Coupling device for echo wall microcavity and on-chip waveguide

Abstract

The invention discloses an echo wall microcavity and on-chip waveguide coupling device. The echo wall microcavity and on-chip waveguide coupling device comprises a sub-wavelength grating waveguide planar photon chip and an echo wall microcavity, the sub-wavelength grating waveguide planar photon chip is horizontally placed, a sub-wavelength grating structure is prepared in the middle of the sub-wavelength grating waveguide through photoetching and etching processes, and the two ends of the waveguide are of gradually-changed inverted-cone-shaped structures used for being matched with a light spot mode field when the waveguide is coupled with an optical fiber array; the echo wall microcavity is fixed above the planar photon chip, and an evanescent field diffracted upwards by the sub-wavelength grating waveguide is coupled into the echo wall microcavity by precisely adjusting the relative position of the sub-wavelength grating waveguide and the echo wall microcavity; and after the required coupling efficiency is achieved, the sub-wavelength grating waveguide planar photon chip is cured to complete device manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated optics, and in particular to a whispering gallery microcavity and on-chip waveguide coupling device. Background Art

[0002] With the development of wireless communications, radar, sensing and other fields, the demand for high-frequency and high-spectral-purity microwave sources has become more urgent. Photogenerated microwave technology has broken through the technical bottleneck of traditional electric microwave oscillators, and can achieve ultra-low phase noise performance in the high-frequency band, and the entire system can be miniaturized or even monolithically integrated. Crystal whispering gallery microcavities can be used as the core components of photogenerated microwave oscillators due to their extremely high quality factor (Q value), and one of the key technologies for device engineering is the efficient and highly stable coupling packaging of whispering gallery microcavities. Currently, the commonly used coupling methods are tapered fiber coupling and prism coupling. The former has high coupling efficiency but poor stability; the latter has high packaging technology difficulty and low yield rate, resulting in high cost and difficulty in large-scale production. Summary of the invention

[0003] In view of the above defects or improvement needs of the prior art, the present invention provides a whispering gallery microcavity and on-chip waveguide coupling technology, which aims to utilize the evanescent field generated by the subwavelength grating structure integrated in the planar waveguide to couple with the whispering gallery microcavity, thereby resolving the contradiction that is difficult to balance in terms of process difficulty, cost and stability of conventional coupling technologies.

[0004] The present invention discloses a whispering gallery microcavity and on-chip waveguide coupling device, wherein the whispering gallery microcavity and on-chip waveguide coupling device comprises a sub-wavelength grating waveguide planar photonic chip and a whispering gallery microcavity;

[0005] The sub-wavelength grating waveguide planar photonic chip is placed horizontally, a sub-wavelength grating structure is prepared in the middle of the sub-wavelength grating waveguide by photolithography and etching processes, and both ends of the waveguide are gradually inverted tapered structures for matching the light spot mode field when coupled with the optical fiber array;

[0006] The whispering gallery microcavity is fixed above the planar photonic chip, and the relative positions of the subwavelength grating waveguide and the whispering gallery microcavity are precisely adjusted so that the evanescent field diffracted upward by the subwavelength grating waveguide is coupled into the whispering gallery microcavity. After the required coupling efficiency is achieved, the subwavelength grating waveguide planar photonic chip is solidified to complete the device manufacturing.

[0007] Furthermore, the whispering gallery microcavity is a disc-shaped structure, made of low-loss and highly transparent magnesium fluoride or calcium fluoride, with a diameter of 1 to 10 mm, a thickness of 0.1 to 1 mm, and a quality factor Q value of 10. 8 ~10 10 , free spectrum range 3GHz~50GHz.

