A dual-wavelength visible light laser based on synchronous nonlinear frequency conversion

Abstract

The present invention provides a dual-wavelength visible light laser based on a synchronized nonlinear frequency conversion process. The laser comprises a near-infrared laser system and a nonlinear crystal. The near-infrared laser system provides the nonlinear crystal with two time-synchronized near-infrared signal beams of different wavelengths. In the nonlinear crystal, two different types of nonlinear frequency conversion processes (i.e., the nonlinear sum frequency of the two near-infrared signal beams of different wavelengths, and the nonlinear frequency doubling of one of the near-infrared signal beams) can simultaneously achieve phase matching. Visible light of different wavelengths is obtained through synchronized nonlinear frequency conversion. This technical solution facilitates the generation of compact and efficient dual-wavelength visible light lasers.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and in particular relates to a dual-wavelength visible light laser based on synchronous nonlinear frequency conversion. Background Art

[0002] Multi-wavelength visible light laser sources have important application prospects in biomedicine, laser displays, digital holographic displays, spectroscopy, and air pollution detection. Laser frequency conversion technology based on optical second-order nonlinear effects is currently an important means to achieve laser output in the visible light band.

[0003] In order to obtain visible light of multiple wavelengths, it is generally necessary to use near-infrared lasers of multiple different wavelengths as input, and convert the incident near-infrared lasers into visible light through nonlinear frequency doubling and nonlinear sum frequency conversion between them. However, a nonlinear crystal can generally only meet the phase matching of one nonlinear frequency conversion process and obtain a visible light laser output of one wavelength. Therefore, multi-wavelength visible light lasers generally adopt a multi-stage frequency conversion design with steps. However, the multi-stage frequency conversion design not only makes the laser system complicated and expensive, but also limits the overall energy conversion efficiency of the multi-wavelength visible light laser. Summary of the Invention

[0004] The present invention provides a dual-wavelength visible light laser based on synchronous nonlinear frequency conversion, aiming to achieve miniaturization of a multi-wavelength visible light laser and improve its overall energy conversion efficiency.

[0005] To solve the above technical problems, the present invention is implemented as follows: a dual-wavelength visible light laser based on synchronous nonlinear frequency conversion is provided, comprising a near-infrared laser system and a nonlinear crystal; the near-infrared laser system provides the nonlinear crystal with time-synchronized first and second near-infrared signal lights; in the nonlinear crystal, two different types of nonlinear frequency conversion processes can simultaneously achieve phase matching, and through synchronous nonlinear frequency conversion, first and second visible lights are obtained;

[0006] The two different types of nonlinear frequency conversion processes include: within the nonlinear crystal, nonlinearly summing the first near-infrared signal light with the second near-infrared signal light to obtain a first nonlinear frequency conversion process of first visible light, and nonlinearly doubling the first near-infrared signal light to obtain a second nonlinear frequency conversion process of second visible light.

[0007] Furthermore, the nonlinear crystal is a periodically poled crystal, and under a preset poling period and operating temperature, the periodically poled crystal can simultaneously meet the quasi-phase matching of the first nonlinear frequency conversion process and the second nonlinear frequency conversion process.

[0008] Furthermore, the periodically poled crystal is a periodically poled lithium niobate crystal. Under a preset poling period and operating temperature, the periodically poled lithium niobate crystal can simultaneously satisfy type I quasi-phase matching of the first nonlinear frequency conversion process and type I quasi-phase matching of the second nonlinear frequency conversion process; the first near-infrared signal light is o-polarized light, the second near-infrared signal light is o-polarized light, the first visible light is e-polarized light, and the second visible light is e-polarized light.

[0009] Furthermore, the wavelength of the second near-infrared signal light is 800 nm, the wavelength range of the first near-infrared signal light is 1155 nm to 1325 nm, the polarization period range of the periodically poled lithium niobate crystal is 34.8 μm to 35.3 μm, the operating temperature range of the periodically poled lithium niobate crystal is 20°C to 220°C, the wavelength range of the first visible light is 472.6 nm (blue) to 498.8 nm (light green), and the wavelength range of the second visible light is 577.5 nm (orange) to 662.5 nm (red).

