An erbium-ytterbium co-doped double-clad fiber laser with oscillation wavelength covering 1470nm~1510nm

Abstract

The application discloses an erbium-ytterbium co-doped double-clad fiber laser with oscillation wavelength covering 1470nm-1510nm. The laser takes erbium-ytterbium co-doped double-clad fiber as a gain medium, takes a 915nm-976nm multimode semiconductor laser as a pump source, couples the pump light into the inner cladding through a pump combiner, utilizes a pair of fiber Bragg gratings which are respectively fused at two ends of the gain fiber and have a center reflection wavelength of a set oscillation wavelength λ0 to form a resonant cavity, and realizes high-power and single-wavelength stable oscillation output of the wavelength λ0 by optimizing the length and doping concentration of the gain fiber under the premise of overcoming the ground state absorption of erbium ions. The output end of the laser is provided with a short-wave pass filter, the cutoff wavelength λc satisfies λ0<λc≤1520nm, and residual stray light with a wavelength greater than λc until 1600nm is filtered out. The application has the advantages of low cost, power scalability, full fiber, wavelength customization and high spectral purity, and can be directly used as a pump source of a Raman fiber amplifier and a high-power erbium-doped fiber amplifier.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser and fiber amplifier technology, specifically relating to a high-power fiber laser that uses erbium / ytterbium (Er / Yb) co-doped double-clad fiber as the gain medium, a 9XX nm (915nm~976nm) multimode semiconductor laser as the pump source, and a fiber Bragg grating (FBG) with a center wavelength that can be preset in the 1470nm~1510nm band to form the resonant cavity. It can be used as a pump source for Raman fiber amplifiers (FRA) and high-power erbium-doped fiber amplifiers (EDFA). Background Technology

[0002] Laser sources in the 1470nm–1510nm band are key active devices in fiber optic communication systems, widely used for forward and backward pumping of erbium-doped fiber amplifiers (EDFAs) and as pump sources for fiber Raman amplifiers (FRAs). 1480nm is the most widely used typical wavelength within this band. Compared to the commonly used 980nm pump, this band exhibits lower quantum defect and closer energies between pump photons and signal photons, thus offering unique advantages in long-distance, high dynamic range, and L-band amplification scenarios. Furthermore, this band falls within the optimal frequency shift window of the Raman gain spectrum relative to the signal wavelength (around 1550nm), making it an irreplaceable pump wavelength range for broadband Raman amplifiers. In addition, due to considerations such as gain flatness, noise figure, or specific channel planning, different manufacturers' EDFA and Raman amplifier products often require multiple specific pump wavelength specifications such as 1470nm, 1480nm, 1490nm, and 1500nm, which puts forward higher requirements for the customizability of the pump light source wavelength.

[0003] In existing technologies, laser sources in the 1470nm~1510nm band mainly rely on strained multi-quantum-well semiconductor laser diodes (LDs) based on InGaAsP / InP materials. These chips require precise quantum well bandgap engineering design via molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). The manufacturing process is complex, and the requirements for epitaxial layer thickness and composition control are extremely high, resulting in low chip yield and high production costs. Furthermore, limited by factors such as the waveguide cavity surface optical damage threshold (COD), carrier leakage, and thermal effects, the reliable output power of a single semiconductor laser chip in this band is typically in the range of 300mW~600mW, with some high-end products reaching around 1W. Even more disadvantageous is that once the semiconductor LD completes epitaxial growth and chip manufacturing, its emission wavelength is essentially fixed. To cover multiple specific wavelength specifications within the 1470nm~1510nm range, it is often necessary to develop corresponding chip part numbers for each target wavelength, further increasing R&D and inventory costs. When the application scenario requires pump power of 2W or more, or even several watts or tens of watts (such as broadband Raman amplifiers, multi-wavelength multiplexing systems, or high-capacity submarine cable repeater amplifiers), multiple LD chips must be used to combine power through polarization multiplexing, wavelength multiplexing, etc. This not only significantly increases the system cost and size, but also reduces the overall system robustness due to insertion loss of multiplexing devices and reliability issues of multiple chips.

