A hybrid integrated electro-optic modulator

Abstract

A hybrid integrated electro-optic modulator includes a base structure on which a signal input region, a signal modulation region, and a signal output region are sequentially arranged in the signal transmission direction. The signal modulation region includes a metal electrode structure, within which multiple transmission channels are spaced apart along the signal transmission direction and connected at both ends to the signal input region and the signal output region, respectively. Each transmission channel contains a first silicon waveguide, a lead zirconate titanate segment, and a second silicon waveguide sequentially connected in the signal transmission direction, with both sides of the three waveguides adhering to the sidewalls of the transmission channel. The lead zirconate titanate in the signal modulation region has a relatively higher electro-optic coefficient, effectively improving upon the limitations of thin-film lithium niobate modulators in related technologies, which have limited electro-optic coefficients, device lengths typically on the order of centimeters, and difficulties in simultaneously achieving high bandwidth, low driving voltage, and small size.

Description

Technical Field

[0001] This application relates to the field of electro-optic modulators for optical interconnects, and more specifically to a hybrid integrated electro-optic modulator. Background Technology

[0002] With the rapid development of 5G, artificial intelligence, and cloud computing technologies, global network traffic demand is experiencing exponential growth. To address this challenge, integrated optics technology has become a key technology for solving the requirements of high bandwidth, low latency, and low power consumption transmission. By integrating photonic devices onto a single chip, integrated optics can significantly improve data transmission speed and capacity, becoming a core supporting technology for next-generation communication networks. Electro-optic modulators, as core components in the field of integrated optics, determine the overall performance of the chip.

[0003] Current electro-optic modulators are mainly based on the carrier dispersion effect of silicon and the Pockel effect of lithium niobate. However, silicon-based modulators have limited bandwidth, thin-film lithium niobate modulators have etching difficulties, and the electro-optic coefficient is limited. The device length is usually on the order of centimeters, making it difficult to simultaneously meet the requirements of high bandwidth, low driving voltage, and small size. Summary of the Invention

[0004] This application provides a hybrid integrated electro-optic modulator that can solve the related technical problems existing in the prior art.

[0005] This application provides a hybrid integrated electro-optic modulator, which adopts the following technical solution:

[0006] A hybrid integrated electro-optic modulator includes a base structure, wherein a signal input area, a signal modulation area, and a signal output area are sequentially arranged on the base structure in the signal transmission direction;

[0007] The signal modulation region includes a metal electrode structure, and the metal electrode structure is provided with multiple transmission channels spaced apart along the signal transmission direction and connected at both ends to the signal input region and the signal output region, respectively.

[0008] The transmission channel is provided with a first silicon waveguide, a lead zirconate titanate segment, and a second silicon waveguide connected in sequence in the direction of signal transmission, and both sides of the three are attached to the two side walls of the transmission channel.

[0009] In one embodiment, the widths of the first silicon waveguide and the second silicon waveguide gradually decrease to be equal to those of the lead zirconate titanate segment in the direction approaching the lead zirconate titanate segment, so that the first silicon waveguide and the second silicon waveguide form a tapered coupler for switching between optical waveguide modes and surface plasmon resonance modes.

[0010] In one embodiment, the metal electrodes forming the two side walls of the transmission channel are arranged perpendicular to the base structure.

[0011] In one embodiment, the lead zirconate titanate segment is disposed in the transmission channel by spin coating.

[0012] In one embodiment, the width of the lead zirconate titanate segment is in the range of 50 nm to 200 nm.

[0013] In one embodiment, the length of the lead zirconate titanate segment is in the range of 70 μm to 300 μm.

[0014] In one embodiment, the first silicon waveguide and the second silicon waveguide are symmetrical about the center of the signal modulation region, and have a length of 40-50 μm in the signal transmission direction.

[0015] In one embodiment, the base structure includes a silicon layer, a buried oxide layer, and a silicon substrate distributed sequentially from top to bottom.

[0016] In one embodiment, the signal input area includes a grating coupler and a multimode interference coupler disposed on the substrate structure.

[0017] In one embodiment, the signal output area includes a grating coupler and a multimode interference coupler disposed on the substrate structure.

