Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2001-07-05
2003-12-30
Zarroli, Michael C. (Department: 2839)
Optical waveguides
With optical coupler
Particular coupling structure
C385S140000
Reexamination Certificate
active
06671439
ABSTRACT:
TECHNICAL FIELD
The invention relates to an integrated waveguide arrangement which includes a waveguide region, a foreign region and a temperature-adjustment unit.
BACKGROUND ART
Typically, the waveguide region consists of glass, for example SiO
2
, and includes a waveguide with glass core and glass sheath. The refractive index of the glass cores is greater than the refractive index of the glass sheath. The waveguide is such that it carries an electromagnetic wave with low losses. The foreign region consists of a material other than glass and extends in the vicinity of the waveguide. A typical distance between foreign region and waveguide is, for example, 1 micrometer (&mgr;m) or 2 &mgr;m.
The temperature-adjustment unit is used to heat and/or cool the foreign region, so that it is possible to influence the wave propagation in the waveguide. A typical working range of the temperature-adjustment unit is between −40° C. and 150° C.
A waveguide arrangement of this type is known form the article “Hybrid switches offer the best of both worlds”, fiber systems, 05/2000, Vol.4, No.4, p.15, by Pauline Rigby. The wave arrangement explained in that document includes two waveguides made from glass which are connected by a waveguide made from polymer.
When producing waveguides from glass, the procedure is usually as follows:
1. An intermediate layer of silicon dioxide, which is known as a buffer layer, is applied to a silicon substrate.
2. A core layer, the refractive index of which is greater than the refractive index of the silicon dioxide layer, is applied to the silicon dioxide layer. The core layer likewise consists of silicon dioxide.
3. Regions at which there are to be no waveguide cores are removed from the core layer, usually by dry-chemical etching.
4. The remaining waveguide cores of the core layer and those areas of the intermediate layer which have been exposed in the previous process step are coated with a sheath coating of silicon dioxide which has the same refractive index as the silicon dioxide of the intermediate layer. This process is also known as cladding.
The known integrated waveguide arrangement is hybrid in the sense that it includes a waveguide made from glass and a waveguide made from polymer. Waveguides made from glass are distinguished by low transmission losses when carrying the waves. By contrast, waveguides made from polymer have a significantly higher thermo-optical coefficient than waveguides made from glass and are therefore more suitable for switching operations with the aid of the temperature-adjustment unit. The thermo-optical coefficient is a measure of the change in the refractive index as a function of the change in temperature of a material. For SiO
2
, the thermo-optical coefficient is approximately dn/dT=1e−6/K. On account of using both materials, the hybrid approach exploits both advantages. The result is a switching element which operates with a low switching power and low transmission losses.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an integrated waveguide arrangement which is of simple structure and in which the advantages of the hybrid structure are retained. Moreover, it is intended to provide a process for producing a waveguide arrangement of this type.
The object relating to the waveguide arrangement is achieved by means of a waveguide arrangement having the features of patent claim 1. Refinements are given in the subclaims.
The invention is based on the discovery that the good properties of a polymer waveguide with regard to the high temperature coefficient are retained even if only the waveguide core consists of polymer. The waveguide sheath can be produced from glass without the transmission properties being changed significantly. Furthermore, the discovery is based on the consideration that materials other than glass, for example polymer, have a better capacity to conduct heat. When using a waveguide core made from a material other than glass in a region consisting of glass, the energy emitted by the temperature-adjustment unit can be concentrated in a smaller area, since less heat is dissipated via the waveguide sheath.
In the waveguide arrangement according to the invention, in addition to the features listed in the introduction, the foreign region is integrated or embedded in the waveguide region. The foreign region forms the region in which switching operations take place with the aid of the temperature-adjustment unit. In the waveguide arrangement according to the invention, waveguides are made from glass apart from the foreign region and therefore have low transmission losses. The foreign region itself consists of a material other than glass, which therefore has a higher thermal conductivity and a greater thermo-optical coefficient.
The integration of the foreign region in the waveguide region facilitates production of the waveguide arrangement. In addition to the process steps listed in the introduction, the following steps are carried out:
5. A trench is etched into the sheath layer.
6. The entire structure is coated with a polymer, for example by means of spinning.
Therefore, during production of the waveguide arrangement according to the invention it is simply necessary to apply a polymer layer. The manufacturing tolerances are low, because a trench of defined depth can be etched with very great accuracy.
The advantages of the hybrid approach are retained in the waveguide arrangement according to the invention. In addition, however, the effect is achieved that the heat which is dissipated by the temperature-adjustment unit is concentrated on the waveguide core made from polymer, since a glass sheath is being used. Also, during cooling operations, heat is initially extracted only from the foreign region. This leads to a reduction in the switching power required.
The refractive index of the material in the foreign region is not critical, since the high thermo-optical coefficient means that it can be set within wide limits with the aid of the temperature-adjustment unit.
The integrated waveguide arrangement according to the invention opens up the route to a large number of new types of waveguide components. Depending on the arrangement of the foreign region with regard to a glass waveguide or with regard to a plurality of glass waveguides, it is possible, inter alia, to construct switching units, coupling units, attenuators and radiators.
In a refinement of the waveguide arrangement according to the invention, the waveguide region is arranged on a planar substrate. On the side which is remote from the substrate, the waveguide region forms a surface which lies approximately parallel to the interface between substrate and waveguide region. The waveguide arrangement can be produced using the technically highly developed lithographic processes. When using the process steps 1 to 4 listed in the introduction, therefore, the waveguide region includes the intermediate layer, parts of the core layer, specifically the waveguide cores made from glass and the sheath covering. On account of flow processes during its application to the side remote from the substrate, the sheath covering has a surface which is approximately parallel to the substrate surface.
In a subsequent refinement, the foreign region is produced from a material with a thermo-optical coefficient, the magnitude of which differs significantly from the magnitude of the thermo-optical coefficient of the glass. By way of example, coefficients which in terms of magnitude are 100 times greater than the thermo-optical coefficient of glass are used. The reference temperature selected, by way of example, is room temperature, i.e. 20° C.
In a further configuration, the material used in the foreign region is a plastic, for example, a polymer. An example of a polymer with a positive thermo-optical coefficient is a fluoroacrylate polymer which contains pentafluorostyrene (PFS), trifluoroethylmethacrylate (TFM) and glycidylmethacrylate (GMA). An example of a polymer with a negative thermo-optical coefficient is benzocyclobutene resin (RCB),
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