23-07-2012, 03:22 PM
MATERIALS AND FABRICATION ISSUES OF OPTICAL FIBER ARRAY
[attachment=28531]
Abstract.
Photonic devices are becoming widespread as an advanced information-communications
network of the 21st century. With the increased use of photonic devices, there is a need for
optical connecting path between photonic devices. The optical fiber array is such a smart approach
for all optical functionality of the optical chip without any need of electrical wiring. However,
it remains a challenge to develop the reliable fabrication know-how in manufacturing of fiber array.
This paper will discuss the issues required in the reliable fabrication of optical fiber array, and
integrating them to address the future needs of the information and communication technology
sector. Issues affecting the quality of the optical fiber array mainly include the material selection,
processing condition, and bonding technique. The advantages and disadvantages of each materials
and fabrication method are discussed with the major failure issues. The findings can serve as
a guide for optimizing the materials and process parameters in the reliable fabrication of optical
fiber array in Photonic industry.
INTRODUCTION
Fiber optic communications have been developed
since optical fibers were fabricated in 1970 and
playing an important role in development of modern
information technology. Planar lightwave circuit
(PLC) technology based optical communication
offers the advantages of low cost, ease in handling,
highly reliable, multi-functionalities, low loss
characteristics and high production through-put. In
order to implement such optical fiber communication
system, many passive optical devices are used
[1]. Now-a-days such passive devices are fabricated
on silicon wafer [2]. To package such devices
for commercialization, individual PLCs must
be cut from the wafer and fibers must be attached
to the input-output (IO) ports. In such an approach,
it needs to align each fiber individually to the corresponding
IO port of the optical chip. This is very
desirable especially when the port counts is very
large, causing a very high production.
STRUCTURE OF FIBER ARRAY
Fig. 1 is the schematic cross-section of a single
fiber on V-groove block for sub-micron positioning
accuracy. However, a typical fiber array consists
of 8, 16, 32, and 48 symmetrical single fiber in
V-groove. The fiber array packages are mainly
made up of four different parts: the V-groove, fibers,
lid glass, and bonding materials [5].
Wet etching of silicon wafer
In general, due to different orientations of [(100)
and (110)] silicon wafer, it can be etched for fabrication
V-groove. The first step in the proposed fabrication
process is to grow a masking layer to be
used for the anisotropic etch of the V-groove. Thermally
grown SiO2 on same silicon as mask is suitable
for this purpose, whereas other types of mask
also can be used. A combination of wet and dry
oxidation method can be used to grow 1.5 μm of
silica oxide [8]. This oxide layer is then patterned
using hydrofluoric acid (HF) to form the mask for
the anisotropic etch. Anisotropic etchants of silicon
include potassium hydroxide (KOH), tetramethyl
ammonium hydroxide (TMAH), and ethylene
diamine pyrocatechol (EDP) [9]. If the mask
opening is accurately aligned with the primary orientation
flat, i.e., the [110] direction, after prolonged
etching the {111} family of planes is exposed down
to their common intersection and the (110) plane
disappears creating a V-groove with <111> oriented
sidewalls at 54.74o to the (100) surface [9-10]. Although
this traditional Silicon wet etching technique
is easier and less expensive, however has some
limitations.
Machining with V-shaped
diamond wheel
It is a typical transferring process in which material
is removed by the abrasive grains of two edge surfaces
of the machining wheel to form the desired
V-grooves. The machined V-groove can be obtained
on both brittle and ductile materials keeping
the precision of submicron level. The typical materials
in making machined V-groove are pyrex, silica
glass, zirconia, and quartz. In general, cutting effects
during the V-grooves machining process result
from interaction between the actual cutting
points on the abrasive grains at the wheel surface
and work piece materials. The machining wheel
topography, macroscopic wheel shape, especially
the edge sharpness of the wheel, significantly influences
the profile accuracy of machined Vgrooves
[11].
Types of fiber used
Optical fibers are classifies as Single Mode, Multimode
and Polarization Maintaining (PM) fibers.
Again on the material point of view, it can be in two
class; glass optical fiber (GOF) and polymer optical
fiber (POF) [14]. The typical diameter of the
single mode & multimode fibers are 125 μm and
250 μm. The V-Groove array assemblies can be
made with all types of fibers and precise passive
alignment of individual fibers. The V-grooves are
designed according to the fiber dimension.
