Hybrid integrated electro-optical modulator

Abstract

A hybrid integrated electro-optical modulator comprises a base layer structure, and a signal input area, a signal modulation area and a signal output area are sequentially arranged on the base layer structure in the signal transmission direction. The signal modulation area comprises a metal electrode structure, a plurality of transmission channels are arranged in the metal electrode structure at intervals, the transmission channels are arranged in the signal transmission direction, and the two ends of each transmission channel are communicated with the signal input area and the signal output area respectively; a first silicon waveguide, a lead zirconate titanate section and a second silicon waveguide which are sequentially connected in the signal transmission direction are arranged in the transmission channel, and the two sides of the first silicon waveguide, the lead zirconate titanate section and the second silicon waveguide are attached to the two side walls of the transmission channel. The lead zirconate titanate in the signal modulation region has a relatively high electro-optic coefficient, so that the problems that the electro-optic coefficient of a thin-film lithium niobate modulator is limited, the length of the device is generally in the centimeter magnitude, and high bandwidth, low driving voltage, small size and the like are difficult to meet at the same time in the related technology are effectively solved.

Description

Technical Field

[0001] The present application relates to the field of electro-optic modulators for optical interconnection, and in particular to a hybrid integrated electro-optic modulator. Background Art

[0002] With the rapid development of 5G, artificial intelligence and cloud computing technologies, the global network traffic demand is growing exponentially. To meet this challenge, integrated optical technology has become a key technology to meet the needs of high-bandwidth, low-latency and low-power transmission. By integrating photonic devices on a single chip, integrated optics can greatly improve data transmission speed and transmission capacity, becoming the core supporting technology for the next generation of communication networks. As a core device in the field of integrated optics, the electro-optic modulator determines the overall performance of the chip.

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

[0004] The present application provides a hybrid integrated electro-optical modulator, which can solve the related technical problems existing in the above-mentioned prior art.

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

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

[0007] The signal modulation area includes a metal electrode structure, in which a plurality of transmission channels are arranged at intervals along the signal transmission direction and the two ends of which are connected to the signal input area and the signal output area respectively;

[0008] The transmission channel is provided with a first silicon waveguide, a lead zirconate titanate segment and a second silicon waveguide which are sequentially connected in the signal transmission direction, and both sides of the three are in contact with 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 in a direction approaching the lead zirconate titanate segment to be equal to the lead zirconate titanate segment, so that the first silicon waveguide and the second silicon waveguide form a tapered coupler for converting an optical waveguide mode and a surface plasmon mode.

[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 um to 300 um.

[0014] In one embodiment, the first silicon waveguide and the second silicon waveguide are symmetrical about the center of the signal modulation area, and the length of each of the first silicon waveguide and the second silicon waveguide in the signal transmission direction is 40-50 um.

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

[0016] In one embodiment, the signal input region includes a grating coupler and a multi-mode interference coupler disposed on the base structure.

[0017] In one embodiment, the signal output region includes a grating coupler and a multi-mode interference coupler disposed on the base structure.

[0018] The beneficial effects brought by the technical solution provided in the embodiments of the present application include:

[0019] The relatively higher electro-optic coefficient of lead zirconate titanate in the signal modulation area effectively improves the problems of limited electro-optic coefficient of thin-film lithium niobate modulator in related technologies. The device length is usually in the centimeter range, which makes it difficult to simultaneously meet the requirements of high bandwidth, low driving voltage, and small size. BRIEF DESCRIPTION OF THE DRAWINGS

[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 diagram of the LN plasmon electro-optic modulator and the hybrid integrated electro-optic modulator provided in the present application in their respective signal modulation regions;

[0023] Figure 4 for lead zirconate titanate plasmon polariton modes and radio frequency electric fields;

[0024] Figure 5 The overlap integral and half-wave voltage analysis diagram of the hybrid integrated electro-optic modulator provided by the present application;

[0025] Figure 6 It is a RLGC analysis diagram of the electrode equivalent circuit based on the hybrid integrated electro-optic modulator provided by the present application;

[0026] Figure 7 The electro-optical bandwidth analysis diagram of the circuit obtained by simulation of the hybrid integrated electro-optical modulator provided by the present application;

[0027] Reference numerals:

[0028] 1. Signal input area;

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

[0030] 3. Signal output area. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below with reference to the accompanying drawings.