[0018] The beneficial effects of the technical solutions provided in this application include:

[0019] Lead zirconate titanate in the signal modulation region has a relatively higher electro-optic coefficient, which effectively improves the problems of limited electro-optic coefficient, device length usually on the order of centimeters, and difficulty in simultaneously meeting the requirements of high bandwidth, low driving voltage, and small size in related technologies. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the hybrid integrated electro-optic modulator provided in this application;

[0021] Figure 2 This is a schematic diagram of the first silicon waveguide structure provided in this application;

[0022] Figure 3 A cross-sectional comparison of the LN plasmonic electro-optic modulator and the hybrid integrated electro-optic modulator provided in this application in their respective signal modulation regions;

[0023] Figure 4 For lead zirconate titanate plasmon polariton mode and radio frequency electric field;

[0024] Figure 5 The diagram shows the overlap integral and half-wave voltage analysis of the hybrid integrated electro-optic modulator provided in this application.

[0025] Figure 6 The RLGC analysis diagram is shown for the electrode equivalent circuit of the hybrid integrated electro-optic modulator provided in this application.

[0026] Figure 7 The electro-optic bandwidth analysis diagram of the circuit is obtained from the simulation of the hybrid integrated electro-optic modulator provided in this application;

[0027] Figure label:

[0028] 1. Signal input area;

[0029] 2. Signal modulation region; 20. Metal electrode structure; 21. First silicon waveguide; 22. Lead zirconate titanate segment; 23. Second silicon waveguide;

[0030] 3. Signal output area. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0033] In a first aspect, embodiments of this application provide a hybrid integrated electro-optic modulator.

[0034] In one embodiment, reference is made to Figure 1 A hybrid integrated electro-optic modulator includes a base structure, wherein a signal input area 1, a signal modulation area 2 and a signal output area 3 are sequentially provided on the base structure in the signal transmission direction;

[0035] The signal modulation region 2 includes a metal electrode structure 20, in which a plurality of transmission channels are spaced apart along the signal transmission direction and connected at both ends to the signal input region 1 and the signal output region, respectively.

[0036] The transmission channel is provided with a first silicon waveguide 21, a lead zirconate titanate segment 22 and a second silicon waveguide 23 connected in sequence in the signal transmission direction, and both sides of the three are attached to the two side walls of the transmission channel.

[0037] Specifically, the base structure includes a buried oxide layer (i.e., a silicon oxide insulating layer, BOX, about a few micrometers thick) and a bottom silicon substrate.

[0038] The electro-optic modulator mainly comprises three parts set on the base structure: the first part is the signal input area 1 of the electro-optic modulator, the second part is the signal modulation area 2 of the modulator, and the third part is the signal output area 3 of the modulator.

[0039] The signal input area 1 includes a grating coupler and a multimode interference coupler formed of silicon material, disposed on the substrate structure. The signal light emitted by the laser can be coupled into the chip through the grating coupler, and then split by the multimode interference coupler (MMI). The signal light is then guided to two phase modulator regions through silicon waveguides to complete signal modulation.

[0040] The signal modulation region 2 of the second part is between the first part and the third part, and includes three metal electrodes arranged side by side in the direction perpendicular to the signal transmission direction. A transmission channel is formed between each pair of metal electrodes. A first silicon waveguide 21 formed of silicon layer material, a lead zirconate titanate segment 22 formed of lead zirconate titanate material, and a second silicon waveguide 23 formed of silicon layer material are arranged in sequence in the transmission channel. Both sides of the three are attached to the two side walls of the transmission channel, that is, attached to the metal electrodes on both sides.

[0041] The signal output area 3 includes a multimode interference coupler and a multimode interference coupler formed of silicon layer material disposed on the base structure. The phase-modulated light output from the signal output area 3 is combined by a 1x2 multimode interference coupler to achieve intensity modulation, and finally coupled out through a grating coupler.

[0042] This configuration allows the lead zirconate titanate material in signal modulation region 2 to have a significantly stronger electro-optic coefficient than lithium niobate, which can significantly reduce the length of the device to the millimeter level.

