A terahertz detector integrating an on-chip whispering gallery mode waveguide

Abstract

The present invention provides a terahertz detector with an on-chip integrated whispering gallery mode waveguide. The whispering gallery mode waveguide includes a whispering gallery mode micro-ring, a straight waveguide, first and second tapered coupling waveguides, and a substrate. The terahertz detector is located on the upper surface of the whispering gallery mode micro-ring. The whispering gallery mode micro-ring adopts a circular or racetrack shape and is used to resonate signals of a specific frequency. The straight waveguide is located on one side of the whispering gallery mode micro-ring and is used to transmit terahertz signals. The first and second tapered coupling waveguides are located at both ends of the straight waveguide and serve as the input and output ports of the signals respectively. The substrate is used to fix the whispering gallery mode micro-ring and the straight waveguide. The present invention utilizes the resonance and low-loss characteristics of the whispering gallery mode waveguide to realize the functions of on-chip efficient transmission and resonance filtering of terahertz signals, and at the same time enhances the interaction between terahertz waves and the sensitive elements of the detector, thereby improving the sensitivity of the terahertz detector and realizing the efficient detection of terahertz waves.

Description

Technical Field

[0001] The present invention relates to the field of terahertz signal detection, and particularly to a terahertz detector integrated with an on-chip whispering gallery mode waveguide. Background Art

[0002] Terahertz waves refer to electromagnetic waves with frequencies between 0.1 - 10 THz, which have extensive applications in fields such as astronomical observation, high-speed wireless communication, radar imaging, and life science. As one of the frontier technologies, great progress has been made in the development of key components in terahertz science and technology, which is the high point of the development of the new generation of information electronics technology. Terahertz detectors, as the key components for sensing terahertz waves, are crucial for the research and application of terahertz science and technology, and are of great significance in solving problems in fields such as terahertz security inspection, terahertz spectral test analysis, terahertz laser communication, and 6G mobile communication. At present, there is still a large room for improvement in the terahertz detector in terms of equivalent noise power, response rate, detection bandwidth, dynamic range, functional integration, etc. In particular, the current terahertz detector has a low integration level, resulting in difficulties in its application. Therefore, it is necessary to integrate the terahertz detector with other devices to improve the actual application effect of the current terahertz technology.

[0003] Due to the two advantages of high quality factor and small mode volume, the whispering gallery mode resonator has made great progress in the optical and optoelectronic fields and has been widely used in optical switches, biosensing, material testing, etc. The whispering gallery mode resonator has the function of modulating terahertz waves. When in the resonant state, the electric field intensity in the resonator will be enhanced, and when not in resonance, the electric field intensity in the resonator is almost zero. The types of whispering gallery mode resonators include ring-shaped, disk-shaped, spherical, etc. The resonant state is related to the signal frequency input into the resonator. Integrating it with a terahertz detector can achieve an efficient and multifunctional multi-channel terahertz detector. Currently, there is no report on the terahertz detector integrated with an on-chip whispering gallery mode waveguide, mainly because: First, the whispering gallery mode resonator is easily affected by external interference. After the terahertz detector is behind the resonator surface, it will change the whispering gallery mode state of the resonator, and simply assembling them together will deteriorate the sensitivity of the terahertz detector; Second, the transmission loss of the whispering gallery mode resonator based on the free space coupling method is large, and the coupling efficiency is low, resulting in a low detection efficiency of the detector. Summary of the Invention

[0004] The object of the present invention is to provide a terahertz detector integrating an on-chip whispering gallery mode waveguide. The technical solution for achieving the object of the present invention is as follows: A terahertz detector integrating an on-chip whispering gallery mode waveguide is composed of a terahertz detector and a whispering gallery mode waveguide integrated. The whispering gallery mode waveguide includes a whispering gallery mode micro-ring, a straight waveguide, first and second tapered coupling waveguides, and a substrate. The terahertz detector is located on the upper surface of the whispering gallery mode micro-ring. The whispering gallery mode micro-ring adopts a circular or racetrack shape and is used to resonate signals of a specific frequency. The straight waveguide is located on one side of the whispering gallery mode micro-ring and is used to transmit terahertz signals. The first and second tapered coupling waveguides are located at both ends of the straight waveguide and serve as the input and output ports of the signal respectively. The substrate is used to fix the whispering gallery mode micro-ring and the straight waveguide.

