Optics letters最新文献

Spontaneous Parametric Downconversion (SPDC) is key to generating broadband spectrally entangled photons for quantum optical spectroscopy. Here, we use a common-path birefringent interferometer to experimentally map the spatial-spectral distribution of SPDC in Type I and II β-barium borate crystals using hyperspectral k-space imaging. Under broadband pulsed pumping, we observe strong spatial variations in the spectra, with distinct features for each phase-matching type. Simulations based on biphoton amplitudes and phase-matching conditions qualitatively match our results. This spatial-spectral mapping enables control over biphoton entanglement entropy, paving the way for optimized quantum-light sources for material spectroscopy.

In this Letter, we have fabricated a diamond pillar array device from an in-situ grown nitrogen-vacancy (NV)-doped diamond epi-layer. The device can achieve an imaging function of current-induced magnetic fields thanks to the elaborately patterned circular truncated cones. Through a simple continuous-wave optically detected magnetic resonance scheme as a demo, a 7-fold improvement in fluorescence collection intensity, a 40% narrower line-width, and a 2-fold improvement in the contrast have been achieved on the device, leading to a considerable improvement on the magnetic sensitivity. With these improvements, the device can resolve a line current one order of magnitude smaller than the non-patterned NV layer on diamond, demonstrating artificially patterned NV ensembles being implemented to the magnetic field imaging of an external sample. It will promote wider adoption of 2D sensing/imaging using the NVs.

We report efficient generation of high-field multi-cycle terahertz (THz) radiation from optical rectification (OR) in axially cut β-barium borate (β-BBO) crystals driven by an 800 nm femtosecond laser. Both b-cut and c-cut crystals produce coherent THz waveforms featuring two narrowband components centered near 10 THz and 14 THz, with weaker sidebands extending up to 25 THz. At a pump power of 3.95 W, the b-cut crystal delivers 34 µW of THz power and a focused peak field of 355 kV/cm, while the thinner c-cut crystal achieves comparable output and a higher peak field of 390 kV/cm. The high-field strength, experimental simplicity, and high scalability potential make axially cut β-BBO a compact and robust solid-state source for driving strong-field dynamics and fundamental excitations in the 5-15 THz range.

Topological photonic crystals (TPhcs), enabling unprecedented capability in manipulating electromagnetic (EM) waves using the nontrivial edge state (ES) and corner state (CS), provide a flexible platform to develop integrated photonic devices, leading to unique applications in optical communications and information processing. However, current approaches for manipulating EM waves in TPhcs, i.e., a topological cavity-waveguide system, can only enable fixed functions, which inevitably degrade its practical applications. Here, we propose a magnetic-field controllable platform consisting of a magnetic field-tunable TCS cavity coupled with an ES waveguide to dynamically modulate the transmission behaviors of EM waves. First, a topological cavity-waveguide system mimicking tunable and topologically protected filter function is demonstrated. Furthermore, the tunable electromagnetically induced transparency-like (EIT-like) phenomenon can also be achieved based on the magnetic-field controllable platform. The robust approach for dynamically controlling EM waves in a topological cavity-waveguide system may open a window to design multi-functional devices and time-varying systems.

Optical spin Hall effect (OSHE) is a typical phenomenon of the coupling of spin and orbit degrees of freedom of photons during transmission in a medium, which has significant applications in novel spin photon devices and information transmission. However, the OSHE is weak in inorganic semiconductor microcavities and usually requires an external magnetic field for enhancement, which limits its practical applications. In this work, we demonstrate the OSHE of polariton condensation in organic crystal microcavities without external magnetic field. The significant separation of left- and right-handed (σ⁺/σ^-) circular polarization components of polariton condensate is observed in the two-dimensional (2D) momentum space and real space, which is the most notable feature of OSHE. Additionally, by adjusting the incident wavevector of the non-resonant excitation pump, the individual σ⁺ or σ^- circular polarization components of the polariton condensate can emerge in 2D momentum space and real space. The OSHE based on polariton condensation in organic crystal microcavities without external magnetic field opens up for polariton spintronics and topological photonics devices.

