Ring cavity fiber laser

Abstract

The utility model discloses an annular cavity fiber laser which comprises a pumping fiber laser and an annular cavity. The first end and the third end of the first circulator are connected into the ring, the second end of the first circulator is connected with the first fiber grating, the first input end and the first output end of the first coupler are connected into the ring, the second input end and the second output end of the first coupler are connected into the ring, and the input end and the first output end of the second coupler are connected into the ring. The second output end of the second coupler is the output end of the annular cavity; the pumping fiber laser emits first pumping light with the wave band of 1.5 micrometers, the first pumping light is input into the annular cavity through the pumping end of the wavelength division multiplexer, and the annular cavity absorbs the first pumping light and outputs single-frequency laser with the wave band of 1.6 micrometers. According to the ring cavity fiber laser provided by the utility model, the 1.5 [mu] m fiber laser is used for pumping, and the output of 1.6 [mu] m waveband single-frequency laser is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of optical fiber lasers, in particular to a ring cavity optical fiber laser. Background Art

[0002] Single-frequency narrow-linewidth lasers in the 1.5-1.6μm band have been proven to be widely used in applications such as industrial gas detection, free-space optical communications, and coherent Doppler wind lidar systems due to their advantages in terms of eye safety and high atmospheric transmission transmittance. In addition, there is an urgent need to expand the output wavelength of single-frequency laser sources from the traditional C-band (1530-1565nm) to the L-band (1565-1625nm), especially the 1.6μm band, to meet the needs of coherent communications. Taking the 1620nm laser as an example, in addition to communication applications, it can also be frequency-multiplied to 810nm for use in laser medical fields such as skin treatment, beauty, and ophthalmic surgery.

[0003] At present, most 1.6μm single-frequency laser solutions mainly rely on bulky solid-state lasers. Although fiber lasers have outstanding advantages in high conversion efficiency, high beam quality and compact structure, the 1.6μm band is located in Erbium-doped Optical Fiber (EDF). 3+ The emission edge of the optical fiber has a relatively low gain, making it difficult to achieve single-frequency narrow-linewidth laser output. To this end, a relatively long EDF must be used to provide sufficient optical gain to achieve laser oscillation, making it a major challenge to achieve 1.6μm single-frequency laser output using an ultrashort linear cavity, because the length of the gain fiber is usually limited to a few centimeters or even a few millimeters, in order to shorten the cavity length and increase the spacing between two adjacent longitudinal modes (Free Spectral Range, FSR) to achieve single longitudinal mode operation. In other words, the gain fiber must have an extremely high gain coefficient. In 2016, someone used a 16mm long Er in an ultrashort linear cavity. 3+ / Yb 3+ Co-doped phosphate fibers have successfully achieved a single-frequency laser at 1603nm, with a linewidth of less than 1.9kHz and a power output of more than 20mW. However, these soft glass fibers have poor mechanical strength, are sensitive to the environment, and are difficult to weld, which inevitably affects their long-term stability in practical applications.

[0004] Compared with the strict requirements on the gain fiber length in ultrashort linear cavity single-frequency lasers, ring cavities can also achieve single longitudinal mode operation, and relatively long gain fibers can be achieved by introducing additional narrowband filters in the cavity, such as fiber filters, composite cavity filters, and saturable absorbers. For ring cavity lasers, the use of longer EDFs can suppress short-wave C-band amplified spontaneous emission (ASE) and provide sufficient gain for the L-band (especially wavelengths above 1600nm) by reducing the population inversion along the fiber transmission direction.

