technologies. Here include even fiber optic interferometers, allowing very sensitive sensing, they are immune to electromagnetic interference and are entirely passive regarding electric power supply. This type of sensor is dependent on the phase shift, the principle of the function based on interference of light. Fiber optic interferometers are used especially in areas that require high sensitivity and measurement accuracy. The fundamental problem of fiber optic interferometry is a proposal storing and fixing the measuring arm of the interferometer and its influence on the frequency range and sensitivity of the interferometer. The authors focused on this issue and analyzed different types of fixing materials. We used a total of 8 different fixation elements with the different composition. We defined the standardized method of fixation and compared it with a reference measurement without fixation. For the analysis of the frequency characteristic of the prototype was used generator harmonic signal with fixed amplitude signal. Sensitivity verified using the size of the amplitude response. The signal processed by the application written in LabView development environment. The results clearly showed that it is necessary to pay attention to fixation materials in the design of the measuring arm of the interferometer for use in practical applications. In the frequency range, thanks to the fixing material increased the value of bandwidth about value 2430Hz against the reference measurements. The sensitivity of the interferometer has increased threefold. The results verified by retesting assembled prototype.

The need for precision guidance of systems in tactical theaters is becoming increasingly more important. This need has renewed interest in Interferometric Fiber Optic Gyroscopes (IFOG) that are capable of delivering navigation grade performance. The challenges however, include satisfactory performance over a large and severe operating temperature range (-60°C to +90°C), low unit cost and relatively small footprint. Performance of the IFOG depends critically on the quality of the sensing element, optical fiber coil, and many of the performance limiting issues of the IFOG can be traced back to coil quality. Although significant progress has been made in the fabrication of temperature insensitive coils with high optical reciprocity, more needs to be done. In this paper, data is presented on the performance of similar size (inside diameter, outside diameter, height) freestanding coils that were wound in quadrupole winding pattern at low tension using different polarization maintaining fibers. Performance characteristics of the coils were measured under variables including (i) fiber geometry, (ii) fiber coating, (iii) winding epoxy, and (iv) epoxy curing profile. Although each coil had the same footprint, they contained different lengths of fiber based on the fiber coating size. Coils were characterized as a function of temperature with respect to: (i) optical loss, (ii) polarization extinction ratio (PER), and (iii) coherence. The data suggests that high performance navigation grade coils can be realized over a large and severe temperature range with careful choice of fiber, winding epoxy and cure cycle.

We have developed a chip-scale optofluidic sensor for biomolecular detection, by tapering laterally aligned silica microfiber and capillary to form a modal interferometer. With the pre-immobilization of DNA probes, the sensor is capable of selectively detecting single-stranded microRNA-let7a (molecular weight: 6.5 k) by measuring the spectral shift of the interferometric spectrum. A log-linear response from 2 nM to 20 μΜ and a minimum detectable concentration of 212 pM (1.43 ng/mL) have been achieved. The sensor is promising for future diagnosis applications due to its high sensitivity, resistance to environmental perturbations, improved portability, and intrinsic connection to fiber optic measurement.

High-resolution simultaneous measurement of vibration and temperature using an optical fiber sensor is presented. Strain and temperature can be measured simultaneously by using two types of reflection spectra of a Fabry-Perot interferometer consisted of fiber Bragg gratings in a polarization maintaining fiber. The fine structure of reflection spectrum of the interferometer, i.e. PM-FBG-FPI, enables high-resolution detection of wavelength shifts. In oder to measure solid vibration, we present a fast interrogation method using current modulation of a laser diode for PM-FBG-FPI sensors. The resulting fast measurement is demonstrated experimentally

This paper presents a cascaded fiber interferometer sensor, which is fabricated by fusion splicing of single-mode fibers. The coupling and interference for the CFI were mathematically and experimentally studied. An equal model has been built for the CFI. Furthermore, the curvature sensitivity were explored in sensor application. The curvature sensitivity for the cascaded fiber interferometer is very high, which can achieve 790.18 pm/m−1. Besides, the proposed sensor has advantages like good repeatability, low cost, and simple structure.

Refereed/Peer-reviewed A Mach-Zehnder interferometer was created from a cavity milled in the taper region next to a microfiber knot resonator. A focused ion beam was used to mill the cavity with 47.8 mu m in length. The microfiber knot resonator was created from an 11 mu m diameter taper, produced using a filament fusion splicer. After milling the cavity, the microfiber knot resonator spectrum is still visible. The final response of the presented sensor is a microfiber knot resonator spectrum modulated by the Mach-Zehnder interference spectrum. A preliminary result of -8935 +/- 108 nm/RIU was obtained for the refractive index sensitivity of the cavity component in a refractive index range of n = 1.333 to 1.341. Simultaneous measurement of refractive index and temperature using this combined structure is a future goal.

The stray interference peaks (SIPs) are an important factor resulting in the misjudgment of measurement information in white light interferometer (WLI). SIPs are generated by the residual reflected light beams. We theoretically analyze the interference conditions of the SIP. The analysis shows that these SIPs are discrete main interference peak outside and have different orders. We present a stagger optical path (SOP) method for suppressing or eliminating these SIP which will appear in the interference pattern. The SOP means that there is an appropriate fiber length determined by the delay amount of delay line between each joint. Moreover, an experiment with two joints, for simplicity, is given as an example. Experimental results show that the high-order SIP from the joints can be suppressed by the SOP to obtain a clean interference pattern.

We reported a simple, robust, and highly sensitive temperature sensor using intrinsic Mach-Zehnder interferometer formed by means of bending a tapered microfiber, embedded in polydimethylsiloxane. The outer temperature perturbations modulate the refractive index of the polymer through thermo-optic and thermal expansion effects of the polymer. This leads to a phase difference between interfering guided modes through the bent-microfiber, which ultimately results prominent wavelength shift in the transmission spectrum. The sensor exhibits a linear temperature response with a sensitivity as high as −6.25nm/°C over the temperature range from 24° to 40 °C. The sensitivity of the sensor increases as wavelength increases.

We presented a type of refractive index sensor based on Michelson interferometer by using asymmetrical twin-core fiber. The central-core and side-core of the asymmetrical twin-core fiber are used as the reference arm and sensor arm respectively, and the D-shape side-polish sensing region are fabricated on the sensing arm by the side-polishing technique. The optical path difference is formed between the two arms due to the sensing region of the side-core sensitive to the change of the surrounding refractive index. Thus, through the reflection of the end and taper of the fiber to achieve the interference of transmission to form Michelson interferometer. Therefore, the changes of the surrounding will lead to the shift of the transmission spectrum to reach the purpose of the sensing. The experimental results show that the device has a maximum refractive index sensitivity of about −80nm/RIU in the range of 1.333–1.3824 and the result is basically consistent with the simulation. This sensor is a simple structure and convenient in its production advantages, and can be used in many areas such as biological sensing and chemical sensing.