CN1834706A - Method of generating hollow hight beam and tuning by utilizing optical fiber intermodal interference - Google Patents

Abstract

The invention discloses a method of using optical fiber intermode interference to generate hollow light beam and tune. The process includes the following steps: adopts optical fiber and taking unbiased connection, and the diameter of multimode optical fiber is 5-50um, the light energy is gathered ON LPO1 and LPO2, selecting the length of multimode optical fiber to satisfy interference condition. The output end and the compounding light beam is hollow light beam. The tuning process includes the following steps: using temperature component to alter circumstance temperature or impressing axial stress to the multimode optical fiber. The invention is simple structure and is easy to tune.

Description

Utilize the optical fiber intermode interference to produce hollow beam and tuning method

Technical field

The present invention relates to a kind of hollow beam and tuning method of producing, particularly a kind of optical fiber intermode interference that utilizes produces hollow beam and tuning method, belongs to optics and optical fiber technology field.

Background technology

So-called hollow beam is meant that on the direction of propagation of light beam central light strength is lower or is zero annular beam.General laser beam all is that its central light strength is maximum, radially weakens gradually, and in most cases available Gauss model is described.Hollow beam has the not available physical characteristics of Gaussian beam, and as little blackening size, transmission unchangeability, some hollow beam also has spin and orbital angular momentum.Because the characteristic of hollow beam makes it at modern physics, biomedicine, there is important application prospects in fields such as optical communication and light sensing.For example, utilize the characteristic of hollow beam, can carry out accurate contactless control comprising micro-and nano-particles, molecule, atom, free electron microscopic particle.Also can adopt hollow beam that biological cell is operated.Light tweezer (Optical tweezers) technology of employing Gaussian beam has been widely used in the optics imprison and the control of biological cell and small insulating particles, but the light tweezer that adopts Gaussian beam can only be used to imprison the particle of the projecting medium refraction index of refractive index, and the particle that can't refractive index be lower than the surrounding medium refractive index is controlled.Adopt hollow beam then not have this restriction.In addition, because the hollow beam central light strength is lower or it is zero to be, so the possibility of the particle fire damage that is caused by light absorption reduces greatly.

The light beam of general laser instrument output is fundamental transverse mode, i.e. common Gaussian beam.Then can make it operate in the high-order mode state as in laser cavity, adding the transverse mode selector switch, thereby obtain high-order Gaussian, i.e. hollow beam.Adopt transverse mode to select technology, CO at He-Ne ₂And successfully obtain hollow beam on the dye laser.Using circular cone prism (Axicon) is a kind of geometrical optics approach of generation hollow beam of practicality, and circular cone prism produces the refraction of symmetry vertically to the Gaussian beam of incident, changes the space distribution of incident beam, thereby forms hollow beam.The employing circular cone prism can obtain the conversion efficiency near 100%.In addition, can also use circular cone prism that Laguerre-Gaussian beam is transformed to the high-order bessel beam.The method Identification with Method of Optical Holography of other generation hollow beam and calculation holographic method etc.The method of above-mentioned generation hollow beam is generally complicated, and the method that has can only produce approximate or bottle beams.

Summary of the invention

Purpose of the present invention just provides a kind of optical fiber intermode interference that utilizes and produces hollow beam and tuning method.This method has the realization of being easy to, optical beam transformation and beam Propagation and finish (thereby having compact conformation), characteristics such as tunable simultaneously in optical fiber.

The present invention is realized by the following technical programs, a kind of method of utilizing the optical fiber intermode interference to produce hollow beam, it is characterized in that comprising following process: adopt used light wavelength is single-mode fiber and is two kinds of optical fiber of multimode optical fiber to used light wavelength, after two kinds of optical fiber are docked without acceptance of persons, the diameter of elected majority mode fiber is 5～50 microns, and then luminous energy concentrates on two lowest-order circle line of symmetry polarization mode LP in multimode optical fiber ₀₁And LP ₀₂On, and select the length L of multimode optical fiber to make two lowest-order circle line of symmetry polarization mode LP ₀₁And LP ₀₂When the condition that the satisfied interference of the output terminal of multimode optical fiber is subtracted each other, be hollow beam then at the output terminal of multimode optical fiber and the synthetic light beam of free space generation.