[0043] Because silicon waveguide materials have a large refractive index difference, a smaller bending radius can be used during transmission. Furthermore, in some embodiments, the widths of the first silicon waveguide 21 and the second silicon waveguide 23 gradually decrease towards the lead zirconate titanate segment 22 until they are equal to the width of the lead zirconate titanate segment 22, so that the first silicon waveguide 21 and the second silicon waveguide 23 form a tapered coupler for converting between optical waveguide modes and surface plasmon resonance modes. Specifically, the width of the end of the first silicon waveguide 21 and the second silicon waveguide 23 furthest from the lead zirconate titanate segment 22 is 450 nm, and the width of the lead zirconate titanate segment 22 is in the range of 50 nm to 200 nm, preferably 100 nm in this embodiment. The length of the lead zirconate titanate segment 22 is 70 μm to 300 μm, preferably 100 μm in this embodiment.

[0044] Specifically, as the width of the first silicon waveguide 21 decreases, its ability to confine light weakens, and the mode field gradually increases. When the spacing between the metal electrodes forming the transmission channel reaches the nanoscale, a metal-insulator-metal structure is constructed by connecting it to the spin-coated lead zirconate titanate segment 22. This effectively excites surface plasmon polariton modes, which can propagate in a subwavelength manner near the interface between the metal and the electro-optic material, forming a strong local electromagnetic field. The refractive index of the lead zirconate titanate material changes under the influence of an external electric field, affecting the propagation characteristics of the surface plasmon polaritons and causing changes in the phase and intensity of the output signal, thus modulating the signal. After modulation, the second silicon waveguide 23 also gradually widens along the propagation direction at a certain angle. At this point, the sidewalls of the second silicon waveguide 23 are tightly fitted to the sidewalls of the metal electrodes, again achieving the conversion of the surface plasmon polariton mode back to the optical waveguide mode.

[0045] Meanwhile, although there are methods in this field to fabricate plasmonic modulators using lithium niobate (LN), the metal electrodes need to be tightly bonded to the lithium niobate material to form a metal-insulator-metal structure to excite surface plasmonic modes. However, because lithium niobate is difficult to etch, current micro / nano fabrication waveguides using thin-film lithium niobate always involve a certain angle of sidewall tilt, such as... Figure 3 As shown in (a), the metal electrode sidewalls forming the transmission channel inevitably develop a certain degree of tilt, causing the electric field direction to no longer be completely horizontal. Due to the birefringence effect of lithium niobate, to achieve maximum electro-optic modulation, an X-cut, Y-transmitted lithium niobate film is typically used, with the Z-axis horizontal for modulation. This results in a certain degree of mismatch between the electric field direction and the Z-axis, reducing modulation efficiency. However, by using lead zirconate titanate, this drawback can be avoided by utilizing its spin-coating properties. After polarization, the electric field and the polarized electro-optic coefficient are in the same direction.

[0046] Based on the above analysis, further, in some embodiments, reference is made to... Figure 3 (b) The metal electrodes forming the two side walls of the transmission channel are arranged perpendicular to the base layer structure. After the metal electrodes first form the corresponding vertical structure, the lead zirconate titanate segments 22 are applied to the transmission channel via spin coating.

[0047] To demonstrate that the plasmonic lead zirconate titanate electro-optic modulator proposed in this patent has significantly better electro-optic overlap integral and half-wave voltage than currently commercial lithium niobate modulators, we first used COMSOL Multiphysics to simulate the plasmonic mode field and the electric field generated by the electrodes, as follows: Figure 4As shown, the plasmon modes are almost entirely localized within the metal-insulator (lead zirconate titanate)-metal gap, exhibiting excellent field enhancement and good overlap with the radio frequency field, enabling full electro-optic interaction. Currently, commercially available modulators typically have a half-wave voltage of around 2-3 V / cm, while CMOS circuit driving voltages are usually less than 1 V. Therefore, modulator lengths are typically around 2 cm to achieve a π-phase transition at a 1 V driving voltage, significantly increasing device size and hindering the miniaturization trend of photonic chips. To quantitatively demonstrate that the modulator proposed in this patent can significantly improve modulation efficiency, we performed quantitative calculations and simulations of the overlap integral and half-wave voltage for different metal-insulator (lead zirconate titanate)-metal gaps.

