Assembly procedure for two structures and apparatus produced by the procedure applications to microlasers

This invention relates to a procedure for assembling two structures (2, 4) comprising: PA1 formation on at least one of the structures of studs (12, 14, 16) made of a material that can flow and is wettable on both structures, PA1 positioning of the two structures such that said studs are on their interface, PA1 assembly of the two structures by heating the studs causing them to flow, and by bringing the two structures together as intimately as possible. According to a different procedure, joints made of a fluidizable, wettable material are incorporated in notches etched into one of the structures to be assembled. Application to microlasers.

FIELD OF THE INVENTION 
This invention relates to techniques for assembling two structures, and 
particularly structures requiring good mechanical resistance and parallel 
facing surfaces. 
The invention relates particularly to the field of optronics, for example 
solid microlasers pumped by diodes and associated micro-optical 
components. 
The invention also concerns the field of microlasers and microlaser 
cavities with solid active mediums. 
Microlasers have many applications in fields as varied as the automobile 
industry, the environment, scientific instruments and telemetry. 
A microlaser consists of a stack of multilayers. 
The active laser medium consists of a small piece (a few square mm) of a 
thin film of material (between 150 and 1,000 .mu.m thick) on which 
dielectric cavity mirrors are directly disposed. This active medium may be 
pumped by a III-V diode laser that is either directly hybridized on the 
microlaser or coupled to the microlaser by an optical fiber. The 
possibility of assembly-line production using microelectronics means 
ensures that such lasers can be mass produced. 
PRIOR ART 
In order to assemble two structures, the usual method is to use a film of 
glue between the two structures. However, this method does not give both 
good mechanical resistance of the assembly and good parallelism between 
the facing surfaces of the structures. 
Concerning microlasers, document EP-653 824 (U.S. Pat. No. 5, 495,494) 
describes a procedure for producing a solid microlaser that is passively 
switched by a saturable absorber. The saturable absorber is disposed 
directly on the solid active medium as a thin film using liquid phase 
epitaxy (LPE). 
However LPE cannot be used for all materials. In particular, when the 
active medium of the laser is not crystalline in structure, e.g. glass 
doped with erbium and/or ytterbium ions, LPE cannot be used. Similarly 
when an active medium microlaser cavity is combined with an active cavity 
switching device such as an electro-optical device such as that described 
in J.J. Zayhowski's article "Diode-pumped Microchip Lasers 
Electro-optically Q-switched at High Pulse Repetition Rates" (Optics 
Letters Vol. 17, No. 17, pages 1201-1203, 1992), LPE cannot be used. The 
same problem is encountered when a microlaser cavity is combined with a 
non-linear material such a frequency doubler or tripler or an optical 
parametric oscillator (OPO). 
In all these special cases the manufacturing procedures developed include a 
hybridization phase between two plates of material, for example a plate of 
the material constituting the active laser medium and a plate of material 
constituting the active switching means or non-linear material. The two 
plates are glued together by means of an optical glue with a known 
refractive index (e.g. 1.5). The surfaces to be glued are first polished 
to a roughness of the order of a few angstroms RMS and they have a 
localized divergence in surface evenness of better than .lambda./10 (100 
nm at .lambda.=1.06 .mu.m) . Once the other stages, such as forming the 
mirror layers, have been completed, the plates of material are cut to form 
individual microlaser cavities. Each cavity is then coupled to pumping 
means such as a III-V laser diode. The microlasers thereby produced only 
function correctly if natural optical loss and the thickness of the glue 
are slight and if the surface parallelism at the plate interfaces is also 
slight, i.e. less than approximately 10" arc. Moreover the glue must 
provide good adhesion to enable plate assemblies to be cut into chips; 
this operation is usually carried out using a diamond saw. 
Irrespective of the structure assembled, but particularly when the 
structure is a microlaser, assembly using glue has several drawbacks: 
firstly, the thickness of the glue bonding depends on the quantity of glue 
used, the initial quality of the application site and the pressure 
applied, 
in principle it is impossible to adjust the parallelism between two 
surfaces. One solution that has been tried is to reduce the thickness of 
the glue to the same order of magnitude as the irregularities in surface 
evenness, but no real control is possible. The result is therefore random, 
and thus a problem for mass production such as is used to produce 
microlaser cavities. 
Glue can undergo changes over time, particularly where microlasers are 
concerned, under the influence of radiation or heating, thereby modifying 
the mechanical resistance and the parallelism of the assembly and 
components. The glue may also be subject to local degassing in active 
zones, thereby introducing additional losses. 
