Nonlinear amplification loop mirror linear cavity mode-locked fiber laser

Abstract

The utility model discloses a nonlinear amplification loop mirror linear cavity mode-locked fiber laser. Comprising a first high-reflection mirror, a first wavelength division multiplexing collimator, a second wavelength division multiplexing collimator and a second high-reflection mirror, wherein the first high-reflection mirror, the first wavelength division multiplexing collimator and the second wavelength division multiplexing collimator are sequentially and linearly arranged and jointly form a resonant cavity; a transmission end of the first wavelength division multiplexing collimator is arranged opposite to the first high-reflection mirror; the second wavelength division multiplexing collimator is arranged at the transmission end of the first wavelength division multiplexing collimator, the second high reflection mirror is arranged opposite to the transmission end of the second wavelength division multiplexing collimator, the 1 / 2 wave plate and the polarization splitting prism are sequentially arranged between the second wavelength division multiplexing collimator and the second high reflection mirror, and the gain optical fiber is a non-polarization-maintaining gain optical fiber; and the pumping source is connected with the tail end of the second wavelength division multiplexing collimator. The filter has the advantages of long cavity length, small volume, capability of providing high repetition frequency output and the like.

Description

Technical Field

[0001] This utility model relates to the field of fiber laser technology, and in particular to a nonlinear amplifying ring mirror linear cavity mode-locked fiber laser. Background Technology

[0002] The rapidly growing industrial high-end micromachining market in recent years has led to a sustained increase in demand for high-end picosecond and femtosecond lasers. These fields, primarily industry and scientific research, are increasingly demanding higher repetition rates, smaller sizes, and lower costs for ultrafast laser high-repetition-rate seed sources.

[0003] Chinese patent CN214589674U discloses a phase-biased nonlinear polarization rotation mode-locked fiber laser, comprising a pump source and, sequentially arranged in the optical path to form a laser resonant cavity, a first high-reflectivity mirror, a birefringent crystal, a Faraday rotator, a first collimator, a second collimator, a half-wave plate, a polarization beam splitter, and a second high-reflectivity mirror. The first and second collimators are connected via a polarization-maintaining gain fiber. This phase-biased linear fiber laser has a large number of optical components arranged in the optical path of its laser resonant cavity, resulting in a long cavity length. This not only makes it difficult to increase the repetition frequency of the laser but also makes the laser larger in size, hindering its integration into other systems and affecting its practical application. Utility Model Content

[0004] This invention aims to solve at least one of the technical problems existing in the prior art by proposing a nonlinear amplifying ring mirror linear cavity mode-locked fiber laser, which features short cavity length, small size and the ability to provide high repetition rate output.

[0005] This invention proposes a nonlinear amplifying ring mirror linear cavity mode-locked fiber laser, comprising:

[0006] The resonant cavity consists of a first high-reflectivity mirror arranged linearly in sequence, a first wavelength division multiplexing collimator with its transmission end opposite to the first high-reflectivity mirror, a second wavelength division multiplexing collimator connected to the first wavelength division multiplexing collimator via a gain fiber, a second high-reflectivity mirror positioned opposite to the transmission end of the second wavelength division multiplexing collimator, a half-wave plate and a polarization beam splitter sequentially positioned between the second wavelength division multiplexing collimator and the second high-reflectivity mirror, with the gain fiber being a non-polarization-maintaining gain fiber.

[0007] A pump source connected to the tail end of the second wave division multiplexing collimator;

[0008] After the pump light output from the pump source is coupled into the resonant cavity, it forms random small pulses when the fiber laser oscillates. The small pulses start from the polarization beam splitter and are projected onto the fast and slow axes of the half-wave plate by rotating the half-wave plate, so that the small pulses are split into two orthogonal polarized beams.

[0009] Two orthogonally polarized beams enter a non-polarization-maintaining gain fiber and accumulate a nonlinear phase shift difference. After being reflected by the first high-reflectivity mirror, they return to the non-polarization-maintaining gain fiber and accumulate a nonlinear phase shift again. Then, they are re-injected onto a half-wave plate by the second wavelength division multiplexing collimator. Interference and mode locking occur in the polarization beam splitter to form two orthogonal pulse beams. One of the orthogonal pulse beams is reflected back into the resonant cavity by the second high-reflectivity mirror, and the other orthogonal pulse beam is used as the output of the fiber laser.

[0010] In some preferred embodiments, the first wavelength division multiplexing collimator and the second wavelength division multiplexing collimator have the same structure, both including a wavelength division multiplexer and a collimator. The collimator is welded to the transmission end of the wavelength division multiplexer, and the collimator and the transmission end of the wavelength division multiplexer are connected by optical fiber to form an integrated structure.

