Digital Signal Processing Reference
In-Depth Information
and an optical fiber; and a tapered guiding portion for converting mode size
between the fiber and the planner waveguide. They claim that this design may
be implemented as the grating portion which consists of a second grating section
having:
1. Uniform periods,
2. Linearly chirped periods, or
3. Optical fiber, which may be positioned normal to a surface of the grating por-
tion [
11
].
A similar coupler is shown in Fig. (
4.5
).
The authors [
12
] introduced a waveguide coupling probe for sending/receiving
light into/from an optical waveguide on a substrate, this investigation comprises:
1. An optical element for guiding the light in the propagation direction, and
2. A facet where the light enters or exits the optical element.
The waveguide coupling probe is provided for being placed with the propagation
direction under a predetermined angle orthogonal to the waveguide. In [
13
], Zhaolin
Lu and Dennis W. Prather reported an optical coupler for parallel coupling from a
single-mode optical fiber or fiber ribbon, into SOI waveguide for integration with
silicon optoelectronic circuits. The optical coupler incorporates the advantages of the
vertically tapered waveguides and prism couplers, yet offers the flexibility of pla-
nar integration. Intel Corporation has recently introduced a method and apparatus for
efficient coupling between a silicon photonic chip and an optical fiber [
14
].
4.5 Nonlinear Optics
The response of any dielectric to light that becomes nonlinear for strong electro-
magnetic fields, and optical fibers are no exemption. Basically, the origin of non-
linear response is related to inharmonic motion of bound electrons in the influence
of an applied field. As a result, the total polarization
P
induced by electric dipoles
is not linear in the electric field
E
, but suit the more general relation,
χ
(
1
)
·
E
+ χ
(
2
)
:
EE
+ χ
(
3
)
.
EEE
+···
(4.1)
P
= ε
0
Fig. 4.5
Sample structures of
optical coupling device [
14
]
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