Parameter-adjustable 9-shaped cavity mode-locked fiber laser based on liquid crystal phase delayer

Abstract

The invention discloses a parameter-adjustable 9-shaped cavity mode-locked fiber laser based on a liquid crystal phase retarder, and belongs to the technical field of mode-locked lasers. Comprising a reflector, a first polarization beam splitter prism, a first liquid crystal phase delay adjustable wave plate, a Faraday rotator, a second liquid crystal phase delay adjustable wave plate and a second polarization beam splitter prism which are sequentially distributed in the light path direction. An optical fiber loop is arranged on one side of the polarization beam splitter prism II and comprises an optical fiber collimator I, a gain optical fiber, a wavelength division multiplexing-light splitting mixer and an optical fiber collimator II which are connected in sequence; the tail fiber slow axis of the optical fiber collimator I is aligned with the horizontal direction of the polarization beam splitter prism II; a tail fiber slow axis of the second optical fiber collimator is aligned with the vertical direction of the second polarization beam splitter prism; the pumping input end of the wavelength division multiplexing-light splitting mixer is connected with a pumping semiconductor laser, and the signal output end of the wavelength division multiplexing-light splitting mixer is connected with an FCAPC jumper wire; therefore, continuous and rapid adjustment of laser parameters is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of mode-locked lasers, and in particular relates to a parameter-adjustable figure-9 cavity mode-locked fiber laser based on a liquid crystal phase retarder. Background Art

[0002] Figure-9 mode-locked fiber lasers have received a lot of research attention due to their low noise and good self-starting performance, which is very important for applications such as optical frequency combs and precision measurements. This laser is the core component of the optical frequency comb product of Menlo Systems in Germany, and the company has applied for a patent for this (EP 2 637 265 A1).

[0003] As can be seen from the patent, there are two main architectural schemes for Figure-9 lasers, namely polarization beam combining (PBC) and optical coupler (OC) beam combining (Appl.Phys.B 123(41),331-340(2017)). In the PBC-based scheme, studies have found that the combination of a rotating half-wave plate (HWP) and a 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-locking state of the laser. For example, by rotating the wave plate, Duan Dian et al. proposed and demonstrated a method to achieve high pulse energy emission in a self-started mode-locked F9 fiber laser (Opt. Express 28 (22), 33603-33613 (2020)); Li Jiahe et al. explored the 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 control of the non-reciprocal phase shift amount can also be achieved by adjusting the angles of HWP and QWP (Opt. Express 27 (10), 14705-14715 (2019)). However, this scheme is inconvenient to adjust the splitting ratio because it requires replacing the optical coupler and re-welding, making continuous adjustment difficult.

[0004] It can be seen that the existing technology adjusts the laser parameters by mechanically rotating the wave plate, which is not conducive to compact packaging and improving response speed, is inconvenient to control, and has the risk of wear and failure in long-term use.

[0005] In view of these problems, the present invention proposes a parameter-adjustable figure-9 cavity mode-locked fiber laser based on a liquid crystal phase retarder. Summary of the invention

[0006] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a parameter-adjustable figure-9 cavity mode-locked fiber laser based on a liquid crystal phase retarder, which solves the problems in the prior art.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A parameter-adjustable 9-shaped cavity mode-locked fiber laser based on a liquid crystal phase retarder comprises the following components, which are sequentially distributed along the optical path: a reflector, a polarization beam splitting prism 1, a liquid crystal phase delay adjustable wave plate 1, a Faraday rotator, a liquid crystal phase delay adjustable wave plate 2, and a polarization beam splitting prism 2; a fiber loop is arranged on one side of the polarization beam splitting prism 2, and the fiber loop comprises sequentially connected: a fiber collimator 1, a gain fiber, a wavelength division multiplexing-light splitting mixer, and a fiber collimator 2; a pigtail slow axis of the fiber collimator 1 is aligned with the polarization beam splitting prism 2 in the horizontal direction; and a pigtail slow axis of the fiber collimator 2 is aligned with the polarization beam splitting prism 2 in the vertical direction;

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

[0010] Furthermore, the bit line of the pump semiconductor laser is fused to the pump input end of the wavelength division multiplexing-splitting mixer; the signal input end of the wavelength division multiplexing-splitting mixer is aligned and fused to the slow axis of the gain optical fiber, the signal output end of the wavelength division multiplexing-splitting mixer is aligned and fused to the slow axis of the pigtail of the optical fiber collimator 2; the signal output end of the wavelength division multiplexing-splitting mixer is aligned and fused to the slow axis of the FCAPC jumper.

