Optics express最新文献

Mode-division multiplexing has emerged as a powerful strategy for enhancing the capacity of photonic integrated circuits, where compact and versatile mode manipulation devices in bus waveguides play a central role. In this work, we present the inverse design of two ultra-compact mode cyclic converters with size of only 7 µm in length, enabled by the integration of the finite-element method, Bernstein polynomial-based deformation parameterization, and the gradient-based method of moving asymptotes. The first device, a dual-mode cyclic converter (DMCC) with efficient TE0/TE1 mutual conversion, is obtained within just 20 optimization iterations. Three-dimensional finite-difference time-domain simulations on a silicon-on-insulator platform confirm high conversion efficiencies of -0.053 dB (TE0-to-TE1) and -0.043 dB (TE1-to-TE0), with mode purities reaching 99.3%. Extending this approach, a triple-mode cyclic converter (TMCC) for TE0/TE1/TE2 cyclic conversion is realized through a two-stage optimization strategy, converging at around 100 iterations. The TMCC exhibits conversion efficiencies of -0.67 dB (TE0-to-TE1), -1.1 dB (TE1-to-TE2), and -0.67 dB (TE2-to-TE0), accompanied by high mode purities of 96.4%, 93.6%, and 98.3%, respectively. Robustness analyses further demonstrate tolerance to fabrication deviations of ±10 nm. These results highlight the potential of inverse design in deformed multimode silicon waveguides for realizing efficient mode cyclic conversion, thereby advancing mode-division multiplexing in photonic integrated circuits.

In this study, we demonstrate a high-power and widely-tunable Tm-doped all-fiber master oscillator power amplifier (MOPA) in a core- and tandem-pumping configuration. The ground-state bleaching effect of Tm-doped fiber tandem-pumped at 1943nm was investigated. The master oscillator is a Tm-doped fiber ring laser incorporating a tunable bandpass filter to realize a narrow linewidth and wavelength-tunable operation. The MOPA delivered 103 W of output power at 1980nm, with >83 W maintained over a 60 nm tuning range from 1960 to 2020nm, achieving a high slope efficiency of ∼ 80%. The laser exhibited a spectral linewidth of ∼0.15 nm and a high optical signal-to-noise ratio (OSNR) of >42 dB, attributed to the effective suppression of amplified spontaneous emission (ASE) by tandem pumping. The power stability (RMS) at a scale of ∼10 min was measured to be approximately 0.75%. A diffraction-limited beam quality factor M² of ∼1.18 (horizontal) and 1.16 (vertical) was measured at the maximum laser output. The laser power is pump-limited without the onset of parasitic oscillation or thermal-induced transverse mode instability (TMI) effect, even at the maximum power level. This represents the first demonstration, to the best of our knowledge, of an all-fiber-integrated, wavelength-tunable Tm-doped fiber laser reaching the 100-watt level under efficient tandem pumping.

In this work, a systematic analytical procedure of Tm-doped germanate glass optimization and corresponding fiber amplifier simulation is established. First, a method for adjusting the Tm-Tm distance in the glass matrix is proposed and validated by molecular dynamics combined with microscopic energy transfer parameters. The results show that the shortest Tm-Tm distance increases from 3.8 Å to 8.5 Å, leading to a weakening of the cross-relaxation (CR) process and an enhancement of the S-band emission of Tm. Secondly, a swarm intelligence algorithm that can derive both the forward and reverse macroscopic CR rates synchronously is established for the first time, to the best of our knowledge. The calculated results show that the forward and reverse macroscopic CR rates are regulated from 0.36(± 0.01) × 10^-22 m³/s and 5.60(± 0.01) × 10^-22 m³/s to 0.30(± 0.01) × 10^-22 m³/s and 7.92(± 0.01) × 10^-22 m³/s, respectively, while the reverse-forward ratio increases from 15.58 ± 0.01 to 26.36 ± 0.01. Finally, the numerical model of the Tm-doped fiber amplifier on the basis of the presented two kinds of germanate glasses is studied. The numerical results indicate that the ASE power in the 1800-nm band can be reduced by enlarging the reverse-forward CR rate ratio, while the S-band amplification effect is improved.

