Studying Rydberg microwave frequency comb (MFC) spectroscopy helps increase the working bandwidth of the Rydberg receiver. This Letter demonstrates off-resonant Rydberg MFC spectroscopy in a meta-waveguide-coupled Rydberg atomic system. An off-resonant MFC field couples with the Rydberg atoms through a meta-waveguide. The system can receive the microwave field in the working band from 0.5 GHz to 13.5 GHz, and the MFC spectroscopy covers a span of 36 MHz at three different arbitrarily-chosen frequencies of 2 GHz, 3 GHz, and 5.8 GHz. The MFC spectrum that covers a wide range of 125 MHz is also verified. This work is significant for tunable wide-band instant microwave signal detection in the Rydberg atomic system, which is useful in microwave frequency metrology, communication, and radar.

Accurate control of magnetic fields is crucial for cold-atom experiments, often necessitating custom-designed control systems due to limitations in commercially available power supplies. Here, we demonstrate precise and flexible control of a static magnetic field by employing a field-programmable gate array and a feedback loop. This setup enables us to maintain exceptionally stable current with a fractional stability of 1 ppm within 30 s. The error signal of the feedback loop exhibited a noise level of 10-5 A·Hz-1/2 for control bandwidths below 10 kHz. Utilizing this precise magnetic field control system, we investigate the second-order Zeeman shift in the context of cold-atom coherent population-trapping (CPT) clocks. Our analysis reveals the second-order Zeeman coefficient to be 574.21 Hz/G2, with an uncertainty of 1.36 Hz/G2. Consequently, the magnetic field stabilization system we developed allows us to achieve a second-order Zeeman shift below 10-14, surpassing the long-term stability of current cold-atom CPT clocks.

In this Letter, an autofocusing method in optical scanning holography (OSH) system is proposed. By introducing Lissajous scanning into multiple signal classification (MUSIC) method in time-reversal (TR) OSH, the axial locations of the targets can be retrieved with better resolution and the peak prominence increases from 0.21 to 0.34. The feasibility of this method is confirmed by simulation as well as experiment.

The hologram, which is formed by phases coupled through cascade devices for secret information sharing, still carries a cracking risk. We propose a liquid crystal planar doublet as the information carrier, and new holograms generated by the new coupled phases when the relative displacements of the different liquid crystal layers change. The designed geometrical phases are generated by an optimized iterative restoration algorithm, and each holographic image formed by these phases is readable. This scheme achieves an increase in the capacity of the stored secret information and provides more misdirection, which is expected to have potential value in optical steganography and storage.

We demonstrated an optical fiber frequency comb stabilized to an acetylene-filled photonic microcell. The short-term instability of the comb at 1 s gate time was 1.66 × 10-12 for a 4.2-h measurement in a laboratory environment with air conditioning. This is the best short-term stability reported for a compact fiber comb stabilized to an acetylene-filled photonic microcell at telecom wavelengths. It is particularly significant in the development of compact fiber combs with target instability of 10-13. Such a device has the potential to serve as an alternative to GPS in areas lacking signal coverage, including remote locations, regions with adverse weather conditions, and military intelligence areas.

In this work, we proposed and experimentally demonstrated a novel probabilistic shaping (PS) 64-ary quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) with low-density parity-check (LDPC)-coded modulation in a W-band radio-over-fiber (RoF) system using envelope detection. The proposed PS scheme has the advantages of no complex multiplication and division operations and low hardware implementation complexity. In our experiments, the two-stage bit weight distribution matching-based PS-64QAM OFDM signals with a rate of 28.13 Gb/s transmission over 4 m wireless + 45-km standard single-mode fiber transmission can be achieved. The system performance is investigated under one LDPC code rate (3/4) and two PS parameter values (k = 3 and 9). The experimental results show that the receiver power sensitivity and the system fiber nonlinear effect tolerance can be significantly improved compared with uniformly distributed OFDM signals.

