Optical Interference Principle Research Articles

Random telegraph noise characteristic of nonvolatile resistive random access memories based on optical interference principle

The influence of random telegraph noise (RTN) could reduce the reading margin, which would cause computational errors in data recognition. This paper proposes a current sensor based on the principle of optical fiber interference, which can avoid the interference generated during the RTN testing process and improve the accuracy due to its passive characteristics. In this study, a hafnium oxide based memristor was fabricated, the switching voltages of Cu and TiN as the top electrodes are 0.2 V and 0.15 V, respectively. In addition, the RTN spectral density of the two device structures in LRS increases from 10−5 to 10−1 A2 Hz−1 and from 10−5 to 101 A2 Hz−1 with increasing applied voltage. While the RTN in high resistance state is independent of the applied voltage. Furthermore, based on the analysis of the experimental data, the generation mechanism of the RTN is attributed to local defects and the capture or emission of carriers by traps.

Stimuli-Responsive Structural Colored Gel That Exhibits the Three Primary Colors of Light by Using Multiple Photonic Band Gaps Acquired from Photonic Balls.

A material that can capture changes in environmental stimuli as a color change can be used to develop sensors and displays. By producing an ordered structure in a polymer gel that reflects particular wavelengths of light, we can express the volume change that occurs based on the environment as the change in the wavelength of reflected light, i.e., structural color. To date, many systems have been developed to change the hue of the structural color as a function of temperature, pH, substance, applied force, and so on. However, as is expected from the principle of optical interference, the gel usually shows a red-shift with increasing volume. In this study, we propose a method for preparing structurally colored stimuli-responsive polymer gels that display appropriate color changes according to changes in environmental stimuli. For this purpose, we employ the photonic balls, which are spherical colloidal crystals consisting of monodisperse silica particles, as templates. By combining the wavelength-selective reflection generated from different photonic band gaps of the photonic balls, we succeeded in developing porous stimuli-responsive polymer gels that exhibited various types of color change, which are not observed in conventional systems.

Research of Optical Performance of VO2/V2O5 Composite Film with Ultra-High Luminous Transmittance

The optical performance of vanadium dioxide film is important for the application in smart windows. In this work, we prepared ultra-thin vanadium oxide films with thickness from 30 nm to 120 nm and investigated the influence of thickness on the optical performance of ultra-thin vanadium oxide films. The experimental results show that the composite of vanadium pentoxide (V2O5) with a low refractive index can improve luminous transmittance, which reaches 66.32% at the film thickness of 30 nm. The transmittance of metallic phase ultra-thin vanadium oxide film in the visible band is higher than that in the semiconductor phase, which leads to cross-points in transmittance curve and negative solar energy modulation. With the increase of thickness, the position of cross-points in transmittance curve shifts to long-wavelength, and the absolute value of negative solar energy modulation increases from 0.73% to 1.5%, which is related to the principle of optical interference. These conclusions will inspire ultra-thin vanadium dioxide film in improving the solar energy modulation of smart windows under the high luminous transmittance.

Design and analysis of all‐optical 1‐to‐2 line decoder based on linear photonic crystal

A new design of 1-to-2 line all-optical logic decoder has been proposed based on a two-dimensional photonic crystal (PhC) structure. The decoder operates based on the principle of optical interference within the PhC waveguides. An optical bias has been used to generate high-logic states at zero input conditions. Simulations explore a high contrast ratio, in the order of 11.3 dB, for both the output ports of the device. Response times have been calculated from the transient responses of the output ports, and are found as 0.65 and 0.77 ps for the ports 1 and 2, respectively. These results in a bit rate of ≃625 Gbps, considering the worst-case scenario. Phase sensitivity analysis has also been performed which shows that the device output is quite sensitive to the differences in phases of the bias and signals. However, a strategy has been proposed to make the same insensitive to the phase changes. Finally, the small footprint (in the order of 234 μm 2 ); standard operating wavelength; and silicon-based design of the decoder, along with its said merits, make the device highly potential for on-chip photonic-integrated-circuit applications.

Multiband notch filter based guided-mode resonance for mid-infrared spectroscopy

A dielectric guided-mode resonance (GMR) notch filter with multiple channels was designed to operate in the mid-wave infrared (MWIR, 3∼4μm). The transmission characteristics of filters were analyzed using a finite difference time domain (FDTD) method. In the structure of notch filter, two different periodic (p1=1.6μm and p2=2.0μm) silicon (Si) grating waveguide layers (GWLs) are constructed on the CaF2 substrate. Si waveguide layer thickness and CaF2 cladding layer thickness were designed based on optical interference principle to give maximum transmission across the MWIR. The transmission spectrum presents two narrow band located at 3.410μm and 3.833μm with not only a high bandstop coefficient (>99%), but also a broadband high transmission (>90%) off-resonance. The resonant wavelengths can be flexible modulated in wide range by changing grating periods or filling factors, and it is proved that filter is stable and useful in actual atmospheric conditions. Because of the good performance in the bandstop features, the multiband GMR notch filter designed in this method may have a potential for a variety of imaging or detection applications.

