Optics letters最新文献

Thin-film lithium niobate (TFLN) based integrated photonic devices have been intensively investigated due to their promising properties, enabling various on-chip applications. Grating couplers (GCs) are wildly used for their flexibility and high alignment tolerance for fiber-to-chip coupling. However, achieving high coupling efficiency (CE) in TFLN GCs often requires the use of reflectors, hybrid materials, or extremely narrow linewidths of the grating arrays, which significantly increases the fabrication difficulty. Therefore, there is a demand for high-CE GCs on TFLN with simple structure and easy fabrication processes. In this paper, combining process capabilities, we demonstrate a highly efficient apodized GC by linearly optimizing the period length and the fill factor on a 600-nm-thick TFLN platform. Without any reflector or hybrid material, we achieve a remarkable coupling loss of -2.97 dB at 1555 nm on the 600-nm-thick X-cut TFLN platform with only a single lithography and etching step. Our work sets a new benchmark for CE among GCs on the 600-nm-thick TFLN platform.

We present a new, to the best of our knowledge, method to simulate diffraction images accounting for both coherent and incoherent effects, based on the Wigner distribution function of the exit wave. This permits the simulation of wave and particle effects simultaneously and simulates images photon by photon. It is motivated by artifacts observed in x ray phase-contrast images after phase retrieval, present as noise in the low spatial frequency range, which can make analysis of such images challenging. Classical simulations have so far not been able to reproduce these artifacts. We hypothesize that these artifacts are due to incoherent scatter present in the images, hence the interest in developing a simulator that permits the simulation of both diffraction and incoherent scattering. Here, we give a first demonstration of the method by simulating the Gaussian double-slit experiment. We demonstrate the capability of combining diffraction and incoherent scattering, as well as simulating images for any propagation distance.

We propose that a transition from positive optical torque (OT) to negative OT occurs in a dipolar nanoparticle subjected to a simple optical field composed of two circularly polarized plane waves. This phenomenon can be observed in a phase-change nanoparticle comprising insulating and metallic phases. The analytical expression based on the multipole expansion theory reveals that the positive OT in the metallic phase originates from the electric response during light-matter interaction. However, in the insulating phase, the magnetic response is excited, leading to a significant negative OT due to the contribution of the magnetic field-magnetic dipole interaction. It is noted that the phenomenon of reversible transverse OT is robust to the angle between two constituent plane waves, ensuring its practical application.

We have demonstrated the capability of spectral multiplexing in multi-distance diffractive imaging, enabling the reconstruction of samples with diverse spectral responses. While previous methods such as ptychography utilize redundancy in radial diffraction data to achieve information multiplexing, they typically require capturing a substantial amount of diffraction data. In contrast, our approach effectively harnesses the redundancy information in axial diffraction data. This significantly reduces the amount of diffraction data required and relaxes the stringent requirements on optical path stability.

In this paper, we propose bifocal lenses based on bilayer structures composed of a liquid crystal (LC) cell and LC polymer, and the relative intensity of two foci can be adjusted arbitrarily through applying an external voltage. Two LC layers have different light modulation functions: when circularly polarized light passes through the first layer, part of the outgoing light is converted with PB phase modulation and another part is not converted; followed by the second layer, PB modulation of these two parts would be simultaneously realized but with opposite signs; thus the transmitted left- and right-handed circularly polarized (LCP and RCP) light can be independently controlled. As proof-of-concept examples, longitudinal and transverse bifocal lenses are designed to split an incident LCP light into two convergent beams with orthogonal helicity, and the position of the two foci can be flexibly arranged. Benefitting from the electrically controlled polarization conversion efficiency (PCE) of the LC cell, the relative intensity of the two foci can be adjusted arbitrarily. Experimental results agree well with theoretical calculations. Besides, a broadband polarization and an edge imaging system based on the proposed bifocal LC lenses have also been demonstrated. This paper presents a simple method to design a functional multilayer LC device and the proposed bifocal lenses may have potentials in the optical interconnection, biological imaging, and optical computing.