In this Letter, we innovatively present general analytical expressions for arbitrary n-step phase-shifting Fourier single-pixel imaging (FSI). We also design experiments capable of implementing arbitrary n-step phase-shifting FSI and compare the experimental results, including the image quality, for 3- to 6-step phase-shifting cases without loss of generality. These results suggest that, compared to the 4-step method, these FSI approaches with a larger number of steps exhibit enhanced robustness against noise while ensuring no increase in data-acquisition time. These approaches provide us with more strategies to perform FSI for different steps, which could offer guidance in balancing the tradeoff between the image quality and the number of steps encountered in the application of FSI.

The optoelectronic performance of quantum cascade detectors (QCDs) is highly sensitive to the design of the energy level structure, leading to the inability of a single structure to achieve broad wavelength tuning. To address this issue, we propose and demonstrate a modular concept for very long wave infrared (VLWIR) QCDs based on a miniband diagonal transition scheme. The modular design makes the wavelength tuning only need to be adjusted for the absorption quantum well module rather than for the whole active region. Theoretical simulation shows that the wavelength tuning range is 39.6 meV (∼14–30 μm). To prove the feasibility of the scheme, three samples with different absorption well widths were fabricated and characterized. At 10 K, the response wavelengths of the three QCDs are 14, 16, and 18 μm, respectively, corresponding to responsivities and detectivities exceeding 2 mA/W and 1 × 1010 Jones.

In this study, an innovative technique is introduced to significantly enhance the sensitivity of electronic speckle pattern interferometry (ESPI) for the dynamic assessment of specular (mirrorlike) object deformations. By utilizing a common-path illumination strategy, wherein illumination and observation beams are precisely aligned, this method effectively doubles the optical path difference, leading to a twofold increase in measurement sensitivity. In addition, this method mitigates the effects of speckle noise on the measurement of minor deformations, expanding the applications of ESPI. Theoretical and experimental evaluations corroborate the efficacy of this approach.

The metabolic process of chiral drugs plays a significant role in clinics and in research on drugs. Here, we experimentally demonstrate by all-optical means that the chiral molecules can be quickly discriminated and monitored with the ultrahigh-order modes excited in a metal cladding optofluidic chip, achieving over 5 times sensitivity with a low-dosage sample. We show that the varying concentration of the chiral drugs can be monitored both in cell and animal experiments, presenting a significant difference between chiral enantiomers at the optimal function time and the effect of the reaction. To our knowledge, this approach provides a new way to achieve important chiral discrimination for the pharmacokinetics and the pharmacodynamics and may present opportunities in indicating the health status of humans.

The optical frequency comb has attracted considerable interest due to its diverse applications in optical atomic clocks, ultra-low-noise microwave generation, dual-comb spectroscopy, and optical communications. The merits of large frequency spacing, high integration, and low power consumption have shown that microresonator-based Kerr optical frequency combs will become mainstream in the future. Two methods of pump frequency tuning and self-injection locking were used to obtain Kerr combs in the same silicon nitride microresonators with free spectral ranges of 50 GHz and 100 GHz. Single-soliton combs are realized with both methods. Simplicity, pump power, spectrum bandwidth, conversion efficiency, and linewidth are compared and analyzed. Our results show that the advantages of pump frequency tuning are a wider spectrum and higher soliton power while the advantages of self-injection locking are simplicity, compactness, low cost, significant linewidth narrowing, and high conversion efficiency.

An 8-channel hybrid-integrated chip for 200 Gb/s (8 × 25 Gb/s) signal transmission has been demonstrated. The channels are all within the O-band, and with a spacing of 800 GHz. The core of this chip is a monolithic integrated multi-wavelength laser array of 8 directly-modulated distributed feedback (DFB) lasers. By using the reconstruction equivalent chirp technique, multi-wavelength integration and asymmetric phase shift structures are achieved in the laser array. The output laser beams of the array are combined by a planar light-wave circuit, which is hybrid-integrated with the laser array by photonic wire bonding. Experiment results of this transmitter chip show good single-mode working of each unit laser, with a side-mode suppression ratio above 50 dB, and the modulation bandwidth is above 20 GHz. Clear eye diagrams are obtained in the lasers for 25 Gb/s non-return-to-zero modulation, which implies a total 200 Gb/s transmission rate for the whole chip.

