JP3067299B2 - Embedded quartz optical waveguide and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Industrial applications]

The present invention relates to a buried quartz optical waveguide used in the field of optical waveguide circuit components. More specifically, the present invention relates to a quartz-based optical waveguide structure in which peeling and cracking hardly occur, and a method of manufacturing the same.

[0002]

2. Description of the Related Art For further spread of optical communication systems, there is an urgent need to develop small, low-cost and reliable optical components. Optical components used in the optical communication field and the like can be roughly classified into a bulk type, a fiber type, and a waveguide type according to the form. The bulk type is configured by combining a micro lens, a prism, an interference film filter, and the like. Although it is at a practical level, it requires a long time for assembling adjustment, and leaves problems in terms of long-term reliability and price. The fiber type uses the optical fiber itself as a constituent material for polishing, fusion,
Although it is constructed through a stretching step, its production requires craftsmanship and has a problem of poor productivity. On the other hand, the waveguide type has an advantage that it can be collectively formed on a flat substrate by a photolithography process, and is attracting attention as a component form to be connected to a future optical integrated circuit.

In order to manufacture a waveguide type optical component, it is fundamental to form an optical waveguide having a pattern shape suitable for a purpose on a flat substrate. Various optical waveguides using glass, plastics, oxide crystals, semiconductor crystals, etc. as materials have been tried. Among them, quartz-based glass and silicon Silica-based optical waveguides composed of materials are also expected to provide practical waveguide-type optical components because of their excellent connection characteristics with silica-based optical fibers as transmission lines. I have.

FIG. 4 is an explanatory view of a structure example of a conventional silica-based optical waveguide, in which eight directional couplers are provided on a silicon substrate.
An example in which 21, 22,…, 28 are arranged is shown. (a) is a plan view,
(b) is an enlarged cross-sectional view taken along the line AA 'in the plan view (a), wherein 1 is a silicon substrate having a diameter of 3 inches, 2 is a quartz-based glass buffer layer, 3 is a quartz-based glass clad layer, and 11
a, 11b, 12a, 12b,..., 18a, 18b are quartz glass cores embedded between the buffer layer 2 and the cladding layer 3.

[0005] These two adjacent core portions form a pair, and a part thereof is close to each other to form directional couplers 21, 22, ..., 28. Although it is a matter of course that the main body of the silica-based optical waveguide is located in the core portions 11a, 11b, 12a, 12b,..., 18a, 18b that perform light propagation, the buffer layer 2 absorbs signal light into the silicon substrate 1. The cladding layer 3 regulates the mode of the signal light propagating in the core portion, and plays an important role of protecting the core portion, for example, in addition to the role of providing a single mode condition. The cross-sectional dimension of the core part is about 8 μm square when adjusted to the single mode condition, and the thickness of each of the buffer layer 2 and the cladding layer 3 is 20 μm to
It is about 30 μm. The optical waveguide of FIG. 4 is cut out as an optical waveguide chip for each directional coupler unit surrounded by a broken line in FIG. 4 (a), and an input / output optical fiber is connected to the end of the optical waveguide core as necessary. Thus, the appearance as a waveguide type optical component that acts such as light branching and merging can be adjusted.

In order to manufacture the buried quartz optical waveguide shown in FIG. 4, a quartz glass film deposition technique utilizing a flame hydrolysis reaction of silicon tetrachloride or the like, and a fine processing technique for a glass film by reactive ion etching are used. Can be formed by a known combination. That is, a quartz optical waveguide film composed of a buffer layer and a core layer is deposited on the silicon substrate 1 by a flame hydrolysis reaction deposition method, and then unnecessary portions of the optical waveguide film core layer are removed by reactive ion etching. Remaining only the desired core portion, again by the flame hydrolysis reaction deposition method,
It can be formed by depositing a thick cladding layer so as to cover the core portion.

However, the structure of the conventional buried silica-based optical waveguide shown in FIG. 4 and its manufacturing method often have a problem that peeling or cracking occurs between the buffer layer 2 and the cladding layer 3. there were. Peeling and cracking tend to occur when a strong mechanical external force is applied to the cladding layer in the step of cutting out the optical waveguide chip. Therefore, the cutting must be performed carefully over a long period of time. Also, in the step of mirror-polishing the end face of the chip after cutting, it was observed that the peeling occurred when a mechanical shock was applied.