[0004] Meanwhile, after more than 20 years of large-scale development in the fiber laser industry, the epitaxial growth process, chip packaging and pigtail coupling technology of 9XX nm (915nm~976nm) band multimode semiconductor laser pump modules have become highly mature. The output power of a single pump module can easily reach the level of tens of watts or even hundreds of watts, and the cost is far lower than that of single-mode 1470nm~1510nm band semiconductor lasers of the same power. The supply chain is stable and the sources are wide, making it the most widely used pump source in the field of fiber laser / amplifier cladding pumping.

[0005] Existing technologies have attempted to generate short-wavelength laser oscillations using erbium-doped fiber itself. However, erbium ions (Er³⁺) exhibit strong ground-state absorption (GSA) in the 1470nm–1510nm band, and the shorter the wavelength, the larger the ground-state absorption coefficient, and the more difficult it is to start oscillation. The stimulated emission cross-section in this band is significantly smaller than the absorption cross-section, representing a typical short-wavelength edge of a quasi-three-level system. Extremely high population inversion ratios are required to achieve net gain; otherwise, it is easily suppressed by its own ground-state absorption. Therefore, conventional erbium-doped fiber lasers generally operate in the 1530nm–1610nm C / L band, which offers higher gain and is easier to start oscillate. Achieving high-efficiency, high-power, and stable oscillation output directly in the 1470nm–1510nm band presents significant technical challenges. Currently, there is a lack of practical, industrially viable fiber laser solutions that can replace traditional semiconductor lasers in this band, and whose wavelengths can be flexibly customized according to applications.

[0006] In summary, how to utilize a low-cost, high-power, and technologically mature 9XX nm multimode pump source, combined with appropriate gain fiber and resonant cavity design, to overcome the ground-state absorption problem of erbium ions in the 1470nm~1510nm band and achieve all-fiber laser output with flexible wavelength setting within this range, high power, compact structure, and high reliability is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm. This invention uses erbium-ytterbium co-doped double-clad fiber as the gain medium, a 9XX nm multimode semiconductor laser as the cladding pump source, and a pair of fiber Bragg gratings with center wavelengths matched to the set oscillation wavelength λ0 to form the resonant cavity. Through synergistic optimization design of the gain fiber parameters and the resonant cavity parameters, high-efficiency, high-power, and stable single-wavelength oscillation output at the λ0 wavelength is achieved while overcoming erbium ion ground-state absorption. This invention replaces the traditional, expensive, and fixed-wavelength semiconductor laser in the 1470nm~1510nm band with a low-cost, easily scalable, and customizable all-fiber structure, serving as the pump source for Raman fiber amplifiers and high-power EDFAs.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: an erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm, wherein the oscillation wavelength λ0 can be preset within the range of 1470nm~1510nm according to application requirements, comprising a multimode pump source unit, a pump beam combining unit, a resonant cavity gain unit, and an output processing unit connected in sequence, specifically including the following parts:

[0009] 1. Erbium-ytterbium co-doped double-clad gain fiber

[0010] The core of the gain fiber is co-doped with erbium ions (Er). 3+ ) and ytterbium ions (Yb 3+ The concentration of ytterbium ions is significantly higher than that of erbium ions. As sensitizing ions, ytterbium ions efficiently absorb the 9XX nm pump light transmitted in the inner cladding and transfer energy through the Förster resonance between ytterbium and erbium ions (Yb). 3+ : 2 F5 / 2 → Er 3+ : 4 I11 / 2 / 4 I13 / 2) transfers the excitation energy to erbium ions, enabling erbium ions to... 4 High-concentration population inversion at the I13 / 2 energy level. The inner cladding of the gain fiber uses asymmetric multimode waveguide cross-sections such as D-shape, octagon, or petal shape to improve the absorption efficiency of pump light, while the outer cladding is a low-refractive-index fluorinated polymer coating, forming a double-cladding structure.