The problem is thus to achieve assembly of two structures, in particular 
that of two microlaser cavity components, using a technique that allows 
both the parallelism and the mechanical resistance of the two structures 
or components to be controlled, thereby ensuring better aging qualities of 
the assembly. 
DISCLOSURE OF THE INVENTION 
The invention relates to a procedure for assembling two structures, 
comprising: 
formation on at least one of the structures of studs made of a material 
that can flow and is wettable on both structures, 
positioning of the two structures such that said studs are at their 
interface, 
assembly of the two structures by heating the studs causing them to flow, 
and by bringing the two structures together as intimately as possible. 
Two structures can thus be assembled in intimate contact by means of an 
adhesive substance. The use of studs made of a fluidizable, wettable 
material at the interface of the two structures ensures that when the two 
structures are brought together under pressure a joint is created that 
will ensure that the assembly holds together to allow the structures to be 
cut. In structures intended to be used to make microlaser cavities, 
cutting may be carried out with a diamond saw without weakening the 
mechanical resistance of the two structure assembly thereby effected. 
Intimate contact between the two surfaces is understood to include both 
simple contact between said surfaces and contact using molecular adhesion 
forces such as Van der Waals forces or the use of adhesive substances such 
as glue, resin, etc. 
This assembly method ensures excellent control of the parallelism of the 
contact surfaces. Normally, if it is applied to entire blanks of 
components or cutting, e.g. microlaser or micro-ootical components 
designed to be cut, the cutting operation can destroy the mechanical 
resistance of the elementary assemblies since the contact surface 
delimited by the cut lines is generally very small compared with the 
thickness of said elementary assemblies. Moreover, depending on the type 
of application, the materials placed in contact are not necessarily 
compatible: the surfaces may be physically and chemically different, or 
the materials used may have different thermomechanical coefficients. 
The procedure according to the invention thus gives both good parallelism 
characteristics and good mechanical resistance. 
The invention also relates to a procedure for assembling two structures 
comprising: 
the creation of at least one spacer stud on the first of the two 
structures, the edges of said spacer stud(s) defining one or more lateral 
notches, each lateral notch presenting a bottom, 
the creation on the bottom of at least one lateral notch of a joint made of 
a material that is fluidizable and wettable on the two structures, 
positioning of the two structures such that said joint is at the interface, 
assembly of said structures by heating the joints causing them to flow, and 
by bringing the two structures together as intimately as possible. 
A joint is understood to be any stud, strip or other component capable, 
after being caused to flow, of bonding the two structures together. 
The invention also relates to a procedure for assembling two structures 
comprising: 
the creation of at least one spacer stud in the first of the two 
structures, the edges of said spacer stud(s) defining one or more lateral 
notches, each lateral notch presenting a bottom, 
the creation on the second structure of at least one joint made of a 
material that is fluidizable and wettable on the two structures, 
positioning of the two structures so that each joint in the second 
structure is inserted into the notch of the first, 
assembly of the two structures by heating the joints causing them to flow, 
and by bringing the two structures together as intimately as possible. 
In the second two procedures the material forming the fluidizable joint(s) 
can flow into said notch or notches and the two structures are brought 
into intimate contact, for example by molecular adhesion remote from the 
notches. The mechanical resistance of the assembly is essentially ensured 
by the fluidizable material in the notches and parallelism is ensured by 
said intimate contact. 
If only spacer studs and their matching notches are created, said studs of 
fluidizable material are preferably located so that when the studs flow 
they create the thinnest possible film of uniform thickness. The 
characteristics of the studs are therefore determined to provide a uniform 
film of minimum thickness. 
The fluidizable, wettable material may be a photosensitive resin or a 
meltable material of the silica Sol-Gel (SOG) type, an In or Pb-Sn metal 
alloy or a negative resin. The latter gives better adhesion after 
reticulation of the polymer. 
Irrespective of the envisaged embodiment, two structures assembled 
according to the invention can subsequently be cut. The cutting phase does 
not affect the intimate contact due to the mechanical resistance provided 
by the fluidizable material components. 
The invention also relates to the assembly of a first and second structure 
each having at least one plane surface, said plane surfaces being in 
intimate contact, an adhesive joint made of a fluidizable, wettable 
material being disposed at the interface of the two plane surfaces. 
The invention also relates to the assembly of a first and second structure 
each having at least one plane surface, one of said plane surfaces also 
comprising at least one lateral notch whose bottom is set back from the 
plane surface, the two plane surfaces being in intimate contact, an 
adhesive joint made of a fluidizable, wettable material being disposed in 
at least one lateral notch and joining the two structures. 
