Search Results (99)

This work addresses the challenge of realizing broadband, low-loss fiber-to-waveguide coupling in the short-wavelength near-infrared range (700–1050 nm), where the required fine structural dimensions and taper tips approach or even exceed current fabrication limits, resulting in tight fabrication tolerances and degraded coupling efficiency. We propose a broadband trilayer adiabatic edge coupler on a thin-film lithium tantalate platform that requires only two standard lithography and etching steps. The design integrates a crossed bilayer taper and a dual-core mode converter to achieve adiabatic mode transformation from a ridge to a thin strip waveguide, ensuring excellent fabrication tolerance and process simplicity. Simulations predict a minimum coupling loss of 0.57 dB at 850 nm, which includes the transmission through the complete edge-coupler structure, along with a 0.5-dB bandwidth exceeding 140 nm. The proposed structure provides a broadband, low-loss, and fabrication-tolerant interface for short-wavelength photonic systems such as quantum photonics, biosensing, and visible-light communications. Full article

Thin-film lithium niobate (TFLN) electro-optic modulators (EOMs) offer distinct advantages, including high speed, broad bandwidth, and low power consumption. However, their large size hinders the density of integration, which trades off with the half-wave voltage. Photonic crystal (PC) structures can effectively reduce the device footprint via the slow-light effect; however, they experience significant losses due to fabrication defects and sharp corners. Here, we theoretically demonstrate an ultracompact Mach–Zehnder interferometer (MZI) EOM based on a TFLN valley photonic crystal (VPC) structure. The design can achieve a high forward transmittance (>0.8) due to defect-immune unidirectional propagation in the VPC, enabled by the unique spin-valley locking effect. The EOM, with a small footprint of 21 μm × 17 μm, achieves an extinction ratio of 16.13 dB and a modulation depth of 80%. The design can be experimentally fabricated using current nanofabrication techniques, making it suitable for broad applications in optical communications. Full article

This work introduces a dual-capacitance upper and lower T-electrode structure for high-performance silicon-based thin-film lithium niobate electro-optic modulators. Employing this structure reduces the distributed capacitance per unit length, suppresses the slow light effect, and lowers the microwave refractive index, consequently achieving group velocity matching between optical and microwave waves. For a 1 cm long device, this design simulates a half-wave voltage of 1.18 V, an electro-optic bandwidth exceeding 70 GHz, and an optical loss of 0.1 dB/cm. Furthermore, the proposed modulator demonstrates compatibility with standard photonic integrated circuit fabrication processes, indicating strong potential for large-scale manufacturing. Full article

Electro-optic modulators with high bandwidth, high modulation efficiency, and low loss play a crucial role in many fields, such as artificial intelligence, analog communications, and satellite data links. The modulation efficiency and loss, which are related to the chip size and integration, are important parameters for modulators. However, the modulation efficiency and optical loss of electro-optic modulators are interrelated in general. In this study, an improved scheme combining sunken electrodes and dual-layer capacitance-loaded electrodes is exhibited, improving the constraint between the modulation efficiency and optical loss of thin-film lithium niobate electro-optic modulators by enhancing the electric field effect. An electro-optic modulator with a high bandwidth (>60 GHz), low optical loss (0.14 dB/cm), and low half-wave voltage–length product (1.52 V·cm) has been realized using finite element analysis software. Full article

Lithium niobate (LN) materials have become a key platform for constructing core optoelectronic devices such as electro-optic (EO) modulators, optical frequency combs, and integrated optical waveguides, owing to their broad transparent window, mature waveguide processes, and excellent electro-optic effect. They demonstrate revolutionary application value in light source generation, signal transmission, and intensity modulation of optical communication systems, and are hailed as the “silicon of the photonics field,” attracting significant attention from both academia and industry. Especially with the commercialization of high-quality thin-film lithium niobate (TFLN) materials, the performance of thin-film optoelectronic devices based on waveguide structures has achieved leapfrog improvements, with their loss characteristics and modulation bandwidth far exceeding those of traditional bulk material devices. This paper systematically combs the photonic properties of LN materials, introduces in detail the electro-optic effect and electro-optic modulation principle of LN electro-optic modulators, reviews some recent research achievements of scholars, focuses on expounding the preparation processes of waveguide-based TFLN, the types of waveguide-based optoelectronic devices, and the research progress of these devices, and discusses and compares the advantages and development potential of different routes. Full article