[0011] 2. 9XX nm multimode pump source

[0012] It consists of one or more multimode semiconductor laser pump modules with center wavelengths in the range of 915nm to 976nm. The multimode pigtail of each pump module is fused to the inner cladding coupling end of the gain fiber via one or more (N+1)×1 fiber combiners (such as (2+1)×1 or (6+1)×1 type combiners) to realize spatial beam combining and coupling injection of multiple pump beams; the pumping mode can be forward pumping, reverse pumping or bidirectional pumping.

[0013] 3. Resonant cavity

[0014] A linear FP-type resonant cavity is constructed from a high-reflectivity fiber grating (HR-FBG) and an output-coupled fiber grating (OC-FBG). The center reflection wavelength of both is designed to be consistent with the set oscillation wavelength λ0 (λ0 is selected from a wavelength in the range of 1470nm~1510nm, and the wavelength matching tolerance between the two is ±1nm). Both are fused to the two ends of the gain fiber. The HR-FBG is located on the pump incident side, with a reflectivity of not less than 99% and a reflection bandwidth of 0.5nm~3nm. The OC-FBG is located on the laser output side, with a reflectivity of 5%~30%, which can be adjusted according to the required output power and the power density inside the cavity. Its reflection bandwidth is comparable to or slightly wider than that of the HR-FBG to ensure stable feedback of the optical field inside the resonant cavity.

[0015] 4. Optimization of gain fiber length

[0016] The length of the gain fiber is designed within the range of 0.5m to 10m based on the set oscillation wavelength λ0. The specific value can be optimized and adjusted in implementation according to the actual pump absorption coefficient and output power requirements. The closer λ0 is to the 1470nm short-wavelength edge, the stronger the erbium ion ground state absorption, the higher the required population inversion ratio, and the shorter the length of the gain fiber should be, along with a higher pump power density. The closer λ0 is to the 1510nm long-wavelength edge, the relatively weaker the ground state absorption, and the longer the length of the gain fiber can be appropriately increased. While ensuring sufficient absorption coefficient for the 9XX nm pump light (typically the inner cladding pump absorption coefficient is 0.5dB / m~3dB / m) and achieving near-depletion absorption of the pump light, the length of the gain fiber should be shortened as much as possible to reduce the ground-state absorption loss of the signal light during round-trip propagation in the long fiber. At the same time, competitive amplification and parasitic oscillations of spontaneous emission (ASE) in the 1530nm~1610nm C / L band caused by excessive fiber length and an increase in the population inversion insufficiency region should be suppressed, thereby ensuring that the net gain advantage in the resonant cavity is concentrated at the λ0 design wavelength.

[0017] 5. Cladding Light Stripper (CLS)

[0018] Located on the output fiber after OC-FBG, the residual 9XX nm cladding pump light that is not completely absorbed by the gain fiber is filtered out and dissipated as heat by roughening the surface of the fiber cladding or coating it with a high refractive index absorption coating, thus preventing it from entering downstream devices and causing interference, optical damage or measurement errors.

[0019] 6. Fiber optic isolator

[0020] Located at the end of the output fiber, it is used to suppress back-reflected light from subsequent optical paths (such as Raman amplifier transmission fiber or EDFA gain fiber) from re-entering the resonant cavity, and to prevent instability in laser output power and wavelength caused by external feedback.

[0021] 7. Shortwave Pass Filter

[0022] The final output of the laser, located after the fiber optic isolator, has a passband covering the set oscillation wavelength λ0, a passband cutoff wavelength λc satisfying λ0 < λc ≤ 1520 nm, and a stopband covering the λc to 1600 nm band. This is used to filter out residual long-wavelength stray light in the output light (mainly spontaneous emission and potential parasitic oscillation components in the C / L band of the gain fiber that are not completely suppressed by the resonant cavity), allowing only light with wavelengths less than λc to pass through and be output, thereby further purifying the laser's output spectrum. When λ0 takes different values ​​within the range of 1470 nm to 1510 nm, the cutoff wavelength λc of the short-pass filter can be adjusted accordingly to balance the smooth passage of the oscillation wavelength with the effective blocking of stray light in the 1530 nm to 1610 nm signal band. This short-pass filter can effectively filter out residual spontaneous emission and parasitic oscillation components with wavelengths longer than λc up to 1600nm, avoiding wavelength overlap and crosstalk between such stray light and the 1530nm~1610nm signal band amplified by downstream Raman amplifiers or EDFAs, thereby ensuring the spectral purity of the pump source and system compatibility.

