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Browse Prior Art Database

Electronically Variable Tap for Multimode Planar Ribbon Optical Waveguides

IP.com Disclosure Number: IPCOM000085157D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Heidrich, PF: AUTHOR [+2]

Abstract

While optical fibers are suitable for long distance, low-loss connections, planar structures are necessary for signal processing and input and output functions. One of the basic components of any signal processing or communication circuit is an electronically variable or switchable tap. The illustrated apparatus provides efficient multimode coupling between two ribbon waveguides.

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Electronically Variable Tap for Multimode Planar Ribbon Optical Waveguides

While optical fibers are suitable for long distance, low-loss connections, planar structures are necessary for signal processing and input and output functions. One of the basic components of any signal processing or communication circuit is an electronically variable or switchable tap. The illustrated apparatus provides efficient multimode coupling between two ribbon waveguides.

An isometric projection of the apparatus is shown in Fig. 1, wherein two ribbon waveguides 10 and 20 are deposited in a substrate 40 and joined in their medial region by a coupling layer 30, the cross section of which is shown in Fig.
2. The relative indices of refraction of the optical materials constituting the substrate 40, the two waveguides 10 and 20 and the coupling region 30 are shown in Fig. 3 by corresponding numerical subscripts.

The relationship, n(10) > n(20) > n(30) > n(40) is shown graphically with the index scale reversed. The "effective depths" of the several regions are determined by a combination of the refraction index and the physical depth of the surface layers. The structure presupposes the existence of waveguides with sufficiently smooth sides, so the lower order modes can exist without exciting higher order modes when coupling between the fibers is not desired.

With respect to the modes, Fig. 3 shows a mode diagram in the various regions. In constructing this, an analogy has been drawn to quantum mechanics, where the wave function equations in quantum mechanics and the energy profile are analogous to mode function equations in an optical guide and the dielectric constant profile (index of refraction squared). Thus, the mode diagram (or "energy level diagram") for modes with different values of k/2/(x) equates "energ...