FR3066614B1 - METHOD FOR MANUFACTURING AN OPTICAL DEVICE - Google Patents

Abstract

The invention relates to a method of manufacturing an optical device (20) in a glass plate (23) comprising a waveguide (24), one end (24A) of which is directed towards a mirror (26). comprising the following successive steps: forming a first trench according to the drawing of the waveguide (24) to be formed and a second trench (28), the first trench having one end opening on the second trench (28); treat with hydrofluoric acid; covering with a reflective layer (26) the wall (28A) of the second trench (28) opposite the outlet of the first trench; fill the first trench with a material having an index different from that of the glass; and depositing an encapsulation layer (29).

Description

METHOD FOR MANUFACTURING AN OPTICAL DEVICE

Field

The present application relates to a method of manufacturing an optical device and more particularly to a method of manufacturing an optical device comprising a waveguide and a mirror.

Presentation of the prior art

Optical signals can be used to transmit data. Optical devices, such as the one presented in connection with FIG. 1, enable the connection between an optical fiber and one or more optical signal processing circuits.

Figure 1 is a sectional view of an optical device 10 adapted to transmit a light beam 12 of an optical fiber to an optical signal processing circuit. The device 10 is made in a glass plate 13, and comprises a waveguide 14 and a mirror 16. The waveguide 14 is adapted to receive the light beam 12 and to guide it towards the mirror 16. The guide The mirror 16 is disposed at the end of the waveguide 14 and is inclined to direct the light beam 12 in a direction substantially orthogonal to the main surface. of the plate 13, for example in the direction of an optical signal processing circuit disposed above the plate 13. The device 10 further comprises an encapsulation layer 17 which covers the upper face of the waveguide 14 , the upper face of the mirror 16 and the accessible upper face of the plate 13.

There is provided here a method improving the performance of the waveguide / mirror device and minimizing the number of manufacturing steps. summary

Thus, an embodiment provides a method of manufacturing an optical device in a glass plate comprising a waveguide, one end of which is directed towards a mirror, which method comprises the following successive steps: forming a first trench according to the drawing of the waveguide to be formed and a second trench, the first trench having one end opening on the second trench; treat with hydrofluoric acid; cover with a reflective layer the wall of the second trench opposite the outlet of the first trench; filling the first trench with a material having a refractive index different from that of the glass; and depositing an encapsulation layer.

According to one embodiment, the first trench and the second trench are formed by laser etching.

According to one embodiment, the laser is a pulsed laser whose pulse duration is between 2 and 500 femtoseconds.

According to one embodiment, the mirror is inclined relative to the vertical.

According to one embodiment, the mirror is inclined at an angle of between 40 and 50 degrees.

According to one embodiment, the second trench has a width of less than 50 μm.

According to one embodiment, the refractive index of the glass of the glass plate is less than the refractive index of the material filling the first trench and the refractive index of the material of the encapsulation layer is less than refractive index of the material filling the first trench.

According to one embodiment, the mirror can be curved.

According to one embodiment, the mirror is made of aluminum, copper or an alloy of aluminum and copper.

According to one embodiment, the first trench has a width of between 5 and 10 μm.

According to one embodiment, the encapsulation layer is made of silicon oxide or a polymer.

According to one embodiment, the material filling the first trench is a polymer.

Another embodiment provides an optical device comprising a waveguide and a mirror formed in a glass plate, said waveguide having one of its ends directed towards the mirror, said oblique mirror being separated from the end of the mirror. waveguide with a distance of less than 60 μm. Brief description of the drawings

These and other features and advantages will be set forth in detail in the following description of particular embodiments made without implied limitation in relation to the appended figures among which: FIG. 1, previously described, is a sectional view an optical device; Figure 2 is a sectional view of an embodiment of an optical device; Figures 3A and 4 to 9 are sectional views illustrating steps of an embodiment of a method of manufacturing the optical device of Figure 2, and Figure 3B is a top view corresponding to Figure 3A; and FIGS. 10A and 10B are a sectional view and a top view of an alternative embodiment of the optical device of FIG. 2.

detailed description

The same elements have been designated by the same references in the various figures and, in addition, the various figures are not drawn to scale. For the sake of clarity, only the elements useful for understanding the described embodiments have been shown and are detailed.

In the description which follows, when reference is made to relative position qualifiers, such as the terms "above", "top", etc., or to qualifiers for orientation, such as the term "vertical", reference is made to the orientation of the figures. Unless otherwise specified, the expression "of the order of" means within 10%, preferably within 5%.

FIG. 2 is a sectional view of an embodiment of an optical device 20 adapted to transmit a light beam 22, coming for example from an optical fiber, to a circuit (not shown) for optical signal processing arranged for example above the optical device. The device 20 is made in a support plate 23, for example made of glass, and comprises a waveguide 24 and a mirror 26, both of which are covered with an encapsulation layer 29.

