Device for introduction of laser emission into fibre

FIELD: electrical engineering .

SUBSTANCE: device for introduction of laser emission in fibre, which contains optical single-mode or multimode fibres equipped with microlenses that are shaped of transparent materials, differs because microlenses are made of optical glass, refractive exponent of which is higher than the refractive exponent of light conducting thread of fibre, in the shape of sphere that embraces light conducting thread at the end of fibre, and the end surface of fibre is made in the form of polished cylindrical surface, besides, axis of cylindrical surface intersects with fibre axis and is perpendicular to fibre axis.

EFFECT: increases coefficient of emission introduction and reduces dependency of introduction coefficient on misalignment.

5 cl, 5 dwg

 

The invention relates to the field of technical physics, in particular, fiber optics, and can be used to generate laser radiation modules with fiber output.

Currently, the efficiency of input optical radiation into the fiber is the main characteristic of the system, the radiation source fiber, and its value depends on the value of the optical power that can be entered into the light guide. The problem of efficiency of input optical radiation into the fiber lies in the fact that whatever the design of the radiation source (injection semiconductor laser or light emitting diode), its radiation characteristics, unfortunately, not consistent with the distribution of the field strength of the main fashion excited by optical fiber. This discrepancy forced to resort to the use of different ways of matching the emissivity characteristics of the field emitter and the primary (native) mode fibers to reduce losses in the input radiation.

As a significant input efficiency can only be obtained by turning the diverging beam of the radiation source in a convergent, between his radiant face and the receiving end of the fiber is placed particular optical system.

The lens unit focus optical radiation into the fiber core, increasing the effect of the want to make the input of this radiation. However, such devices make a noticeable loss in the "source - lens - fiber, called constructive. Therefore, even with the introduction of a matching lens is not always possible to increase the efficiency of input and, moreover, it can even worsen. Therefore, the lens device must be such that the agreement was maximal, and constructive losses that lens makes, were as small as possible. Such requirements can be met by the microlens formed on the end face of the fiber, it is the most simple constructive solution to the coordination of the laser beam and fiber.

Known input devices laser radiation in the fiber (1), based on the following principles:

1. The alignment of the optical axes of the emitter and the optical fiber, both the position and the angle.

2. Matching the size of the beam and the numerical aperture.

3. Eliminate reflections due to the antireflection coatings.

A device (1)for inputting the laser radiation in the fiber, the essence of which is that the purpose of the expansion angle of the entrance end surface of the light guide is formed as a descending cone on the end of which the microlens is formed from a fiber material. In common with the invention is the presence of the input microlens. However, the known device (1) is Adelino the Oh symmetric system, and when using it with lasers having different divergence in different planes, has a low coefficient of input about 57%, low reliability, requires a more complex device alignment.

A device (2), where at the end of the fiber is thermally lens is formed from a fiber material, having in common with the invention of the features is the presence of the input microlens. However, the known device is used with an optical fiber in the form of svetovida areas surrounded by a hollow longitudinal channel, which has an aperture of about 0.4-0.6, which is much more aperture standard applicable fibers, which is usually 0,22. When using this device with lasers having different divergence in parallel and perpendicular planes of the p-n junction, the input efficiency will be about 90%, but in the subsequent coupling with standard fibers will be power loss of about 50%, the total factor input will be 45%, which is a significant drawback in the application.

A device (3), which describe fibers with lenses formed in the end peaks of transparent polymeric material at the end of the fiber through which is provided the maximum data constructive communication between the optical fiber and laser diode is, which is closest to the proposed invention, taken as a prototype.

This device has in common with the invention symptoms:

1) use the same types of fibers,

2) the input microlens,

3) different material of the microlenses and fiber,

4) microlens mounted on the end face of the fiber.

The known device (3), selected as a prototype, based on the principle of harmonizing the beam emitter with a fiber size and numerical aperture. This applies to a microlens on the end of the fiber. This device has a fairly good efficiency input by selecting the options under each microlens laser diode. Based on the known prototype create laser module with fiber output. In particular, the input efficiency of the semiconductor laser with a width of the emitting region 100 μm and a height of 1 μm, with divergence at the level of 0.1 of the maximum energy parallel fields 2 Θ=12 degrees and perpendicular fields 2Θ=90 degrees and a wavelength of radiation λ=1300 nm fiber core 100 microns and a cladding of 125 microns and the aperture of NA=0,22 comes to 65%. Efficiency input or factor input is the ratio of the optical power at the output to the input optical power efficiency of the device).

