Electro-optical modulator and electro-optical modulation method

Abstract

This invention relates to the field of optical communication, providing an electro-optic modulator and electro-optic modulation method, comprising: an optical input interface, a first nanocavity connected to the optical input interface, a second nanocavity coupled to the first nanocavity, and an optical output interface connected to the second nanocavity; wherein, the first nanocavity has a first PN junction, and the second nanocavity has a second PN junction, the first PN junction and the second PN junction being used to adjust the coupling between the first nanocavity and the second nanocavity after a single-ended push-pull electrode is applied, thereby controlling the intensity of light output from the optical output interface. This invention, by energizing two waveguides to adjust the coupling between the resonant cavities, controls the output of light in the lower waveguide, thereby reducing waveguide scattering and modulator size, achieving a high Q value, and realizing frequency selection.

Description

Technical Field

[0001] This invention relates to the field of optical communication based on integrated optics, and more particularly to silicon-based integrated electro-optic modulators based on coupling modulation. Background Technology

[0002] Silicon-based photonic devices possess advantages such as high bandwidth, high speed, and compatibility with traditional microelectronic processes, enabling excellent optoelectronic integration. Therefore, silicon-based optoelectronics has developed rapidly as an emerging discipline and plays a crucial role in the field of communications. Among these, silicon-based modulators, as the core device for electro-optic conversion, have received extensive research. In silicon-based modulators, an external electric field is typically applied to alter the carrier concentration in the silicon waveguide, thereby changing the waveguide's refractive index and absorption coefficient, and ultimately altering the phase of the transmitted light. This phase change is then converted into a change in light intensity through interference structures or resonant cavity structures.

[0003] Common optical structures for electro-optic modulators include Mach-Zehnder interferometer (MZI) and microring resonator (MRR) types. In an MZI modulator, the incident light is split into two beams that enter the two waveguide arms of the MZI, and then the beams are combined and interfered with to form the output light. In an MRR modulator, the incident light enters a straight waveguide and is partially coupled into a microring. The optical field of the straight waveguide and the optical field coupled from the microring into the straight waveguide interfere with each other to form the output light field. Existing silicon-based integrated electro-optic modulators have relatively low quality factors (Q), large waveguide scattering, large modulator size, and high power consumption. Summary of the Invention

[0004] The present invention provides an electro-optic modulator and an electro-optic modulation method. By energizing two waveguides to adjust the coupling between the resonant cavities, the output of light in the lower waveguide can be controlled to reduce waveguide scattering and modulator size, resulting in a high Q value and frequency selection function.

[0005] To address the aforementioned technical problems, this invention provides an electro-optic modulator, comprising: an optical input interface, a first nanocrystal connected to the optical input interface, a second nanocrystal coupled to the first nanocrystal, and an optical output interface connected to the second nanocrystal; wherein, the first nanocrystal has a first PN junction, and the second nanocrystal has a second PN junction, the first PN junction and the second PN junction being used to adjust the coupling between the first nanocrystal and the second nanocrystal after a single-ended push-pull electrode is applied, thereby controlling the intensity of light output from the optical output interface.

[0006] This invention also provides an electro-optic modulation method, comprising: emitting a laser to the optical input interface of the electro-optic modulator, allowing the laser to enter a first nano-beam cavity of the electro-optic modulator through the optical input interface; and energizing a first PN junction on the first nano-beam cavity and a second PN junction on a second nano-beam cavity of the electro-optic modulator through a single-ended push-pull electrode to obtain modulated light.

[0007] Compared to existing technologies, this invention provides an electro-optic modulator structure based on coupled modulated nanocavities. This structure includes two coupled nanocavity waveguides, with single-ended push-pull electrodes loaded on the two waveguides. By applying a voltage, the effective refractive index of each waveguide is changed, thereby adjusting the coupling between the resonant cavities and controlling the output ratio of light from the lower waveguide, thus achieving electro-optic coupling. Since the waveguides are two coupled nanocavities, waveguide scattering and modulator size can be reduced, resulting in a high Q value and frequency selection functionality. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of an electro-optic modulator according to the first embodiment;

[0009] Figure 2 This is a schematic diagram of an electro-optic modulator according to the second embodiment;

[0010] Figure 3 This is a schematic diagram of an electro-optic modulator according to the third embodiment;

[0011] Figure 4 The transmittance spectrum of the optical output port of the electro-optic modulator according to the third embodiment is shown without electrical modulation.