These assemblies solve the same problems and have the same advantages as 
those described above in relation to the disclosure of the procedures: the 
parallelism of the contact surfaces of the two structures is ensured by 
the intimate contact and good mechanical resistance is ensured by the use 
of an adhesive joint made of a fluidizable, wettable material. 
The first and second structures may be a solid active medium for a 
microlaser cavity and a saturable absorber for a microlaser cavity 
respectively. 
Similarly, the first and second structures may be, respectively, a solid 
active medium for a microlaser cavity and a component made of an optically 
non-linear material, e.g. a frequency doubler or tripler, or an optical 
parametric oscillator. 
In another embodiment, the first and second structures may be a solid 
active medium for a microlaser cavity and a micro-optical component such 
as a microprism, micromirror, etc. They may, in fact, be any type of 
micro-optical components. 
The invention also relates to an assembly for a microlaser cavity 
comprising a solid active medium, an intermediate plane mirror disposed on 
one plane surface of the active laser medium, a component made of a 
material whose optical index can be modulated by outside perturbation, 
this component having a plane surface that is in intimate contact with the 
mirror, a joint made of a fluidizable, wettable material being disposed at 
the interface formed by the two plane surfaces. 
The invention also relates to an assembly for a microlaser cavity 
comprising a solid active medium, an intermediate plane mirror disposed on 
one plane surface of the active laser medium, a component made of a 
material whose optical index can be modulated by outside perturbation, 
this component having a plane surface, the mirror and possibly the active 
medium and/or the modulable-index component having at least one lateral 
notch with a bottom set back from the plane surface in question, the plane 
surface of the modulable-index component being in intimate contact with 
the intermediate plane mirror, an adhesive joint made of a fluidizable, 
wettable material being disposed in at least one lateral notch and bonding 
the modulable-index component and the solid active medium. 
An actively-switched microlaser cavity assembly is thus produced. 
The invention also relates to an apparatus for emitting infrared light 
comprising an assembly like that described above in which the first and 
second structures respectively are: 
a semiconductor component able to emit infrared radiation, 
a microlaser cavity incorporating switching means disposed so as to 
oprically pump the semiconductor component.

DETAILED DISCLOSURE OF EMBODIMENTS OF THE INVENTION 
The stages in a procedure according to a first embodiment of the invention 
are shown in FIGS. 1A to 1E. In these figures references 2 and 4 designate 
two structures to be assembled. These structures are, for example, a 
section 4 of an active laser material and a section 2 of a saturable 
absorber material. Examples of materials for these two components are 
given in document EP-653 824 (U.S. Pat. No. 5,495,494); these documents 
also give criteria for selecting said materials. 
In another example, structure 4 may be a section of a saturable absorber 
material while structure 2 is a section of an optically non-linear 
material capable of multiplying the basic frequency of a microlaser cavity 
by a whole number n (n.gtoreq.2). 
Each of these structures has a plane surface 6, 8. A layer of 
photo-sensitive resin is deposited on one of said surfaces (FIG. 1B). 
Masked photolithography techniques are used to etch layer 10 to produce 
studs 12, 14 and 16. The studs are preferably distributed uniformly so 
that they form a layer of uniform thickness during the subsequent stage of 
applying pressure. 
The two structures, or sections, 2, 4 are then brought face to face (FIG. 
1D). By heating resin studs 12, 14, 16 under pressure, the two structures 
are brought into intimate contact and adhere to one another under the 
adhesive effect of the polymerized resin (FIG. 1E). 
This stage leaves an interface layer of adhesive 18 of a thickness of the 
order of a few tens of microns, for example 0.1 .mu.m. This layer 18 
ensures the mechanical stability of the two structures to one another, in 
particular during the later cutting stage carried out, for example, using 
a diamond saw to produce laser cavity components. The parallelism of the 
two surfaces in contact with one another is ensured by the thinness of the 
resin. The thickness and distribution of the studs of fluidizable material 
12, 14, 16 is controlled to give improved control of parallelism. Doping 
techniques can also be used to control the refraction index of layer 18; 
silica Sol-Gel can, for example, be doped with oxynitrides SiO.sub.x 
N.sub.y. The index jumps at the interface of materials 2, 4 can thus be 
adapted and loss reduced to a minimum. 
