Tunable Microwave Source Based on Dual-Wavelength Laser in a Single Whispering-Gallery-Mode Optical Microcavity

Abstract

The present invention discloses a tunable microwave source based on a dual-wavelength laser of a single whispering gallery mode optical microcavity, comprising: a dual-wavelength laser based on a single whispering gallery mode optical microcavity, which is used to generate dual-wavelength lasing with adjustable spacing, narrow linewidth and low threshold; an optical fiber or optical waveguide amplifier, which is used to amplify optical signals; an optical filter, which is used to filter out other optical signals and noises; a high-speed detector, which is used to generate microwave signals with narrow bandwidth and tunability; wherein, the dual-wavelength laser based on a single whispering gallery mode optical microcavity includes: a pump light source, an optical waveguide or a tapered optical fiber, a substrate, a single whispering gallery mode optical microcavity and a pair of gold electrodes; the adjustable-spacing dual-wavelength lasing is realized by adjusting the magnitude of the applied voltage of the pair of gold electrodes. The present invention provides a realization scheme of a dual-wavelength laser with adjustable spacing, which has a simple structure. Based on the beat frequency of this laser, a tunable microwave source can be obtained.

Description

Technical Field

[0001] The present invention relates to the fields of optical communication, semiconductor optoelectronics, integrated photonics, and microwave photonics. Specifically, it relates to a tunable microwave source based on dual-wavelength lasers in a single whispering-gallery-mode optical microcavity. More specifically, the present invention proposes a dual-wavelength laser based on a single whispering-gallery-mode optical microcavity with a simple structure, small size, and adjustable spacing, as well as a tunable microwave source generation system based on this. Background Art

[0002] Optical microcavity lasers represented by whispering-gallery-mode microcavity lasers utilize the continuous total internal reflection of light on a smooth sidewall to achieve strong confinement of the optical field, and have the advantages of very high mode quality factor, very small mode volume, low pump power, and easy integration. However, the whispering-gallery modes are very dense, there is mode competition, and it is difficult to achieve single-mode lasing or stable dual-wavelength and even multi-wavelength output while obtaining high-efficiency gain. To obtain low-noise, high-intensity, and tunable microwave signals by beating dual-wavelength optical signals, it is usually necessary to use two independent lasers for beating. Compared with two independent lasers, achieving stable dual-wavelength laser output in a single whispering-gallery-mode optical microcavity, which is generated in the same microcavity, can obtain microwave signals with good stability, very narrow linewidth, less affected by the external environment, simple structure, simple manufacturing process, small size, low cost, easy integration, and high stability. The frequency spacing of the dual wavelengths is determined by the microcavity mode spacing, which can cover from several GHz to several hundred GHz, and the generated microwave signal range after beating is wide. However, using a single whispering-gallery-mode optical microcavity to achieve a stable dual-wavelength laser and then generating a tunable microwave source by beating faces a problem: how to achieve a stable and tunable-spacing narrow-linewidth dual-wavelength laser. Summary of the Invention

[0003] The object of the present invention is to propose a tunable microwave source based on dual-wavelength lasers in a single whispering-gallery-mode optical microcavity, overcome the challenges in the preparation of existing on-chip dual-wavelength micro-lasers, and provide a tunable microwave source based on dual-wavelength lasers in a single whispering-gallery-mode optical microcavity. Compared with an independent dual-laser system, this dual-wavelength laser only requires a single whispering-gallery-mode optical microcavity, and has the characteristics of simple preparation process, small size, high quality factor, low pump threshold, and easy integration. The microwave source generated by beating has the advantages of wide signal range, narrow bandwidth, tunability, and frequency stability.

[0004] The specific technical solution to achieve the object of the present invention is as follows:

[0005] A tunable microwave source based on dual-wavelength lasers in a single whispering-gallery-mode optical microcavity, comprising:

[0006] A dual-wavelength laser based on a single whispering-gallery-mode optical microcavity, which is used to generate dual-wavelength lasing with adjustable wavelength spacing, narrow linewidth, and low threshold;

[0007] An optical fiber or optical waveguide amplifier, whose input end is connected to the output end of the dual-wavelength laser, and is used to amplify optical signals;

[0008] An optical filter, whose input end is connected to the output end of the optical fiber or optical waveguide amplifier, and is used to filter out other optical signals and noise;

[0009] A high-speed detector, whose input end is connected to the output end of the optical filter, and is used to generate a microwave signal with narrow bandwidth and tunable frequency. Its characteristics are that the dual-wavelength laser based on a single whispering-gallery-mode optical microcavity includes:

[0010] A pump light source;