[0005] However, the use of long low-gain optical fibers may hinder subsequent power increases. Based on a 5.2-meter-long commercial silicate EDF, a 1612.19nm, sub-kHz linewidth, and wavelength-tunable single-frequency laser has been realized, but the output power is only at the level of hundreds of microwatts, and the optical signal-to-noise ratio at 1612.19nm is only 40dB. At the same time, due to the long length of the ring cavity and the small interval between two adjacent longitudinal modes, mode hopping or multi-longitudinal mode operation is particularly prone to occur. Therefore, in order to balance the trade-off between output power and single-frequency stability, it is necessary to select erbium-doped fiber and ring cavity structure with appropriate gain. Utility Model Content

[0006] The utility model provides a ring cavity fiber laser, which uses commercial erbium-doped fiber as a gain medium. Since the absorption coefficient of the erbium-doped fiber at 1.5μm is much greater than that of 0.9μm, in order to obtain laser oscillation at 1.6μm, it is creatively proposed to use a 1.5μm fiber laser for pumping, thereby improving the light conversion efficiency. By inserting a coupler into the ring cavity to form a fiber ring, the etalon effect is utilized so that only the longitudinal modes that simultaneously meet two FSR conditions can oscillate, thereby realizing the output of 1.6μm single-frequency laser. This 1.6μm single-frequency narrow-linewidth laser fully meets the application requirements in the fields of industrial gas detection and coherent communication.

[0007] According to a first aspect of the utility model, a ring cavity fiber laser is provided, comprising: a pump fiber laser and a ring cavity;

[0008] The ring cavity comprises a wavelength division multiplexer, an erbium-doped optical fiber, a first circulator, a first coupler and a second coupler connected to form a ring and a first optical fiber grating, the first end and the third end of the first circulator are connected to the ring, the second end of the first circulator is connected to the first optical fiber grating, the first input end and the first output end of the first coupler are connected to the ring, the second input end and the second output end of the first coupler are connected, the input end and the first output end of the second coupler are connected to the ring, and the second output end of the second coupler is the output end of the ring cavity;

[0009] The pump fiber laser emits a first pump light in the 1.5 μm band, the first pump light is input into the ring cavity from the pump end of the wavelength division multiplexer, the ring cavity absorbs the first pump light and outputs a single-frequency laser in the 1.6 μm band.

[0010] Optionally, the pump fiber laser comprises a linear cavity fiber laser.

[0011] Optionally, the linear cavity fiber laser comprises a light source assembly, a pump combiner, a second fiber Bragg grating, an erbium-ytterbium co-doped fiber, a third fiber Bragg grating and a second circulator, and the second fiber Bragg grating, the erbium-ytterbium co-doped fiber and the third fiber Bragg grating are sequentially connected to form a linear cavity;

[0012] The light source assembly emits a second pump light in the 0.9 μm band, the second pump light is input into the linear cavity from the input end of the pump combiner, the linear cavity outputs the first pump light in the 1.5 μm band to the first end of the second circulator, and is output from the second end of the second circulator.

[0013] Optionally, the linear cavity fiber laser further comprises a pump stripper;

[0014] The pump stripper is located between the second fiber grating and the third fiber grating.

[0015] Optionally, the reflectivity of the second fiber grating is smaller than the reflectivity of the third fiber grating, the first end of the third fiber grating is located in the linear cavity, and the end face of the second end of the third fiber grating is inclined at an angle of 8°.

[0016] Optionally, the annular cavity also includes an isolator.

[0017] Optionally, the second end of the first circulator is connected to the first end of the first fiber grating, and the end face of the second end of the first fiber grating is inclined at an angle of 8°.

[0018] Optionally, the pump fiber laser emits a first pump light of 1532 nm, and the ring cavity fiber laser emits a single-frequency laser of 1620 nm wavelength.

[0019] Optionally, the erbium-ytterbium co-doped optical fiber is a double-clad optical fiber.

[0020] Optionally, the light source assembly includes at least one 20W laser diode with a wavelength of 940nm.