[0008] The cause of the peeling is presumed as follows. That is, a glass composition having a lower softening temperature than the core layer and the buffer layer is selected as the clad layer constituting the buried quartz optical waveguide. This is to prevent the core layer and the buffer layer from being deformed during the filling step. The cladding layer and the buffer layer having different softening temperatures also have different thermal expansion coefficients, and a residual stress acts on the boundary between the cladding layer and the buffer layer. It is presumed that the aforementioned peeling and cracking are caused by external stimuli such as cutting and polishing due to the residual stress.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and is directed to a buried quartz that is resistant to external stress, hardly causes peeling or cracking, and is easy to handle during cutting and mounting steps. An object of the present invention is to provide a system optical waveguide and a method for manufacturing the same.

[0010]

The buried quartz optical waveguide of the present invention comprises a substrate, a core made of quartz glass, formed on the substrate, and a core made of the same material as the substrate. An anchor portion having substantially the same height and comprising a projection portion arranged in a mesh shape or a lattice shape so as to substantially cover a portion where optical coupling does not occur with the core portion on the substrate; and It is characterized by comprising a core portion and a cladding layer for embedding the anchor portion. Such a buried quartz optical waveguide of the present invention may be formed on a buffer layer formed on a substrate.

In the method of manufacturing a buried quartz optical waveguide according to the present invention, a quartz glass optical waveguide film including at least a core layer is formed on a substrate, and an unnecessary portion of the core layer is removed by etching. And forming a core portion that performs light propagation action, and other than the core portion of the core layer,
And a step of partially etching a portion that does not cause optical coupling with the core portion to leave a projection in a mesh or lattice shape,
Forming a quartz-based glass clad layer in which the core and the protrusion are buried at the same time. In the method of manufacturing the buried quartz optical waveguide of the present invention, in the step of forming the quartz glass optical waveguide film, a quartz glass buffer layer is deposited on the substrate,
A core layer may be formed thereon.

[0012]

In the buried quartz optical waveguide having such a structure, the cladding layer is in contact with the substrate or the buffer layer by embedding a projection (anchor) formed of a core layer left in a mesh or lattice shape. In this case, a part of the material constituting the clad layer cuts into the gap between the protrusions of the anchor portion, the anchor portion holds the clad layer together, and the clad layer is separated from the substrate, the buffer layer, and the core portion by a so-called anchor action. To prevent Stress concentration between the buffer layer and the substrate or the cladding layer is also dispersed by the presence of the anchor portion, and cracks are less likely to occur.

The conventional buried optical waveguide is greatly different from the conventional buried optical waveguide in that a dummy is embedded in the same layer as the core portion, not to have a light propagation effect, but to act as an anchor for preventing peeling.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to the drawings. 1A and 1B show an embodiment of a buried quartz optical waveguide according to the present invention, wherein FIG. 1A is a plan view, and FIG.
It is a sectional enlarged view in B '. The difference from the conventional example shown in FIG. 4 is that the directional couplers 21, 22, 23, 24, 25, 26, 2
In addition to the core portions 11a, 11b,..., 18a, 18b constituting the portions 7, 28, projections (anchor portions) 5 arranged in a mesh or lattice shape at positions where optical coupling does not occur with the core portions [FIG. 1 (a) is hatched in the cladding layer 3 together with the core. In the anchor portion 5 of this embodiment, square protrusions having a width of 20 μm and a length of 40 μm are arranged in a mesh at a distance of 60 μm or more from the core portion with a vertical and horizontal pitch of 60 μm.

