A monolithic integrated terahertz wave generating device and method

Abstract

This invention discloses a monolithically integrated terahertz wave generation device and method, belonging to the field of optoelectronic technology. The device is a monolithically integrated structure, with a laser module, a Y-type beam combiner module, and a semiconductor optical amplifier sequentially integrated along the waveguide transmission direction. The laser module includes multiple parallel distributed feedback laser units. The Y-type beam combiner module couples the multiple distributed feedback laser units into a single waveguide. From bottom to top, the device includes a lower electrode, a substrate, a buffer layer, a high-refractive-index mode extension layer, a lower confinement layer, a multi-quantum-well active layer, an upper confinement layer, a transition layer, a grating, a ridge waveguide, and an upper electrode. The refractive index of the high-refractive-index mode extension layer material is higher than that of the buffer layer material. This invention has advantages such as a wide frequency tuning range, high power, and high spectral purity.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology and relates to a terahertz wave generating device, and more particularly to a monolithically integrated terahertz wave generating device and method. Background Technology

[0002] Terahertz (THz) waves have enormous application potential in high-speed wireless communication, medical imaging, and security detection. Using dual-wavelength semiconductor lasers for optical heterodyne beat frequency generation is an effective way to generate continuous-wave (CW) terahertz radiation. However, existing monolithic integrated solutions still face many technical challenges. First, output power and linewidth limitations: constrained by traditional waveguide structures, output power is often limited, and the spectral linewidth is relatively wide (typically on the order of MHz), resulting in significant phase noise in the terahertz signal. Second, tuning coupling issues: traditional laser tuning relies on the Joule heating effect generated by the injected current, which leads to severe nonlinear coupling between wavelength changes and optical output power, making it difficult for the system to maintain a constant radiation intensity during frequency sweeping. Third, mode stability and loss: reducing bending loss and suppressing parasitic reflections are key challenges in improving the performance of monolithic integrated devices when achieving multi-wavelength beam combining. Summary of the Invention

[0003] This invention provides a monolithically integrated terahertz wave generation device and method to overcome the shortcomings of the prior art.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a monolithically integrated terahertz wave generation device. The device is a monolithically integrated structure, in which a laser module, a Y-type beam combiner module, and a semiconductor optical amplifier (SOA) are sequentially integrated along the waveguide transmission direction. The laser module includes multiple parallel distributed feedback (DFB) laser units. The Y-type beam combiner module couples the multiple DFB laser units into a single waveguide. The device, from bottom to top, includes a lower electrode, a substrate, a buffer layer, a high refractive index mode extension layer, a lower confinement layer, a multi-quantum well active layer, an upper confinement layer, a transition layer, a grating, a ridge waveguide, and an upper electrode, wherein the grating is located only at the DFB laser units. The refractive index of the high refractive index mode extension layer material is higher than that of the buffer layer material.

[0005] To optimize the above technical solution, the specific measures also include: Furthermore, each of the distributed feedback laser units has a conductive film heater above its ridge waveguide, independent of the upper electrode of the distributed feedback laser unit.

[0006] Furthermore, the conductive film heater is a titanium-platinum alloy film.

[0007] Furthermore, in the distributed feedback laser unit: the conductive film heater is disposed above the upper electrode; or, the ridge waveguide is divided into two parts, the upper electrode is disposed on one part of the ridge waveguide, and the conductive film heater is disposed on the other part of the ridge waveguide.

[0008] Furthermore, the material of the high refractive index mode extension layer is InGaAsP.

[0009] Furthermore, the distributed feedback laser unit uses reconstruction equivalent chirp (REC) technology to fabricate a grating, forms a uniform seed grating through a single holographic exposure, and presets its wavelength difference by changing the ultraviolet lithography sampling period of multiple parallel distributed feedback laser units.

[0010] Furthermore, the Y-type beam combiner module includes at least one Y-type beam combiner; when the number of distributed feedback laser units is two, the number of Y-type beam combiners is one, and the two input terminals of the Y-type beam combiner are respectively located at the front end of the output terminals of the two distributed feedback laser units, and the Y-type beam combiner couples the two distributed feedback laser units into a single waveguide; when the number of distributed feedback laser units is multiple, the number of Y-type beam combiners is multiple, and the multiple Y-type beam combiners form a cascaded Y-type beam combiner structure, which couples the multiple distributed feedback laser units into a single waveguide, that is, every two distributed feedback laser units are coupled into a single waveguide through one Y-type beam combiner, every two Y-type beam combiners are then coupled into a single waveguide through another Y-type beam combiner, and finally coupled into a single waveguide through a Y-type beam combiner.

