LiNbO3 Research Articles

Ferroelectric Domain Intrinsic Radiation Resistance of Lithium Niobate Ferroelectric Single−Crystal Film

The study of the properties of ferroelectric materials against irradiation has a long history. However, anti−irradiation research on the ferroelectric domain has not been carried out. In this paper, the irradiation of switched domain structure is innovatively proposed. The switched domain of 700 nm lithium niobate (LiNbO3, LN) thin film remains stable after gamma irradiation from 1 krad to 10 Mrad, which was prepared by piezoresponse force microscopy (PFM). In addition, the changing law of domain wall resistivity is explored through different sample voltages, and it is verified that the irradiated domain wall conductivity is still larger than the domain. This domain wall current (DWC) property can be applied to storage, logic, sensing, and other devices. Based on these, a ferroelectric domain irradiation resistance model is established, which explains the reason at an atomic level. The results open a possibility for exploiting ferroelectric materials as the foundation in the application of space and nuclear fields.

Flexible epitaxial LiNbO3 thin film with ferroelectricity and nonlinear optical response

Flexible or wearable devices are of great interests in the modern technologies, and oxide thin films are critical components for such applications. In this work, epitaxial LiNbO3 (LNO) thin film integrated on flexible mica substrate has been achieved. Al-doped ZnO (AZO) layer has been first deposited as buffer layer to obtain the epitaxial LNO film, furthermore AZO serves as bottom electrode for electrical measurement. The as-deposited LNO film exhibits high epitaxial quality with c-direction growth. The transmittance measurement indicates the high transparency of the film, ～85 % in visible range and ～90 % in near infrared region up to 1500 nm. The second harmonic generation (SHG) measurement confirms the nonlinearity of the flexible LNO film. The LNO/AZO/mica film also presents apparent ferroelectric response. Overall, the high-quality LNO integrated on flexible mica could be potentially applied in wearable optical and electrical devices.

Estimation of losses caused by sidewall roughness in thin-film lithium niobate rib and strip waveguides

Samples of dielectric optical waveguides of rib or strip type in thin-film lithium niobate (TFLN) technology are characterized with respect to their optical loss using the Fabry-Pérot method. Attributing the losses mainly to sidewall roughness, we employ a simple perturbational procedure, based on rigorously computed mode profiles of idealized channels, to estimate the attenuation for waveguides with different cross sections. A single fit parameter suffices for an adequate modelling of the effect of the waveguide geometry on the loss levels.

Invertible all-optical logic gate on chip.

We demonstrate an invertible all-optical gate on chip, with the roles of control and signal switchable by slightly adjusting their relative arrival time at the gate. It is based on the quantum Zeno blockade (QZB) driven by sum-frequency generation (SFG) in a periodically poled lithium niobate microring resonator. For two nearly identical nanosecond pulses, the later arriving pulse is modulated by the earlier arriving one, resulting in 2.4 and 3.9 power extinction between the two, respectively, when their peak powers are 1 mW and 2 mW, respectively. Our results, while to be improved and enriched, herald a new, to the best of our knowledge, paradigm of logical gates and circuits for exotic applications.

Thin-film lithium niobate circulator-free dispersion compensator in a time-lens system for femtosecond-pulse generation.

We demonstrate a circulator-free thin-film lithium niobate (TFLN) dispersion compensator based on the cascading 2 × 2 multimode interferometer (MMI) and two identical chirped Bragg gratings (CBGs). The cascaded MMI-CBG structure provides a dispersion value of 920 ps/nm/m over a 20 nm bandwidth covering 1537 to 1557 nm, featuring a compact footprint of 1 mm × 0.7 mm. Utilizing this device within a TFLN electro-optic time-lens system, we successfully generate 863-fs pulses at a 37 GHz repetition rate. Our compact, scalable, low-loss, and circulator-free dispersion compensator is the building block for the efficient generation of high-peak-power femtosecond laser pulses.

Enhanced Infrared Vision by Nonlinear Up-Conversion in Nonlocal Metasurfaces.

