Multiple-beam Interference Research Articles

Dynamic Spatial-Selective Metasurface with Multiple-Beam Interference.

The emergence of the metasurface has provided a versatile platform for the manipulation of light at the nanoscale. Recent research in metasurfaces has explored a plethora of dynamic control and switching of multifunctionalities, paving the way for innovative applications in fields such as imaging, sensing, and communication. However, current dynamic multifunctional metasurfaces face challenges in terms of functional scalability and selective activation. In this work, we introduce and experimentally demonstrate a strategy that utilizes multiple plane waves to create arbitrary periodic patterns on the metasurface, thus enabling the dynamic and arbitrary spatial-selective activation of its embedded multiplexed functionalities. Furthermore, our strategy facilitates dynamic light control through mechanical translation, as demonstrated by a high-speed, dynamically switchable beam deflection scenario. Our method effectively overcomes the limitations associated with traditional spatially multiplexing techniques, offering greater flexibility and selectivity for dynamic control in multifunctional metasurfaces.

Single-shot digital holography of multiple-beam Fizeau holograms for optical phase reconstruction through the focal depth of optical fibers

Multiple-beam Fizeau interference (MBFI) is characterized by its ability to represent the fine features of phase objects. Single-shot digital holographic interferometry (SSDHI) is used for numerical focusing of the recorded holograms. In this work, the two methods are gathered and employed for solving the problem of studying the thick phase objects. The problem of thick phase objects, such as optical fibers, in MBFI is the full focusing of the fiber's optical phase in one-time single shot phase map. The proposed method is designed to collect the optical phase map due to the optical fiber through the focal depth. The main idea is based on the analysis of the MBFI to several two-beam interference sets. Each two-beam interference is treated by SSDHI method to get the optical phase at different planes of focus inside the object. Then, the resultant optical phase due to the optical fiber is collected from these planes of focus. Retrieving the optical phase maps of the multiple-beam holograms through the focal depth, for the first time, is possible using the angular spectrum method. In this case, a laser source with quite long coherence length is used as a light source.The proposed method is applied on two thick samples of, single mode and graded index, optical fibers to reconstruct the resultant optical phase maps through the focal depth. The reconstructed optical phase maps are determined for the harmonics of MBFI holograms’ angular spectra. The method proves its ability to provide more accurate, numerical focusing and phase maps reconstruction. Where, MBFI analyses indicate the magnification of optical phase differences.

Dual-parameter fiber sensor for temperature and strain based on SMS-FP composite structure

A dual-parameter sensor for simultaneous strain and temperature measurement is proposed and demonstrated based on the introduction of higher-order modes in a single-mode-multimode-single-mode (SMS) structure cascaded with a Fabry–Perot (FP) cavity as a compact and low-cost fiber optic sensor. In this structure, a multimode fiber is spliced between two single-mode fibers, and the single-mode fiber at the other end is fusion spliced to the HF-corroded single-mode fiber to form the SMS-FP cascade structure. Light transmitted from the multimode fiber to the FP cavity can couple light into the cladding, introducing higher-order modes into modal interference. Moreover, multiple-beam interference generates spectra. The experimental results indicate that the sensor performs effectively within the range of 150∘C–250∘C and 0–875[Formula: see text][Formula: see text]. The strain sensitivities of SMS and FP were found to be −2.45 and −2.34[Formula: see text]pm/[Formula: see text], respectively, and their temperature sensitivities are 11.85 and 5.59[Formula: see text]pm/∘C, respectively. The interesting features of the sensor include good operating linearity, compact size, high sensitivity, simple structure and low cost.

Optical vector fields with kaleidoscopic quasicrystal structures by multiple beam interference.

An easily accessible approach is proposed to create structured beams with various quasicrystal structures and polarization distributions based on multi-beam interference. By controlling the azimuthally-dependent polarization for Q evenly and circularly distributed beams to be interfered, the intensity and polarization structures for the generated quasicrystal field with Q-fold rotational symmetry are flexibly adjusted. Using the diffraction theory for interfering Q vector Gaussian beams, an analytical wave function is derived to reconstruct the polarization-resolved intensities and the distributions of Stokes parameters measured in the experiment. With good agreement between the numerical and experimental results, the derived wave function is further employed to characterize the propagation-variant states of polarization, providing fundamentally important information for the vector quasicrystal beams.

