2.8 MICROMETER AND 3.5 MICROMETER DUAL-WAVELENGTH MID-INFRAREDFIBER LASER

Abstract

The present disclosure discloses a 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser, which employs 0.98 ?m+1.15 ?m pumping scheme, uses a fiber combiner to combine two pump lights into the double cladding Er-doped fluoride fiber. The Er ions in the ground state are first promoted to .sup.4I.sub.11/2 level by the 0.98 ?m pump light, realizing 2.8 ?m lasing based on .sup.4I.sub.11/2.fwdarw..sup.4I.sub.13/2 transition, and further promoted to .sup.4F.sub.9/2 level by the 1.15 ?m pump light, generating 3.5 ?m lasing based on .sup.4F.sub.9/2.fwdarw..sup.4I.sub.9/2 transition; followed by the 3.5 ?m laser transition, the Er ions would rapidly decay to .sup.4I.sub.11/2 level via non radiative transition, realizing the re-population of .sup.4I.sub.11/2 level, effectively enlarge the population inversion of 2.8 ?m transition, suppressing the self-termination of 2.8 ?m lasing and achieving 2.8 ?m and 3.5 ?m dual-wavelength cascaded lasing output.

Claims

1. A 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser, comprising a first pump source, a second pump source, a fiber combiner, a first fiber Bragg grating, a second fiber Bragg grating, a double cladding Er-doped fluoride fiber and a long pass filter; an output end of the double cladding Er-doped fluoride fiber is perpendicularly cleaved, the cleaved output end and the first fiber Bragg grating forms a 3.5 ?m resonator, the cleaved output end and the second fiber Bragg grating form a 2.8 ?m resonator; the first pump source and the second pump source correspond to a ground state absorption with an Er ion .sup.4I.sub.15/2.fwdarw..sup.4I.sub.11/2 transition and an excited state absorption with an Er ion .sup.4I.sub.13/2.fwdarw..sup.4F.sub.9/2 transition, respectively, pump lights generated by the first pump source and the second pump source are combined by the fiber combiner and then injected into the double cladding Er-doped fluoride fiber to provide gain for both 2.8 ?m and 3.5 ?m transitions, as well as to suppress the self-termination of 2.8 ?m laser caused by long level lifetime, enabling 2.8 ?m and 3.5 ?m dual-wavelength transmission simultaneously based on a single piece of double cladding Er-doped fluoride fiber.

2. The 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser according to claim 1, wherein the first pump source is a multimode laser with an output wavelength of 0.98 ?m.

3. The 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser according to claim 1, wherein the second pump source is a single-transverse-mode Yb-doped fiber laser with an output wavelength of 1.15 ?m.

4. The 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser according to claim 1, wherein the input port of the fiber combiner includes a single-mode fiber and a multimode fiber, and the output fiber is a double cladding fiber which is capable of propagating 1.15 ?m single-mode pump laser inside the core and propagating 0.98 ?m multimode pump laser inside the inner cladding.

5. The 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser according to claim 1, wherein a central wavelength of the first fiber Bragg grating is a certain wavelength within the emission band of Er ion .sup.4F.sub.9/2.fwdarw..sup.4I.sub.9/2 transition, the of the first fiber Bragg grating is greater than 99.5%, the FWHM is narrower than 5 nm and the insertion loss at pump wavelengths is lower than 0.5 dB.

6. The 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser according to claim 1, wherein the central wavelength of the second fiber Bragg grating is a certain wavelength within the emission band of Er ion .sup.4I.sub.1/2.fwdarw..sup.4I.sub.13/2 transition, the reflectivity of the second fiber Bragg grating is greater than 99.5%, the FWHM is narrower than 5 nm and the insertion loss at pump wavelengths is lower than 0.5 dB.

7. The 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser according to claim 1, wherein the long pass filter has a cutoff wavelength of 1.5 ?m, a reflectivity at 0.98 ?m and 1.15 ?m are greater than 95%, and a transmission at both of the 2.8 ?m and 3.5 ?m are greater than 95%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows the energy level of Er ions in fluoride glass host and the important transitions involved in this disclosure;

[0018] FIG. 2 is a schematic of the 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser;

[0019] In which: [0020] 1: first pump source; [0021] 2: second pump source; [0022] 3: fiber combiner; [0023] 3-1: single-mode fiber input port; [0024] 3-2: multimode fiber input port; [0025] 3-3: output port; [0026] 4: first fiber Bragg grating; [0027] 5: second fiber Bragg grating; [0028] 6: double cladding Er-doped fluoride fiber [0029] 7: long pass filter.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

[0030] To make the objectives, technical solutions, beneficial effects of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings provided in the embodiments of the present disclosure.

