Fiber optic system with open fiber safety interlock

An open fiber safety interlock that disables the light transmitter whenever the cable is disconnected or broken. In one embodiment, a cable containing an optical fiber and an electrical conductor is coupled between a local receiver and a remote transmitter. The remote transmitter transmits a light signal to the local receiver via the optical fiber. The power for the remote transmitter is provided to the remote transmitter via the electrical conductor from a local power supply. Disconnecting or breaking the cable results in a loss of power to the transmitter, thereby halting any further light emissions. Broadly speaking, the present invention contemplates a remote module which implements an open fiber safety interlock. The remote module comprises a transmitter for transmitting light through an optical fiber in a cable, where the cable includes an electrical conductor. The transmitter is configured to transmit light when the cable is coupled to the remote module and a voltage is applied to the electrical conductor. The present invention further contemplates an open fiber safety interlock comprising an electrical conductor, a transmitter, and a power supply. The electrical conductor is part of a cable having an optical fiber for transporting a light beam. The transmitter is configured to provide the light beam, and the power supply is coupled to power the transmitter via the electrical conductor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the field of optical systems, and more 
particularly to safety interlocks for preventing accidental exposure to 
concentrated light beams conveyed by optical fibers. 
2. Description of the Related Art 
Optical fiber interconnections used for data communications or 
telecommunications applications usually operate in the near infrared. 
Typical wavelengths of these links, i.e. those used in most commercial 
fiber systems, are 830 nm, 1.3 .mu.m, and 1.55 .mu.m. These wavelengths 
are invisible to human vision, but may be focused by the human eye. This 
produces a potential hazard when a person looks into the end of an 
apparently dark fiber that is connected to an operating transmitter, or 
into the transmitter itself. 
A transmitter for coupling a modulated light signal to a optical fiber 
transmission line produces a narrow cone of light at the exit of the 
transmitter or at the exit of the optical fiber. To mitigate the hazard, 
legal requirements exist to regulate the amount of external radiation when 
an optical fiber coupler is disconnected. These pose an obstacle to use of 
lasers with optical fiber channels. Existing systems have overcome this 
obstacle through the use of safety interlocks. These have taken the form 
of mechanical shutters that cover the end of unplugged fiber cables and 
other coupler-engagement sensing schemes which fail to address the danger 
of a broken or cut cable. 
An electronic scheme which monitors for reflection from an open end has 
also been implemented, but involves pulsing the transmitter at a low duty 
cycle. While this keeps the radiation dosage below the retina-damage 
threshold, it adds significant complexity and cost to the transceiver. 
As fiber optic systems become adapted to a greater number of everyday 
applications, fiber optic cables will become more accessible to the 
general public, and a consequent increase in danger of retinal damage will 
result. A need exists for an inexpensive fail-safe interlock that is not 
easily damaged or defeated, and which prevents accidental radiation 
exposure in the event of a broken or cut optical fiber cable without 
reducing the available data transmission bandwidth. 
SUMMARY OF THE INVENTION 
The problems outlined above are in large part solved by an optical system 
including an open fiber safety interlock that disables a light transmitter 
whenever an associated cable is disconnected or broken. In one embodiment, 
a cable containing an optical fiber and an electrical conductor is coupled 
between a local receiver and a remote transmitter. The remote transmitter 
transmits a light signal to the local receiver via the optical fiber. The 
power for the remote transmitter is provided to the remote transmitter via 
the electrical conductor from a local power supply. Disconnecting or 
breaking the cable results in a loss of power to the transmitter, thereby 
halting any further light emissions. 
Broadly speaking, the present invention contemplates a remote module which 
implements an open fiber safety interlock. The remote module comprises a 
transmitter for transmitting light through an optical fiber in a cable, 
where the cable includes an electrical conductor. The transmitter is 
configured to transmit light when the cable is coupled to the remote 
module and a voltage is applied to the electrical conductor. 
The present invention further contemplates an optic system which implements 
an open fiber safety interlock. The optic system comprises a cable, a 
remote module, and a local module. The cable includes an optical fiber and 
an electrical conductor. The remote module includes a transmitter for 
transmitting light through the optical fiber. The local module includes a 
receiver for sensing light transmitted through the optical fiber and a 
power supply configured to supply power to the transmitter via the 
electrical conductor only if the cable is unbroken and properly coupled to 
both the local and remote modules. 
The present invention still further contemplates an open fiber safety 
interlock comprising an electrical conductor, a transmitter, and a power 
supply. The electrical conductor is part of a cable having an optical 
fiber for transporting a light beam. The transmitter is configured to 
provide the light beam, and the power supply is coupled to power the 
transmitter via the electrical conductor.

While the invention is susceptible to various modifications and alternative 
forms, specific embodiments thereof are shown by way of example in the 
drawings and will herein be described in detail. It should be understood, 
however, that the drawings and detailed description thereto are not 
intended to limit the invention to the particular form disclosed, but on 
the contrary, the intention is to cover all modifications, equivalents and 
alternatives falling within the spirit and scope of the present invention 
as defined by the appended claims. 
