Cascade double-ring silicon light modulator based on Auter-Towns effect

Abstract

The invention discloses a cascaded double-ring silicon optical modulator structure based on an Au1ter-Townes effect and a phase change material. The cascaded double-ring silicon optical modulator structure comprises a single-mode bus waveguide and two annular waveguides, a phase-change material is integrated on the surface of the annular waveguide to adjust the initial resonant wavelengths of the two micro-rings; pN junctions are integrated in the annular waveguide, and phase modulation of light is achieved through carrier injection. An Au1ter-Towns effect is utilized to enable a micro-ring transmission spectrum to form two split super-modes, and the extinction ratio corresponding to the two super-modes is changed by adjusting the resonant wavelengths of the double micro-rings; and meanwhile, the cascaded double-micro-ring structure can realize large modulation bandwidth and meet the high-speed transmission requirement. The micro-ring waveguide deposition phase-change material enables resonant wavelength tuning to have non-volatility, and compared with a traditional thermal tuning mode, the micro-ring waveguide deposition phase-change material can greatly reduce regulation and control power consumption. According to the invention, the technical bottleneck of the existing silicon optical modulator is overcome, and the practical application requirements of the fields of optical interconnection, optical communication, optical calculation and the like on the high-extinction-ratio high-speed modulator can be met.

Description

Technical Field

[0001] This patent belongs to the field of silicon-based optoelectronic integrated chips, and particularly relates to a cascaded dual-ring silicon optical modulator based on the Aulter-Townes effect. Background Art

[0002] Modulators are key components in optical communications and optical interconnection systems, responsible for converting electrical signals into optical signals. Silicon-based electro-optic modulators change the effective refractive index in silicon waveguides through carrier dispersion effects, thereby controlling the output light intensity and achieving high-speed modulation. With the help of technologies such as wavelength division multiplexing and mode division multiplexing, optical communication systems can support transmission rates of up to 100 Tbps, and the modulation rate of silicon-based electro-optic modulators directly determines the overall rate of the communication system.

[0003] At present, silicon-based electro-optic modulators are mainly divided into two types: one is the Mach-Zehnder modulator based on interference structure, which modulates the output light intensity by changing the phase difference between the two arms. It has good thermal stability, but its size is usually in the millimeter level, making it difficult to achieve large-scale integration. The other is the micro-ring modulator, which adjusts the output at a fixed wavelength by changing the resonant wavelength of the resonant cavity. It is smaller in size and more suitable for large-scale integration. However, the electro-optic bandwidth f of the micro-ring modulator is EO The electrical bandwidth f EE and the optical bandwidth f Optical The restriction usually satisfies the formula In order to improve the electro-optical bandwidth of the micro-ring modulator, commonly used methods include increasing the electrical bandwidth by adding an inductor, and reducing the resonant Q value by increasing the doping concentration, thereby increasing the optical bandwidth. For example, patent document CN115639698A discloses a C-band silicon waveguide micro-ring modulator based on phase change material antimony sulfide, which modulates the light amplitude by adjusting the phase state of antimony sulfide, thereby achieving large-scale integration of silicon-based optoelectronic devices with higher speed and low power consumption. However, increasing the loss of the ring waveguide will also lead to a decrease in the amplitude of light modulation. The static extinction ratio of the micro-ring modulator is related to the loss of the ring waveguide and the coupling strength between the ring waveguide and the bus waveguide. In theory, by adjusting these two parameters, critical coupling can be achieved to achieve the maximum extinction ratio. However, due to the errors in the actual processing technology, the static extinction ratio of the micro-ring modulator is usually around 20dB.

[0004] Compared with a single-ring modulator, a cascaded dual-ring modulator can provide a larger optical bandwidth and a steeper spectrum, thereby achieving a higher modulation efficiency. Compared with a single micro-ring modulator, the extinction ratio of the dual micro-ring is also affected by the resonant wavelength of the two rings. Increasing the coupling strength between the two rings will produce even-symmetric and odd-symmetric supermodes, and the transmission spectrum will split. Patent document CN104170189A discloses an optical semiconductor device that solves the resonant wavelength offset caused by the processing error of the ring resonator. The resonant wavelength of the laser oscillator is determined by the average value of the resonant wavelengths of multiple cascaded rings 13. The modulation section adopts a micro-ring-assisted MZM. On the one hand, the resonant wavelength with the maximum modulation efficiency is located near the ring resonator 23, which plays a role in averaging the processing error, and on the other hand, it increases the modulation efficiency. Summary of the invention