The ability to detect and image short-wave infrared light has important applications in surveillance, autonomous navigation, and biological imaging. However, the current infrared imaging technologies often pose challenges due to large footprint, large thermal noise and inability to augment infrared and visible imaging. Here, infrared imaging is demonstrated by nonlinear up-conversion to the visible in an ultra-compact, high-quality-factor lithium niobate resonant metasurface. Images with high conversion efficiency and resolution quality are obtained despite the strong nonlocality of the metasurface. The possibility of edge-detection image processing augmented with direct up-conversion imaging for advanced night vision applications is furthershown.

Optimization of waveguide fabrication processes in lithium-niobate-on-insulator platform.

Lithium niobate (LN) is used in diverse applications such as spectroscopy, remote sensing, and quantum communications. The emergence of lithium-niobate-on-insulator (LNOI) technology and its commercial accessibility represent significant milestones. This technology aids in harnessing the full potential of LN's properties, such as achieving tight mode confinement and strong overlap with applied electric fields, which has enabled LNOI-based electro-optic modulators to have ultra-broad bandwidths with low-voltage operation and low power consumption. Consequently, LNOI devices are emerging as competitive contenders in the integrated photonics landscape. However, the nanofabrication, particularly LN etching, presents a notable challenge. LN is hard, dense, and chemically inert. It has anisotropic etch behavior and a propensity to produce material redeposition during the reactive-ion plasma etch process. These factors make fabricating low-loss LNOI waveguides (WGs) challenging. Recognizing the pivotal role of addressing these fabrication challenges for obtaining low-loss WGs, our research focuses on a systematic study of various process steps in fabricating LNOI WGs and other photonic structures. In particular, our study involves (i) careful selection of hard mask materials, (ii) optimization of inductively coupled plasma etch parameters, and finally, (iii) determining the optimal post-etch cleaning approach to remove redeposited material on the sidewalls of the etched photonic structures. Using the recipe established, we realized optical WGs with total (propagation and coupling) loss value of -10.5 dB, comparable to established values found in the literature. Our findings broaden our understanding of optimizing fabrication processes for low-loss lithium-niobate waveguides and can serve as an accessible resource in advancing LNOI technology.

Sandwiched structure for temperature compensated laterally excited bulk wave resonators based on lithium niobate film

Recently, lithium niobate thin film laterally excited bulk wave resonators (XBARs) have attracted much attention because of their advantage of high frequency and outstanding electromechanical coupling factor (K2) enabling wide filter bandwidths. These can satisfy the increasing 5G communication demand. However, their large temperature coefficient limits their development to some extent. To improve their temperature stability with little K2 reduction, this paper has proposed a sandwiched structure for temperature compensated XBARs (TC XBARs). This structure includes the top silicon dioxide (SiO2) layer and the bottom SiO2 layer. One layer can improve temperature stability, and the other layer can increase K2. The optimized XBARs have a temperature coefficient of frequency (TCF) of −90.77 ppm⁄°C. The common two-layer TC XBARs can achieve a TCF of −22 ppm⁄°C sacrificing K2 to 8%. However, the proposed sandwiched TC XBARs can achieve a K2 of 12.15 and a TCF of −28.94 ppm⁄°C simultaneously, with a large FoM. Meanwhile, spurious modes can be suppressed in the sandwiched structure. Thus, this sandwiched structure can provide a good solution for the high performance of XBARs.