Ledue is to be noted, what this device (3) is osesimmetrichnoi system, i.e. the same focal length in two mutually perpendicular planes.

The disadvantages of the known device (3) when used with lasers having different divergence in parallel and perpendicular planes of the p-n junction, and such sources are semiconductor laser diodes and LEDs, and when the diameter svetovida veins of the same with bigger side of the radiating surface of the laser diode are:

1. Inability to obtain coefficient input more than 65% because of a disagreement with the aperture of the laser radiation, therefore, 35% of the optical power will be allocated in the device in the form of heat, and in the case of high-power lasers need additional heat removal system.

2. The high dependence of the maximum coefficient input from resustance, i.e. deviations from the axis of the device from the axis of the laser radiation and, therefore, need complex on the accuracy of the system alignment and fastening.

The present invention is free from the above shortcomings in similar coordination of the invention with lasers having different divergence in parallel and perpendicular planes p-n junction, and when the diameter svetovida veins of the same with bigger side of the radiating surface of the laser diode.

The technical result of the invention consists of:

1. In a large ratio of the input radiation, up to 80%.

2. In a small dependence of maximum coefficient of input from resustance.

This allows you to create more powerful and high quality in its physical parameters of laser modules, which have a higher margin for the alignment is poor under different thermal and mechanical effects than the prototypes. In particular, using the same emitter and the fiber, which is above that of the prototype, the proposed device has achieved a coefficient input 81%.

This technical result is achieved due to the use of two systems, one of which is spherical, and the other cylindrical surface, and a cylindrical surface formed on the end face of the fiber and spherical covers part of the cylindrical surface of the light guide; an input device of the laser radiation in the fiber-containing optical single-mode or multimode fiber with microlenses formed in the end peaks of transparent material, in accordance with the invention, the microlenses are made of optical glass with a refractive index greater than the refractive index svetovida veins fiber, in the form of spheres, covering teratology, and the diameter of which is not less than the diameter svetovida veins fiber and the end surface of the fiber is made in the form of a polished cylindrical surface, the diameter of which is not less than the diameter svetovida strands of fiber, and the axis of the cylindrical surface intersects the axis of the fiber and perpendicular to the fiber axis.

In addition, this technical result is achieved by the fact that in the proposed device, the fiber end is a polished cylindrical surface the axis of which intersects the axis of the fiber inside the fiber.

In addition, this technical result is achieved by the fact that the fiber end is a polished cylindrical surface, the axis of which intersects the axis of the fiber outside of the fiber.

However, this technical result is achieved by the fact that in the proposed device, the microlens applied ar coating.

In addition, this technical result is achieved by the fact that in the proposed device as an optical fiber used multimode fiber with a gradient refractive index.

The invention is illustrated graphical materials figure 1-4, description and the specific example of the graphical results figure 5

On Figa presents the projection on the plane of OZ and XOZ, and Figb three-dimensional drawing of the proposed device, in which the fiber end is a polished cylindrical surface, the axis of which intersects the axis of the fiber inside the fiber and perpendicular to the fiber axis.

On Figa presents the projection onto the plane YOZ and XOZ, and Figb three-dimensional drawing of the proposed device, in which the fiber end is a polished cylindrical surface, the axis of which intersects the axis of the fiber on the outside of the fibers and perpendicular to the fiber axis.

Figure 3 presents a view in the plane XOZ and YOZ input device in figure 1, connected with a semiconductor laser.

4 shows two views in isometric input device in figure 1, connected with a semiconductor laser.

Figure 5 presents a graph of the dependence of the coefficient input from longitudinal and lateral movement of the input device relative to the axis of the laser diode.

The proposed device 1 and 2 contains the optical fiber 1 and the microlens 2, which covers the cylindrical surface 3 of the end face of the fiber, and the surface of the microlens 4 is a sphere and the axis of the cylindrical surface 5 intersects the axis of the optical fiber 6 at a right angle.

