All-optical tuning controllable optical comb generation system and method based on functionalized micro-bottle cavity

Abstract

The invention discloses an all-optical tuning controllable optical comb generation method based on a functionalized echo wall mode optical micro-bottle cavity. Comprising a 1550nm narrow linewidth continuous wave laser, a single-mode fiber, an erbium-doped fiber amplifier, a polarization controller, an optical isolator, a functionalized micro-bottle cavity-fiber taper coupling system, an optical attenuator, a spectrum analyzer and a 1550nm power tunable laser. The free spectral range of the microcavity is reduced by utilizing the unique axial characteristic of the echo wall mode microbottle cavity, the axial mode microcavity optical frequency comb with the small free spectral range is generated, the functionalized microbottle cavity is prepared based on an all-optical tuning method, and the generated axial mode microcavity optical frequency comb is tuned through the photo-thermal material titanium dioxide, so that the optical frequency comb with the small free spectral range is obtained. And remarkable spectral range tuning is realized. The limitation that the WGM microcavity optical frequency comb cannot be effectively tuned due to a large free spectral range is solved, and practical application of the microcavity optical frequency comb in the fields of optical communication, optical frequency synthesis and the like is facilitated.

Description

Technical Field

[0001] The present invention belongs to microcavity optical frequency comb technology and can be used in the fields of optical communication, optical frequency synthesis, etc. Specifically, the present invention relates to an all-optical tunable controllable optical comb generation system and method based on a functionalized whispering gallery mode optical microbottle cavity. Background Art

[0002] In recent years, whispering gallery mode (WGM) optical microcavities have developed rapidly. Due to their extremely small mode volume, ultra-high quality factor, fast dynamic response and ultra-high sensitivity, they have important applications in high-sensitivity sensing, microlasers, nonlinear optics and other fields. Based on WGM optical microcavities, optical frequency combs can be generated, which have unique advantages such as high repetition rate, wide spectrum and high integration, and have broad research prospects in scientific and technological fields such as low-threshold microlasers, atomic clocks and optical communications.

[0003] However, in practical applications such as wavelength division multiplexing coherent communications and optical frequency synthesis, the tunability of the optical frequency comb to adjust the comb lines at any position within the free spectral range (FSR) is a key function. However, the comb frequency distribution of the microcavity optical frequency comb is affected by the microcavity material and structure. Without external assistance, when the microcavity is deterministically prepared, the generated optical frequency comb cannot be effectively tuned.

[0004] All-optical tuning is an effective means to achieve microcavity resonant frequency tuning. By coating the microcavity surface with photothermal materials and applying an external control light source, the microcavity size and refractive index are changed based on the photothermal effect, thereby changing the resonant mode and tuning the optical frequency comb. However, since the FSR of the microcavity is generally in the GHz to THz range, this hinders the tunability of the optical frequency comb. At present, the maximum tuning range of the microcavity optical frequency comb is less than 70% FSR, and comb tuning exceeding FSR has not yet been achieved.

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention is proposed. Summary of the invention

[0006] In view of the shortcomings of the traditional WGM microcavity optical frequency comb, the present invention provides an all-optical tunable controllable optical comb generation system and method based on a functionalized microbottle cavity. Its purpose is to reduce the FSR based on the unique axial characteristics of the WGM microbottle cavity, and use the photothermal material titanium dioxide to achieve significant tuning of the microcavity optical frequency comb spectrum through all-optical tuning.

[0007] To achieve the above purpose, the technical solution provided by the present invention is:

[0008] A functionalized WGM micro-bottle cavity all-optical tunable controllable optical comb generation system, comprising a 1550nm narrow linewidth continuous wave laser 1, a 1550nm single-mode optical fiber 2, an erbium-doped fiber amplifier 3, a polarization controller 4, an optical isolator 5, a functionalized micro-bottle cavity-fiber taper coupling system 6, an optical attenuator 7, an optical spectrum analyzer 8, and a 1550nm power adjustable laser 9;

[0009] The 1550nm narrow linewidth continuous wave laser 1 is used to output 1550nm tunable continuous laser to excite the functionalized microbottle cavity-fiber taper coupling system 6 to generate a microcavity optical frequency comb;

[0010] The erbium-doped fiber amplifier 3 is connected to the 1550nm narrow linewidth continuous wave laser 1 through the single-mode optical fiber 21, and is used to increase the power of the laser output by the 1550nm narrow linewidth continuous wave laser 1, so that the laser power coupled into the WGM microcavity is greater than the threshold of the microcavity optical frequency comb excitation;

[0011] The polarization controller 4 is connected to the erbium-doped fiber amplifier 3 via the optical fiber 22, and is used to adjust the polarization state of the laser input into the functionalized micro-bottle cavity-fiber taper coupling system 6;

[0012] The optical isolator 5 is connected to the polarization controller 4 through the optical fiber 23, and is used to isolate the reverse transmission light through the forward transmission light to prevent the reverse transmission light from damaging the instrument;

[0013] The functionalized microbottle cavity-fiber cone coupling system 6 comprises: a functionalized fiber WGM microbottle cavity and a fiber cone 62 .

