DAST nonlinear crystal ultra-wideband tunable continuous terahertz radiation source system

Abstract

The invention provides a DAST nonlinear crystal ultra-wideband tunable continuous terahertz radiation source system, and belongs to the technical field of terahertz. Based on the ultrahigh second-order nonlinear effect of a DAST crystal, an ultra-wideband terahertz signal is generated by using a dual-wavelength laser difference frequency method, and the frequency of the terahertz radiation source is adjustable by changing the relative wavelength of a laser. Terahertz signal power is detected through a high lyocell detector, and the tuning performance of the radiation source is measured through a terahertz scanning Fabry-Perot interferometer. The frequency range of the terahertz radiation source provided by the invention is 0.5-6 THz, and the tuning precision is 0.01 THz. Compared with the prior art, the terahertz source has the advantages of being wide in terahertz frequency range, tunable and the like, and has important significance for solving the problems that the terahertz source frequency spectrum coverage range is narrow, and the resolution ratio is limited and the like.

Description

Technical Field

[0001] This invention relates to the field of terahertz technology, specifically to the DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system. Background Technology

[0002] Terahertz electromagnetic waves (0.1-10 THz), as a transitional frequency band between microwaves and the infrared spectrum, possess both non-ionizing properties (photon energy of approximately 4.1 meV) and the ability to penetrate non-polar materials, making them promising and valuable for applications in basic scientific research, security imaging, and interplanetary communication. However, the core bottleneck restricting technological transformation lies in the lack of high-performance continuous terahertz radiation sources. Traditional solutions mostly focus on pulsed terahertz radiation sources, which rely on femtosecond lasers, limiting the tuning accuracy of terahertz frequencies. Meanwhile, continuous terahertz waves, due to their tunability (typically <100 MHz), can achieve precise measurements of molecular vibrational-rotational energy levels, supporting high-resolution spectral analysis. Mainstream continuous terahertz radiation suffers from several drawbacks. First, it has low nonlinear coefficients, insufficient phase matching width, and low mechanical tuning flexibility. This can lead to extremely low energy conversion efficiency and limited bandwidth in difference-frequency terahertz radiation. Second, when using novel organic crystals such as DAST nonlinear crystals as excitation devices for continuous terahertz radiation, high-power, narrow-linewidth, and wavelength-stable pump lasers are required. However, most of these light sources use single-frequency femtosecond lasers, which limit the terahertz frequency tuning accuracy. Summary of the Invention

[0003] In order to solve the problems of limited tuning accuracy and bandwidth of the adjustable continuous terahertz frequency in the prior art, the present invention provides a DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system.

[0004] This invention is achieved using the following technical solution:

[0005] A DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system includes a first tunable laser and a second tunable laser. The first and second tunable lasers have different optical frequencies. The first tunable laser is connected to the input of a first fiber optic isolator, the output of the first fiber optic isolator is connected to the input of a first polarized laser, the output of the first polarized laser is connected to the input of a first erbium-doped fiber amplifier, and the output of the first erbium-doped fiber amplifier is connected to the first input of a beam splitter coupler. The second tunable laser is connected to the input of a second fiber optic isolator, the output of the second fiber optic isolator is connected to the input of the second polarized laser, the output of the second polarized laser is connected to the input of the second erbium-doped fiber amplifier, the output of the second erbium-doped fiber amplifier is connected to the second input of the beam splitter coupler, the output of the beam splitter coupler is connected to the input of a polarization beam splitter, the output of the polarization beam splitter is connected to the input of a fiber collimator, and the output of the fiber collimator is connected to the input of a chopper via a DAST nonlinear crystal.

[0006] Principle Explanation: By changing the wavelength difference between two tunable lasers, a differential condition is met; two fiber optic isolators isolate the optical signals between the input and output, preventing reflection and echo interference, and providing protection and stability for the optical signals; two polarization controllers adjust the polarization state of the laser in the optical path to meet the conditions for exciting terahertz radiation; the erbium-doped fiber amplifier enhances the pump light power to meet the high-energy excitation conditions of the DAST nonlinear crystal; a polarization beam splitter ensures the consistency of the pump light's polarization state and optimizes the phase matching condition; the excitation light is collimated and focused to reduce losses during propagation in space.

[0007] Furthermore, a filter is installed after the output of the chopper to improve the signal-to-noise ratio of the generated continuous terahertz wave.

[0008] Furthermore, a Gore-Leigh cell detector is installed after the filter to detect the power of the ultra-wideband tunable continuous terahertz radiation source. The detection frequency range is 0.03-20THz, and the maximum detectable power is 10μW.

