Biomedical Engineering Reference
In-Depth Information
Guide
Al
x
Ga
1 -
x
As
Al
y
Ga
1 -
y
As
Cladding
y
>
x
Substrate
Raised RIB guide
Guide
Al
y
Ga
1 -
y
As
Cladding
Al
x
Ga
1 -
x
As
Al
z
Ga
1 -
z
As
y
≥
z
>
x
Cladding
Substrate
Buried encapsulated guide
Cladding
Al
z
Ga
1 -
z
As
Al
x
Ga
1 -
x
As
Guide
Al
y
Ga
1 -
y
As
y
≥
z
>
x
Cladding
Substrate
Buried strip-loaded waveguide
FIGURE 5.15
Fundamental AlGaAs waveguides.
presents significant difficulty when considering electronic and full optical
integration in conjunction with the waveguides.
For the above reasons the buried strip-loaded structure may be the opti-
mum approach. This structure has better vertical confinement which keeps
the guided energy away from the surface and minimizes scattering losses.
The fact that the etched boundaries are located within the cladding layer
also reduces their effect on scattering losses, particularly in comparison to
the raised rib guide. The additional layering provides for the incorporation
of fabrication features such as a stop etch layer. In addition this structure
gives better p-n junction characteristics when an electro-optic modulator
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