CMOS-compatible high-speed endless automatic polarization controller

Automatic polarization controllers find broad applications in various fields, including optical communication, quantum optics, optical sensing, and biomedicine. Currently, the predominant integrated automatic polarization controllers employ either lithium niobate or silicon platforms. Devices based on lithium niobate platforms exhibit excellent performance; however, their fabrication complexity hinders widespread commercial deployment. In contrast, silicon-based integrated automatic polarization controllers benefit from complementary metal–oxide–semiconductor compatibility and reduced fabrication costs. Nevertheless, these silicon automatic polarization controllers suffer from low tracking speeds, peaking at merely 1.256 krad/s. In this study, we demonstrated a silicon high-speed automatic polarization controller, incorporating innovative thermal tuning units combined with a sophisticated control algorithm. The response time of these thermal tuning units has been markedly decreased to 3.2 µs. In addition, we have implemented a novel automatic polarization control algorithm, utilizing gradient descent techniques, on a field-programmable gate array control board. The synergy of the rapid thermal tuning unit and the advanced control algorithm has enabled us to attain an unprecedented polarization control speed of up to 20 krad/s, with this rate being solely limited by the capabilities of our characterization equipment. To our knowledge, this speed is the fastest yet reported for a silicon-based integrated automatic polarization control chip. The proposed device represents a significant breakthrough in the field of silicon-based automatic polarization controllers, paving the way for the future integration of additional polarization management devices. Such an advancement would mark a substantial leap in the realm of integrated photonics, bridging the gap between performance efficiency, cost-effectiveness, and technological integration.

Micro-Transfer-Printed InP-Based Membrane Photonic Devices on Thin-Film Lithium Niobate Platform

Micro-Transfer-Printed InP-Based Membrane Photonic Devices on Thin-Film Lithium Niobate Platform

Investigation of the Properties of Surface Acoustic Waves in a Lithium Niobate Single Crystal with a Silicon Dioxide Film by the Finite-Element Method

Investigation of the Properties of Surface Acoustic Waves in a Lithium Niobate Single Crystal with a Silicon Dioxide Film by the Finite-Element Method

The Operation of Lithium Niobate Ferroelectric Domain Wall Memory at 673 K

The Operation of Lithium Niobate Ferroelectric Domain Wall Memory at 673 K

Erratum to “23.8-GHz Acoustic Filter in Periodically Poled Piezoelectric Film Lithium Niobate With 1.52-dB IL and 19.4% FBW”

Erratum to “23.8-GHz Acoustic Filter in Periodically Poled Piezoelectric Film Lithium Niobate With 1.52-dB IL and 19.4% FBW”

Investigation of the effect of the applied voltage to the control electrodes of a lithium niobate phase modulator on the intensity distribution at the ends of channel waveguides and on parasitic amplitude modulation

Investigation of the effect of the applied voltage to the control electrodes of a lithium niobate phase modulator on the intensity distribution at the ends of channel waveguides and on parasitic amplitude modulation

Thin-film lithium niobate-based electro-optic comb cloning for self-homodyne coherent communication.

As the optical communication industry advances, metropolitan area networks (MANs) and radio access networks (RANs) are extensively deployed on a large scale, demanding energy-efficient integrated light sources and simplified digital signal processing (DSP) technologies. The emergence of thin-film lithium niobate (TFLN) has given rise to high-performance, energy-efficient on-chip modulators, making on-chip optical frequency comb (OFC) more appealing. Owing to the phase uniformity and stability of this chip-scale device, it has been possible to eliminate the carrier frequency phase estimation (CPE) in DSP stacks using comb-clone-enabled self-homodyne detection. Here we report the first use, to our knowledge, of a TFLN on-chip electro-optic (EO) frequency comb to realize comb cloning and self-homodyne coherent detection. We transmit three optical pilot tones and eight data channels encoded with 20 Gbaud polarization-multiplexed 16-ary quadrature amplitude modulation (PM-16-QAM) over 10 km and 80 km standard single-mode fibers. The bit error ratios (BERs) of the eight channels reach below 10-3, a result made possible by our on-chip comb. The scalability and mass producibility of on-chip EO combs, combined with the simplified DSP, show potential in our proposed fifth-generation (5G) RAN and MAN transmission scheme.

