WO2002011251A2

WO2002011251A2 - Wave beam converter and method for making same

Info

Publication number: WO2002011251A2
Application number: PCT/FR2001/002479
Authority: WO
Inventors: Christian Larat; Eric Lallier; Gilles Feugnet
Original assignee: Thales
Priority date: 2000-07-28
Filing date: 2001-07-27
Publication date: 2002-02-07
Also published as: FR2812407A1; WO2002011251A3; EP1305667A2; FR2812407B1

Abstract

A wave beam is used more efficiently the closer its geometric scope is to rotational symmetry. In order to achieve that, a system can use a converter of one or several parameters of a wave beam comprising N sub-beams (N being an integer ≥ 1). The invention is characterised in that it comprises at least a solid material comprising at least: a first end including at least N inputs, each of the N sub-beams being received by one of the N inputs, and a second end including an output delivering the beam whereof the conversion parameter(s) have one or more predetermined value(s). The converted parameter may be the geometric scope so as to fulfil the condition of efficacy.

Description

WAVE BEAM CONVERTER AND MANUFACTURING METHOD THEREOF

The invention relates to the field of wave propagation.

Even if the invention can be applied to any type of wave, the problem which it proposes to solve is described in the case of emission of optical beams. Laser diode arrays are monolithic assemblies of diodes. The light beams, which they make it possible to deliver, have high optical powers. Their emissive surface is, in general, 1cm wide in the direction parallel to the plane of the junction (D _// ). And, in the perpendicular direction (D ±), it is approximately ^" Iμm high. A strip is, thus, a source of emission presenting a strong asymmetry. Indeed, it is approximately 10,000 times wider than high. Likewise, the radiation from the emission source does not diverges symmetrically: it is greater than 25 ° (30 ° to 50 °) according to Di, it is approximately 10 ° along D _// . By definition, l "Geometric extent is the product of dimension by divergence in one direction. The product of these two characteristics leads to a linear geometric extent. Indeed, it is about 2.000 times greater according to D _// than according to Dj ..

This strong asymmetry is a real detriment to the use of these components. Indeed, it does not allow efficient use of these components and this in the case of many applications. This is why it is advantageous to have a beam whose geometric extent is close to the symmetry of revolution. This type of beam is injected into an optical fiber or it is used directly. The solution is therefore to optically distribute the geometric extent of such a source in both directions. This is done while retaining its overall value at best. This subject has inspired many works. Some of this work is described in the following documents: J.R LEGER et al, IEEE Journal of Quantum Electronics, vol. 18, No. 4, April 1992, and French patents FR 2,741,726, FR 2,748, 127, 2,783,056 (THOMSON-CSF).

The present invention overcomes or, at the very least, reduces the drawbacks of existing solutions. The geometrical extent is distributed by inscribing three-dimensional waveguides in a solid material. The advantage of such a system is the obtaining of a source whose geometric extent is distributed more uniformly according to the two directions than the original source. Hence a field of application which is much wider.

The invention provides a converter for one or more parameters of a wave beam comprising N sub-beams, characterized in that it comprises at least one solid material comprising at least:

A first end comprising at least N inputs, each of the N sub-beams being received by one of the N inputs, and

• a second end comprising at least one output delivering the beam, the conversion parameter or parameters of which have one or more predetermined values.

This converter makes it possible to modify the geometric extent by implementing a method of converting one or more parameters of a wave beam comprising N sub-beams, characterized in that it comprises at least the guidance of each of the N sub-beams by N index lines in the three-dimensional space constituted by a solid material, the index lines forming elementary waveguides.

The invention also relates to a method of manufacturing a converter for one or more parameters of a wave beam comprising N sub-beams, characterized in that it includes the local modification of the index of a solid material so as to form N lines of indices constituting elementary waveguides between a first and the second end of the material such that the parameter or parameters of the beam delivered by the material at its second end have one or more predetermined values.

The characteristics and advantages of the invention will appear more clearly on reading the description, given by way of example, and of the figures relating thereto which represent:

FIG. 1, a block diagram of a system for transmitting a rectangular geometric extent according to the invention,

- Figure 2, an external view of the geometric extent converter used in Figure 1.

