A Synchronous Multiwavelength High Repetition Rate Pulsed Fiber Laser Based on Off-core Fusion

Abstract

This invention discloses a synchronous multi-wavelength high repetition rate (HRPR) pulsed fiber laser based on off-core fusion splicing. In the fiber laser, the passive fiber and gain fiber are off-core fused using a fiber fusion splicer. The other ends of the passive fiber and gain fiber are inserted into and pass through a first ferrule and a second ferrule, respectively. A dielectric film is disposed on the end face of a third ferrule. The end face of the first ferrule is aligned with a semiconductor saturable absorber mirror, and the end face of the second ferrule is aligned with the dielectric film. A wavelength division multiplexer is connected to the pigtail of the third ferrule, the pump end is connected to a pump source, and the signal end is connected to an isolator. The high repetition rate mode-locked pulsed laser is output from the isolator. This invention achieves synchronous multi-wavelength high repetition rate mode-locked pulse output by off-core fusion splicing of the passive fiber and gain fiber within the laser resonant cavity and introducing spectral comb filtering within the ultrashort resonant cavity. It has advantages such as an all-fiber structure, integrability, and high stability.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to a synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing. Background Technology

[0002] Multiwavelength lasers can simultaneously generate two or more wavelengths of laser output within a single laser, showing broad application prospects in high-capacity fiber optic communication and fiber optic sensing. Synchronous multiwavelength laser sources, by outputting different wavelengths while achieving time synchronization of laser pulse sequences, are widely used in multicolor pump-probe, spectral detection, and nonlinear frequency conversion. In high-speed optical communication, synchronous multiwavelength lasers can simultaneously provide multiple wavelengths to multiple channels, while high repetition rate (>1 GHz) synchronous multiwavelength pulsed lasers can accelerate optical information processing and increase system communication capacity in dense wavelength division multiplexing (DWDM) systems. Furthermore, high repetition rate mode-locked pulsed lasers, with their short pulse intervals, have significant application value in precision spectroscopy, optical frequency measurement, biological imaging, and high-precision materials processing, and have become a research hotspot both domestically and internationally in recent years. Compared to traditional solid-state lasers and gas lasers, fiber lasers offer advantages such as high beam quality, high conversion efficiency, and excellent heat dissipation, making them an important method for achieving synchronous multiwavelength high repetition rate laser output. In particular, all-fiber mode-locked fiber lasers offer advantages such as simple and compact structure and strong anti-interference capabilities. Synchronous multi-wavelength high-repetition-rate pulsed fiber lasers have been widely used in terahertz wave generation, spectral analysis, and coherent ultrashort pulse synthesis, and are among the most promising laser sources in the field of novel lasers. Therefore, the development of synchronous multi-wavelength high-repetition-rate pulsed laser sources based on all-fiber structures has become a cutting-edge research topic in ultrafast optics and laser technology.

[0003] Traditional methods for achieving synchronized multi-wavelength pulses in synchronous multi-wavelength mode-locked fiber lasers mainly include: one approach is based on a single gain medium, constructing multiple laser resonators to achieve multi-wavelength output, and combining this with intracavity polarization adjustment to obtain time synchronization of the multi-wavelength pulse sequence; the other approach involves adding filtering devices such as Fabry-Perot etalons, fiber gratings, cavity mirror coatings, and narrowband filters, or dispersive elements, into the laser resonator cavity to achieve multi-wavelength output. For the first approach, the use of multiple laser resonators and pump modules significantly increases costs and complicates the system structure, making it unsuitable for practical applications. For the second approach, the use of intracavity filtering devices introduces greater insertion loss and makes the laser susceptible to interference from environmental vibrations, temperature, and other external factors, reducing its operational stability. Furthermore, a stable synchronization mechanism for multiple wavelengths is also crucial. Common multi-wavelength synchronization methods include active synchronization controlled by servo systems, frequency locking, and temperature control, as well as complex pulse sequence time synchronization devices. These methods, to some extent, complicate the structure, disrupt the all-fiber system structure, and increase costs.