Miniature fiber pressure sensor based on an in-fiber confocal cavity

A new type of miniature pressure sensor based on a hybrid Fabry-Perot (F-P) interferometer is proposed. The in-line air cavity of the sensor is a micro-confocal air cavity, which is formed by splicing together a single mode fiber (SMF) and a solid-core photonic crystal fiber (PCF) with the specific splicing parameters. The sensor is fabricated by simple steps involving only fusion splicing, cleaving and polishing. Optical interference principle of the sensor is analyzed and the parameters in sensor design are discussed. Due to low propagation loss, experiments show that the reflection spectrum of the sensor has a fringe contrast of more than 30 dB. By tracing the trough wavelength in the interference spectrum, the pressure can be demodulated. Within the pressure measurement range of 0–1 MPa, the sensitivity is −193 pm/MPa. The experimental results indicate that the deflection is consistent with the theoretical analysis and the sensor has a good linearity. Easy fabrication, low-cost and high-contrast make it appropriate for practical application.

MWIR/LWIR filter based on Liquid–Crystal Fabry–Perot structure for tunable spectral imaging detection

An electrically tunable medium-wave infrared (MWIR)/long-wave infrared (LWIR) filter based on the key structure of Liquid–Crystal (LC) Fabry–Perot (FP), which works in the wavelength range from 2.5μm to 12μm, is designed and fabricated successfully in this paper. According to the optical interference principle of the FP cavity and electrically controlled birefringence of nematic LC molecules, the particular functions including spectral selection and spectral staring and spectral adjustment, can be realized by the developed MWIR/LWIR filter driven and controlled electrically. As to the LC-FP filter, both planar reflective mirrors are shaped by depositing a layer of aluminum (Al) film (∼60nm) over one side of double-side polished Zinc Selenide (ZnSe) wafer (∼1mm), and then polyimide (PI) layer with the thickness of ∼100nm is coated directly on Al film. With typical sandwich architecture, the depth of the cavity with nematic LC molecules sealed in is ∼7.5μm. To make sure the LC molecules parallel aligned and twist regularly under voltage driving signal applied on Al film, which also acts as electrode, the V-grooves are formed in PI layer with the depth of ∼90nm and the width of ∼350nm at average by strong rubbing. The typical transmission spectrum in MWIR&LWIR wavelength range and several spectral images in MWIR wavelength range based on the fabricated LC-FP filter, have been obtained through applying a voltage driving-signal with different root-means-square (RMS) value over the electrodes of LC-FP filter in the selected voltage range from 0VRMS to 19.8VRMS. The testing result demonstrates a prospect of realization smart spectral imaging and further integrating the LC-FP filter with infrared focal plane arrays (FPAs) to achieve the purpose infrared multispectral imaging. The developed MWIR&LWIR LC-FP filters show some obvious advantages such as wide working wavelength range, electrically tunable spectral selection, ultra-compact, low cost, being compatible with standard microelectronic technology.

Development of Testing Machine for Measuring Unsteady State EHL Film under Heavy Load

In order to study elastohydrodynamic lubrication characteristics of cylindrical roller under heavy load and unsteady state, a testing machine is designed for measuring line contact film thickness and shape according to optical interference principle. The experimental apparatus is mainly made of glass block reciprocating motion systems, ball or roller rolling rotation system, loading system, speed control systems, lighting systems and image acquisition system. Moving parts is formed by the slider-crank mechanism. Specimen is accompanied by a pair of floating trial roller bearing. Specimen load is applied by leverage. The entrainment velocity of roller is approximate sinusoidal variation during a cycle. Experiment interference image is satisfactory, can provide reliable experimental data for future research.

Wavelet-based image fusion for securing multiple images through asymmetric keys

Image fusion is one of the popular methods which provides better quality fused image for interpreting an image data. Discrete wavelet transform based fusion technique is one such method, in which low and high frequency components are merged together to improve the image content. In this paper, we propose this fusion technique for generating asymmetric keys for securing multiple images. An input image to be encrypted is digitally encoded into two phase-only masks employing the principle of optical interference. This process has been repeated for three different input images; however, it can be extended to n images. Now, one of the phase-only masks corresponding to each input image is preserved as a phase key while another set of phase masks are fused together. This fused image is called the encrypted image. Unlike optical asymmetric encryption technique based on amplitude- and phase-truncation approach, here, four asymmetric keys are generated corresponding to each image. Asymmetric keys corresponding to each image, fractional orders, phase-only masks, level of decomposition and type of wavelet, enlarge the key space and hence offer enhanced security. The proposed method is demonstrated through the simulation results.

