A terahertz signal generator on chip and a preparation method thereof

Abstract

This invention provides an on-chip terahertz signal generator and its fabrication method. A radio frequency signal with a frequency of is input via a probe. An intensity modulator and a phase modulator modulate a continuous laser beam to generate an electro-optic frequency comb with equal frequency intervals. When the electro-optic frequency comb passes through the signal generation module, a terahertz signal is generated through sideband parametric down-conversion of the optical frequency based on second-order nonlinear optics. Finally, the terahertz signal is radiated outward through the signal radiation module without introducing significant phase noise, thus improving the quality of the generated terahertz signal. Furthermore, this invention integrates the electro-optic frequency comb generation module, the signal generation module, and the signal radiation module on the same substrate, eliminating the complex spatial optical path alignment and waveguide coupling of traditional discrete component systems. This greatly improves the system's stability, reliability, and compactness. In addition, this invention avoids dependence on expensive femtosecond pulsed laser sources, reducing the cost of generating terahertz signals.

Description

Technical Field

[0001] This invention relates to the field of integrated optoelectronic device technology, and in particular to an on-chip terahertz signal generator and its fabrication method. Background Technology

[0002] In the information technology era, with the explosive growth of big data, artificial intelligence, and global interconnectivity, the demand for information processing speed and transmission capacity is increasing, placing higher requirements on hardware integration and processing speed. Traditional microelectronic devices, limited by their physical principles, face bottlenecks in transistor miniaturization, clock frequency increases, and signal integrity maintenance. Compared to electrons, photons possess multi-dimensional, stable, and controllable modulation and multiplexing characteristics, including amplitude, phase, wavelength, polarization state, and mode, offering greater bandwidth, higher spectral efficiency, and communication capacity. Integrated photonics technology, with its high integration, small size, and compatibility with microelectronic processes, demonstrates enormous application potential in data centers, communications, and sensing.

[0003] Terahertz technology has attracted much attention in many cutting-edge applications due to its unique spectral characteristics, but the generation of on-chip terahertz signal sources has always been a core bottleneck in the development of this field. Integrated photonics has provided a promising on-chip solution for generating terahertz signals, and the main technical approaches currently include schemes based on cascaded multiple independent lasers and schemes based on the nonlinear effect of optical rectification. However, both of these mainstream schemes have significant drawbacks: in the cascaded laser scheme, the random phase difference between the independent lasers introduces significant phase noise, resulting in a noisy terahertz signal that is difficult to meet the signal quality requirements of practical applications; while the scheme based on the nonlinear effect of optical rectification can generate terahertz signals, it relies on a high-performance, expensive femtosecond pulsed laser source, which is not advantageous in terms of economy and system integration.

[0004] Therefore, how to provide an economical, stable, and efficient on-chip terahertz signal source is an urgent problem to be solved. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an on-chip terahertz signal generator and its fabrication method, which solves the problems of poor signal quality or reliance on high-performance and expensive femtosecond laser pulses, high cost and low system integration in the existing terahertz signal generation schemes due to significant phase noise introduced by random phase differences.

[0006] To achieve the above and other related objectives, the present invention provides an on-chip terahertz signal generator, comprising:

[0007] A probe and a tunable continuous laser, the probe generating a frequency of The radio frequency signal, wherein the tunable continuous laser is used to generate laser with the required output power and center wavelength and enter the optical input terminal;

[0008] An electro-optic frequency comb generator module, connected to the probe, generates a free spectral range based on the radio frequency signal. The frequency comb, and one end of the electro-optic frequency comb generating module is connected to the optical input end through a first transmission waveguide;

[0009] A signal generation module, comprising a first straight waveguide and a first ground electrode and a first signal electrode symmetrically distributed about the first straight waveguide, wherein the first straight waveguide is connected to the electro-optic frequency comb generation module through a second transmission waveguide, and a terahertz signal is generated by the frequency comb generated by the electro-optic frequency comb generation module.

[0010] The signal radiation module includes a second straight waveguide and an antenna structure. One end of the second straight waveguide is connected to the signal generation module, and the other end of the second straight waveguide is connected to the optical output terminal. The antenna structure is connected to the first ground electrode and the first signal electrode to radiate terahertz signals into free space through the antenna structure.

[0011] Optionally, the electro-optic frequency comb generating module includes at least two cascaded intensity modulators and phase modulators, wherein the intensity modulators and phase modulators are of the type of Mach-Zehnder modulator, Michelson modulator, IQ modulator, optical transmission straight waveguide, or polarization modulator.

[0012] Optionally, the intensity modulator is a Mach-Zehnder modulator, which includes a first optical waveguide, a second optical waveguide, a coupler, a second ground electrode, a second signal electrode, and a third ground electrode. The first and second optical waveguides are arranged in parallel. The coupler is disposed at both ends of the first and second optical waveguides. One end of the coupler is connected to the first and second optical waveguides respectively via two bent waveguides. The other end of the coupler is connected to the first transmission waveguide and the phase modulator. The second and third ground electrodes are disposed outside the first and second optical waveguides respectively. The second signal electrode is disposed in the middle of the first and second optical waveguides, and the probe is connected to the second signal electrode. The phase modulator includes at least a third straight waveguide and a third signal electrode, wherein the third straight waveguide is connected to the intensity modulator and the second transmission waveguide.