The possibility of improved control over parallelism and the index of the 
intermediary layer is considerably more advantageous than those offered by 
standard "optical" glues in standard use. Moreover, as compared with a 
glue, the only diffusion possible from studs 12, 14, 16 between the two 
surfaces is very localized. A final advantage is that the thickness 
obtained is considerably reduced compared with that of a glue, i.e. only a 
few microns. 
FIGS. 2A to 2G show another embodiment of a procedure according to the 
invention. FIGS. 2A and 2B show two more structures 2, 4 to be assembled; 
these may be of the same type as those described above with reference to 
FIGS. 1A and 1B. 
The second procedure enables spacer studs to be disposed on one or other 
surface of the structures to be bonded, thereby defining lateral notches 
in which joints or studs made of fluidizable, wettable material are 
inserted to ensure mechanical cohesion of the assembly during subsequent 
cutting. 
The procedure then comprises two masking levels of masking. The first level 
is effected after etching of one of the substrates and defines the spacer 
studs and notches embedded in relation to the bonding interface. The 
second level is designed to define the strips, or studs of fluidizable, 
wettable material around each spacer stud (or around each microcomponent 
chip, e.g. microlaser) that will be embedded once the two structures are 
brought into intimate contact. 
A layer 10 of photo-sensitive resin is thus first deposited on the surface 
of one of the structures (FIG. 2B). This layer is etched using masked 
photolithography techniques to create spacer studs 20, 22, 24, 26 (FIG. 
2C). 
Substrate 4, on which the spacer studs have been created, is then etched to 
define spacer studs 31, 33, 35, 37 bordered by lateral notches 21, 23, 25, 
27, 29. These notches have a depth (i.e. the distance between the bottom 
of the notch and the upper surface of the neighboring spacer studs) 
measurable in .mu.m. Where the substrate is an active laser material this 
etching may be effecting using ionic machining or chemical etching. Where 
the substrate is made of solid silica (as in a support substrate for a 
microlens) reactive ionic etching (RIE) techniques may also be used. 
Once the resin studs 20 to 26 have been removed from the structure thereby 
obtained, a layer 30 of fluidizable, wettable material is spread (FIG. 
2E). This layer is etched (FIG. 2F) to create connecting studs 32, 34, 36 
inside notches 23, 25, 27 etched into substrate 4. Where the fluidizable, 
wettable material is a photo-sensitive resin, this etching may be effected 
by masked photolithography. Once substrates 2 and 4 have been aligned, 
they are assembled (FIG. 2G), for example under pressure at a temperature, 
T.apprxeq.200.degree. C. Intimate contact is established between surface 8 
of structure 2 and the upper surface of spacer studs 31, 33, 35, 37. The 
spacer studs act as mechanical stops. The strips or studs 32, 34, 36 of 
fluidizable, wettable material may flow within the notches etched around 
the spacer studs. The advantage of this procedure over the first procedure 
disclosed in the present invention is that the bonding parameters have no 
influence on control of the parallelism obtained; there is no intermediate 
layer between structures 2, 4 after assembly. 
Where the fluidizable, wettable material is a photo-sensitive resin, 
maintenance of the two substrates 2, 4 is ensured as soon as reticulation 
of the resin is complete. 
The height of the strips or studs 32, 34, 36 is preferably greater, for 
example by a few microns, than the depth of the notches 23, 25, 27. 
Once the two structures 2, 4 have been assembled, it is possible to cut 
individual components. A side view and top view of such a component is 
shown in FIGS. 3A and 3B respectively. Two elementary components 40, 42 
present a contact surface 46. Resin studs 44-1, 44-2, 44-3, etc. ensure 
the mechanical maintenance of the assembly during cutting and thereafter. 
In FIGS. 2F, 2G, 3A, 33 the fluidizable, wettable material is shown as 
discontinuous studs. It is also possible to use continuous strips of 
fluidizable, wettable material. However, creating discontinuous studs has 
the advantages of encouraging compression of the fluidizable material 
during bonding without overflowing from the notches and of encouraging any 
degassing caused by the intimate contact (e.g. solvent degassing during 
reticulation heating where the fluidizable material is a resin). 