A novel, to the best of our knowledge, electro-optical modulation method is proposed for measuring third-order intermodulation distortion of photodetectors (PDs) based on de-coupling and de-embedding modulation distortion of modulators. The method utilizes dual parallel intensity modulation to generate electro-optical stimulus signals with fast and fine sweeping capability, and it eliminates the nonlinear impact of modulators by using low-frequency bias swing, allowing a direct extraction of the third-order output intercept point (OIP3) of PD from the combined nonlinear response contributed by both the modulators and the PD. The OIP3 of PD is frequency-swept measured with our method and compared to those with the conventional method to check for consistency. The proposed method enables a modulator-distortion-free, fast, and fine sweeping measurement of PDs using a simple system.

Fast steering mirrors (FSMs) offer a potential alternative for large-range deflection of light beams. However, for a large-stroke FSM, its pointing precision is unacceptably deteriorated due to the actuator non-uniformity, mechanical axis coupling, and the coupling of line-of-sight (LOS) kinematics. This Letter proposes a comprehensive beam-pointing algorithm by decoupling the LOS kinematic model and establishing a two-dimensional correction mapping to compensate for the non-uniformity and mechanical coupling. Moreover, the incident angle is calibrated by a non-contact method to construct the LOS kinematic model accurately. The experimental results proved that the beam-pointing accuracy can achieve a sub-milliradian level within the square field of regard (FOR) of ±25° horizontally and ±14° vertically. A pointing error of 0.87 mrad can be guaranteed within the horizontal range of -30° to 36° and the vertical range of ±24°. Therefore, the proposed method can achieve high-precision beam pointing in a large FOR and contributes to the miniaturization of optical systems.

Lithium niobate (LN) is an excellent nonlinear optical material due to its large nonlinear coefficient, low loss, and broad optical transparency window. So, it is widely used in the generation of nonlinear harmonics. Magnetic toroidal dipole (MTD) resonance is a special optical resonance mode, which can effectively localize the light field inside the device, thus enhancing the nonlinear effects of the materials. In this work, we numerically study the second-harmonic generation (SHG) effect of the LN metasurface based on the MTD mode with a high quality factor (Q-factor). The designed LN nanorod dimer metasurface supports high Q-factor MTD guided mode resonances (GMRs), which are excited by varying the center spacing of the two nanorods, and the Q-factor can be controlled by the offset distance. The excited MTD can effectively confine the electric field within the device, which enables the LN metasurface SHG conversion efficiency to reach 1.15 × 10^-2. In addition, by adjusting the structural parameters, it is possible to effectively modulate the wavelength and conversion efficiency of the SHG. Our results provide a new route for high-quality nonlinear light sources.

The surface properties of target substrates are crucial for the in situ crystallization and growth of metal halide perovskite films fabricated by the anti-solvent method. In this work, a high-quality quasi-2D perovskite film with various-n phases is fabricated on the commonly used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by introducing a branched polyethylenimine (PEI) modifying layer. PEI suppresses the influence of acidic surface of the PEDOT:PSS and regulates the components of the perovskite film, increasing the proportion of large-n phases. Additionally, PEI reduces the formation of defects in perovskite films, leading to higher photoluminescence quantum efficiency and longer photoluminescence lifetime. Based on this high-quality perovskite film, a flexible light-emitting diode with an ultimate current efficiency of 63.2 cd/A is achieved, nearly twofold higher than that of the device (35.1 cd/A) without a PEI modifying layer.

The surging growth in data traffic has necessitated the development of higher-speed, lower-latency intensity modulation and direct detection (IM/DD) passive optical networks (PONs) with higher power budgets. To address the inherent limitations of traditional silica-based solid-core fibers, anti-resonant hollow-core fibers have garnered significant attention from both academia and industry. In this Letter, we present an experimental demonstration of 100 Gb/s PAM-4 IM/DD PON transmission over a 20 km anti-resonant hollow-core fiber in the C band, utilizing low-complexity digital signal processing (DSP). The result achieves a record high power budget of 42.5 dB, facilitated by a 3-tap weighted lookup table (LUT) at the optical line terminal (OLT) side and a semiconductor optical amplifier used as a preamplifier at the optical network unit (ONU) side. This represents the highest power budget reported for IM/DD PON to date, to the best of our knowledge, and offers a promising alternative for the future evolution of PON systems.