Continuous terahertz wave radiation source based on optical parametric oscillation in waveguide cavity and method of use and method of manufacture thereof

Abstract

This invention discloses a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, its usage method, and its fabrication method, belonging to the field of optical communication technology. The continuous terahertz parametric oscillation radiation source includes a nonlinear dielectric waveguide layer and a substrate waveguide layer disposed on the upper and lower surfaces of the nonlinear dielectric waveguide layer. Reflective films are disposed on two opposite sides of the nonlinear dielectric waveguide layer to form a waveguide cavity within the nonlinear dielectric waveguide layer. The thickness and width of the nonlinear dielectric waveguide layer both satisfy the wave vector matching condition, and the thickness of the nonlinear dielectric waveguide layer is 5~50 μm. By obtaining a large nonlinear coupling coefficient, a small terahertz propagation loss, and achieving wave vector matching, the continuous terahertz wave radiation source provided by this invention can achieve high terahertz conversion efficiency, the waveguide cavity has a high quality factor, enhances the effective field strength within the nonlinear dielectric waveguide layer, and significantly reduces the terahertz parametric oscillation threshold.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, and more specifically, relates to a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, and its usage and preparation methods. Background Technology

[0002] Terahertz radiation is an electromagnetic wave with a frequency between 0.1 and 10 terahertz (THz). Due to its advantages such as high penetration, low loss, fingerprint spectral characteristics and ultra-wideband communication potential, it is expected to be widely used in fields such as spectral analysis, astronomical observation, medical imaging, chemical identification, high-speed wireless communication (such as 6G), radar and terahertz time-domain spectroscopy.

[0003] Currently, there are two main categories of methods for generating terahertz radiation: electronic methods and photonic methods. Electronic methods suffer from significant losses at high frequencies, limiting output power and hindering device miniaturization and integration. While semiconductor quantum cascade lasers can provide high power, they typically require low-temperature operation and struggle to cover the low-frequency range below 1 THz. In contrast, nonlinear photonic methods can generate terahertz radiation at room temperature, offering significant advantages.

[0004] Chinese invention patent application CN120566203A discloses a terahertz generation chip based on thin-film lithium niobate. It employs a multilayer structure design of thin-film lithium niobate, silicon dioxide, silicon, and a polytetrafluoroethylene substrate. Two pump beams with a frequency difference at the terahertz level are input into the lithium niobate layer. The two beams undergo a difference-frequency effect in the lithium niobate layer, generating a terahertz wave that propagates in the silicon layer. In the aforementioned prior art and similar technologies, terahertz radiation requires two laser beams for difference-frequency generation. Although room temperature operation and frequency tuning are possible, the generation and propagation of the terahertz wave occur in two different media, resulting in extremely low spatial overlap between the pump mode and the terahertz mode, thus significantly limiting the nonlinear conversion efficiency. Summary of the Invention

[0005] 1. The problem to be solved To address the low terahertz conversion efficiency in existing continuous terahertz radiation sources, this invention provides a continuous terahertz wave radiation source based on optical parametric oscillations in a waveguide cavity, achieving high terahertz conversion efficiency by adjusting its structure and parameters. Furthermore, this invention also provides methods for using and fabricating the aforementioned continuous terahertz wave radiation source based on optical parametric oscillations in a waveguide cavity.

[0006] 2. Technical Solution To solve the above problems, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, comprising a nonlinear dielectric waveguide layer and a substrate waveguide layer disposed on the upper and lower surfaces of the nonlinear dielectric waveguide layer; a reflective film is disposed on two opposite sides of the nonlinear dielectric waveguide layer to form a waveguide cavity within the nonlinear dielectric waveguide layer; the thickness and width of the nonlinear dielectric waveguide layer both satisfy the wave vector matching condition, and the thickness of the nonlinear dielectric waveguide layer is 5~50μm.

[0007] Preferably, the nonlinear dielectric waveguide layer is a rectangular waveguide layer or a ridge waveguide layer.