[0033] In a first aspect, an embodiment of the present application provides a hybrid integrated electro-optic modulator.

[0034] In one embodiment, referring to Figure 1 , a hybrid integrated electro-optical modulator, comprising a base structure, on which a signal input area 1, a signal modulation area 2 and a signal output area 3 are sequentially arranged in a signal transmission direction;

[0035] The signal modulation area 2 includes a metal electrode structure 20, and a plurality of transmission channels are arranged in the metal electrode structure 20 along the signal transmission direction and the two ends of the transmission channels are connected to the signal input area 1 and the signal output area 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 which are sequentially connected in the signal transmission direction, and both sides of the three are in contact with the two side walls of the transmission channel.

[0037] Specifically, the base structure includes a buried oxide layer (ie, a silicon oxide insulating layer, BOX, which is about several microns thick) and a bottom silicon substrate (silicom substrate).

[0038] The electro-optic modulator mainly includes three parts arranged 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 multi-mode interference coupler formed of a silicon layer material and arranged on the base structure. The signal light emitted by the coupling laser can enter the chip through the grating coupler, and the signal light can be split through the multi-mode interference coupler (MMI), and the signal light can be transmitted to the two phase modulator areas through the silicon waveguide to complete the signal modulation.

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

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

[0042] This arrangement makes it possible to utilize the electro-optical coefficient of the lead zirconate titanate material in the signal modulation area 2 which is significantly stronger than that of lithium niobate, and can significantly reduce the length of the device to the millimeter level.

[0043] Due to the large refractive index difference of the silicon waveguide material, a smaller bending radius can be used during transmission. Furthermore, in some embodiments, the width of the first silicon waveguide 21 and the second silicon waveguide 23 gradually decreases in the direction close to the lead zirconate titanate segment 22 to be equal to 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 the optical waveguide mode and the surface plasmon mode. The width of the first silicon waveguide 21 and the second silicon waveguide 23 away from the lead zirconate titanate segment 22 is specifically 450nm, and the width of the lead zirconate titanate segment 22 is in the range of 50nm to 200nm, preferably 100nm in this embodiment. The length of the lead zirconate titanate segment 22 is 70um to 300um, preferably 100um in this embodiment.

[0044] Specifically, as the width of the first silicon waveguide 21 decreases, the waveguide's ability to bind light becomes weaker, and the mode field gradually increases. When the spacing of the metal electrodes forming the transmission channel reaches the nanometer scale, by connecting to the spin-coated lead zirconate titanate segment 22, a metal-insulator-metal structure is constructed, which can effectively excite the surface plasmon mode. Plasmons can propagate in a sub-wavelength manner near the interface of the metal and the electro-optical material, and form a strong local electromagnetic field. Through the action of the external electric field, the refractive index in the lead zirconate titanate material changes, thereby affecting the propagation characteristics of the surface plasmon, resulting in changes in the phase and intensity of the output signal, and realizing the modulation of the signal. After the signal is modulated, the second silicon waveguide 23 also gradually widens along the propagation direction at a certain angle. At this time, the sidewalls of the second silicon waveguide 23 are closely attached to the sidewalls of the metal electrode, and the surface plasmon mode is transformed back to the optical waveguide mode again.

[0045] Meanwhile, although there are methods in the art to use lithium niobate (LN) materials to make plasmon modulators, the metal electrode needs to be closely attached to the lithium niobate material to form a metal-insulator-metal structure to excite the surface plasmon mode. However, since lithium niobate materials are difficult to etch, there is a certain angle of side wall inclination in the micro-nano processing waveguide of thin-film lithium niobate, such as Figure 3 As shown in (a), the metal electrode sidewalls that form the transmission channel will inevitably have a certain degree of inclination, causing the electric field direction to no longer be completely horizontal. Due to the birefringence effect of lithium niobate materials, in order to obtain the maximum electro-optical modulation, an X-cut Y-transmitted lithium niobate film is usually used, and the Z crystal direction is in the horizontal direction for modulation. In this way, there will be a certain degree of mismatch between the electric field direction and the Z crystal direction, reducing the modulation efficiency. The use of lead zirconate titanate material and the spin-coatable characteristics of the material can avoid this shortcoming. After the material is polarized, the electric field and the polarized electro-optic coefficient are in the same direction.

