Terahertz echo wall mode waveguide on light control chip

Abstract

The invention provides a terahertz echo wall mode waveguide on a light control chip, which comprises an echo wall mode micro-ring, a straight waveguide and a conical coupling waveguide which are integrated on the same substrate, and a solid-state laser source positioned above the micro-ring. And the conductivity and the inherent loss of the high-resistance silicon micro-ring are dynamically changed through the photon-generated carrier effect, so that switching of an echo wall mode among an over-coupling state, a critical coupling state and an under-coupling state is accurately and continuously regulated and controlled. According to the invention, based on an active regulation and control mechanism of a photoconductive effect, large-depth and high-speed dynamic control of terahertz signal transmission amplitude and phase can be realized, the bottleneck of low integration level and limited modulation performance of an existing terahertz regulation and control device is solved, and a key technical scheme is provided for realizing a high-performance on-chip terahertz switch, an attenuator and a modulator.

Description

Technical Field

[0001] This invention relates to the field of terahertz signal modulation, and more specifically to an on-chip terahertz whispering-gallery mode waveguide. Background Technology

[0002] Terahertz waves (0.1-10 THz), as a special frequency band bridging microwaves and infrared, have shown great potential in fields such as high-speed communication, non-destructive imaging, and spectral analysis. As terahertz science and engineering deepen from basic "detection and emission" to complex "active control and modulation," developing core devices capable of dynamically manipulating parameters such as amplitude and phase of terahertz waves is crucial for realizing system-level functions such as reconfigurable terahertz communication links, high-speed data transmission, active imaging, and real-time spectral line selection. Therefore, developing high-performance, low-power, and integrable terahertz modulation technology is of significant strategic and engineering importance for promoting 6G and higher frequency wireless communication, portable / high-resolution terahertz imaging, and in-situ spectroscopic analysis.

[0003] Among numerous candidate technologies, devices based on whispering-gallery mode resonators offer an ideal platform for achieving low-power, high-sensitivity terahertz modulation due to their extremely high quality factor (Q value) and strong electromagnetic field localization capabilities. However, static resonators cannot meet the needs of dynamic signal processing. Therefore, achieving efficient and rapid modulation of their resonant characteristics is the core challenge driving their functionalization and practical application.

[0004] Currently, common modulation methods such as thermo-optical, electro-optical, or mechanical modulation often face inherent limitations in the terahertz band, such as slow response speed, limited modulation depth, high power consumption, or poor mechanical stability. In contrast, photoconductive modulation utilizes ultrafast lasers to excite transient carriers in semiconductors (such as high-resistivity silicon), thereby rapidly changing their dielectric constant and conductivity, providing an ideal technical path for resonant modulation with fast response speed, large modulation depth, and non-contact operation.

[0005] Despite the inherent advantages of photoconductivity, achieving low-loss, high-precision three-dimensional heterogeneous integration with high-performance on-chip whispering-gallery waveguide structures to form a compact, stable, and easily packaged monolithic functional device remains a pressing engineering challenge. Existing technologies either sacrifice integration density, introduce excessively high insertion loss, or struggle to achieve precise and stable optical alignment, severely limiting their application in practical systems. Summary of the Invention

[0006] The purpose of this invention is to provide an on-chip terahertz whispering-gallery mode waveguide.

[0007] The technical solution to achieve the purpose of this invention is as follows:

[0008] Compared with the prior art, the significant advantages of this invention are:

[0009] 1) Achieving a balance between high integration and high performance: By precisely heterogeneously integrating a solid-state laser source with a whispering-gallery mode waveguide chip in three-dimensional space, a complete dynamic control system was successfully miniaturized within a standard waveguide package. This structure not only inherits the high Q-value and low-loss transmission advantages of the whispering-gallery mode, but also eliminates the problems of inaccurate component mating and low coupling efficiency through on-chip integration, laying the foundation for realizing chip-level terahertz systems.