FIGS. 2 (I), (II), (III), (IV) and (V) correspond to FIG.
FIG. 6 is an enlarged sectional view group for explaining an example of a manufacturing process of the optical waveguide of the present invention corresponding to FIG. In FIG. 2 (I), first, a silica glass fine particle layer 2a for a buffer and a silica glass fine particle layer 10a for a core are deposited on a silicon substrate 1 by using a flame hydrolysis reaction of silicon tetrachloride or the like. Subsequently, in FIG. 2 (II), the glass fine particle layer was put together with the substrate in an electric furnace at a high temperature (about 13 ° C.).
(00 ° C.) to form a vitreous transparent film by virtue of the quartz glass buffer layer 2 and the core layer 10. Next, in FIG. 2 (III), an unnecessary portion of the core layer 10 is removed by a reactive ion etching process to leave desired core portions and protrusions. Next, in FIG. 2 (IV), the silica glass fine particle layer 3a for cladding, whose softening temperature is lower than that for the buffer or the core, is deposited again using the flame hydrolysis reaction. Specifically, a large amount of boron trichloride or phosphorus trichloride was added to silicon tetrachloride to deposit the cladding glass fine particle layer 3a. FIG.
In (V), heating is again performed in an electric furnace, and the silica-based glass fine particle layer 3a for a clad is transparently vitrified to obtain a silica-based glass clad layer 3. In this way, a buried quartz optical waveguide corresponding to FIG. 1 can be manufactured. The specifications of the optical waveguide manufactured in this example are as follows:
m, core size 8 μm × 8 μm, cladding layer thickness 25 μm,
The relative refractive index difference between the core and the clad was 0.25%, the core interval at the coupling part of the directional coupler was 4 μm, and the coupling length was 0.5 mm.

The silicon wafer with the optical waveguide manufactured as described above was cut out by a dicing saw at a speed of 0.8 mm / sec to obtain an optical waveguide chip, but no peeling or cracking occurred. For comparison, when a silicon wafer with an optical waveguide with a conventional structure without an anchor portion was cut out at the same speed, peeling and cracking occurred at a rate of about 30%, and to suppress the occurrence of peeling, etc.
The cutting speed had to be reduced to 1/4 or less.

In the buried quartz optical waveguide and the method of manufacturing the same according to the present invention, in addition to the effect of preventing chipping of the optical waveguide and peeling during mounting such as a polishing step, cracking, etc., We found that there were some side effects. That is, in the optical waveguide manufacturing process shown in FIG. 2, there is also an effect of preventing the quartz glass fine particle layer 3a for cladding from peeling off during the vitrification. Dopant oxide P ₂ O ₅ for lowering the softening temperature, B ₂ O
Silica-based fine glass particle layer 3a containing a large amount of ₃ for cladding
In the case of transparent glass, it suddenly shrunk during the vitrification, peeled off from the cladding layer, the embedding process itself failed, and occasionally a situation where the optical waveguide itself could not be produced was seen, but when the anchor portion of the present invention was arranged, the cladding This is a point that no peeling of the silica-based glass fine particle layer occurred. It is presumed that the anchor portion plays the role of an anchor and holds the silica-based glass fine particle layer for cladding to prevent its rapid shrinkage and peeling.

When the protrusions of the anchor portion are densely provided as in the above embodiment, the height of the clad layer on the upper surface of the anchor portion exceeds the height of the clad layer on the upper surface of the optical waveguide core portion (see FIG. 2 (V)), even when the chip is pressed with a metal frame or the like from the upper surface of the optical waveguide chip in the mounting process of the casing, etc., there is also a secondary effect that can prevent the external stress from being directly applied to the core of the optical waveguide. Note that there is.

FIG. 3 is a diagram showing an example of a mesh-like and lattice-like pattern of an anchor portion which plays an important role in the present invention. FIG. 3A shows the one described in the above embodiment. FIG. 3 (b) shows a rectangular projection having a width of 20 μm and a length of 50 μm, for example.
They are arranged at a pitch of 0 μm. The difference from FIG. 3A is that the square projections are arranged only in one direction.
FIG. 3C shows circular projections having a diameter of 25 μm arranged at a pitch of 50 μm. FIG. 3 (d) shows a linear projection having a width of 30 μm arranged in a lattice pattern with a pitch of 100 μm. The desired anchor action was observed in any of the patterns. However, in the case of a lattice pattern having a closed area as shown in FIG. 3D, when the pitch was reduced to about 50 μm or less,
In the embedding process, a phenomenon that air bubbles are left in the anchor portion is observed, and it is not advisable to set the pitch too small in a lattice pattern having a closed region as shown in FIG.

Although the structure and the manufacturing method of the buried quartz optical waveguide of the present invention have been described by taking the directional coupler as an example, the present invention is not limited to the directional coupler, Optical splitter / combiner, optical switch, optical multiplexer / demultiplexer,
Needless to say, the present invention can be applied to various and various waveguide type optical component menus. Further, in the above-described embodiment, the example in which the silicon substrate is used as the substrate for supporting the quartz optical waveguide has been described, but the present invention can also be applied to a quartz optical waveguide on a quartz glass substrate. On the quartz glass substrate, it is possible to omit the buffer layer 2 in the above embodiment and form the core portion and the anchor portion directly on the substrate. However, it is possible to suppress light scattering loss due to irregularity of the interface with the substrate. For this purpose, it is desirable to provide a buffer layer having a thickness of at least about 10 μm.