[0014] Furthermore, the functionalized WGM optical fiber micro-bottle cavity includes a main micro-bottle cavity 60 and a secondary micro-cavity 61, and the photothermal material titanium dioxide is doped in the secondary micro-cavity 61. The secondary micro-cavity 61 is a spherical cavity, the purpose of which is to increase the doping area of ​​the photothermal material.

[0015] Furthermore, the method for preparing the functionalized WGM optical fiber microbottle cavity comprises the following steps:

[0016] The method for preparing the functionalized WGM optical fiber microbottle cavity comprises the following steps:

[0017] SⅠ. Take a section of single-mode G652D bare fiber, use a wire stripper to remove the coating, wipe it clean with alcohol, and use a fiber cleaver to cut the end of the fiber flat; weld the other end of the fiber to the fiber jumper;

[0018] SII, placing the cut optical fiber end in the above step S1 in an optical fiber fusion splicer; starting the optical fiber fusion splicer, and performing discharge treatment on the optical fiber end using a high-voltage arc; the optical fiber end is heated and melted, and microspheres are formed under the action of surface tension;

[0019] SⅢ, take another section of single-mode optical fiber G652D bare fiber, strip the coating layer of the optical fiber section, clean and cut it according to the steps in the above step SⅠ; then place the optical fiber end and the microsphere described in the above step SⅡ in the optical fiber fusion splicer at the same time, ensuring that the two are aligned and attached in a horizontal position; start the optical fiber fusion splicer, and use a high-voltage arc to discharge the microsphere and the optical fiber end; under the action of surface tension, a micro-bottle cavity structure is formed;

[0020] SIV, using a wire stripper to cut off one end of the fiber microbottle cavity that is not fused with the fiber jumper in the above step SIII, leaving a fiber rod of about 100 μm in length;

[0021] SⅤ, placing the vertical fiber fixture at the edge of the Z-axis lifting platform 1, and placing the main micro-bottle cavity on the vertical fiber fixture, wherein the fiber rod end described in step SⅣ above is facing downward, and the clamping position is at the fiber position above the fiber rod and the micro-bottle cavity; observing the micro-bottle cavity and the fiber rod through a microscope to ensure that the micro-bottle cavity is in the middle of the microscope imaging screen;

[0022] SVI, placing the glass slide containing the mixture of titanium dioxide powder and ultraviolet glue on another Z-axis lifting platform 2, so that the center of the glass slide is placed directly below the position described in step SⅠ above;

[0023] SVII, controlling the Z-axis lifting platform 2 described in step S2 to rise until the optical fiber rod is observed to be in full contact with the mixture described in step S6 on the microscope imaging screen;

[0024] SⅧ, controlling the Z-axis lifting platform 2 to descend until the optical fiber rod and the mixture are observed to be separated on the microscope imaging screen, and then fully irradiating the optical fiber rod with the mixture in the above step under an ultraviolet lamp;

[0025] SIX, placing the optical fiber microcavity in the above step SⅧ into the optical fiber fusion splicer again, wherein the middle part of the optical fiber rod is placed in the center of the electrode of the optical fiber fusion splicer; starting the optical fiber fusion splicer, the optical fiber rod is melted into a microsphere under the action of surface tension, wherein the microsphere is doped with the photothermal material titanium dioxide.

[0026] The fiber taper 62 is connected to the optical isolator 5 through the optical fiber 24. After the laser passes into the fiber taper, an evanescent field is generated in its waist cone region, and then the light is coupled into and out of the functionalized fiber WGM microbottle cavity through the evanescent field;

[0027] Further, the fiber taper waist diameter is 1.8 to 2.2 μm, preferably 2 μm, and the diameters at both ends are 125 μm;

[0028] Furthermore, it is necessary to couple the fiber cone 62 with the main micro-bottle cavity 60 in the functionalized fiber WGM micro-bottle cavity. The equatorial circumference of the main micro-bottle cavity 60 is contacted with the fiber cone 662 to stabilize the micro-cavity-fiber cone system and to allow light to better enter the main micro-bottle cavity 60. When light is transmitted into the main micro-bottle cavity 60 through the fiber cone 62, it will continue to be totally reflected on the inner wall of the cavity, and the light that meets the resonance wavelength of the WGM micro-cavity will be confined in the cavity.

