2-micron wave band adjustable all-fiber high repetition frequency pulse light source generator

Abstract

The invention discloses a 2-micron-waveband adjustable all-fiber high-repetition-frequency pulse light source generator, belongs to the technical field of laser light source manufacturing, and aims to solve the problem that an existing 2-micron-waveband passive all-fiber mode-locked pulse laser light source is difficult to give consideration to fs-magnitude narrow pulse width and ultra-short-cavity-length high-fundamental-frequency repetition frequency output. The laser comprises a semiconductor laser pumping source, a wavelength division multiplexer, an extrusion type polarization controller I, a polarization-maintaining highly-doped gain fiber, an extrusion type polarization controller II, a long cone region tapering micro-nano fiber, a 2 * 2 fiber coupler and a fiber Faraday mirror. According to the invention, the long-cone micro-nanofiber is introduced into the cavity, and the long-cone micro-nanofiber has the characteristic of high nonlinear coefficient, so that the cavity length can be greatly shortened, enough nonlinear phase shift can be accumulated, and fs-magnitude ultrashort pulse can be output. The device is low in loss, stable in performance and easy to integrate with other optical fiber systems. The laser can be applied to the fields of optical communication, non-metallic material processing, laser medical treatment, intermediate infrared laser pumping sources and the like.

Description

Technical Field

[0001] The present invention relates to an adjustable all-fiber high-repetition-rate pulse light source generator, belonging to the technical field of laser light source manufacturing. The light source generator can be applied to multiple fields such as optical communications, non-metallic material processing, laser medical treatment, and mid-infrared laser pump sources. Background Art

[0002] Fiber laser sources are currently one of the most important laser light sources due to their low threshold, high efficiency, compact size, tunability, and cost-effectiveness. The 2-micron wavelength band is particularly attractive due to its eye-safe nature. Ultrafast fiber laser sources, characterized by high pulse energy, high operational stability, and easy maintenance, are widely used in laser processing, laser medical treatment, biosensing, and other fields. The mode-locking mechanisms of ultrafast fiber lasers are primarily categorized as active and passive. Active mode-locking typically relies on the introduction of an active modulation element within the laser cavity to achieve mode-locking. However, this approach is difficult to construct in an all-fiber configuration, and the output pulse width is typically in the picosecond range. In contrast, passive mode-locking achieves self-starting mode-locking by manipulating intracavity nonlinear effects and dispersion characteristics. This approach is feasible for all-fiber configurations, and can achieve output pulse widths in the femtosecond range, offering greater research and application potential. However, passive mode-locking lasers typically require sufficient nonlinear effects to accumulate within a relatively long fiber cavity to maintain mode-locking operation. This results in a relatively long resonant cavity, resulting in a low pulse repetition rate. This makes it difficult to achieve both ultrashort pulse output and a high repetition rate output. At present, the pulse width output of the mode-locked laser of all-quartz fiber used in the 2-micron band is in the order of fs, and the general repetition frequency is maintained at the level of tens of MHz.

[0003] The Chinese patent, "A 2.0-μm-band passively mode-locked ultrashort pulse all-fiber laser," published as CN102368584A, describes a laser pump source connected to the pump input of a pump combiner; the common end of the pump combiner is connected to a rare-earth-doped fiber; the other end of the rare-earth-doped fiber is connected to the input of a circulator, and a reflective saturable absorber is located at the common end of the circulator. The output of the circulator is connected to a laser beam splitter. The laser beam splitter has two outputs: one for the output of the mode-locked ultrashort laser pulses and the other for the signal end of the pump combiner. The laser pump source, pump combiner, rare-earth-doped fiber, circulator, saturable absorber, and laser beam splitter together form a ring cavity structure for a 2.0-μm-band passively mode-locked ultrashort pulse all-fiber laser. However, the entire laser resonator of this structure is approximately 24 meters long, and the repetition rate of its passively mode-locked laser pulses is only 8.3 MHz. In addition, since the optical power fed back into the laser cavity accounts for only about 30%, the power density in the laser cavity is low and the nonlinear effect is weak, the laser does not produce ultrashort pulses with shorter pulse widths. Summary of the Invention