[0004] Most reported synchronous multiwavelength fiber lasers are based on a ring resonator structure, which has a relatively long length, limiting the high repetition rate (PRR) output of the laser. To achieve high PPR mode-locked pulse output, the length of the laser resonator needs to be shortened to the centimeter level, making conventional methods such as adding filtering devices within the resonator difficult. Based on previous reports, using tapered fiber inside the resonator may solve this problem, such as the tapered fiber for multiwavelength high PPR output, its manufacturing method, and mode-locked laser (CN114498267A). This method constructs a laser resonator by drawing low-intensity, high-loss coaxial tapered fiber, and modulates the gain intensity of the gain fiber to achieve spectral filtering, thereby outputting multiwavelength high PPR laser. However, using tapered fiber requires careful consideration of the fiber waist diameter and modulation depth; otherwise, mutual coupling and interference effects between modes can easily occur, as illustrated by a laser fabrication method based on tapered active fiber to reduce the mode-locking threshold (CN113823988A). These effects lead to significant transmission loss in the gain fiber due to the transmission of the fundamental mode and other higher-order modes, thus preventing the synchronous multi-wavelength high-repetition-rate pulse output. Another approach is to incorporate fiber gratings within the ultrashort resonant cavity of a mode-locked fiber laser; however, drawing fiber gratings with different center wavelengths requires multi-phase masking, greatly increasing costs, and incorporating fiber gratings within the ultrashort resonant cavity length is challenging. Therefore, researching and realizing a fully fiber-based, compact, highly stable, and low-cost synchronous multi-wavelength high-repetition-rate pulsed fiber laser has significant research and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing. By eccentrically splicing the passive fiber and gain fiber in the laser resonant cavity, and introducing spectral comb filtering in the ultra-short resonant cavity, synchronous multi-wavelength high repetition rate mode-locked pulse output is achieved. It has the advantages of all-fiber structure, integrability, and high stability, and solves the problems of complex time synchronization device and low pulse repetition rate in multi-wavelength mode-locked fiber lasers.

[0006] The objective of this invention is achieved by at least one of the following technical solutions.

[0007] A synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing includes a first ferrule, a second ferrule, a passive fiber, a gain fiber, a semiconductor saturable absorber mirror, a dielectric film, a third ferrule, a pump source, a wavelength division multiplexer, and an isolator.

[0008] In this system, the passive optical fiber and the gain optical fiber are eccentrically fused together using a fiber optic fusion splicer. The other ends of the passive optical fiber and the gain optical fiber are then inserted into and pass through the first ferrule and the second ferrule, respectively. A dielectric film is disposed on the end face of the third ferrule. The end face of the first ferrule is aligned with a semiconductor saturable absorber mirror, and the end face of the second ferrule is aligned with the dielectric film. The wavelength division multiplexer is connected to the pigtail of the third ferrule, the pump end is connected to the pump source, and the signal end is connected to the isolator. A high-repetition-rate mode-locked pulsed laser is output from the isolator.

[0009] Furthermore, the end faces of the first, second, and third ferrules all need to be polished first.

[0010] Furthermore, the core diameter of the passive optical fiber is less than 3 μm to reduce the contact area between the light and the semiconductor saturable absorber mirror, thereby increasing the energy density of the light per unit area on the semiconductor saturable absorber mirror.

[0011] Furthermore, the gain fiber has a high gain coefficient greater than 1 dB / cm to achieve high repetition rate mode-locked pulse output.

[0012] Furthermore, the sum of the length of the passive fiber and the length of the gain fiber needs to be less than 10 cm in order to achieve high repetition rate mode-locked pulse output greater than 1 GHz.

[0013] Furthermore, the eccentric fusion splice loss of the passive optical fiber and the gain optical fiber is less than 0.2dB to reduce cavity loss.

[0014] Furthermore, the semiconductor saturable absorber mirror, as a mode-locking device, has a reflectivity of more than 80% for signal light.

[0015] Furthermore, the dielectric film has a reflectivity of greater than 90% for signal light and a transmittance of greater than 90% for pump light output from the pump source.

[0016] Furthermore, the pump source is a semiconductor laser or a fiber laser, and the emission wavelength is matched with the pump absorption wavelength of the gain fiber.

[0017] Furthermore, the isolator's operating wavelength covers the signal light wavelength range, preventing reflected light from the output end from returning into the resonant cavity and affecting the stability of the mode-locked state.

[0018] Compared with existing technologies, the advantages of this invention are:

[0019] This invention provides a synchronous multi-wavelength high repetition rate (HPR) pulsed fiber laser based on off-core fusion splicing. On one hand, by utilizing a novel spectral filtering mechanism, a comb-like spectral filter is introduced through off-core fusion splicing of the passive and gain fibers within the laser resonant cavity, achieving synchronous multi-wavelength HPR mode-locked pulse output. This simplifies the structure of the synchronous multi-wavelength HPR pulsed fiber laser and solves the problems of complex time synchronization devices and low pulse repetition rates in traditional multi-wavelength mode-locked fiber lasers. On the other hand, because this invention employs all-optical passive synchronization, it does not require any active feedback circuitry. Therefore, the device is simple, compact, highly integrable, and has strong anti-interference capabilities, enabling an all-fiber structure, which is beneficial for practical applications. Attached Figure Description