[0011] In some preferred embodiments, the pump source is a 976nm single-mode pump, the first and second wavelength division multiplexing collimators are both coated with a 1550nm anti-reflection film, the front and rear opposing surfaces of the half-wave plate are both coated with a 1550nm anti-reflection film, the transmission-reflection ratio of the polarizing beam splitter is 50:50, and the first and second high-reflection mirrors are both coated with a 1550nm total reflection film.

[0012] In some preferred embodiments, a dispersive element is also provided between the polarizing beam splitter and the high-reflectivity mirror to provide dispersion compensation.

[0013] In some preferred embodiments, the dispersive elements are grating pairs or prism pairs.

[0014] In some preferred embodiments, the pump source is a 976nm single-mode pump, the first and second wavelength division multiplexing collimators are both coated with a 1030nm anti-reflection film, the front and rear opposing surfaces of the half-wave plate are both coated with a 1030nm anti-reflection film, the transmission-reflection ratio of the polarizing beam splitter is 50:50, the grating pair uses a 1600-line transmission grating to compensate for dispersion at 1030nm, and the first and second high-reflection mirrors are both coated with a 1030nm total reflection film.

[0015] Compared with the prior art, the fiber laser disclosed in this utility model has the main characteristics of short cavity length, small size and ability to provide higher repetition rate output:

[0016] 1. This invention reduces the number of optical components used in fiber lasers, especially the use of Faraday rotators and 1 / 8 waveplates. The reduced number of optical components allows for a shorter cavity length in the fiber laser, which is beneficial for increasing the repetition rate output of the fiber laser. This also reduces the size of the laser, making it easier to integrate into other systems, which meets the future laser industry's demand for low-cost, small-sized, high-repetition-rate mode-locked fiber lasers.

[0017] 2. The gain fiber adopts non-polarization-maintaining gain fiber. Taking advantage of the fact that there is no fast axis and slow axis in non-polarization-maintaining gain fiber (or traditional fiber), a loop equivalent to a nonlinear amplifying ring mirror is formed, thereby achieving the effect of an artificial saturable absorber. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the first embodiment of the laser proposed in this utility model.

[0019] Figure 2 This is a schematic diagram of the structure of the second embodiment of the laser proposed in this utility model. Detailed Implementation

[0020] To further illustrate the technical means and effects adopted by this application to achieve its intended purpose, the specific implementation methods, structures, features, and effects according to this application are described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0021] This utility model discloses a nonlinear amplifying ring mirror linear cavity mode-locked fiber laser (hereinafter referred to as "fiber laser"), which has the advantages of short cavity length, small size and the ability to provide higher repetition rate output, and meets the actual needs of the laser industry for low cost, small size and high repetition rate mode-locked fiber laser. Example

[0022] like Figure 1 As shown, the fiber laser disclosed in this embodiment specifically includes: a first high-reflectivity mirror 1a arranged linearly in sequence to form a resonant cavity; a first wavelength division multiplexing collimator 2a with its transmission end opposite to the first high-reflectivity mirror 1a; a second wavelength division multiplexing collimator 2b connected to the first wavelength division multiplexing collimator 2a via a gain fiber 3; a second high-reflectivity mirror 1b arranged opposite to the transmission end of the second wavelength division multiplexing collimator 2b; a half-wave plate 5 and a polarization beam splitter 6 arranged sequentially between the second wavelength division multiplexing collimator 2b and the second high-reflectivity mirror 1b; and a pump source 4 connected to the tail end of the second wavelength division multiplexing collimator 2b; wherein the gain fiber 3 is a non-polarization-maintaining gain fiber (or a conventional fiber).

[0023] Therefore, the resonant cavity of the fiber laser in this embodiment is a linear cavity. The cavity length (or simply "cavity") refers to the length of the cavity formed by the sequential arrangement of optical elements along the optical path. Specifically, it is the sum of the spatial cavity length between the first high-reflectivity mirror 1a and the first wavelength division multiplexing collimator 2a, the spatial cavity length between the second high-reflectivity mirror 1b and the second wavelength division multiplexing collimator 2b, and the length of the gain fiber 3. Therefore, having fewer optical elements along the optical path is beneficial for reducing the cavity length of the fiber laser, thus enabling a miniaturized design of the fiber laser.

[0024] The first high-reflectivity mirror 1a, the first wavelength division multiplexing collimator 2a, the gain fiber 3, the second wavelength division multiplexing collimator 2b, the half-wave plate 5, and the polarization beam splitter 6 constitute an equivalent nonlinear amplifying ring mirror (NALM) structure.