[0011] A single whispering-gallery-mode optical microcavity;

[0012] An optical waveguide or tapered optical fiber, which is directly connected to the single whispering-gallery-mode optical microcavity or is laterally or vertically coupled through an evanescent wave, and is used to input pump light, output laser light, and introduce mode perturbation, causing coherent recombination of quasi-degenerate whispering-gallery modes with similar geometric characteristics, generating quasi-degenerate polygon modes with similar spatial distribution characteristics in the pump light and lasing light bands respectively. The quasi-degenerate polygon mode includes a localized periodic orbit composed of a polygon mode and at least one multiple localized periodic orbit composed of polygon modes;

[0013] A substrate;

[0014] A pair of gold electrodes.

[0015] The material of the substrate is lithium niobate, silicon, silicon dioxide, silicon nitride, silicon carbide, group-IV semiconductor materials and their compounds, group-III-V compounds, group-II-VI compounds, group-IV-VI compounds, organic semiconductor materials, or sapphire doped with rare earth ions or quantum dots.

[0016] The gain medium of the single whispering-gallery-mode optical microcavity is rare earth ions or quantum dots; the configuration of the single whispering-gallery-mode optical microcavity is a microdisk cavity, a deformed cavity, a ring microcavity, or a racetrack microcavity.

[0017] The quasi-degenerate polygon mode has the following characteristics: the difference value of the eigenfrequencies is on the order of several GHz to THz, the difference values of the radial quantum number and the angular quantum number are fixed, and the specific difference values are determined by the eigenfrequencies and the corresponding quantum numbers, so that the modal field geometric distributions of the modes are close.

[0018] The quasi-degenerate polygon modes with similar spatial distribution characteristics are far from the microcavity edge, encounter small surface scattering losses, and have 10 6Above quality factor to obtain a narrow linewidth laser.

[0019] The polygon shape of the quasi-degenerate polygon modes with similar spatial distribution characteristics is selectively excited by changing the diameter of a single whispering gallery mode optical microcavity, the coupling distance between an optical waveguide or a tapered optical fiber and the single whispering gallery mode optical microcavity, and the pump light wavelength, so as to obtain different frequency spacings of the dual-wavelength laser, thereby controlling the dual-wavelength working range.

[0020] There are small spatial distribution differences in the quasi-degenerate polygon modes with similar spatial distribution characteristics generated in the lasing light band. By means of electro-optic, thermo-optic or plasma dispersion physical effects, the local refractive index is changed, thereby obtaining the tuning of the dual-wavelength spacing.

[0021] In the single whispering gallery mode optical microcavity of the present invention, the quasi-degenerate polygon modes with similar spatial distribution characteristics generated in the pump light and lasing light bands are far from the microcavity edge, encounter small surface scattering losses, and have a quality factor of 10 6 Above, so as to obtain a narrow linewidth laser; the frequency intervals of the quasi-degenerate polygon modes generated in the lasing light band are small, and the spatial distribution characteristics are similar, and similar high optical gains can be obtained, which is easy to achieve stable dual-wavelength and even multi-wavelength lasing. Moreover, there are small spatial distribution differences in the quasi-degenerate polygon modes with similar spatial distribution characteristics generated in the lasing light band. By means of electro-optic, thermo-optic or plasma dispersion physical effects, the local refractive index is changed, thereby obtaining the tuning of the dual-wavelength spacing.

[0022] The beneficial effect of the present invention is that an optical waveguide or a tapered optical fiber is coupled with a single whispering gallery mode optical microcavity to introduce mode perturbation, causing the coherent recombination of quasi-degenerate whispering gallery modes with similar geometric characteristics, and quasi-degenerate polygon modes with similar spatial distribution characteristics are generated in the pump light and lasing light bands respectively to obtain a dual-wavelength laser; the generated optical signal is amplified and filtered, and then a tunable microwave signal is generated through a high-speed detector, providing a solution with a simpler structure and smaller size for a tunable optical frequency comb and a tunable microwave signal source. Description of the Drawings

[0023] Figure 1 is a schematic diagram of the system of the tunable microwave source based on the dual-wavelength laser of the single whispering gallery mode optical microcavity of the present invention;

[0024] Figure 2 is the mode field distribution diagram of the quasi-degenerate polygon modes with similar spatial distribution characteristics generated in the pump light and lasing light bands in the embodiment of the present invention;

[0025] Figure 3 is the evolution curve diagram of the output power of the dual-wavelength laser with respect to the pump power in the embodiment of the present invention;

[0026] Figure 4 This is the spectral diagram of the dual-wavelength laser in the embodiment of the present invention, and the inset is its fine spectral diagram;

[0027] Figure 5 This is the microwave spectral diagram generated after the dual-wavelength laser in the embodiment of the present invention is optically amplified, filtered, and detected by a high-speed detector;

[0028] Figure 6 This is the tuning diagram of the tunable microwave with the applied voltage (electro-optic effect) in the embodiment of the present invention. Detailed implementation manners

[0029] The following further describes the present invention in detail with reference to the accompanying drawings and embodiments.