[0011] Furthermore, the ridge waveguide of the Y-type combiner has an S-shaped curved structure.

[0012] Furthermore, the ridge waveguide of the semiconductor optical amplifier is a curved structure that is tilted relative to the waveguide transmission direction, and the light-emitting end face has an anti-reflection film.

[0013] Furthermore, the ridge waveguide of the semiconductor optical amplifier has a gradually tapered structure, and the width of the ridge waveguide gradually increases along the waveguide transmission direction.

[0014] Furthermore, an electrical isolation groove with a depth to the grating is provided between the laser module and the Y-type beam combiner module, and between the Y-type beam combiner module and the semiconductor optical amplifier.

[0015] Secondly, the present invention also provides a method for generating monolithically integrated terahertz waves: the above-mentioned device is connected to a control circuit, the injection current of all the distributed feedback laser units is fixed to maintain stable output power, and the injection current of the conductive film heater of some of the distributed feedback laser units is adjusted to change the lasing wavelength of the corresponding distributed feedback laser units by means of thermal effect. The wavelengths output by multiple distributed feedback laser units are combined by the Y-type beam combiner module and amplified by the semiconductor optical amplifier before being output, thereby generating terahertz radiation with continuously adjustable frequency and stable power.

[0016] The beneficial effects of this invention are as follows: I. This invention achieves extremely high monolithic integration, significantly improving the robustness and reliability of the system. Specifically, multiple parallel distributed feedback laser units, a Y-type beam combiner, and a semiconductor optical amplifier are monolithically integrated on the same substrate. This integrated structure eliminates the complex optical alignment and mechanical calibration steps in the spatial optical path, while simultaneously reducing the physical package size of the device. Furthermore, this structure effectively suppresses the interference of environmental temperature fluctuations and external micro-vibrations on the optical path coupling efficiency, fundamentally improving the long-term operational stability and environmental adaptability of the terahertz wave generation device.

[0017] II. This invention overcomes the limitations of output power in monolithic integrated structures, achieving high-power continuous wave output. Specifically, the single-end continuous wave output power is improved through the physical synergy of the vertical epitaxial structure and the horizontal waveguide morphology. In the vertical direction, an InGaAsP high-refractive-index mode extension layer is introduced, strongly pulling the optical waveguide mode center towards the n-type substrate, thereby reducing the confinement factor of the optical field in the p-type high-absorption doped region, significantly suppressing internal absorption loss, and supporting stable transmission of the fundamental mode under a wide ridge waveguide. In the horizontal direction, the semiconductor optical amplifier adopts a tapered waveguide structure, effectively diluting the local photon density under high power conditions, avoiding the local hotspot effect and gain saturation limitation, and ensuring efficient and stable amplification under a large mode field volume.

[0018] Third, this invention achieves significant narrowing of the Lorentz linewidth, greatly improving the spectral purity of terahertz radiation. Specifically, the Lorentz linewidth of the lasing spectrum of this device is effectively narrowed to below 300 kHz, providing an extremely high-quality seed source for the generation of low-phase-noise terahertz waves. On the one hand, the mode field expansion mechanism dominated by the high-refractive-index mode extension layer effectively increases the photon energy storage volume and reduces the average photon density within the cavity, suppressing phase noise caused by spontaneous emission at its source. On the other hand, to address the backscattering problem under high-gain conditions, the semiconductor optical amplifier employs a tilted curved structure and an optical end face with an anti-reflection film, blocking parasitic oscillation circuits within the device and eliminating the disturbance interference of residual reflected waves on the lasing frequency of the front-end distributed feedback laser unit, ensuring extremely high lasing spectral purity.

[0019] IV. This invention achieves decoupled control of terahertz radiation frequency and output power. Specifically, this invention employs an injection-locked, thermally swept tuning mechanism. A conductive film heater, independent of the upper electrode, is installed on the ridge waveguide of the distributed feedback laser unit. This allows for the independent adjustment of the conductive film heater voltage, using purely thermal effects to change the equivalent refractive index of the resonant cavity, while maintaining a fixed upper electrode injection current (locked output power). This physically solves the inherent problem of nonlinear coupling between wavelength and power in traditional current tuning, achieving wide-range continuous tuning and absolutely stable output power.