[0021] The utility model discloses a ring cavity fiber laser, comprising: a pump fiber laser and a ring cavity; the ring cavity comprises a wavelength division multiplexer, an erbium-doped fiber, a first circulator, a first coupler and a second coupler connected to form a ring and a first fiber grating, the first end and the third end of the first circulator are connected to the ring, the second end of the first circulator is connected to the first fiber grating, the first input end and the first output end of the first coupler are connected to the ring, the second input end and the second output end of the first coupler are connected, the input end and the first output end of the second coupler are connected to the ring, and the second output end of the second coupler is the output end of the ring cavity; the pump fiber laser emits a first pump light in a 1.5μm band, the first pump light is input into the ring cavity from the pump end of the wavelength division multiplexer, the ring cavity absorbs the first pump light, and outputs a single-frequency laser in a 1.6μm band. The ring cavity fiber laser provided by the utility model uses commercial erbium-doped fiber as the gain medium. Since the absorption coefficient of the erbium-doped fiber at 1.5μm is much greater than that at 0.8μm, in order to obtain laser oscillation at 1.6μm, it is creatively proposed to use a 1.5μm fiber laser for pumping, thereby improving the light conversion efficiency. By inserting a coupler into the ring cavity to form a fiber ring and utilizing the standard tool effect, only the longitudinal modes that simultaneously meet two FSR conditions can oscillate, thereby realizing the output of 1.6μm single-frequency laser. This 1.6μm single-frequency narrow-linewidth laser fully meets the application requirements in the fields of industrial gas detection and coherent communication.

[0022] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present utility model, nor are they intended to limit the scope of the present utility model. Other features of the present utility model will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a schematic diagram of the structure of a ring cavity fiber laser provided by an embodiment of the utility model;

[0025] Figure 2 This is a schematic diagram of another structure of a ring cavity fiber laser provided by an embodiment of the utility model;

[0026] Figure 3 It is a structural schematic diagram of a pump fiber laser in a ring cavity fiber laser provided by an embodiment of the utility model;

[0027] Figure 4 This is a schematic diagram of another structure of a ring cavity fiber laser provided by an embodiment of the utility model;

[0028] Figure 5 This is a schematic diagram of the single longitudinal mode operation of a ring cavity fiber laser provided by an embodiment of the utility model;

[0029] Figure 6 This is an output spectrum diagram of a ring cavity fiber laser provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the solution of the utility model, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is only a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0031] It should be noted that the terms "first", "second", etc. in the specification and claims of the utility model and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the utility model described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0032] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0033] Figure 1 This is a schematic diagram of the structure of a ring cavity fiber laser provided by the embodiment of the utility model, referring to Figure 1The ring cavity fiber laser comprises a pump fiber laser 1 and a ring cavity 2; the ring cavity 2 comprises a wavelength division multiplexer 3, an erbium-doped fiber 4, a first circulator 5, a first coupler 6 and a second coupler 7 connected to form a ring and a first fiber grating 8, the first end a and the third end d of the first circulator 5 are connected to the ring, the second end b of the first circulator 5 is connected to the first fiber grating 8, the first input end and the first output end of the first coupler 6 are connected to the ring, the second input end and the second output end of the first coupler 6 are connected, the input end and the first output end of the second coupler 7 are connected to the ring, and the second output end Output of the second coupler 7 is the output end of the ring cavity 2;

[0034] The pump fiber laser 1 emits a first pump light in the 1.5 μm band. The first pump light is input into the ring cavity 2 from the pump end of the wavelength division multiplexer 3. The ring cavity 2 absorbs the first pump light and outputs a single-frequency laser in the 1.6 μm band.