[0004] To address the difficulty of existing 2-micron-band passive all-fiber mode-locked pulse laser sources in achieving both fs-order narrow pulse width and high fundamental frequency repetition rate output with an ultrashort cavity length, the present invention proposes a 2-micron-band tunable all-fiber high-repetition rate pulse light source generator. This is an ultrashort figure-9 cavity mode-locked fiber laser based on a long-tapered micro-nano fiber. The introduction of the micro-nano fiber significantly shortens the cavity length. Furthermore, wavelength tuning can be achieved through the polarization-maintaining gain fiber and the polarization controllers on both sides, with a tuning range of up to 37nm.

[0005] The present invention adopts the following technical solutions:

[0006] A 2-micron band adjustable all-fiber high repetition rate pulse light source generator comprises: a semiconductor laser pump source, a wavelength division multiplexer, a squeezed polarization controller 1, a polarization-maintaining high-doped gain fiber, a squeezed polarization controller 2, a long-tapered region tapered micro-nano fiber, a 2×2 fiber coupler, and a fiber Faraday reflector; the semiconductor laser pump source is connected to the a-end of the wavelength division multiplexer; the c-end of the wavelength division multiplexer is connected to the squeezed polarization controller 1, the squeezed polarization controller 1 is connected to the polarization-maintaining high-doped gain fiber, and the polarization-maintaining high-doped gain fiber is connected to the squeezed polarization controller 2; the squeezed polarization controller First, the polarization-maintaining highly doped gain fiber and the squeezed polarization controller II together form a Lyot filter for adjusting the output wavelength; the squeezed polarization controller II is connected to the long-tapered micro-nano fiber; the long-tapered micro-nano fiber is connected to the d-end of the 2×2 fiber coupler; the f-end of the 2×2 fiber coupler is connected to the b-end of the wavelength division multiplexer to form a closed loop as the ring arm of the figure-9 cavity mode-locked laser; the g-end of the 2×2 fiber coupler is connected to the fiber Faraday reflector to form a linear reflective arm to form a figure-9 cavity structure; the e-end of the 2×2 fiber coupler serves as the output end, outputting pulses;

[0007] The semiconductor laser pump source generates pump signal light and transmits the pump signal light to a wavelength division multiplexer, which couples the pump signal light to a high-doped gain optical fiber; the high-doped gain optical fiber absorbs the pump 1.5-micron pump light to generate 2-micron signal light; the wavelength of the 2-micron signal light is adjusted in a LYOT filter structure composed of a squeezed polarization controller 1, a polarization-maintaining high-doped gain optical fiber, and a squeezed polarization controller 2, wherein the squeezed polarization controller 1 and the squeezed polarization controller 2 adjust the cavity loss by adjusting their pressure and deflection angle, thereby adjusting the output wavelength of the laser; the signal light is transmitted to the long-tapered region tapered micro-nano optical fiber and is nonlinearly broadened; the signal light is transmitted to the d-end of the 2×2 optical fiber coupler, which is connected to the g-end of the 2×2 optical fiber coupler and the optical fiber Faraday reflector to form a reflection arm, where the reflected signal light with an initial phase shift interferes; and the pulse signal light is output via the e-end of the 2×2 optical fiber coupler as the output end.

[0008] The beneficial effects of the present invention are:

[0009] The squeezed polarization controller, the polarization-maintaining high-doped gain optical fiber and the squeezed polarization controller together form a Lyot filter, which can adjust the output wavelength.

[0010] By introducing a micro-nano fiber with a long taper region into the cavity, the high nonlinear coefficient of the micro-nano fiber in this region can significantly shorten the cavity length while accumulating sufficient nonlinear phase shift to output ultrashort pulses on the order of femtoseconds. Furthermore, the all-fiber structure of the present invention eliminates the need for spatial structural components, resulting in low loss, stable performance, and ease of integration with other fiber systems.

[0011] The present invention has low cost, high integration, high cost performance, and practical application value in the fields of mid-infrared laser pump sources and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the structure of the 2-micron band adjustable all-fiber high repetition rate pulse light source generator described in the present invention.

