Silicon-based electro-optic modulator of a micro-ring resonator

Abstract

This invention relates to a silicon-based electro-optic modulator with a microring resonator, comprising: a microring resonator and a straight waveguide. The microring resonator includes an inner ring and an outer ring, both of which are closed circular rings with their centers at the same point. Both the inner and outer rings have doped regions, including P-type and N-type doped regions. The straight waveguide is radially disposed on one side of the outer ring and coupled to it to form an input terminal and a through terminal at its two ends. By changing the doping concentration of the doped regions, the refractive index and absorption coefficient of the waveguide can be altered, thereby achieving tuning and modulation of the microring. Furthermore, during simulation and design, by selecting appropriate parameters for the concentric inner and outer rings, mutual coupling between the two rings can be achieved to adjust the resonance splitting caused by backscattering due to limitations in the resonator's manufacturing process.

Description

Technical Field

[0001] This invention relates to the field of optical communication device technology, and in particular to a silicon-based electro-optic modulator with a micro-ring resonator. Background Technology

[0002] Over the past two decades, driven by the growing demand for mobile internet, high-definition streaming media, the Internet of Things, and cloud computing, the fifth-generation technology standard (5G) has emerged, leading to an explosive growth in communication data exchange. Communication systems require high-speed, high-bandwidth, and low-power functional modules and devices, necessitating the use of chips with smaller manufacturing processes to meet these requirements.

[0003] Silicon-based photonic platforms compatible with CMOS processes meet the above requirements and are among the most promising photonic integration platforms currently available. Among the many units of a silicon photonic chip, the microring resonator is a very common structure, characterized by its small size, high Q value, and strong wavelength selectivity. It is a key component in the integration of silicon-based optoelectronics and has been widely used in various functional devices in the field of silicon photonics, including filters, modulation, delay, optoelectronic oscillators, and biosensors.

[0004] In related technologies, during the fabrication process of silicon photonic chips, the extremely small chip size, mask defects, and extensive ion bombardment increase the roughness of the waveguide sidewalls. This not only leads to additional propagation losses but also introduces random backscattering. This backscattering causes clockwise and counterclockwise propagation modes to couple in the ring waveguide, resulting in the splitting of the resonance peak and affecting the modulation depth and linearity of the micro-ring modulator.

[0005] Therefore, it is necessary to design a new silicon-based electro-optic modulator with a micro-ring resonator to overcome the above problems. Summary of the Invention

[0006] This invention provides a silicon-based electro-optic modulator with a micro-ring resonant cavity to solve the problems affecting the modulation depth and linearity of micro-ring modulators in related technologies.

[0007] In a first aspect, a silicon-based electro-optic modulator with a microring resonator is provided, comprising: a microring resonator including an inner ring and an outer ring, both the inner ring and the outer ring being closed circular rings, and the centers of the inner ring and the outer ring being located at the same point, and both the inner ring and the outer ring having doped regions; and a straight waveguide disposed radially along one side of the outer ring and coupled to the outer ring to form an input terminal and a through terminal at both ends of the straight waveguide.

[0008] In some embodiments, the doped region has an N-type doped region and a P-type doped region, which form a PN junction.

[0009] In some embodiments, the P-type doped region includes interconnected heavily doped P-type regions and lightly doped P-type regions, and the N-type doped region includes interconnected heavily doped N-type regions and lightly doped N-type regions.

[0010] In some embodiments, both the N-type lightly doped region and the P-type lightly doped region include a first region and a second region located above the first region, wherein the width of the second region in the radial direction is smaller than the width of the first region in the radial direction.

[0011] In some embodiments, the thickness of the second region is greater than the thickness of the first region.

[0012] In some embodiments, the doped regions on the inner ring and the doped regions on the outer ring are both located on the side away from the straight waveguide, and the start and end positions of the doped regions on the inner ring and the doped regions on the outer ring are the same.

[0013] In some embodiments, the inner ring and the outer ring are spaced apart, and the distance W between the inner ring and the outer ring is determined according to the inner diameter of the outer ring.

[0014] In some embodiments, both the inner ring and the outer ring are provided with two doped regions spaced apart, the two doped regions on the inner ring being of different sizes, and the two doped regions on the outer ring being of different sizes.

[0015] The beneficial effects of the technical solution provided by this invention include:

[0016] This invention provides a silicon-based electro-optic modulator with a micro-ring resonant cavity. Because doped regions are provided on the inner and outer rings, the refractive index of the waveguide can be altered by doping, thereby achieving tuning and shifting the position of the resonant peak. This suppresses resonant peak splitting and improves the modulation effect. Furthermore, the mutual coupling between the concentric inner and outer rings also significantly affects the resonant output; by adjusting the distance between the inner and outer rings, the resonant splitting of the resonant cavity can be regulated. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A top view schematic diagram of a silicon-based electro-optic modulator with a micro-ring resonant cavity provided in an embodiment of the present invention;

[0019] Figure 2 A top view schematic diagram of another silicon-based electro-optic modulator with a micro-ring resonator provided in an embodiment of the present invention;

[0020] Figure 3 This is a cross-sectional schematic diagram of the doped region provided in an embodiment of the present invention.