[0029] Furthermore, the resonance condition of the main micro-bottle cavity 60 is:

[0030]

[0031] Where λ is the resonance wavelength of the microcavity, R is the equatorial radius of the microbottle cavity, and n neff is the effective refractive index of the micro-bottle cavity, m is the effective refractive index of the micro-bottle cavity, q is the axial quantum number of the micro-bottle cavity, which is related to the axial length of the micro-bottle cavity, △E m is the energy difference between energy levels;

[0032] Furthermore, due to the unique axial characteristics of the WGM microbottle cavity, there are two transmission modes for the optical signal in the WGM microbottle cavity: transmission along the inner wall of the equatorial circumference and axial spiral transmission. The existence of axial spiral transmission greatly increases the mode distribution in the cavity and reduces the FSR of the microbottle cavity. Compared with the microsphere cavity with the same radius, the FSR of the microbottle cavity is one order of magnitude smaller. This small axial FSR makes it easy for the WGM to achieve tuning within a FSR range;

[0033] Furthermore, the FSRs corresponding to the two WGM microbottle cavity light transmission modes are expressed as:

[0034]

[0035] Among them, FSR m is the free spectral range of the microbottle cavity when light is transmitted along the inner wall of the equatorial circumference, FSR q is the free spectral range of the microbottle cavity when light is transmitted in a spiral manner along the axial direction. λ0 is the input light wavelength, △k is the curvature of the microbottle cavity;

[0036] Further, when the optical power transmitted into the main microbottle cavity 60 is higher than the microcavity optical frequency comb excitation threshold and meets the threshold, the microcavity optical frequency comb can be generated by scanning the wavelength of the narrow linewidth continuous wave laser from the blue detuning region to the red detuning region of the resonant mode of the microcavity;

[0037] Furthermore, since the WGM micro-bottle cavity has a rich mode distribution, a micro-cavity optical frequency comb can be generated by directly and continuously manually increasing the wavelength of the narrow linewidth continuous wave laser 1. And multiple scans can repeatedly generate the same micro-cavity optical frequency comb at the same wavelength;

[0038] Furthermore, due to the unique axial characteristics of the WGM micro-bottle cavity, the WGM micro-bottle cavity has an axial resonance mode with a smaller FSR. Therefore, compared with the microsphere cavity with the same radius, the WGM micro-bottle cavity can excite an axial mode microcavity optical frequency comb with a smaller FSR.

[0039] The optical attenuator 7 is connected to the optical fiber cone 62 via the optical fiber 25, and is used to attenuate the optical power transmitted from the functionalized optical fiber WGM micro-bottle cavity to the optical fiber cone 60, thereby protecting the optical spectrum analyzer 8;

[0040] The optical spectrum analyzer 8 is connected to the optical attenuator 7 via the optical fiber 26, and is used to receive the light transmitted from the functionalized optical fiber WGM microbottle cavity and measure the spectrum information;

[0041] The 1550nm power adjustable laser 9 is connected to the functionalized fiber WGM microbottle cavity through the optical fiber 27, and is used to generate power adjustable laser to excite the titanium dioxide to generate heat, change the temperature of the microcavity, and then change the resonant wavelength of the microcavity;

[0042] Furthermore, the change of temperature will affect the radius and refractive index of the microcavity. The effect of temperature on the radius and refractive index of the microcavity can be expressed as:

[0043]

[0044] Wherein, α is the thermo-optic coefficient of the microcavity material; β is the thermal expansion coefficient of the microcavity material;

[0045] Furthermore, changes in the radius and refractive index of the microcavity will cause changes in the resonant wavelength of the microcavity. The change in the resonant wavelength can be expressed as:

[0046]

[0047] Right now:

[0048] dλ=λ(α+β)dT (7)

[0049] Furthermore, gradually increasing the laser power of the 1550nm power adjustable laser 9 will gradually increase the temperature of the microcavity, and at this time, the resonance wavelength of the microcavity will gradually redshift;

[0050] Furthermore, after the axial mode microcavity optical frequency comb is excited, the laser power of the 1550nm power adjustable laser 9 is increased to redshift the resonance wavelength of the microbottle cavity. At this time, the output laser wavelength of the 1550nm narrow linewidth continuous wave laser 1 is increased to align the pump wavelength with the resonance wavelength after the redshift, so that the same axial mode microcavity optical frequency comb as that when not tuned can be generated;

[0051] Furthermore, since the FSR of the axial mode microcavity optical frequency comb is one order of magnitude smaller than that of the equatorial azimuthal mode microcavity optical frequency comb, the spectral tuning range exceeding the FSR can be achieved by tuning the axial mode optical frequency comb.