[0005] In view of the problems existing in the existing single micro-ring modulator, the present invention proposes a cascaded double micro-ring silicon optical modulator structure, which controls the optical bandwidth and extinction ratio of the double micro-ring modulator by adjusting the coupling coefficient between the two rings and between the ring waveguide and the bus waveguide, and the resonant wavelength of the two rings.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A cascaded double-ring silicon optical modulator based on Aulter-Townes effect and phase change material, which has the following characteristics:

[0008] A single-mode bus waveguide;

[0009] Two ring waveguides, the two ring waveguides are respectively coupled with the single-mode bus waveguide, and one of the ring waveguides is also coupled with the other ring waveguide to form a cascaded double-ring structure;

[0010] A phase change material is integrated on the surface of the ring waveguide to adjust the initial resonance wavelengths of the two ring waveguides;

[0011] A PN junction is integrated in the ring waveguide to achieve phase modulation of light through carrier injection;

[0012] The Aulter-Townes effect is used to make the transmission spectrum of the ring waveguide form two split supermodes, and the extinction ratio corresponding to the two supermodes is changed by adjusting the resonant wavelengths of the two ring waveguides. At the same time, the cascaded double-ring structure realizes a large modulation bandwidth.

[0013] Furthermore, there are two coupling regions between the two ring waveguides, forming a second-order filter structure. When the coupling strength between the two ring waveguides is large enough, the transmission spectrum is split into two supermodes, and the extinction ratio corresponding to the two supermodes is related to the resonant wavelengths of the two ring waveguides. The resonance splitting intensity is controlled by controlling the coupling strength between the two rings, thereby realizing a high-performance silicon-based optical modulator.

[0014] Furthermore, the coupling strength is controlled by the coupling region length and the coupling spacing.

[0015] Furthermore, the two ring waveguides are doped to obtain two low Q value resonances, wherein one ring is doped with P inside and N outside, and the other ring is doped with N inside and P outside; or, both rings are doped in the same way but form a horizontal PN junction structure or an S-type PN junction structure at different positions, and the doping structure is controlled by controlling the ion implantation angle and position.

[0016] Furthermore, the modulation method includes: modulating one of the loops; or modulating both loops simultaneously, which is implemented by a push-pull PN junction or a series PN junction.

[0017] Furthermore, it also includes a phase change structure design: the phase change material used is tellurium selenide (Sb2Se3), tellurium sulfide (Sb2S3) or germanium tellurium selenide (Ge2Sb2Se4Te1); the phase change material is deposited on the surface of the annular waveguide, an aluminum oxide film covers the phase change material, a single layer of graphene is on the aluminum oxide film, and a metal electrode is above the single layer of graphene; the single layer of graphene and the metal electrode are in contact with each other to form an ohmic contact, and current flows through the single layer of graphene to generate heat, which is conducted through the aluminum oxide film below to provide the required heat for the phase change of the phase change material.

[0018] Furthermore, the single-mode bus waveguide and the two ring waveguides are both silicon waveguides, with a width of 0.4-0.5 microns and a height of 0.22 microns, and operate in the C band or the O band.

[0019] Furthermore, before applying the modulation signal, a higher static extinction ratio is achieved by adjusting the resonant wavelength difference between the two ring waveguides, and after applying the modulation signal, dynamic modulation is performed through the Aulter-Townes effect and the free carrier dispersion effect to achieve high-performance optical modulation.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The cascaded double micro-ring structure is adopted, and the extinction ratio can be adjusted by controlling the coupling strength and the resonant wavelength of the two rings;

[0022] (2) The cascaded double microring structure can take advantage of the steep spectral characteristics of the second-order filter and the larger optical bandwidth to achieve a better trade-off between the optical modulation amplitude and the electro-optical bandwidth;

[0023] (3) By using phase change materials to change the resonant wavelengths of the two rings, repeated non-volatile adjustments can be achieved.