[0010] 2) Achieving a synergistic effect of large modulation depth and high-speed response: Utilizing the fast photoconductivity of high-resistivity silicon as a modulation mechanism, the inherent loss of the microring is directly and rapidly modulated by changing the pump laser power, thereby achieving a dynamic modulation depth exceeding 22 dB for terahertz wave transmission amplitude. Compared to traditional thermo-optical modulation, this method significantly improves speed; compared to electro-optical modulation, it achieves a much larger modulation depth, solving the problem of traditional methods struggling to balance speed and depth.

[0011] 3) It provides dynamic and reconfigurable multi-functional control capabilities: By precisely controlling the laser power, the coupling state of the whispering galvanic microring can be continuously driven from "overcoupled" to "critically coupled" and then to "undercoupled". This unique control capability enables a single device to dynamically realize multiple functions such as switching, attenuator, amplitude modulator and phase modulator, with strong reconfigurability, which greatly enhances the application flexibility of the device.

[0012] 4) Ensuring ease of use and system compatibility: The use of tapered coupled waveguides as input / output ports allows for direct, low-loss interface with standard WR series rectangular waveguides. Simultaneously, precision positioning vias on the package housing secure the optical fiber, ensuring long-term stability and reliability of the optical pump excitation. This design enables the invention to be seamlessly integrated into existing terahertz systems as a "plug-and-play" standard component. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a terahertz whispering-gallery mode waveguide structure on an optical control chip.

[0014] Figure 2 This is a schematic diagram of the dimensions of the terahertz whispering-gallery mode waveguide on the optical control chip.

[0015] Figure 3 This is a schematic diagram of a terahertz whispering-gallery mode waveguide microassembly on a light-controlled chip.

[0016] Figure 4 The figure shows the simulation results of the terahertz whispering-gallery mode waveguide transmission rate on the optical control chip.

[0017] Figure 5 The normalized electric field distribution inside the whispering-gallery mode waveguide is shown in the unpumped (a) and strongly pumped (b) states.

[0018] Figure 6 The results show the S-parameters of the device and the dynamic modulation of transmittance under different laser powers.

[0019] Figure 7 The image shows the phase test results of the terahertz whispering-gallery mode waveguide transmission on the optical control chip.

[0020] Among them, 1-solid-state laser source fiber, 2-whispering-gallery mode micro-ring, 3-straight waveguide, 4-first tapered coupling waveguide, 5-substrate, 6-second tapered coupling waveguide, 7-encapsulation positioning through hole, 8-rectangular waveguide, 9-UG-387 / U series flange. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] like Figure 1-2 As shown, a terahertz whispering-gallery mode waveguide on a photoconductive sheet is integrated with a solid-state laser source emitting light from fiber 1 and a whispering-gallery mode waveguide chip, wherein:

[0023] The whispering-gallery mode waveguide chip comprises a whispering-gallery mode microring 2, a straight waveguide 3, first and second tapered coupled waveguides 4 and 6, and a substrate 5. The whispering-gallery mode microring 2 is either ring-shaped or racetrack-shaped, used to generate resonance for signals of a specific frequency. The straight waveguide 3 is used to transmit terahertz signals, with the first and second tapered coupled waveguides 4 and 6 at its two ends serving as the signal input and output ports. The substrate 5 is used to integrate and fabricate the whispering-gallery mode microring 2 and the straight waveguide 3. The terahertz signal is fed into the whispering-gallery mode microring 2 through the first tapered coupled waveguide 4, satisfying the microring resonance condition. The terahertz waves converge in the whispering-gallery mode microring 2, where m is the whispering-gallery mode number, representing the number of phase shifts of the terahertz signal during one revolution in the whispering-gallery mode microring 2; v is the vacuum electromagnetic wave velocity; and r is the radius of the whispering-gallery mode microring 2. is the effective refractive index of the waveguide. Terahertz signals that do not meet the microring resonance condition are directly filtered out by the straight waveguide 3, and the filtered terahertz signals are output through the second tapered coupling waveguide 6.