[0008] Preferably, a buffer layer is provided between the nonlinear dielectric waveguide layer and the substrate waveguide layer, and the refractive index of the buffer layer, the nonlinear dielectric waveguide layer and the substrate waveguide layer increases sequentially for light waves.

[0009] More preferably, the thickness of the buffer layer is 2~3μm, and the buffer layer is one or more of the following: silicon dioxide layer, aluminum oxide layer, hafnium oxide layer, diamond layer, silicon nitride layer, or aluminum nitride layer.

[0010] Preferably, the reflective film has a reflectivity of more than 90% for pump light, the wavelength of the pump light is 0.4~100μm, and the reflectivity of the reflective films on both sides is equal.

[0011] Preferably, the reflective film is formed by alternating stacking of a first dielectric layer and a second dielectric layer, wherein the refractive index of the first dielectric layer is greater than that of the second dielectric layer, the first dielectric layer is one or more of tantalum pentoxide, titanium dioxide, hafnium oxide, or niobium oxide, and the second dielectric layer is one or more of silicon dioxide, magnesium fluoride, or aluminum oxide.

[0012] Preferably, the nonlinear dielectric waveguide layer is a lithium niobate layer, a gallium arsenide layer, a gallium nitride layer, or a silicon nitride layer.

[0013] Preferably, the substrate waveguide layer is one or more of a silicon layer, a quartz layer, a polymethylpentene layer, a polyethylene layer, or a traveling wave tube layer.

[0014] A second aspect of the present invention provides a method for using a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, as described in any embodiment of the first aspect of the present invention, comprising the following steps: Adjust the laser frequency of the laser or the resonant frequency of the waveguide cavity until they are equal; The laser is used to inject pump light into the waveguide cavity from a direction perpendicular to the reflective film; The pump light interacts parametrically with the nonlinear dielectric waveguide layer within the waveguide cavity, adjusting the power of the pump light to be greater than the threshold power of the terahertz parametric oscillation and generating terahertz wave radiation.

[0015] A third aspect of the present invention provides a method for fabricating a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, as described in any embodiment of the first aspect of the present invention, comprising the following steps: S1. Bond one surface of the nonlinear dielectric waveguide wafer to the substrate waveguide layer; S2. Thinning and polishing the nonlinear dielectric waveguide wafer to 5~50μm from another surface of the nonlinear dielectric waveguide wafer to obtain the nonlinear dielectric waveguide layer; S3. Bond the other surface of the nonlinear dielectric waveguide layer to another substrate waveguide layer to obtain a hybrid waveguide structure; S4. After cutting the hybrid waveguide structure into the target shape, polish each side. S5. Select two opposite sides to coat with reflective films to obtain the continuous terahertz wave radiation source based on optical parametric oscillation in the waveguide cavity.

[0016] Preferably, the method further includes the following steps: in step S1, a buffer layer is pre-deposited on the surface where the nonlinear dielectric waveguide wafer or the substrate waveguide layer is bonded; in step S3, a buffer layer is pre-deposited on the surface where the nonlinear dielectric waveguide layer or the substrate waveguide layer is bonded.

[0017] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity provided by the present invention has a substrate waveguide layer disposed on the upper and lower surfaces of a nonlinear dielectric waveguide layer, and a reflective film disposed on two opposite sides of the nonlinear dielectric waveguide layer to form a waveguide cavity within the nonlinear dielectric waveguide layer. The thickness of the nonlinear dielectric waveguide layer is limited to 5~50 μm, ensuring that the strongest part of the terahertz wave mode field is retained within the nonlinear dielectric waveguide layer, guaranteeing effective overlap between the terahertz wave and the optical wave in the nonlinear medium, thereby maintaining a large nonlinear coupling coefficient. Simultaneously, a large portion of the terahertz wave mode field is extended to the low-loss substrate waveguide layer for propagation, thereby reducing the absorption loss of the terahertz wave in the high-loss nonlinear material. Wave vector matching is achieved by controlling the thickness and width of the nonlinear dielectric waveguide layer. By achieving a large nonlinear coupling coefficient, a small terahertz propagation loss, and wave vector matching, the continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity provided by this invention can obtain a high terahertz conversion efficiency. The waveguide cavity further enhances the effective field strength within the nonlinear dielectric waveguide layer and significantly reduces the terahertz parametric oscillation threshold.

