Asymmetric double refraction vortex optical fiber and preparation method thereof
(1) technical field
The present invention relates to a kind of optical fiber and technology of preparing thereof, be specifically related to a kind of asymmetric double refraction vortex optical fiber and preparation method thereof, belong to optical fiber technology field.
(2) background technology
A notable feature of vortex beams is to have orbital angular momentum (Physical Review A, 1992,45 (11): 8185-8189), be therefore widely studied in recent years, and obtained very big application in communication, light tweezer, Atomic Manipulation and microtechnic.The common methods that generates vortex beams is usage space photomodulator (OpticsExpress, 2008,16 (21): 16984-16992), but spatial light modulator is generally bulky, expensive, and need in free space, realize optically-coupled, so just bring much inconvenience.
Vortex photoproduction based on optical fiber is grown up to be a useful person and in remote interaction and system miniaturization, is had more advantage.Researchers use acoustics long-period gratings (Physical Review Letters, 2006,43604) or utilize induction pressure (Applied Optics in multimode optical fiber 96 (4):, 1998,37 (3): 469-472) realized vortex optical transmission mode.But Mode Coupling can be destroyed orbital angular momentum pattern in optical fiber, thereby cause multipath interference.In most multimode optical fibers, TE/TM pattern and the HE needing
21pattern coexists, and they can generate linear polarization pattern (LP pattern) at output terminal through Mode Coupling like this, and LP pattern is not the real eigenmodes of optical fiber, and it can not carry orbital angular momentum.Therefore, document (Optics Letters, 2012,37 (13): 2451-2453) has been reported and has been utilized micro-curved grating to slacken high-order LP
11the generation of pattern, and then input pattern is converted into needed HE
21pattern, finally generates highly purified vortex beams.
Desirable standard single-mode fiber has how much good circular symmetries, thereby the basic mode HE transmitting
11the double degenerate mode of orthogonal modes.But in actual fiber, due to the existence of defect, this double degenerate is destroyed, thereby cause mode birefringence, in order to maintain this pattern polarization in standard single-mode fiber, people have designed polarization maintaining optical fibre.Polarization maintaining optical fibre makes
with
the effective refractive index difference of pattern, the propagation constant β of pairwise orthogonal mould
xwith β
ydifference increases, and two-mode coupling probability reduces, if therefore transmission light is by linear polarization in the parallel direction of optical axis of optical fiber, light will keep this polarization state to transmit in optical fiber always so.
United States Patent (USP) (US20080101754) and European patent (EP1705503B1) have proposed a kind of fiber core refractive index only with the gradient index fibre of azimuthal variation, this optical fiber can be regarded the space phase plate of longitudinal tensile strain as, utilizes this optical fiber can generate vortex beams.Although this vortex beams maker structure is very simple, but it is but very difficult to prepare this optical fiber, therefore the present invention, in polarization maintaining optical fibre technical foundation, has proposed a kind of Novel asymmetric birefringence vortex optical fiber, this vortex optical fiber is prepared than being easier to, and can produce class vortex beams.
(3) summary of the invention
The object of the present invention is to provide a kind of asymmetric double refraction vortex optical fiber that generates vortex optical transmission mode and preparation method thereof.
The present invention is achieved in that
A notable feature of vortex beams is to have orbital angular momentum, and in order to obtain orbital angular momentum, optical fiber must carry more higher order mode, for example, phase shift is ± and two HE of pi/2
21the linear combination of pattern can realize orbital angular momentum pattern.Because asymmetric double refraction vortex optical fiber of the present invention exists simple helix or double helix stressed zone, and the material difference of adulterating in two prestress rods of double helix stressed zone, therefore the difference of the mal-distribution of this stressed zone or stressed zone material, just cause the asymmetric stress birefringence in fibre core to distribute, and this is distributed in optical fiber longitudinally in the shape of a spiral, thereby be input to after this optical fiber when light wave, radial phase can be formed poor, thereby make the light field of wherein transmitting obtain orbital angular momentum, produce vortex transmission of phase, realize class vortex optical transmission mode.