[0048] The modulation efficiency of an electro-optic modulator is generally measured by the half-wave voltage-length product. This product is typically related to the electro-optic coefficient of the material and the electro-optic overlap integral of the modulation region, and can be expressed as:

[0049]

[0050] Where λ represents the wavelength of the signal light input to the laser, g represents the gap between the signal electrode and the two ground electrodes, Γ represents the electro-optic overlap integral, and r eo denoted by , n represents the electro-optic coefficient of the lead zirconate titanate electro-optic material, and 'n' represents the refractive index of the lead zirconate titanate material. As can be seen from the expression, electro-optic efficiency can be improved by reducing the electrode gap, increasing the electro-optic overlap integral factor, and thus improving the electro-optic coefficient. Compared to current commercial thin-film lithium niobate electro-optic modulators, the electro-optic coefficient of the polarized lead zirconate titanate material is approximately 100 pm / V, representing about three times the improvement over lithium niobate, significantly enhancing modulation efficiency. Furthermore, current thin-film lithium niobate electro-optic modulators typically use a gap of around 5 micrometers between the signal line and ground line to balance metal absorption loss. In contrast, the electro-optic modulator described in this patent, based on a metal-insulator-metal surface plasmon mode, tightly adheres the metal to the spin-coated lead zirconate titanate material sidewalls, with a spacing of approximately 100 nanometers between the metal electrodes. This reduces the modulator electrode spacing by about an order of magnitude, significantly improving modulation efficiency. Moreover, the electro-optic overlap integral is also significantly improved through the local field enhancement effect of the plasmon mode. The electro-optic overlap integral can be expressed as:

[0051]

[0052] It can be seen that the electro-optic overlap integral is related to the spatial distribution of the electric and optical fields. Local field enhancement is achieved by exciting plasmon modes, and the radio frequency electric field is significantly enhanced as the electrode spacing decreases. In this embodiment, a gold electrode with a thickness of 300 nm and a spin-coated lead zirconate titanate material with a thickness of 500 nm were used. The overlap integral and corresponding half-wave voltage for different electrode spacings were simulated using COMSOL multiphysics simulation software. Figure 5 It can be seen that when the metal electrode spacing is 100nm, an overlap integral factor of 0.9 and a corresponding half-wave voltage of 0.12V / mm can be obtained, which is far superior to the thin-film lithium niobate electro-optic modulator.

[0053] In traditional electro-optic modulators utilizing thin-film lead zirconate titanate, the high dielectric constant of lead zirconate titanate (approximately 400-2000) often results in significant microwave losses in Mach-Zehnder modulators with traveling-wave electrode structures, severely impacting the modulator bandwidth. This patent proposes a hybrid integrated electro-optic modulator based on lead zirconate titanate and surface plasmon resonances. Due to its ultra-high modulation efficiency and ultra-small electrode gap, it significantly reduces device size by employing lumped electrodes for modulation. The electro-optic modulator's size is on the order of micrometers, and microwave losses are negligible. The bandwidth of the lumped electrode electro-optic modulator can typically be expressed as:

[0054]

[0055] Simulation using electromagnetic simulation software can yield the parameters of the equivalent RLGC (resistance, inductance, capacitance, conductance) of the lumped electrodes, such as... Figure 6 As shown, due to the high dielectric constant of lead zirconate titanate, the capacitance of the lumped electrode equivalent circuit is relatively large. However, because the device size is short, a high bandwidth can still be obtained. Considering both the photon transit time and the lumped electrode parameters, simulations show that the bandwidth does not decrease significantly within 70 GHz (e.g., Figure 7 (As shown). Therefore, the electro-optic modulator described in this patent simultaneously meets the requirements of large bandwidth, low driving voltage, and small size, making it suitable for future high-speed communication applications.

[0056] Ultimately, the advantages of the device of the present invention are as follows: it utilizes the spin-coating property of lead zirconate titanate material, allowing the device to be fabricated on SOI wafers; it significantly reduces the size of the device by using a hybrid integrated surface plasmon method; it further reduces the half-wave voltage of the modulator by utilizing the high electro-optic coefficient of lead zirconate titanate material; and due to the small device size, it can be modulated using a lumped electrode method, resulting in ultra-high bandwidth.