[0013] Optionally, the thickness of the second signal electrode is 0.5~20μm, the width of the second signal electrode is 30~80μm, and the distance between the second signal electrode and the second ground electrode and the third ground electrode is 2~7μm.

[0014] Optionally, the materials forming the second ground electrode, the second signal electrode, the third ground electrode, and the third signal electrode include at least one of titanium, gold, silver, copper, niobium, aluminum, and chromium.

[0015] Optionally, the antenna structure includes at least a first antenna and a second antenna, the first antenna and the second antenna being symmetrically distributed about the second straight waveguide, and the first antenna being connected to the first ground electrode and the second antenna being connected to the first signal electrode.

[0016] Optionally, the first antenna and the second antenna have the same shape and are either an L-shaped antenna or a butterfly-shaped antenna.

[0017] Optionally, the height of the first ground electrode and the first signal electrode is 700~900nm, and the distance between the first ground electrode and the first signal electrode is 1.5~3μm.

[0018] Optionally, the electro-optic frequency comb generating module, the signal generating module, and the signal radiating module are all formed on the same substrate, and an optical isolation layer and a photoelectric thin film layer are also formed on the substrate. The refractive index of the optical isolation layer is less than that of the photoelectric thin film layer, and the thickness of the optical isolation layer is 0.3~20μm.

[0019] The present invention also provides a method for fabricating an on-chip terahertz signal generator, which is used to fabricate the above-mentioned on-chip terahertz signal generator. The fabrication method includes the following steps:

[0020] A substrate is provided, on which an optical isolation layer and a photoelectric thin film layer are sequentially formed;

[0021] A first photoresist layer is formed by coating a photoresist layer on the surface of the photoelectric thin film layer, and the first photoresist layer is exposed and developed to transfer the waveguide pattern of the electro-optic frequency comb generation module, the waveguide pattern of the signal generation module, and the waveguide pattern of the signal radiation module into the first photoresist layer.

[0022] The photoelectric thin film layer is subjected to dry etching, removal of the first photoresist layer and wet etching processes in sequence, thereby transferring the waveguide pattern of the electro-optic frequency comb generation module, the waveguide pattern of the signal generation module and the waveguide pattern of the signal radiation module into the photoelectric thin film layer.

[0023] A second photoresist layer is formed by coating the photoelectric thin film layer again, and the second photoresist layer is exposed and developed to define the electrode pattern.

[0024] A metal layer is deposited in the electrode pattern to form a first ground electrode, a first signal electrode, a second ground electrode, a second signal electrode, a third ground electrode, a third signal electrode, and an antenna structure.

[0025] As described above, the on-chip terahertz signal generator and its fabrication method of the present invention have the following beneficial effects: By inputting a frequency of [frequency value missing] through a probe... The invention utilizes an optical waveguide to input a continuous laser beam. When the continuous laser beam passes through the electro-optic frequency comb generation module, an intensity modulator and a phase modulator modulate the continuous laser beam to generate an electro-optic frequency comb with equal frequency intervals. When the electro-optic frequency comb passes through the signal generation module, a terahertz signal is generated by down-converting the sideband parametric of the optical frequency based on second-order nonlinear optics. Finally, the terahertz signal is radiated outward through the signal radiation module without introducing significant phase noise, thus improving the quality of the final generated terahertz signal. Furthermore, this invention integrates the electro-optic frequency comb generation module, the signal generation module, and the signal radiation module on the same substrate, eliminating the complex spatial optical path alignment and waveguide coupling of traditional discrete component systems, greatly improving the stability, reliability, and compactness of the system. In addition, this invention can avoid dependence on expensive and complex femtosecond pulsed laser sources, thereby reducing the cost of generating terahertz signals. Attached Figure Description

[0026] Figure 1 The diagram shows the connection between the modules in the on-chip terahertz signal generator of the present invention.

[0027] Figure 2 The diagram shown is a top view of the on-chip terahertz signal generator of the present invention.

[0028] Figure 3 The diagram shown is a top view of the electro-optic frequency comb generating module according to an embodiment of the present invention.

[0029] Figure 4 The diagram shown is a top view of the electro-optic frequency comb generating module in another embodiment of the present invention.

[0030] Figure 5 The diagram shows a frequency comb spectrum generated by the laser after passing through the electro-optic frequency comb generation module in one embodiment of the present invention.

[0031] Figure 6The graph shows the normalized gain versus interaction length curves under different refractive index mismatch values ​​in an on-chip terahertz signal generator of an embodiment of the present invention, where the terahertz signal is 0.8 THz.

[0032] Figure 7 The diagram shows the process flow of the fabrication method of the on-chip terahertz signal generator of the present invention.