[0023] Furthermore, the HR-FBG and OC-FBG can adjust the grating period during the fiber grating writing process to arbitrarily set the center reflection wavelength within the range of 1470nm~1510nm. This allows the same design platform consisting of a gain fiber, pump source, and peripheral devices to cover multiple specific wavelength specifications such as 1470nm, 1480nm, 1490nm, 1500nm, and 1505nm simply by replacing or rewriting the FBG grating. This eliminates the need to redesign the chip or optical path structure for each wavelength, significantly improving the product's spectrum coverage and R&D efficiency.

[0024] Furthermore, in the erbium-ytterbium co-doped double-clad fiber, the molar ratio of ytterbium ion concentration to erbium ion concentration is controlled within the range of 10:1 to 50:1 to ensure that the energy transfer efficiency is not less than 80% while suppressing the concentration quenching effect caused by erbium ion clusters. This molar ratio can be adjusted according to the set oscillation wavelength λ0. The closer λ0 is to the short-wavelength edge, the lower the erbium ion concentration is to reduce self-absorption loss.

[0025] Furthermore, the OC-FBG can employ an apodized grating design to suppress sidelobes and narrow the reflection bandwidth, thereby obtaining a λ0 laser output with narrower linewidth and higher spectral purity, meeting the requirements of the Raman amplifier for pump source relative intensity noise (RIN) and spectral width. Alternatively, a chirped grating design can be used to broaden the reflection spectrum and reduce the influence of nonlinear effects such as stimulated Brillouin scattering (SBS) under high-power operating conditions. In specific implementations, those skilled in the art can select one or combine and optimize the design between apodized gratings and chirped gratings according to the required linewidth, power, and tolerance to nonlinear effects of the output laser.

[0026] Furthermore, the 9XX nm multimode pump source can use one or more wavelength combinations of 915 nm, 940 nm or 976 nm. Among them, the pump light wavelengths of 915 nm and 940 nm deviate from the main absorption peak of ytterbium ions at 976 nm, and the pump absorption coefficient is relatively flat and less affected by temperature, making it more suitable for stable operation in high-power and high-temperature scenarios.

[0027] Furthermore, the fiber laser described in this invention can adopt a bidirectional pumping structure, that is, 9XX nm pump light is coupled at both ends of the gain fiber through wavelength division multiplexing devices to improve pump utilization efficiency, achieve a more uniform population inversion distribution, and further increase the upper limit of output power.

[0028] Furthermore, multiple single-module fiber lasers can be cascaded or combined in parallel using wavelength division multiplexers or spatial beam combiners to obtain λ0 laser output with power in the tens of watts or even higher, meeting the pumping requirements of ultra-wideband, multi-wavelength Raman amplification systems.

[0029] Furthermore, the short-pass filter can be implemented using one of the following: a fused tapered wavelength division multiplexer (WDM), a thin-film dielectric filter type coaxial fiber device, a long-period fiber grating (LPG), or a tilted fiber grating (TFBG). Its cutoff wavelength λc can be customized in the range of 1472nm~1520nm according to the set oscillation wavelength λ0. The insertion loss at λ0 is not greater than 0.5dB, and the stopband rejection ratio in the λc to 1600nm band is not less than 20dB. This ensures that stray light components that may cause crosstalk to the downstream Raman amplifier or EDFA signal band (usually located in the 1530nm~1610nm range) are fully filtered out with almost no loss of effective laser power.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Replacing the complex and costly 1470nm~1510nm band single-mode semiconductor laser chip with a mature, low-cost, and scalable 9XX nm multimode semiconductor laser pump source significantly reduces the manufacturing cost and technical threshold of laser sources in this band. The pump source cost can be reduced by more than 50% compared with traditional solutions.