[0030] Refer to Figure 1 , a tunable microwave source based on a single whispering-gallery-mode optical microcavity dual-wavelength laser provided by the present invention includes: a dual-wavelength laser 1 based on a single whispering-gallery-mode optical microcavity, which is used to generate dual-wavelength lasing with adjustable spacing, narrow linewidth, and low threshold; a fiber or optical waveguide amplifier 2, which is used to amplify the optical signal; an optical filter 3, which is used to filter out other optical signals and noise; a high-speed detector 4, which is used to generate a microwave signal 5 with narrow bandwidth and tunability. The output light of the dual-wavelength laser 1 based on a single whispering-gallery-mode optical microcavity passes through the fiber or optical waveguide amplifier 2 and the optical filter 3 for optical signal amplification and filtering respectively, and then passes through the high-speed detector 4 to generate a tunable microwave signal 5. The dual-wavelength lasing with adjustable spacing is realized by adjusting the magnitude of the applied voltage of the gold electrode pair 16. Embodiment

[0031] The following details each part of the tunable microwave source based on a single whispering-gallery-mode optical microcavity dual-wavelength laser in this embodiment.

[0032] The dual-wavelength laser based on a single whispering-gallery-mode optical microcavity is as Figure 1 shown, and includes: a pump light source 11 with a laser wavelength of 970 nm; a tapered fiber 12 with a waist size of 2 μm; a substrate 14 which is a lithium niobate crystal; the configuration of a single whispering-gallery-mode optical microcavity 15 is a microdisk cavity with a diameter of 106 μm and a thickness of 700 nm; there is a circular silica pillar with a thickness of 2 μm and a diameter of 10 μm between the single whispering-gallery-mode optical microcavity 15 and the substrate 14; the interval of the gold electrode pair 16 is 60 μm, which is used to apply an external electric field to tune the dual-wavelength frequency interval.

[0033] The single whispering-gallery-mode optical microcavity 15 is fabricated on an erbium-doped lithium niobate thin film in the z-tangential direction by using a femtosecond laser lithography-assisted chemical mechanical polishing preparation process. The doping concentration of erbium ions in the erbium-doped lithium niobate thin film is 0.1 mol%. The tapered fiber 12 is fabricated by thermally pulling a standard single-mode fiber into a micro-nano fiber with a waist of 2 μm in the middle and adiabatic mode transition.

[0034] The tapered fiber 12 is coupled with the single whispering-gallery-mode optical microcavity 15 to introduce mode perturbation, causing coherent recombination of quasi-degenerate whispering-gallery modes with similar geometric characteristics, and generating quasi-degenerate polygon modes 13 with similar spatial distribution characteristics in the pump light and lasing light bands respectively. Refer to Figure 2 , where Figure a is the mode field distribution diagram of the multi-localized octagon mode 132 generated in the pump light band; Figures b and c are the mode field distribution diagrams of the localized octagon mode (also known as the localized periodic orbit) 131 and the multi-localized octagon mode 132 with similar spatial distribution characteristics and close eigenfrequencies generated in the lasing light band. The spatial mode fields of these two modes are coherently superposed into a quasi-degenerate octagon mode. Under the optical drive of the pump light source 11, when the pump power exceeds the pump threshold power, these two modes form a dual-wavelength laser with very close wavelengths. By applying an external voltage on the gold electrode pair 16, an inhomogeneous refractive index distribution is caused, affecting the wavelength spacing between these two modes with similar but not identical mode field distributions. Thus, tunable dual-wavelength lasing can be achieved by adjusting the magnitude of the applied voltage.

[0035] Figure 3 is the evolution curve of the output power of the dual-wavelength laser in the embodiment of the present invention with respect to the pump power. The pump threshold power is only 80 μW. When the pump power is higher than the pump threshold power, the output power of the dual-wavelength laser increases linearly with the pump power. This curve indicates that the device realizes lasing under continuous optical pumping at room temperature.

[0036] Figure 4 is the spectrogram of the dual-wavelength laser in the embodiment of the present invention. The inset is its fine spectrogram. The dual-wavelength interval is 9.9 pm, and a microwave signal in the GHz range will be generated after beat frequency.

