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.

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.

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.

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 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.

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.

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.

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.

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.

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 (Ef) 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.