[0005] The terahertz signal is fed into the whispering gallery mode micro-ring through the first tapered coupling waveguide. The terahertz wave that satisfies the micro-ring resonance condition is locally converged at the terahertz detector, increasing the electric field strength at the terahertz detector and improving the response of the terahertz detector. The terahertz signals that do not satisfy the micro-ring resonance condition are directly filtered out through the straight waveguide, realizing the on-chip filtering function. The filtered terahertz signal is output through the second tapered coupling waveguide.

[0006] Furthermore, the position of the terahertz detector on the upper surface of the whispering gallery mode micro-ring can be integrated at any place on the upper surface of the micro-ring.

[0007] Furthermore, the terahertz detector can be, but is not limited to, a microbolometer, a field effect transistor, a pyroelectric diode, a Schottky diode, graphene, and other two-dimensional material semiconductor detectors, etc.

[0008] Furthermore, the terahertz detector is prepared on the upper surface of the whispering gallery mode micro-ring by using a micro-nano processing technology, or the terahertz detector is directly attached to the upper surface of the whispering gallery mode micro-ring.

[0009] Furthermore, the resonance frequency of the whispering gallery mode micro-ring needs to be determined according to the formula f=(mv) / (2πrn eff ), where m is the whispering gallery mode number, representing the number of cycles of the phase shift of the terahertz signal traveling one week in the whispering gallery mode micro-ring; v is the speed of electromagnetic waves in vacuum; r is the radius of the whispering gallery mode micro-ring; n eff is the effective refractive index of the waveguide.

[0010] Furthermore, the width of the straight waveguide is equal to the width of the whispering gallery mode micro-ring, the height of the straight waveguide is equal to the height of the whispering gallery mode micro-ring, the thickness of the substrate is less than the height of the straight waveguide, the height of the tapered coupling waveguide is equal to the sum of the height of the straight waveguide and the thickness of the substrate, and the tapered coupling waveguide is symmetric about the extension direction of the straight waveguide.

[0011] Further, the distance d between the straight waveguide and the whispering gallery mode micro-ring is determined by the following formula d = λ 2 / (2παr), where λ is the central wavelength of the working range, α is the absorption rate of the micro-ring material and the terahertz detector, and r is the radius of the whispering gallery mode micro-ring.

[0012] Further, the whispering gallery mode waveguide is fabricated on the same substrate through micro-nano processing. The substrate material can be but is not limited to high-resistance silicon, silicon dioxide, silicon carbide, gallium nitride, lithium niobate, etc.

[0013] A preparation method of a terahertz detector realizes the preparation of the terahertz detector based on the terahertz detector with an on-chip integrated whispering gallery mode waveguide.

[0014] A terahertz detection method is based on the terahertz detector with an on-chip integrated whispering gallery mode waveguide. By utilizing the resonance and low-loss characteristics of the whispering gallery mode waveguide, the efficient transmission and resonance filtering of terahertz waves on the on-chip integrated waveguide are realized, thereby enhancing the interaction between terahertz waves and the sensitive elements of the detector, improving the sensitivity of the terahertz detector, and realizing the efficient detection of terahertz waves.

[0015] Compared with the prior art, the remarkable advantages of the present invention are as follows: 1) Structures such as the whispering gallery mode micro-ring, straight waveguide, and tapered coupling waveguide are all on the same substrate. Compared with the discrete structures commonly used for whispering gallery mode resonators in other fields, the on-chip integrated design can reduce the distance error between the whispering gallery mode micro-ring and the straight waveguide and improve the coupling efficiency of the whispering gallery mode micro-ring; 2) The terahertz detector is integrated with the whispering gallery mode micro-ring. Since the whispering gallery mode micro-ring has the characteristic of electric field enhancement, the responsivity of the terahertz detector can be effectively improved, and the accurate detection of terahertz signals can be realized. At the same time, since the resonance frequency of the on-chip waveguide is related to the effective refractive index and radius of the micro-ring, multi-channel detection of terahertz signals can be realized; 3) It is easy to package and use. By using the tapered coupling waveguide as the input and output ports of the signal, it can be connected to the standard terahertz rectangular waveguide, with low insertion loss. After packaging, it can be used as a terahertz detector with a standard interface and can be used in complex systems such as terahertz imaging or communication. Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of a terahertz detector with an on-chip integrated whispering gallery mode waveguide.