Electro-optic modulators in the near-infrared spectrum are finding applications in atomic clocks, quantum sensing, quantum information processing, and high-precision measurement. We developed thin-film lithium niobate electro-optic modulators operating at 795 nm for modulation around the D₁ line of ⁸⁷Rb with satisfactory overall performance. Specifically, we made a systematic improvement to reduce the insertion loss, including widening the modulation waveguides, thickening the overcladding, polishing and coating the facets. The fabricated device possesses a low insertion loss of 7.6 dB, an extinction ratio exceeding 30 dB, a 3 dB modulation bandwidth of ~22 GHz, a half-wave voltage-length product of ~1.8 Vcm, and strong adaptability for packaging. Full article

Lithium niobate (LiNbO₃, LN) is a multifunctional material with broad applicability in photonic and electronic devices. Recent advances in lithium niobate on insulator (LNOI) technology have significantly enhanced the integration density and miniaturization potential of LN-based platforms. Among the various fabrication techniques available, pulsed laser deposition (PLD) presents a cost-effective and versatile alternative to crystalline ion slicing (CIS), particularly advantageous for achieving high doping concentrations. However, a persistent challenge in PLD-grown lithium niobate film is cracking, primarily induced by the substantial thermal stress resulting from the mismatch in thermal expansion coefficients between LN and the substrate. In this study, we implemented a series of process modifications to address the cracking issue and successfully achieved crack-free LN films by introducing a lithium-deficient phase. This approach enabled the successful fabrication of highly Fe³⁺-doped LN films with a high electrical conductivity of 9.95 × 10⁻⁵ S/m while also exhibiting characteristic polarization switching behavior. These results demonstrate that PLD enables the fabrication of highly doped, structurally robust LN films and holds significant potential for the development of advanced electronic and optoelectronic devices. Full article

In the field of modern optical communication, radar signal processing and optical sensors, true time delay technology, as a key means of signal processing, can achieve the accurate control of the time delay of optical signals. This study presents a novel design that integrates a 2 × 2 Multi-Mode Interference (MMI) structure with a Mach–Zehnder modulator on a silicon nitride–lithium niobate (SiN-LiNbO₃) heterogeneous integrated optical platform. This configuration enables the selective interruption of optical wave paths. The upper path passes through an ultralow-loss Archimedes’ spiral waveguide delay line made of silicon nitride, where the five spiral structures provide delays of 10 ps, 20 ps, 40 ps, 80 ps, and 160 ps, respectively. In contrast, the lower path is straight through, without introducing an additional delay. By applying an electrical voltage, the state of the SiN-LiNbO₃ switch can be altered, facilitating the switching and reconfiguration of optical paths and ultimately enabling the combination of various delay values. Simulation results demonstrate that the proposed optical true delay line achieves a discrete, adjustable delay ranging from 10 ps to 310 ps with a step size of 10 ps. The delay loss is less than 0.013 dB/ps, the response speed reaches the order of ns, and the 3 dB-EO bandwidth is broader than 67 GHz. In comparison to other optical switches optical true delay lines in terms of the parameters of delay range, minimum adjustable delay, and delay loss, the proposed optical waveguide digital adjustable true delay line, which is based on an optical switch and an Archimedes’ spiral structure, has outstanding advantages in response speed and delay loss. Full article