For different tasks of the optical fiber 1 can be both single and multimode and multimode can be settled with graded refractive index and gradient.

The microlens 2 is made of optical glass with a refractive index greater than the refractive index svetovida strands of fiber.

The spherical surface microlenses 4 has a diameter not less than the diameter svetovida veins fiber 1, the optimal radius of the sphere is approximately equal to the fiber diameter. You can choose different diameters of the cylindrical surface 3 of the end so as not less than the diameter svetovida veins fiber, the optimum diameter approximately equal to the diameter of the fiber.

The cylindrical surface 3 of the end face may be convex, then its axis 5 will intersect with the axis of the fiber 6 inside the fiber.

The cylindrical surface 3 of the end face may be concave, then the axis 5 to intersect with the axis of the fiber 6 on the outside of the fiber.

In order to reduce the reflection losses on the spherical surface of the microlens 4 is applied ar coating on the calculated wavelength.

The proposed device operates as follows : Fig 3 and 4.

The axis of the fiber 6 is aligned with the axis of the laser diode 7. Further, the device is rotated so that the plane with the maximum focal distance of the input device is parallel to the plane facing the laser radiation, in which the invariant of the laser beam maximum, in particular figure 3, the axis of the cylindrical surface 5 is perpendicular to the larger side 7 of the laser diode.

p> The distance from the end face of the laser radiation to the spherical surface of the microlens 4 is not greater than the radius of the sphere of microlenses, it is chosen from the maximum coefficient of input.

Laser radiation from the laser diode 7 with envelope 9 or 10 hits on the spherical surface 4 of the microlenses and according to the law of refraction is transformed into a beam, which then goes to the cylindrical surface 3 of the fiber. The parameters of the microlenses and the cylindrical surface 3 are selected such that the radiation from the envelope 9 and 10 is not greater than the aperture of the fiber at the entrance to the cylindrical surface 3 of the fiber, which will allow you to enter all of the radiation power in the fiber.

The input device of the laser radiation in the fiber, where the polished cylindrical convex 1 or concave Figure 2 the surface of the end face of the fiber is lens with a spherical surface of optical glass with a refractive index greater than the refractive index of the fiber core, and the radius of the larger radius of the fiber core, which covers or Svetovidov core of the fiber or in which the fiber is at a certain length. This microlens has ar coating. Thus, a two-optical system with different focal lengths in two mutually perpendicular planes.

Figure 1-3 by the dotted line p. the cauldron shape of the end face of the fiber inside the microlenses with a spherical surface, and the dash-dotted line shows the axis of the cylindrical surface and fiber.

Figure 1-3 the following notation:

1 - optical fiber,

2 - lenses with a spherical surface,

3 is a cylindrical surface of an end face of the fiber,

4 - spherical surface microlenses,

5 - axis cylindrical surface,

6 - axis optical fiber,

7 - laser diode type, the parallel p-n-transition,

8 - laser diode type, perpendicular to p-n-transition,

9 - the shape of the envelope of the laser diode, a parallel p-n-transition,

10 - the envelope of the laser diode, perpendicular to p-n-transition,

11 is a back focal length in the projection YOZ,

12 is a back focal length in the projection XOZ.

Also in figure 1-3 shows optional:

Rc is the radius of the spherical surface microlenses,

Rcem. - the radius of the cylindrical surface of the end face of the fiber,

R is the radius of the fiber,

d is the maximum distance between the cylindrical and spherical surface,

s - the distance from the end face of the laser diode to a spherical surface microlenses,

a - width of the emitting region of the laser,

b - height of the emitting region of the laser,

n0 is the refractive index of air,

n1 is the refractive index of the microlenses,

n2 is the refractive index svetovida veins fiber,

f x - back focal is the leg in the plane XOZ,

f y - back focal length in the plane YOZ,

Θthe beam divergence in the plane XOZ,

Θthe beam divergence in the plane YOZ.

Next to each projection of the indicated coordinate system XOZ or YOZ.