[0057] Secondly, this application also proposes a process method for preparing the above-mentioned hybrid integrated modulator, including the following steps:

[0058] S100. Prepare a standard SOI wafer. Thin-layer SOI wafers are usually selected. SOI wafers consist of three layers: a top silicon layer (usually 220nm), a middle silicon oxide insulating layer (called buried oxide layer, about a few micrometers thick), and a bottom silicon substrate.

[0059] S200. Photoresist is uniformly coated onto the silicon layer of the SOI wafer. Ultraviolet lithography is then used to irradiate the photoresist through a photomask. The photomask has a waveguide pattern. After exposure, the properties of the exposed areas of the photoresist change, and the pattern is formed through development and fixing.

[0060] S300. After the waveguide pattern is formed on the photoresist, a dry etching method is used to transfer the pattern to the silicon layer. This step uses shallow etching to form the grating structure.

[0061] S400. Repeat the above steps. This step uses full etching to form the waveguide structure and multimode interference coupler structure. Note that you should use the overlay marks for overlay alignment.

[0062] The S500 uses photolithography and metal stripping techniques to grow metal layers and form metal patterns.

[0063] S600 uses the CSD method to spin-coat lead zirconate titanate material.

[0064] S700 performs partial lead zirconate titanate etching on the metal pad to create a window, facilitating high-frequency probe testing.

[0065] In the description of this application, 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 this application 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 this application. 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 application can be understood according to the specific circumstances.

[0066] It should be noted that in this application, 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.

[0067] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. 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 this application. Therefore, this application 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 hybrid integrated electro-optic modulator, characterized in that, It includes a base structure, on which a signal input area, a signal modulation area and a signal output area are sequentially arranged in the signal transmission direction; The signal modulation region includes a metal electrode structure, and the metal electrode structure is provided with multiple transmission channels spaced apart along the signal transmission direction and connected at both ends to the signal input region and the signal output region, respectively. The transmission channel is provided with a first silicon waveguide, a lead zirconate titanate segment, and a second silicon waveguide connected in sequence in the direction of signal transmission, and both sides of the three are attached to the two side walls of the transmission channel.

2. The hybrid integrated electro-optic modulator as described in claim 1, characterized in that, The widths of the first silicon waveguide and the second silicon waveguide gradually decrease to be equal to those of the lead zirconate titanate segment in the direction close to the lead zirconate titanate segment, so that the first silicon waveguide and the second silicon waveguide form a tapered coupler for converting optical waveguide modes and surface plasmon resonance modes.

3. The hybrid integrated electro-optic modulator as described in claim 2, characterized in that, The metal electrodes forming the two side walls of the transmission channel are arranged perpendicular to the base layer structure.

4. The hybrid integrated electro-optic modulator as described in claim 3, characterized in that, The lead zirconate titanate segment is applied to the transmission channel by spin coating.

5. The hybrid integrated electro-optic modulator as described in claim 1, 2, 3, or 4, characterized in that, The width of the lead zirconate titanate segment is in the range of 50nm to 200nm.

6. The hybrid integrated electro-optic modulator as described in claim 5, characterized in that, The length of the lead zirconate titanate segment is in the range of 70um to 300um.

7. The hybrid integrated electro-optic modulator as described in claim 6, characterized in that, The first silicon waveguide and the second silicon waveguide are symmetrical about the center of the signal modulation region, and their lengths in the signal transmission direction are 40~50µm.

8. The hybrid integrated electro-optic modulator as described in claim 1, characterized in that, The underlying structure includes a buried oxide layer and a silicon substrate distributed from top to bottom.

9. The hybrid integrated electro-optic modulator as described in claim 1, characterized in that, The signal input area includes a grating coupler and a multimode interference coupler disposed on the underlying structure.

10. The hybrid integrated electro-optic modulator as described in claim 1, characterized in that, The signal output area includes a grating coupler and a multimode interference coupler disposed on the underlying structure.

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