Single-beam image encryption using spatially separated ciphertexts based on interference principle in the Fresnel domain

A new optical security system for image encryption based on optical interference principle and translation property of Fresnel transform (FrT) has been proposed in this article. The algorithm of this proposal is specially designed for single-beam optical decryption and can thoroughly resolve the silhouette problem existing in the previous interference-based scheme. Different from earlier schemes using interference of phase-only masks (POMs), the inverse FrT of primitive image is digitally decomposed into a random POM and a complex field distribution. Information associated with the primitive images can be completely smoothed away by the modulation of this random POM. Through the translation property of FrT, two linear phase-only terms are then used to modulate the obtained random POM and the complex distribution, respectively. Two complex ciphertexts are generated by performing digital inverse FrT again. One cannot recover any visible information of secret image using only one ciphertext. Moreover, to recover the primitive image correctly, the correct ciphertexts must be placed in the certain positions of input plane of decryption system, respectively. As additional keys, position center coordinates of ciphertexts can increase the security strength of this encryption system against brute force attacks greatly. Numerical simulations have been given to verify the performance and feasibility of this proposal. To further enhance the application value of this algorithm, an alternative approach based on Fourier transform has also been discussed briefly.

Security enhancement of color image cryptosystem by optical interference principle and spiral phase encoding: erratum

Security enhancement of color image cryptosystem by optical interference principle and spiral phase encoding: erratum

Optical image-hiding method with false information disclosure based on the interference principle and partial-phase-truncation in the fractional Fourier domain

An image-hiding method based on the optical interference principle and partial-phase-truncation in the fractional Fourier domain is proposed. The primary image is converted into three phase-only masks (POMs) using an analytical algorithm involved partial-phase-truncation and a fast random pixel exchange process. A procedure of a fake silhouette for a decryption key is suggested to reinforce the encryption and give a hint of the position of the key. The fractional orders of FrFT effectively enhance the security of the system. In the decryption process, the POM with false information and the other two POMs are, respectively, placed in the input and fractional Fourier planes to recover the primary image. There are no unintended information disclosures and iterative computations involved in the proposed method. Simulation results are presented to verify the validity of the proposed approach.

Plasmonic Focusing in Nanostructures

In this review, we show that by designing the metallic nanostructures, the surface plasmon (SP) focusing has been achieved, with the focusing spot at a subwavelength scale. The central idea is based on the principle of optical interference that the constructive superposition of SPs with phase matching can result in a considerable electric-field enhancement of SPs in the near field, exhibiting a pronounced focusing spot. We first reviewed several new designs for surface plasmon focusing by controlling the metallic geometry or incident light polarization: We made an in-plane plasmonic Fresnel zone plates, a counterpart in optics, which produces an obvious SP focusing effect; We also fabricated the symmetry broken nanocorrals which can provide the spatial phase difference for SPs, and then we propose another plasmon focusing approach by using semicircular nanoslits, which gives rise to the phase difference through changing refractive index of the medium in the nanoslits. Further, we showed that the spiral metallic nanostructure can be severed as plasmonic lens to control the plasmon focusing under a linearly polarized light with different angles.

Multiple-image encryption based on interference principle and phase-only mask multiplexing in Fresnel transform domain

In this article, a multiple-image encryption method based on the optical interference principle and phase-only mask (POM) multiplexing is proposed. During the encryption process, each secret image is encoded into two analytically obtained POMs and one computer-generated random POM, in which no iterative computation is required. The analytically obtained POMs taken from different secret images are then synthesized by POM multiplexing and further encoded into two complex ciphertext images. The silhouette problem that exists in the earlier interference principle-based encryption approaches is totally resolved by the proposal. Both digital and optical means can be used for decryption. The crosstalk effect between the secret images will not appear in the decrypted results by using the proposed system. Numerical simulations have been given to verify the performance and feasibility of the proposal. We also discuss briefly the influence of information compression on the quality of decrypted images.