[attachment=28531]
Abstract.
Photonic devices are becoming widespread as an advanced information-communications
network of the 21st century. With the increased use of photonic devices, there is a need for
optical connecting path between photonic devices. The optical fiber array is such a smart approach
for all optical functionality of the optical chip without any need of electrical wiring. However,
it remains a challenge to develop the reliable fabrication know-how in manufacturing of fiber array.
This paper will discuss the issues required in the reliable fabrication of optical fiber array, and
integrating them to address the future needs of the information and communication technology
sector. Issues affecting the quality of the optical fiber array mainly include the material selection,
processing condition, and bonding technique. The advantages and disadvantages of each materials
and fabrication method are discussed with the major failure issues. The findings can serve as
a guide for optimizing the materials and process parameters in the reliable fabrication of optical
fiber array in Photonic industry.
INTRODUCTION
Fiber optic communications have been developed
since optical fibers were fabricated in 1970 and
playing an important role in development of modern
information technology. Planar lightwave circuit
(PLC) technology based optical communication
offers the advantages of low cost, ease in handling,
highly reliable, multi-functionalities, low loss
characteristics and high production through-put. In
order to implement such optical fiber communication
system, many passive optical devices are used
[1]. Now-a-days such passive devices are fabricated
on silicon wafer [2]. To package such devices
for commercialization, individual PLCs must
be cut from the wafer and fibers must be attached
to the input-output (IO) ports. In such an approach,
it needs to align each fiber individually to the corresponding
IO port of the optical chip. This is very
desirable especially when the port counts is very
large, causing a very high production.
STRUCTURE OF FIBER ARRAY
Fig. 1 is the schematic cross-section of a single
fiber on V-groove block for sub-micron positioning
accuracy. However, a typical fiber array consists
of 8, 16, 32, and 48 symmetrical single fiber in
V-groove. The fiber array packages are mainly
made up of four different parts: the V-groove, fibers,
lid glass, and bonding materials [5].
Wet etching of silicon wafer
In general, due to different orientations of [(100)
and (110)] silicon wafer, it can be etched for fabrication
V-groove. The first step in the proposed fabrication
process is to grow a masking layer to be
used for the anisotropic etch of the V-groove. Thermally
grown SiO2 on same silicon as mask is suitable
for this purpose, whereas other types of mask
also can be used. A combination of wet and dry
oxidation method can be used to grow 1.5 μm of
silica oxide [8]. This oxide layer is then patterned
using hydrofluoric acid (HF) to form the mask for
the anisotropic etch. Anisotropic etchants of silicon
include potassium hydroxide (KOH), tetramethyl
ammonium hydroxide (TMAH), and ethylene
diamine pyrocatechol (EDP) [9]. If the mask
opening is accurately aligned with the primary orientation
flat, i.e., the [110] direction, after prolonged
etching the {111} family of planes is exposed down
to their common intersection and the (110) plane
disappears creating a V-groove with <111> oriented
sidewalls at 54.74o to the (100) surface [9-10]. Although
this traditional Silicon wet etching technique
is easier and less expensive, however has some
limitations.
Machining with V-shaped
diamond wheel
It is a typical transferring process in which material
is removed by the abrasive grains of two edge surfaces
of the machining wheel to form the desired
V-grooves. The machined V-groove can be obtained
on both brittle and ductile materials keeping
the precision of submicron level. The typical materials
in making machined V-groove are pyrex, silica
glass, zirconia, and quartz. In general, cutting effects
during the V-grooves machining process result
from interaction between the actual cutting
points on the abrasive grains at the wheel surface
and work piece materials. The machining wheel
topography, macroscopic wheel shape, especially
the edge sharpness of the wheel, significantly influences
the profile accuracy of machined Vgrooves
[11].
Types of fiber used
Optical fibers are classifies as Single Mode, Multimode
and Polarization Maintaining (PM) fibers.
Again on the material point of view, it can be in two
class; glass optical fiber (GOF) and polymer optical
fiber (POF) [14]. The typical diameter of the
single mode & multimode fibers are 125 μm and
250 μm. The V-Groove array assemblies can be
made with all types of fibers and precise passive
alignment of individual fibers. The V-grooves are
designed according to the fiber dimension.