The evolution dynamics of mode locking for a solid-state femtosecond Yb:KGW laser is demonstrated and detected with time-stretch dispersive Fourier transform (DFT) technique for the first time, to the best of our knowledge. The Yb:KGW laser is constructed first with a classical X-shaped cavity, and SESAM-assisted Kerr lens mode locking is obtained. Then, a DFT device is built to record the buildup and extinction dynamics of the mode-locked laser. The results suggest that the time of extinction is slightly shorter than the buildup time and both of them experience complex transitions. The results indicate that DFT could also be suitable to detect the transient buildup and extinction process in solid-state lasers, which would help investigate both the evolution of mode locking and characteristics determination for solid-state lasers.

We demonstrated an actively acousto-optic Q-switched pulsed laser based on Pr:YLF at 604 nm. A 604 nm continuous-wave (CW) laser with a maximum output power of 3.84 W was achieved for the first time, to the best of our knowledge. The Q-switched laser with a maximum average output power of 0.384 W, a narrowest pulse duration of 44.5 ns, a maximum single pulse energy of ∼64.1 µJ, and a maximum peak power of ∼1.44 kW was obtained at a repetition rate of 6 kHz. As far as we know, this was the first report of such a narrow pulse duration, high-power, and high-energy Q-switched pulsed laser at 604 nm. The beam quality factors Mx2 and My2 were measured to be 2.87 and 2.40, respectively. The results show that acousto-optic Q-switching is a promising method for obtaining pulsed lasers.

Lasers from 1I6 to 3F4 transitions were first demonstrated in a Pr3+:YLF crystal by inserting a birefringent filter. Output powers up to 2.44 W, 2.10 W, 2.01 W, and 2.42 W were obtained at 691.7 nm, 701.4 nm, 705.0 nm, and 708.7 nm, respectively. Their slope efficiencies were 19.8%, 16.5%, 15.8%, and 19.4%, respectively. The Mx2 and My2 factors were measured to be 2.29 and 2.03 at 691.7 nm, 2.23 and 1.86 at 701.4 nm, 2.31 and 2.08 at 705.0 nm, and 2.41 and 2.04 at 708.7 nm, with corresponding power fluctuations of less than 5.3%, 5.6%, 5.8%, and 2.9%.

We report on a compact, high-efficiency mid-infrared continuous-wave (CW) Fe:ZnSe laser pumped by a 2.9 µm fiber laser under liquid nitrogen cooling. A maximum output power of 5.5 W and a slope efficiency of up to 66.3% with respect to the launched pump power were obtained. The overall optical-to-optical (OTO) conversion efficiency, calculated from the output of the 2.9 µm fiber laser to the 4 µm laser, was as high as ∼54.5%. The OTO efficiency and the slope efficiency are, to the best of our knowledge, the highest ever reported in Fe:ZnSe lasers. A rate-equation-based numerical model of CW operation was established, and the simulation agreed well with the experiment, identifying the routes used in the experiment for such high efficiency.

Pulse duration is considered as one of the most important characteristics of high-power femtosecond lasers. However, pulses output from the laser system are susceptible to ambient changes and manifest the instability of pulse durations in an open environment. In this paper, incorporating the algorithmic framework of the improved stochastic hill-climbing search and incremental proportional-integral controller, temperature-induced fluctuations of pulse duration can be effectively compensated by an automatic feedback control in an all-fiber chirped-pulse amplification system. In the experiment, sub-hundred femtosecond fluctuation of pulse duration is introduced to verify the performance robustness of the proposed pulse-duration feedback control (PDFC). The stability of pulse duration is obviously higher than the case without the feedback control, and the peak-to-peak fluctuation of pulse duration is reduced to 6.5%. Furthermore, the robust switching between different pulse durations proves the versatility of the PDFC. We expect that the proposed feedback control method could provide a novel insight into high-power femtosecond lasers widely applied in fundamental researches and industrial fields.