[0052] The present invention also provides a method for generating an all-optically tunable controllable light comb based on a functionalized micro-bottle cavity, comprising the following steps:

[0053] Sa, system construction;

[0054] Build an all-optical tunable and controllable light comb generation system based on a functionalized micro-bottle cavity as described in claims 1-3, comprising a narrow linewidth laser 1, an erbium-doped fiber amplifier 3, a polarization controller 4, an optical isolator 5, a functionalized micro-bottle cavity-fiber taper coupling system 6, an optical attenuator 7, a spectrum analyzer 8, and a 1550nm power adjustable laser 9, which are sequentially connected by a 1550nm single-mode optical fiber to form an optical path;

[0055] Sb, turn on the narrow linewidth continuous wave laser 1 to output 1550nm laser, which is amplified by the erbium-doped fiber amplifier 3; when the light enters the fiber cone 62 of the functionalized microbottle cavity-fiber cone coupling system 6, it is coupled into and out of the functionalized WGM microbottle resonant cavity at the waist cone position through the evanescent field; then, the light is connected to the spectrum analyzer 8 through the attenuator 7; at this time, only the 1550nm pump light spectrum can be observed on the spectrum analyzer 8;

[0056] Sc, continuously increase the wavelength of the narrow linewidth continuous wave laser 1 in steps of 0.1 nm wavelength until a stable microcavity optical frequency comb is observed on the spectrum analyzer 8, and record the wavelength of light generated by the optical frequency comb for repeated tuning to generate the optical frequency comb; the tuning range of the laser wavelength of the narrow linewidth continuous wave laser 1 is 1550 nm-1570 nm; repeat the scan until the generation of a small free spectral range axial mode microcavity optical frequency comb is observed on the spectrum analyzer 8;

[0057] Sd, when the existence of the axial mode microcavity optical frequency comb is observed on the spectrum analyzer 8, the 1550nm power adjustable laser 9 is turned on, and the power of the laser 9 is increased in steps of 10mW. At each power, the wavelength of the narrow linewidth continuous wave laser 1 is increased in steps of 0.001nm until the generation of an optical frequency comb with the same FSR as the free spectrum range of the initial axial mode microcavity optical frequency comb is observed;

[0058] Se. Continue to repeat step Sd until the tuning range of the optical frequency comb exceeds the free spectrum range.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] 1. Prepare the WGM micro-bottle cavity based on the fiber fusion machine and prepare microspheres doped with titanium dioxide at one end of the micro-bottle cavity. The presence of titanium dioxide-doped microspheres ensures that the photothermal material doping content is high enough to fully stimulate the photothermal effect, while also ensuring that the photothermal material content will not decrease over a long period of time. Therefore, the micro-cavity device has stable all-optical tuning performance over a long period of time;

[0061] 2. Based on the unique advantages of the WGM micro-bottle cavity, an axial mode micro-cavity optical frequency comb with a smaller FSR is generated for micro-cavity optical comb spectrum tuning, which can tune the resonant mode beyond the FSR range, and thus achieve a comb tooth tuning range exceeding the mode spacing. This advantage makes the present invention applicable to optical communications, optical frequency synthesis and other fields;

[0062] 3. Based on the unique advantages of the WGM micro-bottle cavity, an axial mode micro-cavity optical frequency comb with a smaller FSR is generated. The all-optical tuning of the micro-cavity optical frequency comb requires lower laser power, which reduces the laser energy consumption required for tuning;

[0063] Terminology explanation:

[0064] WGM micro-bottle cavity is the abbreviation of whispering gallery mode optical micro-bottle cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0066] Figure 2 Schematic diagram of the fiber-optic WGM microbottle cavity;

[0067] Figure 3 This is the optical frequency comb spectrum of the micro-bottle cavity. DETAILED DESCRIPTION

[0068] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings.

[0069] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 1 As shown, a functionalized micro-bottle cavity all-optical tunable controllable light comb generation system of the present invention comprises a 1550nm narrow linewidth continuous wave laser 1, a 1550nm single-mode optical fiber 2, an erbium-doped fiber amplifier 3, a polarization controller 4, an optical isolator 5, a functionalized micro-bottle cavity-fiber taper coupling system 6, an optical attenuator 7, an optical spectrum analyzer 8 and a 1550nm power adjustable laser 9;

[0070] The 1550nm narrow linewidth continuous wave laser 1 is used to output 1550nm band tunable continuous laser to excite the WGM microcavity to generate a light comb;

[0071] The erbium-doped fiber amplifier 3 is connected to the 1550nm narrow linewidth continuous wave laser 1 through the optical fiber 21, and is used to increase the power of the output light of the 1550nm narrow linewidth continuous wave laser 1, so that the laser power coupled into the WGM microcavity is greater than the threshold of the microcavity light comb excitation;

[0072] The polarization controller 4 is connected to the erbium-doped fiber amplifier 3 via the optical fiber 22, and is used to keep the polarization state of light in the system constant;

[0073] The optical isolator 5 is connected to the polarization controller 4 through the optical fiber 23, and is used to allow the forward transmitted light to pass through and isolate the reverse transmitted light to prevent the reverse transmitted light from damaging the device;

[0074] The functionalized microbottle cavity-fiber cone coupling system 6 comprises: a functionalized fiber WGM microbottle cavity and a fiber cone 62 .

[0075] The functionalized WGM optical fiber micro-bottle cavity comprises a main micro-bottle cavity 60 and a secondary micro-cavity 61, wherein the photothermal material titanium dioxide is doped in the secondary micro-cavity 61. The secondary micro-cavity 61 is a spherical cavity, and the purpose is to increase the doping area of ​​the photothermal material.