[0010] Furthermore, the wavelength of the second near-infrared signal light is 800 nm, the wavelength of the first near-infrared signal light is 1180 nm, the polarization period of the periodically poled lithium niobate crystal is 34.8 μm, the operating temperature of the periodically poled lithium niobate crystal is 65°C, the wavelength of the first visible light is 476.8 nm (blue), and the wavelength of the second visible light is 590 nm (orange).

[0011] Furthermore, the dual-wavelength visible light laser based on synchronous nonlinear frequency conversion further includes a temperature control device, and the temperature control device is used to make the temperature of the nonlinear crystal be a preset operating temperature.

[0012] Furthermore, the near-infrared laser system includes a first laser, a second laser, and an optical coupling mirror, wherein the first laser is used to output the first near-infrared signal light, and the second laser is used to output the second near-infrared signal light, and the first near-infrared signal light and the second near-infrared signal light respectively pass through the optical coupling mirror and enter the nonlinear crystal; or,

[0013] The near-infrared laser system includes a laser, a beam splitter, a frequency converter and an optical coupling mirror. The laser output by the laser passes through the beam splitter to obtain two beams of laser light with the same wavelength, one of which passes through the frequency converter to obtain the first near-infrared signal light, and the other is the second near-infrared signal light. The first near-infrared signal light and the second near-infrared signal light respectively pass through the optical coupling mirror and enter the nonlinear crystal.

[0014] Compared with the prior art, the dual-wavelength visible light laser based on synchronous nonlinear frequency conversion provided by the present invention has the following advantages:

[0015] The present invention is based on a synchronous nonlinear frequency conversion process, using a nonlinear crystal as a nonlinear medium that can simultaneously meet the phase matching of two different parallel nonlinear frequency conversion processes. In the same nonlinear crystal, two different types of nonlinear frequency conversion (i.e., the nonlinear sum frequency of the first near-infrared signal light and the second near-infrared signal light, and the nonlinear frequency doubling of the first near-infrared signal light) are simultaneously completed, converting the incident near-infrared laser into visible light, thereby achieving dual-wavelength visible light output. Compared to a multi-stage frequency conversion design, the present invention integrates two different nonlinear frequency conversion processes that originally needed to be completed in steps into the same nonlinear crystal, which can effectively simplify the optical system, realize the miniaturization of multi-wavelength visible light lasers, reduce manufacturing costs, and help improve the energy conversion efficiency of near-infrared lasers to the visible light band. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The periodically poled lithium niobate crystal provided in Example 1 of the present invention has a minimum poling period required for the first nonlinear frequency conversion process and the second nonlinear frequency conversion process to meet type I quasi-phase matching at different operating temperatures;

[0017] Figure 2 The present invention provides, in Example 1, that the wavelength of the second near-infrared signal light is fixed at 800 nm, and that sum frequency light and frequency-doubled light of different wavelengths can be obtained as the wavelength of the first near-infrared signal light increases from 1155 nm to 1325 nm, as well as the poling period and operating temperature of the periodically poled lithium niobate crystal required to achieve the corresponding synchronous nonlinear frequency conversion;

[0018] Figure 3 A schematic structural diagram of a dual-wavelength visible light laser based on synchronous nonlinear frequency conversion provided in Example 2 of the present invention;

[0019] Figure 4 This is a curve showing how the output power of 590nm orange light and 476.8nm blue light varies with the incident power of 1180nm near-infrared signal light, as provided in Example 2 of the present invention.

[0020] Figure numerals: 1. Ti: sapphire laser; 2. beam splitter; 3. frequency converter; 4. delay light path; 5. optical coupling mirror; 6. periodically poled lithium niobate crystal. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] Example 1:

[0023] To obtain visible light of multiple wavelengths, it is generally necessary to use multiple near-infrared lasers of different wavelengths as input. The incident near-infrared lasers are converted into visible light through nonlinear frequency doubling and nonlinear sum frequency conversion between them. However, a nonlinear crystal can generally only meet the phase matching requirements of one nonlinear frequency conversion process, resulting in a visible light laser output of one wavelength. Multi-wavelength visible light lasers generally adopt a multi-step frequency conversion design. To achieve efficient energy conversion, the operating conditions of each frequency conversion step (including laser intensity, crystal length, etc.) need to be optimized, which inevitably increases the design difficulty of the laser system. At the same time, the same wavelength near-infrared laser often needs to be used for different nonlinear frequency conversion processes (for example, nonlinear sum frequency and frequency doubling). Therefore, it is necessary to design a multi-path splitter. This not only further increases the complexity of the laser system, but also limits the overall energy conversion efficiency of the multi-wavelength visible light laser because each "parallel" nonlinear frequency conversion process cannot fully utilize the full energy of the near-infrared laser. People have proposed various technical ideas to achieve the miniaturization of multi-wavelength visible light lasers. Among them, integrating different nonlinear frequency conversion processes into the same nonlinear crystal is a technical approach with great potential to simplify the structure of optical systems.

