FR2860653A1 - Optical component e.g. resonant micro-cavity, producing method, involves assembling micro-lens matrix and microphone plate having laser active material layer between two reflector units, and cutting individual assemblies - Google Patents

Abstract

The method involves assembling a micro-lens matrix (42) and a microphone plate (50) having a laser active material layer between two reflector units. Individual assemblies (45) having lenses and IR or ultraviolet radiation sources are cut. The microphone plate and the reflector units are assembled at the matrix of micro-lenses by splicing. The plate is placed directly on the matrix of micro-lenses by deposit and/or by growth.

Description

2860653 1

  RADIATION EMITTER ASSOCIATED WITH A MICROLENGTH

DESCRIPTION

  TECHNICAL FIELD AND STATE OF THE PRIOR ART The invention relates to the field of resonant microcavities, in particular based on cadmium, or mercury, or tellurium and their manufacturing processes.

  Such cavities are optically excited in order to make emitters in the infrared spectrum. These emitters can in particular be used for gas detection applications by spectrometry and differential absorption.

  A resonant microcavity is usually formed of an absorbent layer based on cadmium, or mercury, or tellurium, and is between two reflective layers.

  The absorbent layer is for example made by an epitaxial technique.

  The reflective layers are made by a thin layer stacking technique of dielectric materials.

  The length of the resonant microcavity thus formed to obtain an emission peak located in the infrared spectrum is a few tens of micrometers.

  In order to guarantee its mechanical strength, the resonant microcavity is transferred by bonding to a thicker substrate, transparent to the wavelengths involved.

  The usual manufacturing steps are as follows (FIGS. 1A-1F).

  The first step is to generate the absorbent layer 2 based on cadmium, or mercury, or tellurium, by epitaxy on a sacrificial substrate 4 adapted in terms of mesh agreement (FIG. 1A).

  Then (FIG. 1E), the first mirror 6 of the cavity is deposited by PECVD: a stack of materials of the ZnS or YF3 type is in fact constituted.

  The assembly is reported (mirror side) on a transparent support 8 (Figure 1C).

  The sacrificial substrate 4 is removed by mechano-chemical thinning (FIG. 1D).

  Finally (FIG. 1E), a second mirror 10 of the cavity is formed by deposition, for example of the PECVD type: a stack of materials of the ZnS or YF3 type is thus formed.

  The plate thus produced is then cut (FIG. 1F) to obtain individual emitters.

  In operation, such a resonant microcavity produces radiation, coherent or not, by optical pumping by a source that can be of the laser diode type.

  Indeed, a laser diode has the advantage of emitting all its power on a narrow spectral peak that can be adjusted on a line of absorption of the microcavity so as to optimize the efficiency between the pump power and the power emitted by the resonant microcavity.

  The resonant microcavity is placed very close to the pump optical source in order to minimize the size or radius of the pumping zone and to maximize the power density in the pumping zone, and hence the efficiency.

  Indeed, the beam from the pump source is generally divergent.

  In order to increase the pumping efficiency, a solution, known to date, and applied for example in the field of microlasers with a solid active medium, is to insert a lens-type component 20 between the pump optical source 22 and the resonant microcavity 24. , in order to focus the generally divergent beam 23 coming from the pump source into the resonant microcavity (FIG. 2). The reference 25 designates the beam emitted by the latter.

  This solution requires to align the 3 components transversely on the optical axis and longitudinally, so as to obtain the focusing of the pump beam in the resonant microcavity.

  Such an alignment becomes difficult to achieve because of the reduction in the size of the components, for example below the millimeter.

  However, this reduction in size is desirable in order to improve the compactness of the optical system, which is essential in the case of an on-board system, and especially in order to produce more transmitters from the same fabricated surface (see the method described in connection with FIGS. Figures 1A-1F).

  In addition, reducing the size of the transmitters also proportionally reduces the exploitable area on the transmitter.

  Indeed, micro-cutting techniques with a circular saw, from micro-electronics and applied to this type of component, leave a flaking component edge that is no longer exploitable. Given the fragility of the materials used, this chipping may be of the order of a few tens of microns.