Where the fluidizable material used is not a resin (e.g. silica Sol-Gel or 
other meltable material such as In, Pb-Sn) the procedure described above 
with reference to FIGS. 2A to 2D is followed. Then (FIG. 4A) a layer 50 of 
fluidizable, wettable material is created on substrate 4. A layer 52 of 
photo-sensitive resin is then spread on this layer (FIG. 4B). The outline 
of the strips or studs forming the joints is defined in this layer 52 
using a masked photolithography technique (FIG. 4C). Strips or studs 54, 
56, 58 of fluidizable material may then be etched in notches 23, 25, 27 
etched into substrate 4 (FIG. 4D). Substrates 2, 4 may then be aligned and 
assembled, for example by heating under pressure (FIG. 4E). Intimate 
contact is achieved at the interface of substrate 2 and spacer studs 31, 
33, 35, 37, mechanical maintenance during subsequent cutting being ensured 
by the studs or strips of fluidizable, wettable material. Cutting produces 
a component comprising two elementary structures 40, 42 in intimate 
contact, the assembly of these two structures being maintained by studs 
60-1, 60-2 made of fluidizable, wettable material (FIG. 5). 
The procedure for creating spacer studs and etching notches was described 
above in its "single-face" version. A "double-face" may also be produced. 
In FIGS. 6A and 6B, notches 21, 23, 25, 27, 29 are etched in substrate 4 
while the strips or studs forming the joints of fluidizable, wettable 
material 62, 64, 66, whether made of resin or other material, are formed 
by techniques equivalent or identical to those disclosed above on the 
other structure 2. Alignment and assembly are then carried out as 
described above. 
As shown in FIGS. 7A and 7B, it is also possible to etch notches in the two 
substrates 2, 4, studs or strips of fluidizable, wettable material being 
subsequently formed on one and/or the other of the two substrates. 
Alignment and assembly are carried out as described above: intimate 
contact takes place at the surface of the spacer studs defined in each 
structure 2, 4 (FIG. 7C). FIG. 8 shows an individual component obtained 
after cutting. 
Either of the procedures according to the invention described above can be 
applied to the hybrid assembly of microlaser components and micro-optical 
components. As an example, production of a microlaser actively switched by 
means of an external control voltage will be described. 
FIG. 9A is a schematic diagram of the structure of an actively-switched 
microlaser chip. Reference 75 designates an active laser medium, for 
example a YAG medium doped with neodymium (Nd). This medium is located 
between an entrance mirror 77 and an intermediate mirror 85 with which it 
constitutes a first resonating cavity. A second resonating cavity is 
constituted by the intermediate mirror 85, an exit mirror 83 and a 
material 81 having a refractive index capable of varying with external 
perturbations. This material may, for example, be an electro-optical 
material such as LiTaO.sub.3, to which a difference in potential is 
applied by means of two contact electrodes 95, 97. In operation, this type 
of microlaser structure is pumped by a pumping beam 100 obtained for 
example using a III-V laser diode that is either directly hybridized onto 
the microlaser or coupled to the microlaser via an optical fiber. A 
pumping beam 100 at 800 nm is suitable when material 75 is YAG doped with 
neodymium. 
In FIG. 9A entrance micromirror 77 of the microlaser cavity has a radius of 
curvature capable of reducing the size of the laser beam within material 
81. This radius of curvature is preferably greater than the total length 
of the microlaser (length L.sub.1 of active medium 75+length L.sub.2 of 
medium 81). The radius of curvature is thus typically greater than 
approximately 1.5 mm. This condition makes the cavity optically stable. 
The diameter .PHI. of the laser beam 102 inside the small medium 81 is 
typically a few tens of microns. Under these conditions, the thickness e 
of medium 81 required for active switching of the cavity is typically 
between 100 .mu.m and 500 .mu.m. This thickness compares very favorably 
with thicknesses used in the prior art: for example, the apparatus 
described in J. J. Zayhowski's article published in Optics Letters Vol. 17 
No. 17, pp. 1201-1203, 1992, requires an electro-optical component with a 
thickness of 1 mm. In order for the switching mechanism to operate 
correctly, a thickness of 1 mm requires a voltage of the order of 1,000 
volts between the two electrodes; a thickness of approximately 100 .mu.m 
enables the voltage required to be limited to a value of between 50 and 
100 volts. 
The structure shown in FIG. 9A also has a concave micromirror 83 at the 
microlaser exit. In this situation the radii of curvature R.sub.1 and 
R.sub.2 of micromirrors 77, 83 are chosen to give two optically stable 
cavities. Where two cavities are coupled as in FIG. 9A, R.sub.1 &gt;L.sub.1 
and R.sub.2 &gt;L.sub.2 to meet this requirement. In a plane-concave cavity 
(the exit mirror is plane), R.sub.2 =.infin.. 
The invention can be applied similarly to the creation of a plane-plane 
structure, the only difference being the greater thickness e of 
electro-optical material 81. 
