A cascaded double-ring silicon optical modulator based on aulter-townes effect

Abstract

A kind of based on Aulter-Townes effect and phase change material's cascade double-ring silicon light modulator structure, including a single-mode bus waveguide and two ring waveguides;Phase change material is integrated on the surface of ring waveguide to adjust the initial resonant wavelength of two micro-rings;PN junction is integrated in ring waveguide, and phase modulation to light is realized by carrier injection.Aulter-Townes effect is utilized to make micro-ring transmission spectrum form two split supermodes, and the extinction ratio corresponding to two supermodes is changed by adjusting the resonant wavelength of double micro-rings;Meanwhile, cascade double micro-ring structure can realize large modulation bandwidth, and meet the demand of high-speed transmission.Micro-ring waveguide deposits phase change material, and the resonant wavelength tuning has non-volatility, compared with traditional thermal tuning mode, can greatly reduce the regulation power consumption.The application overcomes the technical bottleneck of existing silicon light modulator, and can meet the practical application demand of high-extinction-ratio high-speed modulator in optical interconnection, optical communication and optical computing fields.

Description

TECHNICAL FIELD

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

[0002] Modulators are key devices in optical communication and optical interconnection systems, responsible for converting electrical signals into optical signals. Silicon-based electro-optical modulators change the effective refractive index in the silicon waveguide through the carrier dispersion effect, 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 as high as hundreds of Tbps, and the modulation rate of silicon-based electro-optical modulators directly determines the overall rate of the communication system.

[0003] At present, silicon-based electro-optical modulators mainly fall into two types: one is a Mach-Zehnder modulator based on an interference structure, which modulates the output light intensity by changing the phase difference between the two arms, and has good thermal stability, but its size is usually in the millimeter level, making it difficult to achieve large-scale integration. The other is a micro-ring modulator, which adjusts the output at a fixed wavelength by changing the resonant wavelength of the resonant cavity, and has a smaller size, making it more suitable for large-scale integration. However, the electro-optical bandwidth f EO of the micro-ring modulator is limited by the electrical bandwidth f EE and the optical bandwidth f Optical , usually satisfying the formula To improve the electro-optical bandwidth of the micro-ring modulator, common methods include increasing the electrical bandwidth by adding an external inductor, and increasing the optical bandwidth by reducing the resonant Q value through increasing the doping concentration. 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 realizing large-scale integration of silicon-based optoelectronic devices with higher speed and lower power consumption. However, increasing the loss of the ring waveguide will result in a decrease in the light modulation amplitude. 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 errors in the actual processing technology, the static extinction ratio of the micro-ring modulator is usually around 20dB.

[0004] Compared with single-ring modulator, the cascaded double-ring modulator can provide larger optical bandwidth and steeper spectrum line, so as to obtain higher modulation efficiency. Compared with single micro-ring modulator, the extinction ratio of double micro-ring is also affected by the resonant wavelength of the two rings. Increasing the coupling strength between the two rings will produce even and odd symmetry supermodes, and the transmission spectrum will split. The patent document CN104170189A discloses an optical semiconductor device, which solves the resonant wavelength shift 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 the multiple cascaded rings 13. The micro-ring assisted MZM is used in the modulation section. On the one hand, the resonant wavelength of the maximum modulation efficiency is located near the ring resonator 23, which plays the role of average processing error. On the other hand, the modulation efficiency is increased. SUMMARY

[0005] In view of the problems existing in the prior art single micro-ring modulator, the present application provides a cascaded double micro-ring silicon optical modulator structure. The optical bandwidth and extinction ratio of the double micro-ring modulator are controlled by adjusting the coupling coefficients between the two rings and between the ring waveguide and the bus waveguide, and the resonant wavelengths of the two rings.

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0007] A cascaded double-ring silicon optical modulator based on Aulter-Townes effect and phase change material, characterized in that it comprises:

[0008] a single-mode bus waveguide;

[0009] two ring waveguides, which are coupled with each other with the single-mode bus waveguide, and one of the two ring waveguides is also coupled with the other ring waveguide, forming a cascaded double-ring structure;

[0010] A phase change material is integrated on the surface of the ring waveguide, which is used to adjust the initial resonant wavelength of the two ring waveguides;

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

[0012] Among them, the Aulter-Townes effect is used to form two split supermodes in the transmission spectrum of the ring waveguide, and the resonant wavelength of the two ring waveguides is adjusted to change the extinction ratio corresponding to the two supermodes. At the same time, the cascaded double-ring structure realizes large modulation bandwidth.