[0018] (2) Compared with the continuous terahertz difference frequency radiation source based on optical parametric oscillation in waveguide cavity provided by the present invention, the continuous terahertz wave radiation source based on optical parametric oscillation in waveguide cavity only requires one laser beam to generate terahertz radiation, without the need for two laser beams, and does not rely on an extremely strong local field to achieve nonlinear action. Therefore, it can effectively reduce the power density of pump light in the local region of nonlinear medium, reduce the risk of material reaching the damage threshold, and withstand the continuous input of higher power pump light, thereby improving the output power of terahertz wave and the stability of device operation, and is more suitable for application scenarios with higher power requirements.

[0019] (3) The continuous terahertz wave radiation source based on optical parametric oscillation in waveguide cavity provided by the present invention can use a low-power laser during use because the terahertz parametric oscillation has a low oscillation threshold.

[0020] (4) The method for preparing a continuous terahertz radiation source based on optical parametric oscillation in a waveguide cavity provided by the present invention is simple. It can prepare a terahertz radiation source with high terahertz conversion efficiency and low terahertz parametric oscillation threshold by using only traditional bonding, thinning and polishing processes. Attached Figure Description

[0021] Figure 1 A schematic diagram of the structure of the continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity provided by the present invention; Figure 2 A schematic diagram of the working principle of the continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity provided by the present invention; Figure 3 The terahertz wave dispersion curve of the continuous terahertz wave radiation source based on optical parametric oscillation in the waveguide cavity in this embodiment of the invention. Figure 4 This is the terahertz wave loss curve of the continuous terahertz wave radiation source based on optical parametric oscillation in the waveguide cavity in this embodiment of the invention. Figure 5 This is a diagram showing the optical mode field distribution of a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, as described in an embodiment of the present invention. Figure 6 This is a terahertz wave mode field distribution diagram of a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity according to an embodiment of the present invention. Figure 7 The optical transmission spectrum of a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity in an embodiment of the present invention; Figure 8 This is a graph showing the relationship between the signal optical power, terahertz wave power, and pump power of a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, according to an embodiment of the present invention.

[0022] In the figure: 1. Nonlinear dielectric waveguide layer; 2. Buffer layer; 3. Substrate waveguide layer; 4. Reflective film; 5. Pump light; 6. Signal light; 7. Terahertz wave. Detailed Implementation

[0023] It should be noted that when a component is referred to as being "mounted" on another component, it can be directly on the other component or the two components can be integrated as one unit; when a component is referred to as being "connected" to another component, it can be directly connected to the other component or the two components can be integrated as one unit. Furthermore, terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0024] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0025] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0026] like Figure 1 As shown, this invention provides a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, comprising a nonlinear dielectric waveguide layer 1 and a base waveguide layer 3 disposed on the upper and lower surfaces of the nonlinear dielectric waveguide layer 1. Reflective films 4 are disposed on two opposite sides of the nonlinear dielectric waveguide layer 1 to form a waveguide cavity within the nonlinear dielectric waveguide layer 1. When the refractive index of the nonlinear dielectric waveguide layer 1 for light waves (including pump light 5 and signal light 6) is less than the refractive index of the base waveguide layer 3 for light waves, a buffer layer 2 is disposed between the nonlinear dielectric waveguide layer 1 and the base waveguide layer 3. The refractive index of the buffer layer 2 for light waves is less than that of the nonlinear dielectric waveguide layer 1 for light waves, thus providing total internal reflection between the nonlinear dielectric waveguide layer 1 and the base waveguide layer 3, confining the light waves to propagate within the nonlinear dielectric waveguide layer 1.