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

[0047] In order to illustrate that the plasmon lead zirconate titanate electro-optic modulator proposed in this patent has significantly better electro-optic overlap integral and half-wave voltage than the current commercial lithium niobate modulator, we first used Comsol Multiphysics to simulate the plasmon mode field and the electric field generated by the electrode. Figure 4As shown, it can be seen that the plasmon modes are basically all localized in the gap between the metal-insulator (lead zirconate titanate)-metal, which has a good field enhancement effect and a good overlap effect with the radio frequency field, and can achieve full electro-optical effect. For current commercial modulators, the half-wave voltage is usually around 2-3V / cm, while the driving voltage of CMOS circuits is usually less than 1V, so the length of the modulator is usually around 2cm to achieve a π phase shift under a driving voltage of 1V, which greatly increases the size of the device, which is not conducive to the development trend of miniaturization of photonic chips. In order to quantitatively illustrate that the modulator proposed in this patent can significantly improve the modulation efficiency, we simulated the overlap integral and half-wave voltage of different metal-insulator (lead zirconate titanate)-metal gaps through quantitative calculations.

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

[0049]

[0050] Where λ represents the wavelength of the signal light input by the laser, g represents the gap between the signal electrode and the ground electrodes on both sides, Γ represents the electro-optical overlap integral, and r eo 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. It can be seen from the expression that the electro-optic efficiency can be improved by reducing the electrode gap, increasing the electro-optic overlap integral factor, and improving the electro-optic coefficient. Compared with the current commercial thin-film lithium niobate electro-optic modulator, the electro-optic coefficient of the lead zirconate titanate material after polarization is about 100pm / V, which is about three times higher than that of lithium niobate, significantly improving the modulation efficiency. In addition, in order to balance the metal absorption loss problem, the gap between the signal line and the ground line of the current thin-film lithium niobate electro-optic modulator is usually about 5 microns. The electro-optic modulator based on the metal-insulator-metal surface plasmon mode described in this patent is closely fitted to the side wall of the metal and the spin-coated lead zirconate titanate material, and the spacing between the metal electrodes is about 100 nanometers, which reduces the modulator electrode spacing by about an order of magnitude, greatly improving the modulation efficiency, and through the local field enhancement effect of the plasmon mode, the electro-optic overlap integral is also significantly improved. The electro-optic overlap integral can be expressed as:

[0051]

[0052] It can be seen that the electro-optical overlap integral is related to the spatial distribution of the electric field and the optical field. By exciting the plasmon mode, the local field is enhanced, and as the electrode spacing decreases, the RF electric field is significantly enhanced. This embodiment uses a gold electrode with a thickness of 300nm and a spin-coated lead zirconate titanate material with a thickness of 500nm. The overlap integral and the corresponding half-wave voltage of different electrode spacings are simulated by the comsol multi-physics field 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 beyond the thin film lithium niobate electro-optic modulator.

[0053] In traditional electro-optic modulators using thin film lead zirconate titanate, since the dielectric constant of lead zirconate titanate material is usually large (about 400-2000), the Mach-Zehnder modulator using the traveling wave electrode structure usually has large microwave loss, which seriously affects the modulator bandwidth. The hybrid integrated electro-optic modulator based on lead zirconate titanate and surface plasmon proposed in this patent can significantly reduce the size of the device due to its ultra-high modulation efficiency and ultra-small electrode gap, and uses lumped electrodes for modulation. The size of the electro-optic modulator is in the micron range, and the microwave loss can be ignored. The bandwidth of the lumped electrode electro-optic modulator can usually be expressed as:

[0054]