[0020] V. This invention achieves efficient optical wave synthesis. Specifically, the Y-type beam combiner adopts an S-shaped curved ridge waveguide structure, and the bending radius is determined by multiple constraints, successfully offsetting radiation overflow under the weak confinement condition of wide-mode field, and ensuring efficient and low-loss synthesis of dual-wavelength signals. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural diagram of a monolithically integrated terahertz wave generator; Figure 2 This is a side view of the structure of a monolithically integrated terahertz wave generator; Figure 3 This is a top view of the structure of a monolithically integrated terahertz wave generator; Figure 4This is a dual-wavelength spectral characteristic diagram of a monolithically integrated terahertz wave generator during terahertz wave generation. In the diagram, a~c are the dual-wavelength spectral evolution diagrams when the injection current of the conductive film heater of one distributed feedback laser unit (DFB1) is fixed and the injection current of the conductive film heater of another distributed feedback laser unit (DFB2) is changed, respectively. The curves showing the change of the lasing wavelength of the distributed feedback laser unit with current and the change of the side-mode suppression ratio (SMSR) of the distributed feedback laser unit are also shown. d~f are the dual-wavelength spectral evolution diagrams when the injection current of the conductive film heater of one distributed feedback laser unit (DFB2) is fixed and the injection current of the conductive film heater of another distributed feedback laser unit (DFB1) is changed, respectively. Figure 5 The graph shows the optical output power characteristics of a monolithically integrated terahertz wave generator. In the graph, a is the PIV superposition curve of the distributed feedback laser unit, and b is the power amplification characteristic curve of the semiconductor optical amplifier. Figure 6 The figure shows the spectral linewidth measurement results of a monolithically integrated terahertz wave generator. Figure a and b are the delay self-heterodyne measurement spectra and Lorentz fitting curves of two distributed feedback laser units under a specific bias current, respectively. The labels in the attached figure are as follows: 1. Distributed feedback laser unit; 2. Y-type beam combiner; 3. Semiconductor optical amplifier; 4. Lower electrode; 5. Substrate; 6. Buffer layer; 7. High refractive index mode extension layer; 8. Lower confinement layer; 9. Multi-quantum well active layer; 10. Upper confinement layer; 11. Transition layer; 12. Grating; 13. Ridge waveguide; 14. Upper electrode; 15. Conductive film heater. Detailed Implementation

[0022] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the present invention provides a monolithic integrated terahertz wave generating device.

[0024] The device is a monolithic integrated structure, sequentially integrating a laser module, a Y-type beam combiner module, and a semiconductor optical amplifier 3 along the waveguide transmission direction. The laser module includes multiple parallel distributed feedback laser units 1. The Y-type beam combiner module couples the multiple distributed feedback laser units 1 into a single waveguide. The multi-wavelength lasers generated by the multiple distributed feedback laser units 1 are combined with low loss by the Y-type beam combiner module and then enter the semiconductor optical amplifier 3 for power amplification. A continuously tunable terahertz wave is generated through optical heterodyne beat frequency generation.

[0025] Specifically, the Y-type beam combiner module includes at least one Y-type beam combiner 2. When there are two distributed feedback laser units 1, there is one Y-type beam combiner 2. The two input terminals of the Y-type beam combiner 2 are respectively set in front of the output terminals of the two distributed feedback laser units 1, and the Y-type beam combiner 2 couples the two distributed feedback laser units 1 into a single waveguide. When there are multiple distributed feedback laser units 1, there are multiple Y-type beam combiners 2. Multiple Y-type beam combiners 2 form a cascaded Y-type beam combiner structure, which couples multiple distributed feedback laser units 1 into a single waveguide. That is, every two distributed feedback laser units 1 are coupled into a single waveguide through one Y-type beam combiner 2, and every two Y-type beam combiners 2 are then coupled into a single waveguide through another Y-type beam combiner 2, and finally coupled into a single waveguide through the Y-type beam combiner 2.

[0026] In this embodiment, the device is equipped with two distributed feedback laser units 1 and a Y-type beam combiner 2.

[0027] like Figure 1 and Figure 2 As shown, the device comprises, from bottom to top, a lower electrode 4, a substrate 5, a buffer layer 6, a high refractive index mode extension layer 7, a lower confinement layer 8, a multi-quantum well active layer 9, an upper confinement layer 10, a transition layer 11, a grating 12, a ridge waveguide 13, and an upper electrode 14, wherein the grating 12 is located only at the distributed feedback laser unit 1.