The shape of the projection of the anchor portion is not limited to that shown in FIG. 3, but it is essential that the shape be such that it can easily penetrate the cladding layer and be easily embedded. Since it is inconvenient if optical coupling occurs between the anchor portion composed of the mesh-like or lattice-like residual protrusions and the optical waveguide core portion, the size of the optical waveguide core portion and the relative refractive index difference between the core and the clad are reduced. The distance between the anchor and core is 30 to
It is desirable to be separated by about 200 μm.

[0022]

As described above, according to the present invention, together with the core portion of the optical waveguide, the anchor portion composed of a mesh-like or lattice-like projection for preventing the cladding layer from peeling is cut out by embedding it in the cladding layer. This can prevent the cladding layer from peeling or cracking during mounting, and is extremely effective in producing a waveguide type optical component with stability and reproducibility. The formation of the anchor portion can be performed simultaneously with the formation of the core portion, and since the shapes of the core portion and the anchor portion can be drawn on one mask pattern, a process that does not require mask pattern alignment or a separate process. The above advantages cannot be overlooked.

[0023]

As described above, according to the present invention, together with the optical waveguide core portion, a mesh-shaped anchor portion for preventing the clad layer from peeling is buried in the clad layer, so that the clad layer can be cut out or mounted at the time of mounting. Peeling and cracking can be prevented, and this is extremely effective in producing a waveguide type optical component stably and with good reproducibility. The formation of the mesh anchor portion can be performed simultaneously with the formation of the core portion.
Since the shapes of the core portion and the terrace portion can be drawn on a single mass pattern, the advantages of the process that does not require mask pattern alignment or another process cannot be overlooked.

[Brief description of the drawings]

FIG. 1 (a) is a plan view of one embodiment of a buried quartz optical waveguide of the present invention. (b) is BB 'in FIG. 1 (a).
FIG.

FIG. 2 is a view showing an example of a manufacturing process of a buried quartz optical waveguide of the present invention.

FIG. 3 is a diagram showing an example of the arrangement of a mesh anchor portion according to the present invention.

FIG. 4A is a plan view of a structure example of a conventional buried quartz optical waveguide. FIG. 4B is an enlarged cross-sectional view taken along line AA ′ of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Quartz glass buffer layer 3 Quartz glass clad layer 3a Glass fine particle layer for cladding 4 Convex part 5 Network anchor 10 Quartz glass core layer 10a Glass fine particle layer for core 11a, 11b, 12a, 12b, 13a , 13b, 14a, 14b, 15a, 16b,
17a, 17b, 18a, 18b Silica glass optical waveguide core 21, 22, 23, 24, 25, 26, 27, 28 Directional coupler

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor ▲ Yoshi ▼ Tetsuo Sawa 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References Patent 2862625 (JP, B2) (58) Survey Field (Int.Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (4)

(57) [Claims] 1. A substrate comprising: a substrate; a silica-based glass; a core portion formed on the substrate; and a same material as the core portion, having substantially the same height as the core portion; An anchor portion composed of projections arranged in a mesh or lattice shape so as to substantially cover a portion where optical coupling does not occur with the core portion above, and a cladding layer made of quartz glass and burying the core portion and the anchor portion. A buried silica-based optical waveguide, comprising: 2. The buried silica-based optical waveguide according to claim 1, wherein said core portion and said anchor portion are formed on a silica-based glass buffer layer deposited on said substrate. 3. A step of forming a silica-based glass optical waveguide film including at least a core layer on a substrate, and forming a core portion having a light propagation function by removing unnecessary portions of the core layer by etching. A step of partially etching a portion of the core layer other than the core portion and not causing optical coupling with the core portion to leave projections in a mesh or lattice shape, and quartz for simultaneously embedding the core and the projections Forming a system-based glass clad layer. 4. The burying method according to claim 3, wherein in the step of forming the quartz glass optical waveguide film, a quartz glass buffer layer is deposited on a substrate, and a core layer is formed thereon. Of manufacturing a quartz optical waveguide.