[0017] Figure 2 It is a schematic size diagram of a terahertz detector with an on-chip integrated whispering gallery mode waveguide.

[0018] Figure 3 It is a schematic micro-assembly diagram of a terahertz detector with an on-chip integrated whispering gallery mode waveguide.

[0019] Figure 4 S-parameter results diagram of a terahertz detector with an on-chip integrated whispering gallery mode waveguide.

[0020] Figure 5 Frequency domain response curve diagram of a terahertz detector with an on-chip integrated whispering gallery mode waveguide.

[0021] Figure 6 Electric field distribution diagram of the waveguide vertical cross-section at the terahertz detector in the resonant state.

[0022] Figure 7 Electric field distribution diagram inside the whispering gallery mode waveguide in the resonant state.

[0023] In the figure, 1 is the terahertz detector, 2 is the whispering gallery mode micro-ring, 3 is the straight waveguide, 4 is the first tapered coupling waveguide, 5 is the substrate, 6 is the second tapered coupling waveguide, 7 is the RF output flange, 8 is the present invention, 9 is the standard rectangular waveguide, 10 is the UG-387 / U series flange, 11 is the UG-387 / U series flange, 12 is the standard rectangular waveguide, 13 is the electric field strength at the center of the terahertz detector in the waveguide vertical cross-section, and 14 is the electric field strength at the projection of the center of the terahertz detector in the horizontal cross-section inside the waveguide. Detailed implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] As Figure 1-2 shown, a terahertz detector with an on-chip integrated whispering gallery mode waveguide is integrated by a terahertz detector 1 and a whispering gallery mode waveguide. The whispering gallery mode waveguide includes a whispering gallery mode micro-ring 2, a straight waveguide 3, first and second tapered coupling waveguides 4, 6, and a substrate 5. The terahertz detector 1 is located on the upper surface of the whispering gallery mode micro-ring 2. The whispering gallery mode micro-ring 2 adopts a circular or racetrack shape and is used to generate resonance for signals of a specific frequency. The straight waveguide 3 is used to transmit terahertz signals, and its two ends are the first and second tapered coupling waveguides 4, 6. The first and second tapered coupling waveguides 4, 6 are symmetric about the extension direction of the straight waveguide 3 and serve as signal input and output ports. The substrate 5 is used to integrally fabricate the whispering gallery mode micro-ring 2 and the straight waveguide 3.

[0026] The input signal enters the straight waveguide 3 through the tapered coupling waveguide 4, is coupled into the whispering gallery mode micro-ring 2 through this straight waveguide 3. After the terahertz signal propagates for one period in the whispering gallery mode micro-ring, the generated phase change φ is: where n effis the effective refractive index, r is the radius of the microring, and λ is the wavelength of the incident signal. The phase shift of a signal at a specific frequency is an integer multiple of 2π, i.e., φ = 2πm (m is an integer), and m is the mode number. When the resonance state is reached, the signal will resonate in the whispering gallery mode microring all the time, enhancing the electric field intensity inside the microring. Combining the above two formulas, it can be known that the resonance frequency of the whispering gallery mode microring is related to the radius r and m. In this embodiment, m is 40 - 60, and r is 1800μ m .

