Parametrically tunable 9-shaped cavity mode-locked fiber laser based on liquid crystal phase retarder

Abstract

This invention discloses a 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delay device, belonging to the field of mode-locked laser technology. It includes, along the optical path, a mirror, a polarizing beam splitter prism, a liquid crystal phase delay adjustable waveplate, a Faraday rotator, a liquid crystal phase delay adjustable waveplate, and a polarizing beam splitter prism. A fiber optic loop is provided on one side of the polarizing beam splitter prism, comprising, in sequence, a fiber collimator, a gain fiber, a wavelength division multiplexing-splitter mixer, and a fiber collimator prism. The slow axis of the fiber collimator prism's pigtail is aligned horizontally with the polarizing beam splitter prism prism 2; the slow axis of the fiber collimator prism 2's pigtail is aligned vertically with the polarizing beam splitter prism prism 2. A pump semiconductor laser is connected to the pump input of the wavelength division multiplexing-splitter mixer, and an FCAPC jumper is connected to the signal output of the wavelength division multiplexing-splitter mixer. This enables continuous and rapid adjustment of the laser parameters.

Description

Technical Field

[0001] This invention belongs to the field of mode-locked laser technology, specifically relating to a 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delayer. Background Technology

[0002] The Figure-9 mode-locked fiber laser has attracted considerable research attention due to its low noise and excellent self-starting performance, which is crucial for applications such as optical frequency combs and precision measurement. This laser is a core component of the optical frequency comb products of Menlo Systems, a German company that has filed a patent for it (EP 2 637 265 A1).

[0003] As can be seen from this patent, the Figure-9 laser mainly has two architectural schemes: polarization beam combining (PBC) and optical coupler (OC) beam combining (Appl. Phys. B 123(41), 331-340(2017)). In the PBC-based scheme, it has been found that the combination of rotating half-wave plate (HWP) and quarter-wave plate (QWP) can achieve any desired splitting ratio and non-reciprocal phase shift (Opt. Express 28(13), 18946-18968(2020), Opt. Laser Technol. 180, 111573(2025)), which is very important for controlling the mode-locked state of the laser. For example, by rotating waveplates, Duan et al. proposed and demonstrated a method for achieving high pulse energy emission in a self-starting mode-locked F9 fiber laser (Opt. Express 28(22), 33603-33613(2020)); Li et al. explored mode-locking modes in the parameter space of the F9 laser, and these data can provide support for intelligent mode-locking (Opt. Lett. 47(10), 2606-2609(2022), IEEE Photonics Technol. Lett. 35(18), 1018-1021(2023)). In the OC-based scheme, the non-reciprocal phase shift can also be controlled by adjusting the angles of HWP and QWP (Opt. Express 27(10), 14705-14715(2019)). However, adjusting the splitting ratio in this scheme is inconvenient because it requires replacing the optical coupler and re-fusion, making continuous adjustment difficult.

[0004] It is evident that existing technologies adjust laser parameters by mechanically rotating waveplates, which is not conducive to compact packaging and improving response speed, is inconvenient to control, and carries the risk of wear and failure with long-term use.

[0005] To address these issues, this invention proposes a parameter-tunable 9-cavity mode-locked fiber laser based on a liquid crystal phase delayer. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delayer, thus solving the problems in the prior art.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delay includes, in sequence along the optical path: a mirror, a polarization beam splitter prism I, a liquid crystal phase delay tunable waveplate I, a Faraday rotator, a liquid crystal phase delay tunable waveplate II, and a polarization beam splitter prism II; a fiber loop is provided on one side of the polarization beam splitter prism II, and the fiber loop includes, in sequence: a fiber collimator I, a gain fiber, a wavelength division multiplexing-splitter mixer, and a fiber collimator II; the slow axis of the pigtail of the fiber collimator I is aligned horizontally with the polarization beam splitter prism II; the slow axis of the pigtail of the fiber collimator II is aligned vertically with the polarization beam splitter prism II.

[0009] The pump input of the wavelength division multiplexing-splitter is connected to a pump semiconductor laser, and the signal output of the wavelength division multiplexing-splitter is connected to an FCAPC jumper to serve as the output of the entire fiber laser.