Signal processing integrated with fiber-optic Vernier effect for the simultaneous measurement of relative humidity and temperature.

A novel inline Fabry-Perot interferometer (FPI) for simultaneous relative humidity (RH) and temperature monitoring is proposed. The sensing probe consists of a section of hollow core Bragg fiber (HCBF) spliced with a single-mode fiber pigtail. The end-face of the HCBF is coated with Chitosan and ultraviolet optical adhesive (UVOA), forming two polymer layers using a well-designed fabrication process. The surfaces of the layers and splicing point will generate multiple-beam interference and form Vernier-effect (VE) related envelopes in the reflection spectrum. A signal processing (SP) method is proposed to demodulate the VE envelopes from a complicated superimposed raw spectrum. The principle of the SP algorithm is analyzed theoretically and verified experimentally. The sensor's RH and temperature response are studied, exhibiting a high sensitivity of about 0.437 nm/%RH and 0.29 nm/ ∘C, respectively. Using a matrix obtained from experiment results, the simultaneous RH and temperature measurement is achieved. Meanwhile, the simple fabrication process, compact size and potential for higher sensitivity makes our proposed structure integrated with the SP algorithm a promising sensor for practical RH and temperature monitoring.

Multiple-beam grating interferometry and its general Airy formulae

Multiple-beam grating interferometry, a hybrid of the multiple-beam interference and grating interferometry, is introduced and conducted by building a Littrow-type cavity with a diffraction grating. Based on multi-beam interference and grating interferometry, mathematical derivation reveals that the fringes of the multi-beam grating interferometry follow a general form of Airy formulae, while the period of which is additively determined by phases from grating pitches and laser wavelength. Two crucial parameters, peak transmission and finesse describing brightness and sharpness of fringes, are defined and investigated, whose results reveal that fringe shape of multiple-beam grating interferometry is determined by amplitude coefficients of two surfaces forming the cavity and could be explained by multiple beam interference with intensity loss. Consistency of simulation and experiment results are proved and analyzed. Multiple-beam grating interferometry is promising for in-plane and multi-dimensional displacement measurements and might inspire novel enhancement for sensors and instruments based on Fabry-Pérot interferometry.

Fabry-Pérot angle sensor using a mode-locked femtosecond laser source.

An angle sensor based on multiple beam interference of a Fabry-Pérot etalon employing a mode-locked femtosecond laser as the measurement beam is proposed. Output angles are evaluated by using estimated local maxima within a measurement bandwidth of an output fringe spectrum detected by an optical spectrum analyzer. In the proposed method, fringe spectra produced by beams from transmittance and a reflectance side of the Fabry-Pérot etalon are detected individually, and intensities of two spectra are divided to increase the visibility by narrowing a spectrum width. Confirmation of an increase in the visibility is conducted by comparing full width half maximum values of spectra obtained by a constructed optical setup, and evaluation accuracies were compared by repeating measurements for 100 times. The output angle using estimated local maxima of the divided spectra is then evaluated to verify the feasibility of the proposed method. As a result, it is confirmed that the proposed method improves the accuracy of angle determination by one order of magnitude.

Broadband Bilayer Antireflective Coating with Metasurfaces and Chebyshev Transformer

Antireflection coatings with a broad relative bandwidth (RBW) and reduced electrical length are desirable for a variety of applications in the microwave frequencies. Here, we propose the design principle of bilayer metasurfaces with 100% RBW and subwavelength thickness based on the traditional Chebyshev transformer, with excellent agreement with our experimental validation for both transverse electric and magnetic polarizations. We utilize the multiple-beam interference theory to reveal the underlying mechanism of the preferred choices for nonresonant or weakly resonant metasurface unit cells. Being able to manipulate the transmissions and reflections within the bilayer structure, we further demonstrate the universality and sensitivity of the designs capable of providing near-unity microwave transmission from air into the full range of natural media, with prescribed RBW and reduced electrical length.