  Thus with a given flaking width, the exploitable proportion of the surface of the emitter is even smaller than the component is small.

  Given these alignment drawbacks and constraints related to the miniaturization of the components, one solution is to produce a monolithic element comprising the focusing lens and the transmitter.

  Thus, the transverse and longitudinal adjustments are pre-set.

  The realization of such monolithic elements, including the lens and the transmitter, nevertheless poses problems.

  In order to limit the difficulties of optical alignments of the lens with the transmitter, one solution is to directly assemble the lens 20 on the transmitter 24, as illustrated in FIG.

  Longitudinally, the thickness e of the lens can thus be adjusted beforehand so as to pre-adjust the focusing distance.

  Transversally (in a plane perpendicular to the direction of propagation of the beams 23, 25 of Figure 3), the transmitter 24 is centered on the lens during the report.

  Applied to miniature components, this transverse adjustment can be achieved with the aid of adapted micromanipulators, which generally provide a vision system for precisely aligning the components to be assembled with one another. This technique, however, has two major drawbacks: - Each transmitter is manipulated with the risk of degrading it, because it is a very fragile component, - The assemblies are carried out unit by issuer.

  There are positioning machines, but their cost is very high.

  As a numerical example, a typical pump laser diode emitting surface lx3pm2 and a focusing optical system adapted magnification G = 100. The image of the emitting surface at the level of the resonant micro-cavity is thus dimensions 0.1 x0.3mm2.

  Moreover, a resonant micro-cavity of surface 4x4mm2. If we consider a scaling width 50pm on the edge of the transmitter, the exploitable area is reduced to 3.9x3.9mm2.

  Since it is sought to have a useful area, on the pumping zone, of at least 3 times the size of the image of the emitting surface at the level of the resonant micro-cavity (3 × 0.1 × 0.3 = 0.3 x 0.9 mm2), then there is a centering tolerance of the emitter on the image of the emitting surface of about 3.6mm and 3.Omm (for a usable surface of 3.9 mm x 3 , 9 mm and a beam of 0.3 mm x 0.9 mm, the tolerance is 3.6 mm x 3 mm).

  On the other hand, on a micro-resonant cavity of surface lxlmm2, always considering a scaling of width 50pm on the edge of the emitter, the exploitable surface is reduced to 0.8 x 0.8 mm2. With the same beam size as above, the centering tolerance of the transmitter on the image of the emitting surface is then about 0.5 mm and - 0.1 mm (for a usable area of 0.8 mm × 0, 8 mm and a beam of 0.3 mm x 0.9 mm, the tolerance is 0.5 mm x (-0.1) mm, which is not tolerable).

  There is thus the need to eliminate centering errors in the alignment of miniature components, especially those whose emitting surface, measured in a plane perpendicular to a direction of propagation of pump beam and / or emitted beam, is less than 1 or 2 mm2.

  There is therefore the problem of finding a new method for producing optical components, in particular when these components are microcomponents, of size or emitting surface, as defined above, of less than 1 or 2 mm 2.

  There is also the problem of finding a new method for assembling optical components, in particular microlenses and resonant micro-cavities, allowing component alignment to minimize centering and / or positioning errors, especially when the components are size or emitting surface, as defined above, less than 1 or 2 mm2.

  There is also the problem of focusing a pump beam in a resonant microcavity in order to increase the conversion efficiency in the microcavity, while maintaining the compactness of the resonant microcavity, and by maintaining a structure that is compatible with collective fabrication, in particular when the microcavity is of size or emitting surface, as defined above, less than 1 or 2 mm 2.

  DISCLOSURE OF THE INVENTION The invention therefore relates to a method for producing optical components each comprising a radiation emitter and a microlens, comprising: the production of an assembly of a plate or matrix of microlenses and a plate or matrix of radiation emitters, and then the cutting of individual assemblies each comprising a lens and a radiation emitter.