Compared with traditional grating-based spectrometers, a coherent optical spectrum analyzer (COSA) can provide much higher resolution by converting optical spectral signals into electrical beat signals via heterodyne detection. However, the heterodyning process produces two symmetric sideband peaks for each spectral component, i.e., the mirror effect, which fundamentally limits the resolution. To overcome this constraint, we introduce an instantaneous frequency masking algorithm to eliminate the mirror effect in this study. Experimental results demonstrate a spectral resolution of 2 MHz using the same hardware previously limited to 6 MHz. Furthermore, a compact silicon-photonic wavelength reference for sweep linearization is utilized in the system, achieving long-term wavelength accuracy of ±0.1 pm. The proposed method establishes a cost-effective new paradigm for surpassing the inherent resolution limits of COSA.

A method for direct phase difference reconstruction using single-shot dual-wavelength off-axis digital holography is presented. This approach enables direct imaging of samples with high steps without the need to reconstruct phase images at each individual wavelength. As the dual wavelengths in the reference and object arms pass through a common path in this configuration, single-wavelength arrangements can be applied. Due to the unique capability of the presented method, a sodium-vapor lamp source has been utilized to obtain two closely spaced wavelengths (λ₁=589 nm and λ₂=589.6 nm), with a synthetic wavelength of Λ=578.8 µm in the Michelson configuration. The proposed method is validated by measuring the height of an air wedge using two approaches based on the synthetic and average wavelengths. The capability of the proposed technique to image samples with high-step structures is further demonstrated by measuring four consecutive steps, each separated by a height interval of 30 µm, as well as a glass plate with a thickness of approximately 140 µm.

We present a theoretical framework for spatial phase coherence in femtosecond rotational coherent Raman scattering (fs-RCRS), demonstrating how phase-matching geometry couples temporal dynamics to the transverse structure of the detected signal. On this basis, we identify two configurations with significant practical implications. In one case, the geometry allows single-shot measurements of collisional dephasing and rotational energy transfer, as well as multi-species detection. In the other, the geometry provides a straightforward scheme for one-dimensional thermometry. Together, these results establish geometry-driven space-time coherence as a versatile tool for femtosecond rotational spectroscopy and diagnostics.

In this Letter, we present a centroid detection method based on a Multi-pixel Photon Counter (MPPC) array and an intensity spatial distribution modulator array. This method is adept at efficiently determining the two-dimensional centroid position, even when only a small number of photons are detected. We have integrated every single-point MPPC with an intensity spatial distribution modulator, which enhances its ability to discern positions. Only two units are required to detect the two-dimensional centroid position of the spot. Additionally, a third unit can be used to monitor the overall intensity flicker of the spot, which significantly enhances the stability and robustness of the detection. Under 500 root mean square (RMS) photons detected, the sensor consistently extracts the two-dimensional centroid with an impressive frame rate of 30 kHz and a root mean square error (RMSE) of 7.11 μm. These results demonstrate a promising approach that could significantly improve the detection of faint targets with high sensitivity while still maintaining a fast frame rate. Therefore, this method has the potential to enhance the detection capability of tilt aberrations, thereby providing the foundation of the adaptive optics system for the coming extremely large telescopes.

Direct modulation lasers (DMLs) are a low-cost technology for short-reach intensity modulation and direct detection (IM/DD) systems due to their small footprint and low power consumption. However, their performance is limited by nonlinear distortion arising from chirp-dispersion interaction. Neural network (NN) autoencoders (AE)-based geometric shaping (GS) offers a promising solution through end-to-end (E2E) constellation optimization. This approach relies on differentiable and accurate channel models, leading to the adoption of NN-based models that require large training datasets and retraining for different configurations. In this Letter, we propose a low-complexity model-driven framework that establishes a surrogate channel based on composite second-order (CSO) distortion theory, enabling AE-based geometric constellation optimization to suppress chirp-dispersion interaction. This approach combines physics-based interpretability with deep learning's adaptive capabilities. Experimental results demonstrate a 1-dB receiver sensitivity improvement for 64-QAM signals after 10-km standard single-mode fiber (SSMF) transmission, confirming the effectiveness of the proposed scheme in mitigating nonlinear distortions.