[0024] A solid-state laser source has its output fiber 1 precisely positioned above the whispering-gallery mode microring via a fixed structure, at the end furthest from the straight waveguide 3. The pump light emitted by the solid-state laser source acts on the whispering-gallery mode microring, changing the equivalent conductivity and inherent loss of the microring through the photogenerated carrier effect, thereby dynamically controlling the resonant coupling state between the whispering-gallery mode microring and the straight waveguide.

[0025] The optimization design of each part will be explained in detail below.

[0026] (1) Whispering-gallery mode waveguide chip

[0027] High-resistivity silicon is one of the most important materials for integrated circuits. It also exhibits low loss in the terahertz frequency band, with an absorption rate of only 0.05 dB / cm at 0.4 THz. This invention selects high-resistivity silicon as the substrate material. Deep silicon etching is a micro-nano fabrication process that uses deep silicon etching to obtain functional structures with feature sizes ranging from tens to hundreds of micrometers. In this invention, all structures of the waveguide chip are integrally formed on a high-resistivity silicon substrate through deep silicon etching, ensuring process consistency and low transmission loss.

[0028] Effective refractive index of dielectric waveguide The effective refractive index of the straight waveguide 3 and the whispering-gallery mode microring 2 is kept consistent, depending on the material, width, and height of the dielectric waveguide. In this invention, the width of the straight waveguide 3 is equal to the width of the whispering-gallery mode microring 2, and 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. The heights of the first and second tapered coupling waveguides 4 and 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 and 6 are symmetrical about each other along the extension direction of the straight waveguide 3. In some embodiments, the specific meanings of the dimensional parameters are described in [the following text is missing from the original extract]. Figure 2 As shown, the design width w is 190 μm, the height is 140 μm, the substrate thickness is 60 μm, the fundamental mode of the silicon-based through waveguide transmission is TE mode, and the effective refractive index is 2.78.

[0029] The signal transmitted by the chip's straight waveguide 3 is a TE-polarized continuous terahertz wave. By adjusting the coupling distance between the straight waveguide 3 and the whispering-gallery microring 2, the whispering-gallery microring 2 is kept in a resonant overcoupled state when not laser-pumped. In some embodiments, to ensure the overcoupling efficiency of the whispering-gallery microring 2, the coupling distance between the whispering-gallery microring 2 and the straight waveguide 3 is designed to be 10 μm to ensure efficient coupling of the terahertz evanescent wave. The coupling strength k and the coupling distance g satisfy: ,in Let be the field coupling constant. For effective coupling length, The characteristic length of coupling decreases with distance.

[0030] By continuously increasing the output power of the solid-state laser source, the inherent loss of the whispering-gallery mode microring can be continuously varied, causing its resonant coupling state to undergo a dynamic evolution from overcoupled to critically coupled and then to undercoupled. During this dynamic evolution of the resonant coupling state, the transmission amplitude of the terahertz signal output from the second tapered coupled waveguide at the resonant frequency exhibits a trend of first decreasing and then increasing, and its transmission phase jump variable also changes continuously accordingly.

[0031] At room temperature, the band gap of silicon is 1.12 eV. When the energy of the incident photon exceeds this band gap, photogenerated carriers are generated in the silicon substrate, i.e., electron-hole pairs with equal concentrations. The concentration of these photogenerated carriers directly depends on the wavelength and power density of the incident pump light. The excitation of the carriers causes the conductivity of the whispering-gallery microrings (2) to follow... surge, of which For charge quantity, Photoinduced carrier concentration, and These represent the mobilities of electrons and holes, respectively. As the optical pump power increases, photoinduced carrier excitation occurs, and the absorption loss of silicon follows... The conductivity of the whispering-gallery microring 2 increases with increasing conductivity, where... The vacuum permittivity, The absorption attenuation of silicon is the angular frequency of the transmitted electromagnetic wave. satisfy: ,in and These represent the vacuum wavelength and the real part of the refractive index, respectively.

[0032] The resonant coupling state of the chip is determined by the coupling efficiency between the whispering-gallery mode microring 2 and the straight waveguide 3. Inherent loss of the microring 2 in whispering-gallery mode The decision was made jointly, and the specific relationships are as follows:

[0033] (i) In the overcoupled state, the power coupled to the whispering-gallery mode microring 2 exceeds its internal losses. The excess energy is coupled back into the straight waveguide 3, causing leakage to the output port and reducing the resonance depth.

