Optics letters最新文献

In large-area quantum networks based on optical fibers, photons are the fundamental carriers of information as so-called flying qubits. They may also serve as the interconnect between different components of a hybrid architecture, which might comprise atomic and solid-state platforms operating at visible or near-infrared wavelengths, as well as optical links in the telecom band. Quantum frequency conversion is the pathway to change the color of a single photon while preserving its quantum state. Currently, nonlinear crystals are utilized for this process. However, their performance is limited by their acceptance bandwidth, tunability, polarization sensitivity, and undesired background emission. A promising alternative is based on stimulated Raman scattering (SRS) in gases. Here, we demonstrate polarization-preserving frequency conversion in a hydrogen-filled antiresonant hollow-core fiber. This approach holds promises for seamless integration into optical fiber networks and interfaces to single emitters. Disparate from related experiments that employ a pulsed pump field, we here take advantage of two coherent continuous-wave pump fields.

The same scalar illumination used in a linear optical system with a single lens is experimentally shown to carry information about two objects placed at different positions along the axis with arbitrary lateral overlap. The images of both objects can be obtained either sequentially by adjusting the placement of the camera or concurrently, with the help of a beam splitter. The effect utilizes the average intensity and the spatial coherence state of a partially coherent beam as two degrees of freedom available in a scalar optical channel.

Single-pixel imaging (SPI) stands out in computational imaging for its simplicity and adaptability, yet its performance has been hampered by artifacts from translational motion. Existing solutions heavily rely on accurate motion modeling, requiring additional hardware and computational costs. In this Letter, we propose translational motion-agnostic SPI (TMA-SPI), a novel, to the best of our knowledge, single-object SPI framework agnostic to arbitrary translational motion. Our dual-domain optimization method leverages the translation invariance property of the amplitude spectrum in the Fourier domain, combined with the spatially finite and nonnegative constraints in the image domain, to produce a clear image of the moving object without any motion estimation or compensation. Through both simulation and the deployment of a real imaging prototype, we demonstrate its superior performance over the conventional SPI method. Our framework is expected to extend the applicability of SPI, offering significant improvements for dynamic sensing applications.

Terahertz (THz) radar offers significant advantages, notably high-frequency and strong penetration ability, making it highly promising for applications in aerospace, non-destructive testing, and other imaging scenarios. However, existing THz radar imaging technologies face challenges in large-scale target detection due to the complexity and high costs of the system, which limits their development and commercial application. Here we establish a radar system based on a one-dimensional photonic crystal structure-enhanced 4-inch spintronic strong-field THz emitter and obtain THz radar signals and imaging with a signal-to-noise ratio of ∼58 dB and a bandwidth exceeding 5 THz. Through the precise design of the emitter structure, we ensure not only the generation of a high-quality uniform plane wave when the THz beam diameter reaches 4 in. but also the applicability of the THz field strength for radar imaging measurements within a 4-in. field of view area. The approach provides a promising platform for ultra-broadband, high-resolution, near-monostatic THz radar imaging, with broad potential applications in aerospace engineering, stealth testing, THz 3D reconstruction, and THz tomography.

Mode-locked lasers are of interest for applications such as biological imaging, nonlinear frequency conversion, and single-photon generation. In the infrared, chip-integrated mode-locked lasers have been demonstrated through integration of laser diodes with low-loss photonic circuits. However, additional challenges, such as a higher propagation loss and smaller alignment tolerances, have prevented the realization of such lasers in the visible range. Here, we demonstrate the first, to the best of our knowledge, chip-integrated mode-locked diode laser in the visible using an integrated photonic circuit for cavity extension. Based on a gallium arsenide gain chip and a low-loss silicon nitride feedback circuit, the laser is passively mode-locked using a saturable absorber (SA) implemented by focused ion beam (FIB) milling. At a center wavelength of 642 nm, the laser shows an average output power of 3.4 mW, with a spectral bandwidth of 1.5 nm at a repetition rate of 7.84 GHz.