[0076] The method for preparing the functionalized WGM optical fiber microbottle cavity comprises the following steps:

[0077] SⅠ. Take a section of single-mode G652D bare fiber, use a wire stripper to remove the coating, wipe it clean with alcohol, and use a fiber cleaver to cut the end of the fiber flat; weld the other end of the fiber to the fiber jumper;

[0078] SII, placing the cut optical fiber end in the above step S1 in an optical fiber fusion splicer; starting the optical fiber fusion splicer, and performing discharge treatment on the optical fiber end using a high-voltage arc; the optical fiber end is heated and melted, and microspheres are formed under the action of surface tension;

[0079] SⅢ, take another section of single-mode optical fiber G652D bare fiber, strip the coating layer of the optical fiber section, clean and cut it according to the steps in the above step SⅠ; then place the optical fiber end and the microsphere described in the above step SⅡ in the optical fiber fusion splicer at the same time, ensuring that the two are aligned and attached in a horizontal position; start the optical fiber fusion splicer, and use a high-voltage arc to discharge the microsphere and the optical fiber end; under the action of surface tension, a micro-bottle cavity structure is formed;

[0080] SIV, using a wire stripper to cut off one end of the fiber microbottle cavity that is not fused with the fiber jumper in the above step SIII, leaving a fiber rod of about 100 μm in length;

[0081] SⅤ, placing the vertical fiber fixture at the edge of the Z-axis lifting platform 1, and placing the main micro-bottle cavity on the vertical fiber fixture, wherein the fiber rod end described in step SⅣ above is facing downward, and the clamping position is at the fiber position above the fiber rod and the micro-bottle cavity; observing the micro-bottle cavity and the fiber rod through a microscope to ensure that the micro-bottle cavity is in the middle of the microscope imaging screen;

[0082] SVI, placing the glass slide containing the mixture of titanium dioxide powder and ultraviolet glue on another Z-axis lifting platform 2, so that the center of the glass slide is placed directly below the position described in step SⅠ above;

[0083] SVII, controlling the Z-axis lifting platform 2 described in step S2 to rise until the optical fiber rod is observed to be in full contact with the mixture described in step S6 on the microscope imaging screen;

[0084] SⅧ, controlling the Z-axis lifting platform 2 to descend until the optical fiber rod and the mixture are observed to be separated on the microscope imaging screen, and then fully irradiating the optical fiber rod with the mixture in the above step under an ultraviolet lamp;

[0085] SIX, placing the optical fiber microcavity in the above step SⅧ into the optical fiber fusion splicer again, wherein the middle part of the optical fiber rod is placed in the center of the electrode of the optical fiber fusion splicer; starting the optical fiber fusion splicer, the optical fiber rod is melted into a microsphere under the action of surface tension, wherein the microsphere is doped with the photothermal material titanium dioxide.

[0086] The fiber taper 62 is connected to the optical isolator 5 through the optical fiber 24. After the laser passes into the fiber taper, an evanescent field is generated in its waist cone region, and then the light is coupled into and out of the functionalized fiber WGM microbottle cavity through the evanescent field;

[0087] The fiber taper waist diameter is 1.8 to 2.2 μm, preferably 2 μm, and the diameters at both ends are 125 μm;

[0088] It is necessary to couple the fiber cone 62 with the main micro-bottle cavity 60 in the functionalized fiber WGM micro-bottle cavity. The equatorial circumference of the main micro-bottle cavity 60 is contacted with the fiber cone 62 to stabilize the micro-cavity-fiber cone system and to allow light to better enter the main micro-bottle cavity 60. When light is transmitted into the main micro-bottle cavity 60 through the fiber cone 62, it will continue to be totally reflected on the inner wall of the cavity, and the light that meets the resonance wavelength of the WGM micro-cavity will be confined in the cavity.

[0089] The resonance condition of the main micro-bottle cavity 60 is:

[0090]

[0091] Where λ is the resonance wavelength of the microcavity, R is the equatorial radius of the microbottle cavity, and n neff is the effective refractive index of the micro-bottle cavity, m is the effective refractive index of the micro-bottle cavity, q is the axial quantum number of the micro-bottle cavity, which is related to the axial length of the micro-bottle cavity, △Em is the energy difference between energy levels;

[0092] Due to the unique axial characteristics of the WGM microbottle cavity, there are two ways for the light signal to be transmitted in the WGM microbottle cavity: transmission along the inner wall of the equatorial circumference and axial spiral transmission. The existence of axial spiral transmission greatly increases the mode distribution in the cavity and reduces the FSR of the microbottle cavity. Compared with the microsphere cavity with the same radius, the FSR of the microbottle cavity is one order of magnitude smaller. This small axial FSR makes it easy for the WGM to achieve tuning within a FSR range.