Embodiment 1

[0031] A 2.8 ?m and 3.5 ?m dual-wavelength mid-infrared fiber laser, as shown in FIG. 2, including: a first pump source 1, a second pump source 2, a fiber combiner 3, a first fiber Bragg grating 4, a second fiber Bragg grating 5, a double cladding Er-doped fluoride fiber 6 and a long pass filter 7.

[0032] Wherein, the first pump source 1 is a 976 nm wavelength multimode laser diode providing a maximum output power of 10 W, an output fiber thereof is connected with the multimode fiber input port 3-2 of the fiber combiner 3; the second pump source 2 is a 1150 nm wavelength single-transverse-mode Yb-doped fiber laser providing a maximum output power of 50 W, an output fiber thereof is connected with the single-mode fiber input port 3-1 of the fiber combiner 3.

[0033] Wherein, the central wavelength of the first fiber Bragg grating 4 is 3540 nm, at which the first fiber Bragg grating 4 provides a reflectivity >99.9% and FWHM of 2 nm, and the insertion loss is 0.2 dB; the central wavelength of the second fiber Bragg grating 5 is 2820 nm, at which the second fiber Bragg grating 5 provides a reflectivity >99.9% and FWHM of 2 nm, and the insertion loss is 0.2 dB. The insertion loss of both the first fiber Bragg grating 4 and the second fiber Bragg grating 5 at 976 nm and 1150 nm are lower than 0.3 dB. Wherein, the double cladding Er-doped fluoride fiber 6 is non polarization maintaining fiber. It has a core and inner cladding diameters of 15 ?m and 250 ?m, respectively, the core numerical aperture, doping concentration, and length of the fiber are 0.125, 1 mol. %, and 10 m, respectively. Wherein, the long pass filter 7 has a cutoff wavelength of 1.5 ?m, it provides a greater than 95% reflectivity at 976 nm and 1150 nm as well as a greater than 95% transmission both at 2820 nm and 3540 nm.

[0034] In practice, 976 nm and 1150 nm pump lights are first combined by the fiber combiner 3 and then injected into the double cladding Er-doped fluoride fiber 6, where the 976 nm and 1150 nm pump lights propagate in the inner cladding and core, respectively. The Er ions in the ground state are first promoted to .sup.4I.sub.11/2 level by the 976 nm pump light, realizing the first population inversion of .sup.4I.sub.11/2 level. After a 976 nm pump power exceeds the 2.8 ?m laser threshold, the 2820 nm lasing can be generated in the laser resonator formed between the second fiber Bragg grating 5 and the output end facet of the double cladding Er-doped fluoride fiber 6. Followed by the 2820 nm laser transition, the Er ions would transit to .sup.4I.sub.13/2 level and accumulate gradually in this level. These Er ions would be further promoted to .sup.4F.sub.9/2 level by the 1150 nm pump light, de-populating the .sup.4I.sub.13/2 level and realizing the population inversion of 3.5 ?m transition. After a 1150 nm pump power exceeds the 3.5 ?m laser threshold, the 3540 nm lasing can be generated in the laser resonator formed between the first fiber Bragg grating 4 and the output end facet of the double cladding Er-doped fluoride fiber 6. Followed by the 3540 nm laser transition, the Er ions would rapidly decay to .sup.4I.sub.11/2 level via non radiative transition, realizing the re-population of .sup.4I.sub.11/2 level and enhancing the 2.8 ?m laser gain. Such multi population behavior can effectively suppress the self-termination of 2.8 ?m laser, enabling efficient 2.8 ?m and 3.5 ?m dual-wavelength operation based on a single piece of double cladding Er-doped fluoride fiber.

[0035] In the fiber laser of the present disclosure, at 976 nm pump power of 10 W and 1150 nm pump power of 50 W, the 2820 nm and 3540 nm output power can reach up to 20 W and 10 W, respectively.

Embodiment 2

[0036] In the embodiment of the present disclosure, the second pump source can be an Yb-doped silica fiber laser or a Raman fiber laser, as long as it can provide sufficient output power at 1150 nm, the type of second pump source is not limited.

[0037] In the embodiment of the present disclosure, the model of each device is not limited except for special instructions.

[0038] Those skilled in the art must understand that the accompanying drawings are only schematic diagrams of a preferred embodiment, and the serial numbers of the above-mentioned embodiments of the present disclosure are only for description, and do not represent the superiority or inferiority of the embodiments.

[0039] The foregoing embodiments and specific examples are merely for describing the technical solutions of the present disclosure and not intended to limit the present disclosure. Although the present disclosure has been described in details by the foregoing embodiments, it should be understood by a person of ordinary skill in the art that modifications may be made to the technical solutions recorded in the foregoing embodiments or equivalent replacements may be made to some or all of the technical features, and these modifications or replacements shall not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present disclosure. Non-essential improvements and adjustments or replacements made according to the content of this specification by those skilled in the art shall fall into the protection scope of the present disclosure.