[0013] Figure 2 This is a schematic diagram of the long-tapered region tapered micro-nano optical fiber structure of the present invention.

[0014] Figure 3 This is a schematic diagram of the long-tapered region tapered micro-nano optical fiber packaging structure of the present invention.

[0015] Figure 4 This is the output spectrum of the 2-micron band adjustable all-fiber high repetition rate pulse light source generator described in the present invention.

[0016] Figure 5 This is a pulse time domain diagram of the 2-micron band adjustable all-fiber high repetition rate pulse light source generator described in the present invention.

[0017] Figure 6 This is a wavelength tuning example of the 2-micron-band tunable all-fiber high-repetition-rate pulse light source generator described in the present invention.

[0018] Figure 7 This is an autocorrelation curve diagram of the 2-micron band adjustable all-fiber high repetition rate pulse light source generator described in the present invention.

[0019] Figure 8 The invention discloses an output power stability of the 2-micron band adjustable all-fiber high repetition rate pulse light source generator. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings.

[0021] like Figure 1As shown, a 2-micron-band tunable all-fiber high-repetition-rate pulse light source generator includes: a semiconductor laser pump source 1, a wavelength division multiplexer 2, a squeezed polarization controller 1 3, a polarization-maintaining high-doped gain fiber 4, a squeezed polarization controller 2 5, a long-tapered region tapered micro-nano fiber 6, a 2×2 fiber coupler 7, and a fiber Faraday reflector 8.

[0022] The wavelength of the semiconductor laser pump source 1 is 1550 nm.

[0023] The wavelength division multiplexer 2 is a 1550 / 2000nm wavelength division multiplexer.

[0024] The gain fiber 3 is a polarization-maintaining high-thulium-doped gain fiber.

[0025] The coupling ratio of the 2×2 optical fiber coupler 7 is 30:70.

[0026] The semiconductor laser pump source 1 is connected to the a-end of the wavelength division multiplexer 2; the c-end of the wavelength division multiplexer 2 is connected to the squeezed polarization controller 1 3, and the squeezed polarization controller 1 3 is connected to the polarization-maintaining high-doped gain fiber 4; the polarization-maintaining high-doped gain fiber 4 is connected to the squeezed polarization controller 2 5, wherein the squeezed polarization controller 1 3, the polarization-maintaining high-doped gain fiber 4 and the squeezed polarization controller 2 5 together constitute a Lyot filter, which can adjust the output wavelength; the squeezed polarization controller 2 5 is connected to the long-tapered region tapered micro-nano fiber 6; the long-tapered region tapered micro-nano fiber 6 is connected to the d-end of the 2×2 fiber coupler 7; the f-end of the 2×2 fiber coupler 7 is connected to the b-end of the wavelength division multiplexer 2 to form a closed loop as the ring arm of the 9-cavity mode-locked laser; the g-end of the 2×2 fiber coupler 7 is connected to the fiber Faraday reflector 8, and the e-end of the 2×2 fiber coupler 7 serves as the output end to output pulses.

[0027] The 2-micron-band adjustable all-fiber high-repetition-rate pulse light source generator of the present invention adopts a figure-9 cavity structure for mode locking. The figure-9 cavity structure is composed of a ring circuit formed between a 2×2 fiber coupler 7 and a wavelength division multiplexer 2, and a linear reflection arm formed by an optical fiber Faraday 8th reflector connected to the g-end of the 2×2 fiber coupler 7.