[0093] The FSRs corresponding to the two WGM microbottle cavity light transmission modes are expressed as:

[0094]

[0095] Among them, FSR m is the free spectral range of the microbottle cavity when light is transmitted along the inner wall of the equatorial circumference, FSR q is the free spectral range of the microbottle cavity when light is transmitted in a spiral manner along the axial direction. λ0 is the input light wavelength, △k is the curvature of the microbottle cavity;

[0096] When the optical power transmitted into the main microbottle cavity 60 is higher than the microcavity optical frequency comb excitation threshold and meets the requirement, a microcavity optical frequency comb can be generated by scanning the wavelength of a narrow linewidth continuous wave laser from the blue detuning region to the red detuning region of the resonant mode of the microcavity;

[0097] Since the WGM micro-bottle cavity has a rich mode distribution, the micro-cavity optical frequency comb can be generated by directly and continuously manually increasing the wavelength of the narrow linewidth continuous wave laser 1. And multiple scans can repeatedly generate the same micro-cavity optical frequency comb at the same wavelength;

[0098] Due to the unique axial characteristics of the WGM micro-bottle cavity, the WGM micro-bottle cavity has an axial resonance mode with a smaller FSR. Therefore, compared with the microsphere cavity with the same radius, the WGM micro-bottle cavity can excite an axial mode micro-cavity optical frequency comb with a smaller FSR.

[0099] The optical attenuator 7 is connected to the optical fiber cone 62 via the optical fiber 25, and is used to attenuate the optical power transmitted from the microcavity to the optical fiber cone 62, thereby protecting the optical spectrum analyzer 8;

[0100] The optical spectrum analyzer 8 is connected to the optical attenuator 7 via the optical fiber 26, and is used to receive the light transmitted from the functionalized optical fiber WGM microbottle cavity and measure the spectrum information;

[0101] The 1550nm power adjustable laser 9 is connected to the functionalized fiber WGM microbottle cavity through the optical fiber 27, and is used to generate power adjustable laser to excite the titanium dioxide to generate heat, change the temperature of the microcavity, and then change the resonant wavelength of the microcavity;

[0102] Generally, a microcavity optical frequency comb can be generated by scanning the wavelength of a narrow linewidth continuous wave laser from the blue detuning region to the red detuning region of the first resonant mode of the microcavity. Since the WGM microbottle cavity has a rich mode distribution, a microcavity optical frequency comb can be generated by directly and continuously increasing the wavelength of the narrow linewidth continuous wave laser 1 manually, and multiple scans can repeatedly generate the same microcavity optical frequency comb at the same wavelength. And compared with the microsphere cavity with the same radius, the WGM microbottle cavity can excite an axial mode microcavity optical frequency comb with a smaller FSR.

[0103] The present invention provides a method for generating an all-optically tunable controllable optical frequency comb based on a functionalized micro-bottle cavity. The steps of generating and tuning the micro-cavity optical frequency comb are as follows:

[0104] Sa, system construction;

[0105] Build an all-optical tunable and controllable light comb generation system based on a functionalized micro-bottle cavity as described in claims 1-3, comprising a narrow linewidth laser 1, an erbium-doped fiber amplifier 3, a polarization controller 4, an optical isolator 5, a functionalized micro-bottle cavity-fiber taper coupling system 6, an optical attenuator 7, a spectrum analyzer 8, and a 1550nm power adjustable laser 9, which are sequentially connected by a 1550nm single-mode optical fiber to form an optical path;

[0106] Sb, turn on the narrow linewidth continuous wave laser 1 to output 1550nm laser, which is amplified by the erbium-doped fiber amplifier 3; when the light enters the fiber cone 62 of the functionalized microbottle cavity-fiber cone coupling system 6, it is coupled into and out of the functionalized WGM microbottle resonant cavity at the waist cone position through the evanescent field; then, the light is connected to the spectrum analyzer 8 through the attenuator 7; at this time, only the 1550nm pump light spectrum can be observed on the spectrum analyzer 8;

[0107] Sc, continuously increase the wavelength of the narrow linewidth continuous wave laser 1 in steps of 0.1 nm wavelength until a stable microcavity optical frequency comb is observed on the spectrum analyzer 8, and record the wavelength of light generated by the optical frequency comb for repeated tuning to generate the optical frequency comb; the tuning range of the laser wavelength of the narrow linewidth continuous wave laser 1 is 1550 nm-1570 nm; repeat the scan until the generation of a small free spectral range axial mode microcavity optical frequency comb is observed on the spectrum analyzer 8;

[0108] Sd, when the existence of the axial mode microcavity optical frequency comb is observed on the spectrum analyzer 8, the 1550nm power adjustable laser 9 is turned on, and the power of the laser 9 is increased in steps of 10mW. At each power, the wavelength of the narrow linewidth continuous wave laser 1 is increased in steps of 0.001nm until the generation of an optical frequency comb with the same FSR as the free spectrum range of the initial axial mode microcavity optical frequency comb is observed;

[0109] Se. Continue to repeat step Sd until the tuning range of the optical frequency comb exceeds the free spectrum range.