[0010] Furthermore, the bit line of the pump semiconductor laser is fused to the pump input of the wavelength division multiplexing-splitter; the signal input of the wavelength division multiplexing-splitter is fused to the slow axis of the gain fiber; the signal output of the wavelength division multiplexing-splitter is fused to the slow axis of the pigtail of the second fiber collimator; and the signal output of the wavelength division multiplexing-splitter is fused to the slow axis of the FCAPC jumper.

[0011] Furthermore, the pigtail of the first fiber collimator is fused with the slow axis of the other end of the gain fiber; the pigtail of the first fiber collimator and the slow axis of the pigtail of the second fiber collimator are aligned with each other.

[0012] Furthermore, the liquid crystal phase delay adjustable waveplate is a full-wave adjustable delay waveplate with a working wavelength of 1550nm or 1030nm, and the fast axis direction makes an angle of 45° with the horizontal plane as an odd multiple.

[0013] Furthermore, the Faraday rotator operates at a wavelength of 1550nm or 1030nm, and rotates at an angle of 45° clockwise or counterclockwise.

[0014] Furthermore, the pigtail of the first optical fiber collimator is a polarization-maintaining fiber, with its slow axis aligned with the horizontal direction; the pigtail of the second optical fiber collimator is a polarization-maintaining fiber, with its slow axis aligned with the vertical direction.

[0015] Furthermore, the gain fiber is a polarization-maintaining erbium-doped or ytterbium-doped single-mode fiber.

[0016] Furthermore, the horizontally polarized light E in The light is transformed into elliptically polarized light by passing through polarizing beam splitter prism one, liquid crystal phase-retardant tunable waveplate one, Faraday rotator, and liquid crystal phase-retardant tunable waveplate two; then it is split into clockwise component E by polarizing beam splitter prism two. cw and counterclockwise component E ccw It enters the fiber optic loop; the beam splitting ratio k is After the clockwise and counterclockwise components complete one round trip in the fiber optic loop, they return along the original path and interfere at a point on the polarization beam splitter, outputting E. out The direction is horizontal.

[0017] Furthermore, the output E out And clockwise component E cw The formula for calculation is:

[0018] E out =M PBC2 M LC2 M FR M LC1 M FL M nps M LC1 M FR M LC2 M PBC2 E in

[0019] E CW =M PBC1 M LC1 M PR M LC2 M PBC2 E in

[0020] In the formula, E CW Indicates the clockwise component; E CCW Indicates the counterclockwise component; E in Indicates the input horizontally polarized light; E out Indicates the horizontally polarized light output; M PBC1 It is the Jones matrix of polarization beam splitter prism one, M LC1 It is the Jones matrix of a liquid crystal phase-delay tunable waveplate, M LC2 It is the Jones matrix of a liquid crystal phase-delay tunable waveplate II, M PBC2 M is the Jones matrix of the second polarization beam splitter prism. FR It is the Jones matrix of the Faraday rotator.

[0021] An asynchronous optical sampling device includes the above-mentioned 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delayer.

[0022] The beneficial effects of this invention are:

[0023] This invention achieves continuous and rapid adjustment of laser parameters by controlling the delay of a liquid crystal phase delay unit through voltage control. It is more convenient to control, easier to integrate with devices, and has a faster response speed. It overcomes the shortcomings of existing technologies that require mechanical rotation to adjust parameters, which leads to difficulties in integration and slow response speed. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the overall structure of the parameter-adjustable 9-cavity mode-locked fiber laser based on a liquid crystal phase delayer according to the present invention;

[0026] Figure 2 This is a structural diagram of a Sagnac fiber optic ring;

[0027] Figure 3 These are the transmittance curves of the Sagnac fiber ring when different splitting ratios and non-reciprocal phase shift parameters are selected;

[0028] Figure 4 The distribution of the splitting ratio k in the delay space of a liquid crystal phase retarder (LC) obtained through simulation and Distribution;

[0029] Figure 5 This is the distribution of laser mode-locking parameters and the spectral diagrams of three selected mode-locking states under the hardware configuration of Embodiment 2 of the present invention;