[0035] Specifically, the pump fiber laser is used to output the first pump light in the 1.5 μm band; the wavelength division multiplexer 3 is a device that can simultaneously transmit multiple optical signals of different wavelengths on the same optical fiber, and can combine light of different wavelengths into a unified optical fiber, thereby transmitting the first pump light to the erbium-doped optical fiber 4; the first circulator 5 has three ports, namely ports a, b and d, and its main function is to ensure that the pump light can be transmitted in sequence and not transmitted in reverse; the second input end and the second output end of the first coupler 6 are connected end to end to form a ring, the first fiber grating 8 is a reflective grating, and the ring formed by the first fiber grating 8 and the first coupler 6 can act as a filter, and the pump fiber laser 1 emits the first pump light in the 1.5 μm band The first pump light is transmitted to the pump end of the wavelength division multiplexer 3, and then transmitted to the ring cavity 2 by the wavelength division multiplexer 3. The first pump light is absorbed by the erbium-doped fiber 4 to generate 1.6μm band laser. The 1.6μm band laser enters the first circulator 5 through the a port of the first circulator 5, and is transmitted to the first fiber grating 8 from the b port of the first circulator 5. The optical fiber reflected by the first fiber grating 8 enters the first circulator 5 from the b port of the first circulator 5 again, and is emitted from the d port of the first circulator 5 to the first input end of the first coupler 6 and emitted from the first output end to the input end of the second coupler 7. A part of the light circulates in the ring cavity, and after stabilization, a single-frequency laser of 1.6μm band is output from the second output end of the second coupler 7.

[0036] Optional, Figure 2 This is a schematic diagram of the structure of a ring cavity fiber laser provided by the embodiment of the utility model, referring to Figure 2 The optical device in the ring cavity fiber laser provided by the embodiment of the utility model can also be as follows Figure 2The arrangement is performed in the manner shown, that is, the ring cavity fiber laser provided in the embodiment of the utility model can adaptively adjust the arrangement sequence of the optical devices according to the requirements, and the utility model does not impose any limitation on this.

[0037] The ring cavity fiber laser provided by the embodiment of the utility model uses erbium-doped fiber as the gain medium and is pumped by a 1.5μm pump fiber laser, thereby improving the light conversion efficiency. A fiber ring is formed by inserting a coupler into the ring cavity and utilizing the etalon effect so that only the longitudinal modes that simultaneously meet two FSR conditions can oscillate, thereby achieving the output of 1.6μm single-frequency laser. This 1.6μm single-frequency narrow-linewidth laser fully meets the application requirements in the fields of industrial gas detection and coherent communication.

[0038] Figure 3 This is a schematic diagram of the structure of a pump fiber laser in a ring cavity fiber laser provided by an embodiment of the utility model, with reference to Figure 3 ,

[0039] Optionally, the pump fiber laser 1 includes a linear cavity fiber laser 11 .

[0040] Optionally, the linear cavity fiber laser 11 includes a light source assembly 111, a pump combiner 112, a second fiber Bragg grating 113, an erbium-ytterbium co-doped fiber 114, a third fiber Bragg grating 115 and a second circulator 116, and the second fiber Bragg grating 113, the erbium-ytterbium co-doped fiber 114 and the third fiber Bragg grating 115 are sequentially connected to form a linear cavity; the light source assembly emits a second pump light in the 0.9 μm band, the second pump light is input into the linear cavity from the input end of the pump combiner 112, and the linear cavity outputs a first pump light in the 1.5 μm band to the first end x of the second circulator 116, and output from the second end y of the second circulator 116.

[0041] For reference Figure 1 Or 2, specifically, the function of the pump combiner 112 is to combine at least one pump light into one optical fiber for output, so as to increase the pump power; a linear cavity fiber laser composed of a light source component 111, a pump combiner 112, a second fiber grating 113, an erbium-ytterbium co-doped fiber 114 and a third fiber grating 115; the formed linear cavity absorbs and converts the second pump light of 0.9 μm band emitted by the light source component 111 to form a first pump light of 1.5 μm band and transmits it to the first port x of the second circulator 116, and outputs it from the second end y of the second circulator 116 to the wavelength division multiplexer 3, and the reverse return light generated by the ring cavity 2 will be output to the outside through the third end z of the second circulator 116, thereby ensuring the safe operation of the pump fiber laser 1.

[0042] Optional, continue to refer to Figure 3The linear cavity fiber laser 11 further includes a pump stripper 117 ; the pump stripper 117 is located between the second fiber grating 113 and the third fiber grating 115 .