[0013] Further, two coupling regions exist between the two ring waveguides, forming a second-order filter structure, when the coupling strength between the two ring waveguides is large enough, transmission spectrum line splits to form two supermodes, and the extinction ratio corresponding to the two supermodes is related to the resonant wavelength of the two ring waveguides, the resonant splitting strength is controlled by controlling the coupling strength between the two rings, and thus a high-performance silicon-based optical modulator is realized.

[0014] Further, the coupling strength is controlled by the coupling region length and the coupling pitch.

[0015] Further, the two ring waveguides are doped to obtain two low-Q resonances, wherein one ring adopts P doping inside and N doping outside, and the other ring adopts N doping inside and P doping outside; or, the two rings adopt the same doping mode but form horizontal PN junction structures or S-shaped PN junction structures at different positions, and the doping structure is controlled by controlling the ion implantation angle and position.

[0016] Further, the modulation mode includes: modulating one of the rings; or simultaneously modulating the two rings in a push-pull PN junction or series PN junction mode.

[0017] Further, a phase change structure design is further included: the phase change material is Sb2Se3, Sb2S3 or Ge2Sb2Se4Te1; the phase change material is deposited on the surface of the ring waveguide, an aluminum oxide film is covered on the phase change material, a single-layer graphene is on the aluminum oxide film, and a metal electrode is above the single-layer graphene; the single-layer graphene and the metal electrode are in ohmic contact with each other, current flows through the single-layer graphene to generate heat, the heat is conducted through the underlying aluminum oxide film to provide the required heat for the phase change of the phase change material.

[0018] Further, the single-mode bus waveguide and the two ring waveguides are silicon waveguides, the width is 0.4-0.5 microns, the height is 0.22 microns, and the working wavelength is in the C band or the O band.

[0019] Further, before the modulation signal is applied, a high static extinction ratio is realized by adjusting the resonant wavelength difference of the two ring waveguides, and after the modulation signal is applied, dynamic modulation is performed through the Aulter-Townes effect and the free carrier dispersion effect, to realize a high-performance optical modulation.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] (1) The cascade 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 use of a cascaded double-micro-ring structure can utilize the steep spectral line characteristics of its second-order filter and larger optical bandwidth to achieve a better trade-off between optical modulation amplitude and electro-optical bandwidth.

[0023] (3) The use of a phase change material to change the resonant wavelength of the two rings can achieve repeated non-volatile adjustment.

[0024] (4) The resonant wavelength of the laser oscillator in patent document CN104170189A is the average of the resonant wavelengths of multiple cascaded rings 13, which reduces the deviation of the resonant wavelength; while this patent uses a phase change material to change the resonant wavelength of the cascaded micro-ring resonator to change its static extinction ratio and improve the performance of the modulator. The use of a cascaded double-micro-ring modulator (two micro-rings coupled to each other) in the modulation process can achieve a large dynamic extinction ratio with a very small driving voltage; before modulation, the resonant wavelength of one of the rings is adjusted using a phase change material, which in turn adjusts the static extinction ratio of the modulator. The change in 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 changes on the performance of the modulator can be partially offset, improving the reliability of the modulator in complex environmental conditions; this structure supports multiple modulation methods, including modulation of a single ring or double rings. 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 DRAWINGS

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

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

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

[0029] Figure 4 is the transmission spectrum corresponding to different coupling strengths between the double micro-rings;

[0030] Figure 5 is the transmission spectrum and the distribution of the optical field in the two resonant structures corresponding to the alignment and misalignment of the resonant wavelengths of the two rings;

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

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

[0033] The application will be further defined with the following drawings and examples, but should not be limited by the protection scope of the application.