  The invention also relates to a method for producing optical components each comprising a radiation emitter and a microlens, comprising: - the production of a plate or matrix of 30 microlenses, - the production of a plate or matrix of emitters of radiation, assembling the two plates or dies, and cutting individual assemblies each having a lens and a radiation emitter.

  The dies or plates of microlenses and emitters can be made in any order.

  Therefore, according to the invention, the plate comprising the emitters can be assembled with a plate comprising a matrix of microlenses.

  This assembly makes it possible to obtain the longitudinal adjustment of the lens with the transmitter, as well as a self-centering of the emitters on the microlenses.

  Cutting of the assembly into unit emitters can be performed after assembly of the plates, for example by a cutting blade.

  For this purpose, positioning marks may be made on the microlens array.

  The microlenses can be refractive microlens or diffractive or gradient index type.

  The assembly of the two dies can be achieved by gluing.

  According to one variant, the emitter plate is made directly on the microlens matrix, by depositing and / or by growth.

  It is possible to carry out beforehand said plate of radiation-emitting material and reflecting means.

  For example, the reflecting means is made by depositing reflective layers on the radiation emitting material.

  The radiation emitters are preferably emitters in the infra-red or visible or ultraviolet domain.

  Each emitter is for example based on cadmium or mercury or tellurium or one of their alloys.

  The embodiment of the microlens array may comprise: a creep or annealing of a binary pattern on a plate of optical material, a transfer of the binary pattern, for example by ion beam, into the optical material.

  Each assembly obtained may have, after cutting, an emitting surface less than 2 mm 2.

  The invention further offers the following particular advantages.

  The optical focusing system is directly integrated with the resonant microcavity, making its operation easier by integrating the focusing of the pumping beam.

  In addition, the optical axis of the focusing optical system is thus self-aligned with the resonant microcavity.

  The small resonant microcavity dimensions are retained, which always allows it to be placed closer to the optical pump source and to maintain the compactness of the system with superior performance.

  Finally, the manufacture of transmitters with integrated lenses can remain collective.

BRIEF DESCRIPTION OF THE DRAWINGS

  FIGS. 1A-1F represent a collective method of manufacturing emitters; Figures 2 and 3 show various assemblies of emitters and lenses; FIGS. 4A-4C show steps for producing preforms for the production of microlenses FIGS. 5A-5C show preform transfer steps for producing a microlens array.

  DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION A resonant microcavity comprises a layer 2 of active laser material, for example based on cadmium, or mercury, or tellurium (FIG. 1A). Each of these materials is absorbent for a pumping beam, generally located in the field of infrared or visible or ultraviolet.

  This microcavity is between two reflector means 6, 10, formed for example by sets of reflective layers (Figure 1E).

  The layer 2 is for example made by an epitaxial technique. The reflector means or the reflective layers may for example be made by thin layer stacking technique of dielectric materials.

  The length of the resonant microcavity makes it possible to obtain an emission peak located in the desired spectral range, infrared or visible or UV. It is, for example for the infra-red, a few tens of micrometers, for example between 10 and 100 micrometers.

  In order to guarantee its mechanical strength, the resonant microcavity is transferred by bonding to a thicker substrate that is transparent to the wavelengths involved (FIG. 1C).

  The usual manufacturing steps are those described above in connection with FIGS. 1A-1E.

  The manufacture of microlens matrices will now be described, in connection with FIGS. 4A-4C.

  This manufacture can take place independently of and before or after the manufacture of the microcavity exposed above.

  A photoresist preform 35 is first made on a wafer or plate 32 of the selected optical material, the latter being, for example, silica and / or sapphire and / or calcium fluoride CaF 2.

  A resin layer 36 is formed on a plate 32 of the selected optical material (Figure 4A).

  A bit pattern 34 is transferred by ultraviolet radiation to the resin 36. The bit patterns are then expanded (Fig. 4B). We can therefore realize these binary patterns by microlithography.

  A preform 35 is then obtained by creep (FIG. 4C), or by annealing, of said binary pattern.