[0032] 2. The double-clad structure significantly improves the pump light coupling efficiency and utilization. Through multi-channel pump beam combining and bidirectional pump design, the power is highly scalable. A single module can achieve watt-level to tens of watt-level λ0 laser output, breaking through the bottleneck that the power of a single tube of traditional semiconductor lasers in this band is limited to the range of hundreds of milliwatts to 1W.

[0033] 3. The entire unit adopts an all-fiber structure. The gain fiber, pump combiner, and FBG resonant cavity are all connected by fusion splicing. There is no need for free-space coupling optical components. The structure is compact, resistant to environmental vibration and shock, maintenance-free, and its reliability and long-term stability are significantly better than the traditional solution of discrete component bundle combining.

[0034] 4. Through the coordinated optimization design of gain fiber length and doping concentration and high-precision FBG wavelength matching, the competitive amplification and parasitic oscillation of spontaneous emission in the 1530nm~1610nm C / L band are effectively suppressed, and high-purity and high-stability oscillation output of λ0 single design wavelength is achieved, which meets the strict requirements of Raman amplifier and EDFA pump source for wavelength accuracy and noise characteristics.

[0035] 5. The fiber laser provided by this invention can be directly used as a high-power pump source for broadband Raman fiber amplifiers, or as a secondary / backward pump source for high-power EDFAs. It has the characteristics of simple structure, controllable cost, and easy mass production, and has good prospects for industrial application.

[0036] 6. By setting a short-pass filter at the output end, residual light above the cutoff wavelength λc up to 1600nm is strictly filtered out, and only pure λ0 laser with a wavelength less than λc is output. This effectively avoids crosstalk, additional noise, or measurement errors caused by the overlap of residual C / L band light with the signal light amplified by the Raman amplifier and EDFA (usually located in the 1530nm~1610nm band) in wavelength. This further improves the spectral purity and system compatibility of this invention when it is used as a pump source in optical fiber communication systems.

[0037] 7. By designing the resonant cavity FBG center wavelength λ0 and the short-pass filter cutoff wavelength λc as a parameterized scheme that can be adjusted collaboratively within the range of 1470nm~1510nm, the same set of gain fiber and pump source platform can cover different pump wavelength specifications required for multiple specific applications, which significantly improves the product's versatility, spectrum coverage and large-scale production efficiency, and further reduces the overall R&D and manufacturing costs of multi-wavelength product lines. Attached Figure Description

[0038] Figure 1 A schematic diagram of the overall structure of the erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm provided by the present invention (the oscillation wavelength λ0 can be set in the range of 1470nm~1510nm, and λ0=1480nm is used as an example in the figure).

[0039] In the figure: 1. 9XX nm multimode pumped laser module; 2. (N+1)×1 pump combiner; 3. High-reflectivity fiber grating HR-FBG; 4. Erbium-ytterbium co-doped double-clad gain fiber; 5. Output coupling fiber grating OC-FBG; 6. Cladding optical filter CLS; 7. Fiber isolator; 8. Short-pass filter. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0042] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0043] Figure 1 This is a schematic diagram of the overall structure of the erbium-ytterbium co-doped double-clad fiber laser in this embodiment. Figure 1 As shown, the fiber laser provided in this embodiment is composed of a 9XX nm multimode pump laser module 1, an (N+1)×1 pump combiner 2, a high-reflectivity fiber grating HR-FBG 3, an erbium-ytterbium co-doped double-clad gain fiber 4, an output coupling fiber grating OC-FBG 5, a cladding optical filter CLS 6, a fiber isolator 7, and a short-pass filter 8 connected in sequence. The HR-FBG 3 and OC-FBG... 5 are fused to both ends of the gain fiber 4, and the center reflection wavelength of both is designed to be the set oscillation wavelength λ0 (λ0∈[1470nm,1510nm], the figure shows λ0=1480nm as an example), together forming a linear resonant cavity; the short-pass filter 8 is set after the isolator 7 as the final output stage of the laser, its passband covers λ0, the cutoff wavelength λc satisfies λ0<λc≤1520nm, and the stopband covers λc up to 1600nm, used to filter out residual long-wavelength stray light; the pure λ0 laser output from the entire laser can be directly used as the pump source of the Raman fiber amplifier or high-power EDFA after passing through the short-pass filter 8 and connected to the subsequent system.