[0009] Furthermore, a terahertz scanning Fabry-Perot interferometer is installed between the filter and the chopper to measure the frequency of the ultra-wideband tunable continuous terahertz radiation source and verify its tuning frequency accuracy. The Fabry-Perot interferometer operates in the frequency range of 0.1-15 THz and has a free spectrum range of 0.01-1.8 THz.

[0010] Furthermore, the first tunable laser operates in the wavelength range of 1527-1611 nm and has a maximum output power of 11 dBm, while the second tunable laser operates in the wavelength range of 1528-1565 nm and has a maximum output power of 13 dBm.

[0011] Furthermore, both the first and second fiber optic isolators are bipolar polarization-maintaining fiber optic isolators with an operating wavelength range of 1520-1630nm and a maximum power handling capacity of 2W.

[0012] Furthermore, both the first polarization controller and the second polarization controller are three-ring polarization controllers with an operating wavelength range of 1520-1630nm.

[0013] Furthermore, the beam splitter has a splitting ratio of 50:50 and is a polarization-maintaining coupler with an operating wavelength range of 1520-1630nm.

[0014] Furthermore, the first erbium-doped fiber amplifier has an input power range of -6 to 3 dBm and a maximum output power of 27 dBm, while the second erbium-doped fiber amplifier has an input power range of 0 to 10 dBm and a maximum output power of 30 dBm.

[0015] Furthermore, the filter has a diameter of 25.4 mm and a thickness of 2 mm.

[0016] Furthermore, the detection frequency range of the Gale box detector is 0.03-20THz, the maximum detectable power is 10μW, and the modulation frequency range of the chopper is 0-100Hz.

[0017] Furthermore, DAST can generate terahertz phase-matching wavelengths from 720 nm to 1650 nm, mounted on a 1-inch rotatable bracket with a 3 mm diameter hole.

[0018] The beneficial effects of this invention are as follows: Compared with existing terahertz radiation sources based on nonlinear crystals such as DAST, the ultra-wideband tunable continuous terahertz radiation source based on a DAST nonlinear crystal provided by this invention utilizes the high nonlinearity effect of the DAST nonlinear crystal to generate an ultra-wideband terahertz signal through a dual-wavelength laser difference frequency method. Two pump beams are amplified separately using an erbium-doped fiber amplifier to meet the power conditions for crystal-excited terahertz radiation; polarization-maintaining devices such as polarization controllers, beam splitters, and polarization beam splitters are used to maintain the consistency of the polarization state of the optical path, improving the stability of the pump beams and meeting the specific requirements of the DAST nonlinear crystal for the pump source; and the tuning of the ultra-wideband continuous terahertz radiation is achieved by changing the wavelength difference between the two pump beams. The ultra-wideband tunable continuous terahertz radiation source based on a DAST nonlinear crystal provided by this invention can be used in terahertz frequency domain spectral analysis, sensing, and imaging analysis, possessing not only significant market competitiveness but also considerable research value. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the overall system described in this invention;

[0022] Figure 2 The image shows the test results of an embodiment of the present invention.

[0023] In the figure: 1-First tunable laser, 2-Second tunable laser, 3-First fiber isolator, 4-Second fiber isolator, 5-First polarization controller, 6-Second polarization controller, 7-First erbium-doped fiber amplifier, 8-Second erbium-doped fiber amplifier, 9-Optical splitter coupler, 10-Polarization beam splitter, 11-Fiber collimator, 12-DAST nonlinear crystal, 13-Chopper, 14-Filter, 15-Goryley box detector, 16-Fabry-Perot interferometer. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0025] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0027] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] like Figure 1 As shown, a DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system includes a first tunable laser 1 (operating wavelength range of 1527-1611 nm, maximum output power of 11 dBm) and a second tunable laser 2 (operating wavelength range of 1528-1565 nm, maximum output power of 13 dBm). The first tunable laser 1 and the second tunable laser 2 have different optical frequencies. The first tunable laser 1 is connected to the input end of a first fiber isolator 3, the output end of the first fiber isolator 3 is connected to the input end of a first polarized laser, the output end of the first polarized laser is connected to the input end of a first erbium-doped fiber amplifier 7, and the output end of the first erbium-doped fiber amplifier is connected to the first input end of a beam splitter 9. The second tunable laser 2 is connected to the input end of a second fiber isolator 4, and the output end of the second fiber isolator 4 is connected to... The input end of the second polarization laser is connected to the input end of the second erbium-doped fiber amplifier 8. The output end of the second erbium-doped fiber amplifier is connected to the second input end of the beam splitter 9. The output end of the beam splitter 9 is connected to the input end of the polarization beam splitter 10. The output end of the polarization beam splitter 10 is connected to the input end of the fiber collimator 11. The output end of the fiber collimator 11 is connected to the input end of the chopper 13 via the DAST nonlinear crystal 12. A filter 14 is provided after the output end of the chopper 13. A Gore-Leigh cell detector 15 is provided after the filter 14 (in specific implementation, the detection frequency range is 0.03-20THz, and the maximum detectable power is 10μW). A terahertz scanning Fabry-Perot interferometer 16 is also provided between the filter 14 and the chopper 13 (the operating frequency range of the Fabry-Perot interferometer 16 is 0.1-15THz, and the free spectrum range is 0.01-1.8THz).