[0011] Furthermore, the pigtail of the first optical fiber collimator is fused with the other end of the gain optical fiber in a slow-axis aligned manner; and the pigtail of the first optical fiber collimator is aligned with the pigtail of the second optical fiber collimator in a slow-axis aligned manner.

[0012] Furthermore, the first liquid crystal phase retardation adjustable wave plate is a full-wave adjustable retardation wave plate, the working wavelength is 1550nm or 1030nm, and the angle between the fast axis direction and the horizontal plane is an odd multiple of 45°;

[0013] Furthermore, the Faraday rotator has an operating wavelength of 1550 nm or 1030 nm, and a rotation angle of 45° clockwise or counterclockwise.

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

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

[0016] Furthermore, the horizontally polarized light E in It is converted into elliptically polarized light by passing through polarization beam splitter prism 1, liquid crystal phase delay adjustable wave plate 1, Faraday rotator and liquid crystal phase delay adjustable wave plate 2; then it is split into clockwise component E by polarization beam splitter prism 2 cw and the counterclockwise component E ccw , enters the optical fiber loop; the splitting ratio k is After the clockwise and counterclockwise components complete a round trip in the optical fiber loop, they return along the original path and interfere at a point in the polarization beam splitter prism to output E. out The direction is horizontal.

[0017] Furthermore, the output E out and the clockwise component E cw The calculation formula 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 Represents the input horizontal polarized light; E out Represents the output horizontal polarized light; M PBC1 is the Jones matrix of polarization beam splitter prism 1, M LC1 is the Jones matrix of the liquid crystal phase retardation adjustable wave plate, M LC2 is the Jones matrix of the second liquid crystal phase retardation adjustable wave plate, M PBC2 is the Jones matrix of polarization beam splitter prism 2, M FR is the Jones matrix of the Faraday rotator.

[0021] An asynchronous optical sampling device comprises the above-mentioned parameter-adjustable figure-9 cavity mode-locked fiber laser based on liquid crystal phase retarder.

[0022] Beneficial effects of the present invention:

[0023] The present invention controls the delay amount of the liquid crystal phase retarder by voltage to achieve continuous and rapid adjustment of laser parameters; the control is more convenient, easy to integrate with devices, and has a faster response speed, overcoming the shortcomings of the prior art that parameters must be adjusted by mechanical rotation, which leads to difficulty in integration and slow response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

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

[0027] Figure 3 It is the transmittance curve of Sagnac fiber ring when taking different splitting ratios and non-reciprocal phase shift parameters;

[0028] Figure 4 is the distribution of the splitting ratio k in the retardation space of the liquid crystal retarder (LCs) obtained by simulation and Distribution of

[0029] Figure 5 1 is the distribution of laser mode-locking parameters and three selected mode-locking state spectra under the hardware configuration of Example 2 of the present invention;

[0030] In the figure: 1-reflector, 2-polarization beam splitting prism 1, 3-liquid crystal phase delay adjustable wave plate 1, 4-Faraday rotator, 5-liquid crystal phase delay adjustable wave plate 2, 6-polarization beam splitting prism 2, 7-fiber collimator 1, 8-fiber collimator 2, 9-FCAPC jumper, 10-wavelength division multiplexing-beam splitting mixer, 11-pump semiconductor laser, 12-gain fiber. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] like Figure 1 As shown, a parameter-adjustable 9-shaped cavity mode-locked fiber laser based on a liquid crystal phase retarder includes the following components, which are sequentially distributed along the optical path: a reflector 1, a polarization beam splitting prism 2, a liquid crystal phase delay adjustable wave plate 3, a Faraday rotator 4, a liquid crystal phase delay adjustable wave plate 5, and a polarization beam splitting prism 6; a fiber loop is provided on one side of the polarization beam splitting prism 6, and the fiber loop includes the following components, which are sequentially connected: a fiber collimator 7, a gain fiber 12, a wavelength division multiplexing-spectroscopy mixer 10, and a fiber collimator 8, and the pigtail slow fiber of the fiber collimator 7. The axis is aligned with the polarization beam splitter prism 26 in the horizontal direction to ensure that the spatial light output by the polarization beam splitter prism 26 can be coupled to the fiber collimator 1 7; the slow axis of the pigtail of the fiber collimator 28 is aligned with the polarization beam splitter prism 26 in the vertical direction to ensure that the spatial light output by the polarization beam splitter prism 26 can be coupled to the fiber collimator 28; the pump input end of the wavelength division multiplexing-optical splitting mixer 10 is connected to the pump semiconductor laser 11, and the signal output end of the wavelength division multiplexing-optical splitting mixer 10 is connected to the FCAPC jumper 9 to serve as the output end of the entire fiber laser.