[0043] The pump stripper 117 is mainly used to remove the remaining pump light after energy exchange to ensure the stable operation of the pump fiber laser.

[0044] Optionally, the reflectivity of the second fiber grating 113 is smaller than the reflectivity of the third fiber grating 115 , the first end of the third fiber grating 115 is located in the linear cavity, and the end face of the second end of the third fiber grating 115 is inclined at an angle of 8°.

[0045] Specifically, the end face of the second end of the third fiber grating 115 is cut at an angle of 8° to prevent reflection.

[0046] Figure 4 is a schematic diagram of another ring cavity fiber laser structure provided by the embodiment of the utility model; Figure 4 Optionally, the annular cavity 2 also includes an isolator 9.

[0047] The isolator 9 is an optical device that realizes unidirectional transmission of light, and can prevent the existence of reversely transmitted reflected light in the ring cavity 2, thereby avoiding damage to the laser.

[0048] Optional, reference Figure 1 or Figure 2 The second end b of the first circulator 5 is connected to the first end of the first fiber grating 8, and the end face of the second end of the first fiber grating 8 is inclined at an angle of 8°.

[0049] Specifically, the end face of the second end of the first fiber grating 8 is cut at an angle of 8° to prevent reflection.

[0050] Optionally, the pump fiber laser 1 emits a first pump light of 1532 nm, and the ring cavity fiber laser emits a single-frequency laser of 1620 nm wavelength.

[0051] Specifically, since the absorption coefficient of EDF at 1532nm is much greater than that at 976nm, in order to obtain laser oscillation at 1620nm, it is creatively proposed to replace the traditional 976nm single-mode semiconductor laser with a 1532nm fiber laser, thereby improving the light conversion efficiency.

[0052] Optionally, the erbium-ytterbium co-doped optical fiber is a double-clad optical fiber.

[0053] Optionally, the light source assembly 111 includes at least one 20 W laser diode with a wavelength of 940 nm.

[0054] Figure 5This is a schematic diagram of the single longitudinal mode operation of a ring cavity fiber laser provided by an embodiment of the utility model; Figure 6 This is an output spectrum diagram of a ring cavity fiber laser provided in an embodiment of the utility model.

[0055] Optionally, the erbium-doped fiber in the ring cavity fiber laser provided in the embodiment of the utility model is a single-mode polarization-maintaining erbium-doped fiber with a length of 3m, a mode field diameter and a numerical aperture of 7.5μm and 0.2 respectively, and an absorption coefficient of 83dB / m at 1530nm.

[0056] Optional, reference Figure 1 The first fiber grating 8 is written using a polarization-maintaining PM1550 optical fiber with a central wavelength of 1620 nm, a reflectivity of 99.9%, and a bandwidth of 0.1 nm.

[0057] Optionally, the first coupler 6 is a 2*2 optical fiber coupler with a coupling ratio of 50:50; the second coupler 7 is a 1*2 optical fiber coupler with a coupling ratio of 20:80.

[0058] The principle of the ring cavity fiber laser provided by the embodiment of the utility model is as follows:

[0059] Since the gain of erbium-doped fiber in the 1.6μm band is very low, a longer gain fiber length is required to start oscillation. However, a longer cavity length is not conducive to the generation of single longitudinal mode output. Therefore, it is creatively proposed to use 1532nm fiber laser pumping to improve the pump absorption intensity and shorten the fiber length. Only 3m of commercial gain fiber is needed to obtain laser output at 1620nm. In order to avoid the standing wave hole burning effect, a circulator and an isolator are inserted in the cavity to form a traveling wave cavity, which is more conducive to the generation of a single longitudinal mode. The optimized device tail fiber length is about 7-8cm, the total cavity length L = 3.95m, FSR = c / nL = 50.6MHz, the bandwidth of the high-reflection grating is 0.1nm (about 11.4GHz), and there are about 225 modes that start oscillation within the grating bandwidth. In order to reduce the oscillation mode, the first coupler is inserted as an auxiliary cavity to play the role of a filter. At the same time, only the mode that meets the oscillation conditions of the main cavity and the auxiliary cavity can start oscillation. The length of the first coupler is 15cm, and the FSR is 1.33GHz. At this time, only 2-3 modes are oscillated within the bandwidth of the high-reflection grating. Due to the mode competition effect in the cavity, only one mode can oscillate in the end. When the 1532nm pump power is 1.3W, the 1620nm single-frequency narrow-linewidth laser output power is 10mW, and the linewidth is 800Hz, which is much greater than the output laser power currently obtained by the same type of laser.