Thin-film lithium niobate (TFLN) electro-optic modulators serve as critical components in microwave photonic systems. To improve device performance, we developed a U-T double-layer traveling-wave electrode configuration. Using finite element analysis, we systematically simulated and optimized both modulation efficiency and radiofrequency characteristics, ultimately realizing a low half-wave voltage-length product of 1.77 V·cm, a minimal optical loss of 0.022 dB/cm, and an ultra-wide modulation bandwidth surpassing 100 GHz. Full article

As photonic integrated circuits (PICs) gain prominence in quantum communication and quantum computation, the development of efficient and stable cryogenic packaging technologies becomes paramount. This paper presents a robust and scalable cryogenic packaging method for thin-film lithium niobate (TFLN) photonic chips. The packaged fiber-to-chip interface shows a coupling efficiency of 15.7% ± 0.3%, with minimal variation of ±0.5% as the temperature cools down from 295 K to 1.5 K. Furthermore, the packaged chip exhibits outstanding stability over multiple thermal cycling, highlighting its potential for practical applications in cryogenic environments. Full article

A 90° optical hybrid employing an MMI coupler was fabricated on a thin-film lithium niobate (TFLN) platform that can be used for integrated coherent transceivers. The fabricated 90° optical hybrid exhibited a CMRR greater than 20 dB, a phase error below ±7.5°, and an excess loss less than 1.8 dB (including contributions from the 90° hybrid, a 1 × 2 MMI coupler, and an optical delay line, after subtracting the losses from the coupler and delay line, the 90° optical hybrid introduced less than 0.9 dB of loss) over the C-band with a compact footprint of 13.8 × 250 μm², facilitating the future development of high-bandwidth optical coherent transceivers heterogeneously integrated on TFLN. Full article

With the rapid development of information technology, the global data volume has been continuously expanding, placing unprecedented demands on communication networks to accommodate precipitously increasing throughput. Thin-film lithium niobate (TFLN) modulators, characterized by their large theoretical bandwidth, low half-wave voltage, and suitability for high-density integration, show great application potential in high-speed optical modules and optical interconnection networks. However, the persistent issue of velocity mismatch between radio frequency (RF) signals and optical carriers invariably hinders the utilization of higher-frequency bands, which restricts the modulation speed of the fabricated devices. In this paper, an electrode co-loaded with square serrations and T-shaped stubs was utilized to achieve precise velocity matching and excellent impedance matching. Leveraging this approach, a TFLN modulator chip with an electro-optic bandwidth far exceeding 67 GHz and a return loss of greater than 12 dB was successfully fabricated on a silicon substrate. The velocity of RF signals can be tuned by altering the lengths of the slow-wave structures, which provides guidance for the design and optimization of broadband modulators. Full article

Optical modulators are indispensable components in optical communication systems and must be designed to minimize insertion loss, reduce driving voltage, and enhance linearity. State-of-the-art silicon modulator technology has limitations in terms of power, performance, and spatial size. The addition of materials such as thin-film lithium niobate (TFLN), silicon–organic hybrids (SOH), and plasma–organic hybrids (POH) has improved the modulation performance in silicon photonics. An evaluation of the differences among these modulators and their respective performance characteristics is conducted. Full article

We investigate the influence of non-vertical sidewall angles on the band structure characteristics of thin-film lithium niobate (LN) photonic crystals (PhCs), considering both suspended LN membranes and LN on insulator (LNOI) configurations. Utilizing the gap-to-midgap ratio as a figure-of-merit, we observe a 34% reduction for a suspended LN PhC with 60° sidewall angles compared to the one with vertical sidewalls and a more substantial 73% reduction for LNOI PhCs with 70° sidewall angles. We address this challenge through the optimization of geometrical parameters of PhC unit cells with non-vertical sidewalls, taking fabrication feasibility into account. Our work provides a design guideline for the development of realistic LN PhC devices for future large-scale LN photonic circuits. Full article

Lithium niobate (LiNbO₃) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO₃ (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits. Full article