Appeal No. 1997-4033
Application No. 08/589,584
voltage for the wave-guide is reduced when the band gap
wavelength of the wave-guide material approaches the
wavelength of the incident light; however, in that
condition, propagation loss from the wave-guide is high
(see page 4, lines 8-17 of the specification).
The Brief (at 2-3) contains the following description of the
structure of the invention, which correctly states that a
wider mask stripe produces a higher band gap wavelength but
appears to incorrectly state that the wider mask stripe and
higher band gap wavelength are associated with a thinner MQW
structure:
The present invention achieves [the above-noted]
previously conflicting aims by forming the optical
wave-guide as a multiple quantum well (MQW)
structure having controlled thickness in the central
active region relative to the terminal passive
regions. In particular, the MQW structure is
relatively thinner in the central active region and
relatively thicker in the terminal passive regions,
such that, correspondingly, the band gap wavelength
of the optical wave-guide is relatively higher in
the active region and relatively lower in the
passive regions. This allows the band gap
wavelength in the active region to be set to a value
desirably close to that of the incident light which
will pass through the wave-guide, while keeping the
band gap wavelength in the passive regions at a
desirably low level to minimize wave-guide loss. The
controlled variation in the thickness of the optical
wave-guide structure is achieved by forming the MQW
layers by a technique termed Metal Organic Vapor
Phase Epitaxy (MOVPE), using a mask stripe pattern
as shown for example in present Fig. 3. That is,
the relatively wider mask stripes 201 in active
3
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