A two-stage compression framework for computer-generated hologram (CGH) with compressed sensing (CS) and quantum-inspired neural network (QINN) is proposed. A deep learning-based CS model is applied to sample the CGH at sub-Nyquist rates to generate measurements, and its more compact and representative information using interblock information is further extracted by QINN. With two-stage compression framework, the CGH is greatly compressed and suitable for storage and transmission. Experimental results demonstrate that our proposed two-stage compression framework can preserve more important holographic information during the compression, thus significantly improving the overall quality of reconstructed images compared to only using CS or QINN.

A newly constructed pendulum tiltmeter has been described based on the moiré technique, which is specified as a series of dark and light patterns configured by the superposition of two regular gratings. This tiltmeter chiefly consists of two frames that can move with respect to each other, and tilting movements are recorded by using the moiré technique. Double similar gratings are attached to the frames. The gratings are installed in parallel, having no physical contact, so that their lines make a small angle with respect to each other. A diode laser beam passes through the formed moiré pattern, and a narrow slit then hits on a light detector. Due to external stress and making a tilt or incline in the moiré tiltmeter, one of the gratings is displaced respect to the other one, leading to the moiré fringe movement. So, the light intensity on the detector changes and is registered as the output voltage. A digital signal processor samples the voltage and generates a record of the tiltmeter. The recorded signal can be used to measure the tilt. We have investigated the experimental results of the tiltmeter, and the outcomes show that the sensor is quite viable. In total, the proposed tiltmeter is cost-effective, easy to install, and able to detect tilts of the order of 0.00001 rad. It is also insensitive to electromagnetic noise and environmental conditions, such as temperature fluctuations. Therefore, the applications of this device vary from civil engineering and geological studies to industrial monitoring and experimental ones.

Pose estimation is a typical problem encountered in computer vision. Therefore, it is important to improve the accuracy of this method. Aiming at the accuracy of pose estimation, we propose a high-accuracy pose estimation algorithm based on the you only look once network and residual network with a monocular camera as the sensor for visual acquisition. This algorithm uses ArUco markers as a reference for object localization and uses the red, green, and blue (RGB) image as the input. The input image is sampled 16 and 32 times to extract the feature image, and the feature image extracted by 16 times sampling is passed through the pass-through layer and then combined with the feature image extracted by 32 times sampling to accomplish the dimension expansion. The feature image is identified by the convolutional layer. The EPnP algorithm is used to solve the camera poses. The pose information of the target object in the RGB image is used as the output. By comparing the pose estimation accuracy for the LINEMOD dataset with three evaluation metrics—the 2D projection metric, ADD metric, and 5 cm to 5 deg metric—it can be observed that the pose estimation algorithm proposed has advantages in terms of accuracy compared with traditional pose estimation algorithms. When the target is very similar to the background objects, the algorithm also achieves good performance.

We experimentally studied a passive optical network dynamic fault monitoring technology based on optical time domain reflectometry (OTDR), focused on various types of network structures with optical splitter (OS) devices, and analyzed the monitoring data with different lengths of fibers in front of the OS, such as 0, 14.5, and 50 km, respectively. Different from previous studies, we found that the new characteristics of echo curve can be used to realize the identification of different fault branches. We also make a detailed analysis on the feasibility of OTDR for multi-branch monitoring and the corresponding situation of instrument parameters. And the similar distance of the event situation is analyzed experimentally. We believe that these research data will provide effective technical reference for the intelligent management of optical networks in the current network.

Laser-induced breakdown spectroscopy, as an optical technique for material component analysis, was successfully developed and applied for the detection of atmospheric water vapor. By detecting moist air with different humidities, the spectral intensity of H is found to be a linear enhancement with the increase of relative humidity. A model for the comprehensive analysis of H and O atomic spectral lines is established, and a good correlation coefficient is obtained. Moreover, air samples containing elemental impurities are also detected, and the clustering analysis is realized using principal component analysis. Based on the internal standard method, the quantitative analysis of Na and Mg elements is realized by choosing a spectral line of N as the internal standard line.

An efficient design method for plasmonic devices composed of a periodic slit array based on extraordinary optical transmission is proposed using Q factor analysis. The proposed method significantly reduces the required computation time for cavity resonance in slits by calculating the Q factor at a single frequency that is an eigenfrequency of the wave equation instead of computing the entire transmissions. The computation time is reduced by 20.60 times, and the device performance is increased by 2.43 times through a design based on Q factor analysis. The figure of merit for the overall performance is defined as a product of the transmission peak value and the Q factor. The design variables are the slit width, slit height, and period of slit array. The optical field distributions are calculated numerically using the finite element method, and the Q factor is obtained by solving an eigenfrequency for the wave equation for dispersive media.

In this article, a hybrid (dielectric resonator–graphene) MIMO antenna is presented and investigated at THz frequency. The unique properties associated with this antenna design are (i) CP waves are generated with the help of stair-shaped slot excitation; (ii) change in chemical potential of graphene creates the tunability in the proposed design structure; (iii) use of the metallic wall in between the antenna ports slants the far-field pattern by ± 30 deg, providing pattern diversity; and (iv) mirror image of the aperture introduces the concept of polarization diversity. The proposed antenna works between 4.65 and 5.71 THz with CP waves in between 5.25 and 5.5 THz. Polarization and pattern diversity help to improve the diversity performance of designed antenna. Good gain value and stable radiation pattern make the proposed antenna suitable for THz sensing applications.

