Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-03-02
2001-12-11
Lee, John D. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S047000, C385S049000, C385S088000
Reexamination Certificate
active
06328484
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to systems for coupling signals using optical fiber equipment and more particularly to the coupling of signals between optical fibers and devices that generate or detect optical signals.
BACKGROUND ART
In communication applications, high-density packaging is an important issue. This is true whether the communications are based upon transmissions of electrical signals or optical signals. A related consideration is the cost of fabrication. The density of fiber optic modules that can be positioned along a printed circuit board (PCB) of a fiber optic-based Local Area Network (LAN) hub or similar system significantly impacts the per channel cost of the system.
Small-form fiber optic modules allow a high density of transmit and receive channels. Such modules include fiber optic transceivers which enable a light source to be coupled to a transmit fiber and allow a detector to be coupled to a receive fiber.
FIG. 1
illustrates one known arrangement for coupling optical fibers
10
and
12
to a pair of solid state device packages
14
and
16
that are secured to a PCB, not shown. The optical fibers are embedded within a connector
18
. For a standardized MT-RJ fiber pair, the center-to-center distance of the two fibers is 0.75 mm. For example, the connector may be a Mini-Mechanically-transferrable Push-On (Mini-MPO) connector type. Typically, the density of the transmitter and receiver channels is determined by the size requirements of the device packages. The solid state devices must be packaged to provide both optical and electrical isolation of the transmit and receive signals, as well as environmental protection. In the example shown in
FIG. 1
, the packages of the devices are shown as conventional Transistor Outline (TO) style cans. Each of the cans includes a pair of leads
20
and
22
that are soldered to the printed circuit board, which includes the drive and processing electronics for a transmitter chip
24
and a detector chip
26
. The transmitter chip may be a light emitting diode (LED) or a laser diode. The detector chip
26
may be a photodiode.
The TO cans
14
and
16
of
FIG. 1
are positioned such that when the connector
18
is inserted into a female connector seated on the same PCB as the TO cans, the exchange of optical signals is along a single plane. With regard to the transmit channel, the transmitter chip
24
generates an optical signal that is directed to a lens
28
of the TO can
14
. The can lens
28
is cooperative with a collimating lens
30
to produce a collimated beam that impinges the mirror
32
. The first mirror redirects the light path to a second mirror
34
, which again redirects the light path for alignment with the transmit fiber
10
. A lens
36
focuses the signal onto the aligned fiber
10
.
The receive channel follows a path similar to the transmit channel, but in the opposite direction. Light from the fiber
12
is collimated by a lens
38
and impinges a third mirror
40
. The redirected optical signal is again redirected by a fourth mirror
42
. The optical signal is then operated upon by a lens
44
and a can lens
46
to focus the received signals onto the detector chip
26
.
The arrangement of
FIG. 1
provides beam translation along two axes, i.e., the X axis and the Z axis indicated in FIG.
1
. This allows the spacing between the two channels to be increased from the 0.75 mm spacing of the connector
18
to a greater spacing between the two TO cans
14
and
16
, e.g., a spacing of 6.2 mm.
Other optical couplers for connecting optical fibers to TO cans are known. U.S. Pat. No. 4,701,010 to Roberts describes a molded body having reflecting surfaces for connecting a fiber to a detector TO package or an emitter TO package. A slot extends into the body to allow insertion of a filter, such as a dichroic mirror, or a beam splitter, depending upon the desired application.
While the prior art systems operate well for their intended purposes, what is needed is a system that provides further reductions in the fabrication cost, without a sacrifice in optical performance.
SUMMARY OF THE INVENTION
A system for coupling optical fibers to optical devices includes lenses and mirrors which cooperate to provide propagation in perpendicular X, Y and Z directions, so that the devices can have a greater center-to-center spacing than the fibers and can be mounted to have axes perpendicular to the axes of the fibers. In the preferred embodiment, the optical devices include a light detector and a light transmitter that are surface mounted to a printed circuit board, while the lenses and mirrors are formed in a unitary optical member that is also mounted to the surface of the printed circuit board. By enabling surface mounting of the detector and transmitter, the cost of fabrication is reduced. Moreover, the surface mounting potentially reduces the circuit board real estate required for positioning the detector and the transmitter.
The optical member is made of a clear plastic material and includes a pair of light propagation paths that are mirror images of each other, but are oppositely directed. The term “clear” is defined herein as being characterized by low losses in the transmission of an optical signal. A first pair of input/output lenses is positioned on one surface of the optical member. Preferably, the input/output lenses are hyperbolic, so as to provide beam collimation. It is this first pair of input/output lenses that is aligned with the transmit optical fiber and the receive optical fiber. The lenses have axes that are aligned with a first pair of mirrors. The mirrors are total internal reflection (TIR) surfaces for reflecting optical signals. In the preferred embodiment, the TIR surfaces are at 45° angles to the axes of the associated lenses, so that right angle bending occurs. Each of the mirrors is aligned with a second mirror that provides right angle bending to a second pair of input/output lenses on a surface perpendicular to the surface having the first pair of input/output lenses. Again, the input/output lenses are preferably hyperbolic.
At the first surface, the optical member includes alignment pins or equivalent structure for ensuring precise registration between closely spaced duplex fibers and the first pair of lenses. At the opposite ends of the propagation paths, the second pair of lenses is aligned with a photodetector and a light source. For example, the photodetector may be a photodiode and the light source may be an LED or a laser diode. The photodetector and the light source are surface mounted on a PCB.
For the transmitter path, signals are generated by the light source, which is aligned with one of the lenses. The beam from the light source is collimated by the lens for propagation to a first TIR surface. The distance between the first lens and the first TIR surface defines a substratedirected segment of the transmit propagation path. The first TIR surface redirects the beam to a second TIR surface. The intermediate path segment between the two TIR surfaces is perpendicular to the substrate-directed segment and is parallel to the PCB on which the light source is mounted. The second TIR surface reflects the beam along a fiber-aligned segment to the hyperbolic lens which focuses the beam onto the transmit fiber.
For the receiver channel, the receive fiber directs optical signals to the hyperbolic lens having an axis that defines a fiber-aligned segment of a receiver propagation path. The beam is collimated by the lens and is reflected by a TIR surface to an intermediate segment of the path. The beam is again reflected to a substrate-directed segment aligned with the hyperbolic lens which focuses the beam onto the photodetector.
An advantage of the invention is that the photodetector and the light source are mounted directly to the PCB. The two devices may be mechanically and electrically mounted using a silver or gold epoxy to a gold-plated PCB that includes the processing electronics for the photodetector and the drive electronics for the light source. An advantage of
Agilent Technologie,s Inc.
Lee John D.
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