[0027] The nonlinear dielectric waveguide layer 1 serves as an optical waveguide to generate terahertz waves 7. The substrate waveguide layer 3 supports the nonlinear dielectric waveguide layer 1 and can propagate terahertz waves 7. The reflective film 4 is used to form a waveguide cavity, reduce the pump threshold of terahertz parametric oscillations, and increase the field strength inside the cavity.

[0028] It should be noted that, in this invention, the lengths of the nonlinear dielectric waveguide layer 1, the buffer layer 2, and the substrate waveguide layer 3 in the terahertz wave radiation source are... LIts maximum dimension parallel to the incident direction of pump light 5, width w It is its maximum dimension perpendicular to the incident direction of the pump light 5 and the thickness direction of the nonlinear dielectric waveguide layer 1. For example... Figure 1 and Figure 2 As shown, the lengths of each of the above layers within the rectangular terahertz wave radiation source are marked. L and width w .

[0029] The thickness of the nonlinear dielectric waveguide layer 1 is 5~50 μm, and it is selected from dielectric materials with second- or third-order nonlinear effects, such as lithium niobate layers, gallium arsenide layers, gallium nitride layers, or silicon nitride layers. Besides rectangular waveguide layers, the nonlinear dielectric waveguide layer 1 can also be a ridge waveguide layer. When the nonlinear dielectric waveguide layer 1 is a ridge waveguide layer, the thickness is taken as the maximum value in its thickness direction.

[0030] As a preferred embodiment, the thickness of the substrate waveguide layer 3 is 500~1000μm. The lower limit of this thickness ensures that the terahertz wave 7 propagates only within the radiation source in practical applications, while the upper limit considers economic efficiency and the compact size of the terahertz wave radiation source. The two substrate waveguide layers 3 can be made of the same material or different materials. As a preferred embodiment, the material of the substrate waveguide layer 3 is selected from terahertz low-loss waveguides, and the substrate waveguide layer 3 is one or more of the following: silicon layer, quartz layer, polymethylpentene layer, polyethylene layer, or traveling wave tube layer.

[0031] As a preferred embodiment, the reflective film 4 has a thickness of 2.5~5μm and is formed by alternating stacking of a first dielectric layer and a second dielectric layer, wherein the refractive index of the first dielectric layer is greater than that of the second dielectric layer. The first dielectric layer is one or more of tantalum pentoxide, titanium dioxide, hafnium oxide, or niobium oxide, and the second dielectric layer is one or more of silicon dioxide, magnesium fluoride, or aluminum oxide. As a preferred embodiment, the reflective film 4 has a reflectivity greater than 90% for the pump light 5, wherein the wavelength of the pump light is 0.4~100μm. As another preferred embodiment, the reflective films 4 on both sides of the terahertz wave radiation source have equal reflectivity. The composition of the reflective films 4 on both sides of the terahertz wave radiation source can be the same or different.

[0032] As a preferred embodiment, the thickness of the buffer layer 2 is 2~3μm, and it is one or more of the following: silicon dioxide layer, aluminum oxide layer, hafnium oxide layer, diamond layer, silicon nitride layer, or aluminum nitride layer. The two buffer layers 2 can be made of the same material or different materials.

[0033] like Figure 2 As shown, the working principle of the continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity provided by this invention is as follows: The conversion efficiency of terahertz wave 7 is positively correlated with the nonlinear coupling coefficient and negatively correlated with the attenuation coefficient and wave vector mismatch. Specifically, the nonlinear coupling coefficient depends on the degree of mode field overlap between the pump light 5, signal light 6, and terahertz wave 7 in the nonlinear medium; the terahertz attenuation coefficient reflects the loss of terahertz wave 7 during propagation; and the wave vector mismatch determines whether terahertz wave 7 can achieve effective accumulation in the propagation direction. All three factors are simultaneously affected by the width and thickness of the nonlinear dielectric waveguide layer 1. For the nonlinear dielectric waveguide layer 1, being too thin will reduce the nonlinear coupling coefficient, while being too thick will increase the terahertz attenuation coefficient. Furthermore, the width and thickness of the nonlinear dielectric waveguide layer 1 determine the magnitude of the wave vector mismatch.

