Fiber optic bus manifold

A bus manifold utilizing master and slave terminals wherein a single data bus transmits master terminal signals to the slave terminals continuously and simultaneously with transmission from one of the slave terminals. The system uses a single-optical-fiber transmission line coupled to the master terminal for both transmit and receive functions. The slave terminals have sending units coupled to the transmission line and a pair of receivers tap-coupled to the transmission line. Sending by the slave terminals is in the opposite direction from sending by the master terminal, and the tap coupling is effective to tap signals travelling in both directions in the line.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to fiber optic transmission of signals 
through a manifold or data bus. More particularly, the present invention 
relates to the use of a single-optical-fiber transmission line coupled 
with a low-loss launch coupler to provide the data link for information 
transmission to and from the master terminal and with a series of slave 
terminals, each capable of receiving bidirectional signals carried in the 
transmission line and each capable of sending signals through the 
transmission line in a single direction. 
2. Description of the Prior Art 
Fiber optic devices, once a laboratory curiosity, are now receiving 
considerable attention and are used in industry. Fiber optic communication 
cables for telephone systems are not in limited service and conversion to 
"Lightwave Communications Systems" has been predicted for many telephone 
utilities. 
Uses such as those noted above often require multiple connections for 
signal reception and use, since a large number of terminals are provided. 
The interconnection means is commonly described as a data bus. Data buses 
are used in the electronics industry to provide communication links 
between isolated terminals in applications such as computer systems, 
airplane and ship controls, electronic test equipment and weapons control 
systems. It has become generally known that wire transmission lines are of 
limited utility in many of the above uses due to such factors as 
limitations in bandwidth to the extent that the transmission line 
capability is substantially lower than the data production capability of 
the equipment. In addition, wire transmission lines are susceptible to 
electromagnetic interference from external sources and transmit only in a 
given direction at a given time. Thus the only means for utilizing wire 
transmission in a bidirectional manner is multiplexing of the signals that 
are transmitted. Fiber optics, on the other hand, has the potential 
capability of elimination of these problems, since fiber optic units are 
capable of transmission in a bidirectional mode and are immune to 
electromagnetic interference. 
d'Auria et al in U.S. Pat. No. 3,953,727 suggests a system for 
single-optical-fiber transmission utilizing mirrors, photodetectors and 
diodes to generate signals for and receive signals carried in a fiber 
optic line. 
Chown et al in U.S. Pat. No. 4,166,946 and Kogelnik in U.S. Pat. No. 
3,986,020 both suggest optical fiber transmission systems. Chown et al 
uses a bundle of multiple fibers and utilizes couplings to connect the 
fibers to the terminals and remove portions of the signal from the main 
transmission line. Kogelnik, on the other hand, uses a strip guide or 
fiber and laser signals to pick off signals from plural stations and 
selectively transmit them to remote stations. 
In another system, Suzaki in U.S. Pat. No. 4,136,929 utilizes a closed loop 
which receives its signal by tapping off a portion of the signal contained 
in an external transmission line. The closed loop utilizes the signal and 
returns the remaining signal to the transmission line at the point of 
take-off. 
In U.S. Pat. No. 4,089,584 of Polczynski a manifold concept utilizing an 
arbitrary number of terminals is disclosed. The structure of the optical 
couplers and the means of fabrication are not provided. Only one terminal 
transmits to the other terminals at a given time and the signal flow is 
unidirectional. A bus using such a manifold is half duplex and the data is 
time-division-multiplexed. 
SUMMARY OF THE INVENTION 
In the present invention a fiber optic manifold for a data bus is provided 
with input and outputs ports for an arbitrary number of terminals. The 
manifold is capable of full-duplex transmission of optical signals between 
one terminal (master terminal) and the remaining terminals (slave 
terminals). The slave terminals communicate with each other and with the 
master terminal, one at a time. That is, only one slave terminal is 
permitted to transmit at a given time while the master terminal is 
permitted to transmit continuously and all the slave terminals can receive 
signals continuously from the master terminal and from a transmitting 
slave terminal. This full communication capability is provided in the 
present system by utilizing the bidirectional characteristics of a 
single-optical-fiber data bus. The signals generated by and transmitted 
from the master terminal travel in a first direction through the data bus, 
and can be utilized by all of the slave terminals. The signals generated 
by one of the slave terminals, on the other hand, are transmitted in the 
opposite direction through the single-fiber bus and thus are made 
available to all of the slave terminals and the master terminal 
independent of the signals being generated by the master terminal. 
