Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
  • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
  • H01S5/4031—Edge-emitting structures
  • H01S5/4062—Edge-emitting structures with an external cavity or using internal filters, e.g. Talbot filters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
  • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
  • H01S5/1206—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers having a non constant or multiplicity of periods
  • H01S5/1215—Multiplicity of periods
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
  • H01S5/14—External cavity lasers
  • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
  • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
  • H01S5/4087—Array arrangements, e.g. constituted by discrete laser diodes or laser bar emitting more than one wavelength

Definitions

• the invention relates to a device for wavelength multiplexing of a plurality of laser sources and in particular of beams emitted by an array of laser diodes.
• the power delivered by a laser diode being limited (typically less than 10 W), it is conventional to use monolithic assemblies of diodes (called arrays of laser diodes) making it possible to deliver powers up to typically 100 W
• arrays have the following characteristics: disadvantage of delivering an optical beam of very poor quality, the elementary diodes emitting side by side Generally 1 cm wide in the direction parallel to the plane of the junction (D // ), the emissive surface of the bars is about 1 ⁇ m high in the perpendicular direction (Dj .
• a bar is thus a highly asymmetrical source, being approximately 10 000 times wider than high Similarly, the divergence of the radiation is non-symmetrical greater than 25 ° (30 ° to 50 °) according to D ⁇ , it is approximately 10 ° according to D // The combination of these two characteristics leads to a geometric extent approximately 2000 times greater according to D // than selo n D ⁇ This high asymmetry is completely detrimental to the effective use of these components for many applications. In fact, in addition to the difficulty of handling, it is generally advantageous to have a beam of geometric extent close to the symmetry of revolution, for example, for injection into an optical fiber or for the longitudinal optical pumping of solid lasers
• the invention therefore relates to a wavelength multiplexer of laser sources, characterized in that it comprises
• a plurality of laser sources emitting beams at different wavelengths A first diffraction grating forming a cavity mirror for the laser diodes, this grating comprising a set of juxtaposed sub-grids of different pitches, each sub-grating receiving one or more of said laser beams, retroreflecting part of the beam or beams and transmitting the other part of the beam in an exit direction, this direction being the same for all the sub-beams;
• a focusing optic located on the output direction, focusing at a focal point the beams emitted by the laser sources
• a second diffraction grating located at said focal point and receiving said emitted beams, the angles of incidence of these beams on the diffraction grating being such that the latter superimposes the beams after diffraction.
• FIGS. 1a to 1c an example of a detailed embodiment of the multiplexer of the invention
• Figures 2a and 2b an alternative embodiment of the invention
• Figures 1 a to 1 c show an embodiment of the multiplexer according to the invention.
• Figures 1a and 1b show a device for the emission of n laser beams of different wavelengths.
• Figure 1a shows n laser diodes 1.1 to 1.n.
• these n diodes are in fact a strip of laser diodes 1.
• the beams emitted by these diodes are collimated by a first cylindrical lens 21, then focused by a second cylindrical lens 22 on a diffraction grating 3 located substantially at the focusing plane. of the lens 22.
• the axes of the cylindrical lenses 21, 22 are orthogonal to the long length of the diode array and form an afocal system.
• the diffraction grating 3 is in reality a juxtaposition of diffraction sub-grids 3.1 to 3.n having different pitches so as to be effective at different wavelengths.
• the wavelength of each of the n laser diodes 1.1 to 1.n of the strip 1 is imposed by making an external cavity closed by a network 3 placed in the Littrow position, the plane of incidence of which is perpendicular to the plane. of the junction of the laser diodes.
• This orientation of the network is chosen to ensure good selection in wavelength, which would not necessarily be the case for an orientation parallel to the plane of the junction due to the non-monomode spatial emission in this direction of the power diodes. .
• Order 0 of the network corresponds to the output beams 4.1 to 4.n of the cavity and order -1 to the beam reinjected into the cavity.
• the angle of incidence of the beams on the grating and the pitch of the grating fix the value of the emission wavelength of each laser diode. It is necessary for the beam to be collimated in the plane of incidence of the grating, for example by putting a third cylindrical lens 23 between the strip 1 and the grating 3. This third cylindrical lens 23 is orthogonal to the lenses 21, 22. This is visible in Figure 1b which shows a bottom view of the system of Figure 1a.
• each laser diode should light only one sub-array. This is achieved by afocal mounting of the two cylindrical lenses 21 -22 which image the laser diodes on the array 3.
• the n beams coming from the diodes each have a different wavelength and are parallel between them. They are spaced by a distance dx which corresponds to the distance between diodes in the strip multiplied by the magnification of the lenses 21-22.
• a preferential example consists in having the beams 4.1 to 4.n parallel to each other and spatially distributed as a function of their wavelengths.
• the n beams 4.1 to 4.n are then superimposed locally by a lens 5 on a diffraction grating 6.
• the focal point of the lens 5 is placed on network 3.
• Network 6 is placed in the Fourrier plane (image focus).
• the lens 5 can be cylindrical or spherical.
• the network 6 is a network jaded to have a preferential direction at the output 7. For the beams 4n to be spatially superimposed after the network 6, their wavelength ⁇ n must be chosen judiciously.
• the beams of the N laser diodes making up a strip are therefore spatially superimposed.
• the wavelength spacing d ⁇ n between two elementary beams is independent of n (this is verified as long as the incidences on the lens 5 remain low).
• the invention proposes, for example, to use a photosensitive polymer to produce the gratings 3 in the form of a thick hologram, either by using a length d 'fixed writing wave and by varying the incidences of the beams according to the location on the network 3; either by varying the write wavelength for each sub-network.
• the second network 6 has a fixed number of lines, which corresponds to a dispersing power D (which also depends on the working angle chosen).
• D dispersing power
• the beams are separated at the level of the network 3. This is carried out over a distance of the order of a millimeter at the outlet of the bar (spacing of 0.2 mm, divergence of 10 °). We can thus remove the lenses 21 and 22 as we can see in Figures 2a and 2b.
• the beam can be used directly or focused in an optical fiber.
• Diffraction grids 3 and 6 can operate in transmission or in reflection.

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• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Optics & Photonics (AREA)
• Semiconductor Lasers (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

Country Status (4)

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• 1999
  • 1999-12-23 FR FR9916401A patent/FR2803116B1/fr not_active Expired - Fee Related
• 2000
  • 2000-12-21 AU AU28570/01A patent/AU2857001A/en not_active Abandoned
  • 2000-12-21 WO PCT/FR2000/003644 patent/WO2001048882A1/fr not_active Application Discontinuation
  • 2000-12-21 EP EP00993665A patent/EP1155484A1/de not_active Withdrawn

Non-Patent Citations (1)

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