[0029] In this specific embodiment, the first tunable laser 1 operates in the wavelength range of 1527-1611 nm with a maximum output power of 11 dBm, and the second tunable laser 2 operates in the wavelength range of 1528-1565 nm with a maximum output power of 13 dBm. The first fiber isolator 3 and the second fiber isolator 4 are both bipolar polarization-maintaining fiber isolators, operating in the wavelength range of 1520-1630 nm with a maximum power handling capacity of 2 W. The first polarization controller 5 and the second polarization controller 6 are both three-ring polarization controllers, operating in the wavelength range of 1520-1630 nm. The beam splitter coupler 9 is a 50:50 polarization-maintaining coupler with an operating wavelength range of 1520-1630 nm. The first erbium-doped fiber amplifier 7 has an input power range of -6 to 3 dBm and a maximum output power of 27 dBm, and the second erbium-doped fiber amplifier 8 has an input power range of 0 to 10 dBm and a maximum output power of 30 dBm. The filter 14 has a diameter of 25.4 mm and a thickness of 2 mm. The Gore-Ley box detector 15 has a detection frequency range of 0.03-20 THz and a maximum detectable power of 10 μW. The chopper 13 has a modulation frequency range of 0-100 Hz. The DAST can generate terahertz phase-matching wavelengths from 720 nm to 1650 nm and is fixed on a 1-inch rotatable bracket with a 3 mm diameter aperture.

[0030] The frequency curves from 0.5 to 6 THz were obtained through experiments, such as... Figure 2 As shown, this demonstrates that the system described in this invention can generate an ultra-wideband continuous terahertz radiation source, and from Figure 2 As can be seen from the magnified view, the tuning accuracy of the 2.5-3THz tuning curve is 0.01THz, which is relatively high.

[0031] Principle explanation: The nonlinear optical mechanism of the DAST nonlinear crystal is as follows:

[0032] The second-order nonlinear effect of the DAST nonlinear crystal mainly originates from the non-centrosymmetry of its molecular structure. In nonlinear optics, when light waves pass through a crystal with second-order nonlinear polarizability, new frequency components are generated. Specifically, when a beam of fundamental frequency light (frequency ω) passes through a DAST nonlinear crystal, the crystal's nonlinear polarizability can convert the electric field of the fundamental frequency light into second harmonic light (frequency 2ω), a process that generates second harmonics.

[0033] The molecular structure of DAST nonlinear crystals exhibits a large second-order nonlinear polarizability, which contributes to its high conversion efficiency in nonlinear optical processes. Furthermore, the molecular arrangement of DAST nonlinear crystals also significantly influences its nonlinear performance. The ordered arrangement of the dipole moments of its molecules within the crystal effectively enhances the nonlinear polarization effect, converting near-infrared pump light into THz waves via difference frequency modulation.

[0034] Phase matching is a crucial condition in nonlinear optical processes. It requires that the fundamental and harmonic light maintain phase consistency during nonlinear interactions, allowing the harmonic light to accumulate and enhance effectively. Angular phase matching is achieved by adjusting the angle of incidence so that the fundamental and harmonic light propagate at the same speed within the crystal. Due to the birefringence of the DAST nonlinear crystal, the refractive indices of the fundamental and harmonic light change with the incident angle. When the incident angle is adjusted to a specific value, the refractive indices of the fundamental and harmonic light become equal, thus satisfying the phase matching condition.