[0024] (4) The resonant wavelength of the laser oscillator in patent document CN104170189A is the average value of the resonant wavelengths of multiple cascaded rings 13, reducing the deviation of the resonant wavelength; while this patent uses phase change materials to change the resonant wavelength of the cascaded microring resonator to change its static extinction ratio and improve the performance of the modulator. By using the cascaded double microring modulator (two microrings coupled to each other) to change its extinction ratio during the modulation process, a very large dynamic extinction ratio can be obtained at a very small driving voltage; before modulation, the phase change material is used to adjust the resonant wavelength of one of the rings, thereby adjusting the static extinction ratio of the modulator. The change in the resonant wavelength is non-volatile and repeatable and has no effect on the modulator itself.

[0025] (5) Due to the mutual coupling between the two rings, the influence of temperature change on the modulator performance can be partially offset, improving the reliability of the modulator under complex environmental conditions; the structure supports multiple modulation modes, including modulation of a single ring or a dual ring. This provides users with more choices and allows them to optimize the performance of the modulator according to the needs of specific application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of a modulator based on the Aulter-Townes effect and phase change material of the present invention;

[0027] Figure 2 It is the PN junction and its metal electrode design;

[0028] Figure 3 It is the phase change region structure design;

[0029] Figure 4 is the transmission spectrum corresponding to different coupling strengths between the two microrings;

[0030] Figure 5 The alignment and misalignment of the two ring resonant wavelengths correspond to the double micro-ring transmission spectrum and the distribution of the light field in the two resonant structures;

[0031] Figure 6 is the transmission spectrum corresponding to different modulation modes;

[0032] Figure 7 It is the change of the larger wavelength supermode extinction ratio corresponding to the resonant wavelengths of the two different rings. DETAILED DESCRIPTION

[0033] The present invention is further defined below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereto.

[0034] The present invention proposes a cascaded dual micro-ring silicon optical modulator structure, which aims to solve the problems of small modulation bandwidth and low extinction ratio of existing silicon-based single micro-ring electro-optical modulators, and realize high-performance silicon-based optical modulators. The specific technical solution is as follows:

[0035] 1. Cascaded double microring structure

[0036] A cascaded dual-ring silicon optical modulator based on the Aulter-Townes effect and phase change material includes a single-mode bus waveguide 101 and two single-mode ring waveguides, namely an inner ring 201 and an outer ring 202. The waveguide width is 0.4-0.5 microns, the thickness is 0.22 microns, and the thickness of the planar waveguide is between 70-90 nanometers. The two ring waveguides are coupled to each other, and the bus waveguide is coupled to only one of the ring waveguides. The coupling strength is controlled by the length of the coupling region and the coupling spacing, and the resonance splitting strength is controlled by controlling the coupling strength between the two rings.

[0037] The transmittance T of the modulator can be calculated by the following formula using the transfer matrix method.

[0038]

[0039] Where a1, t1, θ1 represent the transmission coefficient of the inner ring (201) (a1 = 1 represents lossless inner ring), the self-coupling coefficient of the inner ring and the bus waveguide coupling (satisfying t1 2 +k1 2 =1, k1 is the coupling coefficient between the ring and the bus waveguide) and the phase change caused by the light circulating in the inner ring; a2, t2, θ2 respectively represent the transmission coefficient of the outer ring (202), the self-coupling coefficient at the coupling point between the outer ring and the inner ring, and the phase change caused by the light circulating in the outer ring.

[0040] The micro-ring transmittance is not only related to the loss within the ring and the coupling between waveguides, but also to the phase change produced by the phase shifters of each ring. The phase change can be calculated by the following formula:

[0041]

[0042] Among them, n eff is the effective refractive index of the waveguide, L is the length of the microring, and λ is the wavelength of the incident light. This θ can be adjusted by different modulation methods.

[0043] 2.PN junction design

[0044] Both ring waveguides are doped to obtain two low Q value resonances. P(N) doping is used inside the two rings and N(P) doping is used outside. The horizontal PN junction structure or S-shaped PN junction structure is formed by controlling the ion injection angle and position.

[0045] 3. Modulation method

[0046] Based on the above PN junction design, the dual micro-ring modulator has two modulation modes: modulating one of the dual micro-rings; and modulating both micro-rings simultaneously (using a push-pull PN junction or a series PN junction).

