CN106301281A - Membrane resonant of a kind of high mechanical quality factor realizes device - Google Patents

Abstract

The invention provides a kind of high mechanical quality factor membrane resonant realizes device, including metal fixed frame (1), the micro-beam of optical fiber (2) and thin film chip (3), described metal fixed frame (1) is square tabular hollow structure, the front surface of its upper and lower side frame is carved with two parallel narrow slot (6) being perpendicular to frame, is used for fixing the micro-beam of optical fiber (2)；The micro-beam of described optical fiber (2) be two be applied in tension force after be fixed on the micro optical fiber of metal fixed frame (1), and four the micro-beams of isometric optical fiber being separated to form by thin film chip (3).The present invention can serve as the principle of acoustic wave filter based on optical fiber micro-beam (2) harmonic oscillator away from resonant frequency, effectively inhibit the phonon tunneling loss of thin film chip (3), improve the mechanical quality factor of membrane resonant, simple in construction, low cost, in room temperature in vacuo and low-temperature vacuum environment, all can keep good mechanical performance, can apply to the fields such as quantum photodynamics.

Description

A thin-film resonator realization device with high mechanical quality factor

technical field

The invention relates to the fields of quantum optomechanics and acoustics, in particular to a device for realizing a thin-film harmonic oscillator with a high mechanical quality factor.

Background technique

High-tension silicon nitride thin-film resonators have become important devices in the field of cavity optomechanics research due to their extremely low absorption coefficient for laser light and high mechanical quality factor. Based on the scheme of resolvable sideband cooling, silicon nitride thin film resonators have been cooled to approach or even reach the quantum ground state, and have been applied to the generation of squeezed light fields, gravitational wave detection, efficient mutual conversion of microwave and light fields, etc. field. It is worth noting that the mechanical quality factor of thin film resonators is a very important technical indicator in the experimental work that has been carried out or will be carried out at present, and a high mechanical quality factor is a prerequisite for the realization of related applications.

At present, the silicon nitride film covered on the silicon substrate can be commercially produced, but in specific applications, it must be fixed on a support for use, but the phonon tunneling loss caused by the fixed structure is extremely large. Limits the mechanical quality factor of silicon nitride thin film resonators. In the previous study, the researchers improved the quality factor of the film by improving the fixing method of the silicon nitride film substrate, that is, reducing the contact area between the substrate and its mounting bracket, and reducing the volume of the fixed glue point. Recently, researchers proposed to use phononic crystals with periodic structures to form phononic bandgap shields to effectively shield acoustic wave propagation, thereby improving the quality factor of mechanical harmonic oscillators. In 2014, the Ball Institute of the University of Copenhagen [Y.Tsaturyan, et al., Opt.Express 22, 6810 (2014)] and the US NIST research group [P.-L.Yu, et al., Appl.Phys.Lett. 104,023510(2014)] introduced this method into the assembly of silicon nitride thin film resonators, and realized a high mechanical quality factor film independent of the fixing method by fabricating phononic crystals on the silicon substrate around the film harmonic oscillator. In the above scheme, only relying on reducing the contact area and the use of glue requires extremely delicate manual operation, and the yield is very low; at the same time, because the quantum optical force experiment needs to place the sample in a high vacuum environment with extremely low temperature, this It is difficult to ensure the stability of the sample during the temperature change from room temperature to extremely low temperature. On the other hand, although the phononic bandgap shield formed by phononic crystals has a good sound wave shielding effect, the design is relatively complicated, and micro-nano processing technologies such as photolithography and chemical etching are required in the production process, and the process is relatively complicated. Costly.

Contents of the invention

The object of the present invention is to provide a device for realizing a thin-film harmonic oscillator with high mechanical quality factor. The device has the advantages of simple structure, high yield and low cost, and can be applied to quantum optomechanical experiment systems.

A device for realizing a thin-film harmonic oscillator with a high mechanical quality factor provided by the present invention includes a thin-film chip (3), a metal fixed frame (1) and an optical fiber microbeam (2);

The metal fixing frame (1) is a square plate-shaped hollow structure, and the distance between the upper and lower sides of the hollow structure is used to accurately control the effective length of the optical fiber microbeam (2); the effective length of the optical fiber microbeam (2) is the upper and lower sides of the hollow structure. Half of the difference between the side spacing and the side length of the thin film chip (3); two pairs of parallel narrow grooves (6) perpendicular to the frame are engraved on the front surface of the upper and lower frames of the metal fixed frame (1), respectively, and the two applied The tensioned micro-optical fibers are respectively fixed in two pairs of parallel narrow grooves (6) on the upper and lower frames of the metal fixed frame (1), and the film chip (3) is fixed in the middle of the two micro-fibers, and is connected with the metal fixed frame (1) The upper and lower borders of the upper and lower frames are parallel and equidistant, and separate the micro-optical fibers to form four equal-length optical fiber micro-beams (2).

