Method and device for generating indication light based on laser frequency doubling, and fiber laser

Abstract

The invention provides a method and device for generating indicating light based on laser frequency doubling and an optical fiber laser, the device comprises a dual-wavelength conversion unit and a frequency doubling crystal, the dual-wavelength conversion unit receives incident laser and converts the incident laser into dual-wavelength laser containing a base wavelength and an original wavelength, the frequency doubling crystal is connected with a light path of the dual-wavelength conversion unit, and the dual-wavelength conversion unit receives the incident laser and converts the incident laser into dual-wavelength laser containing a base wavelength and an original wavelength. The dual-wavelength conversion unit is used for converting dual-wavelength laser into double-wavelength laser, multiplying base-wavelength laser in the dual-wavelength laser into frequency-doubled wavelength laser corresponding to indicating light and outputting the frequency-doubled wavelength laser and original-wavelength laser on the same optical axis, and the dual-wavelength conversion unit comprises a dual-wavelength high-reflection fiber bragg grating, a lead-doped fiber, a dual-wavelength low-reflection fiber bragg grating and a fiber end cap which are connected in sequence. Therefore, the output concentricity of the indicating light and the laser is ensured, and the optical axes of the two laser beams are basically overlapped.

Description

Technical Field

[0002] The invention relates to laser frequency doubling technology, and in particular to a method and device for generating indicator light based on the laser frequency doubling technology, and a fiber laser. Background Art

[0004] Laser frequency doubling technology is also known as second harmonic oscillation. It is a technology that uses the secondary nonlinear effect of nonlinear crystals under the action of strong lasers to double the frequency of the incident laser and halve the wavelength. For example, when the fundamental frequency laser (such as 1064nm infrared light) passes through a nonlinear crystal, it can generate frequency-doubled light with a frequency twice that of the fundamental frequency (such as 532nm green light). This technology can significantly expand the wavelength of the laser and obtain lasers with shorter wavelengths and higher frequencies. Therefore, laser frequency doubling technology is currently widely used, involving fields including but not limited to improving image quality and enhancing signal processing capabilities.

[0005] In order to use the laser more safely, it is necessary to add an indicator light (for example, red light is commonly used as an indicator light) to the invisible light output laser. At present, in fiber lasers, the general method is to directly connect a low-power red light semiconductor laser to the optical path structure to achieve the indicator light, but the disadvantage is that the concentricity is poor. Summary of the invention

[0007] To this end, the main purpose of the present invention is to provide a method and device for generating indicator light based on laser frequency doubling, and a fiber laser, so as to solve the problems mentioned in the background technology.

[0008] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a device for generating indicator light based on laser frequency doubling, which comprises: a dual-wavelength conversion unit and a frequency doubling crystal, wherein the dual-wavelength conversion unit receives incident laser light and converts it into a dual-wavelength laser light containing a fundamental wavelength and an original wavelength, wherein the frequency doubling crystal is connected to the optical path of the dual-wavelength conversion unit so as to multiply the fundamental wavelength laser light in the dual-wavelength laser light into a frequency doubling wavelength laser light corresponding to the indicator light and then output the laser light on the same optical axis as the original wavelength laser light, wherein the dual-wavelength conversion unit comprises: a dual-wavelength high-reflection fiber Bragg grating, a lead-doped optical fiber, a dual-wavelength low-reflection fiber Bragg grating and an optical fiber end cap connected in sequence.

[0009] In a possible preferred embodiment, the light incident surface and the light exit surface of the frequency doubling crystal are coated with a high-transmittance film of the original wavelength of the incident laser and a high-transmittance film of the frequency-doubled wavelength.

[0010] In a possible preferred embodiment, the device for generating indicator light based on laser frequency doubling further includes: a window plate which is tiltedly arranged on the output light path of the frequency doubling crystal.

[0011] In a possible preferred embodiment, the device for generating indicator light based on laser frequency doubling further includes: a packaging shell covering the dual wavelength conversion unit and the frequency doubling crystal.

[0012] In a possible preferred embodiment, the fundamental wavelength of the phase matching of the frequency doubling crystal is 1240nm, the frequency doubling wavelength is 620nm, the reflectivity of the dual-wavelength high-reflection fiber grating is greater than 99.5%, and its wavelengths are 1064nm and 1240nm, the reflectivity of the dual-wavelength low-reflection fiber grating is ≤10%, and its wavelengths are 1064nm and 1240nm, and the wavelength of the laser injected into the dual-wavelength conversion unit is 1064nm.