[0034] (ii) In the critical coupling state, the energy coupled to the whispering-gallery mode microring 2 is balanced with the internal loss. The back-coupling energy and the component of the straight waveguide 3 interfere destructively, and the ideal power of the direct output is 0.

[0035] (iii) In the undercoupled state, the power coupled to the whispering-gallery mode microring 2 is much less than the internal loss. There is no echo-coupled electromagnetic wave, and the output port directly transmits the power not coupled to the whispering-gallery mode microring 2.

[0036] Inherent loss of whispering-gallery microring 2 As the optical pump power increases, the coupling state of the whispering-gallery mode microring 2 follows the pattern from overcoupling to critical coupling to undercoupling, and the output power of the tapered coupled waveguide 6 follows the formula... The output amplitude first decreases and then increases, achieving dynamic control of transmittance. Therefore, the critical coupling is at the lowest point of resonance, while the resonance depths of overcoupling and undercoupling are relatively small. Furthermore, the phase jump during transmission in the overcoupling state exceeds... Critical coupling phase jump Undercoupled phase jump less than Due to the energy exchange intensity between the straight waveguide 3 and the whispering-gallery mode microring 2, the originally static, frequency-selective resonant cavity becomes a dynamic device with adjustable real-time resonance depth and coupling state under the control of the applied laser signal.

[0037] The first and second tapered coupled waveguides 4 and 6 serve as signal ports. Taking the first tapered coupled waveguide 4 as an example, it is placed inside the rectangular waveguide 8, and the chip is micro-assembled as follows: Figure 3 As shown, the dimensions of the rectangular waveguide 8 can refer to the WR series waveguide specifications, and can be WR6.5, WR5.1, WR4.3, WR3.4, WR2.8, WR2.2, WR1.5, WR1.0, etc. Furthermore, to ensure coupling efficiency, the length of the tapered coupling waveguide needs to be more than three times its width. In some embodiments, the length l of the first and second tapered coupling waveguides 4 and 6 is 1200 μm, and the taper angle is approximately 9.5°.

[0038] The optical fiber is positioned on the sounding-gallery chip via a positioning via 7 fabricated in the package upper shell. The terahertz modulation output response is output through a second tapered waveguide 6, and a rectangular waveguide 8 is located at the center of the UG-387 / U series flange 9. This invention utilizes... Figure 3 The rectangular waveguide 8-whispering-gallery chip packaging shown is used to interface with other terahertz systems.

[0039] In addition, in some embodiments, the laser spot diameter is set to 0.9 mm, covering the micro-ring waveguide, and the laser power level can be finely adjusted at the mW level.

[0040] To verify the effectiveness of the present invention, an integrated whispering-gallery mode waveguide on a photoconductive sheet was fabricated and packaged according to the following process, and experimental tests and simulations were performed. The specific steps are as follows:

[0041] 1. Silicon wafer thinning process, reducing the thickness of silicon wafers to 200 μm;

[0042] 2. Using deep silicon etching technology, the silicon wafer is etched to a depth of 140 μm to form a whispering-gallery mode microring and a straight waveguide, and then an overlay process is performed to form a tapered coupled waveguide;

[0043] 3. Based on the size of the individual integrated device and the size of the solid-state laser source fiber, design the corresponding packaging structure for scattering parameter testing.