[0034] Based on this, the terahertz wave radiation source provided by the present invention ensures that the main energy of the terahertz wave 7 is distributed in the low-loss substrate waveguide layer 3 under the premise of ensuring sufficient nonlinear coupling coefficient, and achieves wave vector matching by controlling the geometric parameters of the terahertz wave radiation source, thereby obtaining a high terahertz conversion efficiency.

[0035] Furthermore, to enhance the effective field strength within the waveguide and reduce the terahertz parametric oscillation threshold, the present invention deposits reflective films 4 at both the incident and exit ends of the nonlinear dielectric waveguide layer 1 to form a waveguide cavity. The aforementioned incident and exit ends refer to the sides where the pump light 5 enters and exits the nonlinear dielectric waveguide layer 1, respectively.

[0036] The method of using the continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity provided by the present invention is as follows: by adjusting the laser frequency of the laser, such as by using a tunable laser, or by adjusting the resonant frequency of the waveguide cavity by changing the temperature, the laser frequency of the laser and the resonant frequency of the waveguide cavity are made equal, so as to increase the proportion of pump light 5 coupled into the waveguide cavity; the laser is used to inject pump light 5 into the waveguide cavity from a direction perpendicular to the reflective film 4; the pump light 5 interacts parametrically with the nonlinear dielectric waveguide layer 1 in the waveguide cavity, the power of the pump light 5 (i.e., pump power) is adjusted to be greater than the threshold power of terahertz parametric oscillation, and terahertz wave 7 is generated.

[0037] Pump light 5 generates signal light 6 and terahertz wave 7 within the waveguide cavity, satisfying the energy conservation principle:

[0038] in ω p , ω s and ω T These are the angular frequencies of pump light 5, signal light 6, and terahertz wave 7, respectively.

[0039] Pump light 5, signal light 6, and terahertz wave 7 undergo mode-coupled propagation within the terahertz wave radiation source. The light waves are primarily confined within the nonlinear dielectric waveguide layer 1, while terahertz wave 7 is mainly emitted from the other end. By adjusting the thickness and width of the nonlinear dielectric waveguide layer 1, the effective refractive index of terahertz wave 7 is controlled to equal the group refractive index of pump light 5, thereby satisfying the wave vector matching condition for nonlinear conversion.

[0040] in Δk Let c be the wave vector mismatch, and c be the speed of light. n g,o Let be the group refractive index of pump light 5. n THz The effective refractive index of terahertz wave 7.

[0041] It should be noted that, Figure 1 and Figure 2 The image shows that each layer of the terahertz wave radiation source has a reflective film 4 on both sides. This is because it is easier to operate by coating both sides of each layer of the radiation source during the preparation process. In fact, as long as the nonlinear dielectric waveguide layer 1 has reflective films 4 on opposite sides, a waveguide cavity can be formed.

[0042] The present invention will be further described below with reference to specific embodiments.