[0110] In summary, the method for generating an all-optically tuned controllable optical comb based on a functionalized microbottle cavity of the present invention is based on the unique axial transmission mode of the WGM microbottle cavity, which greatly reduces the FSR of the microcavity, generates an axial mode microcavity optical frequency comb with a small FSR, and tunes the generated axial mode microcavity optical frequency comb by an all-optical tuning method, which can achieve spectral tuning beyond the FSR range. The present invention proposes a method for preparing a functionalized microbottle cavity, including a main microbottle cavity and a sub-cavity. By doping photothermal materials into the sub-cavity, the quality factor of the main microbottle cavity will not be reduced, and while ensuring a high doping content of the photothermal material, efficient excitation of the photothermal effect is achieved, ensuring that the microcavity device has stable all-optical tuning performance for a long time. The present invention solves the limitation that the WGM microcavity optical frequency comb cannot achieve wavelength tuning beyond the FSR, and is conducive to the practical application of microcavity optical frequency combs in the fields of optical communication, optical frequency synthesis, etc.

Claims

1. An all-optical tunable controllable light comb generation system based on a functionalized microbottle cavity, characterized in that: The invention comprises a 1550nm narrow linewidth continuous wave laser (1), an erbium-doped fiber amplifier (3), a polarization controller (4), an optical isolator (5), a functionalized WGM microbottle cavity-fiber taper coupling system (6), an optical attenuator (7), an optical spectrum analyzer (8), and a 1550nm power adjustable laser (9) externally connected to the functionalized microbottle cavity-fiber taper coupling system (6); wherein: The 1550nm narrow linewidth continuous wave laser (1) is used to output tunable continuous laser light in the 1550nm band to excite the WGM microbottle cavity to generate a light comb; The erbium-doped fiber amplifier (3) is connected to the 1550nm narrow linewidth continuous wave laser (1) via an optical fiber (21) and is used to increase the power of the output light of the 1550nm narrow linewidth continuous wave laser (1) so that the laser power coupled into the functionalized WGM microbottle cavity is greater than the threshold value of the functionalized WGM microbottle cavity light comb excitation; The polarization controller (4) is connected to the erbium-doped fiber amplifier (3) via an optical fiber (22) and is used to adjust the polarization state of the laser input into the functionalized WGM micro-bottle cavity-fiber taper coupling system (6) to keep the polarization state of the light in the system constant; The optical isolator (5) is connected to the polarization controller (4) via an optical fiber (23) and is used to allow forward-transmitted light to pass through while isolating reverse-transmitted light, thereby preventing the reverse-transmitted light from damaging the device. The functionalized WGM micro-bottle cavity comprises a main micro-bottle cavity (60) and a sub-micro-bottle cavity (61), wherein the sub-micro-bottle cavity (61) is doped with a photothermal material, titanium dioxide; the equatorial plane of the main micro-bottle cavity (60) of the functionalized optical fiber WGM micro-bottle cavity is in contact with the lumbar part of the optical fiber cone (62), which is used to stabilize the system and better couple the light of the evanescent field into the cavity; when light is transmitted through the optical fiber cone into the main micro-bottle cavity (60), it will continue to be totally reflected on the inner wall of the cavity, and the light that meets the resonance wavelength of the WGM micro-bottle will be confined in the cavity; The optical fiber cone (62) is connected to the optical isolator (5) through the optical fiber (24). After the laser passes into the optical fiber cone (62), an evanescent field is generated in the waist cone region thereof, and then the light is coupled into and out of the functionalized WGM micro-bottle through the evanescent field; The optical attenuator (7) is connected to the optical fiber cone (62) via the optical fiber (25) and is used to attenuate the optical power transmitted from the microcavity to the optical fiber cone (62) to protect the optical spectrum analyzer (8); The optical spectrum analyzer (8) is connected to the optical attenuator (7) via an optical fiber (26) and is used to receive the light transmitted from the functionalized optical fiber WGM microbottle cavity and measure the spectrum information; The 1550nm power adjustable laser (9) is connected to the functionalized optical fiber WGM microbottle cavity via an optical fiber (27) to generate power adjustable laser to excite the titanium dioxide (13) to generate heat and change the temperature of the microbottle.

2. According to claim 1, the all-optical tunable controllable light comb generation system based on functionalized micro-bottle cavity is characterized in that: The fiber taper has a waist diameter of 1.8 to 2.2 μm and a diameter of 125 μm at both ends, and is prepared by a fusion taper method.