[0013] In order to achieve the above-mentioned purpose, according to another aspect of the present invention, there is further provided a fiber laser, which comprises: an indicator light generating unit, a laser light source unit, wherein the indicator light generating unit is any of the above-mentioned devices for generating indicator light based on laser frequency doubling, the laser light source unit is connected to the indicator light generating unit, laser is emitted into the indicator light generating unit, and laser and indicator light with the same optical axis are output through the indicator light generating unit.

[0014] In a possible preferred implementation, the laser light source unit comprises: a laser light source device and a fiber fusion box, and the laser light source device is connected to the indicator light generating unit via the fiber fusion box.

[0015] In order to achieve the above-mentioned purpose, corresponding to the above-mentioned device and fiber laser, according to another aspect of the present invention, a method for generating indicator light based on laser frequency doubling is also provided, the steps comprising: setting the phase matching condition of the frequency doubling crystal to correspond to the preset base wavelength and the frequency doubling wavelength; allowing the incident laser to pass through the dual-wavelength high-reflection fiber grating, the lead-doped fiber and the dual-wavelength low-reflection fiber grating in sequence, to be converted into a dual-wavelength laser containing the base wavelength and the original wavelength, and then emitted to the frequency doubling crystal through the fiber end cap; after the frequency doubling crystal frequency-doubles the base wavelength laser into the frequency-doubled wavelength laser corresponding to the indicator light, it is output on the same optical axis as the original wavelength laser.

[0016] In a possible preferred embodiment, the method for generating indicator light based on laser frequency doubling further comprises the steps of: adjusting the length of the lead-doped optical fiber to affect the Raman gain, nonlinear effect and phase matching conditions, and adjusting the optical power of the indicator light.

[0017] In a possible preferred embodiment, the method for generating indicator light based on laser frequency doubling further includes the steps of: tilting a window plate on the output light path of the frequency doubling crystal to change the propagation direction of the laser and the reflected light of the indicator light.

[0018] The method and device for generating indicator light based on laser frequency doubling and the fiber laser provided by the present invention can ensure that the indicator light and the laser are generated by the same frequency doubling crystal and output in the same optical path, so that the concentricity of the two can be ensured, so that the optical axes of the two laser beams basically coincide. In addition, in the corresponding implementation, due to the ingenious design of the dual-wavelength conversion unit, the scheme can adjust the length of the lead-doped optical fiber to affect the Raman gain, nonlinear effect and phase matching conditions, thereby realizing the function of adjusting the optical power of the indicator light. In addition, in the corresponding implementation, by tilting the window plate, it is possible to change the propagation direction of the reflected light and reduce the power of the laser return light, so that the interference of the return light on the laser system can be stably and effectively reduced and eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0021] Figure 1 It is a schematic structural diagram of a device for generating indicator light based on laser frequency doubling of the present invention;

[0022] Figure 2 It is a structural schematic diagram of the optical fiber laser of the present invention;

[0023] Figure 3 The figure is a schematic diagram of the steps of the method for generating indicator light based on laser frequency doubling of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the specific technical solution of the present invention will be clearly and completely described in conjunction with the embodiments below to help those skilled in the art further understand the present invention. Obviously, the embodiments described in this case are only embodiments of a part of the present invention, not all of the embodiments. It should be pointed out that for those of ordinary skill in the art, the embodiments in this application and the features in the embodiments can be combined with each other without departing from the concept of the present invention and without conflicting with each other. Based on the embodiments in the present invention, all other embodiments obtained without creative work by those of ordinary skill in the art should belong to the disclosure and protection scope of the present invention.

[0026] In addition, the terms "first", "second", "S100", "S200", etc. in the specification, claims and drawings of the present invention are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the features used in this way can be interchanged where appropriate, so that the embodiments of the present invention described here can be implemented in an order other than those described here. At the same time, the stages recorded in each step are not mandatory to be implemented in the same step. It should be understood that the implementation order of the contents in each step stage can be adjusted and interchanged without violating the inventive concept, so that the step embodiments of the present invention described here can be implemented in an order other than those described here. In addition, the terms "including" and "having" and any of their variations in the present invention are intended to cover non-exclusive inclusions. Unless otherwise clearly specified and limited, the terms "set", "layout", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in this case can be understood according to specific circumstances and in combination with the prior art.

