An ultraviolet-mid-infrared waveband flat type supercontinuum all-fiber laser

Abstract

The application discloses a kind of ultraviolet-middle infrared waveband flat type supercontinuum all-fiber laser, belong to fiber laser technical field, including dual-wavelength power amplification and beam combination structure, it includes by first wavelength power amplification substructure, second wavelength power amplification substructure, two wavelengths light output by two substructures is coupled by wavelength division multiplexer;It further includes short-wave ultraviolet waveband supercontinuum generation structure, it includes photon crystal fiber and fifth rare earth ion doped optical fiber connected in order;It further includes long-wave middle infrared waveband supercontinuum generation structure, it includes fifth fiber amplifier, mode field adapter, the high nonlinearity optical fiber of doping concentration 64mol.%-100mol.%, seventh rare earth ion doped optical fiber connected in order, three structures are connected in order.The application dual-wavelength pumped nonlinear optical fiber and introduce rare earth doped optical fiber to eliminate the mode of combination of pump residual peak, on the basis that spectrum is greatly expanded, simultaneously realize the flat output of spectrum full waveband.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and more particularly to a flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band. Background Technology

[0002] Broadband light sources covering the ultraviolet to mid-infrared bands contain a large number of molecular absorption regions and can be widely used in molecular recognition and environmental monitoring. Currently, the main technical approach to developing broadband light sources is supercontinuum generation (SCG). SCG refers to the phenomenon where a high-intensity laser pumps a nonlinear medium, resulting in a maximally broadened spectrum under the combined effects of dispersion and nonlinearity. It has advantages such as high spectral brightness, ultra-wide bandwidth, and ease of integration.

[0003] With the development of commercially available 1μm and 1.55μm ultrafast mode-locked pulsed fiber lasers, as well as photonic crystal fibers (PCFs) and highly nonlinear germanium-doped fibers, current research has shown that pulsed lasers can be amplified via MOPA and then nonlinearly extended via PCFs or highly nonlinear fibers to generate supercontinuum spectra covering the ultraviolet or mid-infrared range. However, the resulting supercontinuum spectra have a narrow spectral range, and residual pump peaks disrupt the flatness of the spectrum. In practical applications, broadband supercontinuum spectra offer higher signal resolution, enabling accurate identification of various frequency components of the signal; flat supercontinuum spectra, on the other hand, have stronger anti-interference capabilities, can operate stably in noisy environments, and are easier to process data. If current technology is improved to cover the ultraviolet to mid-infrared band, and the spectrum remains flat across the entire band without residual pump peaks, this type of supercontinuum will offer higher recognition accuracy and broader monitoring capabilities in molecular recognition and environmental monitoring applications.

[0004] Traditional technical solutions use single-wavelength pumping, which results in a limited spectral range and residual pump spikes, thus limiting the ability to detect and identify molecules. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of the prior art and provide a flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band.

[0006] The objective of this invention is achieved through the following technical solution: a flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band, the all-fiber laser comprising a dual-wavelength power amplification and beam combining structure, a short-wavelength ultraviolet supercontinuum generation structure, and a long-wavelength mid-infrared supercontinuum generation structure connected in sequence.

[0007] The dual-wavelength power amplification and beam combining structure includes a first wavelength power amplification substructure and a second wavelength power amplification substructure. The two wavelengths of light output from the two substructures are coupled via a wavelength division multiplexer. The first wavelength power amplification substructure includes a first laser and a first multi-stage fiber amplifier connected in sequence. The first multi-stage fiber amplifier is used to increase the power of the first wavelength light output from the first laser. The second wavelength power amplification substructure includes a second laser and a second multi-stage fiber amplifier connected in sequence. The second multi-stage fiber amplifier is used to increase the power of the second wavelength light output from the second laser.

[0008] The short-wave ultraviolet supercontinuum generation structure includes a photonic crystal fiber and a fifth rare-earth ion-doped fiber connected in sequence. The photonic crystal fiber is used to generate the ultraviolet supercontinuum of the second wavelength light, and the fifth rare-earth ion-doped fiber is used to absorb the residual pump spike of the second wavelength light.