[0027] To improve the coupling efficiency between the straight waveguide 3 and the whispering gallery mode microring 2, their effective refractive indices need to be kept consistent. The effective refractive index n of the dielectric waveguide eff is related to the material, width, and height of the dielectric waveguide. Therefore, it is designed that the width of the straight waveguide 3 is equal to the width of the whispering gallery mode microring 2, the height of the straight waveguide 3 is equal to the height of the whispering gallery mode microring 2, the thickness of the substrate 5 is less than the height of the straight waveguide 3, and the height of the tapered coupling waveguides 4, 6 is equal to the sum of the height of the straight waveguide 3 and the thickness of the substrate 5. The specific meanings of the dimensional parameters in this embodiment are shown in Figure 2 As shown, the designed width w is 170μm, the height is 140μm, and the thickness of the substrate is 60μm. In addition, to ensure the coupling efficiency, the length of the tapered coupling waveguide needs to be more than 3 times its width. The length l of the tapered coupling waveguides 4, 6 is 1000μm. At this time, the effective refractive index of the waveguide is 2.63, and the transmitted fundamental mode is the quasi-TM mode.

[0028] The device parameter design of the whispering gallery mode waveguide is also affected by the terahertz detector. Due to the absorption of the terahertz signal by the material, there will inevitably be losses when the terahertz signal propagates around the whispering gallery mode microring 2. Define L1 as the material loss of the terahertz signal around the whispering gallery mode microring 2, then where λ is the signal wavelength and α1 is the absorption rate of the material. For integrating a terahertz detector on the whispering gallery mode microring 2, the terahertz detector will affect the whispering gallery mode microring, and part of the energy will be absorbed by the terahertz detector, which is equivalent to increasing the loss of the whispering gallery mode microring. The energy absorbed by the terahertz detector is equivalent to α2, then the total absorption rate is α = α1 + α2, and the total loss is L. In addition, there is also a coupling loss t between the straight waveguide 3 and the whispering gallery mode microring 2. The coupling loss t is related to the distance d between the straight waveguide and the whispering gallery mode microring 2 and the signal wavelength λ. When t = L, it is the critical coupling state. At this time, the transmission loss of the coupler cancels out the energy loss caused by the whispering gallery mode microring 2, and the whispering gallery mode microring is in the best working state. In this embodiment, the designed distance d is 40μ m .

[0029] High-resistivity silicon is one of the most important integrated circuit materials and has low loss in the terahertz frequency band. The absorption rate at 0.4 THz is only 0.05 cm -1 In this embodiment, high-resistivity silicon is selected as the substrate material. Deep silicon etching is a micro-nano processing technology. By using the deep silicon etching technology, functional structures with characteristic dimensions of dozens of micrometers or even up to hundreds of micrometers can be obtained. The whispering gallery mode waveguide in this embodiment is prepared by the deep silicon etching process. In order to verify the effectiveness of the proposed solution of the present invention, based on the above structure and parameters, the following process steps are combined to fabricate an on-chip integrated whispering gallery mode waveguide detector. Further, the fabricated on-chip integrated whispering gallery mode waveguide detector is used for performance testing and electromagnetic simulation. The preparation steps are as follows:

[0030] Step 1. Silicon wafer thinning process, thinning the thickness of the silicon wafer to 200 μ m ;

[0031] Step 2. Fabricate a terahertz detector on the silicon wafer;

[0032] Step 3. Use the deep silicon etching process to etch the silicon wafer 140 μ m deep to form a whispering gallery mode micro-ring and a straight waveguide, and then perform an overlay process to form a tapered coupling waveguide.

[0033] Performance test experiment

[0034] Figure 3 It is a micro-assembly schematic diagram of a terahertz detector with an on-chip integrated whispering gallery mode waveguide. Among them, 7 is the RF output flange, 8 is the terahertz detector of the present invention, 9 and 12 are standard rectangular waveguides, and 10 and 11 are UG-387 / U series flanges. The packaged terahertz detector with an on-chip integrated whispering gallery mode waveguide is docked with other terahertz systems through the UG-387 / U series flanges 10 and 11. The standard rectangular waveguide is located at the center of the UG-387 / U series flanges. The dimensions refer to the WR series waveguide specifications, and specifications such as WR6.5, WR5.1, WR4.3, WR3.4, WR2.8, WR2.2, WR1.5, WR1.0, etc. can be adopted. The first tapered coupling waveguide 4 is used as the signal input end, and the second tapered coupling waveguide 6 is used as the signal output end. During packaging, taking the coupling waveguide 4 as an example, it is placed in the standard rectangular waveguide 9, and the terahertz signal is coupled from the standard rectangular waveguide 9 into the tapered waveguide.