[0033] Component designation explanation

[0034] 10. Probe; 11. Tunable continuous laser; 12. Electro-optic frequency comb generation module; 14. Signal generation module; 141. First signal electrode; 142. First straight waveguide; 143. First ground electrode; 15. Signal radiation module; 151. Second straight waveguide; 152. First antenna; 153. Second antenna; 16. Intensity modulator; 160. First input waveguide; 161. First optical waveguide; 162. Second optical waveguide; 163. Second ground electrode; 164. Second signal electrode; 165. Third ground electrode; 166. Coupler; 167. Bent waveguide; 17. Phase modulator; 170. Third signal electrode; 171. Third straight waveguide; 172. Fourth ground electrode; 173. Fifth ground electrode; S1~S5, Steps. Detailed Implementation

[0035] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0037] It should be understood that the use of terms such as "first" and "second" to define the components is merely for the purpose of distinguishing the aforementioned components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0038] Please see Figures 1 to 7It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0039] Example 1

[0040] Please see Figure 1 , Figure 1 This is a schematic diagram illustrating the connection between modules in an on-chip terahertz signal generator according to an embodiment of the present invention. The on-chip terahertz signal generator in this embodiment includes a probe 10, a tunable continuous laser 11, an electro-optic frequency comb generation module 12, a signal generation module 14, and a signal radiation module 15. The probe 10 is connected to the electro-optic frequency comb generation module 12 and is used to generate a signal with a frequency of... The tunable continuous laser 11 is used to generate continuous laser light. The continuous laser light is directed towards the optical input end and further transmitted to the electro-optic frequency comb generation module 12. The continuous laser light is further modulated by the electro-optic frequency comb generation module 12, so that an electro-optic frequency comb with equal frequency intervals is output at the output end of the electro-optic frequency comb generation module 12. Then, the electro-optic frequency comb signal is transmitted to the signal generation module 14 through the second transmission waveguide. The terahertz signal is generated by the sideband parametric down-conversion of the optical frequency. The terahertz signal is transmitted to the signal radiation module 15 and radiated into the external free space through the antenna structure.

[0041] As an example, the electro-optic frequency comb generating module 12, the signal generating module 14, and the signal radiation module 15 are all formed on the same substrate, and an optical isolation layer and a photoelectric thin film layer are also formed on the substrate. The refractive index of the optical isolation layer is less than that of the photoelectric thin film layer, and the thickness of the optical isolation layer is 0.3~20μm.

[0042] Specifically, in this embodiment, the substrate is a wafer-level single-crystal silicon carbide substrate. Single-crystal silicon carbide is a good thermal conductor with a thermal conductivity exceeding 500 W / (m·K), thereby effectively avoiding interference from thermal effects on the continuous laser modulation of the electro-optic frequency comb generation module 12. Furthermore, single-crystal silicon carbide has low dielectric loss and a dielectric constant that matches the refractive index of the optical group in the high-frequency band, which can enhance the electric field strength and improve modulation efficiency.

[0043] Specifically, in this embodiment, the material of the optical isolation layer includes at least one of silicon dioxide or quartz. The thickness of the optical isolation layer is 0.3~20μm, which is not limited here. Silicon dioxide or quartz has good insulation and low dielectric constant. By setting an appropriate thickness of the optical isolation layer, mutual interference between different layers can be effectively prevented, and losses during continuous laser transmission can be reduced.

[0044] In some embodiments, the material of the photoelectric thin film layer includes one of lithium niobate, lithium tantalate, silicon nitride, silicon carbide, barium titanate, or lead zirconate titanate, and the refractive index of the photoelectric thin film layer is greater than the refractive index of the optical isolation layer. The above-mentioned materials forming the photoelectric thin film layer have excellent electro-optic effects and are suitable for preparing the waveguide structure required for laser transmission in the electro-optic frequency comb generation module 12, signal generation module 14, and signal radiation module 15. The thickness of the photoelectric thin film layer is 300~1000nm, and the thickness of the photoelectric thin film layer can be any value within the above range, which will not be elaborated here.

[0045] As an example, such as Figure 2 As shown, the electro-optic frequency comb generating module 12 includes at least two cascaded intensity modulators 16 and phase modulators 17, wherein the intensity modulators 16 and the phase modulators 17 are of the following types: Mach-Zehnder modulator, Michelson modulator, IQ modulator, optical transmission straight waveguide, or polarization modulator.

[0046] Specifically, in this embodiment, such as Figure 3 As shown, the intensity modulator 16 is a Mach-Zehnder modulator, which includes a first optical waveguide 161, a second optical waveguide 162, a coupler 166, a second ground electrode 163, a second signal electrode 164, and a third ground electrode 165. The first optical waveguide 161 and the second optical waveguide 162 are arranged in parallel. The coupler 166 is disposed at both ends of the first optical waveguide 161 and the second optical waveguide 162. One end of the coupler 166 is connected to the first optical waveguide 162 via two bent waveguides 167. The first optical waveguide 161 and the second optical waveguide 162 are connected. The other end of the coupler 166 is connected to the first transmission waveguide and the phase modulator 17, respectively. The second ground electrode 163 and the third ground electrode 165 are respectively disposed on the outside of the first optical waveguide 161 and the second optical waveguide 162. The second signal electrode 164 is disposed in the middle of the first optical waveguide 161 and the second optical waveguide 162, and the probe 10 is connected to the second signal electrode 164. The probe 10 generates a radio frequency signal to the second signal electrode 164.