Optical characterization of inhomogeneous thin films with randomly rough boundaries exhibiting wide intervals of spatial frequencies.

Results concerning the optical characterization of two inhomogeneous polymer-like thin films deposited by the plasma enhanced chemical vapor deposition onto silicon single crystal substrates are presented. One of these films is deposited onto a smooth silicon surface while the latter film is deposited on a randomly rough silicon surface with a wide interval of spatial frequencies. A combination of variable-angle spectroscopic ellipsometry and spectroscopic reflectometry applied at near-normal incidence are utilized for characterizing both the films. An inhomogeneity of the films is described by the method based on multiple-beam interference of light and method replacing inhomogeneous thin films by multilayer systems. Homogeneous transition layers between the films and substrates are considered. The Campi-Coriasso dispersion model is used to express spectral dependencies of the optical constants of the polymer-like films and transition layers. A combination of the scalar diffraction theory and Rayleigh-Rice theory is used to include boundary roughness into formulae for the optical quantities of the rough polymer-like film. Within the optical characterization, the spectral dependencies of the optical constants at the upper and lower boundaries of both the polymer-like films are determined together with their thickness values and profiles of the optical constants. Roughness parameters are determined for the rough film. The values of the roughness parameters are confirmed by atomic force microscopy. Moreover, the optical constants and thicknesses of both the transition layers are determined. A discussion of the achieved results for both the polymer-like films and transition layers is performed.

The Effect of Molecular Orientation in Disperse Red-1 Film on Its Refractive Index

The refractive index of materials is an important physical quantity in the design of various photonic devices. For thin-film based devices, the fabrication method should be compatible with existing processes in microelectronic fabrication and allow for controlling the refractive index. In this research, the material used is a polar Disperse Red 1 (DR1) molecule. The film fabrication was carried out using the physical vapor deposition method which had been equipped with an electric poling installation. The poling of the electric field during the deposition process was applied perpendicular to the substrate. The thickness measurement and the refractive index of the films were carried out using a reflectometer where the light was incident perpendicular to the substrate. The refractive index was determined by the multiple beam interference method. As a result, it was found that the application of an electric field causes a change in the orientation of the molecules, which were initially parallel to the substrate to become perpendicular. Increasing the field strength further reduces the number of molecules parallel to the substrate. This correlates with a decrease in the refractive index of the film.

Silver-Coated 45° Radiated Tilted Fiber Grating Based Interferometer and Its Sensing Applications

We proposed a silver-coated 45° radiated tilted fiber grating (45° RTFG) based interferometer, in which the 45° RTFG is working as a beam splitter and a coupler, and the light transmitting in the fiber core is radiated out and resonant in the cladding radial cavity formed by the fully coated silver film, which forms multiple beam interference. We have theoretically and experimentally investigated the proposed fiber interferometer in terms of polarization-dependent transmission spectra, the free spectral range (FSR), spectral visibility and sensing characteristics. Due to the single polarization radiation feature of 45° RTFG, only S-polarized light could form the multiple beam interference and P-polarized light would pass through the grating with low loss. And the FSR of the proposed fiber interferometer is around 6.8 nm, which is determined by the 125 μm cladding diameter. The theoretical results show that the spectral visibility of interference is proportional to the coupling efficient of 45° RTFG and when the coupling efficient reaches 0.92, the spectral visibility is the maximum. In the experiment, the fiber interferometer formed by the 45° RTFG with 11 dB polarization extinction ratio has the spectral visibility of 26 dB. Moreover, we have also investigated the temperature, strain and twist characteristics of the proposed interferometer. The experimental results show that the transmission peak has a red shift with increasing temperature, with a sensitivity of 10 ± 0.1 pm/°C; The strain causes a blue shift for the transmission peak with −0.42 ± 0.01 pm/μϵ sensitivity, and the twist sensitivity reaches 22.408 ± 0.2 dB/rad. The proposed silver-coated 45° RTFG based interferometer has an in-fiber and compact structure, which can be potentially used for optical fiber sensing.