In FIG. 1, an initial component 1 generates a beam whose geometric extent has the shape of a more or less thick line. The initial component 1 has at least several wave transmitters, for example the three wave transmitters 1a, 1b and 1c, which each generate a sub-beam. The beam passes through a coupling member 3 before entering the converter 2. The converter 2 has at least the same number of elementary waveguides as the initial component 1 has emitters. These elementary waveguides 2a, 2b and 2c are inscribed in a solid material. The three elementary waveguides 2a, 2b and 2c each have an input E2a, E2b and E2c which is associated with one of the transmitters 1a, 1b, and 1c. These inputs E2a, E2b and E2c are, therefore, distributed in the same way as the transmitters 1 a, 1 b and 1 c. The coupling member 3 makes it possible to adapt the sub-beams coming from the transmitters 1 a, 1b and 1c to the inputs E2a, E2b and E2c. The conversion of the geometric extent of this beam is carried out, for example, by superimposing the outputs S2a, S2b and S2c of the elementary waveguides 2a, 2b and 2c. In FIG. 1, the geometric extent at the outlet of the converter 2 has the shape of a rectangle.

In this case, it is the geometric extent of the beam passing through the material 2 which is converted. In general, the converter 2 can modify one or more parameters. For example, it can convert the beam size. Or, it can transform its divergence in one or more directions.

The sub-beams coming from the three emitters 1a, 1b and 1c are emitted independently of each other. They are emitted in the same direction, the direction [Oz) in FIG. 1. The initial component 1 can be, for example, an array of laser diodes or a stack of arrays. The representation of the converter 2 in FIG. 1 is not complete.

Indeed, only the elementary waveguides 2a, 2b, 2c are visible there. This partial view of the converter 2 makes it easier to read the beam paths in the system of FIG. 1. The superposition of the outputs S2a, S2b and S2c is obtained by the fact that the elementary waveguides 2a, 2b and 2c overlap. This leads to the sub-beams coming from the initial transmitters 1a, 1b and 1c being spatially rearranged. The different elementary guides 2a, 2b and 2c can remain independent or be coupled so as to form only one guide (for example, larger). The S2a, S2b and S2c outputs have therefore been merged into a single S2 output. -The use of a coupling member 3 is not necessary. However, it can make up for a number of drawbacks. First of all, it ensures good power transmission. In addition, it makes it possible to adapt the size and / or the divergence of the beams from the transmitters 1 a, 1 b and 1 c to those of the inputs E2a, E2b and E2c.

For example, the digital aperture of a beam from a laser diode 1a, 1b or 1c is, in general, of the order of 0.5 depending on the direction [Oy). The member 3 makes it possible to reduce the digital aperture of this beam. Thus, it can be reduced to a value less than or equal to that of the input E2a, E2b or E2c. This reduction can be achieved using, for example, one (or more) cylindrical lens. The lens collectively serves all the emitters 1a, 1b and 1c of a diode array. Similarly, in the direction [Ox), the beam can be adapted to the input E2a, E2b or E2c. The digital aperture of a beam from a diode 1 a, 1 b or 1 c is, in general, less than 0.1 in this direction. It is therefore possible that it is compatible with that of the input E2a, E2b or E2c. On the other hand, its spatial dimension is much larger (typically 50 to 500 μm) than the following thickness [Oy) of the beam at the output of the emitter 1a, 1b, 1c. Hence the profile of the inputs E2a, E2b and E2c is preferably rectangular. In the case where the initial component 1 comprises a stack of arrays of laser diodes, the coupling member 3 could be an array of cylindrical lenses. These lenses are placed in the member 3 such that each of them is associated with one of the laser diode arrays of this stack. The coupling member 3 thus makes it possible to reduce the divergence in the direction [Oy). The coupling optics 3 can therefore include:

• either a single cylindrical lens with an axis parallel to [Ox),

Either a network along [Ox) of cylindrical and / or spherical lenses with an axis parallel to [Oy),

• or all other combinations of elements which make it possible to modify the direction, the divergence, etc. of a wave beam.

Figure 2 shows the massive material that makes up the converter

2 of Figure 1, seen from the outside. The traces E2a, E2b, E2c of the elementary waveguides 2a, 2b, 2c are drawn on the input face 21. This face 21 is the first end of the material. And, the traces S2a, S2b, S2c of the elementary waveguides 2a, 2b, 2c are drawn on the face of outlet 22. This face 22 is the second end of the material. The inputs E2a, E2b and E2c, and the outputs S2a, S2b and S2c are plotted for a better understanding of the converter 2.

The inlet 21 and / or outlet 22 faces are anti-reflective treated at one or more given lengths. This reduces the losses due to coupling. In particular, if the wavelength is the wavelength of use emitted by the initial component 1. In addition, the inlet 22 and outlet 22 faces of the system are not necessarily parallel. They can be perpendicular. However, the inlet face 21 and the outlet face 22 may be two parts of one and the same face of the material. This allows deflection of the direction of the output beam from the original direction [Oz).