[0012] Figure 5 The transmittance spectrum of the optical output port of the electro-optic modulator according to the third embodiment under electrical modulation;

[0013] Figure 6 This is a flowchart of the electro-optic modulation method according to the fourth embodiment. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the various embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this invention to facilitate a better understanding of this application. However, the technical solutions claimed in this application can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0015] The first embodiment of the present invention relates to an electro-optic modulator, such as Figure 1As shown, the device includes an optical input port 101, an optical output port 113, a first nanocavity 114, and a second nanocavity 115 coupled to the first nanocavity 114. The first nanocavity 114 has a first PN junction 103, and the second nanocavity 115 has a second PN junction 108. The output end of the optical input port 101 is connected to the optical input end of the first nanocavity 114, and the optical output end of the second nanocavity 115 is connected to the optical output port 113.

[0016] The first nanocrystal 114 and the second nanocrystal 115 are formed by etching a series of air holes in a straight waveguide. The laser enters the nanocrystal through the light input port, and the light is reflected back and forth between the two nanocrystals to form a resonance.

[0017] After the first PN junction 103 and the second PN junction 108 are used to load a single-ended push-pull electrode, the coupling between the first nanocavity beam and the second nanocavity beam is adjusted to control the intensity of the light output from the optical output interface. Specifically, when no electrical modulation is applied, the first nanocavity beam 114 and the second nanocavity beam 115 are coupled while satisfying the phase matching condition; when electrical modulation is applied, the effective refractive index of the first nanocavity beam 114 and the second nanocavity beam 115 changes, and the phase matching modulation is no longer satisfied. The coupling between the first nanocavity beam 114 and the second nanocavity beam 115 weakens, and the light output at the optical output interface 113 weakens, thereby realizing the control of the light output by adjusting the coupling between the resonant cavities through electrical adjustment.

[0018] The first PN junction 103 and the second PN junction 108 are horizontal PN junctions. In other embodiments, other active PN junction structures, such as L-type PN junctions and U-type PN junctions, may also be used.

[0019] The optical input port 101 and the optical output port 113 are inverted conical couplers. In other embodiments, other structures with spot size conversion functions can also be used, such as grating couplers, cantilever beam couplers, double-layer conical structures, etc.

[0020] In the first embodiment of the present invention, compared with the prior art, a single-ended push-pull electrode is loaded onto the first PN junction 103 on the first nanocavity 114 and the second PN junction 108 on the second nanocavity 115. A voltage is applied to change the effective refractive index of the first nanocavity 114 and the second nanocavity 115, thereby adjusting the coupling between the first nanocavity 114 and the second nanocavity 115, controlling the output ratio of light from the second nanocavity 115, and achieving electro-optic modulation. Based on the coupled modulator of the two nanocavities, waveguide scattering and modulator size can be reduced, and a high Q value is achieved, enabling frequency selection.

[0021] The second embodiment of the present invention relates to an electro-optic modulator. The second embodiment is largely the same as the first embodiment, except that the electrical structure of the electro-optic modulator is improved in the second embodiment. Highly doped regions are provided on both sides of the first and second nano-beam cavities, and the electro-optic modulator includes metal electrodes.

[0022] like Figure 2 As shown, the electro-optic modulator in the second embodiment of the present invention includes: an optical input port 101, an optical output port 113, a first nanocrystal 114, a second nanocrystal 115, a first PN junction 103, a second PN junction 108, a first highly doped region 105, a second highly doped region 106, a third highly doped region 110, a first metal electrode 111, and a second metal electrode 112.

[0023] A first nano-beam cavity 114 and a second nano-beam cavity 115 are arranged side by side and coupled together. A first PN junction 103 is provided on the first nano-beam cavity 114, and a second PN junction 108 is provided on the second nano-beam cavity 115. A first highly doped region 105 is located on a first side of the first nano-beam cavity 114, which is the side away from the second nano-beam cavity 115. A second highly doped region 106 is located between the first nano-beam cavity 114 and the second nano-beam cavity 115. A third highly doped region 110 is located on a second side of the second nano-beam cavity 115, which is the side away from the first nano-beam cavity 114.

[0024] The output end of the optical input port 101 is connected to the optical input end of the first part 102 of the first nanocrystal 114, the optical output end of the first part 102 of the first nanocrystal 114 is connected to the optical input end of the first PN junction 103, and the optical output end of the first PN junction 103 is connected to the second part 104 of the first nanocrystal 114.