[0035] The noncritical phase-matching (NCPM) property of the DAST nonlinear crystal allows for adjustment of the pump wavelength under a fixed crystal orientation. , Phase matching conditions:

[0036] in and These are the wavelengths of the two pump beams emitted by the first and second tunable lasers, respectively. The wavelength of terahertz radiation excited by the DAST nonlinear crystal.

[0037] The second-order nonlinear effect of the DAST nonlinear crystal stems from the noncentrosymmetry of its molecular structure, enabling it to effectively convert fundamental frequency light into frequency-doubled light. Phase matching is key to achieving efficient nonlinear optical processes; by achieving phase-matching conditions, the efficiency of nonlinear optical processes can be improved, thereby increasing the conversion efficiency of terahertz radiation.

[0038] By adjusting the wavelengths λ1 and λ2 of the two pump laser beams to satisfy the difference frequency condition. ,Depend on It can be seen that linearly mapping the wavelength tuning to the terahertz frequency can yield the terahertz frequency. :

[0039]

[0040] This enables ultra-wideband continuous terahertz frequency tuning.

[0041] The scope of protection claimed by this invention is not limited to the specific embodiments described above. Moreover, for those skilled in the art, this invention can have various modifications and alterations. Methods for improving the power and stability of differential pump light are not limited to power amplifiers such as erbium-doped fiber amplifiers and the use of polarization-maintaining devices. Methods for detecting power are not limited to Gale cell detectors and thermal power meters. Methods for measuring tuning accuracy are not limited to terahertz scanning Fabry-Perot interferometers and electro-optic crystal detectors. Any modifications, improvements, and equivalent substitutions made within the concept and principles of this invention should be included within the scope of protection of this invention.

[0042] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system, characterized in that, It includes a first tunable laser (1) and a second tunable laser (2). The first tunable laser (1) and the second tunable laser (2) have different light frequencies. The first tunable laser (1) is connected to the input end of the first fiber isolator (3). The output end of the first fiber isolator (3) is connected to the input end of the first polarized laser. The output end of the first polarized laser is connected to the input end of the first erbium-doped fiber amplifier (7). The output end of the first erbium-doped fiber amplifier is connected to the first input end of the beam splitter (9). The second tunable laser (2) is connected to the input end of the second fiber isolator (4). The output end of the second fiber isolator (4) is connected to the input end of the second polarized laser. The output end of the second polarized laser is connected to the input end of the second erbium-doped fiber amplifier (8). The output end of the second erbium-doped fiber amplifier is connected to the second input end of the beam splitter (9). The output end of the beam splitter (9) is connected to the input end of the polarization beam splitter (10). The output end of the polarization beam splitter (10) is connected to the input end of the fiber collimator (11). The output end of the fiber collimator (11) is connected to the input end of the chopper (13) via the DAST nonlinear crystal (12). A filter (14) is provided after the output end of the chopper (13). A Gore-Leigh cell detector (15) is provided after the filter (14). A terahertz scanning Fabry-Perot interferometer (16) is also provided between the filter (14) and the chopper (13).

2. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 1, characterized in that, A filter is provided after the output of the chopper (13).

3. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 2, characterized in that, A Gore-Leigh cell detector (15) is located behind the filter (14).

4. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 3, characterized in that, A terahertz scanning Fabry-Perot interferometer (16) is also provided between the filter (14) and the chopper (13).

5. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 4, characterized in that, The first tunable laser (1) operates in the wavelength range of 1527-1611nm and has a maximum output power of 11dBm. The second tunable laser (2) operates in the wavelength range of 1528-1565nm and has a maximum output power of 13dBm.

6. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 5, characterized in that, The first fiber isolator (3) and the second fiber isolator (4) are both bipolar polarization-maintaining fiber isolators with a working wavelength range of 1520-1630nm and a maximum power capacity of 2W.

7. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 6, characterized in that, The splitting ratio of the beam splitter (9) is 50:50, and the working wavelength range is 1520-1630nm.

8. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 7, characterized in that, The first erbium-doped fiber amplifier (7) has an input power range of -6 to 3 dBm and a maximum output power of 27 dBm. The second erbium-doped fiber amplifier (8) has an input power range of 0 to 10 dBm and a maximum output power of 30 dBm.

9. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 8, characterized in that, The filter (14) has a diameter of 25.4 mm and a thickness of 2 mm.

10. The DAST nonlinear crystal ultrawideband tunable continuous terahertz radiation source system according to claim 9, characterized in that, DAST can generate terahertz phase-matching wavelengths from 720nm to 1650nm, mounted on a 1-inch rotatable bracket with a 3mm diameter hole.

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