WO1990013159A1

WO1990013159A1 - Partially transmitting laser apertures

Info

Publication number: WO1990013159A1
Application number: PCT/AU1990/000156
Authority: WO
Inventors: John Leonard Hughes
Original assignee: Phased Array Lasers Pty Ltd
Priority date: 1989-04-19
Filing date: 1990-04-19
Publication date: 1990-11-01

Abstract

This invention relates to a fiber bundle (1) based laser beam transmitting aperture (2) which is only partially utilised to emit said laser beam (4) over any portion of said aperture (2) at a given time, said invention consisting of a coherently packed bundle of single mode optical fibers (1) whose optically polished ends (2) one positioned relative to each other to form a flat (2), concave (10) or convex (15) output aperture, said output faces being scaleable by adding more fibers.

Description

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PARTIALLY TRANSMITTING LASER APERTURES

FIELD OF THE INVENTION

This invention relates to a fiber bundle based laser beam transmitting aperture which is only partially utilized to emit said laser beam over any portion of said aperture at a given time, said invention consisting of a coherently packed bundle of single mode optical fibers whose optically polished ends are positioned relative to each other to form a flat, concave or convex output aperture surface, said bundle being composed of either laser fibers or undoped optical fibers, being scaleable simply by adding more fiber ends to increase the size of said output aperture as required.

The invention has application for moving a laser beam output simply by selecting different areas of said aperture over which said beam is emitted. The invention has application for laser beam scanning in the industrial, medical, mass entertainment, commercial and defence fields.

5 SUMMARY OF THE PRIOR ART

In prior art laser beam transmitting aperture systems, the laser output beam was emitted over the whole, effective output areas of laser beam transmitting apertures rather than parts of said apertures.

Prior art laser beam scanners involved either reflection off a moving mirror 0 or lens system or via the inertia-less beam steering of a phase-locked laser beam achieved via the appropriate phase delays to tilt the wave front of the emitted laser beam. Prior art moving mirror laser beam scanning systems suffered because of the inertia of the moving mirror which limits both the scanning rate and its response time. Such mechanically based prior art scanning systems also 5 suffered from jitter due to the mechanical imperfections. -2-

Prior art inertia-less beam steering suffers from the fact that the phase of each of the laser beam transmitters involved has to be adjusted in order to achieve the appropriate tilt of the wave front of said transmitted laser beam.

The present beam scanner overcomes the defects of the prior art simply by - s activating different volumes of a laser medium such as a bundle of single mode optical fibers, the excitation process for such fiber bundles being well known in the art (see for example Hughes, US Patent No, 4,682,335 issued July 1987). This fiber bundle activation process can be used to move a laser output beam across the output aperture of the invention simply by switching on, or off, selected ιo laser transmissions in laser active or passive optical fibers forming said bundle.

_* -#^• BACKGROUND OF THE INVENTION

* »j?v I have pioneered the use of optical fiber bundles to both generate and transmit, phase-locked outputs. In 1963, 1 considered phase-locked passive, single mode optical fiber bundles as the basis for a phased-array, variable is bearrtwidth.laser radar at the Royal Radar Establishment, Malvern, UK.

In 1980, such variable bβamwidth laser radars were patented by the present inventor and classified by the US Patent Office in 1984. This invention encompasses the simplest way known to the inventor of scanning a laser beam so as to eliminate inertia effects, minimise switching speeds and provide "infinite" 2o fast beam scanning rates, bearing in mind that no energy transfer is involved in V the beam movement itself because the old beam is simply replaced with a new one by activating a different position of a laser gain medium or indeed a different gain medium, where several such gain media are fiber bundle coupled into a common aperture.

25 SUMMARY OF THE INVENTION

It is an object of the invention to move a laser beam transmitted by a given output aperture, across said aperture simply by switching different positions of a laser beam generating medium above its lasing threshold.

Another object of the invention is to provide a flat transmitting aperture over which an output laser beam can be moved.

Another object of the invention is to provide a concave surfaced aperture over which the output laser beam moves.

Yet another object of the invention is to provide a convex surfaced output aperture over which the output laser beam moves.

It is an object of the invention to combine the properties of the flat output aperture with a lens to provide linear laser beam scanning.

It is an object of the invention to provide scanned laser beams which are blue, green and red respectively.

Another object of the invention is to provide two dimensional beam scanning.

Yet another object of the invention is to provide three dimensional beam scanning.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A better understanding of the invention may be obtained from the following considerations taken in conjunction with the accompanying drawings which are not meant to limit the scope of the invention in any way.