The diagnostic demand of hot-spot intensity distribution in laser inertial confinement fusion experiment has motivated quantitative measurement experiment to give the response efficiency of grazing incidence system to improve the accuracy of the diagnosis. In our study, a full-aperture intensity response measurement method is proposed, which is based on pinhole-scanning field of view (FOV) to obtain the response efficiency of grazing incidence system. The method is highly repeatable and enables response efficiency measurements over the full FOV with acceptable accuracy. A silicon positive-intrinsic-negative detector with an energy response range of 1.5 to 30 keV is used to directly detect the input and output spectrum. The response efficiency of a single-channel aspheric Kirkpatrick–Baez (KB) microscope coated with W/Si is obtained under the FOV of ±150 μm. The response efficiency of center FOV of the KB system is measured to be 2.52E-7 sr. The value is promising, as it shows a 6.6% maximum deviation from the theoretical value at center FOV, with a global uncertainty of 7.4%.

In the development of miniaturized optical gyroscopes, the resonant micro-optical gyroscope (RMOG) is the most representative sensor of new optical gyroscopes. However, in the manufacturing process of optical elements, the influence of backscattering and optical Kerr noise limits the performance of RMOG. A method of suppressing optical Kerr noise generated by the front end by compensating the optical power difference while suppressing the backscattering noise is introduced. In this method, we study the optimal strategy of double-phase modulation frequency to obtain the maximum spectral gap of clockwise and counterclockwise light, so as to suppress the error related to backscattered light. At the same time, the influence of Kerr noise on the optical path is reduced through the high-precision feedback loop of the intensity modulator. Based on Allan variance, the long-term deviation stability of RMOG reaches 0.98 deg/h.

In spectral beam combining systems, the locked spectra of the diode laser array are determined by the interaction between the internal cavity and the external cavity. Using the multibeam interference theory, spectral modes locked by the coupled cavity are numerically calculated and analyzed. A spectral mode of a diode emitter is divided into a main lobe, a left sidelobe, and a right sidelobe, which is mainly affected by the position of the diode emitter. Based on the locked spectral modes, a beam propagation model in the grating-external cavity is established by the diffraction integral method and the incoherent superposition principle. The effects of the interval between two adjacent emitters, the reflectivity of the front surface, and the distance between the grating and the coupler on the characteristics of the combined beam have been discussed in detail. The results show that the beam quality and the spot size of the combined beam gradually degrade with the increasing interval. By reducing the reflectivity of the front surface of the diode emitter and decreasing the distance between the grating and the coupler, the beam quality can be improved. Among the three factors, such as the interval between two adjacent emitters, the reflectivity of the front surface of an emitter, and the diffraction distance, the interval has the most sensitive impact on the combined beam characteristics. Thus a beam shrinker to convert big beams into small beams in diameter can be adopted to optimize the combined beam.

We have investigated the multi-spectral line output characteristics of a CO₂ pulsed laser at multi-atmospheric pressure. The pulse waveforms, wavelengths, and energies of the output spectral lines and the small-signal gains of the full spectrum were measured at 3, 4, and 6 atm. To explain the experimental results and predict the output at higher pressure, a modified six-temperature multi-frequency dynamic model of the regular and sequence band lines was developed. The output spectrum varying from the 10P to 9R band with the increase of pressure was studied theoretically and experimentally. In addition, the gains of the 9R(16), 9P(16), 10R(16), and 10P(16) lines at 3 to 14 atm were simulated and measured, providing insights into variation regulation of the four band gains as pressure increases.

High sensitivity magnetic sensing is proposed using a sandwich structure with polydimethylsiloxane (PDMS) flexible resonator as the core. The directional sensing feature is provided by the sandwich structure’s preset magnetic field. The small Young’s modulus of flexible material corresponds to larger variation, resulting in a highly sensitive magnetic response. In the unshielded environment, the experimental results demonstrate redshift sensitivity of 1.08 nm / mT and blueshift sensitivity of 1.12 nm / mT, which are attributed to a slight variation in the PDMS’s Young’s modulus. The directivity curve’s concave point has a depth of 34.6 dB. The minimum detectable magnetic field of 0.96 nT · Hz ^{− 1/2} is achieved at 1.4 kHz.

The whispering gallery mode resonator based on a fluoride crystalline material offers the advantage of an ultrahigh quality factor, however, its fast tuning remains a challenge. We propose a tuning method for a CaF₂ crystalline resonator using external pressure loading. Through our theoretical calculations and simulations, we discovered that the frequency shift induced by deformation during the pressure tuning of the crystalline resonator is greater than that induced by changes in refractive index. Both shifts were of the same order of magnitude, indicating that both factors must be considered. The experimental results show tuning rates of 1114.6 and 888.2 MHz/MPa in the transverse electric and transverse magnetic modes, respectively. The tuning system can respond to a signal frequency of up to 1.2 MHz.