[0030] In the diagram: 1-Reflector, 2-Polarizing beam splitter prism I, 3-Liquid crystal phase delay adjustable waveplate I, 4-Faraday rotator, 5-Liquid crystal phase delay adjustable waveplate II, 6-Polarizing beam splitter prism II, 7-Fiber collimator I, 8-Fiber collimator II, 9-FCAPC jumper, 10-Wavelength division multiplexing-splitter mixer, 11-Pump semiconductor laser, 12-Gain fiber. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] like Figure 1 As shown, a 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delay includes, in sequence along the optical path: a mirror 1, a polarizing beam splitter prism 1 2, a liquid crystal phase delay adjustable waveplate 1 3, a Faraday rotator 4, a liquid crystal phase delay adjustable waveplate 2 5, and a polarizing beam splitter prism 2 6; a fiber loop is provided on one side of the polarizing beam splitter prism 2 6, and the fiber loop includes, in sequence: a fiber collimator 1 7, a gain fiber 12, a wavelength division multiplexing-splitter mixer 10, and a fiber collimator 2 8, with the fiber collimator 1 7 having a pigtail. The axis of the fiber optic collimator 8 is aligned horizontally with the polarization beam splitter prism 26 to ensure that the spatial light output from the polarization beam splitter prism 26 can be coupled to the fiber collimator 7. The slow axis of the fiber optic collimator 8 is aligned vertically with the polarization beam splitter prism 26 to ensure that the spatial light output from the polarization beam splitter prism 26 can be coupled to the fiber collimator 8. The pump input of the wavelength division multiplexing-splitter mixer 10 is connected to the pump semiconductor laser 11, and the signal output of the wavelength division multiplexing-splitter mixer 10 is connected to the FCAPC jumper 9 to serve as the output of the entire fiber laser.

[0034] In this embodiment, the bit line of the pump semiconductor laser 11 is fused to the pump input of the 10-wavelength division multiplexing-splitter mixer. The signal input of the wavelength division multiplexing-splitter mixer 10 is fused to the slow axis of the gain fiber 12, and the pigtail of fiber collimator 7 is fused to the slow axis of the other end of the gain fiber 12. The signal output of the wavelength division multiplexing-splitter mixer 10 is fused to the slow axis of the pigtail of fiber collimator 8. The signal output of the wavelength division multiplexing-splitter mixer 10 is fused to the slow axis of the FCAPC jumper 9. The slow axes of the pigtails of fiber collimator 7 and fiber collimator 8 are aligned with each other.

[0035] In this embodiment, the liquid crystal phase delay tunable waveplate 3 is a full-wave tunable delay waveplate with a working wavelength of 1550nm or 1030nm, and the fast axis direction makes an odd multiple of 45° with the horizontal plane.

[0036] In this embodiment, the liquid crystal phase delay tunable waveplate 25 is a full-wave tunable delay waveplate with a working wavelength of 1550nm or 1030nm, and the fast axis direction makes an angle of 45° with the horizontal plane as an odd multiple.

[0037] In this embodiment, the Faraday rotator 4 operates at a wavelength of 1550nm or 1030nm, and rotates at an angle of 45° clockwise or counterclockwise.

[0038] In this embodiment, the pigtail of fiber collimator 7 is a polarization-maintaining fiber, with the slow axis direction aligned with the horizontal direction; the pigtail of fiber collimator 8 is a polarization-maintaining fiber, with the slow axis direction aligned with the vertical direction.

[0039] In this embodiment, the gain fiber 12 is a polarization-maintaining erbium-doped or ytterbium-doped single-mode fiber.

[0040] In this embodiment, the polarizing beam splitter 2 operates at a wavelength of 1000–1700 nm; the polarizing beam splitter 6 operates at a wavelength of 1000–1700 nm.

[0041] The principle of the 9-cavity mode-locked fiber laser with the above-described structure is introduced below:

[0042] The figure-9 cavity mode-locked fiber laser utilizes, for example, Figure 2 The nonlinear transmission characteristics of the Sagnac fiber loop shown construct a saturable absorber, thereby initiating mode-locking. Therefore, the mode-locking state can be controlled by adjusting the parameters of the nonlinear transmittance curve. This control can be analyzed using the Jones matrix.

