Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2002-08-06
2004-08-31
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S014000, C385S130000, C385S131000
Reexamination Certificate
active
06785449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a multi-layer optical planar waveguide which is vertically coupled using multimode interference (MMI) couplers and to the method of manufacturing the same. The purpose of this invention is to increase the degree of integration on the multi-layer optical planar waveguide by applying the concept of via holes of the multi-layer printed circuit board (MLPCB) used in electronic circuits to the optical waveguide devices.
2. Description of the Prior Art
As the technology of optical communications are advanced, various optical planar waveguide technologies have been developed in order to fabricate various integrated optical components such as optical couplers optical switches, optical amplifiers, and so on.
Recently, as the optical planar waveguide has been actively applied in optical communications, the higher integration of the optical planar waveguide devices and the integration of various optical planar waveguide devices on an optical board are frequently demanded. For example, U.S. Pat. No. 6,115,515 (hereinafter, ‘reference document 1’) entitled “Optical Device Mounting Board” issued to M. Itoh, et al. on Sep. 5, 2000 discloses a method by which various optical planar waveguide devices are transversely arranged on an optical board and connected respectively.
The reference document 1 discloses the invention allowing simple attachment of photoelectric devices such as the optical waveguide device as indicated in the title. In the reference document 1, various optical planar waveguide devices are arranged on a mounting board on which grooves are engraved, so that the waveguides are easily connected. This technical idea is one of the methods to connect the optical planar waveguide devices liven though this technical idea can partly contribute to overcoming the difficulty in the connection of various optical waveguide devices, the process should accompany the economical problem in using the expensive aligning equipments, the problem of long process time and the complexity in fabrication. Also, as in the reference document 1 there is a limit in integration using the technical idea in which the optical planar waveguides are transversely connected on a board.
The multi-layer optical planar waveguide with the vertical structure can be another way to simplify the integration of waveguide devices. 1, or example, the multi-layer optical planar waveguide of the vertical structure was disclosed in “Double-Bonded InP—InGaAsP Vertically Coupler 1:8 Beam Splitter” (hereinafter, ‘reference document 2’) by M. Raburn, et al in IEEE Photon. Technol. Lett. (2000) and “InP—InGaAsP Wafer-Bonded Vertically Coupled X-Crossing Multiple Channel Optical Add-Drop Multiplexer” (hereinafter, ‘reference document 3’) by M. Raburn, et al in IEEE Photon. Technol. Lett. (2001).
The reference document 2 discloses a 1:8 beam splitter in which optical planar waveguides of multiple layers are formed in order to increase the degree of integration. The reference document 2 tried to improve the degree of integration of the optical planar waveguide device, by using the coupling characteristics of evanescent field interference between the upper and the lower optical planar waveguides, in which the gap between the upper and the lower layers is narrower than 1 &mgr;W, or narrower than the width of the waveguide itself. In addition, the reference document 3 is about a filter using optical waveguides of two layers and discloses a technical idea in which the degree of integration of the optical planar waveguide device is improved using the coupling characteristics of evanescent field interference between the upper and the lower waveguides as in the reference document 2. These prior arts, however, have a significant limitation that the optical planar waveguide on the upper and the lower layers is highly dependent each other since the gap between the upper and the lower layers is too narrow. There should be high interference between the layers due to the evanescent field with such a narrow gap.
In addition, technologies about the multi-layer optical planar waveguide with vertical structure include “Vertically Stacked Coupler and Serially Grafted Waveguide: Hybrid Waveguide Structures Formed Using an Electro-Optic Polymer” (hereinafter, ‘reference document 4’) by T. Watanabe, et al in ‘J. Appl. Phys. (1998), and U.S. Pat. No. 6, 282, 335 (hereinafter, ‘reference document 5’) entitled “Thermo-Optic Switch” (Aug. 28, 2001).
The reference document 4 discloses an electro-optic switch with relatively low loss using two layer optical waveguides with the lower layer made of electro-optic material, whose loss is generally quite high, and the upper layer made of passive material with low loss. In addition, the reference document 5 discloses a thermo-optical switch in which the main waveguide is formed with glass and in which polymer waveguide with high thermo-optical coefficient is transversely arranged on the glass waveguide, so that light travels from the glass waveguide to the polymer waveguide controlled by the heat applied to the polymer. These two reference documents 4 and 5, however, have the same limitation that the optical planar waveguide on the upper and the lower layers is highly dependent each other since the gap between the upper and the lower layers is too narrow. There should be high interference between the layers due to the evanescent field with such a narrow gap.
As described above, the documents referred made some progress in implementing a switch or a filter using the multi-layer optical planar waveguide structure but have a significant limit in designing because the layers cannot be operated independently in case they are overlapped while the gap between the upper and lower layers should be maintained as narrow as possible to couple the layers directly by the evanescent field interference.
Meanwhile, a technical idea of implementing a multi-layer optical planar waveguide of an independent structure includes “Multilevel Registered Polymeric Mach-Zehnder Intensity Modulator Array” (hereinafter, ‘reference document 6’) by T. A. Tumolillo, Jr. et al in Appl. Phys. Lett” (1993). In the reference document 6, a multi-layer optical planar waveguide device with little interference between the upper and lower layers is implemented. However, the reference document 6 does not disclose how to connect the upper and lower layers. Therefore, there is a need for a technology by which the optical waveguide on the upper and the lower layers can be vertically connected while the interference between the each layer of the multi-layer optical planar waveguide is minimized.
SUMMARY OF THE INVENTION
The present invention is contrived to solve the above problems and an object of the present invention is to provide a multimode interference coupler capable of connecting the optical waveguides on the upper and the lower layers with high coupling ratio at a specialized spot while maintaining the interference between the each layer of the multi-layer optical planar waveguide out of the spot as minimum by keeping the each layer at an enough distance.
Another object of the present invention is to provide a multimode interference coupler with at least one stepped structure in order to increase the coupling ratio between the optical waveguides on the upper and the lower layers.
Still another object of the present invention is to provide a multi-layer optical planar waveguide implemented using a multimode interference coupler of the stepped structure.
Still another object of the present invention is to provide a method of manufacturing a multi-layer optical planar waveguide with a multimode interference coupler.
In order to accomplish the above object, a multimode interference coupler according to the present invention, is characterized in that it comprises an optical waveguide for a multimode interference coupler inserted at a specialized region between a lower optical waveguide and an upper optical waveguide so that the lower optical waveguide and the upper optical waveguid
Ahn Joon Tae
Cho Doo Hee
Kim Kyong Hon
Lee Jong Moo
Lee Myung Hyun
Blakely & Sokoloff, Taylor & Zafman
Electronics and Telecommunications Research Institute
Palmer Phan T. H.
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