A tunable Raman fiber laser

Abstract

The invention discloses a tunable Raman fiber laser, comprising: a Raman laser pump source, which is used to generate laser with tunable pulse width, repetition frequency and wavelength, wherein the tunability of the pulse width and repetition frequency is realized based on the gain modulation principle, and the tunability of the wavelength is realized through a tunable filter; a Raman fiber optically coupled to the Raman pump source, which is used to provide Raman gain and transfer the laser wavelength generated by the pump source to the Raman wavelength; since the pulse width, repetition frequency and wavelength of the Raman laser pump source are tunable, the Raman laser can also be tuned, thereby obtaining a laser output with tunable pulse width, repetition frequency and wavelength based on the Raman effect.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, and in particular to a tunable Raman optical fiber laser. Background Art

[0002] Fiber lasers have the advantages of high beam quality, small size, high efficiency, simple structure, and easy maintenance, and have been widely used in military and civilian fields. Fibers based on rare earth doping, such as ytterbium-doped, erbium-doped, thulium-doped, and holmium-doped, can achieve wide wavelength tunable output, but the wavelength of lasers emitted by rare earth-doped fibers is limited by the emission cross section of rare earth ions, and cannot emit lasers in some special bands such as 1.1-1.35μm, 1.6-1.75μm, and 2.1-2.3μm.

[0003] In the development of fiber lasers, people have found that when optical fiber is used as a light transmission medium, it has a certain nonlinear coefficient and accumulates nonlinear effects during the transmission of light, which can achieve virtual energy level transition luminescence, such as the Raman scattering effect in optical fiber. In this way, by using a suitable pump source, such as a rare earth-doped fiber laser and combining the Raman frequency shift of the optical fiber, fiber laser output with special wavelengths such as 1.1-1.35μm, 1.6-1.75μm and 2.1-2.3μm can be achieved.

[0004] However, existing fiber lasers that obtain wavelength tunable output based on nonlinear effects cannot achieve laser output with simultaneously tunable pulse width, repetition frequency and wavelength. Summary of the invention

[0005] The main purpose of the present invention is to provide a tunable Raman fiber laser, aiming to solve the technical problem that the Raman fiber laser in the prior art cannot achieve laser output with tunable wavelength, pulse width and repetition frequency at the same time.

[0006] To achieve the above-mentioned purpose, the present invention provides a tunable Raman fiber laser, comprising: a Raman laser pump source, used to generate Raman laser pump light with tunable pulse width, repetition frequency and wavelength; a Raman fiber optically coupled to the Raman laser pump source, used to provide Raman gain and output Raman signal light; a broadband total reflection mirror, optically coupled to the Raman fiber, used to provide high feedback for the Raman signal light; and a first wavelength division multiplexer, whose pump end, signal end and common end are respectively coupled to the Raman laser pump source, the broadband total reflection mirror and the Raman fiber, and used to couple the pump light wavelength generated by the Raman laser pump source with the Raman signal light wavelength.

[0007] Furthermore, the tunable Raman fiber laser also includes: a first optical isolator optically coupled to the Raman fiber, used to prevent subsequent light reflection, and the output end serves as the output end of the Raman signal light.

[0008] Furthermore, the tunable Raman fiber laser further includes: a fiber mode field adapter, two ends of which are optically coupled to the common end of the first wavelength division multiplexer and the Raman fiber, respectively.

[0009] Furthermore, the Raman laser pump source includes: a current modulated semiconductor laser for generating a first pump light with tunable pulse width and repetition frequency; and a gain modulated laser optically coupled to the current modulated semiconductor laser for generating a Raman laser pump light with tunable wavelength.