[0009] The long-wave mid-infrared supercontinuum generation structure includes a fifth fiber amplifier, a mode field adapter, a highly nonlinear fiber with a doping concentration greater than 64 mol.%-100 mol.%, and a seventh rare-earth ion-doped fiber connected in sequence. The fifth fiber amplifier is used to boost the power of the first wavelength light. The highly nonlinear fiber with a doping concentration of 64 mol.%-100 mol.% is used to generate the mid-infrared supercontinuum of the first wavelength light. The seventh rare-earth ion-doped fiber is used to absorb the residual pump spike of the first wavelength light.

[0010] In one example, the output end of the seventh rare-earth ion-doped fiber is also connected to a doped fiber with a doping concentration of 70 mol.% to 100 mol.% for extending the long-wave mid-infrared band.

[0011] In one example, the doped optical fiber is germanium-doped optical fiber, fluorotellurate optical fiber, fluoride optical fiber, or sulfide optical fiber.

[0012] In one example, the first laser is a pulsed fiber laser of 1300nm-1700nm or a supercontinuum laser with a spectral range covering 1300nm-1700nm; the second laser is a pulsed fiber laser of 900nm-1200nm or a supercontinuum laser with a spectral range covering 900nm-1200nm.

[0013] In one example, the first multi-stage fiber amplifier includes a first preamplifier and a first main amplifier connected in sequence;

[0014] The first preamplifier includes a third laser, a first combiner, and a first rare-earth ion-doped fiber connected in sequence. The first rare-earth ion-doped fiber is an erbium-doped ytterbium gain fiber, an erbium-doped fiber, or a ytterbium-doped gain fiber. The first main amplifier includes a fourth laser, a second combiner, and a second rare-earth ion-doped fiber connected in sequence. The second rare-earth ion-doped fiber is an erbium-doped ytterbium gain fiber, an erbium-doped fiber, or a ytterbium-doped gain fiber.

[0015] In one example, the second multi-stage fiber amplifier includes a second preamplifier and a second main amplifier connected in sequence;

[0016] The second preamplifier includes a fifth laser, a third combiner, and a third rare-earth ion-doped fiber connected in sequence. The third rare-earth ion-doped fiber is a ytterbium-doped gain fiber, an erbium-doped gain fiber, a neodymium-doped gain fiber, or a thulium-doped gain fiber. The second main amplifier includes a sixth laser, a fourth combiner, and a fourth rare-earth ion-doped fiber connected in sequence. The fourth rare-earth ion-doped fiber is a ytterbium-doped gain fiber, an erbium-doped gain fiber, a neodymium-doped gain fiber, or a thulium-doped gain fiber.

[0017] In one example, an isolator is provided between the preamplifier and the main amplifier.

[0018] In one example, the fifth rare-earth ion-doped fiber is a rare-earth-doped fiber with an absorption peak near the second wavelength, which is an erbium-doped silica fiber, a thulium-doped silica fiber, a neodymium-doped silica fiber, or an erbium-ytterbium-doped silica fiber.

[0019] In one example, the fifth fiber amplifier includes a seventh laser, a fifth combiner, and a sixth rare-earth ion-doped fiber connected in sequence. The sixth rare-earth ion-doped fiber is a large-mode-field double-clad erbium-ytterbium co-doped fiber or a large-mode-field erbium-doped fiber.

[0020] In one example, the seventh rare-earth ion-doped fiber is a rare-earth-doped fiber with an absorption peak near the first wavelength, specifically a single-mode thulium-doped silica fiber, or an erbium-doped silica fiber, an erbium-ytterbium-doped silica fiber, or a thulium-holmium-doped silica fiber. It should be further noted that the technical features corresponding to the above examples can be combined or substituted to form new technical solutions.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention utilizes a combination of dual-wavelength pumped nonlinear optical fiber and rare-earth-doped optical fiber to eliminate residual pump peaks. This approach significantly expands the spectrum while simultaneously achieving flat output across the entire spectral band. On one hand, the second wavelength pump readily generates a spectrum covering the ultraviolet band, while the first wavelength pump readily generates a spectrum covering the mid-infrared band. Dual-wavelength pumping effectively integrates the supercontinuum spectra generated by the two wavelengths into a single spectrum, achieving a supercontinuum output from ultraviolet to mid-infrared and significantly improving the supercontinuum spectral coverage. On the other hand, by incorporating rare-earth-doped silica optical fiber, the absorption bands of rare-earth ions at both wavelengths are utilized to absorb residual pump peaks in the spectrum, achieving flattening and shaping of the output spectrum. This improves the flatness of the supercontinuum, thereby enhancing detection and molecular recognition capabilities. Attached Figure Description

[0023] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, which are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to denote the same or similar parts. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application.