[0025] Compared to the existing patent CN214589674U, this invention reduces the number of optical components used in the fiber laser, specifically the Faraday rotator and 1 / 8 waveplate. Fewer optical components result in a shorter cavity length and smaller overall size, making it easier to integrate into other systems. This meets the future laser industry's demand for low-cost, small-sized, high-repetition-rate mode-locked fiber lasers. Furthermore, the gain fiber 3 is a non-polarization-maintaining gain fiber. Utilizing the absence of fast and slow axes in non-polarization-maintaining gain fibers (or traditional fibers), a loop equivalent to a nonlinear amplifying ring mirror is formed, achieving the effect of an artificial saturable absorber. Therefore, the fiber laser disclosed in this invention features a short cavity length, small size, and the ability to provide a higher repetition rate output.

[0026] The first wavelength division multiplexing collimator 2a and the second wavelength division multiplexing collimator 2b have the same structure, both including a wavelength division multiplexer and a collimator. The collimator is welded to the transmission end of the wavelength division multiplexer, and the collimator and the transmission end of the wavelength division multiplexer are connected by a short optical fiber to form an integrated structure, which is beneficial to the high repetition rate output of the fiber laser.

[0027] The common end of the first wavelength division multiplexing collimator 2a and the common end of the second wavelength division multiplexing collimator 2b are connected through the gain fiber 3. Therefore, the cavity length of the fiber laser can be adjusted by adjusting the length of the gain fiber 3, thereby achieving the effect of controlling the repetition rate.

[0028] The tail end of the first wavelength division multiplexing collimator 2a is left unconnected and not linked to any other devices. The tail end of the second wavelength division multiplexing collimator 2b is connected to pump source 4. The pump light generated by pump source 4 is coupled into the resonant cavity of the fiber laser through the second wavelength division multiplexing collimator 2b. The pump power of pump source 4 is greater than the oscillation threshold of the fiber laser to make the fiber laser oscillate. In addition, appropriately increasing the output power of pump source 4 can facilitate subsequent optical path calibration and coupling, but the pump power should not be increased above the damage threshold of the fiber laser.

[0029] The working principle of a fiber laser is described as follows: Pump light output from pump source 4 is coupled into the resonant cavity of the fiber laser, where it oscillates to form random small pulses. These small pulses originate from polarization beam splitter 6, pass through half-wave plate 5, and are projected onto the fast and slow axes of half-wave plate 5 by rotating it. The small pulses are then split into two orthogonal polarized beams, the intensity ratio of which is determined by the angle between the initial incident pulse polarization direction and the fast axis of half-wave plate 5. Subsequently, the two orthogonal polarized beams enter gain fiber 3, accumulating the first nonlinear phase shift. The difference is related to the intensity difference between the orthogonal pulses and the length of the gain fiber 3. After the first nonlinear phase shift, the light returns to the gain fiber 3 after being reflected by the first high-reflectivity mirror 1a, where the second nonlinear phase shift accumulates again. The light is then re-injected into the half-wave plate 5 by the second wavelength division multiplexing collimator 2b, and then interference mode-locking occurs in the polarization beam splitter 6 to form two orthogonal pulse beams. One of the orthogonal pulse beams is used as the output end of the fiber laser to output the laser signal, and the other orthogonal pulse beam is output towards the second high-reflectivity mirror 1b and then reflected back into the resonant cavity by the second high-reflectivity mirror 1b.

[0030] In this design, the half-wave plate 5 acts as a 1x2 beam splitter with an artificially controllable splitting ratio, allowing a pair of orthogonal beams of different intensities to accumulate a nonlinear phase shift difference in the gain fiber 3. This difference is then reflected back into the gain fiber by the first high-reflectivity mirror 1a and the second high-reflectivity mirror 1b, forming an equivalent loop. Finally, the beams interfere in the polarization beam splitter 6, causing a change in the reflectivity curve, thus acting as an artificial saturable absorber in the mode-locked fiber laser.

[0031] Furthermore, the reflectivity of the pulse is related to the nonlinear phase shift difference caused by the intensity difference between the two orthogonal pulse pairs: reflectivity is a function of the nonlinear phase shift difference between the two orthogonal pulses; the larger the introduced nonlinear phase shift difference, the greater the reflectivity; conversely, the smaller the introduced nonlinear phase shift difference, the smaller the reflectivity. Specifically, the central part of the pulse is stronger, resulting in a larger nonlinear phase difference during oscillation, thus leading to higher reflectivity. This makes it easier for the pulse to oscillate, thereby achieving mode locking in the laser and generating an ultrashort pulse output.