The master terminal is provided with a single receiving port and a single 
transmitting port. Each of the slave terminals is provided with two 
receiving ports and a single transmitting port. All of the ports are 
connected by a single-fiber data transmission bus or "highway" using 
appropriate optical fiber couplers. At the master terminal, the send and 
receive ports are connected together by a directional coupler which 
efficiently couples almost all of the transmitted signal into the optical 
fiber bus without significant loss and without significant reflection to 
the receive side of the coupler. In addition, the signals transmitted to 
the master terminal from the slave terminals, as provided to the coupler, 
are effectively transmitted to the receive side of the master terminal 
without significant loss to the transmission fiber. Travelling along the 
"highway", the fiber is next connected to each of the slave terminals by a 
bidirectional tap coupler, or by a pair of unidirectional tap couplers 
coupled to tap portions of the signals travelling in opposite directions 
in the highway. Each slave terminal is provided with reception circuitry 
to separately utilize signals travelling in each direction, i.e. from the 
master terminal and from other slave terminals. The tap couplers cannot 
connect the slave terminals in series. 
Travelling further along the highway, after connecting all of the 
bidirectional receive ports, the single-fiber bus is serially connected to 
the transmission ports of the slave terminals. This connection is made by 
use of the same type of directional coupler utilized in the main terminal. 
That is, the signal generated in the slave terminal is coupled to the main 
bus through a coupler which does not exhibit significant signal coupling 
loss and is directional in nature. The transmission terminals are 
preferably connected to the main bus in reverse serial order, as compared 
to the serial order of the connection of the reception terminals. That is, 
the last slave terminal to be tap coupled to the bus is the first to be 
launch coupled to the bus. In this manner, the number of slave terminals 
may vary and each slave terminal will communicate with all other slave 
terminals and the master terminal. The number of slave terminals, of 
course, would be limited by the ability of the system to generate a 
sufficiently strong signal to travel through the highway, and by the 
length of the remaining unused, uncoupled lines. Repeater or amplifier 
circuitry could be provided at any point in the bus line to increase the 
capacity of the line to transmit over long distances. 
The transmitting couplers for the slave terminals and the transmit and 
receive coupler for the master terminal are described in applicant's 
concurrently filed application Ser. No. 123,034 entitled OPTICAL FIBER 
LAUNCH COUPLER. Basically, the coupler is directional in nature and is 
made up of a first glass-clad-glass fiber which is formed on an arcuate 
surface and adhered thereto prior to lapping of the external side thereof. 
The lapping is conducted through the glass cladding to expose a small flat 
surface which is utilized to couple the light from a second fiber used in 
producing the coupler. The second fiber is of significantly smaller 
diameter, as defined in the above-identified application. It is also 
formed on an arcuate surface and lapped. However, in this case the lapping 
is allowed to continue until such time as the central core of the 
glass-clad-glass fiber is severed. The result is the formation of two, 
flat, elliptical surfaces on the smaller fiber. The size of one of these 
flat elliptical surfaces is used as a guide for the lapping of the larger 
fiber so that the two surfaces can be placed in a mating relationship and 
sealed together. The mating is effected to maximize the amount of signal 
transmitted to the larger fiber from the joined portion of the severed 
fiber. Also, the amount of signal transmitted through the larger fiber, 
independent of the smaller fiber, is maximized. 
The resulting coupler has only three effective ports. That is, the larger 
fiber is bidirectional in nature in that it can transmit light in both 
directions without significant loss of signal to the smaller severed 
fiber. Signals carried in the joined portion of the severed fiber are 
substantially, if not completely, coupled into the larger fiber at the 
point of mating. However, the signals carried in either of these are not 
transmitted to the other severed fiber portion ("fourth fiber") since it 
is not coupled to any other fiber portion. 