[0025] The output terminal of the first highly doped region 105 is connected to the input terminal of the first PN junction 103, and the output terminal of the first PN junction 103 is connected to the input terminal of the second highly doped region 106. The output terminal of the first metal electrode 111 is connected to the input terminals of the first highly doped region 105 and the third highly doped region 110, respectively.

[0026] The light output terminal of the first part 107 of the second nanocrystal 115 is connected to the light input terminal of the second PN junction 108, the light output terminal of the second PN junction 108 is connected to the light input terminal of the second part 109 of the second nanocrystal 115, and the light output terminal of the second part 109 of the second nanocrystal 115 is connected to the light output interface 113.

[0027] The output terminal of the third highly doped region 110 is connected to the input terminal of the second PN junction 108, and the output terminal of the second PN junction 108 is connected to the input terminal of the second highly doped region 106. The output terminal of the second metal electrode 112 is connected to the input terminal of the second highly doped region 106.

[0028] The first metal electrode 111 and the second metal electrode 112 are aluminum metal electrodes. In other embodiments, other metal electrodes, such as metals or alloys made of Au, Ag, Cu, etc., may also be used.

[0029] The first highly doped region 105 is a highly doped P++ region, the second highly doped region 106 is a highly doped N++ region, and the third highly doped region 110 is a highly doped P++ region. In other embodiments, any structure that can be achieved by highly doping silicon is acceptable.

[0030] When no modulation is applied, the first nanocavity 114 and the second nanocavity 115 are coupled while satisfying the phase-matching condition. When modulation is applied, the laser light enters the nanocavity through the optical input port, and the light resonates back and forth between the two nanocavities. The first highly doped region 105 and the third highly doped region 110 are used to receive the microwave signal forming the single-ended push-pull electrode. The two nanocavities are energized through the single-ended push-pull electrode. The second highly doped region 106 is used to receive the DC signal forming the single-ended push-pull electrode. The effective refractive index of the first nanocavity 114 and the second nanocavity 115 changes, and the phase-matching modulation is no longer satisfied. That is, the coupling between the first nanocavity 114 and the second nanocavity 115 weakens, and the output of the light at the optical output interface 113 weakens. This allows the output of the light to be controlled by adjusting the coupling between the resonant cavities through electrical adjustment. Moreover, in this embodiment, each highly doped region can form an ohmic contact when in contact with the metal electrode, reducing the resistance and minimizing losses.

[0031] The second embodiment of the present invention utilizes a first metal electrode 111 and a second metal electrode 112 to electrically modulate a first PN junction 103 and a second PN junction 108. Specifically, a single-ended push-pull electrode is loaded onto the first PN junction 103 on the first nanocavity 114 and the second PN junction 108 on the second nanocavity 115. By applying a voltage, the effective refractive index of the first nanocavity 114 and the second nanocavity 115 changes, thereby adjusting the coupling between the first nanocavity 114 and the second nanocavity 115 and controlling the output ratio of light from the second nanocavity 115, thus achieving electro-optic modulation. Using a coupled modulator based on two nanocavities can reduce waveguide scattering and modulator size, and the addition of highly doped regions can reduce power consumption.

[0032] The third embodiment of the present invention relates to an electro-optic modulator. The third embodiment is generally the same as the second embodiment, except that the optical structure of the electro-optic modulator is improved in the third embodiment.

[0033] like Figure 3 As shown, the electro-optic modulator includes an optical input port 101, an optical output port 113, a first nanocavity 114, and a second nanocavity 115 coupled to the first nanocavity 114. A first PN junction 103 is provided on the first nanocavity 114, and a second PN junction 108 is provided on the second nanocavity 115. The output end of the optical input port 101 is connected to the optical input end of the first nanocavity 114, and the optical output end of the second nanocavity 115 is connected to the optical output port 113. The first nanocavity 114 and the second nanocavity 115 are asymmetric nanocavities.

[0034] The width of the first and second nano-beam cavities can be 70 nm, the height of the cavities can be 220 nm, the gap between the two cavities can be 330 nm, the cavity length of the nano-beam cavities can be 3 μm, and the distance between the centers of adjacent air holes in the cavities, i.e., the period of the nano-beam cavities, can be 330 nm.

[0035] In the third embodiment, the asymmetric structure of the nanobeam cavity is achieved by changing parameters such as the number and diameter of the air pores within it. For example... Figure 3 As shown, the ratio of the number of air holes at both ends of the first nanobeam cavity 114 and the second nanobeam cavity 115 is 2:1; and the number of air holes at the end of the first nanobeam cavity 114 near the optical input interface 101 is less than the number of air holes at the end away from the optical input interface 101, and the number of air holes at the end of the second nanobeam cavity 115 near the optical output interface 113 is less than the number of air holes at the end away from the optical output interface 113.