[0043] This embodiment provides a method for fabricating a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, including the following steps: S1, A 4-inch diameter, 500μm thick material x A 2μm thick SiO2 buffer layer is deposited on one surface of a lithium niobate wafer, and the SiO2 buffer layer is thermo-bonded to a 4-inch diameter, 500μm thick quartz substrate waveguide layer. S2. Mechanical grinding and chemical mechanical polishing are performed on the other surface of the lithium niobate wafer to obtain a lithium niobate waveguide layer with a thickness of 15 μm and a surface roughness of <1 nm. S3. Deposit a 2μm thick SiO2 buffer layer on the other surface of the lithium niobate waveguide layer, and then hot-press bond the SiO2 buffer layer to another 4-inch diameter, 500μm thick quartz substrate waveguide layer to obtain a hybrid waveguide structure. S4. The hybrid waveguide structure is cut into a rectangle using a precision laser cutting machine. The four sides are polished. After polishing, the width of the rectangle is 445μm, the length is 4cm, and the side roughness is <1nm. S5. Deposit reflective films on two opposite sides of the four sides parallel to the width direction mentioned in step S4 to obtain a terahertz radiation source. The reflective films on both sides have a reflectivity of 99.7% for light waves with a wavelength of 1550nm. The reflective films are formed by alternating deposition of silicon dioxide layers and tantalum pentoxide layers. The optical thickness (refractive index × physical thickness) of each layer is one-quarter of 1550nm, and the total thickness of the reflective films is 3.9μm.

[0044] The dimensional parameters of the terahertz radiation source prepared by the above method are as follows: the thickness of the lithium niobate waveguide layer... h 1 is 15 μm, the thickness of the SiO2 buffer layer h 2 represents the thickness of the quartz substrate waveguide layer, which is 2 μm. h The thickness of the reflective film is 3.9 μm. The width of the lithium niobate waveguide layer, the SiO2 buffer layer, and the quartz substrate waveguide layer are all 445 μm, and the length is 4 cm. The total thickness of the reflective film is 3.9 μm. The following experiments were conducted using this terahertz wave radiation source.

[0045] A pump light 5 with a wavelength of 1550 nm is incident onto the lithium niobate waveguide layer from the incident end using a laser along a direction perpendicular to the reflective film 4. To achieve efficient conversion from light to terahertz wave 7, wave vector matching must first be satisfied. Because the thickness of the lithium niobate waveguide layer is nearly 10 times the wavelength of the pump light 5, the lithium niobate waveguide layer is a bulk layer for the pump light 5. Its group refractive index for the 1550 nm pump light 5 is the group refractive index of the bulk lithium niobate for that wavelength pump light 5, i.e., ... n g,o The value is 2.1744. Because the thickness and width of the lithium niobate waveguide layer are much larger than the wavelength of light, changing the geometric parameters such as the thickness and width of the lithium niobate waveguide layer does not affect its refractive index for light. This ensures that the effective refractive index for terahertz wave 7 can be independently controlled by changing the thickness and width of the lithium niobate waveguide layer, thereby achieving mode wave vector matching between light and terahertz wave 7. In order to utilize... x The largest nonlinear coefficient of lithium niobate d 33 The incident pump light 5 is selected as a transverse electric field mode with the electric field direction along the width direction of the lithium niobate waveguide layer.

[0046] With a constant thickness and varying width of the lithium niobate waveguide layer, the effective refractive index of the terahertz radiation source for terahertz wave 7 was obtained through COMSOL simulation. n THz attenuation coefficient α THz With the width of the lithium niobate waveguide layer w The relationship, and the results are as follows: Figure 3 and Figure 4 As shown. By Figure 3It can be seen that as the width of the lithium niobate waveguide layer increases, the effective refractive index of the terahertz wave radiation source for terahertz wave 7 increases. Wave vector matching is achieved when the width of the lithium niobate waveguide layer is 445 μm. n g,o = n THz =2.1744, at which point the frequency of the generated terahertz wave 7 is 0.328 THz, and the attenuation coefficient of the terahertz wave 7 is... α THz Reduced to 0.148 cm -1 (like Figure 4 (As shown). Compared to the above-mentioned terahertz wave 7, the attenuation coefficient in bulk lithium niobate is 1.06 cm⁻¹. -1 In this embodiment, the attenuation coefficient of terahertz wave 7 in the lithium niobate waveguide layer is reduced by an order of magnitude, and the energy loss rate is significantly reduced.