[0028] The high-refractive-index mode extension layer 7 has a higher refractive index than the buffer layer 6. This layer pulls the optical waveguide mode center towards the substrate 5, reducing the confinement factor of the optical field in the p-type doped region and thus decreasing internal absorption loss. Specifically, the high-refractive-index mode extension layer 7 is made of InGaAsP. The introduction of the high-refractive-index mode extension layer 7 enables the device to support single transverse mode lasing with a ridge waveguide 13 with a width greater than or equal to 3 μm. This means that even when the ridge waveguide 13 is 3 μm or wider, it can still maintain stable fundamental mode (TE0) transmission, significantly improving the device's saturated output power and narrowing the spectral linewidth.

[0029] The distributed feedback laser unit 1 utilizes the reconstruction equivalent chirp (REC) technique to fabricate the grating 12. A uniform seed grating 12 is formed through a single holographic exposure, and the wavelength difference is preset by changing the ultraviolet lithography sampling period of the multiple parallel distributed feedback laser units 1. In this embodiment, by setting the sampling period within the range of 3.993 μm to 4.11 μm, the lasing wavelengths of the two distributed feedback laser units 1 are precisely preset to around 1550 nm and 1547.6 nm, respectively, thereby presetting the wavelength difference by changing the sampling period of the two laser units.

[0030] like Figure 1As shown, each distributed feedback laser unit 1 has a conductive film heater 15 above its ridge waveguide 13, independent of the upper electrode 14. By adjusting the local temperature through the conductive film heater 15, the lasing wavelength is changed using purely thermal effects. This achieves frequency tuning while maintaining a constant injection current in the distributed feedback laser unit 1, as well as decoupled control of the output optical power and radiation frequency, ensuring that the output power remains constant during wavelength changes. Specifically, the conductive film heater 15 can be a titanium-platinum alloy film.

[0031] In this embodiment, the conductive film heater 15 is disposed above the upper electrode 14. Alternatively, the conductive film heater 15 and the upper electrode 14 can also be disposed in segments: the ridge waveguide 13 is divided into two parts, the upper electrode 14 is disposed on one part of the ridge waveguide 13, and the conductive film heater 15 is disposed on the other part of the ridge waveguide 13.

[0032] like Figure 1 and Figure 3 As shown, the ridge waveguide 13 of the Y-type combiner 2 has an S-shaped curved structure to counteract radiation spillover under weak confinement conditions in a wide mode field, ensuring efficient and low-loss synthesis of multi-wavelength signals. The bending radius of the Y-type combiner 2 is optimized in conjunction with the mode field expansion induced by the high-refractive-index mode extension layer 7. Specifically, although the high-refractive-index mode extension layer 7 can pull the center of the mode field towards the substrate 5 to reduce internal absorption loss, it inevitably weakens the lateral confinement force of the waveguide on the optical field, resulting in a decrease in the equivalent refractive index difference (the difference in effective refractive index between the fundamental mode and higher-order modes), which in turn significantly increases the diameter of the horizontal mode field of the fundamental mode. If a conventionally sized Y-type combiner 2 is used under extended mode field conditions, the light wave will generate significant radiation spillover and mode mismatch when propagating in the S-shaped curved waveguide.

[0033] To ensure low-loss beam combining under high-power conditions, the bending radius of the Y-type beam combiner 2 must simultaneously meet the following constraints: Radiation loss constraint: By constraining the radiation loss per unit length, the problem of waveguide sensitivity to radiation loss caused by the reduction in equivalent refractive index difference is solved. The formula for calculating the radiation loss per unit length is: .

[0034] In the formula, Radiation loss per unit length, and It is a proportionality constant. The bending radius of the Y-type combiner 2 is... For the equivalent refractive index difference, This is the operating wavelength of the device.

[0035] By increasing the bending radius, the leakage of the light field under weak confinement conditions is effectively suppressed in an exponential manner, thereby suppressing radiation loss per unit length.

[0036] Mode field compensation constraint: Since the high-refractive-index mode extension layer 7 structure supports a wider ridge waveguide 13, the diameter of the fundamental mode horizontal mode field increases. Therefore, a cubic compensation relationship is maintained between the bending radius and the fundamental mode horizontal mode field diameter to ensure phase consistency of the light wave during bending propagation. The compensation relationship is as follows: .