[0024] Figure 1 This is a schematic diagram of an all-fiber structure device in an example;

[0025] Figure 2 This is a schematic diagram of the dual-wavelength power amplification and beam combining structure of the present invention;

[0026] Figure 3 This is a schematic diagram of the shortwave ultraviolet supercontinuum generation structure of the present invention;

[0027] Figure 4 This is a schematic diagram of the supercontinuum generation structure in the long-wave mid-infrared band of the present invention;

[0028] Figure 5 This is a schematic diagram of an all-fiber structure device in another example; Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the use of ordinal numbers (e.g., "first and second," "first to fourth," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1

[0034] A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band is described, specifically using flat supercontinuum all-fiber lasers in the ultraviolet-mid-infrared band realized with 1.064μm and 1.55μm seed sources as examples. Figure 1 As shown, the all-fiber laser at this time specifically includes a dual-wavelength power amplification and beam combining structure, a short-wave ultraviolet supercontinuum generation structure, and a long-wave mid-infrared supercontinuum generation structure connected in sequence.

[0035] The dual-wavelength power amplification and beam combining structure includes a 1550nm pulsed fiber laser (PFL), a multi-stage erbium-doped ytterbium fiber amplifier (EYDFA, i.e., the first multi-stage fiber amplifier), a 1064nm pulsed fiber laser (PFL), a multi-stage ytterbium-doped fiber amplifier (YDFA, i.e., the first multi-stage fiber amplifier), and a 1064nm / 1550nm wavelength division multiplexer (WDM) to achieve the purpose of power amplification (MOPA) of 1.064μm and 1.55μm seed light and coupling it to the optical fiber via the optical wavelength division multiplexer. The 1550nm pulse seed light is a nanosecond mode-locked fiber pulsed laser with a repetition rate in the KHz-MHz range. After pre-amplification by a first-stage EYDFA (first preamplifier), it is connected to a multi-stage EYDFA (first main amplifier) ​​for main amplification to increase the power in this band. The 1064nm pulse seed light is a femtosecond mode-locked ultrafast fiber laser with a repetition rate in the MHz range. Similarly, after pre-amplification by a first-stage YDFA (second preamplifier), it is connected to a subsequent multi-stage LMA-YDFA (large mode field ytterbium-doped fiber amplifier) ​​for main amplification to increase the power. The amplified light of the two wavelengths is then fused and coupled into a single fiber through a 1064nm / 1550nm wavelength division multiplexer.

[0036] A short-wavelength ultraviolet supercontinuum generation structure is used to provide supercontinuum generation covering the short-wavelength ultraviolet band and eliminate the 1064nm pump residual spike. This structure includes photonic crystal fiber (PCF) and rare-earth-doped silica fiber. The amplified 1064nm light has high peak power, which is beneficial for generating a broadband continuous spectrum when pumping nonlinear fibers. Furthermore, the pump wavelength of 1064nm is near the zero-dispersion wavelength (ZDW) point of the PCF, enabling the widest supercontinuum generation in PCF fiber, thus allowing the short-wavelength spectrum of this invention to cover the ultraviolet band. Since existing techniques of this type all have residual pump spikes in their spectra, i.e., spikes around 1μm, considering the absorption band of rare-earth ions in this band, we use rare-earth-doped silica fiber to absorb the spikes, making the generated spectrum flatter near the 1μm pump wavelength.