[0008] Furthermore, a set of precision six-axis translation stages is used to clamp the subwavelength grating waveguide planar photonic chip and move it under the whispering gallery microcavity, and the working surface of the whispering gallery microcavity is preliminarily aligned with the subwavelength grating waveguide; the tunable laser is modulated by an external arbitrary waveform generator and coupled into the subwavelength grating waveguide through the optical fiber arrays fixed at both ends of the subwavelength grating waveguide planar photonic chip, and the relative position of the subwavelength grating waveguide and the whispering gallery microcavity is observed through top-down and front-view high-magnification lenses and the coupling spacing between the two is adjusted so that the working surface of the whispering gallery microcavity is located directly above the subwavelength grating waveguide and the distance reaches the micrometer level; the transmission spectrum of the whispering gallery microcavity is continuously monitored by an oscilloscope, and when the microcavity resonance spectrum is observed and the required coupling efficiency is met, ultraviolet glue is cured under the subwavelength grating waveguide planar photonic chip to complete the device manufacturing.

[0009] Furthermore, the whispering gallery microcavity and on-chip waveguide coupling device further comprises a thermoelectric cooler;

[0010] The thermoelectric cooler is arranged below the sub-wavelength grating waveguide planar photonic chip so as to control the temperature of the sub-wavelength grating waveguide planar photonic chip.

[0011] Furthermore, the whispering gallery microcavity and on-chip waveguide coupling device further comprises a metal connecting rod, a perforated metal fixture and a locking screw;

[0012] One end of the metal connecting rod is connected to the whispering gallery microcavity, and the other end is embedded in the perforated metal fixture and fixed by a locking screw on the side of the fixture. The perforated metal fixture is arranged on the top of the thermoelectric cooler;

[0013] The metal connecting rod, the perforated metal clamp and the locking screw are made of tungsten copper or brass material and are used to fix the whispering gallery microcavity and conduct heat.

[0014] The beneficial effects achieved by the present invention are:

[0015] The whispering gallery microcavity and on-chip waveguide coupling device provided by the present invention utilizes a sub-wavelength grating waveguide as a coupling region, has high coupling efficiency, and a strong, reliable and non-damageable waveguide structure, and has significantly improved stability compared to a tapered fiber coupling method.

[0016] The whispering gallery microcavity and on-chip waveguide coupling device provided by the present invention has a large coupling area and low coupling alignment requirements, and the coupling efficiency can be flexibly changed by adjusting the distance between the whispering gallery microcavity and the sub-wavelength grating waveguide.

[0017] The whispering gallery microcavity and on-chip waveguide coupling device provided by the present invention can be fabricated by using a standard silicon photonics process for the sub-wavelength grating waveguide planar photonic chip, and the planar waveguide structure is more easily optically coupled with an active laser chip, thereby reducing the device fabrication cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a top view of the device structure of the whispering gallery microcavity and on-chip waveguide coupling device provided by an example of the present invention;

[0019] Figure 2 is a side view of the device structure of the whispering gallery microcavity and on-chip waveguide coupling device provided by an example of the present invention;

[0020] Figure 3 The invention discloses a coupling alignment monitoring experimental system for a whispering gallery microcavity and an on-chip waveguide coupling device provided by an example of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0022] The present invention provides a whispering gallery microcavity and on-chip waveguide coupling device, comprising a sub-wavelength grating waveguide planar photonic chip 1, a whispering gallery microcavity 2, a metal connecting rod 3, a perforated metal clamp 4, a locking screw 5 and a thermoelectric cooler 6, etc.

[0023] The planar photonic chip 1 is horizontally placed on a thermoelectric cooler 6, a subwavelength grating structure is prepared in the middle of the waveguide by photolithography and etching processes, and the two ends of the waveguide are gradually inverted cone structures for matching the light spot mode field when coupled with the optical fiber array; the whispering gallery microcavity 2 is glued and fixed to one end of the metal connecting rod 3, and the other end is embedded in the open metal clamp 4 and fixed by the locking screw 5 on the side of the clamp. The metal clamp 4 and the planar photonic chip 1 are placed on a thermoelectric cooler 6 as a whole to control the temperature of the whispering gallery microcavity 2 and the planar photonic chip 1 to ensure the stability of the coupling distance between the two; the relative position of the subwavelength grating waveguide and the whispering gallery microcavity 2 is adjusted by a precision displacement stage, so that the edge of the whispering gallery microcavity 2 is located directly above the subwavelength grating waveguide and the distance reaches the micrometer level, at which time the evanescent field diffracted upward by the subwavelength grating waveguide is coupled into the microcavity; the transmission spectrum of the whispering gallery microcavity is observed by a coupling alignment monitoring experimental system, and after the required coupling efficiency is achieved, the planar photonic chip 1 is glued and cured to complete the device manufacturing.