[0047] The mode field distributions of optical wave and terahertz wave 7 were obtained using COMSOL mode analysis, and the results are as follows: Figure 5 and Figure 6 As shown. By Figure 5 It can be seen that the mode field of the light wave is mainly distributed in the lithium niobate waveguide layer. From... Figure 6 It is known that the high field strength region of the terahertz wave 7 mode field is located in the lithium niobate waveguide layer, thus ensuring the effective overlap of the terahertz wave 7 and the light wave in the nonlinear medium, so as to maintain a large nonlinear coupling coefficient. At the same time, a large part of the terahertz wave 7 mode field extends to the quartz substrate waveguide layers on both sides to propagate, thereby reducing the energy ratio of the terahertz wave 7 in the lithium niobate waveguide layer and reducing the absorption loss of the terahertz wave 7 by the lithium niobate waveguide layer.

[0048] The quality factor is a key indicator for measuring the sharpness of the resonance peak and energy loss. A high quality factor means a narrower resonance bandwidth and lower energy attenuation. Assume the reflectivities of the reflective films 4 at both ends of the lithium niobate waveguide layer are respectively... R 1 and R 2. Under resonant conditions, the overall quality factor of the forward-propagating light within the cavity. Q t for:

[0049] in α The attenuation coefficient of light waves is denoted as . n The refractive index of the lithium niobate waveguide layer for light waves. λ The wavelength of the light wave. Under critical coupling conditions... R 1 =R 2 =R Below, with reflectivity R Approaching 1, the overall quality factor increases significantly. Simultaneously, the oscillation threshold power of the terahertz parametric oscillation...P th It also decreased rapidly as a result:

[0050] in, To reduce Planck's constant ，Q p,t , Q s,t and Q THz,t These are the total quality factors of pump light 5, signal light 6, and terahertz wave 7, respectively. Q p,e It is the external coupling quality factor of pump light 5. g 0 represents the nonlinear coupling strength.

[0051] In this embodiment, R 1 and R Both are 99.7%. This was done to measure the quality factor of the resonant cavity. Q A narrow-linewidth tunable continuous-wave laser was used as the light source, with its wavelength finely stepped across the 1550nm band. The laser was adjusted to transverse electric field mode via a polarization controller. A lens coupled light waves near the 1550nm wavelength into the resonant cavity. A photodetector then converted the transmitted wavelength into an electrical signal, which was acquired in real-time using an oscilloscope to obtain the transmission spectrum of the light wave. Figure 7 As shown. The center wavelength was obtained under Lorentz fitting. λ The full width at half maximum (FWHM) of the transmission peak at 0 = 1549.1862 nm is Δ. λ =9.1×10 -6 nm, according to Q = λ 0 / Δ λ The resonant cavity can be calculated. Q The value is as high as 1.7 × 10⁻⁶. 8 It can effectively accumulate photon energy and reduce the pump power required to excite terahertz waves.

[0052] To measure the start-up characteristics of terahertz parametric oscillations, the resonant wavelength of the waveguide cavity was adjusted to be equal to the wavelength of pump light 5 (1550.12 nm) through temperature control. Under resonant conditions, pump light 5 was coupled into the waveguide cavity, and the power of pump light 5 and signal light 6 was measured at the output end using an optical power meter. The power of terahertz wave 7 was then measured using a terahertz detector. The results are as follows: Figure 8 As shown. By Figure 8 It can be seen that when the pump power injected into the waveguide cavity P Pump Power greater than the threshold P thAt 6.5mW, the terahertz parametric oscillation begins to oscillate and radiates terahertz wave 7 and signal light 6. The power of terahertz wave 7 is... P THz and the power of signal light 6 P Signal along with P Pump The increase is due to the increase in power. Traditional terahertz parametric oscillators based on bulk nonlinear crystals typically require kilowatts (kW) of pulse peak power or several watts (W) of high-power continuous wave lasers for support, while the terahertz wave radiation source in this embodiment has an oscillation threshold of only 6.5mW.

