Efficient second and third harmonic generation in dual-layer lithium niobate microdisk resonator

Lithium niobate thin film frequency doubler has extensive applications in the preparation of classical and quantum sources.In this study,we successfully fabricated microdisk resonators with a quality factor of 2.2×10^(5) in reverse-polarization dual-layer x-cut lithium niobate for the first time.Based on the modal phase matching condition,efficient second harmonic generation with a record normalized conversion efficiency of~56000%W-1 and cascaded third harmonic generation with an efficiency of~6500%W-2 were obtained in the microdisk resonator.Compared with the periodically poled lithium niobate microcavity,the complex domain structure preparation processes are avoided.Our work provides a scheme for achieving highly efficient second-order nonlinear effects in non-periodically poled microcavities.

Directional emission in X-cut lithium niobate microresonators without chaos dynamics

We systematically investigate the field distribution of the transverse electric modes in X-cut lithium niobate disks as an example of circular microcavities with anisotropic refractive index. A conserved quantity is discovered, which indicates the absence of chaos that generally exists in deformed microcavities and leads to a nontrivial directional emission. The emission directionality was theoretically investigated and experimentally verified by exciting highorder modes of an X-cut lithium niobate microresonator assisted with second harmonics. The field distribution analysis can enrich the knowledge in designing photonic devices that need precise control of field distribution,such as phase matching in nonlinear processes. Furthermore, the discovered emission phenomenon is momentous in enhancing and controlling communications between on-chip photonic devices.

Integrated lithium niobate single-mode lasers by the Vernier effect

Microcavity lasers based on erbium-doped lithium niobate on insulator(LNOI),which are key devices for LNOI integrated photonics,have attracted significant attention recently.In this study,we report the realization of a C-band single-mode laser using the Vernier effect in two coupled erbium-doped LNOI microrings with different radii under the pump of a 980-nm continuous laser.The laser,operating stably over a large range of pumping power,has a pump threshold of about 200μW and a side-mode suppression ratio exceeding 26 dB.The high-performance LNOI single-mode laser will promote the development of lithium niobate integrated photonics.

Microdisk lasers on an erbium-doped lithium-niobite chip

Lithium niobate on insulator(LNOI) provides a platform for the fundamental physics investigations and practical applications of integrated photonics. However, as an indispensable building block of integrated photonics, lasers are in short supply. In this paper, erbium-doped LNOI laser in the 1550-nm band was demonstrated in microdisk cavities with high quality factors fabricated in batches by UV exposure, inductively coupled plasma reactive ion etching, and chemomechanical polishing. The threshold and conversion efficiency of the erbium-doped LNOI microdisk laser were measured to be lower than 1 m W and 6.5×10^(-5)%, respectively. This work will benefit the development of integrated photonics based on LNOI.

On-chip erbium-doped lithium niobate waveguide amplifiers [Invited]

Lithium niobate on insulator(LNOI), as an emerging and promising optical integration platform, faces shortages of on-chip active devices including lasers and amplifiers. Here, we report the fabrication of on-chip erbium-doped LNOI waveguide amplifiers based on electron beam lithography and inductively coupled plasma reactive ion etching. A net internal gain of ~30 d B/cm in the communication band was achieved in the fabricated waveguide amplifiers under the pump of a974 nm continuous laser. This work develops new active devices on LNOI and may promote the development of LNOI integrated photonics.

Periodically poled lithium niobate whispering gallery mode microcavities on a chip

In this study, we investigate the fabrication of periodically poled lithium niobate(PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using conventional microfabrication techniques.The quality factor of the PPLN microdisk resonators with a 40-μm radius and a 700-nm thickness is 6.7×10~5. Second harmonic generation(SHG) with an efficiency of 2.2×10^(-6) mW(-1) is demonstrated in the fabricated PPLN microdisks. The nonlinear conversion efficiency could be considerably enhanced by optimizing the period and pattern of the poled structure and by improving the cavity quality factors.

Second-harmonic generation using d(33)in periodically poled lithium niobate microdisk resonators

A fabrication process allowing for the production of periodically poled lithium niobate(PPLN)photonic devices with any domain pattern and unit size down to 200 nm is developed by combining semiconductor fabrication techniques and piezo-force-microscopy tips polarization.Based on this fabrication process,PPLN microdisk resonators with quality factors of 8×10~4 were fabricated from a Z-cut lithium niobate film.Second-harmonic generation(SHG)utilizing d(33)in the whole cavity was demonstrated in a PPLN microdisk with a 2μm-spatialperiod radial domain pattern.The SHG conversion efficiency was measured to be 1.44×10^(-5)m W^(-1).This work paves the way to fabricate complex PPLN photonic devices and to obtain efficient nonlinear optical effects that have wide applications in both classical and quantum optics.

Sum-frequency generation in on-chip lithium niobate microdisk resonators

We report the first observation, to the best of our knowledge, of sum-frequency generation in on-chip lithium niobate microdisk resonators. The sum-frequency signal in the 780 nm band, distinct in wavelength from secondharmonic signals, was obtained in lithium niobate microresonators under the pump of two individual 1550 nm band lasers. The sum-frequency conversion efficiency was measured to be 1.4 × 10^(-7) mW^(-1). The dependence of the intensities of the nonlinear signals on the total pump power and the wavelength of one pump laser was investigated while fixing the wavelength of the other. This work paves the way for applications of on-chip lithium niobate microdisk resonators ranging from infrared single-photon detection to infrared spectroscopy.

铌酸锂微纳波导中的二阶非线性光学效应研究进展

由于具有优秀的线性和非线性光学特性,铌酸锂薄膜(lithium niobate thin film, LNTF)被视为一个很有前途的集成光子学平台.作为集成光学系统的基本单元,铌酸锂微纳波导不仅作为传输、控制器件被研究,也展现出优秀的二阶非线性光学特性.本文综述了铌酸锂薄膜微纳波导二阶非线性效应研究的最新进展,以倍频转换效率为例,讨论了影响二阶非线性转换效率的因素,全面总结了LNTF(周期极化)波导的制备,高效、可调谐、宽带二次谐波产生,自发参量下转换研究的现状,并对未来的研究方向进行了展望.

Sum-frequency generation of a laser and its background in an on-chip lithium-niobate microdisk

Lithium-niobate microcavities have not only the ability to resonantly enhance light–matter interaction but also excellent nonlinear optical properties,thereby providing an important platform for nonlinear optical investigations.In this paper,we report the observation of multi-peak spectra in the near infrared range in lithium-niobate microcavities on a chip under the pump of a 1550 nm continuous laser.Such a multi-peak spectrum was attributed to the sum-frequency of the pump laser and its background.The conversion efficiencies of the sum-frequency processes are of the order of61.5%W-1.The influences of the phenomenon on nonlinear processes were further discussed.