Optical: systems and elements – Single channel simultaneously to or from plural channels – By refraction at beam splitting or combining surface
Reexamination Certificate
2002-01-31
2004-11-09
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By refraction at beam splitting or combining surface
C385S033000, C385S052000
Reexamination Certificate
active
06816317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical collimators, and more particularly, to collimators for precise alignment of optical paths and method of making same.
2. Background Art
Optical collimators have been widely used in optical fiber communications networks, systems and devices to collimate light transmitted by optical fibers, in order to form substantially parallel light beams in free space in various types of optical devices, especially non-integrated optical devices, including, for example, optical switches, isolators, attenuators, beam splitters and beam combiners. Collimators perform an important function of preventing excessive insertion loss due to dispersion of light beams in free space in these optical devices.
FIG. 1
shows a side sectional view of a conventional collimator with a graded index (GRIN) lens for collimating a light beam transmitted by an optical fiber. In
FIG. 1
, a section of optical fiber
2
has a terminal
4
connected to a capillary
6
, which has an index of refraction n
1
. The capillary
6
typically has a cylindrical shape with a center axis
8
. In a conventional collimator with a GRIN lens
12
, the capillary
6
typically has an end surface
10
which is slanted slightly off the normal to the center axis
8
, in order to prevent total reflection of an incoming light beam received from the optical fiber
2
back to the optical fiber. The GRIN lens
12
also typically has a cylindrical shape centered about the axis
8
and an end surface
14
opposite the end surface
10
of the capillary
6
.
In a conventional collimator, the end surface
14
of the GRIN lens
12
is also slanted slightly off the normal to the center axis
8
. A gap
16
is typically provided between the end surface
10
of the capillary
6
and the end surface
14
of the GRIN lens
12
. Both of these end surfaces may be slanted at an angle of about 8° off the normal to the center axis
8
, for example, and are made to be substantially parallel to each other. In a conventional collimator, the gap
16
is typically filled with a gas such as air, which has an index of refraction n
2
, while the GRIN lens
12
has an index of refraction n
3
. In a conventional collimator equipped with a GRIN lens, the index of refraction n
3
of the GRIN lens is typically different from the index of refraction n
1
of the capillary
6
because they are made of different materials. Because of the differences between the indices of refraction n
1
and n
2
at the end surface
10
of the capillary
6
and between the indices of refraction n
2
and n
3
at the end surface
14
of the GRIN lens
12
, an incoming light beam that enters the capillary
6
along the center axis
8
typically deviates from the center axis
8
at an angular deviation &agr; with respect to the center axis when the light beam exits the GRIN lens
12
.
Both the capillary
6
and the GRIN lens
12
are enclosed by a cylindrical metal sleeve
18
, which may be made of gold plated stainless steel, for example, with a inner cylindrical surface
20
and an outer cylindrical surface
22
centered about the center axis
8
. One or more concentric cylindrical layers of protective materials may be provided between the inner surface
20
of the metal sleeve
18
and side walls of the capillary
6
and the GRIN lens
12
, depending upon the construction of the collimator. Because of process variations in the manufacturing of a conventional collimator such as the one shown in
FIG. 1
, slight variations in the angles of the slanted end surfaces
10
and
14
of the capillary
6
and the GRIN lens
12
may result in unpredictability of the angular deviation &agr; of the output light beam
24
with respect to the center axis
8
of the collimator.
Furthermore, because the cylindrical collimator may be rotated unpredictably when it is assembled to an optical device, the direction of the output light beam
24
emanating from the collimator is even more unpredictable. In addition, the incoming light beam that enters the capillary
6
of the collimator from the optical fiber
2
may not be perfectly aligned with the center axis
8
of the collimator, thereby causing a translational offset &Dgr; in addition to the angular deviation &agr; with respect to the center axis. Other process variations such as tolerance of GRIN lens specifications may also contribute to the unpredictability of the direction of the output light beam emanating from the collimator.
When conventional collimators such as the one shown in FIG.
1
and described above are assembled to an optical device in which at least some of the light beams need to travel in free space between the collimators, alignment of light beams between different collimators can be very difficult and time-consuming. Translational offset and angular deviation of light beams emanating from collimators usually exist and are usually unpredictable regardless of the types of lenses used, such as conventional GRIN lenses, ball lenses or C lenses, even if they are manufactured with tight specifications. An output light beam emanating from a conventional collimator typically has a very small spot size with a diameter as little as 200 &mgr;m, for example. Therefore, even a slight offset or deviation may cause misalignment of optical paths between collimators in an optical device.
FIG. 2
illustrates a simplified sectional view of a typical non-integrated optical device, which may be an optical switch, an isolator, an attenuator, a beam splitter or a beam combiner, for example, with two collimators
26
and
28
serving as two optical ports of the device. An optical device element
30
may be movably positioned between the collimators
26
and
28
. The optical device element
30
may be a prism or mirror if the optical device is an optical switch, or an attenuator or isolator element if the optical device is an isolator or attenuator, for example. The optical device typically has a metal packaging
32
for enclosing the optical element
30
. In
FIG. 2
, the collimators
26
and
28
are fixed to sidewalls
34
and
36
of the metal packaging
32
, respectively. The collimators may be fixed to the side walls of the packaging in various conventional manners, for example, by using epoxy gluing, tin soldering or laser welding techniques.
In a typical non-integrated optical device, such as a multi-port optical switch, the collimators
26
and
28
may be placed far from each other, with a distance measured in centimeters. The distances between different collimators in a multi-port optical device make optical alignment between the collimators even more difficult. A light beam travelling in free space within an optical device typically has a very narrow beam width that produces a very small light spot with a Gaussian distribution, with negligibly low light levels outside the spot area. A receiving collimator may not collect enough optical energy even if it is slightly out of alignment with the optical path of the light beam emanating from a transmitting collimator, thereby resulting in a huge loss of optical signals.
Alignment of collimators may be achieved in a typical non-integrated optical device by trial and error, although the labor intensiveness of such an approach is self-evident. The problem of alignment using the trial-and-error approach is exacerbated further in a multi-port optical device such as an M×N optical switch, which requires precise alignment of many different combinations of optical paths between the collimators through different combinations of optical switching elements, such as tilted mirrors or prisms. The problem associated with optical alignment is a major factor for the high cost and slow production rate of typical non-integrated multi-port optical switches at the present time.
Furthermore, when the collimators are fixed to the packaging of a typical optical device, whether by using epoxy glue, tin solder or laser welding, an assembly technician may need to continually adjust the orientation of each of the collimators while g
Mao Zhongming
Shen Pai-Sheng
Law Offices of David Pai
Lightel Technologies Inc.
Mack Ricky
Pai C. David
LandOfFree
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