[0024] Preferably, the above-mentioned whispering gallery microcavity is a disc-shaped structure, made of low-loss and highly transparent magnesium fluoride or calcium fluoride, with a diameter of 1 to 10 mm, a thickness of 0.1 to 1 mm, and a quality factor Q value of 10 8 ~10 10, free spectrum range 3GHz~50GHz.

[0025] Figure 2 It is a side view of the device structure of the whispering gallery microcavity and on-chip waveguide coupling technology provided in the embodiment. Among them, the working surface of the whispering gallery microcavity is perpendicular to the subwavelength grating waveguide planar photonic chip, and the edge of the whispering gallery microcavity is located directly above the subwavelength grating waveguide, and the distance between the two is in the micrometer range. The gold metal connecting rod 3 and the perforated metal clamp 4 play a role in fixing and conducting heat for the whispering gallery microcavity, and the materials are tungsten copper, brass alloy, etc. with good thermal conductivity. The planar photonic chip 1 and the metal clamp 4 are fixed to the thermoelectric cooler 6 by heat-conducting silver paste, so as to simultaneously control the temperature of the subwavelength grating waveguide and the whispering gallery microcavity to ensure the stability of the coupling state of the two.

[0026] Figure 3 This is a coupling alignment monitoring experimental system for the whispering gallery microcavity and the on-chip waveguide coupling device provided in the embodiment. First, the thermoelectric cooler 6 is placed on the stage, and then the whispering gallery microcavity 2, the metal connecting rod 3, and the perforated metal clamp 4 are assembled and fixed on the thermoelectric cooler 6 for temperature control. A set of precision six-axis translation stages is used to clamp the planar photonic chip 1 and move it between the whispering gallery microcavity 2 and the thermoelectric cooler 6, and the working surface of the whispering gallery microcavity 2 is roughly aligned with the sub-wavelength grating waveguide. After being modulated by an external arbitrary waveform generator, the tunable laser is coupled into the subwavelength grating waveguide through the optical fiber array fixed at both ends of the photonic chip. The relative position of the subwavelength grating waveguide and the whispering gallery microcavity is observed through top-down and front-view high-magnification lenses and the coupling spacing between the two is adjusted so that the working surface of the whispering gallery microcavity is located directly above the subwavelength grating waveguide and the distance reaches the micrometer level. The transmission spectrum of the whispering gallery microcavity is continuously monitored by an oscilloscope. When the microcavity resonance spectrum is observed and the required coupling efficiency is met, UV glue is cured under the photonic chip to complete the device manufacturing.

[0027] In the present invention, the shape of the whispering gallery microcavity can be disk-shaped, cylindrical, annular, spherical, etc.; the material of the whispering gallery microcavity can be low-loss transparent crystal materials such as magnesium fluoride, calcium fluoride, silicon dioxide, silicon, lithium niobate, etc.; the whispering gallery microcavity can be further prepared with metal electrodes and other electrically controlled tuning structures; the preparation material of the subwavelength grating waveguide can be selected from silicon nitride, lithium niobate, silicon, etc. according to the material type of the whispering gallery microcavity; the type of the subwavelength grating can be a uniform grating, apodized grating, etc.; the metal connecting rod and the open-hole metal clamp are made of materials with good thermal conductivity such as tungsten copper and brass, and the shape of the metal clamp can be flexibly designed as long as it can fix the whispering gallery microcavity and conduct heat.