[0021] In the picture:

[0022] 1. Microring resonator; 11. Inner ring; 12. Outer ring; 13. Doped region; 131. N-type doped region; 1311. Heavily doped N-type region; 1312. Lightly doped N-type region; 132. P-type doped region; 1321. Heavily doped P-type region; 1322. Lightly doped P-type region; 133. First region; 134. Second region;

[0023] 2. Straight waveguide. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a silicon-based electro-optic modulator with a micro-ring resonant cavity, which can solve the problem of modulation depth and linearity of micro-ring modulators in related technologies.

[0026] See Figure 1 and Figure 3 As shown in the illustration, a silicon-based electro-optic modulator with a microring resonator provided in an embodiment of the present invention may include: a microring resonator 1, which may include an inner ring 11 and an outer ring 12, both of which are closed rings, i.e., complete circles, and the centers of the inner ring 11 and the outer ring 12 are located at the same point. The outer ring 12 is fitted outside the inner ring 11. Both the inner ring 11 and the outer ring 12 may have doped regions 13. The waveguide medium of the inner ring 11 and the outer ring 12 is preferably silicon, and the chip used is silicon-on-insulator; a straight waveguide 2, the medium of which is also preferably silicon, is arranged radially along one side of the outer ring 12, and the straight waveguide 2 is coupled to the outer ring 12 to form an input terminal and a through terminal at both ends of the straight waveguide 2. Light can be coupled into the microring from the straight waveguide 2 and resonate.

[0027] Among them, the micro-ring resonator and the straight waveguide 2 can be disposed on the substrate, and the substrate material can be silicon dioxide.

[0028] In this embodiment, since the inner ring 11 and the outer ring 12 are provided with doped regions 13, the refractive index of the waveguide can be changed by doping, thereby achieving tuning and shifting the position of the resonance peak. This can suppress resonance peak splitting and improve the modulation effect. During simulation and design, by selecting appropriate parameters for the concentric inner and outer rings, the two rings can be mutually coupled to adjust the resonance splitting caused by backscattering due to limitations in process technology.

[0029] In some embodiments, see Figure 3 As shown, the doped region 13 has an N-type doped region 131 and a P-type doped region 132, meaning the doped region can include N-type doped region 131 and P-type doped region 132, which form a PN junction. In silicon, free holes have lower optical loss and a larger real refractive index shift than free electrons. The biased PN junction has lower free carrier absorption loss, resulting in better modulation efficiency. The P-type doped region 132 is doped with phosphorus or boron, and the N-type doped region 131 is doped with antimony or indium. Of course, in other embodiments, other modulated materials can also be used.

[0030] Further, see Figure 3 As shown, the P-type doped region 132 includes a connected heavily doped P-type region 1321 and a lightly doped P-type region 1322, and the N-type doped region 131 includes a connected heavily doped N-type region 1311 and a lightly doped N-type region 1312. In this embodiment, by setting the heavily doped P-type region 1321 and the heavily doped N-type region 1311, good ohmic contact and low resistance can be ensured. Light doping is used to improve capacitance, increase breakdown voltage, and reduce metal absorption losses. Heavy doping is used to improve conductivity and form good ohmic contact. The range of light and heavy doping can be determined according to actual needs. For example, as an example, heavy doping is about 10. 20 / cm 3 Lightly doped at approximately 10 18 / cm 3 .

[0031] Figure 3 The arrangement of the PN junctions on the double rings shown is PN and PN. Of course, in other embodiments, the arrangement of the PN junctions on the double rings can also be set as PN and NP, or NP and NP, or NP and PN, etc.

[0032] In some alternative embodiments, see Figure 3As shown, both the N-type lightly doped region 1312 and the P-type lightly doped region 1322 may include a first region 133 and a second region 134 located above the first region 133. The width of the second region 134 in the radial direction is smaller than the width of the first region 133 in the radial direction, so that the second region 134 protrudes upward from the first region 133, allowing the outer ring 12 and the inner ring 11 to form a ridge waveguide, which enables more mode fields to propagate in the waveguide, reduces losses, and facilitates the addition of electrodes.

[0033] Furthermore, in some embodiments, the thickness h of the second region 134 can be greater than the thickness of the first region 133. In other embodiments, the thickness is not required, and a suitable ridge depth is selected according to the actual design. For example, for a 220nm top silicon layer, h = 130nm, and the remaining part is 90nm.

[0034] In some alternative embodiments, see Figure 1 As shown, the doped region 13 on the inner ring 11 and the doped region 13 on the outer ring 12 are both located on the side away from the straight waveguide 2. That is, the doped region 13 on the inner ring 11 and the straight waveguide 2 are distributed on opposite sides of the inner ring 11, and the doped region 13 on the outer ring 12 and the straight waveguide 2 are distributed on opposite sides of the outer ring 12. The starting and ending positions of the doped region 13 on the inner ring 11 and the doped region 13 on the outer ring 12 are the same, so that the curvature of the doped region 13 on the inner ring 11 and the doped region 13 on the outer ring 12 are the same and they correspond completely in the radial direction, so as to ensure that the doped region 13 on the inner ring 11 and the doped region 13 on the outer ring 12 can generate a double-ring mutual coupling resonance.