[0027] In order to achieve the coaxial output of the indicator light and the laser without setting up a low-power red light semiconductor laser, Figure 1 As shown, the present invention provides a device for generating indicator light based on laser frequency doubling, an example of which includes: a dual-wavelength conversion unit and a frequency doubling crystal, the dual-wavelength conversion unit receives incident laser light and converts it into a dual-wavelength laser light containing a base wavelength and an original wavelength, the frequency doubling crystal is connected to the optical path of the dual-wavelength conversion unit to multiply the base wavelength laser light in the dual-wavelength laser light into a frequency doubling wavelength laser light corresponding to the indicator light, and then output it on the same optical axis as the original wavelength laser light, wherein the dual-wavelength conversion unit includes: a dual-wavelength high-reflection fiber Bragg grating, a lead-doped optical fiber, a dual-wavelength low-reflection fiber Bragg grating and an optical fiber end cap connected in sequence.

[0028] Specifically, taking the laser light source outputting 1064nm infrared light as an example, when the laser light source passes through the dual-wavelength high-reflection fiber Bragg grating (reflectivity > 99.5%) of 1064nm and 1240nm, lead-doped fiber, and dual-wavelength low-reflection fiber Bragg grating (reflectivity ≤ 10%) of 1064nm and 1240nm in sequence, it relies on the nonlinear effects of the optical fiber, especially stimulated Raman scattering (SRS) and four-wave mixing (FWM). Because the lead doping increases the nonlinear coefficient of the optical fiber, the SRS process and FWM effect are more significant, making it easier to achieve wavelength conversion.

[0029] In lead-doped optical fibers, since the Raman gain spectrum is usually concentrated at a wavelength slightly longer than 1064nm, each SRS will cause the wavelength to redshift (i.e., the wavelength becomes longer). Therefore, under appropriate phase matching conditions, FWM can cause 1064nm photons to interact with photons of other wavelengths, promoting the wavelength conversion from 1064nm to 1240nm.

[0030] In fact, this process is the synergy of two nonlinear effects:

[0031] That is, first, 1064nm pump light is input into the lead-doped optical fiber, and then Raman scattering induces red shift: the pump photons gradually redshift the wavelength of the photons through stimulated Raman scattering (SRS), forming a series of gradually increasing wavelengths. At this time, 1064nm pump light and other photons with slightly longer wavelengths will exist in the optical fiber at the same time.

[0032] Then there is the four-wave mixing interaction: under phase matching conditions, the 1064nm photons will interact with the photons of other wavelengths generated by Raman scattering. The FWM effect will cause these photons to generate new frequency components, and the wavelength of the new photons will gradually shift to 1240nm.

[0033] Then, the dual-wavelength fiber Bragg gratings of 1064nm and 1240nm ensure that the two wavelengths can stably oscillate and be amplified in the lead-doped optical fiber, and are simultaneously output through the output end cap 6. At this time, the laser beam is aligned with the frequency doubling crystal to effectively double the 1240nm light to 620nm (red light), and the 1064nm light will not be converted in the process.

[0034] Thereby, the 620nm red indicator light and the 1064nm laser light source are generated by the same frequency doubling crystal and output through the same optical path, so the concentricity of the two in space is very good, that is, the optical axes of the two laser beams basically coincide.

[0035] In addition, it is worth mentioning that the structural scheme of the dual-wavelength conversion unit provided in this example, in addition to the coaxial output effect of the indicator light and the laser, also supports the adjustable indicator light power function, that is, by adjusting the length n of the lead-doped optical fiber so that 1<n<10, the gain, nonlinear effect and phase matching conditions can be affected, thereby adjusting the size of the 620nm red indicator light power.

[0036] To explain, in short optical fibers (such as 1 meter in length), the distance of pump light signal transmission is short, the stimulated Raman scattering generated is weak, and the effect of nonlinear effects is small. Therefore, the gain of the indicator light is limited, and the output 620nm red indicator light power is low. For medium-length optical fibers (such as 5 meters in length), when the optical fiber length increases to 5 meters, the distance that the pump light propagates in the optical fiber increases, and the nonlinear effects generated are enhanced, especially the stimulated Raman scattering effect, so that more 1064nm energy can be converted into 620nm red light. At this time, the phase matching conditions in the optical fiber are also relatively good, and the frequency conversion efficiency is high, which significantly increases the power of the red indicator light.