The thin film chip (3) is composed of a square silicon nitride thin film resonator (4) with high tension covered on a square silicon substrate (5) with a square window in the middle.

The micro-fiber is made of a single-mode quartz optical fiber tapered, and the cross-sectional diameter of the optical fiber after tapered is less than 50 microns.

The material of the metal fixed frame (1) is preferably Invar.

The fixing of the parallel narrow grooves (6) and the micro-fiber, and the fixing of the micro-fiber and the film chip (3) are all fixed by epoxy resin glue.

Compared with prior art, advantage and effect of the present invention:

The invention provides a device based on the principle of an optical fiber microbeam resonator acoustic wave filter to realize a high mechanical quality factor thin film resonator, which effectively suppresses the phonon tunneling loss of the thin film resonator and improves the mechanical quality factor of the thin film resonator ; The device has simple structure, low cost, and stable performance. At room temperature and a vacuum environment of 10 ^-6 mbar, the quality factor of the silicon nitride thin film resonator based on the device can reach more than 1.5×10 ⁶ .

Compared with the existing direct fixed assembly method, the device of the present invention can efficiently suppress the phonon tunneling loss from the thin film resonator substrate to the fixed mounting frame on the one hand, on the other hand, the repeatability and stability of the device are high, and It can still have good stability in low temperature vacuum environment.

Compared with the existing phonon bandgap shield structure assembly method, the device of the present invention has the same effect in isolating phonon tunneling loss, but the structure is simple, and it does not need complicated micro-nano processing equipment such as photolithography and chemical etching. The process can be made by yourself in most optical laboratories, and the cost is low.

The metal fixed frame (1) included in the device of the present invention can be changed in appearance according to the requirements of the application under the premise of ensuring the size of the internal space, and can flexibly meet the requirements of various application environments.

Description of drawings

Fig. 1 Schematic diagram of the structure of the silicon nitride thin film resonator realization device of the present invention

Fig. 2 is a side sectional view of the thin film chip (3) in the high mechanical quality factor silicon nitride thin film resonator realization device of the present invention

Fig. 3 Suppression effect diagram of the device of the present invention on phonon tunneling

Fig. 4 is a measurement result diagram of the high mechanical quality factor thin film resonator fundamental mode and (2, 2) mode vibration mode and mechanical quality factor realized by the device of the present invention

detailed description

A high mechanical quality factor thin film harmonic oscillator realization device. Its structure is shown in Figure 1 and Figure 2, including a metal fixed frame (1), an optical fiber microbeam (2) and a silicon nitride film chip (3); the metal fixed frame (1) is a square plate-shaped hollow structure with a square in the middle The width of the space is 7mm, which is used to control the length of the optical fiber microbeam (2). The front surfaces of the upper and lower frames of the frame are respectively engraved with parallel narrow grooves with a width of 0.2mm and a depth of 0.5mm perpendicular to the frame, which are used for the optical fiber microbeam (2) is fixed, and the external shape and size of the metal fixed frame (1) can be designed according to the needs of specific applications; the optical fiber microbeam (2) is drawn from a single-mode quartz optical fiber, and its diameter is 30 microns; The square hole in the middle of the silicon thin film chip (3) has a side length of 500 microns, a thickness of 50 nm, and a square silicon nitride thin film resonator (4) with a tension of 0.9 GPa covering a square silicon substrate with a side length of 5 mm and a thickness of 0.5 mm ( 5), the fundamental mode vibration frequency of the silicon nitride thin film resonator (4) is around 800kHz, and the vibration frequency of the (2,2) mode is around 1.6MHz.