A graphene composite metasurface-based reflective tri-band polarization converter working in the terahertz frequency regime is proposed and investigated by CST Microwave Studio software. The polarization converter achieves high polarization conversion ratios (above 99%) for linear-to-linear polarization conversion at 6.21, 9.11, and 11.66 THz, and for linear-to-circular polarization conversion at 5.14 THz, with a fixed Fermi energy level (E_f) of 1.0 ev due to the excitation of localized surface plasmons. Subsequently, the reason for cross-polarization conversion at three resonant frequencies and the incident angle sensitive property of the converter were discussed. Based on the graphene component, a tunable tri-band polarization converter was obtained and investigated; this converter could be applied in the active modulation area of wireless communication.

We looked into three distinct topologies, using a one-dimensional photonic crystal with a defect layer in two symmetrical and one asymmetrical configurations as an optical biosensor application for detection in tuberculosis (TB). In order to investigate the optical transmission characteristics of such structures, we used a well-known transfer matrix approach. A shift in resonant peak is estimated, when blood of healthy or TB infected human is infiltrated in defect layer. The impact of several parameters, including the thickness of the defect layer, the number of unit cells, and the angle of incidence for all three configurations, has been studied. The sensitivity, quality factor, figure of merit, and detection limit for all structures have been studied and it is found that asymmetric structure is the best suitable structure for optical sensor application in the present case.

We demonstrate the design, analysis, and measurement of an ultra-thin and dual-functional polarization converter to achieve both linear to linear (LTL) and linear to circular (LTC) polarization conversion at the same time. The simulation results illustrate that the LTL polarization conversion can be maintained from 10.1 to 12.3 GHz, 15.0 to 21.0 GHz, and 28.6 to 30.8 GHz with the polarization conversion ratio (PCR) above 80%, and at 11.0, 18.5, and 30.1 GHz, the PCR is nearly 100%. The LTC polarization can be realized in the frequency range of 22.8 to 28.6 GHz, and the axial ratio (AR) is better than 3 dB. In addition, the polarization conversion capability is stable for oblique incident angles up to 15 deg. The experiments are carried out to validate the property, which show that the proposed converter can successfully achieve the broadband LTL and LTC polarization conversion simultaneously with an ultra-thin design. This converter has potential applications in microwave communications, remote sensing, and imaging.

The geometrically shaped 32-ary quadrature amplitude modulation (GS-32QAM) signal enabled by swarm intelligence algorithm is proposed in high-speed and long-haul coherent optical communication system. The geometric shaping (GS) is obtained by constructing a generic constellation optimization scheme applying particle swarm algorithm (PSO), wolf pack algorithm (WPA), and marine predator algorithm (MPA), respectively. The complexity of three algorithms applied to GS-32QAM is systematically analyzed, where MPA can obtain better search results with slightly higher complexity than PSO. The results show that the optimized constellation is significantly better than the uniform signal in terms of reducing bit error rate and increasing generalized mutual information (GMI). The maximum GMI gain of GS signal with PSO and WPA are both 0.25 bit / sym, and the maximum GMI gain of GS signal with MPA is up to 0.3 bit / sym. At the hard-decision forward error correlation limitation of 3.8 × ^{10 − 3}, compared with uniform signal, the GS signal with PSO, WPA, and MPA can provide the optical signal-to-noise ratio gain of 1, 1.1, and 1.6 dB tolerance, respectively. In terms of data rate, compared with uniform signal, three GS signals can increase by 33, 36, and 43 Gbit / s, respectively.

In this paper, the expression for the dispersion relation function for evanescent waves (EWs) is obtained. This expression establishes the basis of the two-dimensional optics where EWs are involved. We make use of the nonhomogeneous character of these types of waves. The dispersion relation function was implemented to analyze the interference effects showing that the resulting optical field has easily tunable polarization features, which were characterized through a set of Poincare’s spheres with its corresponding coherence matrix representation. The interference model was generalized to describe the diffraction effects by proposing the angular spectrum model with EWs. The analysis was further extended to describe the synthesis of evanescent self-imaging optical fields.

The two most significant issues that communication engineers have been confronting since the development of fifth-generation wireless networks are bandwidth increase and energy-saving techniques in data transmission. We present an innovative solution for utilizing a multi-user different-rates visible light communication (VLC) system for sixth-generation applications. Such a solution takes advantage of orthogonal frequency division multiple access (OFDMA) with orthogonal codes as multiple access communication networks. For the achievement of energy-saving and wide beam width of the optical source, the light emitting diode is often used as a transmitter. Furthermore, one of the most popular orthogonal codes in use is the double length modified prime code, which has been utilized for enhancing communication network security and network capacity. Most importantly, the performance of the network is evaluated versus the number of users, taking into consideration the amount of noise resulting from the multiple access interference, shot noise, and thermal noise. The error vector magnitude has also been considered for performance analysis and results. Significantly, the obtained results show the possibility of accommodating 110 users at an error rate of no more than 10 ^{− 9} and a data rate per user of 50 Gbps.