[0028] The above are only specific steps of the present invention and do not constitute any limitation to the protection scope of the present invention; any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention; some parts not elaborated in detail in the present invention belong to the known technologies of those skilled in the art.

Claims

1. A whispering gallery microcavity and on-chip waveguide coupling device, characterized in that: The whispering gallery microcavity and on-chip waveguide coupling device comprises a sub-wavelength grating waveguide planar photonic chip (1) and a whispering gallery microcavity (2); The sub-wavelength grating waveguide planar photonic chip (1) is placed horizontally, a sub-wavelength grating structure is prepared in the middle of the sub-wavelength grating waveguide by photolithography and etching processes, and both ends of the waveguide are gradually inverted tapered structures for matching the light spot mode field when coupled with the optical fiber array; The whispering gallery microcavity (2) is fixed above the planar photonic chip (1), and the relative positions of the subwavelength grating waveguide and the whispering gallery microcavity (2) are precisely adjusted so that the evanescent field diffracted upward by the subwavelength grating waveguide is coupled into the whispering gallery microcavity (2); after the required coupling efficiency is achieved, the subwavelength grating waveguide planar photonic chip (1) is solidified to complete device fabrication.

2. The whispering gallery microcavity and on-chip waveguide coupling device according to claim 1, characterized in that: The whispering gallery microcavity (2) is a disk-shaped structure, made of low-loss and highly transparent magnesium fluoride or calcium fluoride, with a diameter of 1 to 10 mm, a thickness of 0.1 to 1 mm, and a quality factor Q value of 10 8 ~10 10 , free spectrum range is 3GHz~50GHz.

3. The whispering gallery microcavity and on-chip waveguide coupling device according to claim 1, characterized in that: A set of precision six-axis displacement stages is used to clamp the sub-wavelength grating waveguide planar photonic chip (1) and move it under the whispering gallery microcavity (2), and the working surface of the whispering gallery microcavity (2) is preliminarily aligned with the sub-wavelength grating waveguide; a tunable laser is modulated by an external arbitrary waveform generator and coupled into the sub-wavelength grating waveguide through an optical fiber array fixed at both ends of the sub-wavelength grating waveguide planar photonic chip (1); the relative position of the sub-wavelength grating waveguide and the whispering gallery microcavity (2) is observed through a top-view and front-view high-magnification lens, and the coupling distance between the two is adjusted so that the working surface of the whispering gallery microcavity (2) is located directly above the sub-wavelength grating waveguide and the distance reaches the micrometer level; the transmission spectrum of the whispering gallery microcavity (2) is continuously monitored through an oscilloscope, and when the microcavity resonance spectrum is observed and the required coupling efficiency is met, ultraviolet glue is applied below the sub-wavelength grating waveguide planar photonic chip (1) for curing to complete the device manufacturing.

4. The whispering gallery microcavity and on-chip waveguide coupling device according to claim 1, characterized in that: The whispering gallery microcavity and on-chip waveguide coupling device further comprises a thermoelectric cooler (6); The thermoelectric cooler (6) is arranged below the sub-wavelength grating waveguide planar photonic chip (1) so as to control the temperature of the sub-wavelength grating waveguide planar photonic chip (1).

5. The whispering gallery microcavity and on-chip waveguide coupling device according to claim 4, characterized in that: The whispering gallery microcavity and on-chip waveguide coupling device further comprises a metal connecting rod (3), a perforated metal clamp (4) and a locking screw (5); One end of the metal connecting rod (3) is connected to the whispering gallery microcavity (2), and the other end is embedded in the perforated metal clamp (4) and fixed by a locking screw (5) on the side of the clamp. The perforated metal clamp (4) is arranged on the top of the thermoelectric cooler (6); The metal connecting rod (3), the perforated metal clamp (4) and the locking screw (5) are made of tungsten copper or brass material and are used to fix the whispering gallery microcavity (2) and to conduct heat.

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