Optical waveguides – Planar optical waveguide
Reexamination Certificate
2001-05-01
2003-04-01
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Planar optical waveguide
C385S131000, C385S002000, C385S037000
Reexamination Certificate
active
06542684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to planar or “integrated” optical waveguides, and particularly to lithographically-formed single-mode waveguides employing organic and polymeric materials.
2. Technical Background
Multilayer optical waveguiding structures are used to build integrated optical circuits that-route and control optical signals in a optical fiber communication system. In optical communication systems, messages are transmitted at infrared optical frequencies by carrier waves that are generated using sources such as lasers and light-emitting diodes. There is interest in these optical communication systems because they offer several advantages over electronic communications systems using copper wires or coaxial cable. They have a greatly increased number of channels of communication, as well as the ability to transmit messages at much higher speeds than electronic systems.
This invention is concerned with the formation of light-transmissive optical waveguide devices. The operation of an optical waveguide is based on the fact that when a core medium which is transparent to light is surrounded or otherwise bounded by another cladding medium having a lower refractive index, light introduced along the core medium's axis is highly reflected at the boundary with the surrounding cladding medium, thus producing a light-guiding effect.
It is possible to produce polymeric optical waveguides and other optical devices which transport optical signals via optical circuitry or optical fiber networks. One method used to form an optical waveguide device involves the application of standard photolithographic processes. Photopolymers are of particular interest for optical applications because they can be patterned by photolithographic techniques which are well known in the art. Photopolymers also offer opportunities for simpler, more cost-effective manufacturing processes. Lithographic processes are used to define a pattern in a light-sensitive, photopolymer-containing layer deposited on a substrate. This layer may itself consist of several layers composed of the same or different polymeric materials having dissimilar refractive indices, to form a core, overcladding, and under cladding layers or structures.
Among the many known photopolymers, acrylate materials have been identified as suitable for optical waveguides because of their optical clarity, low birefringence, and ready availability of a wide range of monomers.
Planar polymer waveguides typically comprise layers of low loss optical materials of precise indices of refraction. Both step index and gradient index waveguide structures are known in the art. For planar polymer and glass waveguides, step index structures are most easily achieved through successive coating of materials with differing refractive indices. Typically, a core has a refractive index which is 0.5% to 2% higher than its overcladding. The magnitude of this refractive index difference (&Dgr;n) is set to optimize the performance of the planar waveguides, or to match light modes when the transition is made from the planar device to an optical fiber.
In practice, most planar waveguide structures have a configuration wherein a buffer layer is applied to a silicon substrate, then an underclad is applied to the buffer, followed by application and patterning of a core layer, and followed finally by application of an overclad. In some instances, the buffer layer can serve as the under clad.
If these multiple layers are not optimized, several problems can occur. These include high optical loss due to absorption of light by the substrate; high polarization dependent loss (PDL); if heating is performed (for tuning or switching), the increase of temperature alters the index of refraction in such a way as to push light out at least partially out of the core where is can interact with the cladding and/or the substrate to produce a variety of unwanted interactions which can, for example, lead to loss and PDL; and if the waveguide incorporates a grating, secondary reflections or an unwanted broadening of the wavelength of the reflected signal can be observed.
SUMMARY OF THE INVENTION
The invention provides a single-mode optical waveguide fabricated on a substrate, the substrate defining a surface, the single-mode optical waveguide comprising a polymeric, buffer layer is disposed on the surface of the substrate, the polymeric, buffer layer defining a surface and having an index of refraction n
b
. A patterned, light-transmissive core layer disposed directly on the surface of the buffer layer, the patterned, light-transmissive core layer defining a top surface and a pair of side walls, the patterned, light-transmissive core layer having an index of refraction n
c
. An overcladding layer is disposed on the top surface of the core, the pair of side walls of the core, and the buffer layer, the overcladding layer having an index of refraction n
o
, such that n
b
<n
o
<n
c
and &Dgr;n=n
c
−n
o
, wherein the value of &Dgr;n produces a single-mode waveguide at optical communication wavelengths.
The invention also provides a method for forming a single-mode optical waveguide on a substrate, the substrate defining a surface, the method comprising the steps of depositing a polymeric, buffer layer onto the surface of the substrate, the polymeric, buffer layer defining a surface and having an index of refraction n
b
. One then deposits a patterned, light-transmissive core layer directly onto the surface of the polymeric, buffer layer without any intermediate layers, the patterned, light-transmissive core layer defining a core having a top surface and a pair of side walls, the patterned, light-transmissive core layer having an index of refraction n
c
. One then deposits an overcladding layer onto the top surface of the patterned, light-transmissive core layer, the side walls of the patterned, light-transmissive core layer, and a portion of the polymeric, buffer layer, the overcladding layer having an index of refraction n
o
, such that n
b
<n
o
<n
c
and &Dgr;n n
c
−n
o
.
The invention further provides a method for forming a single-mode optical waveguide on a substrate, the substrate defining a surface, the method comprising the steps of depositing a buffer layer onto the surface of the substrate, the buffer layer being fabricated from a polymeric, material having an index of refraction n
b
, the buffer layer defining a surface. One then deposits a core layer directly onto the surface of the buffer layer without any intermediate layers, the core layer being fabricated from a light-transmissive material having an index of refraction n
c
. One then patterns the core layer to define a core with a top surface and a pair of side walls and to expose portions of the buffer layer. One then deposits an overcladding layer onto the top surface of the core layer, the side walls of the core layer, and the exposed portions of the buffer layer, the overcladding layer having an index of refraction n
o
, such that n
b
<n
o
<n
c
and &Dgr;n=n
c
−n
o
, wherein the value of &Dgr;n produces a single-mode waveguide at optical communication wavelengths.
The invention still further provides a method for forming an optical waveguide on a substrate, the substrate defining a surface, the method comprising the steps of depositing a polymeric, buffer layer onto the surface of the substrate, the polymeric, buffer layer defining a surface and having an index of refraction n
b
. One then deposits a photosensitive core layer directly onto the surface of the polymeric, buffer layer without any intermediate layers, the photosensitive core layer defining a top surface, the photosensitive core layer having an index of refraction n
c
. One then imagewise exposes the light-transmissive core layer to actinic radiation and develops the photosensitive core layer to remove non-image areas of the photosensitive core layer and not remove image areas of the photosensitive core layer, thus forming a patterned, light-transmissive optical
Beeson Karl
Boudoughian George
Eldada Louay
Pant Deepti
Corning Incorporated
Knauss Scott
Roberts & Mercanti LLP
Sanghavi Hemang
LandOfFree
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