[0037] The long-wavelength mid-infrared supercontinuum generation structure is used to provide supercontinuum generation covering the long-wavelength mid-infrared band and eliminate the 1550nm pump residual spike. It includes a large-mode-field erbium-ytterbium-doped fiber amplifier (LMA-EYDFA), a mode field adapter (MFA2), highly nonlinear germanium-doped fiber (such as NL1550, 64% mol. germanium-doped fiber, etc.), rare-earth-doped fiber (Rare earth-doped fiber2), and high-concentration germanium-doped fiber (i.e., mid-infrared nonlinear fiber). In the long-wavelength mid-infrared supercontinuum generation structure, a large-mode-field erbium-ytterbium-doped fiber amplifier with high amplification efficiency is used to amplify the 1550nm light, resulting in sufficiently high peak power. Furthermore, its pump wavelength is located near the zero-dispersion point of the highly nonlinear fiber, enabling the widest supercontinuum generation among such fibers, thus allowing the long-wavelength coverage of the invention to reach the mid-infrared band. Meanwhile, the spectrum generated in the long-wave mid-infrared supercontinuum generation structure exhibits a residual spike near 1.55 μm. Considering the absorption band of rare-earth ions in this band, this invention still employs rare-earth-doped silica fiber to absorb the spike, making the generated spectrum flat near the 1.55 μm pump wavelength. Furthermore, due to the inclusion of silica fiber, which has high loss in the long wavelength range >2.8 μm, the generated supercontinuum exhibits a narrowing effect in the long-wavelength band. This invention preferably incorporates a section of long-wave low-loss mid-infrared nonlinear fiber to further extend the supercontinuum into the long-wave mid-infrared, thereby achieving a flat supercontinuum output across the entire ultraviolet to mid-infrared band.

[0038] More specifically, the first wavelength power amplification substructure is used to amplify the power of the 1.55-micron seed light. For example... Figure 2As shown, the 1.55μm seed light is a nanosecond pulsed fiber laser with an adjustable pulse width of 1ns-200ns and an adjustable repetition rate of 200kHz-3MHz. The 1.55μm seed light first passes through the first preamplifier, namely the first-stage erbium-ytterbium co-doped fiber amplifier (EYDFA1), which includes a 976nm semiconductor laser LD (third laser) connected sequentially as Pump1, a first combiner (Combiner1), and a first rare-earth ion-doped fiber, which is an erbium-ytterbium-doped gain fiber (EYDF1). Without using a mode field adapter (MFA) during amplification, using a higher fiber core diameter (core diameter greater than 6μm) can suppress nonlinear effects during laser amplification and improve the pump slope efficiency of the LD. The final amplification stage can boost the seed light power to the watt level. Considering the potential echo feedback between the preamplifier stage and the main amplifier stage, a first isolator (ISO1) is connected after the first amplification stage to ensure unidirectional transmission of the system. After boosting the power of the seed light to the watt level, it is connected to the first main amplifier, namely: the first-stage erbium-ytterbium co-doped fiber amplifier (EYDFA2), which includes a 976nm LD Pump2, a second combiner (Combiner2), and a second rare-earth ion-doped fiber, which is an erbium-ytterbium-doped gain fiber (EYDF2). Finally, the second-stage main amplifier can boost the 1.55μm seed light to the 10-watt level, at which point the peak power of the pulsed laser can reach the 10kW level.

[0039] More specifically, the second-wavelength power amplification substructure is used to amplify the power of the 1.06-micron seed light. For example... Figure 2As shown, the 1.064μm seed light is a commercially available femtosecond pulsed laser with a pulse width <100fs and a repetition rate on the order of MHz. The seed light first passes through the first-stage preamplifier (second preamplifier), namely: the first-stage ytterbium-doped fiber amplifier (YDFA), which includes a 976nm LD Pump3, a third combiner (Combiner3), and a third rare-earth ion-doped fiber, which is a ytterbium-doped gain fiber (YDF1). This first-stage amplification can boost the seed light to the watt level. Similarly, to avoid feedback with the second-stage amplifier, after connecting to the second isolator (ISO2) to ensure unidirectional transmission, a second-stage large-mode-field ytterbium-doped fiber amplifier (LMA-YDFA), i.e., the second main amplifier, is connected sequentially. The second main amplifier includes a 976nm LD (Pump 4), a fourth combiner (Combiner 4), a fourth rare-earth ion-doped fiber, and a first mode field adapter (MFA1). The fourth rare-earth ion-doped fiber is a large-core ytterbium-doped gain fiber. Because the large core diameter of the gain fiber differs significantly from the small core diameter of the wavelength division multiplexer (WDM) fiber, mode field mismatch can easily occur during fiber splicing, resulting in significant loss. Therefore, a mode field adapter is connected between the two fibers to match their mode fields. Finally, the second-stage main amplifier can boost the 1.064μm seed light to the 20-watt range.

