A method and system for generating an optical frequency comb based on photonic crystal coupled three-cavity

Abstract

The present invention discloses a method and system for generating an optical frequency comb based on a photonic crystal coupled three-cavity, comprising a photonic crystal thin plate, on which a first photonic crystal waveguide, a second photonic crystal waveguide, a third photonic crystal waveguide, a first photonic crystal microcavity, a second photonic crystal microcavity and a third photonic crystal microcavity are arranged; the photonic crystal microcavity adopted in the present invention has the characteristics of a large ratio between quality factor and mode volume, can enhance the nonlinear effect of quantum dots in the cavity, reduce the power consumption required for wavelength drift and has a smaller device size; the present invention performs modulation based on the principle of switching between a bright state and a dark state of a coupled three-cavity system, and can still maintain a high modulation depth when the microcavity quality factor is low, thereby ensuring that the flatness and the number of comb teeth of the optical frequency comb are not affected.

Description

Technical Field

[0001] The present invention relates to the field of optical frequency comb technology, and in particular to an optical frequency comb generation method and system based on photonic crystal coupled three-cavity. Background Art

[0002] An optical frequency comb is a laser signal with discrete and equally spaced frequency lines in the frequency domain, with a constant phase relationship between the frequency lines. In addition to its applications in precision frequency measurement, arbitrary waveform generation, and microwave signal generation, optical frequency combs can also replace laser arrays as multi-wavelength light sources for on-chip optical communication systems. When used as a light source for on-chip optical communication systems, the power consumption of the optical frequency comb, the tunability of the comb tooth spacing, and the device size all become issues that need to be considered.

[0003] The generation of optical frequency combs is mainly based on the following three approaches: 1. Using a mode-locked laser to generate an optical frequency comb. The comb teeth generated by this method can cover a spectrum range of tens of nanometers and have a very large number of comb teeth. However, the comb tooth spacing is small and cannot be adjusted. At the same time, the high cost and large size also make it unfavorable for integration. 2. Using the Kerr effect of a microring resonator to generate an optical frequency comb. Although it has the advantage of easy integration, the comb tooth spacing is determined by the size of the microcavity. The reduction in device size will cause the quality factor of the microcavity to decrease, while the comb tooth spacing increases to more than 100 GHz, and the adjustability of the comb tooth spacing is generally an integer multiple of the free spectrum range. 3. Using an electro-optical modulator to generate an optical frequency comb. Its system architecture and the principle of optical frequency comb generation are relatively simple, but this solution is often based on discrete modulators and uses optical fibers to interconnect devices, which is contrary to the requirements of integration and low power consumption.

[0004] Combining the second and third methods, using a photonic crystal microcavity as a modulator can achieve the generation of an optical frequency comb. The ratio of the quality factor of the photonic crystal microcavity to the mode volume is very large, which can enhance the nonlinear effect, reduce the power consumption of the device and improve the integration. On the other hand, since the comb tooth spacing is determined by the pump signal applied to the modulator, it also has the advantage of flexible and adjustable comb tooth spacing. Its working principle is to modulate the transmittance of the signal by moving the resonant wavelength of the cavity mode. However, when the quality factor of the microcavity is reduced, the modulation depth of the microcavity on the signal cannot be guaranteed, which may cause the flatness of the comb teeth to deteriorate, the number of comb teeth to decrease, and the required device power consumption to increase further.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the invention

[0006] In view of the above-mentioned defects of the prior art, the present invention provides a method and system for generating an optical frequency comb based on a photonic crystal coupled three-cavity, aiming to solve the problem that the quality of the optical frequency comb is affected by the reduction of the quality factor in the optical frequency comb generation method based on a microcavity modulator, while further reducing the power consumption of the device.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present application discloses an optical frequency comb generation system based on a photonic crystal coupled three-cavity, comprising a photonic crystal thin plate, on which a first photonic crystal waveguide, a second photonic crystal waveguide, a third photonic crystal waveguide and a coupled three-cavity system are arranged, wherein the coupled three-cavity system comprises a first photonic crystal microcavity, a second photonic crystal microcavity and a third photonic crystal microcavity;

[0009] The first photonic crystal waveguide is coupled to the first photonic crystal microcavity; the first photonic crystal microcavity, the third photonic crystal microcavity, the second photonic crystal waveguide, and the third photonic crystal waveguide are all coupled to the second photonic crystal microcavity;

[0010] The first photonic crystal waveguide is used to couple the pump light into the first photonic crystal microcavity; the second photonic crystal waveguide is used to couple the signal light into the second photonic crystal microcavity; the third photonic crystal waveguide is used to couple the modulated signal light out of the second photonic crystal microcavity;

[0011] The first photonic crystal microcavity and the third photonic crystal microcavity are provided with quantum dot aggregates for providing wavelength drift of the cavity mode.