Figure 1 shows a schematic layout of the invention in the form of a fiber laser bundle laser oscillator end pumped with a diode stack which can be sequentially excited along its length from one end to the other. This sequential excitation process allows the fiber laser bundle oscillator to be excited in sections, generating a phase-locked output beam whose cross-section is much less than the cross-section of the output aperture of the invention. In this way, the smaller cross-section laser beam can be emitted over any part of the output aperture and can be effectively moved across said aperture simply by the appropriate switching of the diode laser pump stack.

Figure 2 shows a schematic layout of the invention with its output aperture having a concave surface. This configuration allows for the scanning of the converging output beam in three dimensions or in two dimensions depending on whether the aperture surface is curved or flat.

Figure 3 shows a schematic layout of the invention with its output aperture having a convex surface. This configuration also allows three dimensional scanning of a diverging output beam in three dimensions. However, if the convex surface is flat, then the output beam is scanable in two dimensions.

Figure 4 shows a schematic layout of the invention with a lens used to focus the scanned output beam onto a surface.

DETAILED DESCRIPTION OF THE INVENTION

In Figure 1 , numeral 1 indicates a bundle of laser fibers whilst numeral 2 indicates their optically coated ends which have been mirrored so as to partially transmit at the laser wavelength. Numeral 3 indicates the opposite, optically polished face of the said fiber laser bundle which has been mirrored for maximum reflection at the laser wavelength and maximum transmission at the laser diode pump wavelength. Numeral 4 indicates the output laser beam whose cross-section is much less than the cross-section of the output aperture 2. Numeral 5 indicates the laser diode pump beam whose cross-section is also less than that of the fiber laser bundle laser oscillator.

Numeral 6 indicates an array of laser diode pumps which can be switched on in groups so as to form beam 5. Numeral 7 indicates an electrical switching unit to activate diode array 6 under the control of the computer system indicated by numeral 8. Numeral 9 indicates the power source to activate diode stack 6.

In Figure 2, numeral 10 indicates a concave surface of the output aperture of the invention which may be flat or curved. Numeral 11 indicates the part of a passive fiber bundle through which the laser beam is being propogated to emerge as the converging beam output indicated by numeral 12. Numeral 13 indicates the position where the converging laser beam 12 attains maximum intensity whilst numeral 14 indicates the manner in which beam 12 can be scanned across the output aperture 10.

In Figure 3, numeral 15 indicates the convex surface of the output aperture of the invention, which may be flat or curved, whilst numeral 16 indicates the input beam propogating through the optical fibers forming said output aperture 15. Numeral 17 indicates the diverging output beam which can be scanned over surface 15 as indicated by numeral 18.

In Figure 4, numeral 19 indicates the cross-section of a fiber bundle which delivers the output beam of a laser which emerges from said bundle as beam 4. Numeral 20 indicates a lens which focuses beam 4 as indicated by numeral 21 onto surface 22, allowing focus beam 21 to be moved over surface 22 via the movement of beam 4 as indicated by numeral 23.

o The invention can incorporate a laser beam generating medium or couple the output of such a medium to its place of application. The invention has applications in the industrial, medical and defence fields and is particularly effective in the office market field where laser beam scanners are in use together with laser beam imaging systems requiring three dimensional scanning.

Claims

I claim,

1. A fiber bundle based laser beam transmitting system whose output aperture is greater in area than the laser beam it transmits, said laser beam being capable of being emitted via any portion of said aperture, said system consisting of a

5 coherently packed bundle of single mode optical fibers whose optically polished ends are positioned relative to each other to form a flat, concave or convex output aperture surface, said bundle being comprised of laser fibers in the case where the said aperture is part of the laser itself, and composed of optical fibers in the case where the invention is used to convey said laser beam from laser beam ιo generator to their place of application.

2. A system as claimed in Claim 1 where the optically polished surface of the said output aperture is flat, allowing the emitted laser beam to be scanned in two dimensions.

3. A system as claimed in Claim 1 where the optically polished surface of the wjfi feid output aperture is concave allowing the converging laser output beam to be scanned in both two and three dimensions.

4. A system as claimed in Claim 1 where the optically polished surface of the said output aperture is concave allowing the diverging emitted laser beam to be scanned in both two and three dimensions.

2o 5. A system as claimed in Claim 1 with the scanned laser output beam being converged onto a surface using a lens.

6. A system as claimed in Claim 1 which emits three laser beams, each one representing a primary colour, namely blue, green or red.

7. A system as claimed in Claim 1 for the beam scanning of a laser beam.

25 8. A system as claimed in Claim 1 for the two dimensional scanning of a laser beam.

9. A system as claimed in Claim 1 for the three dimensional scanning of a laser beam.