Formation of liquid crystal gratings with crystal/quasicrystal patterns through photoalignment

ABSTRACT In this study, a simple method for generation of liquid crystal (LC) grating with crystal/quasicrystal/kaleidoscopic patterns via photoalignment is proposed. The crystal/quasicrystal/kaleidoscopic patterns are created using multiple-beam interference when the recording beam is divided into multiple beams by passing a multiple-aperture mask and focused by a lens. Two-dimensional (2D) patterns are recorded on LC cells based on the laser-induced adsorption of azo dyes that guide the orientation of the LC molecules. Measurements indicate that the 2D LC gratings with crystal/quasicrystal patterns are electro-optically tunable and possess polarisation-independent diffraction efficiency.

Junction temperature measurement in optically-activated power MOSFET

The temperature-dependent optical properties of silicon carbide (SiC), such as refractive index and reflectivity, have been used for a direct monitoring of the junction temperature of a power MOSFET. In particular, the optical response of a 4H–SiC MOSFET-integrated Fabry–Perot (FP) cavity to temperature changes has been investigated through parametric optical simulations at the wavelength of λ = 450 nm. The reflected optical power exhibited oscillatory patterns caused by the multiple beam interference for which the MOSFET epilayer, between the gate-oxide and the doped 4H–SiC substrate, acts as a FP etalon. These results were used to calculate the refractive index change and, therefore, the optical phase shift of Δϕ = π/2 corresponding to a temperature variation that can be considered as a warning for the device ‘health’. In practical applications, the periodic monitoring of the optic spectrum at the interferometric structure output gives an essential information about the device operating temperature condition that, for high power operations, may lead to device damages or system failure. Moreover, the optical monitoring of the junction temperature has been combined with the optical activation of the same device in order to design an all-optically controlled power MOSFET. Electro-optical simulation results show that the application of an UV optical beam (λ = 285 nm) leads to the creation of the electrical channel between drain (D) and source (S). The corresponding current density–voltage (J D–V DS) characteristics have been calculated under different values of the optical power density up to 10 kW cm−2.

Compensation method of the satellite navigation system reflected signals

The factors that cause errors in navigation information during the operation of satellite navigation systems are considered. The errors due to multi-beam interference are investigated. Methods for errors compensating of a satellite navigation system, which make it possible to compensate the influence of disturbing factors, in particular, errors caused by radio signals reflected from obstacles, are presented. It is proposed to build models of reflected signals by means of evolutionary algorithms. In the process of the satellite navigation system functioning, a systematic component model of the reflected signal with parametric identification is used. Keywords satellite navigation system, multiple-beam interference, error compensation, algorithms for building models, systematic component of the error, parametric identification

Handedness control in polarization lattice fields by using spiral phase filters

In scalar optics, a spiral phase plate (SPP) spatial filter, independent of its polarity, can perform radial Hilbert transform for isotropic edge enhancement of objects. The same 4f spatial filter setup is also useful to realize multiple-beam interference. However, the polarity of the SPP phase filter can decide the handedness of certain polarization lattice fields created by multiple-beam interference. It is interesting to note that a phase element is exhibiting polarization control on structured fields. We demonstrate this by creating few lattice structures with and without C-point singularities. Experimental and simulation results are presented. The current study may be useful in optical chirality measurement, signal processing, and structured illumination microscopy.

FECO fringes for investigating the effect of grafting process on the dispersion properties of polyamaide-6 fibers.

Polyamide-6 fiber was modified by grafting it with poly(methyl methacrylate) PMMA polymer. The grafting process is widely used in industry to introduce new properties and overcome some obstacles, for instance, in storing energy applications. Multiple-beam interference techniques are very precise techniques to characterize the different properties of polymeric fibers. Fringes of equal chromatic order FECO technique was used to study the effect of grafting process on the dispersion properties of polyamides fibers. A mechanical drawing device was attached to the FECO system to evaluate the mechanical deformation impact on the samples and on their dispersion properties. The dispersion properties were evaluated by measuring their refractive indices, Cauchy's constants, average excitation energy, dispersion energy, lattice energy, interband oscillator wavelength, static dielectric constant, and Abbe's dispersion number. The results show that grafting polyamide-6 with PMMA produced a new material with a different structure and different dispersion properties. Microinterferograms, graphs and tables were given for illustrations.