[0034] In this embodiment, the bit line of the pump semiconductor laser 11 is fused with the pump input end of the wavelength division multiplexing-splitting mixer 10. The signal input end of the wavelength division multiplexing-splitting mixer 10 is aligned and fused with the slow axis of the gain fiber 12, and the pigtail of the optical fiber collimator 17 is aligned and fused with the slow axis of the other end of the gain fiber 12. The signal output end of the wavelength division multiplexing-splitting mixer 10 is aligned and fused with the pigtail of the optical fiber collimator 2 8. The signal output end of the wavelength division multiplexing-splitting mixer 10 is aligned and fused with the slow axis of the FCAPC jumper 9. The pigtail of the optical fiber collimator 17 and the pigtail of the optical fiber collimator 2 8 are aligned with each other.

[0035] In this embodiment, the liquid crystal phase delay adjustable wave plate 13 is a full-wave adjustable delay wave plate, the working wavelength is 1550nm or 1030nm, and the angle between the fast axis direction and the horizontal plane is an odd multiple of 45°;

[0036] In this embodiment, the liquid crystal phase delay adjustable wave plate 2 5 is a full-wave adjustable delay wave plate, the working wavelength is 1550nm or 1030nm, and the angle between the fast axis direction and the horizontal plane is an odd multiple of 45°;

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

[0038] In this embodiment, the pigtail of the optical fiber collimator 1 7 is a polarization-maintaining optical fiber, and the slow axis direction is consistent with the horizontal direction; the pigtail of the optical fiber collimator 2 8 is a polarization-maintaining optical fiber, and the slow axis direction is consistent 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 operating wavelength of the polarization beam splitter prism 1 2 is 1000-1700 nm; the operating wavelength of the polarization beam splitter prism 2 6 is 1000-1700 nm.

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

[0042] Figure-9 cavity mode-locked fiber laser is based on Figure 2 The nonlinear transmission characteristics of the Sagnac fiber ring shown above construct a saturable absorber, thereby starting the mode locking. Therefore, the mode locking state can be controlled by controlling the parameters of the nonlinear transmittance curve. This control can be analyzed using the Jones matrix.

[0043] The present invention establishes a model based on Jones matrix for studying Figure 2 Transmission characteristics of the structure shown. Horizontally polarized light (E in ) is converted into elliptically polarized light by polarization fractionating prism 2 (PBC1), liquid crystal phase retardation adjustable wave plate 3 (LC1), Faraday rotator 4 (FR) and liquid crystal phase retardation adjustable wave plate 2 5 (LC2); then it is split into clockwise (CW) E by polarization beam splitting prism 2 6 (PBC2) cw and counterclockwise (CCW) E ccw Components enter the optical fiber loop. The splitting ratio k is defined as After the CW and CCW lights complete a round trip in the fiber loop, they return along the original path and interfere at PBC1, outputting E out The direction is horizontal, as shown in formula (1). is the round trip transmission, which depends on the nonlinear phase shift difference between CW and CCW light.

[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] Where Figure 1 The Jones matrix of the corresponding components is listed in Table 1.

[0047] Table 1 Jones matrix of intracavity elements

[0048]

[0049] Formula (1) shows that once the angle and retardation of the liquid crystal retarder (LCs) are set, the corresponding split ratio k and non-reciprocal phase shift can be obtained. When the angle of the liquid crystal phase retarder is fixed at -1 / 4π in the horizontal direction, the minimum value of the transmission curve is fixed at 0 regardless of the delay, as shown in Figure 3 As shown, the peak value of the round-trip transmission curve is related to the k value. When k is equal to 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 about 0.97 and 0.83 respectively. When k is equal to 0 or 1, the round-trip transmission drops to 0. It is equivalent to the initial phase of the transmission curve and corresponds to the horizontal shift of the curve.

[0050] When the phase retardation of the liquid crystal phase retarder is adjusted in steps of 0.02π×0.02π, the corresponding k and Distribution, respectively Figure 4 The 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 this space, the delay amount of each LCs corresponds to a point. Figure 4 (c) in the figure shows 10,000 points in space, which completely occupy the region where k ranges from 0 to 1 and from -π to π, showing that the delay of scanning LCs is traversal An efficient way to use space.