[0037] Figure 5 is the microwave frequency spectrum diagram of the dual-wavelength laser in the embodiment of the present invention generated by amplification, filtering, and a high-speed detector. The frequency of the microwave signal is around 1.2309 GHz.

[0038] Figure 6 is the tuning diagram of the tunable microwave with respect to the applied voltage (utilizing the electro-optic effect of lithium niobate) in the embodiment of the present invention. The tuning efficiency is -166 MHz / V. The results verify thatFigure 1 Feasibility of the tunable microwave source based on a single whispering-gallery-mode optical microcavity dual-wavelength laser as shown.

[0039] In the specific embodiments described above, the purpose, technical solutions and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A tunable microwave source based on a dual-wavelength laser in a single whispering gallery mode optical microcavity, comprising: A dual-wavelength laser (1) based on a single whispering gallery mode optical microcavity, for generating dual-wavelength lasing with adjustable spacing, narrow linewidth and low threshold; An optical fiber or optical waveguide amplifier (2), whose input end is connected to the output end of the dual-wavelength laser (1), for amplifying the optical signal; An optical filter (3), whose input end is connected to the output end of the optical fiber or optical waveguide amplifier (2), for filtering out other optical signals and noise; A high-speed detector (4), whose input end is connected to the output end of the optical filter (3), for generating a microwave signal (5) with narrow bandwidth and tunability, characterized in that the dual-wavelength laser (1) based on a single whispering gallery mode optical microcavity comprises: A pump light source (11); A single whispering gallery mode optical microcavity (15); An optical waveguide or tapered optical fiber (12), directly connected to the single whispering gallery mode optical microcavity (15) or through evanescent wave lateral coupling or vertical coupling, for inputting pump light and outputting laser light, and at the same time introducing mode perturbation, causing coherent recombination of quasi-degenerate whispering gallery modes with similar geometric characteristics, and generating quasi-degenerate polygon modes (13) with similar spatial distribution characteristics in the pump light and lasing light bands respectively. The quasi-degenerate polygon mode (13) includes a localized periodic orbit (131) composed of a polygon mode and at least one multiple localized periodic orbit (132) composed of polygon modes; A substrate (14); A pair of gold electrodes (16); wherein: The quasi-degenerate polygon mode (13) with similar spatial distribution characteristics is far from the microcavity edge, encounters small surface scattering losses, and has a quality factor of at least 10 6 , thereby obtaining a narrow-linewidth laser; The polygon shape of the quasi-degenerate polygon mode (13) with similar spatial distribution characteristics is selectively excited by changing the diameter of the single whispering gallery mode optical microcavity (15), the coupling distance between the optical waveguide or tapered optical fiber (12) and the single whispering gallery mode optical microcavity (15), and the pump light wavelength, so as to obtain different frequency spacings of the dual-wavelength laser, thereby controlling the dual-wavelength working range.

2. The tunable microwave source based on a single whispering gallery mode optical microcavity dual-wavelength laser according to claim 1, wherein The material of the substrate (14) is lithium niobate, silicon, silicon dioxide, silicon nitride, silicon carbide, group IV semiconductor materials and their compounds, group III-V compounds, group II-VI compounds, group IV-VI compounds, organic semiconductor materials or sapphire doped with rare earth ions or quantum dots.

3. The tunable microwave source based on a single whispering gallery mode optical microcavity dual-wavelength laser according to claim 1, wherein, The gain medium of the single whispering gallery mode optical microcavity (15) is a rare earth ion or a quantum dot; the configuration of the single whispering gallery mode optical microcavity (15) is a microdisk cavity, a deformed microcavity, a ring microcavity or a racetrack microcavity.

4. The tunable microwave source based on a single whispering gallery mode optical microcavity dual-wavelength laser according to claim 1, characterized in that, The quasi-degenerate polygon mode (13) has the following characteristics: The eigenfrequencies have a difference value in the order of several GHz to THz, the difference values of the radial quantum number and the angular quantum number are fixed, and the specific difference values are determined by the eigenfrequencies and the corresponding quantum numbers, so that the modal field geometric distributions of the modes are close.

5. The tunable microwave source based on a single whispering gallery mode optical microcavity dual-wavelength laser according to claim 1, characterized in that, There are small spatial distribution differences in the quasi-degenerate polygon modes (13) with similar spatial distribution characteristics generated in the lasing light band. By means of electro-optic, thermo-optic or plasma dispersion physical effects, the local refractive index is changed, so as to obtain the tuning of the dual-wavelength spacing.

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