[0037] When the optical fiber is too long (such as 10 meters), in the longer optical fiber, although the nonlinear effect continues to increase, due to the optical loss in the optical fiber and other nonlinear effects, such as self-phase modulation or stimulated Brillouin scattering, they begin to have a significant impact, which may cause spectrum broadening or phase mismatch, thereby suppressing the output of red light. At this time, the red light indicator light power may decrease, or even generate too much noise signal, affecting the output light quality.

[0038] Therefore, in this example, it is preferred to adjust the length of the lead-doped optical fiber within a range of greater than 1 meter and less than 10 meters, wherein 5 meters is recommended, so as to achieve a balance between gain, nonlinear effect and phase matching as much as possible, so as to output a higher power 620nm red light. If the optical fiber length is too short or too long, it may not produce the best red light output.

[0039] Furthermore, in order to eliminate the interference of the returned light, in an optional example, the device for generating indicator light based on laser frequency doubling also includes: a window piece, which is arranged on the output light path of the frequency doubling crystal and installed at an angle, so as to change the propagation direction of the reflected light and reduce the power of the returned light, thereby stably and effectively reducing the interference of the returned light on the laser system.

[0040] Furthermore, in order to achieve efficient frequency doubling conversion while satisfying the phase matching conditions of the frequency doubling crystal so as to reduce the power loss of the output laser, in an optional example, the light incident surface and the light output surface of the frequency doubling crystal can be coated with a high-transmittance film of the laser light source output laser wavelength and a high-transmittance film of the visible light wavelength after frequency doubling.

[0041] Furthermore, in order to package the device, in an optional example, the apparatus for generating indicator light based on laser frequency doubling further includes: a packaging shell covering the dual wavelength conversion unit and the frequency doubling crystal.

[0042] On the other hand, for the above device example, see Figure 2As shown, the present invention also provides a fiber laser, which includes: an indicator light generating unit, a laser light source unit, wherein the indicator light generating unit is a device for generating indicator light based on laser frequency doubling as described in any of the above examples, wherein the laser light source unit example includes: a laser light source device, a fiber fusion box, the laser light source device is connected to the indicator light generating unit via the fiber fusion box, laser is emitted thereto, and laser and indicator light with the same optical axis are output through the indicator light generating unit.

[0043] On the other hand, for the above device and fiber laser example, please refer to Figure 3 As shown, the present invention also provides a method for generating indicator light based on laser frequency doubling, and its exemplary steps include:

[0044] Step S100 sets the phase matching condition of the frequency doubling crystal to correspond to the preset fundamental wavelength and the frequency doubling wavelength.

[0045] In step S200, the incident laser is converted into a dual-wavelength laser including a fundamental wavelength and an original wavelength through a dual-wavelength high-reflection fiber Bragg grating, a lead-doped fiber and a dual-wavelength low-reflection fiber Bragg grating in sequence, and then emitted to a frequency doubling crystal through an optical fiber end cap.

[0046] In step S300, the frequency doubling crystal doubles the base wavelength laser to a frequency doubling wavelength laser corresponding to the indicator light, and then outputs the laser on the same optical axis as the original wavelength laser.

[0047] Furthermore, in order to be able to adjust the optical power of the indicator light, in the method of generating indicator light based on laser frequency doubling, optional example steps also include: step S400 adjusts the length of the lead-doped optical fiber to affect the Raman gain, nonlinear effect and phase matching conditions, and adjusts the optical power of the indicator light.

[0048] Furthermore, in order to achieve efficient frequency doubling conversion while satisfying the phase matching condition of the frequency doubling crystal so as to reduce the power loss of the output laser, in the method of generating indicator light based on laser frequency doubling, optional example steps also include: step S500 tilts a window plate on the output light path of the frequency doubling crystal to change the propagation direction of the reflected light of the laser and the indicator light.

[0049] In summary, the method and device for generating indicator light based on laser frequency doubling and the fiber laser provided by the present invention can ensure that the indicator light and the laser are generated by the same frequency doubling crystal and output in the same optical path, so that the concentricity of the two can be ensured, so that the optical axes of the two laser beams basically coincide. In addition, in the corresponding implementation, due to the ingenious design of the dual-wavelength conversion unit, the present solution can adjust the length of the lead-doped optical fiber to affect the Raman gain, nonlinear effect and phase matching conditions, thereby realizing the function of adjusting the optical power of the indicator light. In addition, in the corresponding implementation, by tilting the window plate, it is possible to change the propagation direction of the reflected light and reduce the power of the laser return light, so that the interference of the return light on the laser system can be stably and effectively reduced and eliminated.