[0012] Preferably, the photonic crystal thin plate is made of III-V semiconductor material.

[0013] Preferably, the quantum dot aggregate is a group III-V self-assembled quantum dot.

[0014] Preferably, the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are point defect type microcavities.

[0015] Preferably, the first photonic crystal waveguide, the second photonic crystal waveguide and the third photonic crystal waveguide are line defect type photonic crystal waveguides.

[0016] Preferably, the cavity mode wavelengths of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are the same, and the quality factors of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are the same.

[0017] Preferably, there is a detuning between the wavelength of the pump light and the cavity mode wavelengths of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity.

[0018] The present application also discloses a method for generating an optical frequency comb based on a photonic crystal coupled three-cavity, which specifically comprises the following steps:

[0019] S1, the pump light is coupled into the first photonic crystal microcavity through the first photonic crystal waveguide; and then coupled into the second photonic crystal microcavity and the third photonic crystal microcavity in sequence; the coupling effect between the microcavities enables the first photonic crystal microcavity and the third photonic crystal microcavity to establish cavity fields of the same magnitude and opposite signs;

[0020] S2. Due to the large ratio between the quality factor and the mode volume, the cavity field strength of the first photonic crystal microcavity and the third photonic crystal microcavity is enhanced, driving the evolution of the coherence term of the quantum dot aggregate;

[0021] S3. There is a detuning between the wavelength of the pump light and the cavity mode wavelengths of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity, which destroys the symmetry of the response evolution of the coherent term of the quantum dot aggregate. The cavity modes of the first photonic crystal microcavity and the third photonic crystal microcavity exhibit wavelength drifts of the same magnitude and opposite signs, causing the coupled three-cavity system to switch between the bright state and the dark state.

[0022] S4. The signal light is coupled into the second photonic crystal microcavity through the second photonic crystal waveguide, and then modulated into an optical frequency comb signal, and the optical frequency comb signal is coupled out of the second photonic crystal microcavity by the third photonic crystal waveguide.

[0023] Preferably, the comb tooth spacing of the optical frequency comb signal is equal to the microwave envelope frequency of the pump light.

[0024] Beneficial effects of the present invention:

[0025] 1. The photonic crystal microcavity used in the present invention has the characteristics of a large ratio between the quality factor and the mode volume, which can enhance the nonlinear effect of the quantum dots in the cavity, reduce the power consumption required to achieve wavelength drift, and has a smaller device size;

[0026] 2. The present invention performs modulation based on the principle of switching between the bright state and the dark state of the coupled three-cavity system. When the microcavity quality factor is low, it can still maintain a high modulation depth, ensuring that the flatness of the optical frequency comb and the number of comb teeth are not affected.

[0027] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of an optical frequency comb generation system based on photonic crystal coupled three-cavity according to the present invention;

[0029] Figure 2 is a schematic diagram of a specific embodiment of the present invention;

[0030] Figure 3 is a time domain and frequency domain response diagram of each signal in a specific embodiment of the present invention;

[0031] Figure 4 1 is a time domain response diagram and a frequency domain response diagram of the modulated signal light under different microcavity quality factors in the embodiment of the present invention;

[0032] In the figure: 1-first photonic crystal microcavity, 2-second photonic crystal microcavity, 3-third photonic crystal microcavity, 4-first photonic crystal waveguide, 5-second photonic crystal waveguide, 6-third photonic crystal waveguide. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0034] See also Figure 1 The present application discloses an optical frequency comb generation system based on a photonic crystal coupled three-cavity, including a photonic crystal thin plate, on which a first photonic crystal waveguide 4, a second photonic crystal waveguide 5, a third photonic crystal waveguide 6 and a coupled three-cavity system are provided, and the coupled three-cavity system includes a first photonic crystal microcavity 1, a second photonic crystal microcavity 2 and a third photonic crystal microcavity 3;