[0051] Example 2

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

[0053] The locking parameter distribution of the 9-cavity mode-locked fiber laser under the above hardware configuration and the spectra of the three selected mode-locked states are shown in Figure 2. Figure 5 As shown, Figure 5 (a) shows the mode-locked state of the mode-locked fiber laser and the liquid crystal phase retarder. There are three locking states marked, corresponding to Figure 5 Spectra in (b), (c), and (d). The red curve represents the spectrum when self-starting mode locking occurs at a pump power of 1086 mW, while the blue curve represents the spectrum when the laser enters single-pulse operation at reduced pump power.

[0054] Figure 5 It can be seen that by adjusting the driving voltage of the liquid crystal phase retarder, the laser is controlled to be in different mode-locking states.

[0055] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0056] The above shows and describes 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, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A parameter-adjustable figure-9 cavity mode-locked fiber laser based on a liquid crystal phase retarder, characterized in that: The invention comprises: a reflector (1), a polarization beam splitting prism (2), a liquid crystal phase delay adjustable wave plate (3), a Faraday rotator (4), a liquid crystal phase delay adjustable wave plate (5) and a polarization beam splitting prism (6) which are sequentially distributed along the optical path; a fiber loop is arranged on one side of the polarization beam splitting prism (6), and the fiber loop comprises: a fiber collimator (7), a gain fiber (12), a wavelength division multiplexing-light splitting mixer (12) and a fiber collimator (8) which are sequentially connected; the slow axis of the pigtail of the fiber collimator (7) is aligned with the polarization beam splitting prism (6) in the horizontal direction; and the slow axis of the pigtail of the fiber collimator (8) is aligned with the polarization beam splitting prism (6) in the vertical direction. The pump input end of the wavelength division multiplexing-optical splitting mixer (10) is connected to a pump semiconductor laser (11), and the signal output end of the wavelength division multiplexing-optical splitting mixer (10) is connected to a FCAPC jumper (9) to serve as the output end of the entire optical fiber laser.

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

3. The parameter-adjustable figure-9 cavity mode-locked fiber laser based on liquid crystal phase retarder according to claim 2, characterized in that: The pigtail of the optical fiber collimator 1 (7) is fused with the other end of the gain optical fiber (12) in an aligned slow axis manner; the pigtail of the optical fiber collimator 1 (7) is aligned with the pigtail of the optical fiber collimator 2 (8) in a slow axis manner.

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

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

6. The parameter-adjustable figure-9 cavity mode-locked fiber laser based on liquid crystal phase retarder according to claim 1, characterized in that: The pigtail fiber of the optical fiber collimator 1 (7) is a polarization-maintaining optical fiber, and the slow axis direction is consistent with the horizontal direction; the pigtail fiber of the optical fiber collimator 2 (8) is a polarization-maintaining optical fiber, and the slow axis direction is consistent with the vertical direction.

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

8. The parameter-adjustable figure-9 cavity mode-locked fiber laser based on liquid crystal phase retarder according to claim 1, characterized in that: The horizontally polarized light E in The light is converted into elliptically polarized light by passing through polarization beam splitter prism 1 (2), liquid crystal phase delay adjustable wave plate 1 (3), Faraday rotator (4) and liquid crystal phase delay adjustable wave plate 2 (5); and then split into clockwise component E by polarization beam splitter prism 2 (6). cw and the counterclockwise component E ccw , enters the optical fiber loop; the splitting ratio k is After the clockwise and counterclockwise components complete a round trip in the fiber loop, they return along the original path and interfere at the polarization beam splitter prism 1 (2), outputting E out The direction is horizontal.

9. The parameter-adjustable figure-9 cavity mode-locked fiber laser based on liquid crystal phase retarder according to claim 8, characterized in that: The output E out and the clockwise component E cw The calculation formula is: E out =M PBC2 M LC2 M FR M LC1 M FL M nps M LC1 M FR M LC2 M PBC2 E in E CW =M PBC1 M LC1 M FR M LC2 M PBC2 E in In the formula, E CW Indicates the clockwise component; E CCW Indicates the counterclockwise component; E in Represents the input horizontal polarized light; E out Represents the output horizontal polarized light; M PBC1 is the Jones matrix of the polarization beam splitter prism 1(2), M LC1 is the Jones matrix of the liquid crystal phase retardation adjustable wave plate (3), M LC2 is the Jones matrix of the liquid crystal phase retardation adjustable wave plate 2 (5), M PBC2 is the Jones matrix of polarization beam splitter prism 2 (6), M FR is the Jones matrix of the Faraday rotator (4).

10. An asynchronous optical sampling device, characterized in that: A parameter-adjustable figure-9 cavity mode-locked fiber laser based on a liquid crystal phase retarder as described in any one of claims 1 to 9.

Images