Optics letters最新文献

High-sensitivity frequency comb spectroscopy can be realized using optical cavities, which typically requires precise alignment between cavity modes and comb modes. Here, we introduce an off-axis cavity-enhanced dual-comb absorption spectroscopy approach that delivers high spectral resolution and sensitivity, while enabling robust and efficient coupling of dual-frequency combs to an optical cavity. This method eliminates the need for complex optoelectronic feedback control. Utilizing an off-axis injection scheme, we demonstrated effective comb-cavity coupling across various dual-comb parameters, successfully allowing dual-combs to be passively coupled into the optical cavity simultaneously. As a proof of concept, we measured Doppler-broadened transitions of acetylene (C₂H₂) using an electro-optic dual-comb system in the near-infrared. For a concentration of 800 ppm at 0.1 atm, we measured C₂H₂ absorbance over a 350 GHz bandwidth with a spectral resolution of 200 MHz, yielding an enhancement factor of 380 and a signal-to-noise ratio of 335. This method offers significant advantages for high-resolution and high-sensitivity dual-comb spectroscopy for potential field deployment.

In this study, we present experimental and numerical investigations of pulse compression based on high-order soliton dynamics in Ta₂O₅ waveguides. We measure the temporal coherence of supercontinuum generation in the waveguide and deduce the pulse duration using the coherence time-pulse width relation. With a dispersion-engineered waveguide, an input pulse of 140 fs is compressed to 34.26 fs at a coupled peak power of 1.31 kW. Further optimization of dispersion and waveguide design to reduce propagation losses is expected to enable even better compression performance.

All-inorganic CsPbBr₃ perovskites feature exceptional optoelectronic properties and distinct nonlinear optical characteristics, making them highly promising for advanced photonic applications. However, state-of-the-art two-photon absorption photodetectors typically rely on intricate heterojunction configurations, which pose substantial bottlenecks to their large-scale integration and practical deployment. This study employed the "tube-in-furnace" chemical vapor deposition (TIF-CVD) method to prepare centimeter-scale high-quality CsPbBr₃ single-crystal films and systematically investigated their optoelectronic properties. The films demonstrated low-threshold amplified spontaneous emission ~24.7 μJ/cm² under 266 nm one-photon excitation (OPE) and stable lasing emission under 1064 nm two-photon excitation (TPE). Two-photon fluorescence imaging showed higher spatial resolution and contrast than single-photon imaging. Photodetectors with a simple electrode structure achieved high responsivity ~0.82 A/W under OPE and ~9.78 μA/W under TPE. This work provides a high-quality material platform for multifunctional optoelectronic integration and an economically feasible foundation for large-scale applications.

We propose a semiconductor optical amplifier that uses multiple quantum-dot layers with different emission wavelengths to suppress temperature-induced gain variation under a fixed operating current and wavelength. Upon engineering the gain spectrum to offset temperature-driven spectral shifts, the device achieves stable amplification without requiring active temperature control or bias-current adjustment. Experimental measurements show that the gain variation remains within 0.8-0.9 dB over a wide temperature range from 10°C to 85°C. This passive stabilization capability enables reliable operation across harsh outdoor environments, making the device well-suited for LiDAR and outdoor optical communication systems.

A single-shot coherent Rayleigh scattering (CRS) technique capable of measurement times less than 10 ns is presented. The use of a mode-locked picosecond pump laser yields repeatable electrostrictive forcing compared to previous CRS experiments using unseeded nanosecond pump pulses, which are beset by shot-to-shot variations. Quantitative measurements are achieved by dispersing the CRS signal onto an EMCCD sensor using a virtually imaged phased array and comparing the experimental spectra to an existing kinetic model with a least-squares fitting routine. Measurements are demonstrated at ambient and low-pressure (2 Torr), low-temperature (100 K) conditions where the CRS measurement is within the collisionless regime. Single-shot statistics indicated precision and accuracy within 4% at ambient conditions and within 8% at low density and temperature conditions. This single-shot CRS technique is a powerful diagnostic tool with potential for multi-parameter measurements in complex flow environments, including high-speed aerodynamic ground test facilities.