The microlaser shown in FIG. 9A comprises two structures: the first 
composed of the active laser medium 75 and mirrors 77, 85, and the second 
composed of electro-optical material 81, exit mirror 83 and electrodes 95, 
97. These two structures are assembled using the first embodiment of the 
procedure according to the invention, and reference 82 designates a joint 
obtained after compressing studs of fluidizable, wettable material, the 
electro-optical material 81 and the mirror 85 being in intimate contact. 
FIG. 9B shows a variant of the above structure in which the mirror 85 and 
the electro-optical material 81 are in intimate contact without an 
intermediate joint; studs 84, 86 of fluidizable, wettable material are 
formed in the lateral notches, the active laser medium 75 and the mirror 
85 having been etched to create said notches. This structure is an 
actively-switched microlaser obtained using the second embodiment of the 
procedure according to the invention. 
The stages in the procedure used to produce the structure in FIG. 9A will 
be briefly summarized with reference to FIG. 10A to 11F and 11A to 11E. 
1)--In a first stage the radii of curvature R.sub.1 and R.sub.2 are 
calculated if stability of either cavity is required. 
2)--In a second stage (FIGS. 10A, 10B) a section 75 of laser material and a 
section 81 of material with a variable index such as an electro-optical 
material (e.g. LiTaO.sub.3) are subjected to cutting and polishing of both 
faces. 
3)--Photolithography and machining techniques are next used to create a 
micromirror on the entrance face of the laser material (typical diameter 
100 to 500 .mu.m and radius of curvature R.sub.1 of 1 to 2 mm). This stage 
is illustrated in FIGS. 11A to 11E. In a first sub-stage (FIG. 11A) a 
layer of photosensitive resin 73 is deposited on the entrance surface of 
laser material 75. The resin is then insolated through a mask 74 using UV 
radiation (FIG. 11B). In the next stage (FIG. 11C), the resin is 
chemically removed leaving only studs 76, 78 designed to form the 
micromirrors. In the next stage the resin is thermally fluidized (FIG. 
11D) to form resin mirrors 80, 82 and laser material 75 is machined using 
an ion beam 74 (FIG. 11E) to transfer the shape until the resin has been 
eliminated. 
Stages 4) to 9) will now be described with reference to FIG. 10C. 
4)--Entrance mirror 77 is deposited on the entrance face of laser material 
75 (e.g. for the dichroitic entrance mirror with a reflectivity greater 
than 99.5% at the wavelength of the laser beam and transmission greater 
than 80% at the pumping beam wavelength). 
5)--Photolithography and machining techniques are next used to produce 
micro-projections 79 as described above on the exit surface of 
electro-optical material 71 (typical diameter 100 to 500 .mu.m and radius 
of curvature R.sub.2 of 1 to 2 mm). No micro-projections are created on 
the exit surface of the electro-optical material if the exit mirror is to 
be plane. The diameter of the exit mirror (microlens) may be less than the 
diameter of the entrance micromirror. 
6)--The exit micromirror 83 is next deposited on the exit face of the 
electro-optical material 81 (exit mirror with typical reflectivity of 85 
to 99% at the laser beam wavelength and possibly with a reflectivity 
greater than the pumping wavelength to reflect the pumping beam that is 
not totally absorbed on its first passage). 
7)--In the seventh stage an intermediate mirror 85 is deposited at the 
interface between the laser material 75 and the electro-optical material 
81. 
8)--Section 81 and mirror 85 are then brought into intimate contact (FIG. 
10E) and mechanically bonded by joint 82 made of fluidizable, wettable 
material; in conformance with the invention this joint is composed of 
studs 86-1, 86-2, 86-3, etc. previously deposited on the surface of, for 
example, mirror 85. 
9)--The exit surface may be protected by a resin deposit 87 (FIG. 10C). 
10)--It is possible to make grooves 89 (FIG. 10F) in the electro-optical 
material using a microelectronics diamond saw in order subsequently to be 
able to form the electrodes with the required spacing e (of the order of 
100 .mu.m compared with a gap between electrodes of 1 .mu.m in the prior 
art). 
11)--Evaporation techniques are next used to deposit the electrical 
contacts (e.g. deposit of a Cr-Au layer 91 coating resin 87 and 
electro-optical material 81). 
12)--Individual chips 93 measuring more or less 1 mm.sup.2 are then cut 
out. Once the protective resin has been chemically removed and layer 91 
lifted off, the structure shown in FIG. 9A is obtained. 