[0034] The application proposes a structure of a cascaded double-micro-ring silicon optical modulator, aiming to solve the problems of small modulation bandwidth and low extinction ratio existing in the prior art silicon-based single-micro-ring electro-optical modulator, and realize a high-performance silicon-based optical modulator. The specific technical solutions are as follows.

[0035] 1. Cascaded double-micro-ring structure

[0036] A cascaded double-ring silicon optical modulator based on Aulter-Townes effect and phase change material comprises a single-mode bus waveguide 101 and two single-mode ring waveguides, i.e., 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 flat waveguide thickness is 70-90 nanometers. The two ring waveguides are coupled to each other, and the bus waveguide is coupled to one of the ring waveguides. The coupling strength is controlled by the coupling length and the coupling distance, 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 by using the transmission matrix method.

[0038]

[0039] Wherein a1, t1, θ1 represent the transmission coefficient of the inner ring (201) (a1=1 represents no loss in the inner ring), the self-coupling coefficient at the coupling position between the inner ring and the bus waveguide (t1 2 +k1 2 =1, and k1 is the coupling coefficient between the ring and the bus waveguide), and the phase change of light after one round in the inner ring; a2, t2, θ2 represent the transmission coefficient of the outer ring (202), the self-coupling coefficient at the coupling position between the outer ring and the inner ring, and the phase change of light after one round in the outer ring.

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

[0041]

[0042] Wherein, n eff is the effective refractive index of the waveguide, L is the length of the micro-ring, and λ is the wavelength of the incident light. The θ can be adjusted by different modulation modes.

[0043] 2. PN junction design

[0044] Two ring waveguides are doped to obtain two low-Q resonances, the inner ring is doped with P(N) and the outer ring is doped with N(P), and the horizontal PN junction structure or S-shaped PN junction structure is formed by controlling the ion implantation angle and position.

[0045] 3. Modulation mode

[0046] Based on the above-mentioned PN junction design, the modulation mode of the dual-microring modulator is divided into two types: one ring of the dual-microring is modulated; both rings are modulated (push-pull PN junction or series PN junction is used).

[0047] 4. Phase change structure design

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

[0049] Please refer to Figure 1 , Figure 1 is the structure diagram of the modulator based on the Aulter-Townes effect and phase change material, as Figure 1 shown, which 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.

[0050] The working principle is as follows: the ring waveguides 201 and 202 integrate PN junctions to modulate light through 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 single micro-ring structure, double micro-ring structure has two coupling regions, which constitutes a second-order filter structure. When the coupling strength between the two rings is large enough, the transmission spectrum line splits to form two supermodes. In addition, compared with single micro-ring modulator, the extinction ratio of double micro-ring modulator is also related to the resonance wavelength of the two rings, and large extinction ratio change can be obtained in a small wavelength adjustment range. Compared with conventional modulators, the double-ring modulator also integrates a phase change material to adjust the resonance wavelength difference of the two rings, so that the above-mentioned double micro-ring modulator has a large static extinction ratio before the modulation signal is applied.

[0052] Figure 2 The PN junction structure corresponding to different modulation modes is shown. Figure 2 (a) represents that only the outer ring is modulated, the inside of the two rings is P-type doped, and the outside is N-type doped, and the metal electrodes are respectively on both sides of the outer ring waveguide, and the modulation signal is applied on the metal electrode. Figure 2 (b) represents that only the inner ring is modulated, the inside of the two rings is P-type doped, and the outside is N-type doped, and the metal electrodes are respectively on both sides of the inner ring waveguide, and the modulation signal is applied on the metal electrode. Figure 2 (c) represents push-pull modulation of the two rings, the inside of the two rings is P-type doped, and the outside is N-type doped, and the two P-type doped regions are connected by metal to form an electrode for applying a direct current bias voltage, and the outer electrode of the ring waveguide is used to apply a modulation signal. Figure 2 (d) represents that the two rings constitute a series PN junction, wherein the inside of the outer ring is P-type doped, the outside is N-type doped, the inside of the inner ring is N-type doped, and the outside is P-type doped, the inside of the two rings is connected by metal, and the outer metal electrode of the two rings is used to apply a modulation signal.

