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Device for Coupling Laser Beams into High Index Semiconductor Waveguides

IP.com Disclosure Number: IPCOM000107957D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 129K

Publishing Venue

IBM

Related People

Blacha, A: AUTHOR [+2]

Abstract

Techniques for coupling optical beams into optical waveguides are important for characterization purposes (measurement of the propagation constant, refractive indices, layer thickness, attenuation). For the characterization of waveguides in ternary or quarternary semiconductor compounds, i.e., key materials for applications in integrated optics, devices suitable for coupling light into materials with high refractive index (n>3) are required. However, coupling of light into high index materials using the known coupling methods, namely the prism coupling (1) and grating coupling (2) method, is not feasible, or impractical.

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Device for Coupling Laser Beams into High Index Semiconductor Waveguides

       Techniques for coupling optical beams into optical
waveguides are important for characterization purposes (measurement
of the propagation constant, refractive indices, layer thickness,
attenuation). For the characterization of waveguides in ternary or
quarternary semiconductor compounds, i.e., key materials for
applications in integrated optics, devices suitable for coupling
light into materials with high refractive index (n>3) are required.
However, coupling of light into high index materials using the known
coupling methods, namely the prism coupling (1) and grating coupling
(2) method, is not feasible, or impractical.

      A prism coupler suitable for coupling an optical beam via a
thin air gap into dielectric optical waveguides is described in (1).
A necessary condition for beam coupling requires that the prism
refractive index is higher than the index of the waveguide core.
However, low loss prism materials appropriate for coupling light into
high index semiconductor material is simply not available. The
grating coupling method which uses a grating etched into the
waveguide would be suitable for semiconductor waveguides, but the
required grating period is of the order of 0.3 micron, thus requiring
complicated holographic recording methods. Furthermore, the waveguide
samples need extra processing for coupling purposes.

      The coupling scheme disclosed here combines elements of the
prism coupling method and the grating coupling method: a
semiconductor waveguide coupler is described based on a thick
transparent liquid-phase epitaxial layer of lower index than the
waveguide layer where the phase-matching condition is established via
a low-periodicity grating suitable for conventional lithographic
processing.

      The figure shows the proposed waveguide coupling device based
on the Al(x)Ga(1-x)As system. The concept can similarly be extended
to other semiconductor compounds. The device consists of a thick
(approximately 200 micrometer) transparent layer 1 of Al(x)Ga(1-x)As
with x = 0.5 - 0.6, grown by liquid-phase epitaxy (LPE) on a GaAs
substrate 2. In addition, the surface is provided with an etched
grating 3 of periodicity d. The substrate 2 is cleaved or polished
into chips approx.  1 mm x 1 mm in size and bonded to a piston
4 for mounting in a test fixture. To minimize unwanted reflections,
the entrance and exit faces are provided with an antireflection
coa...