The chirp z-Transform (CZT) is introduced to replace the traditional gradient descent (GD) in frequency offset estimation for digital coherent quadrature amplitude modulation reception. Different from GD, CZT is not sensitive to the changes of the parameters and is free of uncertain latency that GD suffers. The implementation of frequency offset estimator based on CZT is presented and numeric simulations demonstrate that CZT can reach the same accuracy as GD. The computation complexity of CZT is analyzed and is roughly equivalent to GD with three iterations.

In this paper, we propose a constant envelop minimum-shift keying orthogonal frequency division multiplexing (CE-MSK-OFDM) modulation scheme. This scheme can mitigate the inherent drawbacks of CE quadrature phase shift keying OFDM (CE-QPSK-OFDM) and MSK-OFDM. Advantages of the proposed CE-MSK-OFDM modulation scheme are theoretically investigated. A CE-MSK-OFDM coherent optical experimental system is presented. In our experiment, 2.5 Gb/s CE-MSK-OFDM signal and 2.5 Gb/s CE-QPSK-OFDM signal are transmitted over a 100 km standard single mode fiber (SSMF) without phase compensation to check its advantages in mitigating intercarrier interference (ICI). In addition, performance under large fiber launch power is also measured to check its advantages in counteracting fiber nonlinear impairments. The experimental results show that the proposed system performs well in decreasing ICI and peak-to-average power ratio (PAPR) as the theoretical analysis reveals.

In this paper, a high-precision arbitrary-mode converter is proposed for mode-division multiplexing optical fiber communication systems. As the kernel of this converter, a phase-only spatial light modulation based on simulated annealing algorithm is used as a spatial spectrum filter. The results demonstrate that our proposed mode converter is of high precision and is capable of converting different modes without any physical change.

A mode multiplexer/demultiplexer based on two mutually spliced tapered multi-core fiber is proposed in this paper. Mode multiplexing occurs in the tapered region, and it is less sensitive to wavelength and structure parameters. Simulation results show that mode multiplexer/demultiplexer for LP01 and LP11 mode exhibited a coupling efficiency greater than 90% over the wavelength bandwidth of 760 nm. Mode multiplexer/demultiplexer for LP01 and LP21 mode exhibited a coupling efficiency greater than 85% over the wavelength bandwidth of 320 nm.

Compact waveguide bends with functionalities of mode manipulation, including certain mode transmission, multimode transmission, and mode conversion, are highly desirable in photonic integrated circuits. In this paper, an inverse design scheme for reshaped waveguide bend is presented, in which mode manipulation is achieved without additional nanoscale structures. We adopt quasi-3D models in finite element method to simulate the optical field, Bernstein polynomials to describe the deformation of two Si/air boundaries, and a gradient-based algorithm to efficiently determine the optimal design from a strict circular arc with a radius of 3.5 µm. 3D FDTD simulations with SOI configuration are implemented to measure the performance of the proposed designs. Three designs for certain mode transmission (individual TE0, TE1 and TE2) are first demonstrated as a validation of the method. For multimode transmission, the simultaneous TE0, TE1 and TE2 mode transmission in the bend requires a multi-target optimization and the design is achieved after 26 iterations. The output mode purities are 0.996, 0.971 and 0.989 at the center wavelength of 1550 nm, respectively. Furthermore, designs for TE0-to-TE1, TE0-to-TE2 and TE1-to-TE2 mode conversions in 90° bends are realized within 30 iterations. The output mode purities reach 0.985, 0.981 and 0.965, respectively. The performances of all designs remain acceptable within an operational bandwidth of 60 nm.

Cognitive impairment is common but often overlooked in patients with inflammatory demyelinating diseases such as multiple sclerosis and neuromyelitis optica spectrum disorder. The conventional assessments may fail to detect subtle deficits and require substantial time and expertise. We collected neuropsychological scores and real-time handwriting data across nine drawing tasks and tasks from the Symbol Digit Modalities Test in 93 patients. Temporal, pressure, and kinematic features were extracted, and machine learning classifiers were trained using five-fold cross-validation with bootstrap confidence intervals. The response timing and pen pressure metrics correlated significantly with global cognitive scores (|r| = 0.30–0.37, p < 0.01). A support vector machine using eight selected features achieved an area under the receiver-operating characteristic curve (AUC) of 0.910, and a streamlined five-feature variant maintained an equivalent performance (AUC = 0.921) while reducing the assessment time by 35%. These results indicate that digital handwriting metrics can complement the standard screening by capturing fine motor and temporal characteristics overlooked in conventional testing. Validation in larger, disease-balanced, and longitudinal cohorts is needed to confirm their clinical utility.