[0024] Phase matching is a fundamental requirement for all nonlinear frequency conversion processes. For synchronous nonlinear sum frequency and frequency doubling processes, the phase matching condition k1+k2=k3 should be satisfied between the first signal light, the second signal light, and the sum frequency light. The phase matching condition k1+k1=k4 should be satisfied between the first signal light and the frequency doubling light. Here, k1, k2, k3, and k4 represent the wave vectors of the first signal light, the second signal light, the sum frequency light, and the frequency doubling light, respectively. Therefore, the key to the present invention lies in designing a suitable nonlinear crystal that can simultaneously satisfy the phase matching requirements for different nonlinear frequency conversion processes.

[0025] If bulk crystals are used as nonlinear media, simultaneous nonlinear frequency conversion processes rarely achieve phase matching at the same crystal angle. In contrast, quasi-phase matching (QPM) technology, with its flexible phase matching approach and designable domain structure, makes it possible to achieve simultaneous nonlinear frequency conversion.

[0026] Taking nonlinear sum frequency as an example, people usually use a nonlinear polarized crystal with a polarization period of Λ=2π / |k3-k1-k2| to satisfy its first-order quasi-phase matching. In fact, a periodically polarized crystal (Λ) with a polarization period of any integer multiple (m) of Λ can meet the first-order quasi-phase matching. m =mΛ) can be used with the same m-order reciprocal lattice vector k m =2π / m∧ m =2π / Λ, achieving m-order quasi-phase matching. Furthermore, quasi-phase matching relaxes the polarization requirements for the interacting first and second signal lights, as well as the sum-frequency light. In addition to conventional Class 0 (ee-e) quasi-phase matching (which requires the first, second, and sum-frequency light to be e-polarized), Class I (oo-e) or Class II (eo-o / oe-o) quasi-phase matching can also be selected.

[0027] In principle, by selecting a suitable phase matching method, or stabilizing the periodically poled crystal at a suitable operating temperature, as long as the minimum pole period required for the nonlinear sum frequency and frequency doubling process can be made equivalent to ∧1=∧2, or an integer multiple relationship ∧1=m∧(∧2=m∧1), the poled crystal with a pole period of ∧1(∧2) can be used as a nonlinear medium, and its reciprocal lattice vectors of different orders can be used to compensate for the phase mismatch of the nonlinear sum frequency process and the frequency doubling process, thereby realizing synchronous nonlinear frequency conversion.

[0028] Periodically poled lithium niobate (LiNbO3) crystal (PPLN) is currently the most commercially available nonlinear polarization crystal. However, the refractive index of LiNbO3 crystal is highly sensitive to temperature, and changes in operating temperature directly affect the polarization period ∧ required for quasi-phase matching. Therefore, PPLN crystals are generally placed in a crystal temperature-controlled furnace to ensure a relatively stable operating temperature. However, this also provides controllable freedom for achieving synchronous nonlinear frequency conversion across a wider spectrum.

[0029] The following describes in detail the design process of the periodically poled lithium niobate crystal used in the present invention.

[0030] The wavelengths of the first near-infrared signal light and the second near-infrared signal light are set to 1180 nm and 800 nm respectively. Based on the dispersion equation of 5% MgO-doped lithium niobate crystal, Figure 1The first nonlinear frequency conversion process of a periodically poled lithium niobate crystal at different operating temperatures is shown, where a first near-infrared signal light of 1180 nm is nonlinearly summed with a second near-infrared signal light of 800 nm to produce 476.8 nm (blue) visible light (first visible light). The second nonlinear frequency conversion process of the first near-infrared signal light of 1180 nm is nonlinearly doubled to produce 590 nm (orange) visible light (second visible light). These processes satisfy the minimum polarization periods Λ1 and Λ2 required for type I quasi-phase matching. The 1180 nm and 800 nm near-infrared signal lights are o-polarized, while the resulting 590 nm and 476.8 nm visible lights are e-polarized. As can be seen from the figure, at a crystal operating temperature of ~65°C, Λ1 and Λ2 are equivalent, at ~34.8 μm. In other words, at a crystal operating temperature of ~65°C, both the first and second nonlinear frequency conversion processes described above can satisfy first-order type I quasi-phase matching in a periodically poled lithium niobate crystal with a polarization period of approximately 34.8 μm.