[0037] In the formula, The shape factor is a constant. The diameter of the horizontal mode field of the fundamental mode. The refractive index of the waveguide core layer (lower confinement layer 8, multi-quantum well active layer 9, and upper confinement layer 10) is given. is the refractive index of the cladding (other layers besides the lower confinement layer 8, the multi-quantum-well active layer 9, and the upper confinement layer 10).

[0038] Size constraints: The upper limit of the bending radius is determined by the total length of the device, the length of the distributed feedback laser unit 1, and the length of the semiconductor optical amplifier 3.

[0039] Transition Matching Constraint: By constraining the mode mismatch loss at the junction of the straight waveguide of distributed feedback laser unit 1 and the curved waveguide of Y-type beam combiner 2, and smoothing the wavefront distortion caused by the expanded mode field, the mode mismatch loss at the junction of the straight waveguide of distributed feedback laser unit 1 and the curved waveguide of Y-type beam combiner 2 is calculated as follows: .

[0040] In the formula, This refers to the mode mismatch loss at the junction of the straight waveguide of the distributed feedback laser unit 1 and the curved waveguide of the Y-type beam combiner 2.

[0041] In this embodiment, the radiation loss per unit length is suppressed to below 0.5 dB / cm. The mode mismatch loss at the junction of the straight waveguide of the distributed feedback laser unit 1 and the curved waveguide of the Y-type beam combiner 2 is controlled to within 0.2 dB due to size constraints. Meanwhile, the total length of the device is approximately 3500 μm, the cavity length of the distributed feedback laser unit 1 is approximately 2000 μm, the semiconductor optical amplifier 3 occupies approximately 500 μm, and the remaining approximately 1000 μm space is used for the layout of the Y-type beam combiner 2. Based on the above constraints, the bending radius of the Y-type beam combiner 2 is determined to be greater than or equal to 1000 µm.

[0042] like Figure 1 and Figure 3As shown, the ridge waveguide 13 of the semiconductor optical amplifier 3 is a curved structure tilted relative to the waveguide transmission direction, and an anti-reflection film is deposited on the light-emitting end face. This structure can eliminate the interference of residual reflection on the stability of the lasing frequency. The ridge waveguide 13 of the semiconductor optical amplifier 3 is also a tapered structure, with the width of the ridge waveguide 13 gradually increasing along the waveguide transmission direction. This structure can reduce the local photon density under high power and prevent overheating. In this embodiment, the tilt angle of the ridge waveguide 13 of the semiconductor optical amplifier 3 is 7°. The width of the ridge waveguide 13 gradually expands from 3 μm at the input end to 8 μm at the output end.

[0043] like Figure 1 As shown, electrical isolation grooves with a depth to the grating 12 are provided between the laser module and the Y-type beam combiner module, and between the Y-type beam combiner module and the semiconductor optical amplifier 3, to cut off heat conduction and carrier crosstalk between the functional modules in the horizontal direction. In this embodiment, the isolation resistance of the electrical isolation groove is greater than 5 kΩ.

[0044] The fabrication method of a monolithically integrated terahertz wave generator includes the following steps: S1. Epitaxial Substrate Growth: On an n-InP substrate 5, an n-InP buffer layer 6, an InGaAsP high-refractive-index mode extension layer 7, a lower confinement layer 8, a multi-quantum-well active layer 9, a p-InP upper confinement layer 10, a transition layer 11, and a grating layer are sequentially grown using metal-organic chemical vapor deposition (MOCVD). The high-refractive-index mode extension layer 7 is used to pull the mode field towards the substrate 5, laying the physical foundation for subsequent wide-ridge single-mode transmission.

[0045] S2, Grating 12 fabrication: Grating 12 is fabricated on the grating layer using the reconstructed equivalent chirp technique. The sampling period is controlled by ultraviolet lithography to preset the center wavelength difference of multiple distributed feedback laser units 1, and an equivalent phase shift is introduced into grating 12 to ensure single-mode lasing.

[0046] S3. Secondary epitaxial growth: Perform secondary epitaxial growth to complete the growth of the waveguide layer.

[0047] S4, Ridge waveguide 13 etching: The ridge waveguide 13 of the monolithically integrated distributed feedback laser unit 1, Y-type beam combiner 2 and semiconductor optical amplifier 3 is fabricated using etching technology.