A kind of method of tuning above-mentioned hollow beam is characterized in that comprising following process: 1, adopt temperature element (TE) to change the environment temperature of multimode optical fiber, carry out tuning to formed synthetic light beam; 2 or multimode optical fiber applied stress vertically, carry out tuning to formed synthetic light beam.

The present invention is based on following principle.

In the rounded step fiber core, the electric field of linearly polarized mode LPmn can be expressed as:

$E_{\mathrm{co}}=\frac{A}{J_n\left(U\right)}{J}_n\left(\frac{U}{a}r\right)\cos \mathrm{m\φ},$ r≤a，

Electric field in covering can be expressed as:

$E_{\mathrm{cl}}=\frac{A}{K_n\left(U\right)}{K}_n\left(\frac{W}{a}r\right)\cos \mathrm{m\φ},$ r＞a，

Wherein, J _n(χ) be n rank Bessel function of the first kind; K _n(χ) be the n rank second class modified Bessel functions; U is the longitudinal propagation constant; W is a transverse propagation constant; A is a rounded step fiber core radius.Following formula shows that the Electric Field Distribution of each rank mould in the multimode optical fiber fibre core is a Bessel's function, and in the center maximal value is arranged.So can't produce hollow beam by single mould.

When above-mentioned first kind of single-mode fiber with after second kind of multimode optical fiber docks without acceptance of persons, be coupled to multimode optical fiber by the light of single-mode fiber transmission.Because symmetry can only excite the symmetrical linearly polarized mode LP of circle in multimode optical fiber ₀N.Determine by following formula by the energy coupling coefficient of the basic mode in the single-mode fiber to the not same order mode coupling of multimode optical fiber

${\mathrm{\η}}_n=\frac{{\left|{\∫}_0^{\∞}{E}_{S1}\left(r\right)E_{\mathrm{Mn}}\left(r\right)\mathrm{rdr}\right|}^2}{{\∫}_0^{\∞}{\left|E_{S1}\left(r\right)\right|}^2\mathrm{rdr}{\∫}_0^{\∞}{\left|E_{\mathrm{Mn}}\left(r\right)\right|}^2\mathrm{rdr}},$

Wherein, W _S1(r) be the electric field of basic mode in the single-mode fiber; E _Mn(r) be LP in the multimode optical fiber ₀The electric field of n rank mould.Analytical calculation shows, can control the energy distribution between each rank mould in the multimode optical fiber effectively by the parameter that changes multimode optical fiber.Suitably select the parameter of multimode optical fiber can make it to produce linearly polarized mode LP ₀₁And LP ₀₂, they are being interfered along producing in the optical fiber co-propagate process.As the length of establishing multimode optical fiber is L, LP ₀₁And LP ₀₂The longitudinal propagation constant of mould is respectively u ₁And u ₂, then as (u ₁-u ₂) during L=(2K+1) π, LP ₀₁And LP ₀₂Produce between the mould and subtract each other interference.At this moment, on multimode optical fiber output terminal free space fibre-optical center line, produce blackening, form hollow beam.

Because longitudinal propagation constant u ₁, u ₂With L all be the function of temperature and the extraneous stress that bears, so the environment temperature of change optical fiber or can carry out tuning to the interference field that is produced to its stress that applies vertically.In addition, have photosensitivity as used multimode optical fiber, it is tuning also can to adopt UV-irradiation to realize.

Method involved in the present invention has realization, optical beam transformation and the beam Propagation of being easy to simple in structure and finish (thereby having compact conformation), characteristics such as tunable simultaneously in optical fiber.Can be applicable to atom optics, contemporary optics, modern physics, material science, fields such as biomedicine.

Description of drawings

Fig. 1 produces the fiber device structural representation of hollow beam for adopting thermal tuning.

Among the figure: 101 is the covering of single-mode fiber; 102 is the fibre core of single-mode fiber; 103 is the covering of multimode optical fiber; 104 is the fibre core of multimode optical fiber; 105 is temperature control component.