[0047] Specifically, such as Figure 3As shown, the phase modulator 17 includes a third straight waveguide 171 and a third signal electrode 170. The third straight waveguide 171 is connected to the intensity modulator 16 and the second transmission waveguide, respectively. In this embodiment, the third straight waveguide 171 and the intensity modulator 16 are connected by a bent waveguide, and the phase modulator 17 and the intensity modulator 16 share the same third ground electrode 165, thereby further improving the integration and saving substrate area.

[0048] In another embodiment of the invention, such as Figure 4 As shown, the phase modulator 17 includes a third straight waveguide 171, a third signal electrode 170, a fourth ground electrode 172, and a fifth ground electrode 173. The fourth ground electrode 172 and the fifth ground electrode 173 are symmetrically distributed about the third signal electrode 170. One end of the third straight waveguide 171 is directly connected to the intensity modulator 16, and the other end of the third straight waveguide 171 is connected to the second transmission waveguide.

[0049] Optionally, the thickness of the second signal electrode 164 is 0.5~20μm, the width of the second signal electrode 164 is 30~80μm, the distance between the second signal electrode 164 and the second ground electrode 163 and the third ground electrode 165 is 2~7μm, and the material forming the second ground electrode 163, the second signal electrode 164, the third ground electrode 165 and the third signal electrode 170 includes at least one of titanium, gold, silver, copper, niobium, aluminum and chromium.

[0050] Specifically, in this embodiment, the second ground electrode 163, the second signal electrode 164, the third ground electrode 165, and the third signal electrode 170 are all titanium / silver / gold electrodes, wherein the thickness of the titanium layer is 30nm, the thickness of the silver layer is approximately 800nm, the thickness of the gold layer is 50nm, the width of the second signal electrode 164 is 30μm, and the distance between the second signal electrode 164 and the second ground electrode 163 and the third ground electrode 165 is 5μm.

[0051] Specifically, in this embodiment, when the continuous laser enters the electro-optic frequency comb generation module 12 through the optical input terminal, the laser signal first enters the intensity modulator 16, and the frequency of the modulation signal input to the intensity modulator 16 must not exceed the maximum frequency of the intensity modulator 16. The DC bias voltage applied to the intensity modulator 16 is 2V, and the radio frequency signal voltage is 1.5V, thereby generating carriers with equal amplitude. The signal modulated by the intensity modulator 16 is used as the carrier and enters the phase modulator 17 for further modulation, further expanding the spectrum and flattening. Finally, an electro-optic frequency comb with equal frequency intervals is output at the output terminal of the phase modulator 17.

[0052] In this embodiment, the carrier signal is mathematically represented as follows: Physically, this is represented by an amplitude in the time domain as... The vibration angular frequency is The monochromatic wave; when the above monochromatic wave signal passes through the electro-optic frequency comb generation module 12, the final output signal is mathematically represented as: The final output signal is then subjected to a Fourier transform to obtain a frequency domain signal, which is mathematically represented as follows: ,in, This illustrates the photoelectric coupling process of an optical signal carrier wave passing through the electro-optic frequency comb generation module 12 in the time domain. The intensity modulator 16 controls the amplitude of the light wave. By setting a suitable DC bias point, the optical signal carrier wave can be suppressed, and a preliminary spectral envelope is formed. The phase modulator 17 is responsible for introducing pure phase modulation, which does not change the intensity of the optical signal but can generate a large number of sidebands. This represents the photoelectric coupling process of an optical signal carrier passing through the electro-optic frequency comb generation module 12 in the frequency domain. The frequency domain signal consists of a series of signals that satisfy... The independent frequency components of the relationship are modulated by phase modulator 17 to a depth of [missing information]. Forming a basic Bessel distribution spectral line pattern, and These are the modulation coefficients of intensity modulator 16 and phase modulator 17. It is the DC bias voltage of intensity modulator 16. It is the input RF source of intensity modulator 16. It is the input RF source of intensity modulator 16. It is the input optical carrier frequency, with a value of 1550nm. It is a Bessel function of the first kind. and It is the modulation depth of intensity modulator 16 and phase modulator 17. V is the source voltage. It is the half-wave voltage of the modulator.

[0053] According to the characteristics of the Bessel function, the amplitude of the comb teeth generated by using the phase modulator 17 alone decays rapidly with the order, while the number of comb teeth generated by using the intensity modulator 16 alone is limited and its symmetry is restricted. In this embodiment, after the carrier signal passes through the electro-optic frequency comb generation module 12, due to the combination of intensity modulation and phase modulation, a second overlap of Bessel spectral lines can be formed on the basic spectral line type. The spectral phase and intensity can be freely adjusted to achieve spectral shaping, and finally, comb teeth with consistent amplitude are obtained within a relatively wide bandwidth. Figure 5 It can be seen that the FSR of its frequency domain spectrum is the electro-optic frequency comb.