The waveguide 24 is arranged so that one of its ends 24A is directed towards the mirror 26. Thus, the light beam 22 is transmitted by the waveguide 24 and then reflected by the mirror 26. The mirror 26 is inclined to reflect the light beam in a direction for example orthogonal to the main surface of the plate 23, for example in the direction of an optical signal processing circuit positioned above the plate 23. Unlike the device of FIG. 1, the end 24A of the waveguide is not in contact with the mirror 26, which eliminates any problem of waveguide / mirror interface defects. So that the beam 22 does not change in the gap between the end 24A of the waveguide and the mirror 26, the mirror is arranged relative to the end 24A at a distance less than 50 pm, for example between between 30 and 50 pm.

The waveguide 24 is conventionally formed of a core 25 and a sheath. The sheath is formed by the plate 23 and the encapsulation layer 29. The core 25 has a cross section of substantially square shape so as to have a form factor (a ratio height / width) of the order of 1. The height and the width of the core 25 are for example between 5 and 10 pm. In this case, the waveguide 24 is monomode for wavelengths between 1300 and 1500 nm. These dimensions are for example adapted to those of a monomode optical fiber. The core 25 of the waveguide 24 is made of a material having a refractive index greater than that of the glass of the plate 23. This material is for example a polymer, for example in the form of a dry stretchable film (c '). that is to say not requiring solvent, known under the name "dry film") shaped by rolling. The difference in refractive index between the glass of the plate 23 and the material of the core 25 of the waveguide 24 is between 10 -1 and 10 2, for example of the order of 5 × 10 3. a suitable polymer material is that distributed by Elga Europe in the form of a dry stretch film under the trade name "Ordyl SY 317".

The mirror 26 is disposed on a wall 28A of a trench 28, this wall 28A being opposite the end 24A of the waveguide 24. As shown in FIG. 2, the mirror 26 can completely cover the wall 28A and overflow on the bottom of the trench 28, but, alternatively, the mirror 26 could rest only on a portion of the wall 28A facing the end 24A. The mirror 26 is inclined relative to the vertical of an angle for example between 40 and 50 degrees, of the order of 42 degrees. The mirror 26 is made of metal, for example copper, aluminum or an alloy of copper and aluminum.

The encapsulation layer 29 covers the upper face of the waveguide 24, the upper face of the mirror 26 and the accessible upper face of the glass plate 23. The layer 29 further fills the trench 28. encapsulation 29 is of a material having a refractive index smaller than that of the waveguide material. The difference in index between the glass of the plate 23 and the material of the encapsulation layer 29 is of the order of 10 -2. The layer 29 is for example made of silicon oxide or a polymer. The layer 29 has a thickness for example between 5 and 50 pm, for example 10 pm.

FIGS. 3A, 3B, 4 to 9 illustrate successive steps of an embodiment of a manufacturing method of the optical device of FIG. 2.

Figures 3A and 3B are respectively a sectional view and a top view of the same step of the method. At this stage, the trench 28 and a trench 30 are etched into the glass plate 23.

The trench 28 is etched obliquely relative to the normal direction on the surface of the plate 23. For this, the glass plate 23 is for example positioned on an oblique support and then etched with a vertical laser beam. Contrary to what is shown, the bottom of the trench 28 is in practice substantially rounded.

The trench 28 has a depth for example between 30 and 50 pm. Trench 28 has for example, in top view, a rectilinear shape.

The trench 30 has a cross section for example of semicircular shape with a depth of between 5 and 10 μm. Trench 30 has for example, in top view, a rectilinear shape. One end 30A of the trench 30 opens onto the trench 28. In the example shown in FIG. 3B, the trenches 30 and 28 form a T.

To form the trenches 28 and 30, the plate 23 is scanned by a laser beam. The laser beam is produced by a laser whose pulses have a duration between 2 and 500 femtoseconds, commonly called femtosecond laser. For example, the trenches 28 and 30 can be obtained for pulses having energies greater than 500 nJ and of duration of the order of 100 fs. This energy is calculated according to the dimensions of the cavity that it is desired to form with a pulse. The femtosecond laser emits these pulses for example at a frequency between 10 and 500 kHz. An advantage of using a femtosecond laser is that the duration of the pulses is quite short in view of the thermal relaxation time of the material. This property allows precise machining of the material and limits the thermal effects around the ablated zone. Femtosecond laser exposure modifies the physical properties of exposed areas by initiating etching. However, after etching, the trenches do not have the desired dimensions, and their walls have a certain roughness. Hydrofluoric acid etching is then performed to obtain the desired dimensions by removing the material in the laser-exposed area and to reduce the roughness of the trenches.