[0040] This invention is based on a sequentially connected 1.064 μm pump source, tapered PCF, and fifth rare-earth ion-doped fiber (erbium-doped silica fiber). 3+ Doped fiber) achieves short-wavelength spectral coverage in the ultraviolet band, and the output becomes a flat supercontinuum output due to absorption near the 1.064μm pump peak. Figure 3As shown, a tapered photonic crystal fiber (PCF) is used as the 1.064 μm pump nonlinear fiber. By reducing the core diameter of the PCF, the nonlinear effect of the fiber is enhanced, thereby broadening the spectral width obtained by the pump source. The zero-dispersion wavelength of this tapered fiber is located near the pump wavelength of 1064 nm. Under the pumping of this source, the spectrum rapidly broadens from near the pump wavelength to both sides due to nonlinear mechanisms such as modulation instability, self-phase modulation, Raman soliton self-frequency shift, and dispersive waves, forming a supercontinuum. With the combined effect of high peak power and highly nonlinear fiber, the supercontinuum can cover 350 nm-1600 nm, spanning the ultraviolet to near-infrared bands. The short-wavelength broadening of the spectrum is mainly due to the Raman soliton self-frequency shift towards the long-wavelength direction. Solitons with phase matching in the short-wavelength direction are formed, meaning that the blue-shifted dispersive wave is the main component of the short-wavelength spectrum. Subsequently, by utilizing the absorption band of rare-earth erbium ions near 1 μm, and by controlling the length of the erbium-doped silica fiber, the absorption of the residual pump peak at 1.064 μm was achieved, thus flattening the spectrum at the peak. Based on the energy level structure of erbium ions, the absorbed residual pump light can also be used as a pump at 1.55 μm, thereby amplifying the light at 1.55 μm.

[0041] This invention achieves a supercontinuum output with long-wavelength spectral coverage in the mid-infrared band and flat distribution, achieved by using a 1.55μm pump source, a large-mode-field erbium-ytterbium co-doped fiber amplifier, highly nonlinear fiber, and single-mode thulium-doped fiber. The output is characterized by absorption near the 1.55μm pump peak. Figure 4As shown, the supercontinuum generation structure in the long-wave mid-infrared band includes a fifth fiber amplifier, a second mode field adapter MFA2, a highly nonlinear NL1550 fiber, a seventh rare-earth ion-doped fiber, and a doped fiber connected in sequence. The fifth fiber amplifier is a large-mode-field erbium-doped ytterbium-gain fiber amplifier (LMA-EYDFA), the seventh rare-earth ion-doped fiber is a thulium-doped fiber, and the doped fiber is a 94 mol.% germanium-doped fiber. More specifically, the large-mode-field erbium-ytterbium co-doped fiber amplifier (LMA-EYDFA) consists of a 976nm LD in Pump 5, a 976nm LD in Pump 6, a sixth rare-earth ion-doped fiber, and a fifth combiner (Combiner 5). The sixth rare-earth ion-doped fiber is a large-core-diameter double-clad erbium-ytterbium co-doped fiber (LMA-EYDF). Specifically, both 976nm LDs are connected to the fifth combiner, and the output of the fifth combiner is connected to the large-core-diameter double-clad erbium-ytterbium co-doped fiber. For low-loss splicing with subsequent fibers, a mode field adapter is also connected after the large-mode-field gain fiber. The final 1.55μm light can be amplified to the level of 20 watts, with a peak power of 10kW. After amplification of the 1.55μm optical power, NL1550 fiber was used as the nonlinear fiber for 1.55μm pumping. This fiber has a small core diameter (2.4μm), and its zero-dispersion wavelength is located near the pump wavelength of 1.55μm, which is extremely beneficial for the generation of a broadband supercontinuum. Under the pumping of this source, the spectrum rapidly broadens from near the pump wavelength to both sides due to nonlinear mechanisms such as modulation instability, soliton splitting, Raman soliton self-frequency shift, and dispersive waves, forming a supercontinuum. With the combined effect of this high peak power pump source and highly nonlinear fiber, the supercontinuum can cover 0.9-3μm, spanning the near-infrared to mid-infrared bands. Among them, the short-wavelength components of the spectrum are related to the blue-shifted dispersive waves, which are essentially blue-shifted short-wavelength light generated by phase matching with red-shifted solitons. Subsequently, utilizing the absorption band of rare-earth thulium ions near 1.5 μm, the absorption of the residual pump peak at 1.55 μm was achieved by controlling the length of the single-mode thulium-doped silica fiber (SM-TDF), thus flattening the spectrum near the peak. Since the thulium ions at the absorption peak are located in the silica-based fiber, and silica fibers exhibit high loss >2.8 μm, the spectrum narrows in the long-wavelength direction. Using a flat supercontinuum spectrum across the entire ultraviolet to mid-infrared band as the pump source, and connecting it to a 94 mol.% high-concentration germanium-doped fiber, the spectrum is further extended towards the long-wavelength mid-infrared direction. Finally, this stage achieves the final wide-spectrum flat supercontinuum laser output covering the ultraviolet to mid-infrared band. In this embodiment, the final wide spectrum covers part of the ultraviolet and part of the mid-infrared band, specifically the full spectrum of 0.4-3.5 μm, corresponding to the following technical principle:

[0042] Based on the nonlinear effects of optical fibers, lasers with high peak power in the 1064nm and 1550nm bands can achieve significant spectral broadening within optical fibers, realizing an ultrawide supercontinuum output. Specifically, due to tuning instabilities and soliton splitting in the fiber, the input laser pulse splits into many ultrashort pulse widths. Under the influence and accumulation of various nonlinear effects such as Raman soliton self-frequency shift, stimulated Raman scattering, self-phase modulation, and four-wave mixing, the spectrum gradually redshifts. Simultaneously, nonlinear effects such as self-phase modulation, four-wave mixing, and wave splitting affect the overall blueshift of the spectrum. Moreover, the two pump wavelengths, 1064nm and 1550nm, are located near the zero-dispersion point of PCF and NL1550 fibers, respectively. This results in a large number of dispersive waves at the short-wavelength end of the spectrum that are phase-matched with solitons generated by soliton self-frequency shift at the long-wavelength end, further causing the blueshift of the spectrum. Therefore, under the above nonlinear mechanism description, the spectrum undergoes redshift and blueshift at both pump wavelengths, ultimately achieving supercontinuum output covering the ultraviolet band in the shortwave and the mid-infrared band in the longwave.

[0043] Specifically, in this example, the optical fibers used to achieve spectral broadening include three types: tapered photonic crystal fiber (PCF), highly nonlinear fiber (HNLF), and mid-infrared nonlinear fiber. First, the amplified 1064nm and 1550nm light are combined via WDM and enter the PCF. Due to the modulation stability and soliton splitting effects in the PCF, the input laser pulse splits into many ultrashort pulses. Under the influence and accumulation of various nonlinear effects such as Raman soliton self-frequency shift, stimulated Raman scattering, self-phase modulation, four-wave mixing, and dispersive waves, the spectrum gradually broadens, with the long-wavelength edge reaching 2μm and the short-wavelength edge reaching 0.4μm, forming a supercontinuum covering the spectral range of 0.4-2μm. Then, the residual peak at 1064nm is absorbed using a fifth rare-earth-doped fiber, making the spectrum in that vicinity flattened. Next, the 1550nm laser is amplified further, following the same mechanism as PCF. Due to the modulation stability and soliton splitting effects in HNLF, the input laser pulse splits into many ultrashort pulses. Under the influence and accumulation of various nonlinear effects such as Raman soliton self-frequency shift, stimulated Raman scattering, self-phase modulation, four-wave mixing, and dispersive waves, the spectrum gradually broadens, reaching 2.8μm on the long-wavelength side and 0.9μm on the short-wavelength side, forming a supercontinuum covering the 0.9-2.8μm spectral range. Combined with the supercontinuum output from PCF, the entire spectral range reaches 0.4μm-2.8μm. Then, the residual peak at 1550nm is absorbed using a seventh rare-earth-doped fiber, making the spectrum in that area flat, thus achieving a flat supercontinuum output across the entire 0.4μm-2.8μm range. Finally, the spectrum is shifted to longer wavelengths using a mid-infrared nonlinear fiber (94 mol.% germanium-doped fiber), achieving a spectral output of 0.4μm-3.5μm.