Mode transformation properties in the integrated bimodal resonance structure

The bimodal resonance phenomena in photonic structure have received particular attention due to their intriguing optical properties and numerous potential applications. In this work, we investigated the mode transformation behaviors of the guided modes in an integrated bimodal resonance structure consisting of a single groove on the surface of an abruptly ended slab waveguide. Numerical simulations demonstrated that the strong mode transformation can occur in the anticrossing region of resonance at the oblique incidence of a transverse electric (TE)-polarized guided mode on the groove. According to the multiple-beam interference model, a theoretical formula was developed to study the resonance and mode transformation behaviors of the guided modes. The results showed that the different anticrossing behaviors of structure are resulting from the constructive and destructive interference of bimodal resonance. The resonance and mode transformation properties of structure can be controlled by adjusting the geometrical parameters of groove. The mode manipulation with high efficiency in the slab waveguide will have many applications in lab-on-a-chip devices, switching and on-chip spectroscopy.

Optimising backscatter from multiple beam interference.

Optical sensing applications are usually reliant on the intensity of the measured signal. For remote sensing applications where a target is probed with a laser beam, the sensitivity will be limited by the amount of backscattered light returned from the target to the detector. We demonstrate a method of increasing the signal returned to the detector by illuminating the target with a number of independently controlled beams, where both the position and phase are optimised. We show an improvement in the backscattered signal that is proportional to the number of beams used. The method is demonstrated within a laser microphone, measuring audio signal due to vibrations in surfaces, showing a significant improvement in the signal-to-noise of the measurement.

Efficient Processing of Spectral Measurements Using Virtually Imaged Phased Array

The virtual bright fringes method (VBFM) has been here designed to analyze the spectrum signal of Brillouin scattering in water using virtually imaged phased array (VIPA) etalon and an intensified charge-coupled device (ICCD) camera. VBFM is based on the principle of multiple-beam interference with a plane-parallel plate and, thus, only needs the output of the sample to calculate the Brillouin Stokes frequency shift. Moreover, this method substantially reduces the experimental requirements and simplifies the experimental processing. In addition, the capability of this new method has been confirmed by processing experimental data from stimulated Brillouin scattering spectra in water. Our results demonstrated that the experimental results processed by VBFM were in good agreement with the theoretical values. Indeed, VBFM provides a feasible scheme for the measurement of Brillouin Stokes frequency shift with sub-GHz accuracy of 10MHz. VBFM facilitates a broader application of Brillouin scattering, including the measurement of liquid materials and the elastography of biological tissue.

Ellipsometric characterization of inhomogeneous thin films with complicated thickness non-uniformity: application to inhomogeneous polymer-like thin films.

The method of variable angle spectroscopic ellipsometry usable for the complete optical characterization of inhomogeneous thin films exhibiting complicated thickness non-uniformity together with transition layers at their lower boundaries is presented in this paper. The inhomogeneity of these films is described by means of the multiple-beam interference model. The thickness non-uniformity is taken into account by averaging the elements of the Mueller matrix along the area of the light spot of the ellipsometer on the films. The local thicknesses are expressed using polynomials in the coordinates along the surfaces of the films. The efficiency of the method is illustrated by means of the optical characterization of a selected sample of the polymer-like thin film of SiOxCyHz prepared by plasma enhanced chemical vapor deposition onto the silicon single crystal substrate. The Campi-Coriasso dispersion model is used to determine the spectral dependencies of the optical constants at the upper and lower boundaries of this film. The profiles of these optical constants are determined too. The thickness non-uniformity is described using a model with local thicknesses given by the polynomial with at most quadratic terms. In this way it is possible to determine the geometry of the upper boundary. The thickness and spectral dependencies of the optical constants of the transition layer are determined as well. Imaging spectroscopic reflectometry is utilized for confirming the results concerning the thickness non-uniformity obtained using ellipsometry.