The existing single-crystal slicing techniques result in significant material wastage and elevate the production cost of premium-quality thin slices of crystals. Here we report (for the first time, to our knowledge) an approach for vertical slicing of large-size single-crystal gain materials by ultrafast laser. By employing aberration correction techniques, the optimization of the optical field distribution within the high-refractive-index crystal enables the achievement of a continuous laser-modified layer with a thickness of less than 10 µm, oriented perpendicular to the direction of the laser direction. The compressed focal spot facilitates crack initiation, enabling propagation under external forces, ultimately achieving the successful slicing of a Φ12 mm crystal. The surface roughness of the sliced Yb:YAG is less than 2.5 µm. The results illustrate the potential of low-loss slicing strategy for single-crystal fabrication and pave the way for the future development of thin disk lasers.

A 4 × 112 Gb/s hybrid-integrated optical receiver is demonstrated based on the silicon-photonic vertical p-i-n photodetector and silicon–germanium transimpedance amplifier. We propose a photonic-electronic co-design technique to optimize both the device-level and system-level performance, based on the end-to-end equivalent circuit model of the receiver. Continuous-time linear equalization and shunt peaking are employed to enhance the frequency response. Experimental results reveal that the optical-to-electrical 3-dB bandwidth of the receiver is 48 GHz. Clear open NRZ eye diagrams at 56 Gb/s and PAM-4 eye diagrams at 112 Gb/s are achieved without an equalizer in the oscilloscope. The measured bit error rates for 56 Gb/s in NRZ and 112 Gb/s in PAM-4 reach 1 × 10-12 and 2.4 × 10-4 (KP4-FEC: forward error correction) thresholds under -4 dBm input power, respectively. Furthermore, the proposed receiver boasts a power consumption of approximately 2.2 pJ/bit, indicating an energy efficient solution for data center traffic growth.

Recently, the Fano resonance has played an increasingly important role in improving the color performance of structural colors. In this study, we further elucidate the asymmetric spectral shape generated by Fano resonance from a phase perspective and explore four distinct continuum state structures. By integrating the proposed cavity-like structure with a metal–dielectric–metal discrete state, multilayered thin-film structural colors with minimal background reflection, as low as 8%, were successfully achieved. The reflection peak of this structure exhibits a bandwidth of approximately 50 nm and reaches up to 80%, indicating heightened saturation and color brightness. Moreover, by adjusting the thickness, we effortlessly obtained a broader color gamut compared to Adobe RGB (45.2%), covering 56.7% of the CIE color space. Even adjusting a single layer can achieve a color gamut of 47.1%. In experiments, by deliberately choosing low oxygen-dependent materials, excellent RGB colors with high brightness and in high consistency with simulation results were successfully achieved. Therefore, the scheme’s simple process for structural color creation, along with its excellent color performance and the ability to effectively replicate simulation characteristics makes it highly valuable in fields like anticounterfeiting, decoration, display devices, and solar cell panels.

Determining the trap density in the absorbing layer thin film of perovskite solar cells is a critically important task, as it directly influences the efficiency of the devices. Here, we proposed time-resolved photoluminescence (TRPL) as a nondestructive method to assess trap density. A model was constructed to investigate carrier recombination and transition in perovskite materials. The model was utilized for numerical calculations and successfully fitted TRPL signals of perovskite materials. Furthermore, a genetic algorithm was employed to optimize the parameters. Finally, statistical methods were applied to obtain the parameters associated with the trap states of the material. This approach facilitates the successful determination of trap densities for different samples with clear differentiation.