[0035] During testing, connect the UG-387 / U series flanges 10 and 11 of the packaged terahertz detector with an on-chip integrated whispering gallery mode waveguide to the test ports of the vector network analyzer to test the S parameters of the device. Take the S11 parameter as the return loss of the device, and the S21 parameter as the insertion loss of the device. The S parameter results are as Figure 4As shown, it can be seen that S11 is all less than 0.1, indicating that the design of the conical coupling waveguide has played a role, and more than 90% of the terahertz signals are coupled into the whispering gallery mode waveguide; the S21 curve has a periodic peak distribution, and the frequency at the peak and valley is the resonant frequency of the whispering gallery mode micro-ring. The value of S21 at the resonant state is very small, all less than 0.1, and S21 is almost 0 at 0.425 THz, indicating that the terahertz signals are almost all resonant in the micro-ring, increasing the electric field inside the micro-ring, thereby improving the response of the terahertz detector.

[0036] The response of the terahertz detector is output through the RF output flange 7, and the corresponding measuring instrument is used according to the type of the response signal of the detector. In this embodiment, a lock-in amplifier is used to measure the output signal of the RF output flange 7, and Figure 5 the obtained terahertz detector frequency-domain response test results are shown. The curve has a periodic peak distribution, and the frequency at the peak tip is the resonant frequency of the whispering gallery mode micro-ring. The response result of the terahertz detector at 0.425 THz is 36.7 V / m, which is more than 3 times higher than 12 V / m at the non-resonant state. Figure 5 Each resonant peak in it is a detection channel. Integrating the terahertz detector on the upper surface of the whispering gallery mode can significantly improve the response rate of the terahertz detector and can also realize multi-channel terahertz signal detection.

[0037] Electromagnetic simulation experiment

[0038] In order to explore the interaction between terahertz waves and the sensitive element of the detector, an electromagnetic simulation software is used to calculate the electric field distribution of the terahertz detector with an on-chip integrated whispering gallery mode waveguide. The simulation frequency is 0.425 THz, which is the resonant state of the micro-ring at this time. Figure 6 is the electric field distribution of the vertical section of the whispering gallery mode waveguide at the terahertz detector. The region with oblique stripes in the figure is the vertical section of the whispering gallery mode waveguide. The terahertz detector is located on the upper surface of the whispering gallery mode waveguide. It can be seen that the electric field intensity of the sensitive element at the center of the detector is very large, reaching 35 V / m. The electric field inside the waveguide is Figure 6 hard to observe in. Therefore, an electric field monitor is added inside the whispering gallery mode waveguide, and Figure 7The shown result is the electric field intensity distribution of the horizontal cross-section of the whispering gallery mode waveguide. It can be seen that the electric field intensity at the central projection of the terahertz detector is the largest, about 1.6 V / m. After the terahertz signal passes through the terahertz detector in the micro-ring, the electric field intensity becomes smaller. In the figure, it is shown that the electric field in the left half of the ring is less than that in the right half, indicating that the terahertz signal is locally concentrated at the terahertz detector. This is because the terahertz detector interferes with the state of the whispering gallery mode. It can be seen from the simulation experiment that integrating the terahertz detector on the upper surface of the whispering gallery mode can significantly improve the response rate of the terahertz detector.

[0039] In summary, the present invention utilizes the resonance and low-loss characteristics of the whispering gallery mode waveguide to achieve efficient transmission and resonance filtering of terahertz waves on the on-chip integrated waveguide, thereby enhancing the interaction between terahertz waves and the sensitive elements of the detector, improving the sensitivity of the terahertz detector, and achieving efficient detection of terahertz waves.

[0040] The implementation mode of the present invention is not limited by the above embodiments. Any changes, simplifications, substitutions, and combinations made without departing from the essence and principle of the present invention should be included within the protection scope of the present invention.

