Optics letters最新文献

Shear-shift self-calibration stitching interferometry for long X-ray flat mirrors cannot reliably recover the meridional power-x term (x²). Calibrating the reference-flat power term and then stitching amplifies any residual power error to an unacceptable level for extreme X-ray optics. We demonstrate a hybrid absolute metrology in which a full-field grazing-incidence absolute test directly measures the power-x term, while a two-dimensional self-calibration stitching procedure determines the remaining surface components at high spatial resolution. This hybrid strategy removes the power-term ambiguity in self-calibration stitching and prohibits the power-error amplification in traditional stitching for long flats. On a 300 × 60 mm mirror (288 × 40 mm clear aperture), the reconstructed absolute surface shows 0.75 nm PV and 0.07 nm RMS repeatability, and the central profile agrees with a slope profiler at the sub-nanometer level.

We demonstrate a high-performance linear polarizer based on layered α-MoO₃ that achieves simultaneous high extinction ratio (ER) and optical reflectivity via cavity-enhanced transparent birefringence. The layered α-MoO₃ shows transparent in-plane birefringence in the visible wavelength range due to its large bandgap above 3.0 eV, which enables the precise tuning of the ERs and optical reflectivity by simply tailoring the resonance conditions of the optical cavities to achieve narrowband polarization selectivity with both markedly high extinction ratios (ERs) and optical reflectivity. Using layered α-MoO₃ on a Si/SiO₂ substrate as an example, systematic analysis based on the scattering matrix method shows that a high-performance polarizer with an ER > 10 dB and an optical reflectivity > 0.5 can be obtained in the wavelength range of 400-490 nm. The central polarization wavelength can be tuned by varying the thickness of the α-MoO₃ layer. Experimental results validate the proposed design strategy, demonstrating the feasibility of constructing high-performance, miniaturized polarizers using transparent anisotropic van der Waals crystals. This approach shows strong potential for applications in on-chip photonic integration, polarization optics, and next-generation optical communication systems.

We propose a novel, to the best of our knowledge, approach for improving the performance of Rydberg atom sensors by utilizing the repetition frequency of pulsed lasers, which has been validated through experimental testing. Rydberg atoms excited by pulsed lasers are influenced significantly by the repetition frequency of the pulsed laser on the Rydberg state population. As the number of Rydberg atoms increases, the measurement sensitivity of the sensor to external fields also increases, directly enhancing the performance of the sensor. This paper investigates the response of the sensor to the same electric field when the repetition frequency of the pulsed laser is at the MHz level, with a focus on its gain effects on the broadcast communication frequency bands of 66 MHz and 88 MHz. This research substantiates the distinctive benefits of pulsed light for Rydberg atom excitation, thereby enhancing the efficacy of the detection of feeble signals and introducing a new approach for the development of more sensitive atomic sensors.

As the output power of laser diodes increases, the resulting thermal load leads to elevated chip temperatures and reduced electro-optical conversion efficiency. To address this challenge, we design a stepped-structure heat sink integrated with multi-channel water cooling in which 15 laser diode chips are arranged in a stepped configuration to achieve efficient thermal management. Experimental results show that the output power of a stepped heat-sink module increases with driving current, accompanied by a center-wavelength redshift of 3.82 nm. The module delivers 138.5 W with a peak electro-optical conversion efficiency of 65.07%, while the maximum device temperature is maintained at approximately 28.6°C under steady-state operation at 8 A. Furthermore, 4 such modules are spectrally beam-combined along the fast axis and coupled into a 200 μm/0.22 NA optical fiber, achieving 422.6 W continuous output power with a maximum efficiency of 59.43% at 6.91 A. These results demonstrate an effective thermal management solution for high-power laser wireless power transmission.