[0010] Furthermore, the gain modulated laser includes: a second optical isolator optically coupled to the current modulated semiconductor laser; a first optical fiber amplifier optically coupled to the second optical isolator; a second wavelength division multiplexer optically coupled to the first optical fiber amplifier; a signal optical isolator optically coupled to the signal end of the second wavelength division multiplexer; a tunable filter optically coupled to the signal optical isolator; a laser gain medium optically coupled to the common end of the second wavelength division multiplexer; and an optical fiber coupler optically coupled to the laser gain medium, which is used to output a part of the wavelength-tunable Raman laser pump light and continue to oscillate the other part in the ring cavity.

[0011] Furthermore, the gain modulated laser further comprises: a second optical fiber amplifier coupled with the Raman laser pump light, for amplifying the light output by the gain modulated laser and then entering the Raman optical fiber. Furthermore, at least two second optical fiber amplifiers are cascaded to amplify the Raman laser pump light signal.

[0012] Furthermore, the laser gain medium is rare-earth doped optical fiber.

[0013] Furthermore, the rare earth doped in the rare earth-doped optical fiber is ytterbium, erbium, thulium, holmium or other rare earths.

[0014] The present invention provides a tunable Raman fiber laser, which has the beneficial effect that: by coupling the laser generated by a Raman laser pump source into a Raman fiber, a Raman laser output based on a nonlinear effect is obtained, and the Raman laser pump source used can tune the pulse width, repetition frequency and wavelength, so that the Raman laser can also be tuned, thereby obtaining a laser output with simultaneously tunable pulse width, repetition frequency and wavelength based on the Raman effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 Schematic diagram of the structure of a tunable Raman fiber laser according to an embodiment of the present invention;

[0017] Figure 2 The figure is a schematic diagram of the structure of a Raman pump source of a tunable Raman fiber laser according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0019] See also Figure 1 , which is a tunable Raman fiber laser, including: a Raman laser pump source 1, a first wavelength division multiplexer 22, a broadband total reflection mirror 21, a fiber mode field adapter 23, a Raman fiber 24 and a first optical isolator 25; the Raman laser pump source 1 is used to generate a Raman laser pump light with tunable pulse width, repetition frequency and wavelength; the Raman fiber 24 is coupled with the Raman pump light to provide Raman gain, which is used to perform Raman frequency shift on the laser generated by the Raman pump source 1 to generate Raman wavelength laser output; the first optical isolator 25 is optically coupled with the Raman fiber 24 to prevent subsequent light reflection, and the output end serves as the output end of the Raman laser, the broadband total reflection mirror is coupled with the signal end of the first wavelength division multiplexer to provide high feedback for the Raman signal; the fiber mode field adapter 23 is used to match the fiber mode field of the common end of the first wavelength division multiplexer with the Raman fiber mode field.

[0020] During use, the pump source 1 generates a pump laser, which is converted into a Raman wavelength laser through the Raman optical fiber 24. After the Raman laser is generated, it passes through the first optical isolator 25, which can prevent the reflection of subsequent light and output the Raman laser. When it is necessary to tune the pulse width, repetition frequency or wavelength of the Raman laser, the pulse width, repetition frequency or wavelength of the Raman laser pump source can be tuned to achieve tuning of the Raman laser, thereby obtaining a laser output with tunable pulse width, repetition frequency and wavelength based on the Raman effect.

[0021] In this embodiment, the pump end, signal end and common end of the first wavelength division multiplexer 22 are optically coupled with the pump source 1, the broadband total reflection mirror 21 and the Raman fiber 24 respectively, so as to achieve coupling of the laser wavelength generated by the pump source 1 with the Raman signal wavelength.

[0022] See also Figure 1In one embodiment, the tunable Raman fiber laser further includes: a fiber mode field adapter 23, two ends of which are optically coupled to the common end of the first wavelength division multiplexer 22 and the Raman fiber 24 respectively.

[0023] Since the mode fields of the pigtail of the first wavelength division multiplexer 22 and the Raman fiber 24 may be mismatched to a certain extent, adding a fiber mode field adapter 23 between the two can reduce the connection loss between the common end of the first wavelength division multiplexer 22 and the Raman fiber 24, thereby reducing the loss during laser transmission.