  The preform 35 is then transferred by means of an ion beam 40 by RIE (reactive ion etching) onto the optical material 32 (FIG. 5A).

  A matrix 42 of microlenses is thus obtained (FIG. 5B).

  This matrix is then assembled with an emitter plate 50 (FIG. 5C). The latter is for example that obtained at the end of the step illustrated in Figure lE and already described above.

  The assembly can be achieved by gluing, for example by molecular adhesion.

  The assembly may be cut, for example by means of a cutting blade, to form individual assemblies 45 (FIG. 5C) each comprising a microlens and a transmitting microcomponent with its mirrors. References 48 and 52 of FIG. 5C indicate cut lines.

  This set consists of: - on one side, a matrix of microlenses, - on the other side, a single microcavity covering the entire surface.

  It is through cutting that the individual sets will be defined: this cut aligns with the microlenses and the resonant cavity of an individual set is then self-defined and self-aligned on its microlens.

  For the purpose of cutting, it is possible to make positioning marks on the lens matrix and then to position the blade on these marks.

  According to a variant, it is possible to directly form the microcavity on the microlens matrix by deposition. In this case, this microlens matrix is used as a transfer medium 8 in the steps of FIGS. 1A-1E. The cutting step then takes place, as indicated above.

  According to another embodiment of the invention, during the manufacture of the resonant microcavity, the deposition step on a rigid substrate is replaced by a transfer of the emitter plate on a substrate having a microlens optical system ( such as that of FIG. 5B) making it possible to compensate the divergence of the pump beam and to reduce its radial size inside the resonant microcavity.

  It is also possible to carry out the direct growth of the emitting materials on the rear face of the microlenses.

  It is therefore possible to use the rear surface of the lenses as surface: either for the deposition, or for the transfer, or for the growth of the micro-cavity.

  Whatever the embodiment of the invention envisaged, transversely, each individual microcavity may have an emitting surface, measured in a plane perpendicular to a direction of propagation of pump beam 23 and / or emitted beam 25 (FIG. 3). , or according to a plane defined by the microemitter plate 50, smaller than 1 or 2 mm2. The invention thus implements a collective fabrication of emitting microdevices and microlenses in order to produce transmitter components each having optical focusing means. a pumping beam, integrated and self-centering.

  The technique described in the invention can be generalized to the manufacture of emitters outside the IR spectrum, for example in the visible or UV spectral domain.

Claims (12)

  A method of producing optical components each comprising a radiation emitter and a microlens, comprising: assembling a matrix (42) of microlenses and a plate (50) comprising a layer (2) of material radiation emitter between two reflector means (6, 10), - then cutting individual assemblies (45) each having a lens and a radiation emitter.   2. Method according to claim 1, wherein the emitter material plate and reflector means is assembled to the microlens matrix by gluing.   3. The method of claim 1, wherein the emitter material plate is made directly on the microlens matrix by deposition and / or growth.   4. Method according to one of claims 1   or 2, wherein said plate (50) of radiation-emitting material and reflector means is previously produced.   5. The method of claim 4, wherein the reflector means (6, 10) is formed by depositing reflective layers on the radiation-emitting material (2).   6. Method according to one of claims 1   at 5, wherein the material of the radiation emitting material plate is of a transmitting material in the infrared, or visible, or ultraviolet spectral range.   7. Method according to one of claims 1   to 6, wherein the emitter material is based on cadmium or mercury or tellurium or one of their alloys.   8. Method according to one of claims 1   to 7, further comprising the prior embodiment of a matrix (42) of microlenses, by: - a creep or annealing of a binary pattern (34) on a plate of optical material (32), - a beam transfer of ions in the optical material.   9. Method according to one of claims 1   8, in which the cutting of individual assemblies 25 is performed using a cutting blade.   10. The method of claim 9, wherein positioning marks are previously formed on the microlens matrix. 15 20   11. Method according to one of claims 1 to 10, wherein the microlenses are microlens refractive or diffractive or index gradient type.   12. Method according to one of claims 1 to 11, each assembly obtained after cutting having an emitting surface less than 2 mm2.