[0055] Through electromagnetic simulation software, the parameters of RLGC (resistance, inductance, capacitance, and conductance) equivalent to the lumped electrode can be obtained, such as Figure 6 As shown in Figure 1, due to the large dielectric constant of lead zirconate titanate material, the capacitance of the lumped electrode equivalent circuit is large, but because the device is short, a high bandwidth can still be obtained. Considering the two factors of photon transit time and lumped electrode parameters, the simulation shows that there is no obvious decrease in bandwidth within 70 GHz (such as Figure 7 As shown). Therefore, the electro-optic modulator described in this patent meets the requirements of large bandwidth, low driving voltage, small size, etc., and is suitable for the future high-speed communication field.

[0056] Finally, the advantages of the device of the present invention are: by utilizing the characteristic that lead zirconate titanate material can be spin-coated, the device can be manufactured on an SOI wafer; by using the hybrid integrated surface plasmon method, the size of the device is significantly reduced; by utilizing the high electro-optic coefficient of lead zirconate titanate material, the half-wave voltage of the modulator is further reduced. At the same time, due to the small size of the device, modulation can be achieved by using a lumped electrode method, which has an ultra-high bandwidth.

[0057] In a second aspect, the present application also proposes a process for preparing the hybrid integrated modulator, comprising the following steps:

[0058] S100, prepare a standard SOI wafer, usually a thin SOI wafer, which consists of three layers: a silicon layer on the top (usually 220nm), a silicon oxide insulating layer in the middle (called a buried oxide layer, about a few microns thick), and a silicon substrate at the bottom.

[0059] S200, uniformly coating the photoresist on the silicon layer of the SOI wafer, and irradiating the photoresist through a photomask using ultraviolet lithography. The photomask has a waveguide pattern, and after exposure, the properties of the exposed area of ​​the photoresist change, and a pattern is formed by developing and fixing.

[0060] S300, after the waveguide pattern is formed on the photoresist, the pattern is transferred to the silicon layer by using a dry etching scheme. This step uses shallow etching to form a grating structure.

[0061] S400, repeat the above steps. This step adopts full etching to form a waveguide structure and a multi-mode interference coupler structure. Attention should be paid to the overlay alignment when using the overlay mark.

[0062] S500: growing a metal layer and forming a metal pattern by using photolithography + metal lift-off technology.

[0063] S600, spin coating lead zirconate titanate material using CSD method.

[0064] S700, partially etch the lead zirconate titanate on the metal pad to complete the window opening to facilitate high-frequency probe testing.

[0065] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present 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 only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0067] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for 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 area includes a metal electrode structure, in which a plurality of transmission channels are arranged at intervals along the signal transmission direction and the two ends of which are connected to the signal input area and the signal output area respectively; The transmission channel is provided with a first silicon waveguide, a lead zirconate titanate segment and a second silicon waveguide which are sequentially connected in the signal transmission direction, and both sides of the three are in contact with the two side walls of the transmission channel.

2. The hybrid integrated electro-optic modulator according to claim 2, characterized in that: The widths of the first silicon waveguide and the second silicon waveguide gradually decrease in a direction approaching the lead zirconate titanate segment to be equal to the lead zirconate titanate segment, so that the first silicon waveguide and the second silicon waveguide form a tapered coupler for converting an optical waveguide mode and a surface plasmon mode.

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

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

5. The hybrid integrated electro-optic modulator according to 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 according to 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 according to claim 6, characterized in that: The first silicon waveguide and the second silicon waveguide are symmetrical about the center of the signal modulation area, and the length of each of the first silicon waveguide and the second silicon waveguide in the signal transmission direction is 40 to 50 um.

8. The hybrid integrated electro-optic modulator according to claim 1, characterized in that: The base structure includes a buried oxide layer and a silicon substrate which are sequentially distributed from top to bottom.

9. The hybrid integrated electro-optic modulator according to claim 1, characterized in that: The signal input region includes a grating coupler and a multi-mode interference coupler arranged on the base structure.

10. The hybrid integrated electro-optic modulator according to claim 1, characterized in that: The signal output region includes a grating coupler and a multi-mode interference coupler arranged on the base structure.

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