CN100456578C

CN100456578C - Dual wave length distributed feedback optical fiber laser based on symmetric Bragg grating

Info

Publication number: CN100456578C
Application number: CNB2007100174709A
Authority: CN
Inventors: 刘雪明; 王涛; 宫永康; 王雷然; 赵卫
Original assignee: XiAn Institute of Optics and Precision Mechanics of CAS
Current assignee: XiAn Institute of Optics and Precision Mechanics of CAS
Priority date: 2007-03-08
Filing date: 2007-03-08
Publication date: 2009-01-28
Anticipated expiration: 2027-03-08
Also published as: CN101055967A

Abstract

The invention relates to a dual wavelength distribution feedback optical fiber laser based on symmetry type Bragg grating, which comprises a pumping source, an isolator, a grating and a beam splitter. The specific structure of the grating is that, uniform grating parts with a width of L1 are distributed alternately with parts without grating, which has two widthes, L2 and L3; the uniform grating parts and the parts without grating are arranged according to the ...L1L2L1L3...L3L1L3...L3L1L2L1... mode, this kind of arrangement mode is symmetry about the central, wherein, L2 = m lambada, L3=(n+0.5)lambada, lambada is the Praha period, and m,n respectively represents integer. The invention has solved the technical problems such as a poor quality of the background technic light beam, a low optical Signal-to-Noise, complex apparatus, costly, narrow output wavelength interval and non-tunable; and the invention has advantage of dual wavelength output,tunable output wavelength, very high optical Signal-to-Noise, capable of efficiently avoid ing mode competition, and a single polarization state.

Description

Dual wavelength distributed feed-back formula fiber laser based on the symmetrical expression Bragg grating

Technical field

The present invention relates to a kind of laser that produces dual wavelength, relate in particular to a kind of distributed feed-back formula fiber laser that produces dual wavelength.

Background technology

Existing fiber laser is single wavelength running mostly.Common distributed feed-back formula (DFB) fiber laser also is single wavelength output.But, need use dual laser at some special occasions.Existing dual laser mainly comprises following several:

1, semiconductor dual laser, this laser are that the semiconductor laser with 2 wavelength is packaged in the same assembly;

2, solid state laser, as: LD side pumping Nd:YAG dual laser;

3, based on the dual wavelength DFB fiber laser of chirp structure.

But these several dual lasers all have tangible deficiency and defective: first kind of beam quality is poor, and complex process; Second kind of device complexity and cost are very high; The third output wavelength too narrow at interval (approximately 40pm) and untunable.

Summary of the invention

The object of the invention provides a kind of dual wavelength distributed feed-back formula fiber laser based on the symmetrical expression Bragg grating, it has solved in the background technology, and beam quality is poor, and Optical Signal To Noise Ratio is low, and device is complicated, the cost height, output wavelength is narrow and non-tunable technical problem at interval.

Technical solution of the present invention is:

A kind of dual wavelength distributed feed-back formula fiber laser based on the symmetrical expression Bragg grating comprises pumping source 1, isolator 2, grating 3 and beam splitter 4, and its special character is, described grating 3 is the symmetrical expression Bragg grating, and the concrete structure of described grating is that width is L ₁Uniform grating part and no-raster partly be alternately distributed, no-raster partly has two width, is respectively L ₂, L ₃, represent each section grating and no-raster part with length, made grating part and no-raster part with L ₁Be the center symmetric mode arrangement at center, wherein L ₁First half is with L ₁, L ₂, L ₁, L ₃For cycle period is arranged in order, L wherein ₂=m Λ, L ₃=(n+0.5) Λ, Λ is a Bragg period, m, n represent integer respectively.

Above-mentioned pumping source 1 is the semiconductor laser of 978nm for output wavelength, and making grating 3 used optical fiber is erbium-ytterbium co-doped fiber.

Above-mentioned Bragg period Λ=534.2nm, m=600, n=584.

The advantage that the present invention has is: overcome single wavelength output of traditional fiber laser, dual wavelength output; Change relevant parameter, output wavelength can change in the 2000pm scope at 50pm at interval; Very high Optical Signal To Noise Ratio, as can be seen from Figure 5, Optical Signal To Noise Ratio is about 65dB; Can effectively avoid mode competition,, therefore can effectively avoid the mode competition in the conventional laser because this laser inside is equivalent to two independently resonant cavitys; Single polarization state.

Description of drawings

Fig. 1 is the structural representation of laser of the present invention, wherein, and 1-pumping source, 2-isolator, 3-grating, 4-beam splitter, 5-spectrometer; Pumping source is that output wavelength is the semiconductor laser of 978nm, between symmetrical grating (SFBG) and pumping source is isolator, be used for isolated feedback light to guarantee the steady operation of pumping source, and the output of symmetrical grating is separated with flashlight by the pump light of beam splitter with the 978nm of remnants;

Fig. 2 is the symmetrical expression bragg grating structural representation of laser of the present invention, and whole grating alternately is made of a plurality of segment uniform gratings and blank optical fiber, and wherein: transverse axis is an optical direction, and the longitudinal axis is a refraction index modulation, L ₁Be the length of every section little uniform grating, L ₂And L ₃It is respectively the spacing of two uniform gratings;

Fig. 3 is the transmitted spectrum schematic diagram of symmetrical grating, and wherein: transverse axis is a wavelength, and the longitudinal axis is a power, and as can be known, three dB bandwidth is 0.7pm, and curve 1 and curve 2 are transmitted spectrum theoretical values;

