Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2001-02-22
2002-11-12
Nguyen, Khiem (Department: 2839)
Optical waveguides
Accessories
External retainer/clamp
C385S033000
Reexamination Certificate
active
06480661
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to optical wavelength division multiplexers/demultiplexers (WDMs)), sometimes termed ADD/DROP filters, and particularly dense wavelength division multiplexers/demultiplexers (DWDMs).
BACKGROUND OF THE INVENTION
The use of optical fibers as a medium for transmission of digital data (including voice) is becoming increasingly more common due to the high reliability and large bandwidth available with optical transmission systems. A well known technique for even further increasing the amount of information which can be carried on a single fiber is wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM). In WDM and DWDM, multiple channels are transmitted on a single fiber simultaneously, each channel being transmitted with a different wavelength of light. The channels can be separated at the receivers with wavelength selective filters. The different channels are combined onto a transmission fiber using components which are commonly termed optical ADD/DROP filters. Typically, each ADD/DROP filter can add (in the case of multiplexing) or drop (in the case of de-multiplexing) one wavelength channel to or from a fiber path.
FIG. 12
is a diagram illustrating a three channel de-multiplexer (or DROP) utilizing two optical ADD/DROP filters
1122
and
1124
to demultiplex an input fiber carrying three (or more) channels to three output fibers, each containing one of the three channels. In particular, an input or common fiber
1112
carries a light beam
1138
A comprising three wavelength channels. In the first ADD/DROP filter
1122
, the input beam
1138
A is input from fiber
1112
through a common port
1113
(so termed because it is the port that corresponds to the beam containing the combined wavelength channels whether the device is being used to multiplex or demultiplex). Common port
1113
is at the front focus of a collimating lens
1126
. The collimating lens may take the form of a gradient index (GRIN) lens, as is well known in the art. In particular, when the beam
1138
A exits input fiber
1112
, the light is not collimated. Lens
1126
collimates the light and directs it onto an interference filter
1128
. Interference filters are well known in the art. In particular, interference filters reflect all light except light in a specific narrow wavelength band. The particular wavelength that will be passed by an interference filter is a function of the angle at which the light strikes the filter (thus, the need for collimating lenses
1126
and
1130
). Thus, filter
1128
is oriented at an angle relative to input fiber
1112
and lens
1126
such that one of the wavelength channels will be transmitted while the other wavelength channels will be reflected. The light beam
1138
B from the transmitted channel passes through collimating lens
1130
into transmit port
1115
(so named because the light passing through this port is transmitted through the interference filter
1128
regardless of whether the device is configured as a multiplexer or demultiplexer) and into the first output fiber
1114
. The remaining light
1138
C comprising the remaining two channels is reflected from filter
1128
back into collimating lens
1126
which is oriented to transmit light
1138
C into reflect port
1117
(so named because the light passing from this port is reflected through the interference filter
1128
regardless of whether the device is configured as a multiplexer or demultiplexer) and into fiber
1116
. Accordingly, ADD/DROP filter
1122
has dropped one wavelength channel and placed it in output fiber
1114
.
Light beam
1138
C is then input from reflect port
1117
into output fiber
1116
to the input/common port
1119
of a second ADD/DROP filter
1124
. Second ADD/DROP filter
1124
is essentially identical to first ADD/DROP filter
1122
and comprises two lenses
1132
and
1136
, which also may comprise GRIN lenses, and an interference filter
1134
. ADD/DROP filter
1124
differs from ADD/DROP filter
1122
in essentially one or two ways. Interference filter
1134
may be a different filter, designed to pass a different wavelength channel. Alternately, interference filter
1134
is identical to interference filter
1128
, but common port
1119
, lens
1132
and filter
1134
are oriented such that light beam
1138
C strikes filter
1134
at a different angle, this angle chosen to drop (i.e., transmit) a different wavelength channel. That beam
1138
D passes through lens
1136
into transmit port
1137
to another output fiber
1118
. The reflected light beam
1138
E now contains one less channel. Light beam
1138
E is reflected back through lens
1132
to reflect port
1133
and into another output fiber
1120
.
The configuration of an optical ADD/DROP filter as a multiplexer should be apparent from the above description of a de-multiplexer configuration.
The construction of ADD/DROP filters such as ADD/DROP filters
1122
and
1124
is difficult, expensive, and time consuming. For instance, since the transmission characteristics of single mode optical fibers are highly dependent on the lateral positioning of one fiber with respect to another, ADD/DROP filters require extremely precise assembly and alignment of the optical components in the assembly and of the assembly with the fiber arrays. Further, losses occur at each interface, i.e., the interfaces between the fibers and the collimating lenses and between the collimating lenses and the interference filter.
In manufacturing optical ADD/DROP filters, the optical components are commonly bonded to each other. This type of ADD/DROP filter construction creates additional potential problems. Adhesive typically appears between the optical components and, thus, in the optical path. Over time, the optical power degrades the adhesive and frequently leads to increased optical losses or even failure of the optical ADD/DROP filter.
Due to the expense of ADD/DROP filters, it is desirable to increase the number of wavelength channels which can be added or dropped in a given ADD/DROP filter. U.S. Pat. No. 5,799,121 discloses an ADD/DROP filter design which allows two channels to be added or dropped per ADD/DROP filter. In the apparatus disclosed in that patent, one side of the ADD/DROP filter has four ports, namely, two common ports and two reflect ports. The other side has two ports, namely, two transmit ports. In short, this patent discloses an ADD/DROP filter in which two input beams are input from two separate input fibers so as to travel adjacent to each other through the ADD/DROP filter whereby the devices add or drop two channels simultaneously.
Accordingly, it is an object of the present invention to provide an improved optical ADD/DROP filter.
It is another object of the present invention to provide an improved method and apparatus for dense wavelength division multiplexing/de-multiplexing.
It is a further object of the present invention to provide an optical ADD/DROP filter that is inexpensive and has low optical loss characteristics.
It is yet another object of the present invention to provide a method of fabricating an optical ADD/DROP filter that is inexpensive.
It is yet a further object of the present invention to provide an optical ADD/DROP filter that can add or drop two or more channels.
SUMMARY OF THE INVENTION
The invention is an optical ADD/DROP filter suitable for dense wavelength division multiplexing/de-multiplexing. In accordance with the invention, an optical bench comprising a unitary body or two mating halves which are coupled together via alignment pins, preferably in a manner such that the two halves are offset from each other, is provided. In a preferred embodiment, the optical bench is formed of a metal such as stainless steel or titanium that is manufactured by wire electrical discharge machining (wire EDM). Alternately, it may be molded of powdered injected metal (PIM) or ceramic. An interference filter is bonded to one of the two collimating lenses with an annulus of adhesive around the lens/filter interface. No adhesive appears i
Green Eric Timothy
Kadar-Kallen Michael Aaron
Lewis Warren Hale
Zhong Shan
Hyeon Hae Moon
Nguyen Khiem
Synnestvedt & Lechner LLP
The Whitaker Corporation
LandOfFree
Optical ADD/DROP filter and method of making same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical ADD/DROP filter and method of making same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical ADD/DROP filter and method of making same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2975745