Zhuo Cheng

Acoustic tomography utilizes sensor arrays to collect sound wave signals, enabling non-contact measurement of physical parameters within an area of interest. Compared to optical technologies, acoustic tomography offers the advantages of low cost, low maintenance, and easy installation. Current research in acoustic tomography mainly focuses on reconstruction algorithms for temperature fields, while monitoring the composition and concentration of gases is significant for ensuring safety and improving efficiency, such as in scenarios like boiler furnaces and aviation engine nozzles. In excitable gases, the speed of sound exhibits an S-shaped curve that changes with frequency, a characteristic that could be potentially useful for acoustic tomography. Therefore, this study primarily discusses the quantitative calculation of gas concentration and temperature based on the dispersion of the speed of sound. By employing graphic processing and pattern matching methods, a coupled relationship of the dispersion of the speed of sound with gas concentration and temperature is established. The projection intersection method is used to calculate the concentration and temperature of binary and ternary gas mixtures. Combined with the inversion method, a joint reconstruction method for gas concentration fields and temperature fields based on the dispersion of the speed of sound is developed. The feasibility of the proposed simultaneous reconstruction method for temperature and concentration fields is validated using numerical simulations. Additionally, an acoustic tomography experimental system was set up to conduct reconstruction experiments for binary gas concentration fields and temperature fields, confirming the effectiveness of the proposed method.

The wavelength demultiplexer (deWMUX) is an indispensable component for the wavelength diversity system. In this paper, we propose a subwavelength-grating-assisted 1 × 2 deWMUX based on the principle of multimode interference, which aims to output 1.55 and 2 µm wavelengths from two different channels. The simulation results show that the contrast of the designed deWMUX at both wavelengths is greater than 24 dB, the insertion loss is less than 0.5 dB, and the 1 dB bandwidth is wider than 100 nm. In addition, the manufacturing tolerances of the device are also studied.

Temporal cavity solitons (CSs) are pulses that can maintain their shape and circulate indefinitely in a resonant cavity under coherent driving. The approach for writing, erasing, and moving of CSs have significant ramifications for optical signal processing such as buffering. Previous work mainly focused on the manipulation of scalar CSs while conventional macroscopic fiber ring cavity usually supports two polarization states simultaneously. Exploring the CSs manipulation for both one is of great significance for today's polarization-multiplexed systems. In this article, the all-optical CSs manipulation associated with two orthogonal polarizations in a monochromatically driven Kerr resonator is investigated. Based on the vectorial mean-field Lugiato-Lefever equations, we theoretically demonstrate the independent writing, erasing, and moving of polarization-multiplexed CSs through intensity-modulation- or phase-modulation-induced perturbation. The results can be useful guidance for high-speed and high capacity information processing.

A single soliton propagating in a microresonator (MRR) is characterized by a smooth spectrum. However, the number of solitons that propagate in an MRR in the anomalous dispersion regime is usually stochastic and gives rise to a complex spectrum. In this paper, we introduce a new passive mechanism based on third-harmonic-induced nonlinear coupling for the formation of a single deterministic soliton in an MRR. We show that with appropriate fundamental and third harmonic mode coupling strength and a slight wave vector mismatch, deterministic single soliton generation can be realized by simply scanning the detuning of a continuous wave and a chirped pulse serving as a pump. Furthermore, the third harmonic generation (THG)-coupled MRR can be utilized as an efficient upconversion stage for absorption sensing. Our work provides a potential approach for on-chip generation of coherent optical Kerr combs and efficient THG conversion.

A polarization beam splitter (PBS) is one of the key components for manipulating different polarization states in the areas of optical interconnection and communication. In this paper, a PBS with two coupling regions using a subwavelength grating (SWG) waveguide as a bridge is proposed and investigated on a 340-nm silicon-on-insulator platform. The PBS is designed with a triple-waveguide directional coupler consisting of two identical silicon waveguides and an SWG waveguide sandwiched between them. The tailorable dispersion relation of the SWG waveguide offers a flexible design freedom. With the optimized grating period and duty ratio, the input TE mode will experience efficient coupling between the silicon waveguide and the SWG waveguide, while the TM mode can directly pass through without influence. The results show that with a device length of 6.5 μm, the extinction ratios and insertion losses of the two modes are higher than 27 dB and lower than 0.3 dB at a wavelength of 1550 nm, respectively.

In this paper, we propose a modified constellation reshaping method for peak-to-average power ratio (PAPR) reduction in polarization division multiplexing (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems based on the selective mapping (SLM) method. A modified quadrature amplitude modulation (M-QAM) constellation is generated that has the same minimum distance as that of the conventional QAM (C-QAM) constellation. The M-SLM method is denoted as the M-QAM constellations combining with the traditional SLM method. At the receiver side, the mean square errors between the constellations of the received data and each M-QAM rotated by different phase rotation factors are calculated. Then, the phase rotation factor with the minimum mean square error is selected to recover the original data. The advantage of the proposed method is that it does not need to send additional side information, while it possesses nearly the same PAPR reduction and bit error rate performance as the traditional SLM method.