[0035] In some embodiments, see Figure 2 As shown, both the inner ring 11 and the outer ring 12 have two doped regions 13 spaced apart. The two doped regions 13 on the inner ring 11 are of different sizes, and the two doped regions 13 on the outer ring 12 are of different sizes. Preferably, the size ratio of the two doped regions 13 on the inner ring 11 is 1:2, and the size ratio of the two doped regions 13 on the outer ring 12 is also 1:2. Setting adjacent modulation regions on the dual rings can achieve high-order PAM4 code modulation. Of course, in other embodiments, the number, length, and position of the doped regions on each ring can be set according to actual conditions; for example, three doped regions 13 can be set on the inner ring 11 and the outer ring 12 respectively.

[0036] In some optional embodiments, the inner ring 11 and the outer ring 12 are spaced apart, and the distance W between the inner ring 11 and the outer ring 12 is determined according to the inner diameter of the outer ring 12 to ensure that the inner ring 11 and the outer ring 12 can generate mutual coupling resonance of the two rings. The distance W between the inner ring 11 and the outer ring 12 and the inner diameter R of the outer ring 12 can satisfy the following formula: RW≥10*W. In the design simulation, by adjusting the distance between the two rings (inner ring 11 and outer ring 12) within this range, the resonance splitting of the resonant cavity can be adjusted. Selecting appropriate parameters can increase the depth of the resonance peak and the modulation depth.

[0037] Further, see Figure 1 As shown, in this embodiment, the radius of the inner ring 11 can be r, the radial width of the inner ring 11 is d2, the radial width of the outer ring 12 is d1, and the spacing between the outer ring 12 and the straight waveguide 2 is GAP.

[0038] Ideally, if resonance splitting occurs, the two symmetrical resonances will have the same dip depth. However, in reality, resonance splitting is not symmetrical. The silicon-based electro-optic modulator provided in this invention can suppress resonance peak splitting, allowing the dip of the resonance peak to decrease smoothly and improving the linearity of modulation. Furthermore, the silicon-based electro-optic modulator provided in this invention can be fabricated using conventional silicon-based chip fabrication processes and doping steps. Device design through simulation does not increase the difficulty of the process or the fabrication flow, nor does it introduce additional process losses.

[0039] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0040] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A silicon-based electro-optic modulator with a micro-ring resonant cavity, characterized in that, It includes: The micro-ring resonator (1) includes an inner ring (11) and an outer ring (12). Both the inner ring (11) and the outer ring (12) are closed rings, and the centers of the inner ring (11) and the outer ring (12) are located at the same point. Both the inner ring (11) and the outer ring (12) are provided with doped regions (13). A straight waveguide (2) is disposed on one side of the outer ring (12) along the radial direction of the outer ring (12), and the straight waveguide (2) is coupled to the outer ring (12) to form an input end and a through end at both ends of the straight waveguide (2); The doped region (13) has an N-type doped region (131) and a P-type doped region (132), and the N-type doped region (131) and the P-type doped region (132) form a PN junction; The P-type doped region (132) includes a P-type heavily doped region (1321) and a P-type lightly doped region (1322) connected to each other, and the N-type doped region (131) includes an N-type heavily doped region (1311) and an N-type lightly doped region (1312) connected to each other.

2. The silicon-based electro-optic modulator with a micro-ring resonator as described in claim 1, characterized in that: Both the N-type light doping region (1312) and the P-type light doping region (1322) include a first region (133) and a second region (134) located above the first region (133), wherein the width of the second region (134) in the radial direction is smaller than the width of the first region (133) in the radial direction.

3. The silicon-based electro-optic modulator with a micro-ring resonator as described in claim 2, characterized in that: The thickness of the second region (134) is greater than the thickness of the first region (133).

4. The silicon-based electro-optic modulator with a micro-ring resonator as described in claim 1, characterized in that: The doped region (13) on the inner ring (11) and the doped region (13) on the outer ring (12) are both located on the side away from the straight waveguide (2). The starting position and ending position of the doped region (13) on the inner ring (11) and the doped region (13) on the outer ring (12) are the same.

5. The silicon-based electro-optic modulator with a micro-ring resonator as described in claim 1, characterized in that: The inner ring (11) and the outer ring (12) are spaced apart, and the distance W between the inner ring (11) and the outer ring (12) is determined according to the inner diameter of the outer ring (12).

6. The silicon-based electro-optic modulator with a micro-ring resonator as described in claim 1, characterized in that: Both the inner ring (11) and the outer ring (12) are provided with two doped regions (13) spaced apart. The two doped regions (13) on the inner ring (11) are different in size, and the two doped regions (13) on the outer ring (12) are different in size.

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