High-gain lithium niobate brillouin laser with tunable phonon frequency of 1∼31 GHz

High-gain lithium niobate brillouin laser with tunable phonon frequency of 1∼31 GHz

Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator

Photonics integration of an optoelectronic oscillator (OEO) on a chip is attractive for fabricating low cost, compact, low power consumption, and highly reliable microwave sources, which has been demonstrated recently in silicon on insulator (SOI) and indium phosphide (InP) platforms at X-band around 8 GHz. Here we demonstrate the first integration of OEOs on the thin film lithium niobate (TFLN) platform, which has the advantages of lower V π , no chirp, wider frequency range, and less sensitivity to temperature. We have successfully realized two different OEOs operating at Ka-band, with phase noises even lower than those of the X-band OEOs on SOI and InP platforms. One is a fixed frequency OEO at 30 GHz realized by integrating a Mach–Zehnder modulator (MZM) with an add-drop microring resonator (MRR), and the other is a tunable frequency OEO at 20–35 GHz realized by integrating a phase modulator (PM) with a notch MRR. Our work marks the first step of using TFLN to fabricate integrated OEOs with high frequency, small size, low cost, wide range tunability, and potentially low phase noise.

Lithium niobate on insulator – fundamental opto-electronic properties and photonic device prospects

Abstract Lithium niobate on insulator (LNOI) combines a variety of optoelectronic properties and can meet practical performance requirements that are uncommon in optoelectronic materials. This review introduces the fundamentals and the photonic device concepts that arise from the LNOI materials platform. Firstly, the nonlinear optical response of LNOI is presented, including birefringent phase matching (BPM), modal phase matching (MPM), and quasi-phase matching (QPM). The tunable properties are also introduced, including electro-optical (EO), thermo-optical (TO), and acousto-optical (AO) effects. The structures of nonlinear optical devices, such as ridge waveguides (including periodically polarized inversion waveguides), Mach–Zehnder interferometer (MZI) modulators and micro-resonators (such as disks and rings) are demonstrated. Finally, the future of LNOI devices is discussed. In the already mature and developed optoelectronic material systems, it is rare to find one particular material system supporting so many basic optical components, photonic devices and optoelectronic devices as LNOI does in the field of integrated photonic chips.

High-efficiency nonlinear frequency conversion enabled by optimizing the ferroelectric domain structure in x-cut LNOI ridge waveguide

Abstract Photonic devices based on ferroelectric domain engineering in thin film lithium niobate are key components for both classical and quantum information processing. Periodic poling of ridge waveguide can avoid the selective etching effect of lithium niobate, however, the fabrication of high-quality ferroelectric domain is still a challenge. In this work, we optimized the applied electric field distribution, and rectangular inverted domain structure was obtained in the ridge waveguide which is beneficial for efficient nonlinear frequency conversions. Second harmonic confocal microscope, piezoresponse force microscopy, and chemical selective etching were used to characterize the inverted domain in the ridge waveguide. In addition, the performance of nonlinear frequency conversion of the periodically poled nano-waveguide was investigated through second harmonic generation, and the normalized conversion efficiency was measured to be 1,720 % W−1 cm−2, which is close to 60 % that of the theoretical value. The fabrication technique described in this work will pave the way for the development of high-efficiency, low-loss lithium niobate nonlinear photonic devices.

Waveguide-integrated van der Waals heterostructure photodetector on a lithium niobate on insulator platform.

Lithium niobate (LN) photonics has gained significant interest for their distinct material properties. However, achieving monolithically integrated photodetectors on lithium niobate on an insulator (LNOI) platform for communication wavelengths remains a challenge due to the large bandgap and extremely low electrical conductivity of LN material. A two-dimensional (2D) material photodetector is an ideal solution for LNOI photonics with a strong light-matter interaction and simple integration technique. In this work, a van der Waals heterostructure photodiode composed of a p-type black phosphorus layer and an n-type MoS2 layer is successfully demonstrated for photodetection at communication wavelengths on a LNOI platform. The LNOI waveguide-integrated BP-MoS2 photodetector exhibits a dark current as low as 0.21 nA and an on/off ratio exceeding 200 under zero voltage bias with an incident power of 13.93 µW. A responsivity as high as 1.46 A/W is achieved at -1 V bias with a reasonable dark current around 2.33 µA. With the advantages of high responsivity, low dark current, and simple fabrication process, it is promising for the monolithically integrated photodetector application for LNOI photonic platforms at communication wavelengths.