[0043] This invention establishes a model based on the Jones matrix for the study of... Figure 2 The transmission characteristics of the structure shown. Horizontally polarized light of unit intensity (E in The light is converted into elliptically polarized light by passing through a polarization fractional prism 2 (PBC1), a liquid crystal phase-retardant tunable waveplate 3 (LC1), a Faraday rotator 4 (FR), and a liquid crystal phase-retardant tunable waveplate 5 (LC2); then it is split into clockwise (CW) E by a polarization beam-splitting prism 6 (PBC2). cw And counterclockwise (CCW)E ccw The component enters the fiber optic loop. The splitting ratio k is defined as... After the CW and CCW beams complete one round trip in the fiber optic loop, they return along the original path and interfere at PBC1, outputting E. out The direction is horizontal, as shown in formula (1). It is a round-trip transmission, which depends on the nonlinear phase shift difference between the CW and CCW lights.

[0044] E out =M PBC2 M LC2 M FR M LC1 M FL M nps M LC1 M FR MLC2 M PBC2 E in (1)

[0045] E CW =M PBCI M LC1 M FR M LC2 M PBC2 E in (2)

[0046] In the formula, is Figure 1 The Jones matrix for the corresponding components is listed in Table 1.

[0047] Table 1 Jones Matrix of Intracavity Components

[0048]

[0049] Equation (1) shows that once the angle and delay of the liquid crystal phase retarders (LCs) are set, a set of segmentation ratios k and non-reciprocal phase shifts can be obtained. The transmission curve. When the angle of the liquid crystal phase retarder is fixed at -1 / 4π in the horizontal direction, regardless of the retardation, the minimum value of the transmission curve is fixed at 0, such as... Figure 3 As shown, the peak value of the round-trip transmission curve is related to the value of k. When k equals 0.5, the peak value is 1; when k deviates from 0.5 to 0.4 / 0.6 and 0.3 / 0.7, the peak value of the round-trip transmission curve decreases to approximately 0.97 and 0.83, respectively. When k equals 0 or 1, the round-trip transmission drops to 0. This corresponds to the initial phase of the transmission curve, which in turn corresponds to the horizontal offset of the curve.

[0050] When the phase delay of the liquid crystal phase retarder is adjusted in steps of 0.02π × 0.02π, the corresponding k and can be obtained. Distribution, respectively as Figure 4 As shown in (a) and (b) above. Simulation results show that by configuring the delay of LCs, k can take any value between 0 and 1, and NRPS (non-reciprocal phase shift) can take any value between -π and π. The simulation results can be mapped to... Space, such as Figure 4 As shown in (c) in the figure, in this space, the delay of each LCs corresponds to a point. Figure 4 (c) in the middle shows The 10,000 points in the space, which completely occupy the regions k from 0 to 1 and from -π to π, indicate that the delay of scanning LCs is traversal. An effective method for using space.

[0051] Example 2

[0052] In this embodiment, a specific figure-9 cavity mode-locked fiber laser is provided, wherein the pump semiconductor laser 11 is selected with a wavelength of 976nm and a power of 1086mW; the wavelength division multiplexing-splitter 10 is selected as 1560 / 980 wavelength division multiplexing, with a splitting end of 10%, and the pigtail is PM1550 fiber with a length of 40cm; the pigtails of fiber collimator 1 7 and fiber collimator 2 8 are both 40cm in length; the gain fiber 12 is Er80-4 / 125-HD-PM from nLight Liekki, with a length of 42cm.

[0053] The distribution of mode-locking parameters of the 9-cavity mode-locked fiber laser under the above hardware configuration and the spectra of the three selected mode-locking states are as follows: Figure 5 As shown, where, Figure 5 In the diagram, (a) represents the mode-locked state of the mode-locked fiber laser and the liquid crystal phase retarder. Displayed in space. A total of three mode-lock states are marked, corresponding to... Figure 5 The spectra in (b), (c), and (d) are shown. The red curve represents the spectrum generated during self-starting mode-locking at a pump power of 1086 mW, while the blue curve represents the spectrum when the laser enters single-pulse operation with a reduced pump power.

[0054] Figure 5 As can be seen, the laser can be controlled to be in different mode-locked states by adjusting the driving voltage of the liquid crystal phase delay unit.

