Special issue-Advanced technology of microcavity photonics materials and devices
Precision measurement is a cornerstone of modern physics, and the development of laser sources directly promotes the progress of science and technology. In the early 21st century, the invention of the optical frequency comb created the optical atomic clock, the most accurate time/frequency standard device, a lot of precision measurement applications have been implemented, including absolute optical frequency measurement, fundamental physical constants measurement, precision distance measurement and molecular spectroscopy measurement. However, the early comb systems were complex and expensive, and worked in large laboratories, which restricted their application scenarios. In recent years, an integrated microresonator-based optical frequency comb (microcomb) has attracted great attention from the scientific and industrial communities because of its advantages such as compact size, low power consumption and excellent scalability. Different from traditional optical frequency combs, which rely on gain media or saturable absorbers to realize the mode locking, this kind of integrated microcomb benefits from the enhanced nonlinear effect of high-quality factor microcavity to realize the excitation and mode locking of the frequency comb. This new mechanism greatly reduces the volume and cost of optical frequency combs, which has great advantages in civilian-based precision measurement applications. The progress of integrated microresonator-based optical frequency combs in precision measurement applications is introduced, which mainly focuses on miniature optical atomic clock, ultra-fast precision distance measurement and high-precision spectroscopy in this paper. Finally, the opportunities and challenges in the future application of integrated microresonator-based optical frequency combs in precision measurement are summarized and prospected.
With the development of topological photonics, topological lasers and semiconductor lasers are promoted by the discovery of the topological edge states and corner states with robustness against defects and perturbations. Firstly, the development history of the topological lasers and the principles of the various kinds of topological lasers was reviewed; Secondly recent realizations of various topological lasers were analyzed and the basic physics about topological edge states and topological corner states was explained. In these experiments, the modes of topological laser were decided by the dielectric structure. The laser was excited by pumping the photonic gain. The analysis show that topological lasers based on topological corner states have higher efficiency and lower threshold than those based on topological edge state, due to the high quality factor and small mode volume of topological corner state, which provides the possibility for future photonic integrated chip. Finally, the challenge and potential applications in the future were outlooked, which was beneficial to explore practical topological laser.
When the interaction between excitons and cavity photons is stronger than the decay of excitons and cavity photons, a strong coupling occurs between exciton energy level and cavity mode, thereby generating the quasi-particles called exciton-polaritons. The small effective mass and strong nonlinearity of exciton-polariton make it great potential in the applications of slow light and low-power-consumption light emission devices. However, weak exciton binding energy of traditional III-V inorganic semiconductor materials and weak nonlinearity of organic semiconductor materials limit their application of exciton-polaritons at room temperature. In contrast, halide perovskites have a series of excellent photoelectric properties such as high absorption coefficient, long diffusion length, high defect tolerance, and low rates of nonradiative recombination. Furthermore, with large exciton binding energy and oscillator strength, halide perovskites become an ideal material for studying strong interaction between light and matter. The research progress on exciton-polaritons based on the strong coupling between halide perovskite and Fabry-Pérot (F-P) microcavities was introduced from two aspects: the structure kinds of halide perovskites and the type of F-P microcavities. Firstly, the research background of polaritons and the basic photoelectric properties of halide perovskites were reviewed. Secondly, the respective characteristics of three-dimensional perovskites and two-dimensional layered perovskites and related research on strong coupling with F-P microcavities were introduced. Afterwards, the regulation and application of self-organized and non-self-organized F-P microcavities to perovskite exciton-polaritons were discussed. Finally, the challenges and future research directions of halide perovskite exciton-polaritons were summarized and prospected.
The vertical cavity is the core structure of lasers, detectors, filters, sensors and so on. The optical field distribution of the vertical cavity has an important impact on the performance of these devices. The structure of the vertical cavity affects the optical field in the vertical cavity, thus affecting the design, fabrication, and performance of devices based on the vertical cavity. In recent years, many studies have been done on the construction and optical manipulation of vertical cavity, and remarkable progresses have been achieved in fundamental theory and device applications. Firstly, the dispersion characteristics of the conventional top/bottom distributed Bragg reflector vertical cavity, the optical manipulation methods and their applications in lasers and filters were introduced; Then, the dispersion characteristics of one- and two-dimensional high-index-contrast subwavelength grating (HCG) based vertical cavities were presented, and the optical manipulation of HCG-based vertical cavities in novel lasers and monolithic multi-wavelength filter arrays were reviewed; Finally, the article was summarized and the new applications of vertical cavity were prospected.
Micro-nano mechanical resonators are believed to be an ideal platform for developing on-chip signal processing devices, in which various kinds of physical fields can be transduced to mechanical phonons for phonon-based information processing. In such a strategy, control of phonon transferring between different mechanical resonators is essential for phonon-based information processing. By coupling two mechanical resonators for a two-mode mechanical system, although coherent phonon transferring between hybridized mechanical modes has been achieved recently, direct control over the effective coupling between disparate mechanical resonators is still desirable. Therefore, coherent control of phonons through Landau-Zenner-Stückelberg (LZS) interference was developed in an optomechanical system in this paper. The hybridization between two mechanical resonators was mediated using the effect of optical trapping, and a parametric driving field was applied through modulating the optical trap so that the system transvered the avoided-crossing point periodically to realize the LZS interference of phonons. The studies demonstrate that coherent phonon transferring between two disparate mechanical resonators can be achieved through the LZS interference when the on-resonance condition is satisfied. The authors' research provides an efficient scheme for high-efficient transferring of phonon-based information in real space.
Lithium niobate on insulator (LNOI) was regarded as a competitive integrated optical platform due to the excellent optical performance of lithium niobate crystal and integration characteristics of thin-film devices. In addition to the research on transmission and control devices, such as waveguides and modulators, significant progress has been made in LNOI lasers recently. The research status of the rapidly developing LNOI microcavity laser was reviewed in this paper. Firstly, the main technical schemes of rare-earth ion doping of bulk lithium niobate and LNOI, as well as the recent exploration on the preparation of rare-earth ion doped LNOI micro-/nano- optical devices, were introduced; Secondly, the research progresses on Erbium-doped lithium niobate on insulator (Er-LNOI) microdisk and microring cavity lasers were summarized; Then, the working mechanism of several common methods to realize single-mode laser in microcavity laser system were described. The research progresses on Er-LNOI single-mode lasers utilizing "Vernier effect" and mode-loss modulation were introduced in the following; Finally, based on the reported research results of LNOI lasers, the limitations of the current research and the future research directions were discussed.
Kerr optical frequency comb has an equidistantly distributed comb-like spectral structure and has important applications in precision measurement, optical clocks, coherent optical communications, microwave and optical arbitrary wave generation, spectroscopy, and calibration of astronomical spectrometers. Firstly, compared with other optical frequency comb systems, the microresonator optical frequency comb has the advantages of strong integration, small size and good flexibility, which greatly expands the application of optical frequency combs. Secondly, a MgF2 microresonator with a quality factor up to 4.8×107 was prepared by an ultra-precision machining method, and a clean, regular and regularly arranged spectrum was obtained. The free frequency range was 9.73 GHz, which provides conditions for generating low repetition rate optical frequency combs. Finally, according to the experimental results and the Lugiato-Lefever equation, the generation process of the MgF2 microresonator optical frequency comb was analyzed, and the influence of the pump power on the optical frequency comb was studied. The soliton state optical frequency comb was obtained by adjusting the detuning parameters. In addition, the optical field mode of the microresonator was optimized through dispersion control, which creates a condition for generating a soliton optical frequency comb with an ultra-smooth spectrum and improves the performance of the optical frequency comb.