[0028] The working process of the 2-micron band adjustable all-fiber high repetition rate pulse light source generator of the present invention is as follows:

[0029] A semiconductor laser pump source 1 generates pump signal light and transmits the pump signal light to a wavelength division multiplexer 2, which couples the pump signal light to a high-doped gain fiber 4; the high-doped gain fiber 4 absorbs the pumped 1.5-micron pump light to generate a 2-micron signal light; the wavelength of the 2-micron signal light is adjusted in a Lyot filter structure composed of a squeezed polarization controller 3, a polarization-maintaining high-doped gain fiber 4, and a squeezed polarization controller 5, wherein the squeezed polarization controller 3 and the squeezed polarization controller 5 adjust the cavity loss by adjusting their pressure and deflection angle, thereby adjusting the output wavelength of the laser; the signal light is transmitted to a long-tapered region tapered micro-nano fiber 6 and is nonlinearly broadened; the signal light is transmitted to a 2×2 fiber coupler 7, where the d end is connected to the g end of the 2×2 fiber coupler 7 and the fiber Faraday reflector 8 to form a reflection arm, where the reflected signal light with an initial phase shift interferes; the e end of the 2×2 fiber coupler 7 is used as the output end to output a pulse signal light.

[0030] like Figure 2 As shown, it is a schematic diagram of the structure of the long-tapered micro-nano optical fiber 6. The long-tapered micro-nano optical fiber 6 includes the single-mode optical fiber regions of segments h and l, which are symmetrically arranged at both ends of the structure, the tapered transition regions of segments i and k, which are respectively located between the long micro-nano cone regions and the single-mode optical fiber regions on both sides, and the long micro-nano cone region of segment j. Among them, the diameters of segments h and l are 125 microns; segments i and k are transition regions, which are used to couple optical signals into segment j to form evanescent field transmission. The diameter of segment j is 1 to 2 microns and the length is 5 to 10 centimeters. The input light field of segment h is transmitted in the fundamental mode, and the light field energy is confined in the fiber core. Part of the light field energy leaks in the tapered region of segment j.

[0031] The long-tapered micro-nano optical fiber 6 is prepared using a single-mode optical fiber SMF-28E by using an oxyhydrogen flame taper method. By adjusting the position of the flame head and the ratio of the oxyhydrogen flame, a long-tapered micro-nano optical fiber 6 with a uniform taper area can be prepared.

[0032] like Figure 3 Figure 6 shows the structure of a long-tapered micro-nano fiber package 6. The package consists of an upper and lower shell with identical structures. The upper shell comprises a substrate 9 and high-strength vibration-isolating sponges 10 positioned around its edges. The substrate 9, made of the polymer PMMA, is used to observe the micro-nano fiber structure. The high-strength vibration-isolating sponges 10 reduce the loss of power and mechanical strength of the micro-nano fiber caused by external vibrations. This package structure reduces system noise introduced by environmental disturbances in the micro-nano fiber, enhancing system stability.

[0033] like Figure 4As shown, the output spectrum of the 2-micron band tunable all-fiber high repetition rate pulse light source generator is tested at a pump power of 30.8dBm. The output spectrum has an output center wavelength of 1940nm and a full width at half maximum of 13nm.

[0034] like Figure 5 The figure below shows a pulse time domain diagram of a 2-micron-band tunable all-fiber high-repetition-rate pulse source generator. The pulse sequence is smooth, with an 8.3ns pulse interval, corresponding to a pulse fundamental repetition frequency of 120.48MHz.

[0035] like Figure 6 Figure 2 shows an example of wavelength tuning for a 2-micron tunable all-fiber high-repetition-rate pulsed light source generator. The output wavelength can be adjusted by adjusting the angles of two squeeze-type polarization controllers. The output wavelength adjustment range is 1910-1947 nm.

[0036] like Figure 7 The following is an autocorrelation curve of a 2-micron tunable all-fiber high-repetition-rate pulse source generator. The autocorrelation results show that the output pulse width is 347 fs.

[0037] like Figure 8 Figure 2 shows the power stability of a 2-micron tunable all-fiber high-repetition-rate pulsed light source generator. The average output power is 56.37 mW, with a power instability of 0.216%. The laser output power is stable.