The bidirectional tap couplers for the slave terminals are described in 
further detail in concurrently filed application Ser. No. 123,038 of John 
P. Palmer and Phillip B. Ward, Jr. entitled DUAL DIRECTIONAL TAP COUPLER, 
assigned to the assignee of this application. These tap couplers are 
prepared by utilizing the single glass-clad-glass fiber and forming it 
over an arcuate surface. The fiber is then lapped to a predetermined 
depth, depending upon the radius of curvature to the arcuate form and the 
diameter of the fiber core. The depth of the lapping determines the size 
of the core section exposed during lapping. This core section is 
specifically selected so that bidirectional signals carried in the core of 
the fiber are partially coupled to separate faces on a prism which is 
mated to the flat, lapped surface. The faces of the prism are reflective 
and each reflects one of the light signals transmitted to the prism 
outwardly to a photodiode. 
The geometry of this system is described in detail in the above-identified 
application. Basically, the arc is selected to remove the appropriate 
amount of signal and depends on the diameter of the fiber. The lapping is 
selected in accordance with the amount of fiber available and the 
percentage of signal to be tapped. An angle of 52.degree..+-.5.degree. is 
used on the reflective prismatic surface to reflect a narrow, highly 
collimated signal out of the prism in a direction substantially 
perpendicular to the upper surface of the prism. In this manner minimal 
reflection back to the prism occurs at the exit point. Photodiodes or 
other appropriate light-sensitive elements are utilized and positioned at 
each of the light exiting locations in order to sense the tapped signal 
and convey it to the slave terminal. The use of this dual directional tap 
coupler allows for the tapping of portions of the master terminal 
transmitted signal as well as portions of slave terminal transmitted 
signals, which travel in opposite directions in the single-fiber 
transmission line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be defined in terms of a master terminal and 
four slave terminals used in the open loop system disclosed in FIG. 1. 
However, a larger or smaller number of slave terminals may be used in the 
system, and the distance between the slave terminals may vary. For 
instance, slave terminals which are located in different buildings may be 
interconnected. In addition, repeating terminals to increase signal 
strength may be utilized where the distance between the master terminal 
and the most remote slave terminal is sufficient to justify their use. 
This depends on the number of terminals as well as the strength of the 
signals generated at the master terminal and at the slave terminals. The 
only communication limitation without multiplexing is that only one slave 
terminal can transmit at a given time. 
In FIG. 1, master terminal 10 is provided with a transmitter 12 and a 
receiver 14. The transmitter receives an internal electrical signal from 
the master terminal, which may, for example, be generated by a computer, 
and amplifies and converts it into a light signal by use of a light 
emitting diode, laser, or other optical signal generating unit. The 
particular light source depends upon the design characteristics of the 
unit. Characteristics such as the number of slave terminals, the 
characteristics of the signal generated by the master terminal and the 
travel distance for the signal are design considerations. The signal 
transmitted conveys the data to the slave terminals, indicated generally 
as 16, and may be amplitude or frequency modulated to carry the data. 
Also, a selected frequency may be used to act as a carrier for the 
signals. Additionally, each slave terminal may be assigned a specific 
frequency so that the master terminal will communicate with a given slave 
terminal only when the master terminal utilizes the correct frequency. 
This is done by generating a different selected frequency carrier signal 
at the master terminal for each slave terminal and providing a bandpass 
filter for the slave terminal, so that only one frequency signal is used 
by the slave terminal. 