Fig. 4 is the chamber energy distribution of two wavelength of laser of the present invention, and wherein, transverse axis is that the chamber is long, and the longitudinal axis is an energy, and empty, solid line is represented two different wave lengths respectively;

Fig. 5 is the output spectrum of laser of the present invention, and wherein, transverse axis is a wavelength, and the longitudinal axis is a power; As seen from the figure, the about 440pm in interval between two output wavelengths;

Fig. 6 is the pump power-power output graph of a relation of laser of the present invention; Transverse axis is a pump power, and the longitudinal axis is a power output;

Fig. 7 is the three-dimensional stability surveillance map of output double wave in 40 fens clock times;

Embodiment

Fiber laser of the present invention is mainly by pumping source, isolator, and symmetrical grating (SFBG), these several parts of beam splitter constitute, and see Fig. 1 for details.(length is L to uniform fiber grating ₁) partly separated by the periodicity no-raster, constituting SFBG, this SFBG is two parts before and after the boundary is divided into the middle of a middle grating, the first half grating is followed successively by L at interval ₂, L ₃, L ₂, L ₃, the latter half grating is followed successively by L at interval ₃, L ₂, L ₃, L ₂, see Fig. 2 for details.Wherein the grating of first half is by 0 to π sampling, and the grating of latter half is taken a sample by π to 0.In making the SFBG process, Bragg period Λ is 534.2nm.By adjusting every L ₂And L ₃Length, make them satisfy L respectively ₂=m Λ, L ₃=(n+0.5) Λ, the m here, n are integers.Therefore, L ₂, L ₃The phase shift of corresponding 2m π, (2n+1) π is equivalent to " 0 " and " π " phase place respectively.Like this, 0 and π sampling just submit for distributing at whole optical fiber, first half optical fiber is 0 to the π order, latter half optical fiber be π to 0 in proper order.

Fiber grating is to scribe with the ultraviolet light that the frequency multiplication argon ion laser produces, and its power is about 130mW, and wavelength is 244nm, and scribing precision is 10 nanometers.In manufacturing process, optical fiber laterally moves, and template is fixed, and the grating total length is about 57mm.

Testing the absorptivity of used erbium-ytterbium co-doped fiber at the 978nm place is 250dB/m, and the absorptivity at the 1535nm place is 35dB/m, and fibre loss is 0.3dB/m.Fig. 5 is the spectrogram that experiment records dual wavelength DFB fiber laser, it uses the AQ6317C spectrometer measurement, this figure shows, under the resolution of 0.01nm, Optical Signal To Noise Ratio is 65dB, the about 4mW of gross output compares (0.412mw) with common Er-doped fiber Distributed Feedback Laser, has obviously improved power output.Our wavelength interval of dual wavelength DFB fiber laser of design is 400pm, and stable Energy distribution and space independent (have only sub-fraction overlapping) are arranged, and sees Fig. 6 for details.In order to confirm the stability of laser, measured once in per at room temperature 4 minutes, to measure altogether 40 minutes, measurement result is seen Fig. 7, visible laser is at room temperature stable fine.

Operation principle of the present invention:

The operation principle of common Distributed Feedback Laser is as follows: when light wave transmits in grating, produce positive direction and reciprocal capable ripple by Bragg diffraction, these row ripples are limited in the core of cavity, thereby form a resonant cavity.

Dual wavelength DFB fiber laser of the present invention and traditional Distributed Feedback Laser operation principle are similar.The theory of Distributed Feedback Laser shows that each π phase shift can produce an optical maser wavelength.But under this special symmetrical expression grating effect that constitutes laser of the present invention, in optical fiber, formed two independently resonant cavitys, thereby realized the output of dual wavelength.

Since our sampling optical-fiber grating equivalence be two independently Bragg grating alternately form, and both each comfortable different fiber position provide a π phase shift.Simultaneously, their wavelength interval is approximately:

Δλ = \frac{λ^{2}}{2 n_{eff} (2 L_{1} + L_{2} + L_{3})} &cong; \frac{λ^{2}}{4 n_{eff} (L_{1} + L_{2})}

As can be seen from the above equation, by regulating L ₁, L ₂, L ₃Can regulate Δ λ, adjustable range is 100pm～2nm.

Claims

1, a kind of dual wavelength distributed feed-back formula fiber laser based on the symmetrical expression Bragg grating, comprise pumping source (1), isolator (2), grating (3) and beam splitter (4), it is characterized in that: described grating (3) is the symmetrical expression Bragg grating, the concrete structure of described grating (3) is that width is L ₁Uniform grating part and no-raster partly be alternately distributed, no-raster partly has two width, is respectively L ₂, L ₃, represent each section grating and no-raster part with length, made grating part and no-raster partly by with L ₁Be the center symmetric mode arrangement at center, wherein L ₁First half is with L ₁, L ₂, L ₁, L ₃For cycle period is arranged in order, L wherein ₂=m Λ, L ₃=(n+0.5) Λ, Λ is a Bragg period, m, n represent integer respectively.

2, a kind of dual wavelength distributed feed-back formula fiber laser according to claim 1 based on the symmetrical expression Bragg grating, it is characterized in that: described pumping source (1) is the semiconductor laser of 978nm for output wavelength, and making the used optical fiber of grating (3) is erbium-ytterbium co-doped fiber.

3, a kind of dual wavelength distributed feed-back formula fiber laser based on the symmetrical expression Bragg grating according to claim 1 and 2 is characterized in that: described Bragg period Λ=534.2nm, m=600, n=584.