[0053] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity, characterized in that: It includes a nonlinear dielectric waveguide layer (1) and a substrate waveguide layer (3) disposed on the upper and lower surfaces of the nonlinear dielectric waveguide layer (1); a reflective film (4) is disposed on two opposite sides of the nonlinear dielectric waveguide layer (1) to form a waveguide cavity in the nonlinear dielectric waveguide layer (1); the thickness and width of the nonlinear dielectric waveguide layer (1) both satisfy the wave vector matching condition, and the thickness of the nonlinear dielectric waveguide layer (1) is 5~50μm.

2. The continuous terahertz wave radiation source according to claim 1, characterized in that: The nonlinear dielectric waveguide layer (1) is a rectangular waveguide layer or a ridge waveguide layer.

3. The continuous terahertz wave radiation source according to claim 1, characterized in that: A buffer layer (2) is provided between the nonlinear dielectric waveguide layer (1) and the substrate waveguide layer (3), and the refractive index of the buffer layer (2), the nonlinear dielectric waveguide layer (1) and the substrate waveguide layer (3) increases sequentially for light waves.

4. The continuous terahertz wave radiation source according to claim 3, characterized in that: The thickness of the buffer layer (2) is 2~3μm, and the buffer layer (2) is one or more of the following: silicon dioxide layer, aluminum oxide layer, hafnium oxide layer, diamond layer, silicon nitride layer or aluminum nitride layer.

5. The continuous terahertz wave radiation source according to claim 1, characterized in that: The reflective film (4) has a reflectivity greater than 90% for the pump light (5), the wavelength of the pump light (5) is 0.4~100μm, and the reflectivity of the reflective films (4) on both sides is equal.

6. The continuous terahertz wave radiation source according to claim 1, characterized in that: The reflective film (4) is formed by alternating stacking of a first dielectric layer and a second dielectric layer. The refractive index of the first dielectric layer is greater than that of the second dielectric layer. The first dielectric layer is one or more of tantalum pentoxide, titanium dioxide, hafnium oxide, or niobium oxide. The second dielectric layer is one or more of silicon dioxide, magnesium fluoride, or aluminum oxide.

7. The continuous terahertz wave radiation source according to claim 1, characterized in that: The nonlinear dielectric waveguide layer (1) is a lithium niobate layer, a gallium arsenide layer, a gallium nitride layer, or a silicon nitride layer.

8. The continuous terahertz wave radiation source according to claim 1, characterized in that: The substrate waveguide layer (3) is one or more of the following: silicon layer, quartz layer, polymethylpentene layer, polyethylene layer or traveling wave tube layer.

9. The method of using the continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Adjust the laser frequency of the laser or the resonant frequency of the waveguide cavity until they are equal; Pump light (5) is injected into the waveguide cavity from a direction perpendicular to the reflective film (4) using the laser; The pump light (5) interacts parametrically with the nonlinear dielectric waveguide layer (1) in the waveguide cavity, adjusting the power of the pump light (5) to be greater than the threshold power of the terahertz parametric oscillation, and generating terahertz wave (7) radiation.

10. The method for fabricating a continuous terahertz wave radiation source based on optical parametric oscillation in a waveguide cavity according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Bond one surface of the nonlinear dielectric waveguide wafer to the substrate waveguide layer; S2. Thinning and polishing the nonlinear dielectric waveguide wafer to 5~50μm from another surface of the nonlinear dielectric waveguide wafer to obtain the nonlinear dielectric waveguide layer; S3. Bond the other surface of the nonlinear dielectric waveguide layer to another substrate waveguide layer to obtain a hybrid waveguide structure; S4. After cutting the hybrid waveguide structure into the target shape, polish each side. S5. Select two opposite sides to coat with reflective films to obtain the continuous terahertz wave radiation source based on optical parametric oscillation in the waveguide cavity.

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