This signal generated at transmitter 12 enters coupler 18 through optical 
fiber 20. Coupler 18 is the type shown in FIG. 2. Main transmission fiber 
22, exiting from coupler 18, is joined to first dual directional tap 
coupler 24. The signal carried from transmitter 12 is partially tapped off 
of main fiber 22 onto line 26 which is directly connected to first slave 
terminal 161 through receiver 28. The remaining signal is then transmitted 
to bidirectional tap coupler 34; a portion is tapped off to line 36 for 
supplying receiver 38 and slave terminal 162. The main signal then enters 
tap coupler 44 where a portion is provided to line 46 which communicates 
with receiver 48 of terminal 163. Finally, the signal is transmitted to 
tap coupler 54 which communicates with line 56 and receiver 58 in slave 
terminal 164. At this point, depending on the strength of the signal 
provided to main transmission fiber 22, the main signal may be 
sufficiently low-powered that it is no longer useful. This signal residue, 
however, travels along the remaining path of main fiber 22 but is of no 
further use in the illustrated embodiment. If more terminals were placed 
downstream of slave terminal 164, a stronger signal or the remaining 
signal, if any, would be utilized. 
Slave terminals 161-164 utilize the signals provided to receivers 28, 38, 
48 and 58 through conventional means. By virtue of the use of the 
photodiode at the tap coupler, as illustrated in FIGS. 3 and 4, the light 
signal is converted into an electronic signal which is carried to the 
receiver by lines 26, 36, 46 and 56. The signal is amplified by the 
receiver and transmitted to the remaining circuitry in the slave terminal, 
which can be a computer terminal, for example. 
Each of terminals 161-164 is provided with a light-emitting diode and 
coupler. The structure is as described for transmission unit 12 and 
coupler 18 in the master terminal. Sending unit 70 for terminal 161 
generates a signal which is converted to an optical signal for fiber 72 
which is coupled into main line 22 by directional coupler 74. Coupler 74 
is generally the same as coupler 18, and will be described with reference 
to FIG. 2. In a like manner, slave terminal 162 is provided with sending 
unit 80 which generates a signal for fiber 82 and coupler 84. Slave 
terminal 163 is provided with sending unit 90 which generates a signal for 
fiber 92 and coupler 94. Lastly, terminal 164 is provided with sending 
unit 100, fiber 102 and coupler 104. Couplers 74, 84, 94 and 104 are 
serially connected in the reverse order when compared with the receiving 
units so that signals generated from the master terminal reach slave 
terminal 161 first, and signals generated by the slave terminal 161 are 
the most remotely coupled to main lines 22. The signals generated and 
transmitted by slave units 16 flow in the opposite direction to main fiber 
22, and thus a signal generated by any one of slave terminals 161-164 is 
available to all of the slave terminals through bidirectional tap 
couplers, 24, 34, 44 and 54. The tapping of these signals travelling back 
toward master terminal 10 is effected through lines 30, 40, 50 and 60 
which tap off signals from couplers 24, 34, 44 and 54, respectively. These 
signals are utilized in slave terminals 161-164, respectively, through 
receivers 32, 42, 52 and 62. Again, the structure described above with 
regard to tapping the main signal is provided within couplers 24, 34, 44 
and 54, which communicate with slave terminals 161-164, in order to 
convert the light signal to an amplified usable electronic signal. 
Exemplary of the appropriate signals are those capable of use in an 
emitter-coupled logic (ECL) or transistor-transistor logic (TTL) unit. 
The signal generated by any one of slave sending units 70, 80, 90 and 100, 
after tapping by couplers 54, 44, 34 and 24, is transmitted to coupler 18 
where it enters master terminal 10 through line 120 and is converted to a 
usable electronic signal by receiver 14. 
In this manner, the master terminal has a single receive port and a single 
send port, and each slave terminal has two receive ports and a single send 
port. All of the transmission and receive ports are connected through a 
single-fiber transmission highway using fiber optic couplers. The 
electro-optical transmitters and detectors provide the necessary interface 
between the electronic terminals and the fiber optic manifold. The data 
transmission by the master terminal is received by one of the two 
receiving ports for each slave terminal; and the data transmitted by any 
slave terminal is received by all of the other slave terminals through 
each slave terminal's second receive port, as well as being returned to 
the master terminal. Because of the properties of the single-optical-fiber 
transmission line, the signals propagating in opposite directions in the 
highway do not interfere with each other and the directional couplers 
steer the signals unidirectionally so that only minor and insignificant 
mixing of the signals occurs at the various transmission and reception 
points. Consequently, the master terminals is permitted to transmit 
continuously, while the slave terminals are preferably 
time-division-multiplexed with respect to each other only. The master 
terminal can continuously direct the transmission of data between the 
slave terminals over a common line, without interruption and without the 
use of additional couplers at the slave terminals. This provides a 
significant reduction in the electronic hardware for the master terminal 
since it is not necessary to time-division-multiplex the master terminal. 