Fig. 2 is for adopting the fiber device structural representation of the tuning generation hollow beam of stress.

Among the figure: 101 is the covering of single-mode fiber; 102 is the fibre core of single-mode fiber; 103 is the covering of multimode optical fiber; 104 is the fibre core of multimode optical fiber; 106 are fixing optical fiber clamping device; 107 are optical fiber clamping device movably.

Fig. 3 is the hollow beam mould field pattern that produces with Fig. 1 fiber device or Fig. 2 fiber device.

Among the figure: 108 is LP ₀₁The mould field pattern; 109 is LP ₀₂The mould field pattern; 110 is the mould field pattern of hollow beam.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is elaborated.As shown in Figure 1, the fibre core of the single-mode fiber of employing (102) diameter is 4 μ m, and covering (101) diameter is 125 μ m, is 0.13 to its numerical aperture of 630nm wavelength.The fibre core of multimode optical fiber (104) diameter is 9 μ m, and covering (103) diameter is 125 μ m, is 0.14 to its numerical aperture of 1310nm wavelength.Use optical fiber splicer that above-mentioned multimode optical fiber and the above-mentioned single-mode fiber of one segment length as 65mm is welded together.The wavelength that adopts the fine output of magnetic tape trailer is that the single mode semiconductor laser of 635nm is made light source.Adopt single-mode optical fiber connector that the tail optical fiber of described single-mode fiber with semiconductor laser output docked.Temperature control component (105) adopts semiconductor cooler, and described multimode optical fiber is fixed on the semiconductor cooler.

According to known optical fiber parameter by Theoretical Calculation as can be known, the light (635nm) by described single-mode fiber output can inspire LP in described multimode optical fiber ₀₁And LP ₀₂Linearly polarized mode, its electric field ratio is about 1.3: 1.By the laser of semiconductor laser output 635nm through the single-mode fiber transmission and be coupled to multimode optical fiber, at multimode optical fiber output terminal free space LP ₀₁And LP ₀₂Linearly polarized mode produces interferes.The temperature of the drive current adjustment multimode optical fiber by changing semiconductor cooler can make on the fiber optic hub line and produce blackening, forms hollow beam.

The two ends of multimode optical fiber are separately fixed on two fibre holders, it is motionless that one of them fibre holder keeps, another fibre holder is fixed on the micro-displacement platform, and this micro-displacement platform can move axially along optical fiber, is applied to tension force on the multimode optical fiber with adjusting.When the tension force on the multimode optical fiber reaches certain value, on multimode optical fiber output terminal free space fibre-optical center line, produce blackening, form hollow beam.

In addition, adopt method provided by the invention, by choosing the parameter of multimode optical fiber, make it to produce the more linearly polarized mode of high-order, these moulds produce multiple-mode interfence, can produce other the extraordinary light beam that comprises bessel beam, and have tunable function.

Claims (3)

1. method of utilizing the optical fiber intermode interference to produce hollow beam, it is characterized in that comprising following process: adopt used light wavelength is single-mode fiber and is two kinds of optical fiber of multimode optical fiber to used light wavelength, after two kinds of optical fiber are docked without acceptance of persons, the diameter of elected majority mode fiber is 5～50 microns, and then luminous energy concentrates on two lowest-order circle line of symmetry polarization mode LP in multimode optical fiber ₀₁And LP ₀₂On, and select the length L of multimode optical fiber to make two lowest-order circle line of symmetry polarization mode LP ₀₁And LP ₀₂When the condition that the satisfied interference of the output terminal of multimode optical fiber is subtracted each other, be hollow beam then at the output terminal of multimode optical fiber and the synthetic light beam of free space generation.

2. the method for the hollow beam of tuning claim 1 generation is characterized in that comprising following process: adopt temperature element (TE) to change the environment temperature of multimode optical fiber, carry out tuning to formed synthetic light beam.

3. the method for the hollow beam of tuning claim 1 generation is characterized in that comprising following process: multimode optical fiber is applied stress vertically, realize carrying out tuning to formed synthetic light beam.

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