Fabry–Perot displacement interferometer for the measuring range up to 100 mm

Current commercial laser interferometers have demonstrated outstanding measuring performances for high precision measurements, but they are very sensitive to environmental or mechanical effects. Owing to the fact that the most laser interferometers are based on the structure of Michelson interferometer, the above-mentioned influences from measuring arms will undisputedly lead to significant errors. To realize the high precision measurement, the environmental conditions must be strictly demanded. As a result of that limit, it’s inconvenient for industrial applications. In comparison with such non-common optical path structure, conventional Fabry–Perot interferometer with common optical path can effectively reduce the measuring errors resulting from environmental disturbances.To minimize the environmental and mechanical effects, a new interferometric displacement system with the structure of common optical path is proposed. By the optical interference principle and the corner cube reflector, the novel system with the common optical path can be designed. Hence, the novel interferometer can hold the advantage of large measurement range, and the signal pattern is nearly the same with that of Michelson interferometer. Because of the folded optical cavity, the resolution of the multi-interference interferometer with corner-cube can be enhanced to λ/16.Through this development, a high accurate interferometric displacement measurement system can be available under ordinary environmental conditions without the compensation requirement of the tilt angles and its prominent measurement characterizations have been proven. It will be demonstrated that measurement range is larger than 100mm and the standard deviation of the comparison experiment is about 0.211μm (within half wavelength) in the whole measuring range.

Security enhancement of color image cryptosystem by optical interference principle and spiral phase encoding

A color information cryptosystem based on optical interference principle and spiral phase encoding is proposed. A spiral phase mask (SPM) is used instead of a conventional random phase mask because it contains multiple storing keys in a single phase mask. The color image is decomposed into RGB channels. The decomposed three RGB channels can avoid the interference of crosstalks efficiently. Each channel is encoded into an SPM and analytically generates two spiral phase-only masks (SPOMs). The two SPOMs are then phase-truncated to get two encrypted images and amplitude-truncated to produce two asymmetric phase keys. The two SPOMs and the two asymmetric phase keys can be allocated to four different authorized users. The order, the wavelength, the focal length, and the radius are construction parameters of the SPM (or third SPOM) that can also be assigned to the four other different authorized users. The proposed technique can be used for a highly secure verification system, so an unauthorized user cannot retrieve the original image if only one key out of eight keys is missing. The proposed method does not require iterative encoding or postprocessing of SPOMs to overcome inherent silhouette problems, and its optical setup alleviates stringent alignment of SOPMs. The validity and feasibility of the proposed method are supported by numerical simulation results.

A measurement method of cell gap for liquid crystal lens

There was a problem in current cell gap measurement of liquid crystal (LC) lens. A method was proposed by adopting interference of linearly polarized light in this paper. It was claimed that the incident light was monochromatic light with a uniform distribution of light intensity. The polarization axis of the analyzer was perpendicular or parallel to the polarization axis of polarizer. The difference between light and dark interference fringes was the biggest when the angle was equal to 45° between the rubbing direction of alignment layer in the LC lens and the polarization axis of polarizer. The cell gap of LC lens can be calculated by the transmittance of LC lens center and the max transmittance of its other locations. The tilt angle was equal to the pre-tilt angle of LC at the LC lens center. This method was simple and reliable. Its accuracy is relatively high due to the use of optical interference principle.

Can interference patterns in the reflectance spectra of GaN epilayers give important information of carrier concentration?

Low-temperature reflectance spectra of a series of Si-doped GaN epilayers with different doping concentrations grown on sapphire by metal-organic chemical vapour deposition were measured. In addition to the excitonic polariton resonance structures at the band edge, interference oscillating patterns were observed in the energy region well below the band gap. The amplitudes of these oscillation patterns show a distinct dependence on the doping concentrations of the samples. From the thin-film optical interference principle, an approach connecting the amplitude of the interference oscillations and the impurity scattering was established. Good agreement between experiment and theory is achieved.

Optical image hiding with silhouette removal based on the optical interference principle

The earlier proposed interference-based encryption method with two phase-only masks (POMs), which actually is a special case of our method, is quite simple and does not need iterative encoding. However, it has been found recently that the encryption method has security problems and cannot be directly applied to image encryption due to the inherent silhouette problem. Several methods based on chaotic encryption algorithms have been proposed to remove the problem by postprocessing of the POMs, which increased the computation time or led to digital inverse computation in decryption. Here we propose a new method for image encryption based on optical interference and analytical algorithm that can be directly used for image encryption. The information of the target image is hidden into three POMs, and the silhouette problem that exists in the method with two POMs can be resolved during the generation procedure of POMs based on the interference principle. Simulation results are presented to verify the validity of the proposed approach.

Information hiding based on the optical interference principle

An information hiding method based on the optical interference principle is proposed. In this method, a secret image can be obtained by two light beams' interference. One of the beams is modulated by our assigned host image; and the other is modulated by a noise-like complex distribution, which is regard as the encrypted image. The transmission of the encrypted image can be implemented by hiding it in the host image to prevent the communication from being perceived by unauthorized person. In addition, this method can also realize simultaneous encryption and hiding for two images. A series of numerical simulation results are presented to verify the feasibility of our proposed method.