Device and method for improving stability of gas raman laser power

Abstract

The application discloses a device and method for improving the stability of gas Raman laser power, which comprises a hollow optical fiber, a single-mode optical fiber, a broadband light source, a pump and a gas pressure measuring unit. One end of the hollow optical fiber is provided with a first coupler, the other end of the hollow optical fiber is provided with a second coupler, one end of the single-mode optical fiber is provided with a third coupler, the other end of the single-mode optical fiber is provided with a fourth coupler, and the output end of the broadband light source is connected with the third coupler. The pump is connected with the first coupler, the fourth coupler combines the output light of the single-mode optical fiber and the output light of the hollow optical fiber to form a Mach-Zehnder interference to obtain an interference signal, and the gas pressure measuring unit obtains the gas pressure inside the hollow optical fiber through the interference signal. The real and real-time gas pressure inside the hollow optical fiber can be obtained in real time, so that the pump power can be adjusted in a targeted manner, and the power stability of the gas Raman laser is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of Raman laser, in particular to a device and method for improving the power stability of gas Raman laser. BACKGROUND

[0002] Special wavelength lasers have important values in the fields of biophotonics, national defense and remote sensing. For example, 1.7 μm is between two absorption peaks of water molecules, and the laser of this band can penetrate biological tissues containing a large amount of water molecules, and is also at the absorption peak position of fat and collagen, so it has important applications in the fields of multi-photon biological imaging and photoacoustic imaging. In addition, mid-infrared band (2-5 μm) lasers also have important applications in the fields of national defense and remote sensing.

[0003] Gas stimulated Raman scattering is considered as an extremely effective way to achieve laser wavelength expansion. Gas Raman laser uses the Raman scattering (molecular vibration / rotation energy level) of gas to realize the conversion of laser frequency, and has the characteristics of not depending on the pump laser wavelength, overcoming the dependence of traditional gas lasers on the precise matching of pump wavelength. As long as the energy density of the pump light is large enough and there is a suitable Raman shift gas, a gas Raman laser can in principle realize laser output of any wavelength. Gas Raman laser technology greatly promotes the application of laser technology in the fields of biophotonics, national defense and remote sensing. Then, due to the low density of gas, the Raman gain is small, and the conversion efficiency of free-space type gas Raman laser is very low. Hollow core optical fiber can confine light and gas in the fiber core of tens of microns at the same time, greatly enhancing the interaction intensity and distance between laser and gas, reducing the Raman threshold and improving the conversion efficiency. This new type of hollow core optical fiber gas Raman laser has the structural advantages of fiber lasers and the advantages of rich gas output wavelengths. The use of hollow core optical fiber has greatly developed gas Raman laser technology. In the past few decades, hollow core optical fiber Raman lasers based on various pump wavelengths and gases have been widely reported.

[0004] However, due to the low density of the gas itself, a high gas pressure is needed to obtain a high gain. In addition, the gas has a very strong flowability, and it is difficult to maintain uniform and stable gas pressure, resulting in extremely unstable gain and laser power, which cannot meet the use requirements. The existing gas Raman laser device such as Figure 1As shown, the pump light is injected into the hollow core fiber through free space or fiber interconnection, and the position of coupling the pump light and the hollow core fiber is filled with gas in the gas cavity 700. The gas cavity 700 is provided with a gas pressure gauge 710 to measure the gas pressure in the gas cavity 700. Since the core of the hollow core fiber filled with gas has a diameter of only tens of microns, and the length of the fiber is long, the pressure of the gas in the hollow core fiber is not equal to the gas pressure in the gas cavity 700, and it takes a long time to balance the pressure in the hollow core fiber and the gas cavity 700. Therefore, the existing measurement method of the gas pressure gauge 710 cannot obtain the actual and real-time gas pressure in the core of the hollow core fiber. Since the gas pressure is positively correlated with the gain of the gas, the gas Raman laser power cannot be adjusted in real time, resulting in poor power stability of the existing gas Raman laser. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a device and method for improving the power stability of a gas Raman laser, which can accurately measure the real gas pressure in the core of a hollow core fiber and improve the power stability of a gas Raman laser.