[0053] Figure 3 The structure design of the phase change region is shown. A ridge-type silicon waveguide is used, in which the waveguide thickness is 0.22 microns, and the silicon flat plate waveguide thickness is 70-90 nanometers; a phase change material (PCM) is covered on the waveguide to change the effective refractive index of the waveguide by phase change of the phase change material. An aluminum oxide film is covered on the phase change material to conduct heat. A single layer of graphene is 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 spectrum lines corresponding to different coupling strengths between the two micro-rings are shown. When the resonances of the two micro-rings are aligned and the coupling is strong, the transmission spectrum line of the double micro-ring splits to form two supermodes of even and odd symmetry. As the coupling strength increases, the splitting degree between the two supermodes increases.

[0055] Figure 5 The transmission spectrum lines in the case of resonance alignment and misalignment between the double micro-rings when there is coupling between the double micro-rings, and the corresponding in-ring light field distribution simulation diagrams in each case are shown.

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

[0057] Figure 7 The extinction ratio of the supermode corresponding to the larger wavelength under different two-ring resonance wavelengths is shown. The supermode extinction ratio changes with the change of the two-ring resonance wavelength, 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 resonator structure, such as a resonant cavity structure composed of a grating or a photonic crystal, which is within the protection scope of the present patent.

[0059] As can be seen, the innovation of the modulator structure is to use the Aulter-Townes effect and the free carrier dispersion effect for modulation, to change the two-ring resonance wavelength through the phase change material, and to change the extinction ratio corresponding to the two supermodes, to obtain an extremely high static extinction ratio in the unmodulated stage, and to realize 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, The application relates to a silicon-based optical modulator. The application comprises: a single-mode bus waveguide; two ring waveguides which 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 resonant wavelength of the two ring waveguides; a PN junction is integrated in the ring waveguide to realize phase modulation of light through carrier injection; the Aulter-Townes effect is used to split the transmission spectrum of the ring waveguide into two supermodes, and the extinction ratio corresponding to the two supermodes is changed by adjusting the resonant wavelength of the two ring waveguides; meanwhile, the cascaded double-ring structure realizes large modulation bandwidth; two coupling regions exist between the two ring waveguides to form 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 wavelength of the two ring waveguides; the resonant splitting strength is controlled by controlling the coupling strength between the two rings, thereby realizing a high-performance silicon-based optical modulator; 2. The cascaded dual-ring silicon optical modulator of claim 1, wherein, the phase change structure design adopts a phase change material which is Sb2Se3, Sb2S3 or Ge2Sb2Se4Te1; the phase change material is deposited on the surface of the two ring waveguides, an aluminum oxide film is covered on the phase change material, a single-layer graphene is on the aluminum oxide film, and a metal electrode is above the single-layer graphene; the single-layer graphene and the metal electrode are in ohmic contact, current flows through the single-layer graphene to generate heat, the heat is conducted through the underlying aluminum oxide film to provide the required heat for the phase change of the phase change material.

3. The cascaded dual-ring silicon optical modulator of claim 1, wherein, The coupling strength is controlled by the coupling region length and the coupling pitch.

4. The cascaded dual-ring silicon optical modulator of claim 1, wherein, The two ring waveguides are doped to obtain two low-Q resonances; one ring is internally P-doped and externally N-doped, and the other ring is internally N-doped and externally P-doped; or the two rings are doped in the same way but form horizontal PN junction structures or S-shaped PN junction structures at different positions, and the doping structure is controlled by controlling the ion injection angle and position.

5. The cascaded dual-ring silicon optical modulator according to any one of claims 1-4, wherein, The modulation mode comprises: modulating one ring; or simultaneously modulating the two rings in a push-pull PN junction or series PN junction mode.

6. The cascaded dual-ring silicon optical modulator according to any one of claims 1-4, wherein, The single-mode bus waveguide and the two ring waveguides are all silicon waveguides, the width is 0.4-0.5 microns, the height is 0.22 microns, and the waveguide works in the C band or the O band. Before a modulation signal is applied, the resonant wavelength difference of the two ring waveguides is adjusted to realize a high static extinction ratio; and after the modulation signal is applied, dynamic modulation is realized through the Aulter-Townes effect and the free carrier dispersion effect, thereby realizing a high-performance optical modulator.

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