[0054] In this embodiment, as Figure 2 As shown, the signal generation module 14 includes a first straight waveguide 142 and a first ground electrode 143 and a first signal electrode 141 symmetrically distributed about the first straight waveguide 142. The first straight waveguide 142 is connected to the output terminal of the electro-optic frequency comb generation module 12 through a second transmission waveguide. The signal generation module 14 generates a terahertz signal using the frequency comb generated by the electro-optic frequency comb generation module 12.

[0055] As an example, the height of the first ground electrode 143 and the first signal electrode 141 is 700~900nm, and the distance between the first ground electrode 143 and the first signal electrode 141 is 1.5~3μm.

[0056] Specifically, in this embodiment, the height of the first ground electrode 143 and the first signal electrode 141 is set to 800 nm, and the distance between the first ground electrode 143 and the first signal electrode 141 is 2 μm, according to the required terahertz signal size.

[0057] The signal generation module 14 is based on second-order nonlinear optics and converts sideband pairs in the optical frequency comb into terahertz signals through sideband parametric down-conversion of the optical frequency. Specifically, in this embodiment, as shown... Figure 5 As shown, an efficient parametric down-conversion process is designed between the 0th-order sideband and the 20th-order sideband, which will generate a signal with a target frequency of 0.8 THz. To improve the generation efficiency of the terahertz signal, a coherent three-wave mixing design is required for the 0th-order sideband, the 20th-order sideband, and the 0.8 THz signal. The design must adhere to phase matching, and the wave vector mismatch of the three waves must satisfy the following conditions during phase matching: ,in The wave vector mismatch refers to the three waves, and L represents the coherence length of the parametric process. To achieve effective phase matching, the coherence length L of the parametric process must satisfy the following conditions: ,in, This is expressed as the refractive index mismatch between the terahertz signal and the light wave. Based on the above design criteria, this embodiment takes a generated terahertz signal of 0.8 THz as an example. When the terahertz signal is 0.8 THz and... At that time, the coherence length of its parametric process can reach the millimeter level.

[0058] The signal generation module 14 generates terahertz fields based on a nonlinear process. ,in The physical lengths of the first ground electrode 143 and the first signal electrode 141 in the signal generation module 14, and the coherence function. This indicates the nonlinear coherent conversion efficiency of the three-wave mixing.

[0059] like Figure 6 As shown, simulations were performed at 0.8 THz at different frequencies. Numerical trend of gain G as interaction length increases. Figure 6 It can be seen that as the phase mismatch worsens, the gain G rapidly decreases over the effective interaction length. Considering 0.8 THz, the transmission line loss is... , Under the phase mismatch design, the normalized effective gain G is 0.65 when the physical length of the first ground electrode 143 and the first signal electrode 141 is 2mm.

[0060] Furthermore, the first ground electrode 143 and the first signal electrode 141 of the signal generation module 14 are interconnected with the antenna structure in the signal radiation module 15. The output terminal of the signal generation module 14 is interconnected with the second straight waveguide 151 in the signal radiation module 15. The other end of the second straight waveguide 151 is connected to the optical output terminal, and the terahertz signal is radiated into free space through the antenna structure.

[0061] Specifically, in this embodiment, the antenna structure includes a first antenna 152 and a second antenna 153. The first antenna 152 and the second antenna 153 are symmetrically distributed about the second straight waveguide 151, and the first antenna 152 is connected to the first ground electrode 143, and the second antenna 153 is connected to the first signal electrode 141.

[0062] In other embodiments, the antenna structure may further include multiple cascaded third and fourth antennas, wherein the third antenna is connected to the first antenna 152 and the fourth antenna is connected to the second antenna 153. By setting multiple antennas, the efficiency of terahertz signal radiation into free space can be achieved.

[0063] In some embodiments, the first antenna 152 and the second antenna 153 have the same shape and are either an L-shaped antenna or a butterfly-shaped antenna.

[0064] Specifically, such as Figure 2 As shown, in this embodiment, the first antenna 152 and the second antenna 153 in the signal radiation module 15 are designed as L-shaped antennas. Furthermore, to ensure good radiation capabilities of the first antenna 152 and the second antenna 153, their vertical lengths are designed to be half the wavelength of the radiated signal. It can be seen that the vertical length of the antenna is approximately 0.2 mm at 0.8 THz.

[0065] Example 2

[0066] This embodiment provides a method for fabricating an on-chip terahertz signal generator, such as... Figure 7 The diagram shown is a process flow chart of the fabrication method of the on-chip terahertz signal generator, which includes the following steps:

[0067] S1: A substrate is provided, on which an optical isolation layer and a photoelectric thin film layer are sequentially formed;

[0068] S2: Coating photoresist on the surface of the optoelectronic thin film layer to form a first photoresist layer, and exposing and developing the first photoresist layer to transfer the waveguide pattern of the electro-optic frequency comb generation module 12, the waveguide pattern of the signal generation module 14, and the waveguide pattern of the signal radiation module 15 into the first photoresist layer.