A chip-scaled single-soliton microcomb source promises wide applications in various fields. We demonstrate the deterministic single-soliton generation from both pump forward and backward tunings via sideband thermal compensation. The total soliton existing range (SER) is effectively expanded due to the thermal-lock effect and remains nearly the same regardless of the soliton states. Besides, we prove the degeneration of the forward-tuning SER, accompanied by the decrease in the soliton number. This scheme remains robust against a significant pump wavelength chirp, sustaining a free-running single soliton for over 9 h with line power fluctuations below 0.6 dB.

In this Letter, a complex-valued double-sideband 16QAM (CV-DSB-16QAM) signaling scheme is proposed and experimentally demonstrated in a 100-Gb/s intensity modulation/direct detection (IM/DD) interconnection system. Unlike the conventional real-valued double-sideband (DSB) quadrature amplitude modulation (QAM) of relatively lower spectral efficiency (SE) and single-sideband (SSB) QAM relying on sharp-edged optical filtering, the CV-DSB-16QAM signal is generated by combining two independent sideband modulated QPSK signals using a single intensity modulator with an optical filtering-free profile, which also saves one photodiode and one analog-to-digital-converter compared with the twin-SSB scheme. Compared to typical pulse amplitude modulation or SSB schemes, the proposed approach offers a compelling alternative for complex-valued DD systems' evolution, particularly in scenarios with high SE demands and controllable chromatic dispersion. The experimental demonstration evaluates a 25-GBaud CV-DSB-16QAM signal over a 2-km standard single-mode fiber (SSMF), achieving a net bit rate of 100 Gb/s and occupying only a 25.1-GHz electrical bandwidth with a 4% guard band.

Grating-assisted, contra-directional couplers (GA-CDCs), owing to their four-port operations, can offer several important advantages over traditional, single waveguide-based Bragg gratings. However, how to flexibly design the spectral responses of GA-CDCs has been much less studied. We report the spectral tailoring methodology of GA-CDCs to achieve arbitrary, physically realizable, complex spectral responses. Silicon GA-CDCs with various customized responses are demonstrated using the methodology, including sidelobe-suppressed filters, single- and multi-channel flattop filters, sawtooth- and triangle-shaped filters, and three-channel photonic Hilbert transformers.

The photon-energy conversion covering the full spectral wave band is crucial for detecting and storing information. Schottky junctions in nanoscale such as TiO₂:Ag enable multicolor photochromism and information storage in the visible region. However, the photoelectrons from the UV-excited semiconductor cause the loss of information. It has become a big challenge to the data memory of Schottky junctions extending from the visible to UV band. Herein, we construct a stacked heterojunction structure of TaO_x/TiO₂:Ag as a full wave band holographic memory. Coherent green laser beams are utilized to inscribe a Fourier transform hologram, followed by burning a computer-generated hologram in a focused UV laser spot array. The holographic array based on UV photothermal effect presents high refractive index modulation in the stacked layered oxide film. Meanwhile, the excellent UV protection of TaO_x/TiO₂ heterojunctions makes it possible to fully preserve previously written Fourier transform holographic data. Information cross talk between the two kinds of holograms is almost inhibited. This work provides a bright way for high-density data storage, wideband optical detection, and advanced manufacturing of micro-optical components.

We predict the existence of a novel type of temporal localized structure in injected Kerr-Gires-Tournois interferometers (KGTI). These bright pulses exist in the normal dispersion regime, yet they do not correspond to the usual scenario of domain wall locking that induces complex shape multistability, weak stability, and a reduced domain of existence. The new states are observed beyond the mean-field limit and out of the bistable region. Their shape is uniquely defined, with peak intensities beyond that of the upper steady state, and they are stable over a broad range of the injection field, highlighting their potential for optical frequency comb (OFC) generation.