Claims

1. 2 micron band adjustable all-fiber high repetition rate pulse light source generator, characterized in that include: Semiconductor laser pump source (1), wavelength division multiplexer (2), squeezed polarization controller 1 (3), polarization-maintaining high-doped gain fiber (4), squeezed polarization controller 2 (5), long-tapered micro-nano fiber (6), 2×2 fiber coupler (7) and fiber Faraday reflector (8); The semiconductor laser pump source (1) is connected to the A end of the wavelength division multiplexer (2); the C end of the wavelength division multiplexer (2) is connected to a squeeze-type polarization controller (3); the squeeze-type polarization controller (3) is connected to a polarization-maintaining high-doped gain optical fiber (4); the polarization-maintaining high-doped gain optical fiber (4) is connected to a squeeze-type polarization controller (5); the squeeze-type polarization controller (3), the polarization-maintaining high-doped gain optical fiber (4) and the squeeze-type polarization controller (5) together form a Lyot filter for adjusting the output wavelength; the squeeze-type polarization controller (3) is connected to a polarization-maintaining high-doped gain optical fiber (4) and the squeeze-type polarization controller (5) The second pressure-type polarization controller (5) is connected to the long-tapered region tapered micro-nano optical fiber (6); the long-tapered region tapered micro-nano optical fiber (6) is connected to the d-end of the 2×2 optical fiber coupler (7); the f-end of the 2×2 optical fiber coupler (7) is connected to the b-end of the wavelength division multiplexer (2) to form a closed loop as a ring arm of the 9-shaped cavity mode-locked laser; the g-end of the 2×2 optical fiber coupler (7) is connected to the optical fiber Faraday reflector (8) to form a linear reflection arm to form a 9-shaped cavity structure, and the e-end of the 2×2 optical fiber coupler (7) serves as an output end to output pulses; The semiconductor laser pump source (1) generates pump signal light and transmits the pump signal light to the wavelength division multiplexer (2); the wavelength division multiplexer (2) couples the pump signal light and transmits it to the high-doped gain optical fiber (4); the high-doped gain optical fiber (4) absorbs the pumped 1.5-micron pump light to generate 2-micron signal light; the 2-micron signal light is wavelength-adjusted in a lyot filter structure composed of a squeeze-type polarization controller (3), a polarization-maintaining high-doped gain optical fiber (4) and a squeeze-type polarization controller (5), wherein the squeeze-type polarization controller (1) 3) and the squeeze-type polarization controller 2 (5) adjust the cavity loss by adjusting its pressure and deflection angle, thereby adjusting the output wavelength of the laser; the signal light is transmitted to the long-tapered region taper micro-nano optical fiber (6) and is subjected to nonlinear broadening; the signal light is transmitted to the d end of the 2×2 optical fiber coupler (7) and the g end of the 2×2 optical fiber coupler (7) and the optical fiber Faraday reflector (8) to form a reflection arm to interfere with the reflected signal light with an initial phase shift; the e end of the 2×2 optical fiber coupler (7) is used as the output end to output the pulse signal light.

2. The 2-micron band tunable all-fiber high repetition rate pulse light source generator according to claim 1, characterized in that: The wavelength of the semiconductor laser pump source (1) is 1550 nm.

3. The 2-micron band tunable all-fiber high repetition rate pulse light source generator according to claim 1, characterized in that: The wavelength division multiplexer (2) is a 1550 / 2000nm wavelength division multiplexer.

4. The 2-micron band tunable all-fiber high repetition rate pulse light source generator according to claim 1, characterized in that: The gain optical fiber (3) is a polarization-maintaining high-thulium-doped gain optical fiber.

5. The 2-micron band tunable all-fiber high repetition rate pulse light source generator according to claim 1, characterized in that: The long taper region tapered micro-nano optical fiber (6) comprises three parts: single-mode optical fiber regions of segments h and l, which are symmetrically arranged at both ends of the structure; tapered transition regions of segments i and k, which are respectively located between the long micro-nano taper regions and the single-mode optical fiber regions on both sides; and a long micro-nano taper region of segment j. The diameters of segments h and l are 125 microns; segments i and k are transition regions, which are used to couple optical signals into segment j to form evanescent field transmission; the diameter of segment j is 1 to 2 microns and the length is 5 to 10 centimeters; the input light field of segment h is transmitted in the fundamental mode, and the light field energy is confined in the fiber core, and part of the light field energy leaks in the tapered region of segment j.

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