[0036] For example, the first nanobeam cavity 114 has 10 air holes near the optical input interface 101 and 20 air holes away from the optical input interface 101; the second nanobeam cavity 115 has 10 air holes near the optical output interface 113 and 20 air holes away from the optical output interface 113.

[0037] For example, such as Figure 3As shown, the aperture of the air hole at the end of the first nanobeam cavity 114 near the optical input interface 101 gradually decreases from large to small in the direction towards the optical input interface 101; the aperture of the air hole at the end of the first nanobeam cavity 114 away from the optical input interface 101 gradually decreases from large to small in the direction away from the optical input interface; the aperture of the air hole at the end of the second nanobeam cavity 115 near the optical output interface 113 gradually decreases from large to small in the direction towards the optical output interface 113; the aperture of the air hole at the end of the second nanobeam cavity 115 away from the optical output interface 113 gradually decreases from large to small in the direction away from the optical output interface 113.

[0038] The gradual decrease in the aperture of the air holes in the first and second nanobeam cavities can be achieved by gradually varying the fill factor of the nanobeam cavities from 0.2 to 0.1. The fill factor is a parameter reflecting the area of ​​the air holes; the larger the air hole area, the larger the fill factor. In other embodiments, the nanobeam cavity can also be other structures with resonant functionality.

[0039] The first nanocavity 114 and the second nanocavity 115 consist of air holes with gradually varying apertures on both sides and a straight waveguide in the middle. The gradually varying air holes act as two mirrors to confine light, creating resonance in the middle, while the straight waveguide region in the middle supports the propagation mode. The structure of multiple air holes in the nanocavity reduces waveguide scattering.

[0040] In the third embodiment, due to the use of an asymmetric nanocrystal structure, the reflection of light in the right port of the first nanocrystal and the left port of the second nanocrystal is increased. Therefore, the output of light in the right port of the first nanocrystal and the left port of the second nanocrystal can be blocked, thereby effectively focusing the light in the nanocrystal. That is, the light is only output from the light output interface connected to the right port of the second nanocrystal.

[0041] When no electrical modulation is applied, energy is confined within the cavity through the resonance of the first and second nano-beam cavities. The first nano-beam cavity 114 and the second nano-beam cavity 115 satisfy the phase-matching condition, enabling light to be coupled from the first nano-beam cavity to the second nano-beam cavity. At this time, as... Figure 4 As shown, at the resonant point of 1548nm at the emission wavelength, the transmittance of the output port can reach 80%.

[0042] When modulation is applied, the first PN junction 103 and the second PN junction 108 are used to load the single-ended push-pull electrode. The effective refractive index of the first nanocavity 114 and the second nanocavity 115 changes, the phase matching condition is mismatched, the coupling between the first nanocavity 114 and the second nanocavity 115 weakens, and the light output at the light output interface 113 weakens. At this time, as... Figure 5 As shown, the transmittance drops to 15% near the resonant point of 1548 nm.

[0043] In the third embodiment, the number and aperture of the air holes can not only form an asymmetric nanobeam cavity and reduce light scattering, but also change the quality factor Q of the resonant cavity, thereby increasing the extinction ratio.

[0044] For example, the quality factor Q of the resonant cavity can be increased by increasing the number of air holes, increasing the size of the air hole diameter, or changing the fill factor of the nanobeam cavity.

[0045] In addition, the appropriate resonant wavelength can be adjusted by changing parameters such as the period and length of the nanocavity.

[0046] In the third embodiment, by energizing the two nanocavities, the coupling between the resonant cavities can be adjusted, thereby controlling the output of light in the lower waveguide. Using a nanocavity-based coupled modulator can reduce waveguide scattering and modulator size. Furthermore, by setting the parameters of the air aperture, the modulator can achieve a high Q value and frequency selection.

[0047] The fourth embodiment of the present invention relates to an electro-optic modulation method, applicable to the modulators in the above embodiments. For example... Figure 6 As shown, the electro-optic modulation method includes:

[0048] S101: Emit laser light to the optical input interface of the electro-optic modulator, so that the laser light enters the first nanobeam cavity of the electro-optic modulator through the optical input interface.

[0049] The laser light enters the nanobeam cavity through the light input port. The light light is reflected back and forth between the two nanobeam cavities to form a resonance. The first nanobeam cavity and the second nanobeam cavity are coupled together to meet the phase matching condition.