When assembling, first place the drawn micro-optical fiber in the parallel narrow groove on the metal fixed frame (1) to determine the relative distance between the two optical fibers, and then use epoxy glue to connect one end of the micro-fiber to the metal fixed frame (1). 1) Relatively fixed, the epoxy resin glue has high hardness after curing, can maintain sufficient strength in a low-temperature vacuum environment, and is not corrosive to the bonded materials; one end of the micro-optical fiber is connected to the metal fixed frame ( 1) After being fixed firmly, hang the metal fixed frame (1) vertically and keep it stable, and at the same time mount a weight of 25g on the suspended end of the micro-optical fiber. Fix the end with epoxy resin glue; place the silicon nitride film chip (3) in the middle of the two micro-optical fibers using a precision adjustment system and fix it with epoxy resin glue. The distance between the upper and lower sides of the metal frame is 1 mm. , between the metal fixed frame (1) and the silicon nitride thin film chip (3), four optical fiber microbeams (2) with a diameter of 30 microns, a length of 1 mm, and a tension of 346.6 MPa were formed. The first four orders of vibration The theoretical values of the eigenvibration frequencies of the modes are 275.3kHz, 587.6kHz, 1024.2kHz and 2368.9kHz respectively, which do not overlap with the eigenvibration frequencies of the fundamental mode and (2,2) mode of the silicon nitride film resonator (4).

Use an optical interferometer to test the vibration isolation effect of the device of the present invention, a beam of 1064nm weak probe light is incident on the square silicon substrate (5) and is reflected, and the reflected light is incident on the 50: Interference is carried out on the 50 beam splitter, the relative phase of the two beams is locked to π/2, and the outgoing light field is injected into the balanced zero-beat detector, so that the square silicon substrate ( 5) Measurement of displacement; in the measurement process, the device of the present invention is fixed on a piezoelectric ceramic driver to load the external mechanical drive, and at the same time, on the metal fixed frame (1), a square silicon substrate (5) is bonded. The substrate is used as the driving force reference; by using a network analyzer to measure the vibration of the sample, the output of the network analyzer is connected to the piezoelectric ceramic with the sample fixed, and the output signal of the balanced zero-beat detector is connected to the network analysis The input terminal of the instrument is recorded.

Figure 3 shows the sample displacement measurement results recorded by the network analyzer in the range of 200kHz to 2MHz. The vibration frequencies of the first three orders of the microbeam are 273.8kHz, 576kHz and 1025kHz, which are consistent with the theoretical calculation values. It can be seen from Fig. 2 that in the range of about 200kHz-1MHz, the optical fiber microbeam (2) suppresses the vibration energy by about 30dB, and the suppression effect can reach 40dB in the range of 600kHz-1MHz.

Figure 4 shows the fundamental mode of the silicon nitride thin film resonator (4) and the eigenvibration mode of the (2,2) mode and the mechanical quality factor of the silicon nitride thin film resonator (4) measured by the ring-down method . It can be seen from the figure that the mechanical quality factors of the fundamental mode and (2,2) mode reached 1.78×10 ⁶ and 1.56×10 ⁶ , respectively, and the measurement conditions were room temperature and vacuum environment.

Claims (5)

1. what high mechanical quality factor membrane resonant was sub realizes a device, including thin film chip (3), it is characterised in that also wrap Include metal fixed frame (1) and the micro-beam of optical fiber (2)；

Described metal fixed frame (1) is square tabular hollow structure, the front surface of its upper and lower side frame is carved with respectively vertical Directly in the parallel narrow slot of corresponding two couple (6) of frame, the micro optical fiber after two applying tension force is separately fixed at metal fixed frame In the parallel narrow slot of two couple (6) of the upper and lower side frame of frame (1), thin film chip (3) is fixed on the middle part of two micro optical fibers, and and metal The upper and lower side frame of fixed frame (1) is parallel and equidistant, is separated by micro optical fiber, forms four the micro-beam of isometric optical fiber (2).

2. according to described in claims 1 high mechanical quality factor membrane resonant realize device, it is characterised in that described Thin film chip (3) covered by the square silicon nitride film harmonic oscillator (4) of high-tension and have the square siliceous of square window in centre Constitute on substrate (5).

3. according to described in claims 1 high mechanical quality factor membrane resonant realize device, it is characterised in that described Micro optical fiber drawn cone to make by single-mode quartz optical fibers, draw after cone the diameter of section of optical fiber less than 50 microns.

4. according to described in claims 1 high mechanical quality factor membrane resonant realize device, it is characterised in that described The material of metal fixed frame be invar.

5. according to described in claims 1 high mechanical quality factor membrane resonant realize device, it is characterised in that described Parallel narrow slot (6) is fixing with micro optical fiber, and micro optical fiber is all bonding solid by epoxide-resin glue with the fixing of thin film chip (3) Fixed.