[0069] S3: The photoelectric thin film layer is sequentially subjected to dry etching, removal of the first photoresist layer and wet etching process, thereby transferring the waveguide pattern of the electro-optic frequency comb generation module 12, the waveguide pattern of the signal generation module 14 and the waveguide pattern of the signal radiation module 15 into the photoelectric thin film layer.

[0070] S4: A second photoresist layer is formed by coating the photoelectric thin film layer with photoresist again, and the second photoresist layer is exposed and developed to define the electrode pattern;

[0071] S5: Deposit a metal layer in the electrode pattern to form a first ground electrode 143, a first signal electrode 141, a second ground electrode 163, a second signal electrode 164, a third ground electrode 165, and a third signal electrode 170, as well as an antenna structure.

[0072] The fabrication method of the on-chip terahertz signal generator is further described below with reference to the accompanying drawings:

[0073] In step S1, a substrate is provided, and an optical isolation layer and a photoelectric thin film layer are sequentially formed on the substrate.

[0074] As an example, the substrate is a wafer-level silicon carbide substrate. Silicon carbide is a good conductor of heat, with a thermal conductivity exceeding 500 W / (m·K), which can effectively avoid the interference of thermal effects on the continuous laser modulation of the electro-optic frequency comb generation module 12. In addition, silicon carbide has low dielectric loss and a dielectric constant that can match the refractive index of the optical group in the high-frequency band, which can improve the electric field strength and increase the modulation efficiency.

[0075] In some embodiments, the thickness of the substrate ranges from 0.2 to 1 mm, but this is not limited here.

[0076] Specifically, in this embodiment, the substrate thickness is 0.5 mm, thereby avoiding the problem of increased light loss during propagation caused by a larger substrate thickness.

[0077] As an example, an optical isolation layer and a photoelectric thin film layer are sequentially formed on the substrate. Specifically, the optical isolation layer is formed on one side surface of the substrate using physical vapor deposition or chemical vapor deposition.

[0078] In some embodiments, the material forming the optical isolation layer includes at least one of silicon dioxide or quartz. Silicon dioxide or quartz has good insulation and low dielectric constant, which can effectively prevent mutual interference between different layers and reduce the transmission loss of optical signals.

[0079] In some embodiments, the thickness of the optical isolation layer is 0.3~20μm, but this is not limited here.

[0080] Specifically, in this embodiment, the optical isolation layer is a silicon dioxide layer with a thickness of 2 μm. By setting the thickness range mentioned above, not only can microwave loss be reduced, but also the interaction between different layers can be avoided.

[0081] Specifically, the steps for forming the optoelectronic thin film layer are as follows: providing an ion-implanted optical waveguide wafer, flip-bonding the optical waveguide wafer to the optical isolation layer, and then performing a high-temperature annealing process to form an optoelectronic thin film layer on the optical isolation layer.

[0082] In this embodiment, the optical waveguide wafer is a lithium tantalate wafer, and the size of the lithium tantalate wafer is equal to the size of the substrate. Specifically, ions are implanted into the lithium tantalate wafer using ion implantation, and the lithium tantalate wafer is sequentially divided into a residual layer, a separation layer, and a lithium tantalate thin film layer. The lithium tantalate wafer is flip-chip bonded to the optical isolation layer, and then a high-temperature annealing process is performed, specifically annealing at 550°C for 6 hours. The residual layer and the lithium tantalate thin film layer are separated, and a photoelectric thin film layer is formed on the optical isolation layer. The photoelectric thin film layer is then chemically and mechanically polished to reduce the roughness of the photoelectric thin film layer.

[0083] In other embodiments, the material forming the photoelectric thin film layer may also include one of lithium niobate, silicon nitride, silicon carbide, barium titanate, or lead zirconate titanate, and the refractive index of the photoelectric thin film layer is greater than the refractive index of the optical isolation layer.

[0084] The thickness of the photoelectric thin film layer is 300~1000nm, and the thickness of the photoelectric thin film layer can be adjusted by adjusting the ion implantation depth. Specifically, the greater the ion implantation depth, the greater the thickness of the prepared photoelectric thin film layer; conversely, the smaller the ion implantation depth, the smaller the thickness of the prepared photoelectric thin film layer. Specifically, in this embodiment, the thickness of the photoelectric thin film layer is 600nm.

[0085] In step S2, photoresist is coated on the surface of the photoelectric thin film layer to form a first photoresist layer, and the first photoresist layer is exposed and developed to transfer the waveguide pattern of the electro-optic frequency comb generation module 12, the waveguide pattern of the signal generation module 14, and the waveguide pattern of the signal radiation module 15 into the first photoresist layer.