[0024] See also Figure 2 In one embodiment, the Raman laser pump source 1 includes: a current modulated semiconductor laser 11 and a gain modulated laser. The current modulated semiconductor laser 11 is used to generate a first pump light with tunable pulse width and repetition frequency, serving as a pump source for the gain modulated laser; the gain modulated laser adopts a ring cavity structure and has a built-in tunable filter for generating Raman laser pump light with tunable wavelength.

[0025] See also Figure 2 The gain modulated laser includes: a second optical isolator 12 optically coupled to the current modulated semiconductor laser 11; a first optical fiber amplifier 13 optically coupled to the second optical isolator 12; a second wavelength division multiplexer optically coupled to the first optical fiber amplifier 13, and a signal optical isolator 14 optically coupled to the signal end of the second wavelength division multiplexer; a tunable filter 15 optically coupled to the signal optical isolator 14; a laser gain medium 18 coupled to the common end of the second wavelength division multiplexer 16; and an optical fiber coupler 17 optically coupled to the laser gain medium 18; one port of the optical fiber coupler outputs the generated gain modulated laser as Raman laser pump light, and the other port feeds back part of the signal light to the ring cavity.

[0026] The current modulated semiconductor laser 11 is the pump source of the gain modulated laser, providing pumping for the gain modulated laser, and adopting the current modulation principle to achieve tunable pulse width and repetition frequency of the first pump source, generally a current modulated semiconductor laser 11, such as 976nm, 1550nm, or around 1950nm. After amplification, it is used as the pump source of the gain modulated laser.

[0027] After receiving the pump from the first optical fiber amplifier 13, the gain modulated laser generates a pump light signal for the tunable Raman fiber laser, uses the above-mentioned current modulated semiconductor laser 11 as a pump source, and utilizes the pulse pump-gain modulation characteristics to achieve tunable pulse width and repetition frequency of the output signal.

[0028] In this embodiment, the signal optical isolator 14, the tunable filter 15, the second wavelength division multiplexer 16, the optical fiber coupler 17 and the laser gain medium 18 constitute a ring cavity structure, or the signal optical isolator 14, the tunable filter 15, the second wavelength division multiplexer 16, the optical fiber coupler 17 and the laser gain medium 18 are all located in a ring cavity structure, the signal optical isolator 14 ensures the unidirectional transmission of the laser in the ring cavity, the second wavelength division multiplexer 16 is used to couple the first pump light into the gain medium, the laser gain medium 18 is used to emit the signal wavelength, the optical fiber coupler 17 has a certain splitting ratio (for example, 50:50, not limited to this ratio), and is used to output a part of the signal laser in the ring cavity, and the tunable filter 15 is added in the ring cavity to realize the tunability of the laser signal wavelength, and the tunable range can reach up to 150nm at most.

[0029] See also Figure 1 In one embodiment, the tunable Raman fiber laser further includes: a broadband total reflection mirror 21 , optically coupled to the signal end of the first wavelength division multiplexer 22 .

[0030] In this embodiment, the Raman signal wavelength end of the first wavelength division multiplexer 22 is connected to a broadband total reflection mirror 21, and the first optical isolator 25 and the fusion point of the Raman optical fiber 24 or the weak reflection of the surface of the laser device form a resonant cavity, which is combined with a tunable pump source to provide tunability of the pulse width and wavelength of the Raman-Stokes laser.

[0031] See also Figure 2 In one embodiment, the gain modulated laser further includes: a second optical fiber amplifier 19 optically coupled to the gain modulated laser signal light, and used to amplify the laser output by the gain modulated laser and then enter the Raman optical fiber 24.

[0032] The function of the second optical fiber amplifier 19 is to amplify the signal light of the gain modulated laser to meet the power requirement of the Raman signal pump light.