[0044] Example 1: Unidirectionally pumped 2W-level 1480nm fiber laser (typical example with λ0=1480nm)

[0045] In this embodiment, four multimode semiconductor laser pump modules with a single-tube output power of 6W and a center wavelength of 976nm are used. These modules are coupled into the inner cladding of an erbium-ytterbium co-doped double-clad gain fiber via a (4+1)×1 pump combiner. The gain fiber has a core diameter of approximately 6μm and a numerical aperture of 0.20. The inner cladding has a diameter of 130μm, an octagonal cross-section, and a numerical aperture of 0.46. The cladding absorption coefficient of the fiber for the 976nm pump light is approximately 1.2dB / m, and the erbium-ytterbium molar ratio is approximately 1:20. The gain fiber length is 6m. The HR-FBG has a reflectivity of 99.5%, a reflection bandwidth of 1.2nm, and a center wavelength of 1480.2nm; the OC-FBG has a reflectivity of 15%, a reflection bandwidth of 1.5nm, and a center wavelength of 1480.0nm. In practical implementation, the OC-FBG can also employ an apodized grating design to suppress sidelobes and narrow linewidth, or a chirped grating design to broaden the reflection spectrum and reduce nonlinear effects such as stimulated Brillouin scattering, to adapt to the differentiated spectral characteristics required by different application scenarios. With a total pump injection power of approximately 22W, the measured 1480nm laser output power is approximately 2.1W, the optical-to-optical conversion efficiency is approximately 9.5%, the output spectral 3dB linewidth is approximately 0.8nm, and the residual ASE suppression ratio in the C-band (1530nm~1565nm) is better than 35dB. This indicates that the structure described in this invention can achieve stable high-power output at a wavelength of 1480nm while effectively suppressing competitive oscillations in the C-band. After connecting a short-pass filter (cutoff wavelength λc=1500nm, insertion loss of about 0.3dB) with a passband less than 1500nm and a stopband covering 1500nm~1600nm after the isolator, the measured proportion of residual stray light in the 1500nm~1600nm band in the total output power was further reduced from about 0.03% before filtering (corresponding to a suppression ratio of about 35dB) to less than 0.0003% (corresponding to a suppression ratio better than 65dB). The effective output power loss at 1480nm was less than 0.1W, which verifies that the short-pass filter can significantly purify the output spectrum without affecting the output power of the main wavelength.

[0046] Example 2: Bidirectional pumping to increase output power

[0047] Based on the structure of Example 1, the pump coupling method was changed to bidirectional pumping. Specifically, approximately 22W of 976nm pump light was injected into each end of the gain fiber via a wavelength division multiplexing combiner, increasing the total pump injection power to approximately 44W. The length of the gain fiber was correspondingly optimized to 8m to ensure uniform absorption of the bidirectional pump light. Measured 1480nm laser output power increased to approximately 4.6W, and the optical-to-optical conversion efficiency increased to approximately 10.5%. Furthermore, the heat load distribution along the fiber length was more uniform, and the local temperature rise of the fiber was reduced by approximately 30% compared to the unidirectional pumping scheme, which is beneficial for improving the reliability of the device under long-term high-power operation.