As seen from the figure 1, 2, input laser radiation in the fiber are two devices, the surfaces of which consist of cylindrical and spherical surfaces. The focal length of these devices are different in two mutually perpendicular planes. In particular, for the device of figure 1 is a back focal distance in the planes XOZ and YOZ are determined by the following formula:

f x=n2*Rc/(n1-n0)

f y=n1*n2*Rc*Rcem./(n1*Rc*(n2-n1)+n1*Rcem.*(n1-n0)-d*(n1-n0)*(n2-n1))

Analyzing these formulas, we find that the back focal distance f x in the plane XOZ is less than the focal length f' in the plane YOZ

f x<f y

Similarly, one can calculate the front focal distance 1 in the planes XOZ and YOZ and find the minimum and maximum focal length.

Similarly, one can calculate the front and back focal distances in the planes XOZ and YOZ for the device in figure 2, and find the minimum and maximum focal length.

Figure 3 and 4 shows a diagram of the connections of the device 1 with a semiconductor laser diode. The basic principles of operation of the device is La coordination laser diode, used input device is the following:

1. The coincidence of the optical axes of the laser and the fiber.

2. The combination of the plane with the maximum focal distance of the input device parallel to the plane facing the laser radiation, in which the invariant of the laser beam maximum.

3. The distance from the end face of the laser radiation to a spherical surface microlenses not greater than the radius of the sphere of microlenses.

The device in figure 2 is joined with the laser diode on the basis of the above principles.

The invariant of the laser beam is an important parameter of the laser radiation and can take different values in different planes, in particular, has the greatest difference in the planes perpendicular and parallel to the plane of the p-n junction. We denote the perpendicular plane as XOZ and parallel as YOZ

Jx=Rpx*n*sinΘx=J=Rp*n*sinΘ=const

Jy=B.*n*sinΘy=J=Rp*n*sinΘ=const, where

Jx=Jinvariants of the beams in the plane XOZ,

Jy=Jinvariants of the beams in the plane YOZ,

Rpx=Rpthe radii of the constrictions of the laser in the plane XOZ,

Pry=Rpthe radii of the constrictions of the laser in the plane YOZ,

Θx=Θthe beam divergence in the plane XOZ,

Θy=Θ- the divergence of the beam in pleskot the x YOZ.

In particular, a semiconductor laser diode with a radiating area of width a, height b in the air and divergence Θand Θthe invariant Jexceeds the invariant J

Using the principles mentioned above, the input device will allow you to shape the waist of the laser radiation, as well as separate banners in two mutually perpendicular planes, with such radii and divergence that are consistent with aperture diameter svetovida core optical fiber. This allows you to achieve maximum coordination of laser and fiber.

Figure 3 presents projected view of an input device in figure 1:

- in the plane XOZ, attached with a semiconductor laser, where the optical axis of the laser and fiber are aligned, the distance s is not more RC, a laser plane perpendicular to the p-n junction parallel to the plane XOZ input device. The back focal distance f x input device is minimal in this design and in the parallel it is the plane of minimal invariant, and that J.

- in the plane YOZ, attached with a semiconductor laser, where the optical axis of the laser and fiber are aligned, the distance s is not more RCthe laser plane parallel p-n-transition parallel to the plane YOZ input device. Focal RA is standing f y input device maximum in this design and in the parallel it is the plane of maximum invariant, and that J.

4 shows two views in isometric input device 1, connected with a semiconductor laser.

The technical result in the application of the invention is that commensurate with the size of the fiber diameter and the width of the emitting surface of the laser diode, the input efficiency of the laser radiation into an optical fibre (system efficiency) is higher than its nearest analogue (3), and is about 80%. Also the higher the reliability of the applied invention, because it has a large input aperture than the prototype, and therefore margin alignment is poor.

The main task, which is aimed by the invention, is increasing the efficiency of the input laser radiation into an optical fibre commensurate with the size of the fiber diameter and the width of the emitting surface of the laser diode. Laser beams can be axisymmetric and nonaxisymmetric. For each kind of the laser beam is calculated individual parameters of optical devices with different sizes and refractive indices of the microlenses.