In addition, a significant reduction in control software and transmission 
line hardware and an increase in the rate of transfer of data are effected 
by this system. 
The present system is made possible through the use of the couplers 
described in FIGS. 2-4. In FIG. 2, the directional signal launching 
coupler used at the sending unit for each of the slave terminals and for 
the sending and receiving functions at the master terminal is shown. This 
coupler is described in more detail in applicant's concurrently filed 
application Ser. No. 123,034 entitled FIBER OPTIC LAUNCH COUPLER. In 
general, the coupler is produced by forming two arcuate surface forms 122 
and 124 and adhering optical fibers 126 and 128 thereto by an epoxy resin, 
for instance. Both of fibers 126 and 128 are surface lapped to produce 
flat elliptical surfaces 130, 132 and 134. Flat elliptical surfaces 130 
and 132 are joined in the final coupler so that light generated in fiber 
128 is coupled directly into fiber 126, through elliptical surface 132. 
Elliptical surface 134, on the other hand, is not coupled and as a result 
fiber section 136 is not functional. Both fibers are glass-clad-glass 
fibers and the core of fiber 128 is completely lapped through so that it 
is severed and produces the two elliptical surfaces. However, the core of 
fiber 126 is not severed and only a small portion of it is removed in 
order to cause the coupler of the present invention to function properly. 
The removal of only a small portion of the fiber is made possible by the 
utilization of fiber 126 which has a larger core diameter than severed 
fiber 128. Fiber 126 forms part of the single-fiber main transmission line 
22 in FIG. 1 and is connected to or forms input line 120 at the master 
terminal. In this manner, signals propagated from master terminal 
transmitter 12 would enter fiber 20 which would be connected to or form 
input fiber 128 and be coupled to main fiber 126 which would be connected 
to main transmission fiber 22. 
The directional characteristics of the coupler shown in FIG. 2 are such 
that only a small portion of the signal traversing line 128 is lost, and a 
very small portion of it is transmitted backward through line 126. Over 
95% of the signal is coupled into fiber 126, and travels outward in the 
direction shown by the arrow in the drawing. On the other hand, signals 
travelling in either direction in fiber 126 are approximately 95% retained 
in the fiber and transmitted downstream for further use. 
In FIG. 3, an optional unidirectional tap coupler is shown. This tap 
coupler is described in detail in concurrently filed application Ser. No. 
123,038 entitled DUAL DIRECTIONAL TAP COUPLER. Details of the fabrication 
of such a device are set forth in application Ser. No. 15,027, filed Feb. 
26, 1979 and assigned to the assignee of this application. Basically, 
fiber 140 is adhered to an arcuate surface on form 142 as described with 
regard to fiber 126 in FIG. 2 and partially lapped. The lapping is 
sufficient to provide tapping of a portion of an optical signal to prism 
144. The curvature utilized for the tap coupler shown in FIG. 3 is 
selected to result in tapping of the desired percentage of the signal 
carried through fiber 140. This signal is transmitted as shown by arrows 
146 to prismatic reflective surface 148 and reflected in a direction 
substantially normal to top surface 150 of prism 144. Photodiode 152 is 
positioned on or adjacent top surface 150 of the prism at a point where 
the maximum signal is obtained. The geometry of this arrangement and 
specific manufacturing procedures are described in further detail in the 
above-mentioned concurrently filed application. It has been found that an 
angle .theta. for reflective surface 148 of 52.degree..+-.5.degree. is 
preferred. This results in a very narrow collimated light signal being 
emitted from prism 144 and impinging upon photodiode 152 so that maximum 
signal transmission with minimum loss can be obtained. Two of these 
couplers would be utilized for the receiving functions of each slave 
terminal. The couplers are connected in opposite directions so that 
signals carried in main fiber 22 of FIG. 1 would be tapped in both 
directions for use by the slave terminal. 