3. The all-optical tunable controllable light comb generation system based on functionalized micro-bottle cavity according to claim 1 is characterized in that: Titanium dioxide particles of the photothermal material are melt-doped into the sub-cavity (61) of the functionalized WGM optical fiber micro-bottle cavity by an optical fiber fusion splicer; the preparation method of the functionalized WGM optical fiber micro-bottle cavity comprises the following steps: SⅠ. Take a section of single-mode optical fiber G652D bare fiber, use wire strippers to remove the coating layer, wipe it clean with alcohol and use a fiber optic cutter to cut the end of the fiber flat; the other end of the fiber is fused with the fiber jumper; SII, placing the cut optical fiber end in the above step S1 in an optical fiber fusion splicer; The optical fiber fusion splicer is started to discharge the optical fiber end with a high-voltage arc; the optical fiber end is melted by heat and forms microspheres under the action of surface tension; SⅢ, take another section of single-mode optical fiber G652D bare fiber, strip the coating layer of the optical fiber section, clean and cut it according to the steps in the above step SⅠ; then place the optical fiber end and the microsphere described in the above step SⅡ in the optical fiber fusion splicer at the same time, ensuring that the two are aligned and attached in a horizontal position; Start the optical fiber fusion splicer and use high-voltage arc to discharge the microspheres and the ends of the optical fibers; under the action of surface tension, a microbottle cavity structure is formed; SIV, using a wire stripper to cut off one end of the fiber microbottle cavity that is not fused with the fiber jumper in the above step SIII, leaving a fiber rod of about 100 μm in length; SⅤ, placing the vertical fiber fixture at the edge of the Z-axis lifting platform 1, and placing the main micro-bottle cavity on the vertical fiber fixture, wherein the fiber rod end described in step SⅣ above is facing downward, and the clamping position is at the fiber position above the fiber rod and the micro-bottle cavity; observing the micro-bottle cavity and the fiber rod through a microscope to ensure that the micro-bottle cavity is in the middle of the microscope imaging screen; SVI, placing the glass slide containing the mixture of titanium dioxide powder and ultraviolet glue on another Z-axis lifting platform 2, so that the center of the glass slide is placed directly below the position described in step SⅠ above; SVII, controlling the Z-axis lifting platform 2 described in step S2 to rise until the optical fiber rod is observed to be in full contact with the mixture described in step S6 on the microscope imaging screen; SⅧ, controlling the Z-axis lifting platform 2 to descend until the optical fiber rod and the mixture are observed to be separated on the microscope imaging screen, and then fully irradiating the optical fiber rod with the mixture in the above step under an ultraviolet lamp; SIX, placing the optical fiber microcavity in the above step SⅧ into the optical fiber fusion splicer again, wherein the middle part of the optical fiber rod is placed in the center of the electrode of the optical fiber fusion splicer; starting the optical fiber fusion splicer, the optical fiber rod is melted into a microsphere under the action of surface tension, wherein the microsphere is doped with the photothermal material titanium dioxide.

4. A method for generating an all-optically tunable controllable light comb based on a functionalized microbottle cavity as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Sa, system construction; Constructing an all-optical tunable and controllable light comb generation system based on a functionalized microbottle cavity as described in claims 1-3, comprising a narrow linewidth laser (1) connected in an optical path in sequence through a 1550nm single-mode optical fiber, an erbium-doped fiber amplifier (3), a polarization controller (4), an optical isolator (5), a functionalized microbottle cavity-fiber taper coupling system (6), an optical attenuator (7), a spectrum analyzer (8), and a 1550nm power tunable laser (9); Sb, turning on the narrow linewidth continuous wave laser (1) to output 1550nm laser light, which is amplified by the erbium-doped fiber amplifier (3); when the light enters the fiber cone (62) of the functionalized microbottle cavity-fiber cone coupling system (6), it is coupled into and out of the functionalized WGM microbottle resonant cavity at the waist cone position through the evanescent field; Afterwards, the light is connected to the spectrum analyzer (8) through the attenuator (7); at this time, only the pump light spectrum of 1550nm can be observed on the spectrum analyzer (8); Sc, continuously increasing the wavelength of the narrow linewidth continuous wave laser (1) in steps of 0.1 nm wavelength until a stable microcavity optical frequency comb is observed on the spectrum analyzer (8), and recording the wavelength of light generated by the optical frequency comb for repeated tuning to generate the optical frequency comb; the laser wavelength tuning range of the narrow linewidth continuous wave laser (1) is 1550 nm-1570 nm; repeatedly scanning until the generation of a small free spectral range axial mode microcavity optical frequency comb is observed on the spectrum analyzer (8); Sd, when the existence of the axial mode microcavity optical frequency comb is observed on the spectrum analyzer (8), the 1550 nm power adjustable laser (9) is turned on, and the power of the laser (9) is increased in steps of 10 mW. At each power, the wavelength of the narrow linewidth continuous wave laser (1) is increased in steps of 0.001 nm until an optical frequency comb with the same FSR as the free spectrum range of the initial axial mode microcavity optical frequency comb is observed; Se. Continue to repeat step Sd until the tuning range of the optical frequency comb exceeds the free spectrum range.

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