[0006] According to the device for improving the power stability of a gas Raman laser according to the first aspect of the present application, the device comprises:

[0007] a hollow core fiber, one end of the hollow core fiber is provided with a first coupler, the output end of the first coupler is connected to the other end of the hollow core fiber, the other end of the hollow core fiber is provided with a second coupler, and the input end of the second coupler is connected to the other end of the hollow core fiber;

[0008] a single-mode fiber, one end of the single-mode fiber is provided with a third coupler, the output end of the third coupler is connected to the other end of the single-mode fiber, the other end of the single-mode fiber is provided with a fourth coupler, and one input end of the fourth coupler is connected to the other end of the single-mode fiber;

[0009] a broadband light source, the output end of the broadband light source is connected to the input end of the third coupler, and the output end of the third coupler is connected to one input end of the first coupler;

[0010] a pump, the other input end of the first coupler is connected to the pump for inputting pump light, one output end of the second coupler is used for outputting laser, and the other output end of the second coupler is connected to the other input end of the fourth coupler for combining the output light of the single-mode fiber and the output light of the hollow core fiber to form a Mach-Zehnder interference to obtain an interference signal;

[0011] An air pressure measuring unit is connected to the output end of the fourth coupler and is used to obtain the gas pressure inside the hollow-core optical fiber through an interference signal.

[0012] The device for improving the power stability of a gas Raman laser according to the first embodiment of the present invention has at least the following beneficial effects:

[0013] In this embodiment of the present invention, the output light of a broadband light source is split into two by a third coupler. The first output light passes through the first coupler into a hollow-core fiber, passes through the gas-filled hollow-core fiber, and then is output through the second coupler into a fourth coupler. The second output light passes through a conventional single-mode fiber and then enters the fourth coupler. The first and second output lights are combined by the fourth coupler to form Mach-Zehnder interferometer. The interference signal can reflect the changes in the gas pressure inside the hollow-core fiber. The pressure measurement unit can obtain the true, real-time gas pressure inside the hollow-core fiber through spectral demodulation. This allows for targeted adjustment of the pump power and improves the power stability of the gas Raman laser.

[0014] According to some embodiments of the present invention, the air pressure measurement unit includes a spectrometer and a demodulator, the spectrometer is used to obtain the spectrum of the interference signal, and the demodulator is used to demodulate the spectrum of the interference signal to obtain the gas pressure inside the hollow-core optical fiber.

[0015] According to some embodiments of the present invention, a control module is further included, wherein the signal output end of the air pressure measurement unit is connected to the feedback end of the control module for feeding back the gas pressure inside the hollow-core optical fiber, and the output end of the control module is connected to the control end of the pump for adjusting the output laser power of the pump according to the gas pressure inside the hollow-core optical fiber.

[0016] According to a second aspect of the present invention, a method for improving the power stability of a gas Raman laser comprises the following steps:

[0017] The output light of the broadband light source is divided into two paths through the third coupler, including a first path of output light and a second path of output light. The first path of output light enters the hollow-core optical fiber through the first coupler, and the second path of output light enters the single-mode optical fiber.

[0018] The first output light enters the hollow-core optical fiber, is output through the second coupler, and enters the fourth coupler. The second output light enters the single-mode optical fiber and enters the fourth coupler. The first output light and the second output light are combined by the fourth coupler to form Mach-Zehnder interference to obtain an interference signal.

[0019] The gas pressure measurement unit performs spectral demodulation on the interference signal and calculates the gas pressure inside the hollow-core fiber.

[0020] The method for improving the gas Raman laser power stability according to the second aspect of the embodiment of the present application has at least the following beneficial effects:

[0021] The embodiment of the present application divides the output light of the broadband light source by the third coupler into two paths, the first path output light enters the hollow core fiber through the first coupler, and after passing through the hollow core fiber filled with gas, the output light is output through the second coupler and enters the fourth coupler, the second path output light is output through the ordinary single-mode fiber and then enters the fourth coupler, the first path output light and the second path output light are combined through the fourth coupler to form a Mach-Zehnder interference, and the interference signal can reflect the change of the gas pressure in the hollow core fiber, and the gas pressure measurement unit can obtain the real-time and real gas pressure in the hollow core fiber through spectral demodulation. Thus, the pump power can be adjusted in a targeted manner, and the power stability of the gas Raman laser is improved.

[0022] According to some embodiments of the present application, the specific steps of the gas pressure measurement unit for spectral demodulation of the interference signal and calculation of the gas pressure in the hollow core fiber are as follows:

[0023] A function relationship between the wavelength λ at the minimum value of the interference light intensity and the gas pressure P in the hollow core fiber is constructed;

[0024] The wavelength λ at the minimum value of the interference light intensity in the interference signal is obtained through spectral demodulation of the interference signal;

[0025] The gas pressure P in the hollow core fiber is calculated by substituting the wavelength λ at the minimum value of the interference light intensity into the function relationship.