[0033] See also Figure 2 In one embodiment, at least two second optical fiber amplifiers 19 are cascaded to amplify the gain-modulated output laser.

[0034] In this embodiment, two second fiber amplifiers, namely, second fiber amplifier 19 and second fiber amplifier 110, are used to amplify the laser output by the gain modulated laser. In other embodiments, different numbers of second fiber amplifiers can be cascaded to amplify the laser output by the rare-earth-doped fiber according to actual needs.

[0035] In one embodiment, the laser gain medium 18 is a rare-earth doped optical fiber.

[0036] In one embodiment, the rare earth doped in the rare earth-doped optical fiber is ytterbium, erbium, thulium, holmium or other rare earths. In this embodiment, the other rare earths may be praseodymium, neodymium, germanium, europium or dysprosium.

[0037] The working process or principle of the tunable Raman fiber laser provided in the embodiment of the present application is as follows:

[0038] The pulse width output by the current modulated semiconductor laser 11 can be in the order of picoseconds and nanoseconds, the repetition frequency can be tunable in the range of 1kHz-20MHz, and the output wavelength depends on the doped fiber pump, which can be around 976nm, 1550nm, 1950nm, etc. Since the direct modulation output power is low, the power can be amplified by the first fiber amplifier 13 according to the specific situation, and the second optical isolator 12 prevents the return light of the first fiber amplifier 13 from damaging the seed light. The wavelength division multiplexer 16 couples the pump light into the rare earth doped fiber, and the signal is terminated in the cavity to form a laser closed loop, that is, a ring cavity structure. The signal optical isolator 14 ensures unidirectional transmission of the laser in the ring cavity. The tunable filter 15 corresponding to the emission band of the rare earth doped fiber realizes the tunable wavelength of the signal laser. The rare earth doped fiber can be doped with ytterbium / erbium / thulium / holmium, etc., as a laser gain medium 18, emitting a signal wavelength. The fiber coupler 17 of the corresponding signal wavelength has a certain splitting ratio (such as 50:50, but not limited to this ratio), and outputs a part of the signal laser in the ring cavity. After that, the signal laser is again amplified by the corresponding rare earth doped second fiber amplifier 19 to meet the pump light power requirement of the Raman laser. The second fiber amplifier 19 is not limited to one stage, and can be cascaded for amplification. For example, after the fiber amplifier 19, a fiber amplifier 110 is added. So far, the pump light source of the Raman fiber laser with tunable pulse width, repetition frequency and wavelength can be realized.

[0039] The pump light emitted by the Raman laser pump light source is coupled into the Raman optical fiber 24 through the first wavelength division multiplexer 22 of the corresponding wavelength. Since there may be a certain mismatch between the mode fields of the common end pigtail of the first wavelength division multiplexer 22 and the Raman optical fiber 24, a fiber mode field adapter 23 is added between the two to reduce the connection loss between the two. The Raman optical fiber 24 provides Raman gain, and the Raman signal band broadband total reflection mirror 21 provides high feedback for the Raman laser signal. The weak reflection generated inside the first optical isolator 25 or at the fusion point between the Raman optical fiber 24 and the pigtail of the first optical isolator 25 serves as the output end of the Raman resonant cavity. The first optical isolator 25 prevents subsequent light reflection, and the output end of the first optical isolator 25 serves as the output end of the Raman laser.

[0040] In the whole process, a current modulated semiconductor laser 11 with tunable pulse width and repetition frequency is used as a pump source, and the gain modulation principle is used to achieve tunability of the output pulse width and repetition frequency of the rare earth doped fiber laser. At the same time, a tunable filter 15 is inserted into the ring cavity to achieve wavelength tunability, and then the power is amplified by the corresponding second fiber amplifier 19 to meet the requirements of Raman laser pump power. At this point, the pulse width, repetition frequency and wavelength can be tunable, and it can be used as a pump source for Raman laser. Combined with the Raman gain of the Raman fiber 24 and the Raman resonant cavity, Raman laser output is achieved, and the pulse width and wavelength of the Raman laser are tunable by adjusting the pulse width and wavelength of the pump source of the Raman laser.

