Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
2000-03-23
2002-06-25
Healy, Brian (Department: 2874)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S014000, C385S129000, C385S130000, C385S132000, C385S039000, C065S385000, C065S386000
Reexamination Certificate
active
06411765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a optical waveguide element that may be employed in, for instance, optical communication and a method for manufacturing the optical waveguide element.
2. Description of the Related Art
Passive light-wave circuits are playing an increasingly crucial role in optical communication systems today. A wave guiding channel type light-wave circuit that achieves a high degree of stability and excellent mass productivity is considered to be an essential component in optical communication systems. In particular, quartz optical waveguides, which make the most of the physical and chemical stability of quartz glass, achieve advantages such as good conformity with optical fibers constituting transmission pathways and have been adopted in applications in PLCs (planar light-wave circuits) having complex and advanced functions to enable control of light phases and interference, and intense research and development efforts have been made in this area.
FIG. 11
illustrates a schematic structure of a optical waveguide element
500
which may be employed in a PLC in the prior art and
FIG. 12
illustrates the process implemented to manufacture quartz optical waveguides in the prior art. A lower clad layer
504
and a core layer
506
having SiO2 as their main constituents are formed on an Si substrate
502
through a method Which uses to its advantage a gas-phase reaction such as the CVD (chemical vapor deposition) method or the FHD (flame hydrolysis deposition) method. The lower clad layer
504
and the core layer
506
are differentiated from each other by forming them with source gases having different compositions.
Next, unnecessary portions of the core layer
506
are removed through dry etching such as RIE (reactive ion etching) or RIBE (reactive ion beam etching). As a result, the remaining core layer
506
, left in ridges, forms core portions
508
.
Lastly, an upper clad layer
510
having SiO2 as its main constituent is formed so as to cover the core portions
508
through a method which uses a gas-phase reaction to advantage. The optical waveguide element
500
in the prior art is thus obtained. It is to be noted that in this optical waveguide element
500
, quartz optical waveguides constituted of the lower clad layer
504
, the core portions
508
and the upper clad layer
510
are formed.
However, as explained above, only one core layer is formed on the substrate constituted of Si or the like at the optical waveguide element in the prior art. Consequently, the optical waveguide element in the prior art is subject to a restriction under-which the light-wave circuits must be formed essentially within a single plane. The number of optical elements mounted at a single chip has been increasing to support even more advanced and diversified functions that PLCs must fulfill in recent years. The optical waveguide element subject to the restriction described above can only keep up with this trend by increasing the chip size, which in turn, leads to an increase in production costs.
As a solution to the common problem of PLCs in the prior art described above, Japanese Unexamined Patent Publication No. 1995/20344, for instance, discloses a method for forming a multilayer light-wave circuit substrate by alternately laminating a light-wave circuit substrate with optical waveguide circuit patterns formed therein and spacers.
However, since a spacer and a substrate are present between light-wave circuit layers that are next to each other, interference or coupling cannot be achieved between light-wave circuits formed in the different light-wave circuit layers through the method disclosed in the publication above. As a result, light-wave circuits must be formed within a single light-wave circuit layer if it is necessary to achieve interference or coupling between the light-wave circuits, just as in standard PLCs.
SUMMARY OF THE INVENTION
The present invention has been completed by addressing the problems discussed above and other problems of the optical waveguide element in the prior art.
Accordingly, the present invention as disclosed in claim
1
provides a optical waveguide element having n light-wave circuit layers each constituted of a core portion and a clad layer covering the core portion that are sequentially laminated to achieve a multilayer structure, with n representing an integer equal to or larger than 2.
According to the present invention as disclosed in claim
1
, at least one optical waveguide with a core portion constituting a transmission path for light is formed within each light-wave circuit layer. Three-dimensional placement of a group of optical waveguides is achieved through the multilayer structure of the light-wave circuit layers. Thus, according to the present invention as disclosed in claim 1, the number of optical waveguides per unit area can be increased.
In addition, according to the present invention as disclosed in claim 1, at least two light-wave circuit layers are sequentially laminated without a substrate or a spacer present between them. Consequently, it is possible to achieve an interaction such as interference or coupling, of guided light-waves in the optical waveguides formed in different light-wave circuit layers. In addition, light-wave circuits can be formed three-dimensionally.
As explained above, according to the present invention a much higher degree of freedom is afforded in the formation of light-wave circuits through the increase in the number of optical waveguides per unit area and the three-dimensional formation of light-wave circuits. As a result, various types of light-wave circuits can be formed without having to take up a larger mounting area for the optical waveguide elements. This is expected to contribute to higher integration and further miniaturization of optical apparatuses.
It is to be noted that the core portions in the individual light-wave circuit layers may be formed at various positions according to the invention. For instance, a core portion may be positioned so that it is in complete contact with the surface constituting the boundary with the adjacent light-wave circuit layer, may be positioned so that it comes into partial contact with the surface constituting the boundary with the adjacent light-wave circuit layer at, at least, one point or may be positioned so that it is completely isolated from the adjacent light-wave circuit layer.
According to a feature of the present invention, an optical waveguide element having formed therein at least one optical coupler astride two or more light-wave circuit layers contiguous to each other in a multilayer structure is provided. This achieves a three-dimensional formation of light-wave circuits over a plurality of light-wave circuit layers. The optical coupler may be constituted of an optical coupler with a uniform distance between the optical waveguides at the coupled area such as a directional optical coupler or a parallel three-wave guiding channel directional optical coupler, or it may be constituted of a directional optical coupler with variable distances between the optical waveguides, for instance.
In addition, the optical coupler may be formed through any of various combinations of core portion groups in the contiguous light-wave circuit layers. According to the present invention, each of the contiguous light-wave circuit layers may include at least one core portion to constitute the optical coupler, the core portions constituting the optical coupler may be included only in every other light-wave circuit layer or the core portions constituting the optical coupler may be completely randomly provided among the contiguous light-wave circuit layers. It is to be noted that the core portions constituting the optical coupler in the structure fulfill a function of guiding light energy, a function of relay coupling two other core portions or a function achieving a combination of these functions.
According to a further feature of the present invention an optical waveguide element having formed therein an optical
Healy Brian
Kunitz Norman N.
Oki Electric Industry Co. Ltd.
Venable
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