SHORT DISTANCE DENSE WAVELENGTH DIVISION MULTIPLEXING OPTICAL COMMUNICATION SYSTEM

Abstract: The present invention provides an expandable and cost-effective high capacity optical communication system using wavelength-division-multiplexing. Low-loss modular multiplexers and demultiplexers are used to increase the flexibility of the system and reduce overall system insertion loss.

Description: SHORT DISTANCE DENSE WAVELENGTH DIVISION MULTIPLEXING OPTICAL COMMUNICATION SYSTEM TECHNICAL FIELD OF THE INVENTION The invention relates to optical communication systems generally and, more particularly, to short distance optical communication systems which carry plural optical signals of different wavelengths simultaneously. BACKGROUND OF THE INVENTION Optical communication systems are a substantial and rapidly growing component of communication networks. "Optical communication systems" are any systems which use an optical signal to convey information across an optical waveguide medium (such as a fiberoptic cable or vacuum). Such optical systems include telecommunications systems, cable television systems, and local area networks (LANs). The majority of optical communications systems in current use are configured to carry an optical channel of a single wavelength over one or more optical waveguides. While the need for communication services is rapidly expanding, the current capacity of existing optical waveguide media in short distance communication networks, such as metropolitan and enterprise networks, is limited. In such networks, the transmission distance is generally less than one-hundred (100) kilometers. Flexibility is advantageous to these networks. For example, a single network ideally should be able to transmit information sent from different sources, at a variety of data transfer rates and transmission formats. Also, an information-bearing signal may be optical or electronic. Furthermore, to make most efficient use of limited optical waveguide media, bi-directional operation (data traveling both directions on a single fiberoptic strand) is also quite advantageous. In short distance networks, system capacity requirements vary from user to user, and a given user may require a system that can be quickly expanded. Thus expandable and flexible configurations are desirable. Low unit cost per channel is also desirable. Because of the expense and difficulty in installing new optical waveguide media, it has become necessary to transmit the maximum amount of information possible over existing media. For instance, various methods have been considered of conveying information from plural sources over a single fiber optic strand, such as time-division multiplexing and frequency-division multiplexing. In time-division multiplexing, use of a single optical channel (or fiberoptic strand) is rotated between various signal sources, with a portion of one signal transmitted, followed by a portion of another, in which complete signals are constructed from the portions of signals collected from each time slot. While this is a useful technique for carrying plural information sources on a single optical channel, its capacity is limited by the speed of electronic switching between time slots, limiting the maximum data transfer rate. In frequency-division multiplexing, a particular sub-carrier frequency is assigned to each signal source, and a complete signal being constructed by combining each sub-carrier frequency. While this is also a useful technique for carrying plural information sources on a single optical channel, its capacity is limited by the need for a high signal-to-noise ratio, requiring higher power systems which in turn limits the number of data channels due to interference, cross talk and the nonlinearity of optical waveguide media. Also, frequency-division multiplexing systems are prone to distortion and the noise characteristics of opto-electronic converters. Wavelength division multiplexing (WDM) has also been explored as an approach for increasing the capacity of existing fiber optic networks. In a WDM system, multiple optical signal channels are carried over a single waveguide (e.g., a single fiberoptic strand), each channel being assigned a particular wavelength. A "dense" WDM (DWDM) system is one in which channel spacing can be approximately in the range of a few nanometers. Prior art DWDM systems were designed for long distance applications, such as cross country fiberoptic cable systems. In such applications, optical wave dispersion is a particular problem due to the distances covered. This has necessitated the use of external modulation of the optical signals. External modulation is more expensive and subject to breakdown than is direct modulation, but external modulation reduces wave dispersion over long distances. In such as system, an unmodulated laser beam is used as a carrier signal, and the specific data to be transmitted is added by a re-modulator. Unfortunately, the use of external modulation increases the cost and adds an additional component which may disable the system in the event of a breakdown. Additionally, external modulation has an inherent inefficiency requiring the use of a higher power