[0047] 4. Phase change structure design

[0048] The phase change material is tellurium selenide (Sb2Se3), tellurium sulfide (Sb2S3) or germanium tellurium selenide (Ge2Sb2Se4Te1); the phase change material is deposited on the surface of the annular waveguide, and an aluminum oxide film covers the phase change material. On the aluminum oxide film is a single layer of graphene, and above the single layer of graphene is a metal electrode; the metal material includes but is not limited to gold, silver, copper, and aluminum; the above-mentioned single layer of graphene and the metal electrode structure contact each other to form an ohmic contact, and the current flows through the single layer of graphene to generate heat, which is conducted through the aluminum oxide film below to provide the heat required for the phase change of the low-loss phase change material. The characteristics of the phase change material are used to achieve fast and efficient light modulation. By controlling the magnitude and duration of the current, the phase state of the phase change material can be precisely controlled, thereby adjusting the intensity or phase of the light after passing through the modulator.

[0049] See also Figure 1 , Figure 1 Schematic diagram of the structure of the modulator based on Aulter-Townes effect and phase change material of the present invention. Figure 1 As shown, it is composed of a single-mode bus waveguide and two ring waveguides, wherein the bus waveguide 101 is coupled with the inner ring waveguide 201 , and the inner ring waveguide 201 is coupled with the bus waveguide 101 and the outer ring waveguide 202 at the same time.

[0050] The working principle is as follows: the integrated PN junction of the ring waveguides 201 and 202 is used to modulate light through the free carrier dispersion effect; the input light is modulated by the ring waveguides 201 and 202 respectively, and finally output at the output port.

[0051] Compared with the single microring structure, the dual microring structure has two coupling regions, forming a second-order filter structure. When the coupling strength between the two rings is large enough, the transmission spectrum splits to form two supermodes. In addition, compared with the single microring modulator, the extinction ratio of the dual microring modulator is also related to the resonant wavelength of the two rings, and a large extinction ratio change can be obtained within a smaller wavelength adjustment range. Compared with conventional modulators, the dual-ring modulator also integrates phase change materials to adjust the resonant wavelength difference between the two rings, so that the above-mentioned dual microring modulator obtains a larger static extinction ratio before the modulation signal is applied.

[0052] Figure 2 Shown are the PN junction structures corresponding to different modulation methods. Figure 2 (a) indicates that only the outer ring is modulated. The interior of the two rings is P-type doped, and the exterior is N-type doped. The metal electrodes are on both sides of the outer ring waveguide, and the modulation signal is applied to the metal electrodes. Figure 2 (b) indicates that only the inner ring is modulated. The interior of the two rings is P-type doped, and the exterior is N-type doped. The metal electrodes are on both sides of the inner ring waveguide, and the modulation signal is applied to the metal electrodes. Figure 2 (c) represents push-pull modulation of the two rings. The interior of the two rings is P-type doped, and the exterior is N-type doped. The two P-type doped regions are connected by metal to form electrodes for applying a DC bias voltage, and the external electrodes of the annular waveguide are used to apply a modulation signal. Figure 2 (d) indicates that the two rings form a series PN junction, where the outer ring is P-type doped inside and N-type doped outside, while the inner ring is N-type doped inside and P-type doped outside. The two rings are connected by metal inside, and the metal electrodes outside the two rings are used to apply modulation signals.

[0053] Figure 3 The design of the phase change region structure is demonstrated. A ridge silicon waveguide is used, where the waveguide thickness is 0.22 microns and the silicon slab waveguide is 70-90 nanometers thick. The phase change material (PCM) is coated on the waveguide, and the effective refractive index of the waveguide is changed by the phase change of the phase change material. The phase change material is covered with an aluminum oxide film to conduct heat. A single layer of graphene is placed on the aluminum oxide, which is used as a micro heater to change the properties of the phase change material by heating.

[0054] Figure 4 The transmission spectra corresponding to different coupling strengths between the two microrings are shown. When the two microrings are resonantly aligned and the coupling is strong, the transmission spectra of the two microrings split, forming two coupled symmetric and odd symmetric supermodes. As the coupling strength increases, the degree of splitting between the two supermodes increases.

[0055] Figure 5 The transmission spectra of the double microrings under resonant alignment and misalignment conditions are shown, as well as the corresponding simulation diagrams of the light field distribution inside the rings in each case.

[0056] Figure 6 The transmission spectra of the dual-ring modulator under different modulation modes and the extinction ratio changes at the respective operating point wavelengths are shown. Among them, the dual-ring push-pull modulation mode can obtain the largest extinction ratio change.