The multi-height lensless imaging technique enables high-throughput imaging with a centimeter-scale field of view via full-frame sensor acquisition. However, minute errors in axial and radial displacements can cause sub-diffraction pattern shifts from their preset positions, compelling conventional approaches to rely on precision positioning devices and complex optical alignment procedures. To reduce system cost and enable rapid acquisition, this work is developed a computational lensless imaging framework integrating adaptive optical calibration and quantitative phase retrieval. The framework achieves automatic alignment through iterative optimization of sub-diffraction pattern spatial coordinates, while simultaneously minimizing the Structural Similarity Index between measured and computed intensities using a partitioned interval strategy coupled with stochastic gradient descent, thereby enabling adaptive calibration of axial displacement error. Simulation and experimental results indicate that, compared to conventional approaches, the proposed method achieves robust reconstruction across various specimens under coupled multi-parameter deviations in the system. This technique attains sub-pixel radial localization accuracy and keeps axial distance correction errors under 1.05%, with the added computational cost limited to only about 1.4× that of conventional methods. Even under extreme conditions relying solely on mechanical scales for rough positioning, high-quality complex-amplitude imaging can still be achieved. This demonstrates that the proposed approach can significantly simplifying system design, reducing hardware costs, and completely eliminating the reliance on demanding physical alignment processes and high-precision displacement devices.

Laser detection and point cloud processing are key elements of measurement, autonomous driving, and defense technology, particularly for high-precision target recognition and environmental sensing. To meet strict requirements for speed and accuracy in target recognition for laser imaging fuzes, this paper presents a new attempted approach named the SC-PointLSTM framework, which is an innovative, rapid target recognition algorithm designed for linear array push-broom laser fuzes. SC-PointLSTM integrates an enhanced PointNet for efficient sparse point cloud processing with a double-layer long short-term memory (LSTM) for temporal feature fusion, addressing the computational challenges inherent to real-time dynamic environments. This approach enables parallel processing to generate linear 3D point clouds from linear push-broom sensors and effectively fuses previously acquired timestamp sequences, resulting in real-time, accurate target recognition at the end of the push-broom scanning process. The robustness and efficiency of the SC-PointLSTM framework were evaluated on both simulated datasets and real-world targets. The results demonstrated competitive results, achieving an F_score exceeding 0.8, with an average recognition time of approximately 32 ms. The SC-PointLSTM framework provides a robust and scalable solution for high-speed target recognition in dynamic environments and real-time laser detection.

We report a quantitative framework for predicting and optimizing the self-starting performance of ultrafast all-polarization-maintaining (PM) nonlinear amplifying loop mirror (NALM) fiber oscillators, where reliable startup remains a key challenge. By introducing a nonlinear phase-asymmetry factor into an analytically defined figure of merit (FoM), the coupled effects of power splitting ratio, nonreciprocal phase bias, and structural asymmetry on small-signal transmission are unified into a single predictive model. The FoM accurately identifies the optimal startup condition and its evolution with increased loop asymmetry. To experimentally validate the theory, short segments of PM highly nonlinear fiber (HNLF) were inserted asymmetrically inside the loop to controllably enhance the nonlinear phase imbalance. As the HNLF length increases from 0 to 0.97 m, the pump threshold is reduced from 920 mW to 273 mW, in excellent agreement with the FoM-predicted trend. Numerical simulations further reproduce the measured spectral and temporal characteristics and enable quantitative extraction of the asymmetry factor, completing the model validation. This FoM-based approach thus provides the first experimentally verified quantitative guideline for designing robust, low-threshold, and environmentally stable PM-NALM fiber oscillators.