13)--The chips are fitted onto a metallized printed circuit with suitable 
impedance; an electricity supply and shielded housing are also provided. 
14)--The units may also be placed in a housing and connected to pumped 
laser diodes and an electric switching connector. 
The invention may also be applied to any microlaser cavity structure. For 
example, FIG. 12 shows a microlaser cavity comprising an active laser 
medium 102, an entrance mirror 106 and an exit mirror 108. Two other 
components are located inside the cavity: 
a component 110 for switching the cavity in active or passive mode. 
a component 104 made of a non-linear material capable of multiplying the 
basic frequency of the active laser medium 102 by a factor n (n.gtoreq.2). 
As can be seen from FIG. 12, two joints 112, 114 of a fluidizable, wettable 
material are disposed respectively at the interfaces of the active laser 
medium 102 with the switching component 110, and the switching component 
110 with the non-linear medium 104. The simultaneous presence within the 
cavity of switching means and the non-linear component 104 results in a 
considerable increase in operating output of the non-linear medium 104. 
In a variant not shown in the figures, notches can be etched in the active 
laser medium and the switching component 110 in order to produce a 
structure incorporating lateral notches to accept joints made of the 
fluidizable, wettable material; the interface between components 102 and 
110, and 110 and 104 is then achieved by intimate contact without a 
transverse joint. This enables a switched microlaser cavity to be produced 
with multiple frequencies and operating at optimum output; the pumping 
beam and laser beam encounter no joint as they pass through the cavity. 
FIG. 12 shows a plane-plane cavity. A stable cavity can also be produced 
with concave micromirrors on cavity entrance and/or exit. The stable 
cavity will have a weaker switching threshold and improved output. 
Moreover, the presence of a concave micromirror enables the size of the 
laser beam in the various mediums within the cavity to be adjusted, giving 
increased power density in the saturable absorber component 110 and the 
multiplying crystal 104. In order to produce this type of structure 
additional preparation stages are required for the laser material plates, 
switching material and non-linear material, all of which are superimposed 
and bonded using one of the procedures described in the present 
application. 
FIG. 13 shows another structure that can be obtained using a procedure 
according to the invention. References 112 and 114 designate entrance and 
exit mirrors of a microlaser cavity that comprises an active laser medium 
116 and means 118 for switching said cavity in active or passive mode. 
Reference 120 is a pumping beam of the cavity. The cavity emits a laser 
beam that in turn pumps an optical parametric oscillator (OPO) structure 
essentially comprising two mirrors 114, 122 between which is disposed a 
non-linear material 124. This cavity in turn emits an OPO beam 126. 
The material constituting medium 124 may be selected from known non-linear 
materials such as, for example, KTiOPO.sub.4 (KTP) , MgO;LiNbO.sub.3, 
.beta.-BaB.sub.2 O.sub.4, LiB.sub.3 O.sub.5 and AgGaSe. The properties of 
KTP materials are described, for example, in an article by Terry et al. 
published in the Journal of the Optical Society of America, B, Vol. 11, 
pages 758-769 (1994). The properties of other non-linear materials that 
can be used to construct an OPO are described in R. W. Boyd "Non-Linear 
Optics" (Academic Press, USA, 1992, ISBN 0-12-121680-2), particularly p. 
85 et seq. 
Pumping with a microlaser makes it possible not only to reduced the 
threshold energy of the OPO cavity, but also to reduce the length of the 
crystal 124 required for operation of the OPO: for example, in the article 
by Terry et al. cited above a 20 mm long crystal is described, whereas the 
present invention makes it possible to use materials only a few mm thick, 
e.g. 5 mm. Generally speaking, the properties of the beam emitted by the 
laser make these properties (i.e. reduced energy threshold and reduced 
crystal length) applicable not only to the KTP crystal described in the 
article by Terry et al. but also to any other crystal or non-linear 
material used to produce an OPO cavity. 
The structure shown in FIG. 13 is extremely compact. Since the microlaser 
cavity itself is very compact (even including a switching component 118), 
it is possible to produce an OPO with a total length, including pumping 
means, not exceeding 6 mm with a cross-section of 1 mm.sup.2, i.e. a total 
volume of 6 mm.sup.3. 