[0026] According to some embodiments of the present application, the method further comprises a feedback adjustment step of adjusting the output laser power of the pump in real time according to the gas pressure in the hollow core fiber.

[0027] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0028] The present application will be further described below in conjunction with the drawings and embodiments, in which:

[0029] Figure 1 It is a structural principle diagram of the existing gas Raman laser device;

[0030] Figure 2 It is a structural principle diagram of the device for improving the gas Raman laser power stability in the embodiment of the present application;

[0031] Figure 3 It is a structural principle diagram of the device for improving the gas Raman laser power stability with feedback adjustment in the embodiment of the present application.

[0032] Reference Signs:

[0033] Hollow core fiber 100, first coupler 110, second coupler 120, single mode fiber 200, third coupler 210, fourth coupler 220, broadband light source 300, pump 400, air pressure measuring unit 500, control module 600, gas cavity 700, air pressure gauge 710. DETAILED DESCRIPTION

[0034] Embodiments of the present application are described in detail below with reference to the attached drawings, which show by way of example, embodiments in which the same or similar elements have the same or similar reference numbers. The embodiments described below are examples only, and are not to be understood as limiting the present application.

[0035] In the description of the present application, it should be understood that the relative description of position, such as up, down, etc. is based on the position or location relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular position, be constructed and operated in a particular position, and therefore cannot be understood as a limitation of the present application.

[0036] In the description of the present application, the plural refers to more than two. If there is a description of the first, second, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the sequence of technical features indicated.

[0037] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be broadly understood, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0038] Reference Figure 2As shown, a device for improving the stability of gas Raman laser power comprises: a hollow optical fiber 100, a single-mode optical fiber 200, a broadband light source 300, a pump 400 and a gas pressure measuring unit 500. Wherein one end of the hollow optical fiber 100 is provided with a first coupler 110, one end of the hollow optical fiber 100 is connected to the output end of the first coupler 110, the other end of the hollow optical fiber 100 is provided with a second coupler 120, and the other end of the hollow optical fiber 100 is connected to the input end of the second coupler 120; one end of the single-mode optical fiber 200 is provided with a third coupler 210, one end of the single-mode optical fiber 200 is connected to one output end of the third coupler 210, the other end of the single-mode optical fiber 200 is provided with a fourth coupler 220, and the other end of the single-mode optical fiber 200 is connected to one input end of the fourth coupler 220; the output end of the broadband light source 300 is connected to the input end of the third coupler 210, and the other output end of the third coupler 210 is connected to one input end of the first coupler 110; the pump 400 is connected to the other input end of the first coupler 110, one output end of the second coupler 120 is used for outputting laser, and the other output end of the second coupler 120 is connected to the other input end of the fourth coupler 220 for forming a Mach-Zehnder interference through beam combination of the first output light of the single-mode optical fiber 200 and the second output light of the hollow optical fiber 100 to obtain an interference signal; and the gas pressure measuring unit 500 is connected to the output end of the fourth coupler 220 for obtaining the gas pressure inside the hollow optical fiber 100 through the interference signal.

[0039] It should be noted that the third coupler 210 and the first coupler 110 are also connected through a single-mode optical fiber, and the second coupler 120 and the fourth coupler 220 are also connected through a single-mode optical fiber.

[0040] The working principle of the present application is as follows:

[0041] The output light of the broadband light source is divided into two parts through the third coupler, the first output light enters the hollow optical fiber through the first coupler, and after passing through the hollow optical fiber filled with gas, it is output through the second coupler into the fourth coupler, and the second output light is output after passing through the ordinary single-mode optical fiber into the fourth coupler, the first output light and the second output light are combined through the fourth coupler to form a Mach-Zehnder interference, wherein one path through the single-mode optical fiber is called a reference arm, and the other path through the hollow optical fiber filled with gas is called a measurement arm, and the gas pressure inside the hollow optical fiber is set as P, when the gas pressure in the signal arm changes from P to P+ΔP, the gas refractive index in the signal arm changes from n(P) to n(P+ΔP) due to the fact that the gas refractive index is a function of pressure, the optical path difference and phase difference of the two lights change, and the interference signal changes, therefore the interference signal of the two lights can reflect the change of the gas pressure, and the gas pressure measuring unit can obtain the real gas pressure inside the hollow optical fiber in real time through spectral demodulation, instead of the pressure in the gas cavity at the filling position.