[0048] S5. Fabrication of the upper electrode 14, conductive film heater 15, and electrical isolation trench: A metal upper electrode 14 for gain injection is deposited on the ridge waveguide 13 of multiple distributed feedback laser units 1. A conductive film heater 15 is then deposited on the upper electrode 14. Alternatively, a segmented layout process can be used, depositing the metal upper electrode 14 for gain injection in one half of the axial region of the ridge waveguide 13 and the conductive film heater 15 in the other half, thus fabricating the carrier injection region and the independent thermal tuning region. Simultaneously, metal upper electrodes 14 are deposited on the ridge waveguide 13 of the Y-type beam combiner 2 and the semiconductor optical amplifier 3. Then, an electrical isolation trench extending to the grating 12 is fabricated between the laser module and the Y-type beam combiner module, and between the Y-type beam combiner module and the semiconductor optical amplifier 3, to achieve independent electrical control between each functional region and the segmented electrodes.

[0049] The method for generating monolithically integrated terahertz waves is as follows: the monolithically integrated terahertz wave generating device is connected to the control circuit, the injection current of all distributed feedback laser units 1 is fixed to maintain stable output power, and the injection current of the conductive film heater 15 of some distributed feedback laser units 1 is adjusted to change the lasing wavelength of the corresponding distributed feedback laser unit 1 by means of thermal effect. The wavelengths output by multiple distributed feedback laser units 1 are combined by Y-type beam combiner and amplified by semiconductor optical amplifier 3 before being output, thereby generating terahertz radiation with continuously adjustable frequency and stable power.

[0050] Spectral test results as follows Figure 4 As shown in the figure, the dual-wavelength beam combining and tuning effect can be observed. Specifically, Figure 4 As can be seen from a~c in the figure, when the injection current of the conductive film heater 15 of one distributed feedback laser unit 1 (DFB1) is fixed, and the injection current of the conductive film heater 15 of another distributed feedback laser unit 1 (DFB2) is increased from 100 mA to 350 mA, the interval between the two wavelengths changes by 1.52 nm, the corresponding frequency range is 0.298 THz to 0.488 THz, and the frequency changes by 0.19 THz. At this time, the SMSR of both wavelengths is greater than 35 dB. Figure 4As can be seen from d~f in the diagram, when the injection current of the conductive film heater 15 of one distributed feedback laser unit 1 (DFB2) is fixed, and the injection current of the conductive film heater 15 of the other distributed feedback laser unit 1 (DFB1) is increased from 100mA to 350mA, the wavelength difference changes by 1.51nm, corresponding to a frequency range of 0.113 THz to 0.300 THz, a change of 0.187 THz. At this point, the SMSR of both wavelengths is greater than 39 dB. Therefore, by changing the injection current of the conductive film heater 15 of the two distributed feedback laser units 1, the wavelength difference between the two distributed feedback laser units 1 can be tuned, achieving tuning from 0.113 THz to 0.488 THz.

[0051] The PIV characteristics of the two distributed feedback laser units 1 were characterized. During the test, the temperature was maintained at 25 °C using a thermoelectric cooler (TEC). The results are as follows: Figure 5 As shown. Figure 5 Figure 'a' shows the PIV superposition curves of the two distributed feedback laser units 1. As can be seen from the figure, when the injection current of the distributed feedback laser unit 1 is in the range of 0 to 600 mA, and the injection current of the semiconductor optical amplifier 3 and the Y-type beam combiner 2 is 200 mA, the threshold current of the two distributed feedback laser units 1 is between 40 mA and 50 mA. At a current of 600 mA, the output power of the two distributed feedback laser units 1 both exceed 170 mW, and the differential resistance is less than 7.35 Ω. Figure 5 Figure b shows the trend of output power as the injection current of semiconductor optical amplifier 3 increases when the two distributed feedback laser units 1 are turned on. As can be seen from the figure, when the injection currents of distributed feedback laser unit 1 and Y-type beam combiner 2 are set to 400 mA and 200 mA respectively, the output power increases from 62 mW to 157 mW as the injection current of semiconductor optical amplifier 3 increases from 0 to 200 mA, and reaches saturation when the injection current of semiconductor optical amplifier 3 is about 170 mA.

[0052] Under the conditions that the injection current of the upper electrode 14 of the distributed feedback laser unit 1 is 100 mA, and the injection current of the Y-type beam combiner 2 and the semiconductor optical amplifier 3 are both 200 mA, the laser linewidth measurement results and Lorentz fitting results are as follows: Figure 6 As shown. From Figure 6 It can be seen that, after Lorentz fitting, the linewidths of the two distributed feedback laser units 1 are 287.8 kHz and 293.7 kHz, respectively.