[0035] The first photonic crystal waveguide 4 is coupled to the first photonic crystal microcavity 1; the first photonic crystal microcavity 1, the third photonic crystal microcavity 3, the second photonic crystal waveguide 5, and the third photonic crystal waveguide 6 are all coupled to the second photonic crystal microcavity 2;

[0036] The first photonic crystal waveguide 4 is used to couple the pump light into the first photonic crystal microcavity 1; the second photonic crystal waveguide 5 is used to couple the signal light into the second photonic crystal microcavity 2; the third photonic crystal waveguide 6 is used to couple the modulated signal light out of the second photonic crystal microcavity 2;

[0037] The first photonic crystal microcavity 1 and the third photonic crystal microcavity 3 are provided with quantum dot aggregates for providing wavelength drift of cavity modes.

[0038] In a feasible embodiment, the material of the photonic crystal thin plate is a III-V semiconductor material.

[0039] In a feasible embodiment, the quantum dot aggregate is a III-V group self-assembled quantum dot.

[0040] In a feasible embodiment, the types of the first photonic crystal microcavity 1, the second photonic crystal microcavity 2 and the third photonic crystal microcavity 3 are point defect type microcavities.

[0041] In a feasible embodiment, the first photonic crystal waveguide 4, the second photonic crystal waveguide 5, and the third photonic crystal waveguide 6 are line defect type photonic crystal waveguides.

[0042] In a feasible embodiment, the cavity mode wavelengths of the first photonic crystal microcavity 1, the second photonic crystal microcavity 2 and the third photonic crystal microcavity 3 are the same, and the quality factors of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are the same.

[0043] In a feasible embodiment, there is a detuning between the wavelength of the pump light and the cavity mode wavelengths of the first photonic crystal microcavity 1 , the second photonic crystal microcavity 2 , and the third photonic crystal microcavity 3 .

[0044] Its working principle is as follows: when the pump light is coupled into the system through the first photonic crystal waveguide 4, the cavity fields established in the first photonic crystal microcavity 1 and the third photonic crystal microcavity 3 show the characteristics of the same size and opposite signs; due to the large ratio between the quality factor and the mode volume, the cavity field intensity of the photonic crystal microcavity is enhanced, thereby driving the evolution of the coherence term of the quantum dot aggregate; as the cavity field is established, the quantum dots absorb photons and transform from the ground state to the excited state, and the coherence term of the quantum dot aggregate is no longer 0, which will modulate the refractive index of the microcavity; and the detuning between the pump light and the cavity mode wavelength destroys the symmetry of the response of the coherence term of the quantum dot aggregate, so the cavity mode wavelengths of the first photonic crystal microcavity and the third photonic crystal microcavity respectively show detuning of opposite signs, which ultimately enables the coupled three-cavity system to switch between the bright state and the dark state and realize the modulation of the continuous wave signal, thereby realizing the generation of the optical frequency comb.

[0045] Example:

[0046] like Figure 2 As shown, the present invention provides an optical frequency comb generation system based on photonic crystal coupled three-cavity, and its system structure and generation method are as follows:

[0047] The pump light is a laser signal with a microwave envelope, and the frequency corresponding to the envelope is 2 GHz. The pump light can be generated by directly modulating the laser with a microwave signal with a frequency of 2 GHz or by modulating a continuous wave laser with a modulator.

[0048] The signal light is a continuous wave laser signal.

[0049] In the photonic crystal thin plate structure, the material of the thin plate is InP, and the quantum dot aggregates contained in the first photonic crystal microcavity 1 and the third photonic crystal microcavity 3 are self-organized and grown InAs quantum dots;

[0050] The first photonic crystal waveguide 4, the second photonic crystal waveguide 5 and the third photonic crystal waveguide 6 are line defect waveguides formed by removing holes;

[0051] The first photonic crystal microcavity 1, the second photonic crystal microcavity 2 and the third photonic crystal microcavity 3 are L3 cavities formed by removing three holes;

[0052] The first photonic crystal waveguide 4 is coupled with the first photonic crystal microcavity 1 to couple the pump light into the coupled three cavities.