[0042] It should be noted that the specific principle of calculating the gas pressure inside the hollow core optical fiber by the interference signal in the gas pressure measuring unit is as follows:

[0043] First, the optical path difference ΔL of the first output light and the second output light is obtained, and the calculation formula of ΔL is

[0044] ΔL = n si L3-[n si L1+n(P,T)L0+n si L2](1)

[0045] Wherein n si L3 is the optical path length of the first output light, L3 is the length of the single-mode optical fiber 200, n si is the refractive index of the single-mode optical fiber 200, n si L1+n(P,T)L0+n si L2 is the optical path length of the second output light, L1 is the length of the single-mode optical fiber between the third coupler 210 and the first coupler 110, L0 is the length of the hollow core optical fiber 100, L2 is the length of the single-mode optical fiber between the second coupler 120 and the fourth coupler 220, n(P,T) is the refractive index of the hollow core optical fiber 100, T is the temperature inside the hollow core optical fiber 100, and P is the gas pressure inside the hollow core optical fiber 100.

[0046] Then, the phase difference of the first output light and the second output light is obtained through the optical path difference ΔL The calculation formula is

[0047]

[0048] Wherein, n(P,T) can be expressed as

[0049]

[0050] Wherein, the temperature T can be considered as a constant.

[0051] The wavelength at the minimum value of the interference light intensity can be expressed as:

[0052] Wherein, m is any positive integer, is the initial phase difference. Then, according to the formula (2)-(4), the functional relationship between the wavelength λ and the gas pressure P can be obtained. Therefore, the gas pressure measuring unit can obtain the value of the gas pressure P by monitoring the wavelength λ, and further obtain the size of the gain in real time.

[0053] Specifically, the gas pressure measuring unit 500 in the embodiment of the present application includes a spectrometer and a demodulator, the spectrometer is used to obtain the spectrum of the interference signal, and the demodulator is used to demodulate the spectrum of the interference signal to obtain the gas pressure inside the hollow core optical fiber 100.

[0054] With reference to Figure 3 As shown in the figure, the present application also includes a control module 600, the signal output end of the gas pressure measuring unit 500 is connected to the feedback end of the control module 600 for feeding back the gas pressure inside the hollow core optical fiber 100, and the output end of the control module 600 is connected to the control end of the pump 400 for adjusting the output laser power of the pump 400 according to the gas pressure inside the hollow core optical fiber 100. Therefore, the present application can not only measure the gas pressure inside the hollow core optical fiber in real time, but also can feedback control the pump power according to the real-time measured gas pressure, so as to realize the improvement of the stability of the gas Raman laser power.

[0055] The present application also relates to a method for improving the stability of the gas Raman laser power applied to the above-mentioned embodiment device, which includes the following steps:

[0056] S100, the output light of the broadband light source 300 is divided into two paths by the third coupler 210, including the first path output light and the second path output light, the first path output light enters the hollow core optical fiber 100 through the first coupler 110, and the second path output light directly enters the single-mode optical fiber 200;

[0057] S200, the first path output light is output by the second coupler 120 after entering the hollow core optical fiber 100 and enters the fourth coupler 220, the second path output light enters the fourth coupler 220 after entering the single-mode optical fiber 200, the first path output light and the second path output light are combined by the fourth coupler 220 to form a Mach-Zehnder interference to obtain an interference signal;

[0058] S300, the gas pressure measuring unit 500 performs spectral demodulation on the interference signal and calculates the gas pressure inside the hollow core optical fiber 100.

[0059] In the step S300, the specific steps of the gas pressure measuring unit 500 performing spectral demodulation on the interference signal and calculating the gas pressure inside the hollow core optical fiber 100 are as follows:

[0060] S301, the function relationship between the wavelength λ at the minimum value of the interference light intensity and the gas pressure P inside the hollow core optical fiber 100 is constructed by the above-mentioned formulas (2)-(4) in the embodiment;

[0061] S302, the wavelength λ at the minimum value of the interference light intensity in the interference signal is obtained by performing spectral demodulation on the interference signal;

[0062] S303, the wavelength λ at the minimum of the interference light intensity is substituted into the function relationship to calculate the gas pressure P in the hollow core optical fiber 100.

[0063] On the basis of the real-time measurement of the gas pressure in the hollow core optical fiber in the above embodiment, in order to realize feedback regulation, the embodiment of the present application further comprises a feedback regulation step:

[0064] S400, the output laser power of the pump 400 is adjusted in real time according to the gas pressure inside the hollow core optical fiber 100.