[0050] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is only limited by the claims and their full scope and equivalents. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0051] Those skilled in the art can understand that, in addition to implementing the system, device, unit and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps. Therefore, the system, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be regarded as structures within the hardware component; the modules for implementing various functions can also be regarded as both software programs for implementing the method and structures within the hardware component.

[0052] In addition, all or part of the steps in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a program, and the program is stored in a storage medium, including a number of instructions to enable a single-chip microcomputer, a chip or a processor to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, RandomAccess Memory), disk or optical disk and other media that can store program codes.

[0053] In addition, various implementation modes of the embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the embodiments of the present invention, they should also be regarded as the contents disclosed by the embodiments of the present invention.

Claims

1. A device for generating indicator light based on laser frequency doubling, comprising: A dual-wavelength conversion unit and a frequency doubling crystal, wherein the dual-wavelength conversion unit receives incident laser light and converts the incident laser light into a dual-wavelength laser light containing a base wavelength and an original wavelength, wherein the frequency doubling crystal is connected to the optical path of the dual-wavelength conversion unit to multiply the base wavelength laser light in the dual-wavelength laser light into a frequency doubling wavelength laser light corresponding to the indicator light, and then output the dual-wavelength laser light on the same optical axis as the original wavelength laser light, wherein the dual-wavelength conversion unit includes: a dual-wavelength high-reflection fiber Bragg grating, a lead-doped optical fiber, a dual-wavelength low-reflection fiber Bragg grating and an optical fiber end cap, which are connected in sequence.

2. The device for generating indicator light based on laser frequency doubling according to claim 1, wherein the light incident surface and the light exit surface of the frequency doubling crystal are coated with a high-transmittance film of the original wavelength of the incident laser and a high-transmittance film of the frequency doubling wavelength.

3. The device for generating indicator light based on laser frequency doubling according to claim 1, further comprising: The window is tilted and arranged on the output light path of the frequency doubling crystal.

4. The device for generating indicator light based on laser frequency doubling according to claim 1, further comprising: The packaging shell covers the dual wavelength conversion unit and the frequency doubling crystal.

5. The device for generating indicator light based on laser frequency doubling according to claim 1, wherein the fundamental wavelength of the phase matching of the frequency doubling crystal is 1240nm, the frequency doubling wavelength is 620nm, the reflectivity of the dual-wavelength high-reflection fiber grating is greater than 99.5%, and its wavelengths are 1064nm and 1240nm, the reflectivity of the dual-wavelength low-reflection fiber grating is ≤10%, and its wavelengths are 1064nm and 1240nm, and the wavelength of the laser injected into the dual-wavelength conversion unit is 1064nm.

6. A fiber laser comprising: An indication light generating unit and a laser light source unit, wherein the indication light generating unit is a device for generating indication light based on laser frequency doubling as described in any one of claims 1 to 5, and the laser light source unit is connected to the indication light generating unit, laser is emitted into the indication light generating unit, and laser and indication light with the same optical axis are output through the indication light generating unit.

7. The optical fiber laser according to claim 6, wherein the laser light source unit comprises: A laser light source device and an optical fiber fusion box, wherein the laser light source device is connected to an indication light generating unit via the optical fiber fusion box.

8. A method for generating indicator light based on laser frequency doubling, comprising: Setting the phase matching condition of the frequency doubling crystal to correspond to the preset fundamental wavelength and the frequency doubling wavelength; The incident laser is converted into a dual-wavelength laser containing a fundamental wavelength and an original wavelength by passing through a dual-wavelength high-reflection fiber Bragg grating, a lead-doped fiber and a dual-wavelength low-reflection fiber Bragg grating in sequence, and then emitted to a frequency-doubling crystal through an optical fiber end cap; The frequency doubling crystal doubles the base wavelength laser to a frequency doubling wavelength laser corresponding to the indicator light, and then outputs it on the same optical axis as the original wavelength laser.

9. The method for generating indicator light based on laser frequency doubling according to claim 8, wherein the steps further include: The length of the lead-doped optical fiber is adjusted to affect the Raman gain, nonlinear effect and phase matching conditions, and to adjust the optical power of the indicator light.

10. The method for generating indicator light based on laser frequency doubling according to claim 8, wherein the steps further include: The window piece is tiltedly arranged on the output optical path of the frequency doubling crystal to change the propagation direction of the reflected light of the laser and the indicator light.

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