[0057] Figure 7 The extinction ratio of the supermode corresponding to the larger wavelength is shown at different resonance wavelengths of the two rings. The supermode extinction ratio changes with the change of the resonance wavelength of the two rings, which also shows that a larger dynamic extinction ratio can be achieved.

[0058] In addition, the resonator structure includes but is not limited to a micro-ring resonant structure, such as a resonant cavity structure composed of a grating or a photonic crystal, all of which are within the scope of protection of this patent.

[0059] It can be seen that the innovation of this modulator structure lies in the use of the Aulter-Townes effect and the free carrier dispersion effect for modulation, changing the resonant wavelength of the two rings through phase change materials, and then changing the extinction ratio corresponding to the two supermodes, obtaining an extremely high static extinction ratio in the unmodulated stage, and realizing high-performance optical modulation.

Claims

1. A cascaded dual-ring silicon optical modulator based on Aulter-Townes effect and phase change material, characterized in that: include: A single-mode bus waveguide; Two ring waveguides, the two ring waveguides are respectively coupled with the single-mode bus waveguide, and one of the ring waveguides is also coupled with the other ring waveguide to form a cascaded double-ring structure; A phase change material is integrated on the surface of the ring waveguide to adjust the initial resonance wavelengths of the two ring waveguides; A PN junction is integrated in the ring waveguide to achieve phase modulation of light through carrier injection; The Aulter-Townes effect is used to make the transmission spectrum of the ring waveguide form two split supermodes, and the extinction ratio corresponding to the two supermodes is changed by adjusting the resonant wavelengths of the two ring waveguides. At the same time, the cascaded double-ring structure realizes a large modulation bandwidth.

2. The cascaded dual-ring silicon optical modulator according to claim 1, characterized in that: There are two coupling regions between the two ring waveguides, forming a second-order filter structure. When the coupling strength between the two ring waveguides is large enough, the transmission spectrum line splits into two supermodes, and the extinction ratio corresponding to the two supermodes is related to the resonant wavelengths of the two ring waveguides. The resonance splitting intensity is controlled by controlling the coupling strength between the two rings, thereby realizing a high-performance silicon-based optical modulator.

3. The cascaded dual-ring silicon optical modulator according to claim 2, characterized in that: The strength of the coupling is controlled by the length of the coupling region and the coupling spacing.

4. The cascaded dual-ring silicon optical modulator according to claim 1, characterized in that: The two annular waveguides are both doped to obtain two low Q value resonances, wherein one ring is doped with P inside and N outside, and the other ring is doped with N inside and P outside; or, both rings are doped in the same way but form a horizontal PN junction structure or an S-type PN junction structure at different positions, and the doping structure is controlled by controlling the ion implantation angle and position.

5. The cascaded dual-ring silicon optical modulator according to any one of claims 1 to 4, characterized in that: The modulation method includes: modulating one of the loops; or modulating both loops simultaneously, which is achieved by using a push-pull PN junction or a series PN junction.

6. The cascaded dual-ring silicon optical modulator according to any one of claims 1 to 4, characterized in that: It also includes a phase change structure design: the phase change material used is tellurium selenide (Sb2Se3), tellurium sulfide (Sb2S3) or germanium tellurium selenide (Ge2Sb2Se4Te1); the phase change material is deposited on the surface of the annular waveguide, an aluminum oxide film covers the phase change material, a single layer of graphene is on the aluminum oxide film, and a metal electrode is above the single layer of graphene; the single layer of graphene and the metal electrode are in contact with each other to form an ohmic contact, and current flows through the single layer of graphene to generate heat, which is conducted through the aluminum oxide film below to provide the required heat for the phase change of the phase change material.

7. The cascaded dual-ring silicon optical modulator according to any one of claims 1 to 4, characterized in that: The single-mode bus waveguide and the two ring waveguides are both silicon waveguides, with a width of 0.4-0.5 microns and a height of 0.22 microns, and operate in the C band or the O band.

8. The cascaded dual-ring silicon optical modulator according to any one of claims 1 to 7, characterized in that: Before applying the modulation signal, a higher static extinction ratio is achieved by adjusting the resonant wavelength difference of the two ring waveguides. After applying the modulation signal, dynamic modulation is performed through the Aulter-Townes effect and free carrier dispersion effect to achieve high-performance optical modulation.

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