[0020] Figure 1 A schematic diagram of a synchronous multi-wavelength high repetition rate pulsed fiber laser structure based on eccentric fusion splicing is provided for an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the eccentric fusion splicing structure of passive optical fiber and gain optical fiber provided in an embodiment of the present invention;

[0022] Figure 3 A spectrum of synchronous multi-wavelength mode-locked pulse output for testing a synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, provided for an embodiment of the present invention;

[0023] Figure 4 A time-domain waveform diagram of the synchronous multi-wavelength mode-locked pulse output for testing a synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, provided for an embodiment of the present invention;

[0024] Figure 5 The fundamental frequency RF spectrum of the synchronous multi-wavelength mode-locked pulse output is provided for testing of a synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, as an embodiment of the present invention.

[0025] Figure 6 A spectrum of five-wavelength mode-locked pulse outputs for testing a synchronous multi-wavelength high-repetition-rate pulsed fiber laser based on eccentric fusion splicing, provided for an embodiment of the present invention;

[0026] Figure 7The image shows the spectrum of the synchronous six-wavelength mode-locked pulse output of a synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing, as provided in an embodiment of the present invention. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1:

[0029] A synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, such as Figure 1 As shown, it includes a first ferrule 1, a second ferrule 2, a passive optical fiber 3, a gain optical fiber 4, a semiconductor saturable absorber mirror 5, a dielectric film 6, a third ferrule 7, a pump source 8, a wavelength division multiplexer 9, and an isolator 10.

[0030] In this process, passive fiber 3 and gain fiber 4 are eccentrically fused together using a fiber optic fusion splicer. The other ends of passive fiber 3 and gain fiber 4 are then inserted into and pass through the first ferrule 1 and the second ferrule 2, respectively. The dielectric film 6 is disposed on the end face of the third ferrule 7. The end face of the first ferrule 1 is aligned with the semiconductor saturable absorber mirror 5, and the end face of the second ferrule 2 is aligned with the dielectric film 6. The wavelength division multiplexer 9 is connected to the pigtail of the third ferrule 7, its pump end is connected to the pump source 8, and its signal end is connected to the isolator 10. High repetition rate mode-locked pulsed laser is output from the isolator 10.

[0031] Furthermore, the end faces of the first insert 1, the second insert 2, and the third insert 7 all need to be polished first.

[0032] Furthermore, the core diameter of the passive optical fiber 3 is less than 3 μm, so as to reduce the contact area between the light and the semiconductor saturable absorber mirror 5 and increase the energy density of the light per unit area on the semiconductor saturable absorber mirror 5.

[0033] Furthermore, the gain fiber 4 has a high gain coefficient greater than 1dB / cm to achieve high repetition rate mode-locked pulse output.

[0034] Furthermore, the sum of the lengths of the passive fiber 3 and the gain fiber 4 needs to be less than 10 cm to achieve high repetition rate mode-locked pulse output greater than 1 GHz.

[0035] Furthermore, the eccentric fusion splice loss of the passive optical fiber 3 and the gain optical fiber 4 is less than 0.2dB to reduce cavity loss.

[0036] Furthermore, the semiconductor saturable absorber mirror 5 serves as a mode-locking device, exhibiting a reflectivity of over 80% for signal light.

[0037] Furthermore, the dielectric film 6 has a reflectivity of more than 90% for signal light and a transmittance of more than 90% for pump light output from the pump source 8.

[0038] Furthermore, the pump source 8 is a semiconductor laser or a fiber laser, and its emission wavelength is matched with the pump absorption wavelength of the gain fiber 4.

[0039] Furthermore, the operating wavelength of the isolator 10 covers the signal light wavelength range, preventing reflected light from the output end from returning into the resonant cavity and affecting the stability of the mode-locked state.

[0040] To achieve synchronous multi-wavelength high repetition rate (HRPR) pulsed fiber laser output, a linear resonant cavity structure is most suitable. The linear resonant cavity structure offers advantages such as short cavity length, high pump efficiency, low intracavity loss, and all-fiber connectivity, which are beneficial for achieving high HRPR mode-locked pulse output. The lengths of the passive fiber 3 and the gain fiber 4 within the resonant cavity affect the net dispersion of the cavity, thus influencing the output characteristics such as the pulse width and spectral bandwidth of the mode-locked pulse. Based on the criteria and quantitative analysis of small-signal gain and continuous-wave mode-locking, when the gain of the gain fiber 4 is insufficient, stable continuous-wave mode-locking cannot be achieved. Therefore, it is necessary to rationally design the dispersion value and length of the fibers within the resonant cavity. One end of the passive fiber 3 is tightly connected to the semiconductor saturable absorber mirror 5; therefore, the mode field diameter of the passive fiber 3 determines the saturation energy of the pulsed light acting on the surface of the semiconductor saturable absorber mirror 5, thereby affecting the pump power threshold of continuous-wave mode-locking.