[0044] Example 1

[0045] To verify the advantages of the on-chip terahertz whispering-gallery mode waveguide, the packaged on-chip whispering-gallery mode waveguide was connected to a vector network analyzer to test the device's S-parameters. The first tapered coupled waveguide 4 served as the signal input, and the second tapered coupled waveguide 6 served as the signal output. The S11 parameter represents the device's return loss, and the S21 parameter represents the device's insertion loss. Figure 6 The S-parameter results show that S11 is greater than 15 dB, indicating extremely high coupling efficiency between the rectangular waveguide and the silicon-based dielectric waveguide, with over 90% of the terahertz signals coupled into the whispering-gallery mode waveguide. The S21 curve exhibits a periodic peak distribution, with an average insertion loss of 2.5 dB in the non-resonant frequency band, demonstrating low loss. The frequencies at the peaks and valleys are the resonant frequencies of the whispering-gallery mode microring. Due to overcoupling in the resonant state, the resonance depth is extremely small, with the resonant peak intensity in the 455-480 GHz range all less than 10 dB, indicating resonant overcoupling. Maintaining the connection between the chip and the vector network analyzer, the fiber 1 of the solid-state laser source is fixed to the positioning via on the package cover. The laser pump power is gradually adjusted from 0-66 mW, and the S21 curve is observed. Under photoconductivity, the transmission curve of the whispering-gallery chip is as follows... Figure 6 As shown in the right figure, the chip exhibits strong photosensitive characteristics, achieving a dynamic modulation depth of up to 22.7 dB in the whispering-gallery waveguide at 458.75 GHz, with a required active power consumption of only 25 mW. The modulator has application value for realizing high-range terahertz attenuators. Regarding the coupling state of the whispering-gallery microring 2, in addition to judging from the trend of resonant intensity changes, phase is also an important factor, such as... Figure 7 As shown. In the overcoupled state, due to the large amount of energy exchange between the straight waveguide 3 and the whispering-gallery microring 2, the phase jump at the resonant frequency exceeds... In the critical coupling state, the phase transition is exactly... In the overcoupled state, due to minimal energy exchange between the two, the phase transition is weak. Therefore, Figure 7 The phase test results shown can determine the coupling state of the whispering galvanic waveguide and demonstrate its potential application in phase modulation.

[0046] Example 2

[0047] To further verify the advantages of terahertz whispering-gallery mode waveguides on photoconductive sheets, electromagnetic simulation software was used to calculate the transmission spectrum and electric field distribution of the terahertz whispering-gallery mode waveguides on photoconductive sheets with the above parameters. Figure 4 The transmission spectrum of the terahertz whispering-gallery mode waveguide on the photoconductive sheet is given by the dielectric loss formula. The imaginary part of the refractive index of high-resistivity silicon was equivalent to the dielectric absorption brought about by photoconductivity. The simulation results showed the same trend as the actual measurements, which further verified the principle of photoconductivity tuning. Figure 5 This is a normalized electric field distribution diagram of a terahertz whispering-gallery mode waveguide on a photoconductive sheet. In the unpumped state, overcoupled energy is backcoupled to the through waveguide. However, under strong pumping, the resonant field loss is significantly enhanced, suppressing the backcoupling of whispering-gallery energy. In the undercoupled state, the transmittance of the through waveguide increases.

[0048] The embodiments of the present invention are not limited to the described examples. Any changes, simplifications, substitutions, or combinations made without departing from the spirit and principle of the present invention should be included within the scope of protection of the present invention.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A light-controlled on-chip terahertz whispering-gallery mode waveguide, characterized in that, include: A whispering-gallery mode waveguide chip, integrated on the same substrate, includes a whispering-gallery mode microring, a straight waveguide, and a first tapered coupling waveguide and a second tapered coupling waveguide located at opposite ends of the straight waveguide. The whispering-gallery mode microring is used to generate resonance for a terahertz signal of a specific frequency. The straight waveguide is used to transmit the terahertz signal and exchange evanescent wave energy with the whispering-gallery mode microring. The first and second tapered coupling waveguides serve as the input and output ports of the terahertz signal, respectively. A solid-state laser source has its output end positioned above the whispering-gallery mode microring via a fixed structure. The pump light emitted by the solid-state laser source acts on the whispering-gallery mode microring, changing the equivalent conductivity and inherent loss of the microring through the photogenerated carrier effect, thereby dynamically controlling the resonant coupling state between the whispering-gallery mode microring and the straight waveguide.

2. The on-chip terahertz whispering-gallery mode waveguide according to claim 1, characterized in that, The entire structure of the whispering-gallery mode waveguide chip is fabricated from a single piece of high-resistivity silicon material.