[0086] In this embodiment, a first photoresist layer is formed by coating photoresist on the optoelectronic thin film layer. The photoresist is MaN2405 electron beam photoresist, and the thickness of the first photoresist layer is 600nm. The first photoresist layer is subjected to drying, exposure, and development processes to transfer the waveguide pattern of the electro-optic frequency comb generation module 12, the waveguide pattern of the signal generation module 14, and the waveguide pattern of the signal radiation module 15 into the first photoresist layer to realize the patterning process of the first photoresist layer. The patterned first photoresist layer is used as a mask for subsequent etching.

[0087] In step S3, the optoelectronic thin film layer is subjected to dry etching, removal of the first photoresist layer and wet etching processes in sequence, thereby transferring the waveguide pattern of the electro-optic frequency comb generation module 12, the waveguide pattern of the signal generation module 14 and the waveguide pattern of the signal radiation module 15 into the optoelectronic thin film layer.

[0088] Specifically, the photoelectric thin film layer is dry etched with a patterned first photoresist layer to form the waveguide structure of the electro-optic frequency comb generation module 12, the waveguide structure of the signal generation module 14, and the structure of the signal radiation module 15 in the photoelectric thin film layer.

[0089] In some embodiments, the dry etching method for the photoelectric thin film layer includes ion beam etching, reactive ion etching, or inductively coupled plasma etching. Preferably, in this embodiment, the dry etching method for the photoelectric thin film layer is reactive ion etching, wherein the etching depth is 500 nm and the width of the retained waveguide structure is 1.0 μm.

[0090] In step S4, photoresist is coated again on the photoelectric thin film layer to form a second photoresist layer, and the second photoresist layer is exposed and developed to define the electrode pattern.

[0091] Specifically, after performing step S3, a second photoresist layer is formed by coating the remaining photoelectric thin film layer with photoresist of type LOR10A and AZ5214 dual-layer photoresist. The thickness of the second photoresist layer is 1000nm. The second photoresist layer is then dried, exposed, and developed to define the electrode pattern.

[0092] In step S5, a metal layer is deposited in the electrode pattern to form a first ground electrode 143, a first signal electrode 141, a second ground electrode 163, a second signal electrode 164, a third ground electrode 165, and a third signal electrode 170, as well as an antenna structure.

[0093] Specifically, in this embodiment, a patterned second photoresist layer is used as an etching mask to form an electrode deposition region on the photoelectric thin film layer. In the electrode deposition region, an electron beam evaporation technique is used to deposit a metal layer to form the first ground electrode 143, the first signal electrode 141, the second ground electrode 163, the second signal electrode 164, the third ground electrode 165, and the third signal electrode 170, as well as the antenna structure. Optionally, before depositing the metal layer in the electrode deposition region using electron beam evaporation, the first photoresist layer and the second photoresist layer need to be removed.

[0094] Optionally, the materials used to form the first ground electrode 143, the first signal electrode 141, the second ground electrode 163, the second signal electrode 164, the third ground electrode 165, and the third signal electrode 170, as well as the antenna structure, include at least one of titanium, gold, silver, copper, niobium, aluminum, and chromium. Specifically, in this embodiment, titanium / silver / gold electrodes are sequentially deposited in the electrode deposition area using electron beam evaporation technology. The titanium layer has a thickness of 30 nm, the silver layer has a thickness of approximately 800 nm, and the gold layer has a thickness of 50 nm. During the deposition process, the deposition rate and thickness are controlled in real time using a film thickness monitor to ensure the uniformity and conductivity of each metal layer. After deposition, chemical mechanical polishing (CMP) is used to planarize the metal layers. By selecting appropriate polishing fluid and polishing pads, and adjusting the polishing pressure and polishing time, the surface flatness of the distributed electrodes is reduced.

[0095] After forming the above structure, a customized RF four-probe 10 can be used to apply a 40 GHz RF source to the electro-optic frequency comb generation module, while an external DC source is connected to adjust the voltage and RF phase shifter. Finally, a spectral frequency comb with high power and high-order sidebands can be generated. The spectral frequency comb is further passed through the signal generation module 14 to generate a terahertz signal, which is then radiated into free space through the antenna structure. In summary, the on-chip terahertz signal generator and its fabrication method of the present invention involve inputting a radio frequency signal with a frequency of Hz via a probe and inputting a continuous laser beam via an optical waveguide. When the continuous laser beam passes through the electro-optic frequency comb generation module, an intensity modulator and a phase modulator modulate the continuous laser beam to generate an electro-optic frequency comb with equal frequency intervals. When the electro-optic frequency comb passes through the signal generation module, a terahertz signal is generated by down-converting the sideband parametric parameters of the optical frequency based on second-order nonlinear optics. Finally, the terahertz signal is radiated outward through the signal radiation module. This process does not introduce significant phase noise, thus improving the quality of the final generated terahertz signal. Furthermore, the present invention integrates the electro-optic frequency comb generation module, the signal generation module, and the signal radiation module on the same substrate, eliminating the complex spatial optical path alignment and waveguide coupling of traditional discrete component systems, greatly improving the system's stability, reliability, and compactness. In addition, the present invention avoids dependence on expensive and complex femtosecond pulsed laser sources, thereby reducing the cost of terahertz signal generation. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0096] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An on-chip terahertz signal generator, characterized in that, include: A probe and a tunable continuous laser, the probe generating a frequency of The radio frequency signal, wherein the tunable continuous laser is used to generate laser with the required output power and center wavelength and enter the optical input terminal; An electro-optic frequency comb generator module, connected to the probe, generates a free spectral range based on the radio frequency signal. The frequency comb, and one end of the electro-optic frequency comb generating module is connected to the optical input end through a first transmission waveguide; A signal generation module, comprising a first straight waveguide and a first ground electrode and a first signal electrode symmetrically distributed about the first straight waveguide, wherein the first straight waveguide is connected to the electro-optic frequency comb generation module through a second transmission waveguide, and a terahertz signal is generated by the frequency comb generated by the electro-optic frequency comb generation module. The signal radiation module includes a second straight waveguide and an antenna structure. One end of the second straight waveguide is connected to the signal generation module, and the other end of the second straight waveguide is connected to the optical output terminal. The antenna structure is connected to the first ground electrode and the first signal electrode to radiate terahertz signals into free space through the antenna structure.