[0031] The above technical solution is not limited to the special case where the wavelengths of the first near-infrared signal light and the second near-infrared signal light are 1180nm and 800nm respectively. Based on the same technical solution, Figure 2 The paper lists the different wavelengths of sum frequency light and frequency-doubled light that can be obtained by fixing the wavelength of the second near-infrared signal light at 800nm and adjusting the wavelength of the first near-infrared signal light from 1155nm to 1325nm, as well as the polarization period and operating temperature of the periodically poled lithium niobate crystal required to achieve the corresponding synchronous nonlinear frequency conversion. Each of the above physical parameters has a one-to-one mapping relationship. Within the temperature range of 20℃-220℃, by adjusting the operating temperature and polarization period of the periodically poled lithium niobate crystal, synchronous nonlinear frequency conversion can be achieved between the 800nm second near-infrared signal light and the 1155nm to 1325nm first near-infrared signal light, resulting in first visible light ranging from 472.6nm (blue) to 498.8nm (light green) and second visible light ranging from 577.5nm (orange) to 662.5nm (red). We believe that the application scope of this technical solution can be further broadened by combining it with more types of periodically poled crystals, such as periodically poled lithium tantalate crystals (PPLST) and periodically poled potassium titanyl phosphate crystals (PPKTP).

[0032] Example 2:

[0033] See Figure 3 , the dual-wavelength visible light laser and optical path diagram based on synchronous nonlinear frequency conversion of the present invention. Figure 3As shown, the dual-wavelength visible light laser based on synchronous nonlinear frequency conversion includes: a titanium sapphire laser 1; a beam splitter 2; a frequency converter 3; a delayed light path 4; an optical coupling mirror 5; and a periodically poled lithium niobate crystal 6.

[0034] The 800nm laser output by the titanium sapphire laser 1 passes through the beam splitter 2 to obtain two beams of 800nm laser light, one of which passes through the frequency converter 3 to obtain a first near-infrared signal light of 1180nm, and the other 800nm laser light is a second near-infrared signal light. The delay light path 4 is arranged on the optical path of the 800nm near-infrared signal light to control the time synchronization of the 800nm near-infrared signal light and the 1180nm near-infrared signal light; the 800nm near-infrared signal light and the 1180nm near-infrared signal light are synchronized. The signal light passes through the optical coupling mirror 5 and enters the periodically poled lithium niobate crystal 6. The polarization period of the periodically poled lithium niobate crystal 6 is 34.8 μm and the operating temperature is approximately 65°C. Under the preset polarization period and operating temperature, the nonlinear sum frequency of the 1180 nm near-infrared signal light and the 800 nm near-infrared signal light is used to obtain 476.8 nm blue light (first visible light). At the same time, the nonlinear frequency doubling of the 1180 nm near-infrared signal light is used to obtain 590 nm orange light (second visible light).

[0035] In the synchronous nonlinear frequency conversion process on which the present invention is based, the 1180nm near-infrared signal light participates in the nonlinear frequency conversion of both frequency doubling and sum frequency simultaneously. Whether the 1180nm near-infrared signal light participates more in the frequency doubling process, obtaining 590nm orange light, or in the sum frequency process, obtaining 476.8nm blue light, depends on the intensity of the two different nonlinear frequency conversion processes, and ultimately affects the output power of the 590nm orange light and the 476.8nm blue light. In addition to the effective nonlinear coefficient deff, the intensity of the nonlinear frequency conversion process is also proportional to the light intensity of each participating light. Therefore, by regulating the incident light intensity of the near-infrared signal light, dual-wavelength visible light of different energy / power can be obtained.