[0053] The second photonic crystal waveguide 5 is coupled with the second photonic crystal microcavity 2 to couple the signal light into the coupled three cavities;

[0054] The third photonic crystal waveguide 6 is coupled to the second photonic crystal microcavity 2 to couple the modulated signal light out of the second photonic crystal microcavity 2 .

[0055] The coupling coefficient between the second photonic crystal microcavity 2 and the first photonic crystal microcavity 1 is equal to the coupling coefficient between the second photonic crystal microcavity 2 and the third photonic crystal microcavity 3;

[0056] The coupling coefficient between the first photonic crystal microcavity 1 and the first photonic crystal waveguide 4, the coupling coefficient between the second photonic crystal microcavity 2 and the second photonic crystal waveguide 5, and the coupling coefficient between the second photonic crystal microcavity 2 and the third photonic crystal waveguide 6 are equal.

[0057] The first photonic crystal microcavity 1 , the second photonic crystal microcavity 2 and the third photonic crystal microcavity 3 have the same cavity mode wavelength and the same quality factor.

[0058] The frequency corresponding to the pump light envelope is set to 2GHz, the cavity mode wavelength of the photonic crystal microcavity is 1551nm, the coupling coefficient between microcavities is 1THz, and the coupling coefficient between microcavity and waveguide is 0.1THz. The wavelength of the pump light is equal to the central wavelength of the quantum dot collection, both 1550nm, and the wavelength of the signal light is 1551nm.

[0059] Thanks to the large ratio between the quality factor and the mode volume of the photonic crystal microcavity and the resonant nonlinear effect provided by the quantum dot aggregate, the pump light power applied in the modulation process is less than 1mW, which is much smaller than the power consumption required by the microcavity optical frequency comb (tens of mW).

[0060] As the pump light is coupled from the first photonic crystal waveguide 4 into the first photonic crystal microcavity 1, the coupling effect between the microcavities enables the first photonic crystal microcavity 1 and the third photonic crystal microcavity 3 to establish cavity fields of the same magnitude and opposite signs, and causes the cavity modes of the first photonic crystal microcavity 1 and the third photonic crystal microcavity 3 to exhibit wavelength drifts of the same magnitude and opposite signs.

[0061] When the wavelength shift is 0, the system is in a dark state, the signal light is completely turned off, and its transmittance is 0.

[0062] When the wavelength drift is not 0, the system is in a bright state and the transmittance of the signal light is not 0.

[0063] The periodic envelope of the pump light is loaded onto the wavelength drift of the microcavity, the system switches between the bright state and the dark state, and the periodic envelope is loaded onto the signal light, eventually forming an optical frequency comb. During the modulation process, the time domain response diagram of the pump light, the time domain response diagram of the signal light, and the time domain response and frequency domain response diagram of the modulated signal light are shown in Figure 1. Figure 3 (a) Figure 3 (b) Figure 3 (c) Figure 3 As shown in (d) in .

[0064] The coupled three-cavity system uses a high coupling coefficient between the microcavities to ensure that the system still has a high modulation depth for the signal light when the quality factor of the photonic crystal microcavity is reduced, thereby ensuring that the flatness of the optical frequency comb and the number of comb teeth are almost unaffected. The time domain response diagram and frequency domain response diagram of the modulated signal light under different quality factors of the microcavity are shown in Figure 2. Figure 4 As shown: When the microcavity quality factor of the photonic crystal coupled three-cavity system is 5000, the time domain response diagram and frequency domain response diagram of the modulated signal light correspond to Figure 4 (a) Figure 4 (b) in the photonic crystal coupled three-cavity system. When the microcavity quality factor is 1800, the time domain response diagram and frequency domain response diagram of the modulated signal light correspond to Figure 4 (c) Figure 4 (d) in.

[0065] It can be seen that when the quality factor of the photonic crystal microcavity decreases, the flatness and the number of comb teeth of the optical frequency comb generated by the coupled three-cavity system are almost unaffected.

[0066] It can be seen from this embodiment that the present invention has the following advantages:

[0067] 1. The photonic crystal microcavity used in the present invention has the characteristics of a large ratio between quality factor and mode volume, can enhance the nonlinear effect of quantum dots in the cavity, reduce the power consumption required to achieve wavelength drift and has a smaller device size.