Figures 4 to 9 are sectional views illustrating the steps of the manufacturing method of the device of Figure 2 following that illustrated in Figures 3A and 3B. In the step of Figure 4, a resin layer 32 is deposited in a conformal manner on the surface of the glass plate 23. The layer 32 is for example a resin sensitive to UV radiation. The layer 32 has a thickness of between 3 and 15 μm. The resin layer 32 is deposited for example by spinning or by rolling. In the step of FIG. 5, the portion of the resin layer 32 covering the wall 28A of the trench 28, this wall being opposite the end 24A of the waveguide 24 (see FIG. 1), is removed by masking. More particularly, the structure of FIG. 4 is masked, exposed to UV radiation and then etched by wet etching. In the step of FIG. 6, a layer of metal 34 is conformally deposited on the structure of FIG. 5. The layer 34 is for example made of aluminum, copper or an alloy of aluminum or copper. The layer 34 has a thickness of between 10 nm and 1 μm, of the order of 100 nm. The layer 34 is for example deposited by a sputtering or PVD (physical vapor deposition) method. In the step of FIG. 7, the resin layer 32 is removed and the portions of the metal layer 34 covering it are removed by the same method according to a method known as "lift off". The portion of the metal layer 34 remaining on the wall 28A of the trench 28 forms the mirror 26. At the step of FIG. 8, the trench 30 is filled with a material 36 having a refractive index greater than that The trench 30 thus filled forms the core 25 of the waveguide 24.

The trench 30 is for example filled with the material 36 by a method comprising the following successive steps: -postily depositing a layer of the material 36 on the structure of FIG. 7, for example by rolling, in the case where the material 36 is a polymer perform a crosslinking annealing; flattening the layer of material 36, for example by means of a mechanochemical planarization, to remove the excess material in contact with the surface of the plate 23; and -drawing by masking the material 36 from the trench 28. In the step of FIG. 9, the encapsulation layer 29 is deposited on the structure of FIG. 29. The layer 29 fills the trench 30.

FIGS. 10A and 10B are a sectional view and a top view of a variant 40 of the optical device of FIG. 2. The device 40 comprises the same elements as the device 20 except that the trench 28 and the mirror 26 are curved so as to focus the reflected light at a chosen point.

As shown in FIGS. 10A and 10B, the trench 28 and the mirror 26 can be bent in a visible curve in plan view and in a visible curve in sectional view. Alternatively, the trench 28 and the mirror 26 could be bent only in one direction.

Particular embodiments have been described. Various variations and modifications will be apparent to those skilled in the art. In particular, there is shown a rectilinear waveguide 24 but the waveguide 24 can be curved.

Various embodiments with various variants have been described above. It will be appreciated that those skilled in the art may combine various elements of these various embodiments and variants without demonstrating inventive step.

Claims (13)

A method of manufacturing an optical device (20, 40) in a glass plate (23) comprising a waveguide (24) having one end (24A) facing a mirror (26), which method comprises the following successive steps: forming a first trench (30) according to the drawing of the waveguide (24) to be formed and a second trench (28), the first trench (30) having one end (30A) opening on the second trench (28); treat with hydrofluoric acid; covering with a reflective layer (26) the wall (28A) of the second trench (28) opposite the outlet (30A) of the first trench (30); filling the first trench (30) with a material having a refractive index different from that of the glass; and depositing an encapsulation layer (29). The method of claim 1, wherein the first trench (30) and the second trench (28) are formed by laser etching. 3. The method of claim 2, wherein the laser is a pulsed laser whose pulse duration is between 2 and 500 femtoseconds. 4. Method according to any one of claims 1 to 3, wherein the mirror (26) is inclined relative to the vertical. 5. The method of claim 4, wherein the mirror (26) is inclined at an angle between 40 and 50 degrees. The method of any one of claims 1 to 5, wherein the second trench (28) has a width less than 50 μm. The method according to any one of claims 1 to 6, wherein the refractive index of the glass of the plate (23) is less than the refractive index of the material filling the first trench (30) and the index of refraction of the material of the encapsulation layer (29) is less than the refractive index of the material filling the first trench (30). The method of any one of claims 1 to 7, wherein the mirror (26) is curvable. 9. A method according to any one of claims 1 to 8, wherein the mirror (26) is aluminum, copper or an alloy of aluminum and copper. The method of any one of claims 1 to 9, wherein the first trench (30) has a width of between 5 and 10 μm. The method of any one of claims 1 to 10, wherein the encapsulation layer (29) is silicon oxide or a polymer. The method of any one of claims 1 to 11, wherein the material filling the first trench (30) is a polymer. An optical device (20, 40) comprising a waveguide (24) and an oblique mirror (26) formed in a glass plate (23), said waveguide (24) having one of its ends (24A). ) directed towards the mirror (26), said oblique mirror (26) being separated from the end (24A) of the waveguide (24) by a distance of less than 50 μm.