[0036] The incident power of 800nm near-infrared signal light is fixed at 17mW. Figure 4The following curves show how the output power of 590nm orange light and 476.8nm blue light changes with the incident power of 1180nm near-infrared signal light. ① When the incident power of 800nm near-infrared signal light is much greater than that of 1180nm, the output power of 476.8nm blue light is significantly greater than that of 590nm orange light. ② As the incident power of 1180nm near-infrared signal light increases, the difference between the two gradually decreases. When the incident power (ratio) of 1180nm to 800nm near-infrared signal light is 1:2, the output power (ratio) of 590nm orange light to 476.8nm blue light is 1:1.4. At this point, the superposition of the two visible light beams produces a near-white light effect. ③ As the incident power of 1180nm near-infrared signal light further increases, the output power of 590nm orange light, obtained by frequency doubling the 1180nm near-infrared signal light, eventually exceeds that of 476.8nm blue light. It can be seen that, to a certain extent, the relative intensity of 590nm orange light and 476.8nm blue light can be regulated by controlling the incident light intensity of the near-infrared signal light.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dual-wavelength visible light laser based on synchronous nonlinear frequency conversion, characterized in that: The invention comprises a near-infrared laser system and a nonlinear crystal; the near-infrared laser system provides the nonlinear crystal with time-synchronized first near-infrared signal light and second near-infrared signal light; in the nonlinear crystal, two different types of nonlinear frequency conversion processes can simultaneously satisfy phase matching, and first visible light and second visible light are obtained through synchronized nonlinear frequency conversion; The two different types of nonlinear frequency conversion processes include: a first nonlinear frequency conversion process in which the first near-infrared signal light and the second near-infrared signal light are nonlinearly summed to obtain first visible light within the nonlinear crystal, and a second nonlinear frequency conversion process in which the first near-infrared signal light is nonlinearly doubled to obtain second visible light; The nonlinear crystal is a periodically poled crystal, and under a preset poling period and operating temperature, the periodically poled crystal can simultaneously meet the quasi-phase matching of the first nonlinear frequency conversion process and the second nonlinear frequency conversion process; The periodically poled crystal is a periodically poled lithium niobate crystal. Under a preset poling period and operating temperature, the periodically poled lithium niobate crystal can simultaneously meet type I quasi-phase matching of the first nonlinear frequency conversion process and type I quasi-phase matching of the second nonlinear frequency conversion process. The first near-infrared signal light is o-polarized light, the second near-infrared signal light is o-polarized light, the first visible light is e-polarized light, and the second visible light is e-polarized light. The wavelength of the second near-infrared signal light is 800 nm, the wavelength range of the first near-infrared signal light is 1155 nm to 1325 nm, the polarization period range of the periodically poled lithium niobate crystal is 34.8 μm to 35.3 μm, the operating temperature range of the periodically poled lithium niobate crystal is 20°C to 220°C, the wavelength range of the first visible light is 472.6 nm to 498.8 nm, and the wavelength range of the second visible light is 577.5 nm to 662.5 nm.

2. The dual-wavelength visible light laser based on synchronous nonlinear frequency conversion according to claim 1, characterized in that: The wavelength of the second near-infrared signal light is 800 nm, the wavelength of the first near-infrared signal light is 1180 nm, the polarization period of the periodically poled lithium niobate crystal is 34.8 μm, the operating temperature of the periodically poled lithium niobate crystal is 65° C., the wavelength of the first visible light is 476.8 nm, and the wavelength of the second visible light is 590 nm.

3. The dual-wavelength visible light laser based on synchronous nonlinear frequency conversion according to claim 1, characterized in that: The dual-wavelength visible light laser based on synchronous nonlinear frequency conversion further includes a temperature control device, which is used to control the temperature of the nonlinear crystal to a preset operating temperature.

4. The dual-wavelength visible light laser based on synchronous nonlinear frequency conversion according to claim 1, characterized in that: The near-infrared laser system includes a first laser, a second laser, and an optical coupling mirror, wherein the first laser is used to output the first near-infrared signal light, and the second laser is used to output the second near-infrared signal light, and the first near-infrared signal light and the second near-infrared signal light respectively pass through the optical coupling mirror and enter the nonlinear crystal; or The near-infrared laser system includes a laser, a beam splitter, a frequency converter and an optical coupling mirror. The laser output by the laser passes through the beam splitter to obtain two beams of laser light with the same wavelength, one of which passes through the frequency converter to obtain the first near-infrared signal light, and the other is the second near-infrared signal light. The first near-infrared signal light and the second near-infrared signal light respectively pass through the optical coupling mirror and enter the nonlinear crystal.

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