InGaN-based long-wavelength micro-LEDs often exhibit a significant blue-shift in emission wavelength with increasing current density due to the pronounced quantum-confined Stark effect (QCSE), which limits their applicability in display technologies and visible light communication. In this study, we report the fabrication of InGaN amber micro-LEDs with a 40 μm pixel size, employing a thick InGaN film (bulk InGaN) as the active region instead of the conventional multiple quantum well (MQW) structure. The devices exhibit a minimal wavelength shift from 618  to 608 nm as the injection current increases from 5  to 5000 μA. This 10 nm shift over three orders of magnitude in current demonstrates excellent wavelength and color stability. These results highlight a promising approach to overcoming the challenge of spectral instability in long-wavelength micro-LEDs, enhancing their viability for high-performance display and communication applications.

Higher-frequency fringe projection inherently has higher 3D measurement accuracy due to its shorter equivalent wavelength, but it also requires encoding more fringe orders. Conventional Gray-code (GC) methods can encode these fringe orders but rely on more auxiliary encoding patterns, limiting 3D reconstruction efficiency. To overcome this, we propose for the first time, to the best of our knowledge, an order-shifting temporal phase unwrapping (OSTPU) based on uneven duty cycle GC. Within the system's measurement range, OSTPU encodes the relative order shifts caused by height variations at a high frequency of 76 or more, reducing the required codewords from 76 absolute orders to just 12 order-shift codewords encoded by only 3 additional patterns. Our OSTPU relaxes the one-to-one mapping between GC word and fringe order, allowing spatial repetition and reducing complexity. Experiments verify that OSTPU achieves high-fidelity reconstruction of complex color geometry with fewer fringes (from 7 to 3), improving projection efficiency by over 57%, providing an accurate, efficient, and robust solution for high-frequency 3D measurement.

We describe an approach to harmonic suppression in soft X-ray monochromators by engineering the reflection grating's diffraction pattern to approximate a sinusoidal amplitude. At synchrotron and free-electron laser sources, X-ray beamlines powered by insertion devices produce a spectrum containing harmonic photon energies that can couple unwanted light into experiments. Beamlines in the soft X-ray energy range (100 eV to 2 keV) commonly employ energy-filtering elements to suppress these harmonics. Available approaches tend to be inefficient, significantly reducing the transmitted power. We show that with pseudo-grayscale binary halftone patterns, gratings can approximate a sinusoidal amplitude and suppress higher diffraction orders. Prototype demonstrations of lithographically fabricated gratings were conducted on a soft X-ray beamline with photon energies of 110 eV and 330 eV. Relative to a square-wave amplitude grating, the third-harmonic intensity was reduced by a factor of 9.0 with a first-order efficiency reduction of 38%.

We present a compact optoelectronic microwave source achieving broadband coverage from 1 to 100 GHz with frequency-independent, ultralow phase noise. The system integrates thin‑film lithium niobate modulation with stimulated Brillouin scattering and common mode noise rejection in a high‑Q fiber resonator, enabling a 100 GHz carrier to reach the phase noise level of -111.4 dBc/Hz at 1 kHz and -130.6 dBc/Hz at 10 kHz offset. Then, a 10 GHz signal generated through electrical frequency division and injection locking of a dielectric oscillator is demonstrated, reaching phase noise levels of -84 dBc/Hz at 10 Hz, -124 dBc/Hz at 1 kHz, -138 dBc/Hz at 10 kHz, and -166.43 dBc/Hz at 10 MHz, limited by the noise floor of the synthesizer chip. This architecture overcomes the conventional trade-off between phase noise and carrier frequency, providing a promising solution for advanced communications, radar, and quantum measurements.

Hyperbolic phonon polaritons offer a unique and powerful platform for enhancing directional light-matter interactions at the nanoscale, benefiting from their long lifetimes and deep subwavelength confinement. In particular, the interaction between free electrons and flat-band-like iso-frequency curves (IFCs) gives rise to strongly enhanced electromagnetic radiation, providing a novel, to the best of our knowledge, route toward compact mid-infrared optical sources without the need for complex nanostructuring. Here, we develop a general theoretical framework to describe free-electron-induced flat-band resonances in a representative graphene/α-MoO₃ heterostructure. Specifically, sharp resonances with quality factors around 200 and tunable frequencies spanning a broad mid-infrared range are presented. Furthermore, we showcase their application in vibrational sensing, where strong coupling between the flat-band resonance and molecular vibrational modes is achieved. Our work thus establishes a compact and flexible strategy for tunable mid-infrared light generation and highlights its potential for in-plane sensing applications.