In integrated photonics, erbium-doped waveguide amplifiers can effectively amplify weak optical signals, making high-efficiency waveguide amplifiers particularly crucial for enhanced power compensation. To date, various material platforms have been employed to realize on-chip waveguide amplifiers. Erbium-doped glass, as a promising optical platform, offers the potential for fabricating high-efficiency waveguide amplifiers. Herein, we demonstrate a waveguide amplifier fabricated by femtosecond laser direct writing in an Er³⁺-Yb³⁺ co-doped phosphate glass. The device achieves a remarkably low propagation loss of 1.84 dB/cm at 1550 nm. An internal net gain of 10.31 dB was obtained at a pump power of 350 mW for a waveguide length of 0.6 cm. Notably, the amplifier exhibits broadband signal enhancement covering the C-band, from 1510 nm to 1570 nm. This work has significant implications for the further development of integrated photonic devices.

Photonic integrated circuits operating at short near-infrared wavelengths are gaining relevance in applications such as on-chip single-photon sources and two-photon microscopy. These systems significantly benefit from compact, low-loss, and polarization-insensitive components. In this work, we design and experimentally demonstrate a polarization-independent single-channel optical add-drop filter operating at a center wavelength of 926 nm. The device is based on a compact grating contra-directional coupler fabricated on a 400-nm-thick silicon nitride (SiN) platform using a standard CMOS-compatible process. Experimental results show a polarization-dependent loss of less than 0.85 dB over a 1.5 nm bandwidth and an extinction ratio greater than 15 dB for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. The proposed filter provides an efficient solution for short-wavelength near-infrared photonic integrated circuits and will enable advancements in on-chip quantum networks and lab-on-chip systems.

We propose and experimentally validate a simplified optoelectronic oscillator (OEO)-based angular velocity sensing scheme with time-division optical carrier switching. This scheme utilizes only a single OEO oscillation loop structure, where the wavelengths of two input lasers are matched to the two output ports of a delay-line interferometer, respectively. Consequently, when the magneto-optic switch toggles between the two wavelength carriers, the phase difference induced by the Sagnac effect generates opposite frequency shifts in the microwave signal generated by the OEO. Meanwhile, the identical OEO loop ensures common-mode suppression of environmental disturbances. Experimental results demonstrate that by performing beat-frequency detection on these oscillation signals, the zero-bias stability is improved by 74.2dB, reaching 1.36×10^-2 °/s. The measurement sensitivity reaches 99.11 kHz/(rad/s). This system configuration is significantly simplified, enhancing its practicality and zero-bias stability.

We report a high-power, ultrafast coherent beam combination system featuring two InnoSlab CPAs based on Yb: YAG crystals. 306 W average power and 1.53 mJ pulse energy are delivered at 200 kHz, with a power fluctuation of 0.52% RMS. The combined beam quality is optimized from M² = 1.24 × 1.41 to M² = 1.1 × 1.18, due to the filtering effect of spatial mode. The combined beam is compressed to 460 fs by a grating compressor with close to the diffraction-limited spatial beam quality. Both excellent spatiotemporal performance and long-time stability are achieved, representing a novel, to the best of our knowledge, kilowatt-class average power amplifier which will greatly benefit the applications.

In-situ microscopy provides critical insights into the dynamic responses of materials and devices under operational conditions. However, image distortions caused by environmental perturbations and sample inherent vibrations significantly obscure these observations. This paper proposes a self-referencing vibration compensation method that models vibrations as a superposition of multiple cosine components. By incorporating physical constraints based on the point cloud consistency at irregularly sampled points, the vibration parameters are accurately estimated, enabling the reconstruction of distortion-free images. Experimental results demonstrate that the proposed method successfully restores structural details at the single-pixel scale, indicating its potential to achieve sub-pixel accuracy in vibration compensation, and exhibits robust performance even when confronted with images of high structural complexity. This work offers a versatile and effective solution for enhancing measurement fidelity in in-situ confocal microscopy.

A method is presented for the fabrication of femtosecond laser written waveguides in glass to remove the need for polishing substrates after processing. It is shown that by amplitude masking the fabrication laser beam near the sample edge and increasing the pulse energy, it is possible to write waveguides that are not affected by edge aberrations and display mode profiles well matched to single mode fiber. Results are presented for different depths in fused silica and borosilicate glass substrates. The transmission from fiber to photonic circuit is significantly improved for situations where it is not possible to polish glass substrates after laser writing, creating new opportunities in photonic packaging.