laser than that used in direct modulation systems, further increasing the cost of the system, and reducing reliability due to the heat generated by such high powered lasers. Prior art DWDM systems typically employ optical combiners and splitters as a means to combine and divide a signal over multiple paths. Such devices cause further attenuation. For this reason, as well as the attenuation resulting from signals traveling long distances over fiberoptic cables, DWDM systems have had to employ optical fiber amplifiers. In addition to their high cost, such amplifiers are unidirectional, that is, they can only pass signals in one direction. Obviously such systems are incapable of efficient bi-directional operation (i.e., a single fiberoptic strand cannot be used for sending information in both directions), a highly desirable characteristic if one is to fully utilize existing fiberoptic carriers. Some prior art WDM and DWDM systems have used a fiber grating or block grating to combine and/or split the signals. Unfortunately such grating systems cause signal loss resulting in the need for amplifiers, with their attendant problems, and are costly. Another problem with prior art WDM and DWDM systems is that typically such systems are useable only in existing long distance telecommunications networks, in which the transmission speed and data format are known, and a clock-recovery circuit is used to recover and retime the high speed signals. Typically, this is immediately prior to the step of combining the signals in an optical combiner. The clock-recovery circuit limits the system to transmitting data at a specified speed and according to a given format, usually the SONET transmission format. Often, short distance communication networks must transmit both optical and electronic information. Unfortunately, prior art DWDM systems are adapted primarily for optical data transmission. Furthermore, data must be transmitted on such networks in a variety of formats, such as ATM, EitherNet, Fiber Channel, FDDI, and others. As noted above, only single a rate format can be accommodated on a typical prior art DWDM systems, usually the SONET rate (such as 2,488.32 Mb/s.). Finally, short distance communications networks are often utilized in urban areas with expanding populations and communications needs. The optical transport portion of known prior art DWDM systems are difficult to expand, are generally not modular, and under any circumstances typically require a system shut down to expand the number of input channels the system can accommodated. This disrupts service and alienates customers. Thus conventional long distance WDM fiber optic systems are not suitable for short distance applications. What is needed is an optical communications systems adapted for short distance communication networks capable of handling data bi- directionally in numerous formats, that is expandable, can handle data at high transmission speeds, achieves this result at a minimal cost in terms of data loss, functionality, reliability and purchase and operational expense), and does not include extraneous components like amplifiers, external modulators, and clock recovery circuits. SUMMARY OF THE INVENTION The present invention provides an optical communication system capable of handling data bi-directionally in numerous formats, that is expandable, can handle data at high transmission speeds, and is cost efficient and reliable. In a first aspect, the present invention provides a bi-directional dense wavelength division multiplexing optical communications system capable of transmitting multiple signals over a single optical waveguide. The system including a plurality of channelizers, for converting optical or electronic input signals from a sending station into an optical signal having a predetermined wavelength range, independent of the optical and electronic characteristics of the original transmission, with each channelizer converting signals into its own predetermined wavelength range; an optical waveguide; at least one wavelength multiplexer, which receives optical signals from the channelizers, combines them into a single combined optical signal and transmits same to the optical wave guide; and at least one wavelength demultiplexer, which receives the combined signals from the optical waveguide and isolates the individual respective modulated optical signals and transmits them to a receiving station, all without significant loss of signal strength. In a second embodiment, the channelizer of the optical communications system also includes a photodetector, an electronic signal amplifier, a laser, and a laser driver, wherein each laser produces a modulated optical signal at a different respective and predetermined wavelength. In another aspect of the present invention, the wavelength multiplexers are capable of combining previously multiplexed signals from other wavelength multiplexers with signals from channelizers, and additional multiplexer's may be added without transmission interruption. In yet another aspect of the invention, the wavelength multiplexers and wavelength demultiplexers are structurally identical and interchangeable with each