[0041] Figure 1 This is a schematic diagram of a synchronous multi-wavelength high repetition rate pulsed fiber laser structure based on off-core fusion splicing in this embodiment. The gain fiber 4 is a high-thulium-doped silica fiber with a core diameter of 5.5 μm and a cladding diameter of 125 μm. The passive fiber 3 is a normal-dispersion silica fiber with a core diameter of 2.1 μm and a cladding diameter of 125 μm. The fibers inside the resonant cavity are tightly fitted into the first ferrule 1 and the second ferrule 2, each with a 125 μm aperture. The resonant cavity is modeled as a Fabry-Perot linear cavity, with a semiconductor saturable absorber mirror 5 and a dielectric film 6 at both ends to achieve optical feedback, thereby generating laser oscillation. The semiconductor saturable absorber mirror 5 has an area of ​​1 × 1 mm, a thickness of 450 μm, a recovery time of 10 ps, ​​a modulation depth of 12%, and a saturation energy of 65 μJ / cm². 2The dielectric film 6 has a thickness of 1 mm, a reflection range of 1850 nm to 2050 nm, and a reflectivity greater than 90% for signal light; its transmission range is 1450 nm to 1650 nm, and its transmittance for pump light is greater than 90%. The pump source 8 is a 1570 nm continuous-wave laser with a maximum output power of 500 mW. The 1570 nm pump light enters from the pump end of the 1570 nm / 1950 nm wavelength division multiplexer 9 and pumps the gain fiber 4 through the dielectric film 6 to generate signal light, which is finally output from the signal end of the wavelength division multiplexer 9. To prevent back-reflected light from the output end from returning to the resonant cavity and affecting the stability of mode locking, an optical fiber isolator 10 is connected to the output end, with an operating wavelength range of 1900 nm to 2000 nm.

[0042] Figure 2 This is a schematic diagram of the off-core fusion splicing structure of the passive fiber and the gain fiber in this embodiment. The lengths of the gain fiber 4 and the passive fiber 3 are 2.6 cm and 0.8 cm, respectively. After off-core fusion splicing of the passive fiber and the gain fiber using a fiber optic fusion splicer, the total length of the resonant cavity is 3.4 cm, and the corresponding pulse repetition frequency is approximately 2.9 GHz.

[0043] In this embodiment, when the pump power is 200mW, the laser outputs a stable synchronous multi-wavelength mode-locked pulse. The spectrum of the tested synchronous multi-wavelength mode-locked pulse output is shown below. Figure 3 As shown in the figure, the peak positions of the multiple wavelengths are 1910.8 nm, 1915.8 nm, 1920.4 nm, and 1925.3 nm, respectively, corresponding to a spectral filter modulation period of approximately 5 nm. The time-domain waveform of the tested synchronous multi-wavelength mode-locked pulse output is shown in the figure. Figure 4 As shown, the output pulses are a continuous wave mode-locked pulse sequence with consistent intensity, and the interval between two pulses is approximately 340 ps, ​​corresponding to the 3.4 cm resonant cavity length. The fundamental frequency RF spectrum of the tested synchronous multi-wavelength mode-locked pulse output is shown below. Figure 5 As shown, the peak position of the fundamental frequency radio frequency signal is 2.9417 GHz, that is, the fundamental frequency of the laser resonator is 2.9417 GHz, and the corresponding signal-to-noise ratio reaches 86 dB, indicating that the laser resonator is in a stable mode-locked state and there are no unstable mode-locking phenomena such as Q-switching.

[0044] Example 2:

[0045] This embodiment provides a synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, which has the same structure as the laser in Embodiment 1. By adjusting the coupling position between the gain fiber 4 and the dielectric film 6, i.e., rotating the position of the dielectric film 6, the contact area of ​​the optical signal output from the dielectric film 6 coupled into the core of the gain fiber 4 is changed. The spectrum of the synchronous five-wavelength mode-locked pulse output is shown in the figure. Figure 6As shown, the peak positions of the five wavelengths are 1905.9nm, 1910.7nm, 1915.6nm, 1920.3nm and 1925.2nm, respectively, and the corresponding spectral filter modulation period is approximately 5nm.