[0048] Example 3: Application as a pump source for Raman fiber amplifiers

[0049] The 1480nm fiber laser prepared in Example 1 was connected to the end of a 20km long standard single-mode transmission fiber via a wavelength division multiplexing coupler to form a back-pumped Raman fiber amplifier. Test results show that, under a 1480nm pump power of 2W, a switched Raman gain of 6dB to 8dB can be obtained in the 1550nm to 1565nm signal band. This verifies that the 1480nm fiber laser described in this invention can directly replace the traditional semiconductor 1480nm laser as the pump source for a Raman fiber amplifier, and the manufacturing cost can be reduced by more than 50% under similar output power conditions.

[0050] Example 4: Short-wavelength edge oscillation at λ0=1470nm (verification of lower wavelength limit)

[0051] In this embodiment, the same pump configuration as in Embodiment 1 (four 6W, 976nm multimode pump modules, (4+1)×1 pump combiner) is used. However, the center wavelengths of both the HR-FBG and OC-FBG are adjusted to 1470nm±1nm. Simultaneously, to overcome stronger ground-state absorption, the length of the gain fiber is shortened to 3m, and the erbium-ytterbium molar ratio is adjusted to 1:25 to improve pump absorption efficiency and reduce self-absorption loss. Under the same 22W pump injection power, the measured 1470nm laser output power is approximately 1.3W, and the optical-to-optical conversion efficiency is approximately 5.9%, lower than the conversion efficiency at λ0=1480nm. This indicates that the closer the oscillation wavelength is to the short-wavelength edge, the more significant the constraint of ground-state absorption on efficiency. However, stable oscillation output at the watt level can still be achieved, verifying the feasibility of the present invention at a wavelength of 1470nm. Accordingly, the cutoff wavelength of the short-pass filter is adjusted to λc=1490nm, and the stopband covers 1490nm~1600nm, so as to fully block long-wave stray light while allowing 1470nm effective laser light to pass.

[0052] Example 5: Long-wavelength edge oscillation at λ0=1510nm (verifying the upper limit of wavelength)

[0053] In this embodiment, the same pump configuration as in Embodiment 1 is used, with the center wavelengths of both the HR-FBG and OC-FBG adjusted to 1510nm ± 1nm. The length of the gain fiber can be appropriately increased to 10m, and the erbium-ytterbium molar ratio is adjusted to 1:15. Under the same 22W pump injection power, the measured output power of the 1510nm laser is approximately 2.6W, and the optical-to-optical conversion efficiency is approximately 11.8%, which is higher than the conversion efficiency at λ0 = 1480nm. This indicates that the closer the oscillation wavelength is to the long-wavelength edge (i.e., closer to the conventional C-band gain advantage region), the weaker the ground-state absorption constraint and the higher the conversion efficiency. Accordingly, the cutoff wavelength of the short-pass filter is adjusted to λc = 1520nm, and the stopband covers 1520nm~1600nm to ensure that the effective 1510nm laser is not blocked while still effectively filtering out residual stray light in the C / L band. Examples 1, 4, and 5 above collectively verify the feasibility and engineering applicability of the fiber laser structure described in this invention within the entire target wavelength range of 1470nm to 1510nm. Specifically, the 6m and 10m gain fiber lengths used in Examples 1 and 5 are both within the range of 0.5m to 10m defined in claim 3, further demonstrating that this length range can effectively support the synergistic optimization requirements of population inversion distribution and ground-state absorption suppression at different oscillation wavelengths.

[0054] Oscillation wavelength λ0 1470nm~1510nm (typically 1480nm) Set by HR / OC-FBG grating period Pump wavelength 915nm~976nm Multimode semiconductor laser pump module Erbium-ytterbium molar concentration ratio 1:10~1:50 As λ0 is adjusted, the concentration ratio at the shortwave end is lower. Gain fiber length 0.5m~5m As λ0 takes short / long values ​​at the short / long wavelength edges, respectively. HR-FBG reflectivity ≥99% Center wavelength λ0, tolerance ±1nm OC-FBG reflectivity 5%~30% Adjustable according to output power requirements Single module output power 10,000 to 100,000 Multiple modules can be cascaded to achieve higher power. C / L band suppression ratio >30dB Guarantee stable oscillation of λ0 single wavelength Shortwave pass filter cutoff wavelength λc λ0<λc≤1520nm With adjustment of λ0, the stopband coverage reaches λc~1600nm. Shortwave pass filter stopband rejection ratio >20dB (typically up to 65dB) Stopband λc ~ 1600nm Shortwave pass filter insertion loss ≤0.5dB λ0 Passband Loss