[0065] Specifically, the specific steps of step S400 are:

[0066] The control module compares the measured gas pressure P and generates a control signal to control the power of the pump laser. Specifically, when the measured gas pressure P is equal to the preset gas pressure P0, the pump power is maintained unchanged; when the real-time gas pressure P is lower than the preset gas pressure P0, the pump power is increased; when the gas pressure P is higher than the preset gas pressure P0, the pump power is reduced. Through this way of real-time measurement of gas pressure and feedback control of pump power, the stability of the gas Raman laser power is improved.

[0067] The embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge range of ordinary skilled in the art without departing from the purpose of the present application.

Claims

1. An apparatus for improving the stability of gas Raman laser power, characterized in that, It comprises: a hollow core fiber (100), one end of the hollow core fiber (100) is provided with a first coupler (110), the output end of the first coupler (110) is connected to one end of the hollow core fiber (100), the other end of the hollow core fiber (100) is provided with a second coupler (120), the input end of the second coupler (120) is connected to the other end of the hollow core fiber (100); a single mode fiber (200), one end of the single mode fiber (200) is provided with a third coupler (210), one output end of the third coupler (210) is connected to one end of the single mode fiber (200), the other end of the single mode fiber (200) is provided with a fourth coupler (220), one input end of the fourth coupler (220) is connected to the other end of the single mode fiber (200); a broadband light source (300), the output end of the broadband light source (300) is connected to the input end of the third coupler (210), the other output end of the third coupler (210) is connected to one input end of the first coupler (110); a pump (400), the other input end of the first coupler (110) is connected to the pump (400) for inputting pump (400) light, one output end of the second coupler (120) is used for outputting laser, the other output end of the second coupler (120) is connected to the other input end of the fourth coupler (220) for combining the output light of the single mode fiber (200) and the output light of the hollow core fiber (100) to form a Mach-Zehnder interference to obtain an interference signal; an air pressure measuring unit (500), the output end of the fourth coupler (220) is connected to the air pressure measuring unit (500) for obtaining the air pressure inside the hollow core fiber (100) through the interference signal; It also comprises a control module (600), the signal output end of the air pressure measuring unit (500) is connected to the feedback end of the control module (600) for feeding back the air pressure inside the hollow core fiber (100), and the output end of the control module (600) is connected to the control end of the pump (400) for adjusting the output laser power of the pump (400) according to the air pressure inside the hollow core fiber (100); Wherein, the control module (600) compares the air pressure with the preset air pressure, when the air pressure is equal to the preset air pressure, the output laser power of the pump (400) is maintained unchanged; when the air pressure is lower than the preset air pressure, the output laser power of the pump (400) is increased; when the air pressure is higher than the preset air pressure, the output laser power of the pump (400) is reduced.

2. The device for improving the Raman laser power stability of the lifting gas according to claim 1, characterized in that: The air pressure measuring unit (500) comprises a spectrometer and a demodulator, the spectrometer is used for obtaining the spectrum of the interference signal, and the demodulator is used for demodulating the spectrum of the interference signal to obtain the air pressure inside the hollow core fiber (100).

3. A method for stabilizing the power of a gas Raman laser, applied to the device of any one of claims 1 to 2, characterized in that, It comprises the following steps: The output light of the broadband light source (300) is divided into two paths by the third coupler (210), including first path output light and second path output light, the first path output light enters the hollow core fiber (100) through the first coupler (110), and the second path output light enters the single mode fiber (200); The first path output light is output through the second coupler (120) after entering the hollow core fiber (100) and enters the fourth coupler (220), and the second path output light enters the fourth coupler (220) after entering the single mode fiber (200), the first path output light and the second path output light are combined by the fourth coupler (220) to form a Mach-Zehnder interference to obtain an interference signal; The gas pressure measuring unit (500) demodulates the interference signal and calculates the gas pressure in the hollow core fiber (100); It also includes a feedback adjustment step: adjusting the output laser power of the pump (400) in real time according to the gas pressure in the hollow core fiber (100).

4. The method of claim 3, wherein: The specific steps of the gas pressure measuring unit (500) demodulating the interference signal and calculating the gas pressure in the hollow core fiber (100) are: Construct a functional relationship between the wavelength λ at the minimum value of the interference light intensity and the gas pressure P in the hollow core fiber (100); By demodulating the interference signal, the wavelength λ at the minimum value of the interference light intensity in the interference signal is obtained; The wavelength λ at the minimum value of the interference light intensity is substituted into the functional relationship to calculate the gas pressure P in the hollow core fiber (100).

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