[0041] In this embodiment, the Raman fiber is a quartz fiber or a fluoride fiber, and the Raman frequency shift δω of the quartz fiber and the fluoride fiber are 440 cm -1 and 580cm -1 , there is a formula for calculating the Raman frequency shift, which is as follows:

[0042]

[0043] Combined with the tunability of the pump fiber laser, the first-order Raman Stokes laser output with a wavelength tunable range greater than 150nm can be theoretically obtained. This makes up for the lack of wavelength range that rare earth-doped laser light sources cannot achieve, and solves the problems of Raman laser pulse width, repetition frequency and wavelength tunability in this band, greatly expanding the application range of this type of light source.

[0044] It should be noted that, for the convenience of description, the aforementioned method embodiments are all described as a series of action combinations, but those skilled in the art should be aware that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0045] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0046] The above is a description of a tunable Raman fiber laser provided by the present invention. For those skilled in the art, according to the concept of the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A tunable Raman fiber laser, characterized in that: include: Raman laser pump source, used to generate Raman laser pump light with tunable pulse width, repetition frequency and wavelength; A Raman optical fiber optically coupled to the Raman laser pump source, used to provide Raman gain and output Raman signal light; A broadband total reflection mirror, optically coupled to the Raman optical fiber, for providing high feedback for the Raman signal light; A first wavelength division multiplexer, whose pump end, signal end and common end are respectively coupled with the Raman laser pump source, the broadband total reflection mirror and the Raman optical fiber, and is used for coupling the pump light wavelength generated by the Raman laser pump source with the Raman signal light wavelength; The Raman laser pump source comprises: a current modulated semiconductor laser, used to generate a first pump light with tunable pulse width and repetition frequency; a gain modulated laser optically coupled to the current modulated semiconductor laser, used to generate a Raman laser pump light with tunable wavelength, wherein the gain modulated laser is a ring cavity structure.

2. The tunable Raman fiber laser according to claim 1, characterized in that: Also includes: The first optical isolator optically coupled to the Raman optical fiber is used to prevent subsequent light reflection, and its output end serves as the output end of the Raman signal light.

3. The tunable Raman fiber laser according to claim 2, characterized in that: It also includes: an optical fiber mode field adapter, two ends of which are optically coupled to the common end of the first wavelength division multiplexer and the Raman optical fiber respectively.

4. The tunable Raman fiber laser according to claim 1, characterized in that: The gain modulated laser comprises: a second optical isolator optically coupled to the current modulated semiconductor laser; a first optical fiber amplifier optically coupled to the second optical isolator; a second wavelength division multiplexer optically coupled to the first optical fiber amplifier; a signal optical isolator optically coupled to the signal end of the second wavelength division multiplexer; a tunable filter optically coupled to the signal optical isolator; a laser gain medium optically coupled to a common end of the second wavelength division multiplexer; The optical fiber coupler optically coupled to the laser gain medium is used to output a part of the wavelength-tunable Raman laser pump light, while the other part continues to oscillate in the ring cavity.

5. The tunable Raman fiber laser according to claim 4, characterized in that: The gain modulated laser further comprises: The second optical fiber amplifier is coupled to the Raman laser pump light and is used to amplify the light output by the gain modulated laser and then input the light into the Raman optical fiber.

6. The tunable Raman fiber laser according to claim 5, characterized in that: At least two of the second optical fiber amplifiers are cascaded to amplify the Raman laser pumping light signal.

7. The tunable Raman fiber laser according to claim 4, characterized in that: The laser gain medium is rare earth doped optical fiber.

8. The tunable Raman fiber laser according to claim 7, characterized in that: The rare earth doped optical fiber is doped with ytterbium, erbium, thulium and holmium.

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