[0032] In this embodiment, the pump source 1 is a 976nm single-mode pump, and the collimators included in the first wavelength division multiplexing collimator 2a and the second wavelength division multiplexing collimator 2b are both coated with a 1550nm anti-reflection film. The front and rear opposing surfaces of the half-wave plate 5 are both coated with a 1550nm anti-reflection film. The transmission-reflection ratio of the polarizing beam splitter 6 is 50:50, and the first high-reflection mirror 2a and the second high-reflection mirror 2b are both coated with a 1550nm total reflection film. Example

[0033] See Figure 2 As shown, with Figure 1 Compared to the first embodiment, the laser in the second embodiment further includes a dispersive element 7, which is disposed between the polarizing beam splitter 6 and the high-reflectivity mirror 1 to provide dispersion compensation. For example, the dispersive element is a grating pair or a prism pair.

[0034] In this embodiment, the pump source 1 is a 976nm single-mode pump, the collimators included in the first wavelength division multiplexing collimator 2a and the second wavelength division multiplexing collimator 2b are both coated with a 1030nm anti-reflection film, the front and rear opposing surfaces of the half-wave plate 5 are both coated with a 1030nm anti-reflection film, the transmission-reflection ratio of the polarizing beam splitter 6 is 50:50, the grating pair 7 adopts a 1600-line transmission grating to compensate for the dispersion at 1030nm, and the first high-reflection mirror 2a and the second high-reflection mirror 2b are both coated with a 1030nm total reflection film.

[0035] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A nonlinear amplifying ring mirror linear cavity mode-locked fiber laser, characterized in that, include: The resonant cavity consists of a first high-reflectivity mirror arranged linearly in sequence, a first wavelength division multiplexing collimator with its transmission end opposite to the first high-reflectivity mirror, a second wavelength division multiplexing collimator connected to the first wavelength division multiplexing collimator via a gain fiber, a second high-reflectivity mirror positioned opposite to the transmission end of the second wavelength division multiplexing collimator, a half-wave plate and a polarization beam splitter sequentially positioned between the second wavelength division multiplexing collimator and the second high-reflectivity mirror, with the gain fiber being a non-polarization-maintaining gain fiber. A pump source connected to the tail end of the second wave division multiplexing collimator; After the pump light output from the pump source is coupled into the resonant cavity, it forms random small pulses when the fiber laser oscillates. The small pulses start from the polarization beam splitter and are projected onto the fast and slow axes of the half-wave plate by rotating the half-wave plate, so that the small pulses are split into two orthogonal polarized beams. Two orthogonally polarized beams enter a non-polarization-maintaining gain fiber and accumulate a nonlinear phase shift difference. After being reflected by the first high-reflectivity mirror, they return to the non-polarization-maintaining gain fiber and accumulate a nonlinear phase shift again. Then, they are re-injected onto a half-wave plate by the second wavelength division multiplexing collimator. Interference and mode locking occur in the polarization beam splitter to form two orthogonal pulse beams. One of the orthogonal pulse beams is reflected back into the resonant cavity by the second high-reflectivity mirror, and the other orthogonal pulse beam is used as the output of the fiber laser.

2. The nonlinear amplifying ring mirror linear cavity mode-locked fiber laser according to claim 1, characterized in that, The first and second wavelength division multiplexing collimators have the same structure, both including a wavelength division multiplexer and a collimator. The collimator is welded to the transmission end of the wavelength division multiplexer, and the collimator and the transmission end of the wavelength division multiplexer are connected by optical fiber to form an integrated structure.

3. The nonlinear amplifying ring mirror linear cavity mode-locked fiber laser according to claim 1, characterized in that, The pump source is a 976nm single-mode pump. Both the first and second wavelength division multiplexing collimators are coated with a 1550nm anti-reflection film. Both the front and rear surfaces of the half-wave plate are coated with a 1550nm anti-reflection film. The transmission-reflection ratio of the polarizing beam splitter is 50:

50. Both the first and second high-reflection mirrors are coated with a 1550nm total reflection film.

4. The nonlinear amplifying annular mirror linear cavity mode-locked fiber laser according to claim 1 or 2, characterized in that, A dispersive element is also provided between the polarizing beam splitter and the high-reflectivity mirror to provide dispersion compensation.

5. The nonlinear amplifying ring mirror linear cavity mode-locked fiber laser according to claim 4, characterized in that, The dispersive elements are grating pairs or prism pairs.

6. The nonlinear amplifying ring mirror linear cavity mode-locked fiber laser according to claim 5, characterized in that, The pump source is a 976nm single-mode pump. Both the first and second wavelength division multiplexing collimators are coated with a 1030nm anti-reflection film. Both the front and rear opposing surfaces of the half-wave plate are coated with a 1030nm anti-reflection film. The transmission-reflection ratio of the polarizing beam splitter is 50:

50. The grating pair uses a 1600-line transmission grating to compensate for dispersion at 1030nm. Both the first and second high-reflection mirrors are coated with a 1030nm total reflection film.

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