DETAILED DESCRIPTION OF THE INVENTION 
Turning now to the drawings, FIG. 1 shows an optical fiber system 100 which 
implements an open fiber safety interlock. The optical fiber system 100 
includes a local module 102 which couples to a remote module 104 via a 
cable 106. The local module 102 includes a power supply 108 and a receiver 
110. The remote module 104 includes a transmitter 112. The cable 106 
includes an optical fiber 114 and an electrical conductor 116. The 
transmitter 112 is coupled to one end of the optical fiber 114 and to one 
end of the electrical conductor 116. The receiver 110 is coupled to the 
other end of the optical fiber 114. The power supply 108 is coupled to the 
other end of the electrical conductor 116 and to the receiver 110. 
As long as the cable 106 of the optical fiber system 100 is unbroken and 
properly coupled at both ends, it transports a light beam from transmitter 
112 to receiver 110 in accordance with a designated communications 
protocol. The cable 106 also transports power for transmitter 112 from 
power supply 108 in local module 102. Any break in the cable 106 removes 
power from transmitter 112, thereby disabling it and preventing any 
external light radiation from a broken optical fiber which could cause 
retinal damage. Similarly, disconnecting either end of the cable 106 
disables transmitter 112. 
Remote module 104 operates to provide high speed data communication to 
local module 102 via an optical link. Examples of remote modules include 
sensors and computer graphics generators. To this end, remote module 104 
includes the transmitter 112. Transmitter 112 is a source of a modulated 
light beam and it is adapted to couple with the optical fiber 114 and the 
electrical conductor 116 in cable 106. Optical fiber 114 transports the 
modulated light beam along its length. 
Transmitter 112 transmits a light beam only if it is powered. The 
transmitter 112 receives its power via electrical conductor 116. Since a 
closed electrical circuit is necessary for supply of power, a return path 
is necessary. It is not necessary that the return path be included in 
cable 106, although that is certainly allowable. The return path may also 
be provided via a separate cable or through use of a common ground 
connection. 
Local module 102 operates to receive high speed data communication from 
remote module 104 via an optical link. Examples of local modules include 
data recording and processing equipment, and data display equipment. Local 
module 102 includes the receiver 110 which is adapted to couple with the 
optical fiber 114 to receive the modulated light beam. Local module 102 
also includes the power supply 108 which is adapted to couple with the 
electrical conductor 116. 
Power supply 108 supplies power to both receiver 110 and transmitter 112. 
In one embodiment, power supply 108 is configured as a current source. 
This advantageously compensates for any resistive power losses in 
electrical conductor 116. It is expected that the power supplied to the 
transmitter would be less than 1 Watt at about 5 Volts. 
The safety interlock implemented in optical system 100 is based on the 
concept that if the optical path between transmitter 112 and receiver 110 
is broken, then transmitter 112 is separated from its power supply 108. 
This safety interlock also finds application in optical systems with 
bi-directional communications as shown in FIG. 2. 
FIG. 2 shows an optical system 200 having a local module 202 coupled to a 
remote module 204 by a cable 206. Optical system 200 includes a power 
supply 108A, a receiver 110A, a transmitter 112A, an optical fiber 114A, 
and an electrical conductor 116A, each of which functionally correspond to 
the similarly numbered parts of FIG. 1. In mirror-image fashion, optical 
system 200 includes a power supply 108B, a receiver 110B, a transmitter 
112B, an optical fiber 114B, and an electrical conductor 116B, each of 
which also functionally correspond to the similarly numbered parts of FIG. 
1 to transmit power and a modulated light beam in directions opposite 
those of FIG. 1 (i.e. the light beam travels from the local module to the 
remote module on optical fiber 114B, and the power is provided from the 
power supply 108B in the remote module to the transmitter 112B in the 
local module). Disconnecting or breaking cable 206 thereby isolates both 
transmitters 112A and 112B from both their respective power supplies 108A 
and 108B. As before, this disables the transmitters, and prevents 
accidental exposure to external light radiation. 
It may not always be feasible to have a power supply in the remote module. 
In this case, the configuration of optical system 300 shown in FIG. 3 may 
be used. Parts which functionally correspond to parts in FIG. 2 are 
numbered identically. A remote module 304 is powered by power supply 108A 
via electrical conductor 116A. A connection is made inside remote module 
304 to provide an electrical path between electrical conductor 116A and 
electrical conductor 116B. In essence, the power supply for remote module 
304 is connected to electrical conductor 116B even though the power supply 
does not reside in remote module 304. 
In a proposed application, system 300 comprises a computer (local module 
202) and a remotely placed display device (remote module 304). In this 
application, the open fiber safety interlock advantageously mitigates the 
hazard of exposure to external light radiation from an easily accessible 
optical fiber cable without significantly increasing the cost of the 
system. 
An alternate embodiment of optical system 300 is shown in FIG. 4. Parts 
which functionally correspond to parts shown in previous figures are 
numbered identically. Local module 402 includes a transmitter 412 which is 
powered by the local power supply 108A. However, transmitter 412 is 
disabled (i.e. does not transmit a light beam) unless it receives an 
asserted signal voltage via electrical conductor 116B. This reduces 
resistive power losses that might result from powering transmitter 412 via 
electrical conductor 116B. This implementation might be particularly 
suited for use in system 300 where the remote module 304 is powered from 
local power supply 108A. 
Numerous variations and modifications will become apparent to those skilled 
in the art once the above disclosure is fully appreciated. It is intended 
that the following claims be interpreted to embrace all such variations 
and modifications.