[0050] S102: The first PN junction on the first nano-beam cavity and the second PN junction on the second nano-beam cavity of the electro-optic modulator are energized by a single-ended push-pull electrode to obtain modulated light.

[0051] By applying a single-ended push-pull electrode and a voltage, the effective refractive index of the first and second nanocavities changes. The first and second nanocavities no longer satisfy phase-matched modulation, meaning the coupling between them weakens, and the light output at the optical output interface weakens. This allows for the control of light output by adjusting the coupling between the resonant cavities through electrical adjustment, achieving electro-optic modulation to reduce waveguide scattering and modulator size. Furthermore, the modulator can achieve a high Q value and frequency selection function by setting the parameters of the air hole.

[0052] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. An electro-optic modulator, characterized in that, include: An optical input interface, a first nanocrystal connected to the optical input interface, a second nanocrystal coupled to the first nanocrystal, and an optical output interface connected to the second nanocrystal; The first nano-beam cavity is provided with a first PN junction, and the second nano-beam cavity is provided with a second PN junction. The first PN junction and the second PN junction are used to adjust the coupling between the first nano-beam cavity and the second nano-beam cavity after a single-ended push-pull electrode is applied, thereby controlling the intensity of the light output from the light output interface.

2. The electro-optic modulator according to claim 1, characterized in that, The first nanobeam cavity and the second nanobeam cavity are arranged side by side, and the electro-optic modulator further includes: A first highly doped region located on a first side of the first nanobeam cavity; wherein, the first side is the side facing away from the second nanobeam cavity; The second highly doped region is located between the first nanobeam cavity and the second nanobeam cavity; A third highly doped region located on the second side of the second nanobeam cavity; wherein the second side is the side facing away from the first nanobeam cavity; The first highly doped region and the third highly doped region are used to receive the microwave signal forming the single-ended push-pull electrode, and the second highly doped region is used to receive the DC signal forming the single-ended push-pull electrode.

3. The electro-optic modulator according to claim 2, characterized in that, The first highly doped region is a P-type doped region, the second highly doped region is an N-type doped region, and the third highly doped region is a P-type doped region.

4. The electro-optic modulator according to claim 2, characterized in that, The electro-optic modulator further includes: a first metal electrode and a second metal electrode; The first metal electrode is connected to the first highly doped region and the third highly doped region, and is used to input the microwave signal into the first highly doped region and the third highly doped region; The second metal electrode is connected to the second highly doped region and is used to input the DC signal into the second highly doped region.

5. The electro-optic modulator according to claim 1, characterized in that, Both the first nanobeam cavity and the second nanobeam cavity are asymmetric nanobeam cavities.

6. The electro-optic modulator according to claim 5, characterized in that, The ratio of air holes at both ends of the first nanobeam cavity and the second nanobeam cavity is 2:1; and the number of air holes at the end of the first nanobeam cavity near the optical input interface is less than the number of air holes at the end away from the optical input interface, and the number of air holes at the end of the second nanobeam cavity near the optical output interface is less than the number of air holes at the end away from the optical output interface.

7. The electro-optic modulator according to claim 6, characterized in that, The aperture of the air hole at the end of the first nanobeam cavity near the optical input interface gradually decreases from large to small in the direction towards the optical input interface; the aperture of the air hole at the end of the first nanobeam cavity away from the optical input interface gradually decreases from large to small in the direction away from the optical input interface. The aperture of the air hole at the end of the second nanobeam cavity near the optical output interface gradually decreases from large to small in the direction toward the optical output interface; The aperture of the air hole at the end of the second nanobeam cavity away from the light output interface gradually decreases from large to small in the direction away from the light output interface.

8. The electro-optic modulator according to claim 7, characterized in that, The number and aperture size of the air holes on the first and second nanobeam cavities are set according to the extinction ratio required for the light output from the optical output interface.

9. The electro-optic modulator according to any one of claims 1 to 8, characterized in that, The optical input interface is implemented using a grating coupler or an inverted conical coupler; The optical output interface is implemented using a grating coupler or an inverted conical coupler.

10. An electro-optic modulation method, characterized in that, Applied to the electro-optic modulator as described in any one of claims 1 to 9; comprising: A laser is emitted to the optical input interface of the electro-optic modulator, and the laser enters the first nanobeam cavity of the electro-optic modulator through the optical input interface. By applying current to the first PN junction on the first nano-beam cavity and the second PN junction on the second nano-beam cavity of the electro-optic modulator using a single-ended push-pull electrode, modulated light is obtained.

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