[0044] Example 2

[0045] This embodiment shares the same inventive concept as Embodiment 1, which describes a flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band. Specifically, this example uses a flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band implemented with a 1530nm pulsed fiber laser seed source and a 1056nm pulsed fiber laser seed source for illustration. Figure 5 As shown, the all-fiber laser structure is similar to that in Example 1, except that the first laser is replaced with a 1530nm supercontinuum laser, the second laser is replaced with a 1056nm supercontinuum laser, the first and second rare-earth ion-doped fibers are replaced with erbium-doped fibers, the third and fourth rare-earth ion-doped fibers are replaced with thulium-doped fibers, the fifth rare-earth ion-doped fiber is replaced with neodymium-doped fiber, the sixth rare-earth ion-doped fiber is replaced with erbium-doped fiber, the seventh rare-earth ion-doped fiber is replaced with thulium-holmium-doped fiber, and the output fiber of the seventh rare-earth ion-doped fiber is replaced with a fluoride ZBLAN fiber. The working principle of the all-fiber laser in this case is as follows:

[0046] The light from the 1530nm and 1056nm wavelengths of the two seed source spectra is pre-amplified and master-amplified, then coupled into the optical fiber via a wavelength division multiplexer. Firstly, the amplified 1056nm light has a high peak power, and the seed supercontinuum spectral peak is located near 1056nm, matching the zero-dispersion wavelength (ZDW) of the PCF fiber. This generates the most effective nonlinear effect in the tapered PCF fiber, resulting in more effective redshift and blueshift of the spectrum, producing the widest supercontinuum generation. This allows the short-wavelength spectrum of this invention to cover the ultraviolet band (0.4μm). Furthermore, considering the absorption band of neodymium ions in the 1μm band, neodymium-doped fiber is used to absorb the residual peak, making the generated spectrum flatter near the 1μm spectral peak. Similarly, a large-mode-field erbium-doped fiber amplifier with high amplification efficiency is then used to amplify the 1530nm light in the seed supercontinuum, resulting in sufficiently high peak power. Since the pump spectral peak is located near the zero-dispersion point of the NL1550 fiber, this enables the generation of the widest supercontinuum in this type of fiber, allowing the long-wavelength coverage of the invention to reach the mid-infrared band (3μm). Considering the absorption band of thulium-holmium ions at 1.5μm, thulium-holmium-doped fiber is used to absorb the residual peak, making the generated spectrum flat near the 1.5μm spectral peak. Furthermore, due to the high loss of silica fiber at wavelengths >2.8μm, the generated supercontinuum narrows in the long-wavelength range. A ZBLAN fiber is then connected after the thulium-holmium co-doped fiber to further extend the spectrum to the long wavelength range (4μm), ultimately achieving a flat supercontinuum output across the entire 0.4μm-4μm spectrum.