Asymmetric double refraction vortex optical fiber of the present invention is from the different of polarization maintaining optical fibre, in the present invention, due to the difference of mal-distribution or the stressed zone material of stressed zone, there will not be the linear polarization property of polarization maintaining optical fibre, but along with the rotation of spiral stressed zone, in fibre core, there is vortex optical transmission mode in the also rotation thereupon of light conducting wave polarization state.
Compared with prior art, advantage of the present invention is:
1, the preparation of asymmetric double refraction vortex optical fiber is simple, can directly be drawn and be formed by the preform rotation with simple helix or double helix stressed zone.
2, refractive index Spiral distribution function and the stressed zone dopant material of asymmetric double refraction vortex optical fiber are controlled in preparation process, finally can realize the control to generating class vortex beams feature.
3, asymmetric double refraction vortex optical fiber space pliability is fabulous, therefore can be chosen in output class vortex beams in the position of any appropriate and direction, is convenient to the application in particulate manipulation and sensing.
(4) brief description of the drawings
Fig. 1 is the asymmetric double refraction vortex optical fiber schematic diagram with simple helix stressed zone;
Fig. 2 is the cross sectional representation with the asymmetric double refraction vortex optical fiber of simple helix stressed zone;
Fig. 3 is stress birefrin (a) three peacekeepings (b) two-dimensional representation with the asymmetric double refraction vortex optical fiber of simple helix stressed zone;
Fig. 4 is the light intensity transmission schematic diagram with the asymmetric double refraction vortex optical fiber of simple helix stressed zone;
Fig. 5 is the asymmetric double refraction vortex optical fiber with simple helix stressed zone at (a) Z=900 μ m, (b) Z=1000 μ m, (c) Z=1100 μ m and (d) the PHASE DISTRIBUTION figure of Z=1200 μ m cross-section;
Fig. 6 is that the preform with single stress district is prepared schematic diagram;
Fig. 7 be have simple helix stressed zone asymmetric double refraction vortex optical fiber prepare schematic diagram;
Fig. 8 is the asymmetric double refraction vortex optical fiber schematic diagram with double helix stressed zone;
Fig. 9 is the cross sectional representation with the asymmetric double refraction vortex optical fiber of double helix stressed zone;
Figure 10 is stress birefrin (a) three peacekeepings (b) two-dimensional representation with the asymmetric double refraction vortex optical fiber of double helix stressed zone;
Figure 11 is the preform preparation method schematic diagram with two stressed zones;
Figure 12 is preparation method's schematic diagram with the asymmetric double refraction vortex optical fiber of double helix stressed zone;
Figure 13 is the connection diagram of the tail optical fiber with light source and the asymmetric double refraction vortex optical fiber with simple helix stressed zone.
Figure 14 is the connection diagram of the tail optical fiber with light source and the asymmetric double refraction vortex optical fiber with double helix stressed zone.
(5) embodiment
For example the present invention is described in more detail below in conjunction with accompanying drawing:
In conjunction with Fig. 1-Fig. 5, the first embodiment of the present invention is to realize like this.
First the ultimate principle how light wave produces vortex light field after the asymmetric double refraction vortex optical fiber providing through one section of the present invention is described.Get one section of asymmetric double refraction vortex optical fiber, this optical fiber comprises covering 1, fibre core 2 and simple helix stressed zone 3.Due to the existence of simple helix stressed zone 3, cross section of optic fibre shown in Fig. 2 is carried out to the stress birefrin that stress analysis just can obtain as shown in Figure 3 to distribute (in Fig. 3 (a), the region representation core region that column fence surrounds, Z axis represents stress birefrin size N
y-N
xin Fig. 3 (b), gray scale size represents stress birefrin size), owing to existing this asymmetrical stress birefrin to distribute in fibre core, so in the time that light source 4 is inputted in the one end to this optical fiber, this optical fiber can generate class vortex optical transmission mode, its light intensity is transmitted as shown in Figure 4, in the PHASE DISTRIBUTION of Z=900 μ m, 1000 μ m, 1100 μ m and 1200 μ m cross-section as shown in Figure 5, as can be seen here, in this optical fiber, conduction light wave has vortex phase place, and it is a kind vortex beams.