3. The on-chip terahertz whispering-gallery mode waveguide according to claim 1, characterized in that, The fixing structure is a metal positioning through hole fabricated on the waveguide package shell. The light-emitting end of the solid-state laser source is an optical fiber, which passes through the positioning through hole and is suspended at a preset distance directly above the whispering gallery mode micro-ring.

4. The on-chip terahertz whispering-gallery mode waveguide according to claim 1, characterized in that, The straight waveguide and the whispering-gallery mode microring are structurally equal in width and height, and the coupling spacing between them is designed so that the whispering-gallery mode microring is in a resonant overcoupled state when there is no laser pump.

5. The on-chip terahertz whispering-gallery mode waveguide according to claim 1, characterized in that, By continuously increasing the output power of the solid-state laser source, the inherent loss of the whispering-gallery mode microring can be continuously changed, thereby causing its resonant coupling state to undergo a dynamic evolution from overcoupled state to critically coupled state, and then to undercoupled state.

6. The on-chip terahertz whispering-gallery mode waveguide according to claim 5, characterized in that, During the dynamic evolution of the resonant coupling state, the transmission amplitude of the terahertz signal output by the second tapered coupled waveguide at the resonant frequency shows a trend of first decreasing and then increasing, and its transmission phase jump variable also changes continuously.

7. The on-chip terahertz whispering-gallery mode waveguide according to claim 6, characterized in that, The pump light generated by the solid-state laser source (1) excites charge carriers in high-resistivity silicon, i.e., electron-hole pairs with the same concentration. The excitation of charge carriers causes the conductivity of the whispering-gallery microrings (2) to follow the... surge, of which For charge quantity, Photoinduced carrier concentration, and These represent the mobilities of electrons and holes, respectively. Since the concentration of these photogenerated carriers directly depends on the wavelength and power density of the incident pump light, as the optical pump power increases, the photogenerated carriers are excited, and the absorption loss of silicon follows... The conductivity increases with the increase of the whispering-gallery microring (2), among which The vacuum permittivity, The angular frequency of the transmitted electromagnetic wave.

8. The on-chip terahertz whispering-gallery mode waveguide according to claim 7, characterized in that, The resonant coupling state between the whispering-gallery mode microring and the straight waveguide is determined by the coupling efficiency between the whispering-gallery mode microring (2) and the straight waveguide (3). The inherent loss of the whispering-gallery mode microring (2) The decision was made jointly, and the specific relationships are as follows: (i) In the overcoupled state, the power coupled to the whispering-gallery mode microring (2) exceeds its internal loss, and the excess energy is coupled back into the straight waveguide (3), causing leakage at the output port and reducing the resonance depth; (ii) In the critical coupling state, the energy coupled to the whispering-gallery mode microring (2) is balanced with the internal loss, the back-coupling energy and the straight waveguide (3) component cancel each other out, and the ideal power of the direct output is 0. (iii) In the undercoupled state, the power coupled to the whispering-gallery mode microring (2) is much smaller than the internal loss, there is no echo-coupled electromagnetic wave, and the output port is a direct pass-through of the power not coupled to the whispering-gallery mode microring (2).

9. The on-chip terahertz whispering-gallery mode waveguide according to claim 8, characterized in that, The power at the output port (6) of the straight waveguide at the resonant frequency and the coupling efficiency between the whispering-gallery mode microring (2) and the straight waveguide (3). The inherent loss of the whispering-gallery mode microring (2) Related, the expression is: .

10. A terahertz signal modulation method, based on the on-chip terahertz whispering-gallery mode waveguide according to any one of claims 1 to 9, characterized in that, The method includes: A terahertz signal is input into the first tapered coupled waveguide; The solid-state laser source is controlled to emit pump light at a specific power to irradiate the whispering-gallery mode microring. By photoinduced carrier loss, the resonant coupling state of the whispering-gallery mode microring is precisely tuned to the target state. The terahertz signal, obtained from the output of the second tapered coupled waveguide and resonantly modulated, enables at least one function, including signal switching, attenuation, amplitude modulation, and phase modulation.

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