Planar optical waveguide element, chromatic dispersion compensator, optical filter, optical resonator and methods for designing the element, chromatic dispersion compensator, optical filter and optical resonator

Abstract

There is provided a planar optical waveguide element in which an optical waveguide comprises a core, and a gap portion that is positioned in a center of a width direction of the core so as to extend in a propagation direction of guided light, and that has a lower refractive index than that of the core; and wherein the core comprises two areas that are separated by the gap portion, and a single mode optical waveguide, in which a single mode is propagated span crossing these two areas, is formed.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This is a Continuation Application of International Application No. PCT / JP2009 / 053763, filed on Feb. 27, 2009, which claims priority to Japanese Patent Application No. 2008-051346, filed Feb. 29, 2008. The contents of the aforementioned applications are incorporated herein by reference.TECHNICAL FIELD[0002]Apparatuses and embodiments described herein related to a planar optical waveguide element and design method thereof, in which the planar optical waveguide element can be used in various applications such as a chromatic dispersion compensator, an optical filter and an optical resonator and the like.BACKGROUND ART[0003]The following are examples of chromatic dispersion compensation in an optical waveguide structure for which polarization dependence is not considered.[0004]An element having a plurality of Bragg grating elements in which the period changes spatially such that chromatic dispersion is compensated in a plurality of wavelength ...

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Benefits of technology

[0036]According to the exemplary aspect described in (1) above, because the mode field diameter of the fundamental mode expands, it is possible to inhibit the effects (i.e., scattering loss) on the optical characteristics from roughness of the core-side walls which are formed from a high refractive index material, in which the roughness is unavoidably generated in the manufacturing process.

[0037]According to the exemplary aspect described in (2) above, a planar optical waveguide element having a Bragg grating pattern can reduce the polarization dependence of the optical characteristics.

[0038]According to the exemplary aspect described in (3) above, it is possible to make the waveguide length shorter than a sampled grating.

[0039]According to the exemplary aspect described in (4) above, compared to a related art chirped grating in which the pitch changes gradually, tolerance control in the manufacturing process is easier and this contributes to an improvement in the manufacturing yield.

[0040]According to the exemplary aspect described in (5) above, compared to a related art embedded type of optical waveguide with high relative refractive index difference which is only formed from two portions, namely, a cladding and a core formed from a high refractive index material, because the confinement of light in an inner side core which is formed from a high refractive index material is weaker, it is possible to inhibit the effects (i.e., scattering loss) on the optical characteristics from roughness of the inner-side of core-side wails, in which the roughness is unavoidably generated in the manufacturing process.

[0041]According to the exemplary aspect described in (6) above, it is possible to achieve a chromatic dispersion compensator having little variation in the optical characteristics.

Problems solved by technology

However, in the fiber Bragg grating, because there are limits to the range over which the refractive index can be changed in order to manufacture a grating pattern, an operation in which the aforementioned spectrum characteristics are apodized by applying an inverse Fourier transform is also carried out so that these limits are not exceeded.

On the other hand, measures to deal with (U) have the problems that, because the transmission line becomes more complex as the number of optical components increases, they lead to increased size, increased complexity, and increased costs for the optical communication equipment.

Solving the above described problems is difficult using conventional technology.

Accordingly, it is not possible for the technology of this document to be applied to the design of chromatic dispersion compensators that are formed from high refractive index optical waveguides in which the polarization dependence on the substrate has been reduced.

Accordingly, the removal of interference between wavelength channels has not been considered in this design method, therefore the problem arises that the chromatic dispersion characteristics are deteriorated by the interference between wavelength channels.

However, this is not possible in the design method of Patent document 1.

Accordingly, it is not possible for the technology of this document to be applied to the design of chromatic dispersion compensators that are formed from high refractive index optical waveguides in which the polarization dependence on a substrate is reduced.

Accordingly, the technology of Patent document 2 is not suitable for the purpose of attaining miniaturization by shortening the grating length as much as possible without reducing the reflectance by widely changing the effective refractive index in a reflective optical waveguide.

In the simple optical waveguide structure of this document, it is only possible to compensate a dispersion slope, and it is not possible to compensate chromatic dispersion.

Because of this, it is not possible to achieve miniaturization by using the technology of this document.

This chromatic dispersion compensator cannot be used to compensate chromatic dispersion in a plurality of channels for the purpose of application to wavelength multiplexing optical fiber communication.

However, the technology of Patent document 5 cannot deal with multichannel chromatic dispersion.

Accordingly, this technology cannot be used to compensate chromatic dispersion in a long distance (e.g., 40 km) optical fiber transmission line for the purpose of application to wavelength division multiplexing optical fiber communication.

Accordingly, it is not possible for the technology of this document to be applied to the design of chromatic dispersion compensators that are formed by high refractive index optical waveguides in which the polarization dependence in a substrate is reduced.

Moreover, because waveguide light is distributed more in the low refractive index portion than the high refractive index portion, this structure is not suited to the purpose of making the optical characteristics variable by making the refractive index of the high refractive index portions variable.

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