[0068] 2. The present invention performs modulation based on the principle of switching between the bright state and the dark state of the coupled three-cavity system. When the microcavity quality factor is low, the modulation depth can still be maintained high, ensuring that the flatness and the number of comb teeth of the optical frequency comb are not affected.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An optical frequency comb generation system based on a photonic crystal coupled three-cavity, comprising a photonic crystal plate, characterized in that: The photonic crystal plate is provided with a first photonic crystal waveguide, a second photonic crystal waveguide, a third photonic crystal waveguide and a coupled three-cavity system, wherein the coupled three-cavity system comprises a first photonic crystal microcavity, a second photonic crystal microcavity and a third photonic crystal microcavity; The first photonic crystal waveguide is coupled to the first photonic crystal microcavity; the first photonic crystal microcavity, the third photonic crystal microcavity, the second photonic crystal waveguide, and the third photonic crystal waveguide are all coupled to the second photonic crystal microcavity; The first photonic crystal waveguide is used to couple the pump light into the first photonic crystal microcavity; the second photonic crystal waveguide is used to couple the signal light into the second photonic crystal microcavity; the third photonic crystal waveguide is used to couple the modulated signal light out of the second photonic crystal microcavity; The first photonic crystal microcavity and the third photonic crystal microcavity are provided with quantum dot aggregates for providing wavelength drift of the cavity mode.

2. The optical frequency comb generation system based on photonic crystal coupled three-cavity as claimed in claim 1, characterized in that: The material of the photonic crystal thin plate is III-V group semiconductor material.

3. The optical frequency comb generation system based on photonic crystal coupled three-cavity as claimed in claim 1, characterized in that: The quantum dot aggregate is a group III-V self-assembled quantum dot.

4. The optical frequency comb generation system based on photonic crystal coupled three-cavity as claimed in claim 1, characterized in that: The first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are point defect type microcavities.

5. The optical frequency comb generation system based on photonic crystal coupled three-cavity as claimed in claim 1, characterized in that: The first photonic crystal waveguide, the second photonic crystal waveguide and the third photonic crystal waveguide are line defect type photonic crystal waveguides.

6. The optical frequency comb generation system based on photonic crystal coupled three-cavity as claimed in claim 1, characterized in that: The cavity mode wavelengths of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are the same, and the quality factors of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity are the same.

7. The optical frequency comb generation system based on photonic crystal coupled three-cavity as claimed in claim 1, characterized in that: There is a detuning between the wavelength of the pump light and the wavelengths of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity.

8. A method for generating an optical frequency comb based on a photonic crystal coupled three-cavity, characterized in that: The specific steps include: S1, the pump light is coupled into the first photonic crystal microcavity through the first photonic crystal waveguide; and then coupled into the second photonic crystal microcavity and the third photonic crystal microcavity in sequence; the coupling effect between the microcavities enables the first photonic crystal microcavity and the third photonic crystal microcavity to establish cavity fields of the same magnitude and opposite signs; S2. Due to the large ratio between the quality factor and the mode volume, the cavity field strength of the first photonic crystal microcavity and the third photonic crystal microcavity is enhanced, driving the evolution of the coherence term of the quantum dot aggregate; S3. There is a detuning between the wavelength of the pump light and the wavelengths of the first photonic crystal microcavity, the second photonic crystal microcavity and the third photonic crystal microcavity, which destroys the symmetry of the response evolution of the coherent term of the quantum dot aggregate. The cavity modes of the first photonic crystal microcavity and the third photonic crystal microcavity present wavelength drifts of the same magnitude and opposite signs. The periodic envelope of the pump light is loaded onto the wavelength drift, so that the coupled three-cavity system switches between the bright state and the dark state. S4. After the signal light is coupled into the second photonic crystal microcavity through the second photonic crystal waveguide, the periodic envelope is loaded onto the signal light, modulating the signal light into an optical frequency comb signal, and the optical frequency comb signal is coupled out of the second photonic crystal microcavity by the third photonic crystal waveguide.

9. The method for generating an optical frequency comb based on a photonic crystal coupled three-cavity as claimed in claim 8, characterized in that: The comb tooth interval of the optical frequency comb signal is equal to the microwave envelope frequency of the pump light.

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