[0047] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band, characterized in that: It includes a sequentially connected dual-wavelength power amplification and beam combining structure, a short-wave ultraviolet supercontinuum generation structure, and a long-wave mid-infrared supercontinuum generation structure. The dual-wavelength power amplification and beam combining structure includes a first wavelength power amplification substructure and a second wavelength power amplification substructure. The two wavelengths of light output from the two substructures are coupled via a wavelength division multiplexer. The first wavelength power amplification substructure includes a first laser and a first multi-stage fiber amplifier connected in sequence. The first multi-stage fiber amplifier is used to increase the power of the first wavelength light output from the first laser. The second wavelength power amplification substructure includes a second laser and a second multi-stage fiber amplifier connected in sequence. The second multi-stage fiber amplifier is used to increase the power of the second wavelength light output from the second laser. The first laser is a pulsed fiber laser with a spectral range of 1300nm-1700nm or a supercontinuum laser with a spectral range of 1300nm-1700nm. The second laser is a pulsed fiber laser with a spectral range of 900nm-1200nm or a supercontinuum laser with a spectral range of 900nm-1200nm. The short-wave ultraviolet supercontinuum generation structure includes a photonic crystal fiber and a fifth rare-earth ion-doped fiber connected in sequence. The photonic crystal fiber is used to generate the ultraviolet supercontinuum of the second wavelength light, and the fifth rare-earth ion-doped fiber is used to absorb the residual pump spike of the second wavelength light. The long-wave mid-infrared supercontinuum generation structure includes a fifth fiber amplifier, a mode field adapter, a highly nonlinear fiber with a doping concentration of 64 mol.%-100 mol.%, and a seventh rare-earth ion-doped fiber connected in sequence. The fifth fiber amplifier is used to boost the power of the first wavelength light. The highly nonlinear fiber with a doping concentration of 64 mol.%-100 mol.% is used to generate the mid-infrared supercontinuum of the first wavelength light. The seventh rare-earth ion-doped fiber is used to absorb the residual pump spike of the first wavelength light.

2. The flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 1, characterized in that: The seventh rare earth ion-doped fiber output end is also connected to a doped fiber with a doping concentration of 70 mol.%-100 mol.% for extending the long-wave mid-infrared band.

3. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 2, characterized in that: The doped optical fiber is germanium-doped optical fiber, fluorotellurate optical fiber, fluoride optical fiber, or sulfide optical fiber.

4. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 1, characterized in that: The first multi-stage fiber amplifier includes a first preamplifier and a first main amplifier connected in sequence; The first preamplifier includes a third laser, a first combiner, and a first rare-earth ion-doped fiber connected in sequence. The first rare-earth ion-doped fiber is an erbium-doped ytterbium gain fiber, an erbium-doped fiber, or a ytterbium-doped gain fiber. The first main amplifier includes a fourth laser, a second combiner, and a second rare-earth ion-doped fiber connected in sequence. The second rare-earth ion-doped fiber is an erbium-doped ytterbium gain fiber, an erbium-doped fiber, or a ytterbium-doped gain fiber.

5. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 1, characterized in that: The second multi-stage fiber amplifier includes a second preamplifier and a second main amplifier connected in sequence; The second preamplifier includes a fifth laser, a third combiner, and a third rare-earth ion-doped fiber connected in sequence. The third rare-earth ion-doped fiber is a ytterbium-doped gain fiber, an erbium-doped gain fiber, a neodymium-doped gain fiber, or a thulium-doped gain fiber. The second main amplifier includes a sixth laser, a fourth combiner, and a fourth rare-earth ion-doped fiber connected in sequence. The fourth rare-earth ion-doped fiber is a ytterbium-doped gain fiber, an erbium-doped gain fiber, a neodymium-doped gain fiber, or a thulium-doped gain fiber.

6. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 4 or 5, characterized in that: An isolator is provided between the preamplifier and the main amplifier.

7. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 1, characterized in that: The fifth rare-earth ion-doped optical fiber is an erbium-doped silica fiber, a thulium-doped silica fiber, a neodymium-doped silica fiber, or an erbium-ytterbium-doped silica fiber.

8. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 1, characterized in that: The fifth fiber amplifier includes a seventh laser, a fifth beam combiner, and a sixth rare-earth ion-doped fiber connected in sequence. The sixth rare-earth ion-doped fiber is a large-mode-field double-clad erbium-ytterbium co-doped fiber or a large-mode-field erbium-doped fiber.

9. A flat supercontinuum all-fiber laser in the ultraviolet-mid-infrared band according to claim 1, characterized in that: The seventh rare-earth ion-doped fiber is a single-mode thulium-doped silica fiber, or an erbium-doped silica fiber, an erbium-ytterbium-doped silica fiber, or a thulium-holmium-doped silica fiber.

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