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm, characterized in that, include: Erbium-ytterbium co-doped double-clad gain fiber, whose core is co-doped with erbium and ytterbium ions, is used to achieve population inversion of erbium ions under 9XX nm pump light excitation and generate optical gain in the 1470nm~1510nm band. A 9XX nm multimode semiconductor laser pump source, with a wavelength range of 915 nm to 976 nm, is coupled into the inner cladding of the gain fiber through a pump combiner. The resonant cavity is composed of a high-reflectivity fiber grating and an output coupling fiber grating respectively fused to both ends of the gain fiber. The center reflection wavelength of the high-reflectivity fiber grating and the output coupling fiber grating are both set oscillation wavelengths λ0±1nm, where λ0 is selected from a wavelength in the range of 1470nm~1510nm, in order to form an oscillating light field of wavelength λ0 in the gain fiber and output laser light of wavelength λ0.

2. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, The molar ratio of ytterbium ions to erbium ions in the gain fiber is 10:1 to 50:

1. The length of the gain fiber is 0.5m to 10m, and the absorption coefficient of its inner cladding for 9XX nm pump light is 0.5dB / m to 3dB / m. The length of the gain fiber is adjusted according to the value of λ0. The closer λ0 is to 1470nm, the shorter the length; the closer λ0 is to 1510nm, the longer the length.

3. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, The high-reflectivity fiber grating has a reflectivity of not less than 99% and a reflection bandwidth of 0.5nm to 3nm; the output-coupled fiber grating has a reflectivity of 5% to 30%.

4. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, The pump combiner is an (N+1)×1 type fiber combiner, where N is a positive integer greater than or equal to 1, used to couple the output light of multiple 9XX nm multimode pump modules into the same gain fiber. The 9XX nm multimode pump source is coupled to the gain fiber using one of the following methods: forward pumping, reverse pumping, or bidirectional pumping.

5. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, It also includes a cladding light filter disposed after the output coupled fiber grating, for filtering out and dissipating the unabsorbed residual 9XX nm pump light in the gain fiber.

6. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, It also includes an optical fiber isolator located at the laser output end to suppress back-reflected light from the subsequent optical path from returning to the resonant cavity.

7. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, The output coupling fiber grating is an apodized grating or a chirped grating.

8. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 6, characterized in that, It also includes a short-pass filter located after the fiber optic isolator as the final output stage of the laser; The shortwave pass filter has a passband that covers the oscillation wavelength λ0, and its cutoff wavelength λc satisfies λ0<λc≤1520nm. Its stopband covers the λc to 1600nm band and is used to filter out the light in the stopband band of the output light, so that only light with a wavelength less than λc is output. The short-pass filter is one of a fused biconical wavelength division multiplexer, a thin-film dielectric filter type coaxial fiber device, a long-period fiber grating, or a tilted fiber grating. The cutoff wavelength λc is customized according to λ0 within the range of 1472nm to 1520nm, with an insertion loss at λ0 of no more than 0.5dB and a stopband rejection ratio of no less than 20dB in the λc to 1600nm band.

9. The erbium-ytterbium co-doped double-clad fiber laser with an oscillation wavelength covering 1470nm~1510nm according to claim 1, characterized in that, The λ0 is one of 1470nm, 1480nm, 1490nm, 1500nm or 1510nm.

10. A Raman fiber amplifier or an erbium-doped fiber amplifier, characterized in that, The erbium-ytterbium co-doped double-clad fiber laser described in any one of claims 1 to 9 is used as the pump source.

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