The apparatus shown in FIG. 13 also comprises a joint 128 made of a 
fluidizable, wettable material that provides an intimate contact 
connection between the active laser medium 116 and the switching medium 
118. The contact between mirrors 114 and component 124 is also assured by 
intimate contact but the joints or studs 130, 132 of fluidizable, wettable 
material are located in the lateral notches etched into the switching 
component 118 and the mirror 114. It is also possible to produce a variant 
(not illustrated in the figures) in which the connection between the 
active medium 116 and the switching component 118 is ensured by intimate 
contact without the transverse joint 128, the joints of fluidizable, 
wettable material being disposed in lateral notches etched, for example, 
in the active laser medium 116. In this configuration the pumping and 
laser beams encounter no joint inside the apparatus, enabling the optical 
parametric oscillator to operate at optimum output. The procedures used to 
produce this component are the same as described above. 
Another structure that can be produced using a procedure according to the 
invention comprises an active laser medium 134 (FIG. 14) situated between 
an entrance micromirror 141 and an intermediate mirror 142. Active 
switching means 136 are disposed between the intermediate mirror 142 and 
an exit mirror 139. Micromirrors 139, 141 are produced as plates on a 
material 143 such as glass or silicon that is transparent at laser 
wavelengths. These substrates comprising micromirrors may then be 
assembled together with the active laser medium 134 and the active 
switching component 136 according to one of the procedures described in 
the present application. In FIG. 14 components 134, 136 have been etched 
to produce notches in which studs 142, 144, 146 made of fluidizable, 
wettable material are incorporated to ensure the mechanical resistance of 
the various components of the microlaser. The connection between different 
components is by intimate contact, giving excellent parallelism. 
In a variant, the apparatus shown in FIG. 14 may also be produced using the 
first embodiment disclosed above so that the joints are disposed 
transversally. 
FIG. 15 is a schematic diagram of another microlaser cavity structure that 
can be produced using a procedure according to the invention. This 
structure comprises an active laser medium 152, means 156 for switching 
the microlaser cavity in active or passive mode; said cavity being defined 
by entrance and exit mirrors 148, 150. The cavity is pumped by optical 
means that are not shown in the figure. Pulses emitted by the microlaser 
are absorbed by semiconductor component 160. The microlaser is a compact, 
robust source that can be integrated to produce a monolithic structure; it 
has enough power to reach the laser threshold of any semiconductor, even 
those with very high thresholds, irrespective of temperature (e.g. 
Pb.sub.x Sn.sub.1-x Se, Pb.sub.x Sn.sub.1-x Te, Pb.sub.x Sn.sub.1-x 
Se.sub.x, Cd.sub.x Pb.sub.1-x S, InAs.sub.x Sb.sub.1-x, Cd.sub.x 
Hg.sub.1-x Te, Bi.sub.1-x Sb.sub.x, 0.ltoreq.x.ltoreq.1, all these 
compounds giving wavelengths .lambda..gtoreq.1 .mu.m but, with 
conventional pumping means, at temperatures below 160K; this also applies 
to InAsSb (InAs.sub.x Sb.sub.1-x) type alloys on InAs substrates). 
The semiconductor component may be a section of a thickness of several 
hundred microns, or may be part of a semiconductor laser, of the VCSEL 
type, for example. 
Semiconductor component 160 is connected to switching component 156 by 
studs 162 made of fluidizable, wettable material and is in intimate 
contact with mirror 150. In a variant, a joint of fluidizable, wettable 
material provides the mechanical link at the interface between the mirror 
component and the semiconductor, while the two surfaces are still in 
contact via the joint. 
A microlaser output can be obtained that peaks at several kilowatts with a 
diameter of 20 to 100 .mu.m, i.e. power densities of several tens of 
megawatts per cm.sup.2. This power density enables a laser effect with 
optical pumping to be obtained for most known semiconductors. 
The power emitted by the semiconductor is thus typically of the order of 
several tens of milliwatts. 
Moreover, the reduced length of microlaser cavity (less than or equal to 1 
mm) ensures that pulses are short (typically less than 1 nanosecond; 
maximum 5 nanoseconds) which avoids any thermal load that could damage the 
semiconductor. 
In optical or optronics applications in general, the material used to 
produce the studs is selected for its optical compatibility, i.e. inducing 
the minimum optical loss from beams. A material is therefore chosen that 
has a refractive index as close as possible to that of the structures to 
be assembled. This is particularly the case with structures produced using 
the first embodiment of the procedure of the invention, i.e. where no 
notches to accept joints made of fluidizable, wettable material are made. 
Where a silica material (silica Sol-Gel) is used, the refractive index can 
be adjusted by doping, for example with oxynitrides SiO.sub.x N.sub.y ; 
the index jumps at the interface of the materials can thus be adapted and 
optical loss correspondingly reduced.