In FIGS. 1 and 2, the three elementary waveguides 2a, 2b and 2C are parallel to each other. And, they are perpendicular to the output face 22. This is the configuration preferably used within a converter 2 whatever the number of elementary waveguides. However, it is not necessary for the operation of converter 2.

The network of inputs E2a, E2b, E2c ... of the elementary waveguides 2a, 2b, 2c can have various forms. In fact, the network of the inputs E2a, E2b, E2c of the converter 2 adapts to the network of the transmitters 1a, 1b, 1c of the initial component 1. The shape of the network can, therefore, be adapted to a possible defect in the known strips 1 under the name of "smile". On a strip 1 "smile", the transmitters 1a, 1b, 1c are arranged in a curve. The deflection of this curve can be, for example, from 1 to 20 μm depending on the transfer technique used.

The output beam is thus rearranged by the converter 2. The geometry obtained is more compact and it can, above all, be square, for example. Unlit areas between outputs S2a, S2b and S2c may be negligible. This is not the case for the inter-transmitter shadow zones 1a, 1b, 1c. The outputs S2a, S2b, S2c ... can, therefore, be adjacent or not and even merged.

The outputs S2a, S2b, S2c ... can be distributed according to a matrix which has X rows and Y columns (for XY elementary guides). Generally, the pattern followed by the outputs S2a, S2b, S2c ... is arbitrary. The pattern is an Anglo-Saxon term which designates the distribution grid. It is defined by its basic shape which is a rectangle or an oval or any polygon ...

The shape of the outputs S2a, S2b and S2c is arbitrary. It is independent of the form of the inputs E2a, E2b and E2c. The elementary waveguides 2a, 2b and 2c, the shape of which differs between the input and the output, have undergone a transformation which is, for example, adiabatic or almost adiabatic. Thus, the outputs S2a, S2b and S2c can be not rectangular but circular, for example.

The outputs S2a, S2b, S2c are such that the parameter (s) of the incident beam are converted. For example, they allow the geometric extent to have a given shape. This shape can be close to the symmetry of revolution so that the wave beam is used more effectively.

The elementary waveguides 2a, 2b and 2c are lines of indices in the material 2. These lines of indices are obtained by locally modifying the index of a solid material. The modified index is, for example, the refractive index. The variation in index Δn can be, for example, of the order of 10 ^"4 to 10 ^{" 3} . It depends on several factors. The first is the material used. The operating conditions are others. It is, for example of the order of Δn = 3.10-4 in Corning 0211 glass.

If the radius of curvature of the index lines is large enough, the guide losses are negligible. This ensures good power transmission.

The index modification is carried out on a volume of the order of 1 μm ³ with light pulses. These are, for example, femtosecond pulses. And, to modify the volume index, they can, for example, be ultra intense. This type of high-speed pulses makes it possible to quickly write the lines of indices. These pulses are delivered by a source. The source can, for example, be a femtosecond oscillator. In addition, an amplifier can be coupled to the oscillator. Consider the case where the oscillator delivers 15nJ pulses at a frequency of 25MHz. The index lines are then written at a speed of 20 mm / s.

In fact, any pattern is feasible in volume. The index lines are created in three dimensions in the material 2 using, for example, conventional techniques of programmable micro-positioning. There is only one only condition. This is because the material 2 is transparent or almost transparent at one or more wavelengths of use. The section of the lines can, for example, be 1x1 μm ² . The numerical aperture of the elementary waveguides 2a, 2b and 2c thus obtained is approximately 0.06. The lines of index 2a, 2b and 2c of the example of FIG. 1 were written using conventional techniques of programmable micro-positioning with femtosecond pulses at high frequency.

The converter 2 presented as an example in FIGS. 1 and 2. In general, the elementary waveguides 2a, 2b, 2c can be multimode, monomode or multimode in one direction and monomode according to another ... The number of guides of elementary waves 2a, 2b, 2c depends, more generally, on the number of elementary beam coming from the initial component 1 which can comprise a flat, matrix or other network of wave sources (strip or stack of strips of laser diodes, for example) but also a flat, matrix or other network of optical fibers or of any device having at least one wave output ...

Some examples of possible direct uses for this type of beam are, for example, the longitudinal optical pumping of solid lasers, marking, welding, cutting of various materials, etc. It can also be used, for example, for injection into an optical fiber.