[0046] Example 3:

[0047] This embodiment provides a synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, which has the same structure as the laser in Embodiment 1. By adjusting the coupling position between the gain fiber 4 and the dielectric film 6, i.e., rotating the position of the dielectric film 6, the contact area of ​​the optical signal output from the dielectric film 6 coupled into the core of the gain fiber 4 is changed. The spectrum of the synchronous six-wavelength mode-locked pulse output is shown in the figure. Figure 7 As shown, the peak positions of the six wavelengths are 1910.9nm, 1915.8nm, 1920.4nm, 1925.4nm, 1930.3nm, and 1935.2nm, respectively, with a corresponding spectral filter modulation period of approximately 5nm.

[0048] This invention utilizes the off-core fusion splicing of passive and gain fibers to introduce spectral comb filtering, constructing a centimeter-scale synchronous multi-wavelength high repetition rate (HRPR) pulse resonator. In the overall structure of the resonator, the repetition rate of the mode-locked pulse is determined by the lengths of the passive and gain fibers. Therefore, by controlling the fiber lengths, synchronous multi-wavelength mode-locked pulse output with a repetition rate >1 GHz can be flexibly achieved. Furthermore, based on the different operating wavelength parameters of the intracavity fiber, pump source, and fiber optic devices, synchronous multi-wavelength HRPR pulsed lasers in different wavelength bands can be realized.

[0049] This invention targets high repetition rate (PRR) mode-locked fiber lasers. By designing a high PPR laser resonant cavity structure based on passive fiber and gain fiber eccentric fusion splicing, and introducing spectral comb filtering within the ultrashort resonant cavity, synchronous multi-wavelength high PPR mode-locked pulse output is achieved. It has advantages such as all-fiber structure, integrability, and high stability, and solves the problems of complex time synchronization devices and low pulse repetition rate in multi-wavelength mode-locked fiber lasers.

[0050] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A synchronous multi-wavelength high repetition rate pulsed fiber laser based on off-core fusion splicing, characterized in that, It includes a first ferrule (1), a second ferrule (2), a passive optical fiber (3), a gain optical fiber (4), a semiconductor saturable absorber mirror (5), a dielectric film (6), a third ferrule (7), a pump source (8), a wavelength division multiplexer (9), and an isolator (10). In this process, the passive optical fiber (3) and the gain optical fiber (4) are eccentrically fused together by an optical fiber fusion splicer, and the other ends of the passive optical fiber (3) and the gain optical fiber (4) are inserted into and pass through the first ferrule (1) and the second ferrule (2), respectively; the dielectric film (6) is disposed on the end face of the third ferrule (7); the end face of the first ferrule (1) is connected to the semiconductor saturable absorber mirror (5), and the end face of the second ferrule (2) is connected to the dielectric film (6); the wavelength division multiplexer (9) is connected to the pigtail of the third ferrule (7), the pump end is connected to the pump source (8), and the signal end is connected to the isolator (10); the high repetition rate mode-locked pulsed laser is output from the isolator (10); The core diameter of the passive optical fiber (3) is less than 3 μm, so as to reduce the contact area between the light and the semiconductor saturable absorber mirror (5) and increase the energy density of the light per unit area on the semiconductor saturable absorber mirror (5). The gain fiber (4) has a gain factor greater than 1 dB / cm; The sum of the lengths of the passive optical fiber (3) and the gain optical fiber (4) is less than 10 cm; The eccentric fusion splice loss of the passive optical fiber (3) and the gain optical fiber (4) is less than 0.2 dB.

2. The synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing according to claim 1, characterized in that, The end faces of the first ferrule (1), the second ferrule (2) and the third ferrule (7) must be polished first.

3. A synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing according to claim 1, characterized in that, The semiconductor saturable absorber mirror (5) serves as a mode-locking device and has a reflectivity of more than 80% for signal light.

4. A synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing according to claim 1, characterized in that, The dielectric film (6) has a reflectivity of more than 90% for signal light and a transmittance of more than 90% for pump light output from the pump source (8).

5. A synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing according to claim 1, characterized in that, The pump source (8) is a semiconductor laser or a fiber laser, and its emission wavelength is matched with the pump absorption wavelength of the gain fiber (4).

6. A synchronous multi-wavelength high repetition rate pulsed fiber laser based on eccentric fusion splicing according to claim 1, characterized in that, The isolator (10) operates within the signal light wavelength range, preventing reflected light from the output end from returning to the resonant cavity and affecting the stability of the mode-locked state.

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