In order to enter the maximum energy of the laser beam in the optical fiber, it is necessary to place the input end in the waist of the beam formed by matching the optical device. Moreover, in the light guide will include only those rays, the angle of which is s smaller than the aperture of the light guide, while the diameter of the banners smaller diameter extending through the light field. That is, the task is to convert the laser beam, in which the confocal parameters of the radiation in two mutually perpendicular planes of different beam with others, but also different values confocal parameter, and banners of the formed beam should be the same. This conversion can be done only anamorphic lens whose focal lengths in two mutually perpendicular planes are different. In this case, a combination of spherical and cylindrical surfaces.

A brief description of the drawings.

On Figa presents, the projection on the plane YOZ and XOZ, and Figb three-dimensional drawing of the proposed device, in which the fiber end is a convex cylindrical surface. At the end of the fiber fixed lens with a spherical surface.

On Figa presents the projection onto the plane YOZ and XOZ, and Figb three-dimensional drawing of the proposed device, in which the fiber end is a concave cylindrical surface. At the end of the fiber fixed lens with a spherical surface.

Figure 3 presents a view in the plane XOZ and YOZ input device 1, connected with a semiconductor laser.

Figure 4 presents two types of isometricity input 1, it is attached to a semiconductor laser.

Figure 5 presents a graph of the dependence of the coefficient input from longitudinal and lateral movement of the input device relative to the axis of the laser diode.

The implementation of the invention is illustrated by the specific implementation of the present invention.

On the basis of calculations was made the device represented in figure 1 with the following parameters:

Rc is the radius of the spherical surface microlenses = 90 ám.

Rcem. - the radius of the cylindrical surface of the end face of the fiber = 80 ám.

d is the maximum distance between the cylindrical and the spherical surface = 90 ám.

n1 is the refractive index of the microlenses = 1,8.

n2 is the refractive index svetovida veins fiber = 1,45.

Were calculated optimal parameters to enter the semiconductor laser with a width of the emitting region 100 μm and a height of 1 μm, with divergence at the level of 0.1 of the maximum energy parallel fields 2Θ=12 degrees and perpendicular fields 2Θ=90 degrees and a wavelength of radiation λ=1300 nm with a power of 1 W in the fiber core 100 microns and a cladding of 125 microns and the aperture of NA=0,22. The agreement with the laser was carried out according to Figure 3

The test results of the fabricated devices were obtained from the following data, presented in Figure 5, namely, not only the t dependence of the coefficient input of the distance s and the parameters of resustance Δ X and ΔY

The graphs in figure 5 are indicated:

On the Y - axis is the ratio of the input laser radiation in percentage(%).

On the X - axis is the distance from the end face of the laser diode to a spherical surface microlenses, unit - 5 microns(μm), moving on the X-axis and Y ΔX and ΔY dimensions microns.

13 dependence of the ratio of input distance s, K(s)

14 dependence of the coefficient input from the axis X, To(ΔX)

15 dependence of the coefficient input from the Y-axis, (ΔY)

The result is maximum efficiency of the input radiation into the fiber was 81% at a distance of s=40 ám.

Similarly, when s=40 ám, we see that in the range of +/-5 μm transverse movement we keep the input efficiency is more than 70%, the maximum input efficiency more than 1.25 times the equivalent.

Literature

1. Fundamentals of optoelectronics. M.: Mir, 1988, p.129-130.

2. Application for invention No. 2002106585/28.

3. Application for invention No. 2004105855/28 - (prototype).

1. The input device of the laser radiation in the fiber-containing optical single-mode or multimode fiber with microlenses formed of a transparent material, wherein the microlenses are made of optical glass with a refractive index greater than the refractive index svetovida veins fiber, in the form of spheres covering the light is ovedose mine at the end of the fiber, and the end surface of the fiber is made in the form of a polished cylindrical surface, the axis of the cylindrical surface intersects the axis of the fiber and perpendicular to the fiber axis.

2. The input device of the laser radiation in the fiber according to claim 1, in which the fiber end is a polished cylindrical surface, the axis of which intersects the axis of the fiber inside the fiber;

3. The input device of the laser radiation in the fiber according to claim 1, in which the fiber end is a polished cylindrical surface, the axis of which intersects the axis of the fiber on the outside of the fibers;

4. The input device of the laser radiation in the fiber of claim 1, wherein the microlens applied ar coating.

5. The input device of the laser radiation in the fiber of claim 1, wherein the optical fiber is a multimode fiber with a gradient refractive index.



 

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