Appeal No. 1997-4033
Application No. 08/589,584
to be thinner in the active region than in the passive
regions.
Rolland discloses a Mach-Zehnder modulator which includes
a "singlemode" section that is 2 Fm wide followed by a
"triple-moded" section that is 4 Fm wide, which branches into
a pair of S-rib waveguides 2 Fm wide and 3 Fm deep, which are
rejoined by another 4 Fm branching section, which is followed
by a final 2 Fm wide section (Rolland at 371, 2d col.).
Rolland does not explain how much of the 3 Fm depth of the rib
sections is occupied by the MQW structure. Nor does Rolland
indicate that the MQW structure has different thicknesses in
the active and passive sections.
As already noted, Sasaki explains that MQW thickness and
band gap wavelength are a function of the width of the mask
stripes used to form the MQW layers. Sasaki explains (at 372-
73) that this bandgap energy control technique can be used to
form smooth junctions between active and passive waveguide
layers in various types of monolithically integrated photonic
devices, such as (1) a DFB-LD (Distributed Feedback Laser
Diode) monolithically integrated with an optical modulator and
(2) a three-section tunable DBR (Distributed Bragg Reflector)-
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