Claims

1. Converter for one or more parameters of a wave beam comprising N sub-beams (N integer> 1), characterized in that it comprises at least one solid material comprising at least: • a first end comprising at minus N entries, each of

N sub-beams being received by one of the N inputs, and

2. Converter according to the preceding claim, characterized in that the conversion parameters include at least one of the following parameters:

• the beam size,

• the divergence of the beam in a given direction.

3. Converter according to the preceding claim, characterized in that the predetermined value taken by the geometric extent (product of the dimension by the divergence in a direction) of the beam at the second end is a geometric shape close to or verifying a symmetry of revolution.

4. Converter according to one of the preceding claims, characterized in that the solid material includes local index variations such that they form index lines in the three-dimensional space formed by the material.

5. Converter according to the preceding claim, characterized in that these index lines form elementary waveguides between, at least, an input and an output.

6. Converter according to one of claims 4 or 5, characterized in that the index lines are refractive index lines.

7. Converter according to one of the preceding claims, characterized in that the inputs / outputs of the solid material have one or more of the following characteristics:

• the inputs are distributed as they are arranged opposite the N incident sub-beams, •. the outputs are distributed in a matrix X rows and Y columns

(N≈X.Y, whole X and Y> 1),

• the exits are adjacent or not,

• the inputs and outputs are distributed, respectively, on a first and a second end which are either opposite or perpendicular faces, or the same face of the solid material.

8. Converter according to one of the preceding claims, characterized in that the first end and / or the second end of the material are treated anti-reflective at the wavelength of the beam.

9. Converter according to one of the preceding claims, characterized in that it is constituted by the solid material having N inputs corresponding to N elementary waveguides formed by N index lines in the solid material and having:

• either a single output constituted by the fusion of the N index lines on the second end,

• or N outputs which correspond to the N elementary waveguides.

10. Method for converting one or more parameters of a wave beam comprising N sub-beams (N integer> 1), characterized in that it comprises at least the guiding of each of the N sub-beams by N index lines in three-dimensional space made of a solid material, the index lines forming elementary waveguides.

11. Conversion method according to the preceding claim, characterized in that the beam parameter or parameters take one or more predetermined values which depend on the distribution and / or the shape of the output or outputs of the N index lines.

12. Method of manufacturing a converter of one or more parameters of a wave beam comprising N sub-beams (N integer> 1), characterized in that it comprises the local modification of the index of a solid material so as to form N lines of indices constituting elementary waveguides between a first and the second end of the material such that the parameter or parameters of the beam delivered by the material at its second end have one or more predetermined values .

13. The manufacturing method according to the preceding claim, characterized in that the distribution and / or the shape of the outputs of the index lines on the second end depend on the predetermined value or values.

14. Manufacturing method according to one of claims 12 or 13, characterized in that the modification of the index is obtained by ultra intense pulses and / or femtoseconds and / or at high rate, and / or by methods of programmable micro-positioning.

15. Manufacturing method according to one of claims 12 to 14, characterized in that the inputs / outputs of the material index lines have one or more of the following characteristics:

• the inputs are distributed such that they can be arranged opposite the N incident sub-beams. • the outlet (s) of the index lines on the second end are distributed such that the geometric extent of the or all or part of the outlets is of predetermined shape.

16. Manufacturing method according to one of claims 12 to 15 characterized in that the first end and / or the second end of the material are anti-reflective treated at the wavelength of the guided wave beams.

17. A system for manufacturing a converter according to one of claims 1 to 9 and / or implementing the method of one of claims 12 to 16, characterized in that it comprises at least one femtosecond source delivering pulses which locally modify the material index.

18. System delivering a wave beam having one or more parameters of predetermined values comprising at least:

• N devices delivering N sub-beams forming a beam whose parameter or parameters have any value (s), • a converter according to one of claims 1 to 9 comprising N inputs and one or more outputs,

19. System according to the preceding claim, characterized in that it further comprises at least one intermediate coupling member between the N devices and the converter making it possible to adapt the size and / or the divergence of the N sub-beams delivered. by the devices at the inputs of the converter.

20. System according to the preceding claim, characterized in that the coupling member comprises one of the following devices:

• a single cylindrical or spherical lens, • at least one array of cylindrical and / or spherical lenses, • at least a combination of cylindrical and / or spherical lens arrays.

21. System according to one of claims 17 to 19, characterized in that the N devices form at least one strip or a stack of strips of laser diodes.

22. Use of a system according to one of claims 17 to 20 either directly or for the injection of beams into an optical fiber.