[0055] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder, characterized in that, The structure includes, along the optical path, a mirror (1), a polarizing beam splitter prism (2), a liquid crystal phase delay adjustable waveplate (3), a Faraday rotator (4), a liquid crystal phase delay adjustable waveplate (5), and a polarizing beam splitter prism (6). A fiber optic loop is provided on one side of the polarizing beam splitter prism (6), which includes, in sequence, a fiber collimator (7), a gain fiber (12), a wavelength division multiplexing-splitter mixer (10), and a fiber collimator (8). The slow axis of the pigtail of the fiber collimator (7) is aligned horizontally with the polarizing beam splitter prism (6); the slow axis of the pigtail of the fiber collimator (8) is aligned vertically with the polarizing beam splitter prism (6). The pump input terminal of the wavelength division multiplexing-splitting mixer (10) is connected to a pump semiconductor laser (11), and the signal output terminal of the wavelength division multiplexing-splitting mixer (10) is connected to an FCAPC jumper (9) to serve as the output terminal of the entire fiber laser. Horizontal polarized light The light is converted into elliptically polarized light by the polarizing beam splitter prism (2), the liquid crystal phase delay tunable waveplate (3), the Faraday rotator (4), and the liquid crystal phase delay tunable waveplate (5); then it is split into clockwise components by the polarizing beam splitter prism (6). and counterclockwise components It enters the fiber optic loop; the beam splitting ratio k is ; After the clockwise and counterclockwise components complete one round trip in the fiber optic loop, they return along the original path and interfere at polarization beam splitter prism (2), outputting... The direction is horizontal; The output and clockwise components The formula for calculation is: In the formula, E CW Indicates clockwise component; E CCW Indicates the counterclockwise component; E in This represents the input horizontally polarized light; E out This indicates the output horizontally polarized light; M PBC1 It is the Jones matrix of polarizing beam splitter prism 1 (2). M LC1 It is the Jones matrix of the liquid crystal phase delay tunable waveplate one (3). M LC2 It is the Jones matrix of the liquid crystal phase delay tunable waveplate two (5). M PBC2 It is the Jones matrix of polarizing beam splitter prism two (6). M FR It is the Jones matrix of the Faraday rotator (4); It is the Jones matrix of the fiber optic loop. It is a Jones matrix with nonlinear phase shift.

2. The 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder according to claim 1, characterized in that, The bit line of the pump semiconductor laser (11) is fused to the pump input of the wavelength division multiplexing-splitter (10); the signal input of the wavelength division multiplexing-splitter (10) is fused to the slow axis of the gain fiber (12); the signal output of the wavelength division multiplexing-splitter (10) is fused to the slow axis of the pigtail of the fiber collimator (8); and the signal output of the wavelength division multiplexing-splitter (10) is fused to the slow axis of the FCAPC jumper (9).

3. The 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder according to claim 2, characterized in that, The pigtail of the first fiber collimator (7) is fused with the slow axis of the other end of the gain fiber (12); the pigtail of the first fiber collimator (7) and the slow axis of the pigtail of the second fiber collimator (8) are aligned with each other.

4. The 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder according to claim 1, characterized in that, The liquid crystal phase delay adjustable waveplate (3) is a full-wave adjustable delay waveplate with a working wavelength of 1550nm or 1030nm and an odd multiple of 45° between the fast axis direction and the horizontal plane.

5. The 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder according to claim 1, characterized in that, The Faraday rotator (4) operates at a wavelength of 1550nm or 1030nm and rotates at an angle of 45° clockwise or counterclockwise.

6. The 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder according to claim 1, characterized in that, The pigtail of the first fiber collimator (7) is a polarization-maintaining fiber, with the slow axis direction consistent with the horizontal direction; the pigtail of the second fiber collimator (8) is a polarization-maintaining fiber, with the slow axis direction consistent with the vertical direction.

7. The 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase retarder according to claim 1, characterized in that, The gain fiber (12) is a polarization-maintaining erbium-doped or ytterbium-doped single-mode fiber.

8. An asynchronous optical sampling device, characterized in that, Includes the 9-cavity mode-locked fiber laser with adjustable parameters based on a liquid crystal phase delayer as described in any one of claims 1-7.

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