[0053] The device provided by this invention is a high-power monolithically integrated terahertz source with power-frequency decoupling characteristics. Through monolithic integration technology, multiple parallel distributed feedback laser units 1, a Y-type beam combiner 2 optimized for mode field matching, and a semiconductor optical amplifier 3 with anti-reflection function are integrated onto the same substrate 5. A high-refractive-index mode extension layer 7 is introduced into the vertical structure to pull the mode field towards the substrate 5 and reduce internal losses. Simultaneously, a conductive film heater 15 is integrated above the distributed feedback laser units 1 to achieve independent control of wavelength tuning and output power, thereby realizing the generation of high-power, narrow-linewidth, and stable terahertz wave signals on a single chip.

[0054] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, the reagents, materials, and procedures used herein are all widely used in the relevant fields.

[0055] It should be noted that the terms such as "upper", "lower", "left", "right", "front", and "back" used in the invention are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0056] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A monolithically integrated terahertz wave generating device, characterized in that: The device is a monolithic integrated structure, in which a laser module, a Y-type beam combiner module, and a semiconductor optical amplifier are sequentially integrated along the waveguide transmission direction; the laser module includes multiple parallel distributed feedback laser units; the Y-type beam combiner module couples the multiple distributed feedback laser units into a single waveguide; The device comprises, from bottom to top, a lower electrode, a substrate, a buffer layer, a high refractive index mode extension layer, a lower confinement layer, a multi-quantum well active layer, an upper confinement layer, a transition layer, a grating, a ridge waveguide, and an upper electrode; the refractive index of the high refractive index mode extension layer material is higher than that of the buffer layer material.

2. The monolithically integrated terahertz wave generating device according to claim 1, characterized in that: Each of the distributed feedback laser units has a conductive film heater above its ridge waveguide, independent of the upper electrode of the distributed feedback laser unit.

3. The monolithically integrated terahertz wave generating device according to claim 2, characterized in that: In the distributed feedback laser unit: the conductive film heater is disposed above the upper electrode; or, the ridge waveguide is divided into two parts, the upper electrode is disposed on one part of the ridge waveguide, and the conductive film heater is disposed on the other part of the ridge waveguide.

4. The monolithically integrated terahertz wave generating device according to claim 1, characterized in that: The material of the high refractive index mode extension layer is InGaAsP.

5. The monolithically integrated terahertz wave generating device according to claim 1, characterized in that: The Y-type beam combiner module includes at least one Y-type beam combiner; When there are two distributed feedback laser units, there is one Y-type beam combiner, which couples the two distributed feedback laser units into a single waveguide. When there are multiple distributed feedback laser units, there are also multiple Y-type beam combiners. The multiple Y-type beam combiners form a cascaded Y-type beam combining structure, which couples the multiple distributed feedback laser units into a single waveguide.

6. The monolithically integrated terahertz wave generating device according to claim 5, characterized in that: The ridge waveguide of the Y-type combiner has an S-shaped curved structure.

7. The monolithically integrated terahertz wave generating device according to claim 1, characterized in that: The ridge waveguide of the semiconductor optical amplifier is a curved structure that is tilted relative to the waveguide transmission direction, and the light-emitting end face has an anti-reflection film.

8. The monolithically integrated terahertz wave generating device according to claim 1, characterized in that: The ridge waveguide of the semiconductor optical amplifier has a gradually tapered structure, and the width of the ridge waveguide gradually increases along the waveguide transmission direction.

9. The monolithically integrated terahertz wave generating device according to claim 1, characterized in that: An electrically isolated groove with a depth to the grating is provided between the laser module and the Y-type beam combiner module, and between the Y-type beam combiner module and the semiconductor optical amplifier.

10. A method for generating terahertz waves using a monolithic integrated circuit, characterized in that: The device according to any one of claims 2 to 9 is connected to the control circuit, the injection current of all the distributed feedback laser units is fixed, and the injection current of the conductive film heater of some of the distributed feedback laser units is adjusted to change the lasing wavelength of the corresponding distributed feedback laser units by means of thermal effect. The wavelengths output by the multiple distributed feedback laser units are combined by the Y-type beam combiner module and amplified by the semiconductor optical amplifier to generate terahertz radiation.

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