[0060] The ring cavity fiber laser provided by the embodiment of the utility model has the following advantages:

[0061] 1. Reference Figure 6, the output wavelength is 1620nm (L band), the line width is narrow, and it is suitable for a variety of communication applications;

[0062] 2. Using 1532nm fiber laser pumping, the output power is significantly improved;

[0063] 3. Simple and flexible structure, easy to make;

[0064] 4. Small size and easy to carry.

[0065] The above specific implementations do not constitute a limitation on the protection scope of the present utility model. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A ring cavity fiber laser, characterized in that: include: Pumping fiber lasers and ring cavities; The ring cavity comprises a wavelength division multiplexer, an erbium-doped optical fiber, a first circulator, a first coupler and a second coupler connected to form a ring and a first optical fiber grating, the first end and the third end of the first circulator are connected to the ring, the second end of the first circulator is connected to the first optical fiber grating, the first input end and the first output end of the first coupler are connected to the ring, the second input end and the second output end of the first coupler are connected, the input end and the first output end of the second coupler are connected to the ring, and the second output end of the second coupler is the output end of the ring cavity; The pump fiber laser emits a first pump light in the 1.5 μm band, the first pump light is input into the ring cavity from the pump end of the wavelength division multiplexer, the ring cavity absorbs the first pump light and outputs a single-frequency laser in the 1.6 μm band.

2. The ring cavity fiber laser according to claim 1, characterized in that: The pump fiber laser comprises a linear cavity fiber laser.

3. The ring cavity fiber laser according to claim 2, characterized in that: The linear cavity fiber laser comprises a light source assembly, a pump combiner, a second fiber Bragg grating, an erbium-ytterbium co-doped fiber, a third fiber Bragg grating and a second circulator, wherein the second fiber Bragg grating, the erbium-ytterbium co-doped fiber and the third fiber Bragg grating are sequentially connected to form a linear cavity; The light source assembly emits a second pump light in the 0.9 μm band, the second pump light is input into the linear cavity from the input end of the pump combiner, the linear cavity outputs the first pump light in the 1.5 μm band to the first end of the second circulator, and is output from the second end of the second circulator.

4. The ring cavity fiber laser according to claim 3, characterized in that: The linear cavity fiber laser also includes a pump stripper; The pump stripper is located between the second fiber grating and the third fiber grating.

5. The ring cavity fiber laser according to claim 3, characterized in that: The reflectivity of the second fiber grating is smaller than that of the third fiber grating. The first end of the third fiber grating is located in the linear cavity, and the end face of the second end of the third fiber grating is inclined at an angle of 8°.

6. The ring cavity fiber laser according to claim 1, characterized in that: The annular chamber also includes a separator.

7. The ring cavity fiber laser according to claim 1, characterized in that: The second end of the first circulator is connected to the first end of the first fiber grating, and the end face of the second end of the first fiber grating is inclined at an angle of 8°.

8. The ring cavity fiber laser according to claim 1, characterized in that: The pump fiber laser emits a first pump light of 1532 nm, and the ring cavity fiber laser emits a single-frequency laser of 1620 nm wavelength.

9. The ring cavity fiber laser according to claim 3, characterized in that: The erbium-ytterbium co-doped optical fiber is a double-clad optical fiber.

10. The ring cavity fiber laser according to claim 3, characterized in that: The light source assembly includes at least one 20W laser diode with a wavelength of 940nm.

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