In the alternative, the bidirectional coupler shown in FIG. 4 may be 
utilized to replace the two, single-direction tap couplers. This dual 
direction tap coupler is also described in more detail in the 
above-mentioned concurrently filed application. Generally, signals 
travelling through fiber 166 in either direction are coupled to fiber 174 
through standard optical couplers 168. Form 170 is used to produce the 
arcuate section 172 of the internal fiber 174. The geometry of this unit 
is substantially similar to that of the unit described above in that 
signals travelling from right to left in the line are partially tapped out 
of line 174 at surface 172, impinge reflective prismatic surface 176 and 
are reflected to photodiode 178 in a narrow collimated beam. Prism 180 is 
provided with second reflective prismatic surface 182 which receives the 
tapped portion of the signal travelling from left to right in fiber 174 
and reflects it to second photodiode 184. 
The unit is manufactured by forming fiber 174 over form 170, and adhering 
it to the form with, preferably, an optically transparent epoxy resin. The 
arcuate surface of the fiber is then lapped a predetermined amount of 
produce a flat section in the core of the glass-clad-glass fiber. Due to 
the curvature of the arc, a portion of the signal carried in the fiber is 
released from the fiber through the lapped surface. The double prismatic 
faced prism 180 is then placed on and adhered to this small, flat, lapped 
surface on fiber 174 and the tap signal is thus reflected by one of the 
mirrors, depending upon its direction of travel in fiber 174. The prism is 
positioned on, mated and adhered to the fiber by an epoxy resin and 
allowed to set. After setting of the resin, a light signal generated, for 
instance, by a laser, is passed in one direction through the fiber and the 
position of the first photodiode adjusted for the generation of maximum 
current. The first photodiode is then adhered in position. The laser is 
then used to generate a signal flowing in the opposite direction and the 
second photodiode positioned by maximizing its output signal. After 
adhering the second photodiode to the prism, the whole unit is sealed 
together with, for example, a potting compound and the appropriate 
electrical and fiber connectors. These bidirectional tap couplers may be 
used as terminals 24, 34, 44 and 54 on the receptor side of the slave 
terminals in FIG. 1. 
There are significant logical extensions to the application of the present 
invention. For example, the data transmitted by the master terminal can be 
transmitted at different optical wavelengths from the data transmitted by 
the slave terminals. Using these different optical wavelength senders and 
coupling them with spectral filters at the receiving ports would allow the 
rejection of undesirable reflections from the couplers and significantly 
enhance the discrimination of the signals at the receivers. For example, 
the master terminal could use a light-emitting diode which transmits at a 
center wavelength of 820 nm, such as an RCA C-30133 LED, and each of the 
slave terminals could be equipped to transmit at, for example, 1060 nm 
with an RCA C-30116 LED. The appropriate narrow bandpass filters would 
then be provided at the reception ports for both master and slave 
terminals, in order to discriminate between the signals generated by the 
master terminal and signals generated by each of the slave terminals. 
Another way of enhancing the directional signal discrimination in the 
present invention is to transmit signals on a sub-carrier at radio or 
audio frequencies. For example, data may be sent by the master terminal 
through modulation of a 4 MHz sine wave, and the data transmitted by the 
slave terminals could be carried by modulation of a 40 MHz sine wave. By 
utilization of the appropriate frequency-sensitive circuitry in the slave 
and master terminal receiver sections, substantial discrimination of the 
signals transmitted to the receivers can be effected. 
Although there have been described above specific arrangements of a fiber 
optic bus manifold system in accordance with the present invention for the 
purpose of illustrating the manner in which the invention may be used to 
advantage, it will be appreciated that the invention is not limited 
thereto. For example, although the invention has been disclosed in the 
context of association with certain signal generating systems, the 
principles of the invention are equally applicable to other signal 
generating and modulating systems and the like. Accordingly, any and all 
modifications, variations or equivalent arrangements which may occur to 
those skilled in the art should be considered to be within the scope of 
the invention as defined in the appended claims.