[0041] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0042] The above-described embodiments merely represent several implementation modes of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A terahertz detector integrating an on-chip whispering gallery mode waveguide, characterized in that, Integrated with a terahertz detector (1) and a whispering gallery mode waveguide, the whispering gallery mode waveguide includes a whispering gallery mode micro-ring (2), a straight waveguide (3), first and second tapered coupling waveguides (4, 6), and a substrate (5). The terahertz detector (1) is located on the upper surface of the whispering gallery mode micro-ring (2). The whispering gallery mode micro-ring (2) is in a circular ring shape or a racetrack shape and is used to resonate signals of a specific frequency. The straight waveguide (3) is located on one side of the whispering gallery mode micro-ring (2) and is used to transmit terahertz signals. The first and second tapered coupling waveguides (4, 6) are located at both ends of the straight waveguide (3) and serve as the input and output ports of the signals respectively. The substrate (5) is used for integrally fabricating the whispering gallery mode micro-ring (2) and the straight waveguide (3). The width of the straight waveguide (3) is equal to the width of the whispering gallery mode micro-ring (2), and the height of the straight waveguide (3) is equal to the height of the whispering gallery mode micro-ring (2). The thickness of the substrate (5) is less than the height of the straight waveguide (3). The heights of the first and second tapered coupling waveguides (4, 6) are equal to the sum of the height of the straight waveguide (3) and the thickness of the substrate (5). The first and second tapered coupling waveguides (4, 6) are symmetric about the extension direction of the straight waveguide. The distance d between the straight waveguide (3) and the whispering gallery mode micro-ring (2) is determined by the formula d = λ 2 / (2παr), where λ is the central wavelength of the working range, α is the absorption rate of the micro-ring material and the terahertz detector, and r is the radius of the whispering gallery mode micro-ring (2); The whispering gallery mode waveguide is fabricated on the same substrate through micro-nano processing. The terahertz signal is fed into the whispering gallery mode micro-ring (2) through the first tapered coupling waveguide (4). The terahertz wave that satisfies the micro-ring resonance condition is locally converged at the terahertz detector (1), increasing the electric field strength at the terahertz detector (1) and improving the response of the terahertz detector (1). The terahertz signals that do not satisfy the micro-ring resonance condition are directly filtered out through the straight waveguide (3), realizing the on-chip filtering function. The filtered terahertz signal is output through the second tapered coupling waveguide (6).

2. The terahertz detector with an on-chip integrated whispering gallery mode waveguide according to claim 1, characterized in that, The terahertz detector (1) is integrated at any position on the upper surface of the whispering gallery mode micro-ring (2).

3. The terahertz detector with an on-chip integrated whispering gallery mode waveguide according to claim 1, characterized in that The terahertz detector (1) is a microbolometer, a field effect transistor, a pyroelectric diode, a Schottky diode, or graphene.

4. The terahertz detector with an on-chip integrated whispering gallery mode waveguide according to claim 1, characterized in that, The terahertz detector (1) is fabricated on the upper surface of the whispering gallery mode micro-ring (2) by using micro-nano processing technology, or the terahertz detector (1) is directly attached to the upper surface of the whispering gallery mode micro-ring (2).

5. The terahertz detector with an on-chip integrated whispering gallery mode waveguide according to claim 1, characterized in that, The resonance frequency of the whispering gallery mode micro-ring (2) is determined according to the formula f = (mv) / (2πrn eff ), where m is the number of whispering gallery modes, representing the number of cycles of phase shift of the terahertz signal traveling one week in the whispering gallery mode micro-ring (2); v is the speed of electromagnetic waves in vacuum; r is the radius of the whispering gallery mode micro-ring (2); n eff is the effective refractive index of the waveguide.

6. The terahertz detector with an on-chip integrated whispering gallery mode waveguide according to claim 1, characterized in that, The substrate material is high-resistivity silicon, silicon dioxide, silicon carbide, gallium nitride, or lithium niobate.

7. A method for preparing a terahertz detector, characterized in that, Based on the structure of the terahertz detector with an on-chip integrated whispering gallery mode waveguide according to any one of claims 1-5, the preparation of the terahertz detector is realized.

8. A method for detecting terahertz waves, characterized in that, Based on the terahertz detector with an on-chip integrated whispering gallery mode waveguide according to any one of claims 1-5, the efficient detection of terahertz waves is realized.

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