Next provides the preparation method of asymmetric double refraction vortex optical fiber.The preparation process of this asymmetric double refraction vortex optical fiber with simple helix stressed zone can be divided into following step (as Fig. 6 and Fig. 7):
Step 1: as Fig. 6, squeeze into an eccentric orfice 7 in the preform 6 that contains core 5, then stressed zone prefabricated rods 8 is inserted in eccentric orfice 7, so just obtain having the preform 9 in single stress district;
Step 2: as Fig. 7, preform 9 is positioned on wire-drawer-tower, under the acting in conjunction of vertical distraction power 10 and twisting resistance 11, reverse wire drawing, after heating and corresponding aftertreatment 12, be prepared into the asymmetric double refraction vortex optical fiber 13 with simple helix stressed zone.
In conjunction with Fig. 8 and Fig. 9, be different from the first embodiment, the asymmetric double refraction vortex optical fiber of the second embodiment of the present invention has two stressed zones 14 and 15, forms double helix stressed zone structure.For this asymmetric double refraction vortex optical fiber with double helix stressed zone, Figure 10 is given in the stress birefrin distribution plan in fibre core, as can be seen from the figure the variation range of its stress birefrin is greater than the stress birefrin variation range (Fig. 3) of the asymmetric double refraction vortex fiber core with simple helix stressed zone, thereby the ability of this optical fiber generation vortex phase place is more outstanding.
The preparation process of this asymmetric double refraction vortex optical fiber with double helix stressed zone can be divided into following step (as Figure 11 and Figure 12):
Step 1: as Figure 11, in core fibre prefabricated rods 6, squeeze into two symmetrical eccentric orfices 7 containing, then two different stressed zone prefabricated rods 16 and 17 of dopant material are inserted respectively in two symmetrical eccentric orfices 7, so just obtained having the preform 18 of two stressed zones;
Step 2: as Figure 12, preform 18 is positioned on wire-drawer-tower, under the acting in conjunction of vertical distraction power 10 and twisting resistance 11, reverse wire drawing, after heating and corresponding aftertreatment 12, be prepared into the asymmetric double refraction vortex optical fiber 19 with double helix stressed zone.
Embodiment 1:
1, optical fiber preparation: prepare the asymmetric double refraction vortex optical fiber 13 with simple helix stressed zone according to the method for preparing optical fiber of the first embodiment;
2, light source coupling: the asymmetric double refraction vortex optical fiber 13 with simple helix stressed zone preparing is cut, then aim at, weld with the single-mode fiber 20 with light source tail optical fiber, as shown in figure 13;
3, vortex beams generates: after input laser 21, will in the asymmetric double refraction vortex optical fiber 13 with simple helix stressed zone, realize the transmission of vortex optical mode, and can be at optical fiber end output class vortex beams.
Embodiment 2:
1, optical fiber preparation: prepare the asymmetric double refraction vortex optical fiber 19 with double helix stressed zone according to the method for preparing optical fiber of the second embodiment;
2, light source coupling: the asymmetric double refraction vortex optical fiber 19 with double helix stressed zone preparing is cut, then aim at, weld with the single-mode fiber 20 with light source tail optical fiber, as shown in figure 14;
3, vortex beams generates: after input laser 21, will in the asymmetric double refraction vortex optical fiber 19 with double helix stressed zone, realize the transmission of vortex optical mode, and can be at optical fiber end output class vortex beams.