Quantum random number generators (QRNGs) based on semiconductor laser phase noise are an inexpensive and efficient resource for true random numbers. Commercially available technology allows for designing QRNG setups tailored to specific use cases. However, it is important to constantly monitor whether the QRNG is performing according to the desired security standards in terms of independence and uniform distribution of the generated numbers. This is especially important in cryptographic applications. This paper presents a test scheme that helps to assess the acceptable operating conditions of a semiconductor laser for QRNG operation, using commonly accessible methods. This can be used for system monitoring, but crucially also to help the user choose the laser diode that better suits their needs. Two specific quality measurements, ensuring proper operation of the device, are explained and discussed. Setup-specific approaches for setting an acceptance boundary for these measures are presented, and exemplary measurement data showing their effectiveness are given. By following the comprehensible procedure described here, a QRNG qualification environment tailored to specific security requirements can be reproduced.

Advances in silicon (Si) photonics at submicrometer wavelengths are unlocking new opportunities that may enable the realization of miniaturized, scalable optical systems for biophotonics, quantum information, imaging, spectroscopy, and displays. Addressing this array of applications with a single integrated photonics technology requires the development of high-performance active components compatible with both visible and near-infrared light. Here, we report waveguide-coupled photodetectors monolithically integrated in a foundry-fabricated, short-wavelength, Si photonics platform. We demonstrate two detector variants that collectively cover a continuous wavelength span of λ = 400 - 955 nm. The devices exhibited external quantum efficiencies exceeding 60% and 12% over 400 - 748 nm and 749 - 955 nm wavelength ranges, respectively. Measured dark currents were < 2 pA at a 2-V reverse bias. High-speed measurements at λ = 785 nm demonstrated optoelectronic bandwidths up to 18 GHz. Avalanche operation was characterized, yielding a gain-bandwidth product of 374 GHz at λ = 785 nm.

With the increasing demands for transmission performance and security in optical access networks, this paper proposes a high-security floating probabilistic encryption method based on chain-embedded masking. The constellation points of this chained structure are distributed in a chain-like pattern across concentric circles. A core hexagon is formed by the points on the first layer around the origin. The second layer is then expanded into a star-shaped structure using external triangles, while the remaining points are fixed in the outermost ring. It effectively reduces both the average transmission power and the peak power while maintaining a minimum Euclidean distance of 1, resulting in a constellation figure of merit (CFM) value of 0.444. Based on this structure, a floating chain-embedded encryption scheme is further proposed. A Lorenz chaotic model is employed to generate sequences that dynamically perturb the positions of the outer-ring constellation points within the chain-like structure according to a "0-hold, 1-shift one step, 2-shift two steps" rule. Experimental validation was performed on a seven-core fiber transmission system. The results demonstrate that at a bit error rate of 3.8 × 10^-3, the proposed Hierarchical Triangular-Distorted Hexagonal (HTDH) 16 Quadrature Amplitude Modulation (16QAM) constellation achieves a 0.48 dB improvement in receiver sensitivity compared with conventional 16QAM. The encrypted signals exhibit an additional 0.33 dB sensitivity enhancement over unencrypted signals. This indicates that the encryption mechanism not only enhances security but also synergizes with the energy concentration characteristics of the constellation, ultimately achieving co-optimization of transmission security and system sensitivity.

Without imaging, single-pixel sensing aims to utilize a single-element detector to directly extract features of interest from a target. We demonstrate an optoelectronic framework for image-free tracking of a few moving targets. It integrates a Fourier filter for background suppression and a nonlinear power-law model that uniquely encodes spatial positions into optical responses. The all-optical encoder is designed based on a specific target template, which allows it to filter out the background and other types of irrelevant targets. The responses are decoded into coordinates via least-squares inversion with cross-target optimization. Using only 12 patterns, the system tracks two and three points with average errors of 1.00 and 1.77 macro-pixels experimentally at 0.67 ms temporal resolution. This work advances single-pixel tracking beyond single-target scenarios toward simultaneous localization of multiple targets with background suppression.