2. The on-chip terahertz signal generator according to claim 1, characterized in that: The electro-optic frequency comb generating module includes at least two cascaded intensity modulators and phase modulators, wherein the intensity modulators and phase modulators are of the type of Mach-Zehnder modulator, Michelson modulator, IQ modulator, optical transmission straight waveguide, or polarization modulator.

3. The on-chip terahertz signal generator according to claim 2, characterized in that: The intensity modulator is a Mach-Zehnder modulator, which includes a first optical waveguide, a second optical waveguide, a coupler, a second ground electrode, a second signal electrode, and a third ground electrode. The first and second optical waveguides are arranged in parallel. The coupler is located at both ends of the first and second optical waveguides. One end of the coupler is connected to the first and second optical waveguides respectively via two bent waveguides. The other end of the coupler is connected to the first transmission waveguide and the phase modulator. The second and third ground electrodes are located outside the first and second optical waveguides respectively. The second signal electrode is located in the middle of the first and second optical waveguides, and the probe is connected to the second signal electrode. The phase modulator includes at least a third straight waveguide and a third signal electrode, wherein the third straight waveguide is connected to the intensity modulator and the second transmission waveguide.

4. The on-chip terahertz signal generator according to claim 3, characterized in that: The thickness of the second signal electrode is 0.5~20μm, the width of the second signal electrode is 30~80μm, and the distance between the second signal electrode and the second ground electrode and the third ground electrode is 2~7μm.

5. The on-chip terahertz signal generator according to claim 3, characterized in that: The materials forming the second ground electrode, the second signal electrode, the third ground electrode, and the third signal electrode include at least one of titanium, gold, silver, copper, niobium, aluminum, and chromium.

6. The on-chip terahertz signal generator according to claim 1, characterized in that: The antenna structure includes at least a first antenna and a second antenna, which are symmetrically distributed about the second straight waveguide. The first antenna is connected to the first ground electrode, and the second antenna is connected to the first signal electrode.

7. The on-chip terahertz signal generator according to claim 6, characterized in that: The first antenna and the second antenna have the same shape and are either L-shaped antennas or butterfly-shaped antennas.

8. The on-chip terahertz signal generator according to claim 1, characterized in that: The height of the first ground electrode and the first signal electrode is 700~900nm, and the distance between the first ground electrode and the first signal electrode is 1.5~3μm.

9. The on-chip terahertz signal generator according to claim 1, characterized in that: The electro-optic frequency comb generating module, the signal generating module, and the signal radiating module are all formed on the same substrate, and an optical isolation layer and a photoelectric thin film layer are also formed on the substrate. The refractive index of the optical isolation layer is less than that of the photoelectric thin film layer, and the thickness of the optical isolation layer is 0.3~20μm.

10. A method for fabricating an on-chip terahertz signal generator, used to fabricate the on-chip terahertz signal generator according to any one of claims 1 to 9, characterized in that, Includes the following steps: A substrate is provided, on which an optical isolation layer and a photoelectric thin film layer are sequentially formed; A first photoresist layer is formed by coating a photoresist layer on the surface of the photoelectric thin film layer, and the first photoresist layer is exposed and developed to transfer the waveguide pattern of the electro-optic frequency comb generation module, the waveguide pattern of the signal generation module, and the waveguide pattern of the signal radiation module into the first photoresist layer. The photoelectric thin film layer is subjected to dry etching, removal of the first photoresist layer and wet etching processes in sequence, thereby transferring the waveguide pattern of the electro-optic frequency comb generation module, the waveguide pattern of the signal generation module and the waveguide pattern of the signal radiation module into the photoelectric thin film layer. A second photoresist layer is formed by coating the photoelectric thin film layer again, and the second photoresist layer is exposed and developed to define the electrode pattern. A metal layer is deposited in the electrode pattern to form a first ground electrode, a first signal electrode, a second ground electrode, a second signal electrode, a third ground electrode, a third signal electrode, and an antenna structure.

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