other, allowing bi-directional operation, and said multiplexers/demultiplexers use at least one optical film filter for wavelength selection and isolation. In still another aspect of the present invention, the channelizers are capable of converting both optical and electrical input signals into directly modulated optical signals having a respective predetermined wavelength range, and includes a directly modulated laser which produces the modulated optical signal. In yet another aspect of the present invention, the optical communication system includes at least five wavelength multiplexers, with the output ports of four of the five multiplexers feeding their combined signals to the fifth wavelength multiplexer, which in turn combines the combined signals and transfers the resultant combined signal to the optical waveguide. These and other features and advantages of this invention will become further apparent from the detailed description and accompanying figures that follow. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the description. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically depicts an optical communication system according to the present invention. FIG. 2 schematically depicts a channelizer (18) used in the optical communication system of FIG. 1. FIG. 3 schematically depicts a parallel cascade combination of multiplexer/demultiplexer sub units used in the optical communication system of FIG. 1. FIG. 4 schematically depicts a serial cascade combination of multiplexer/demultiplexer sub units used in the optical communication system of FIG. 1. FIG. 5 schematically depicts a serial/parallel hybrid cascade combination of multiplexer/demultiplexer sub units used in the optical communication system of FIG. 1. FIG.6 schematically depicts an interference filter-based optical multiplexer and demultiplexer used in the optical communication system of FIG. 1. FIG.7 schematically depicts an interference filter-based optical multiplexer used in the optical communication system of FIG. 1 , used in an alternative combination of multiplexer sub units. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 depicts the optical communications system 10 of the present invention. The optical communications system 10 is interconnected to two or more transmission elements, such as transmission element 12, transmission element 14 and transmission element 16, which form the "input" of the system. Each transmission element 14 transmits an information-bearing signal (not shown) from some outside source, such as a telecommunication system, LAN or cable television system, to the optical communications system 10 of the present invention. Some transmission elements are adapted to transmit an electronic signal, while others are adapted to transmit an optical signal. The optical communications system 10 of the present invention can accommodate a mixture of optical and electronic signals, as well as all the signals being optical or electronic. Optical signals are typically generated by the user's terminal equipment, such as the SONET multiplexer, available from Alcatel, Lucent, Nortel, and NEC, or the FDDI network interface, available from Osicom. Electronic signals are generally produced by a digital tape player or camera, such as the devices available from Sony, Hitachi, and Philips, or by fast network hubs and switches, such as those available from 3Com, Cisco, and Osicom. The optical communications system 10 can accommodate any number of transmission elements, however in a preferred embodiment, sixteen (16) are employed. In FIG. 1 , the dotted line between transmission element 14 and transmission element 16 is to demonstrate that additional transmission elements can be accommodated. The optical communications system 10 also includes a plurality of WDM wavelength channelizers, such as channelizer 18, channelizer 22 and channelizer 24, for receiving the transmitted information-bearing signal from the transmission element and transmitting an information- bearing optical signal at a predetermined wavelength. Typically, a single channelizer, such as channelizer 18, is interconnected with and receives an electronic or optical information-bearing signal from a single transmission element, such as transmission element 12. Referring to FIG.1 , the signal travels from the transmitting station 94 (shown within broken lines) to the receiving station 96 (also shown within broken lines). Optical signals are passed out of the demultiplexer 98 and, if the original signal from the transmission element 12 was electronic, on to an optional receiver 122 which will convert the optical signals back to their original electronic form and format, and then to a receiving element 124. If the original signal from the transmission element 12 was optical, then it is transmitted directly from the demultiplexer 98 to the receiving element 124. The receiving elements accepting optical signals are generally terminal equipment, such as SONET demultiplexer, available from Alcatel, Lucent, and Nortel, or FDDI network interface, available from Osicom. The receiving elements accepting electronic signals are generally digital tape recorders or routing switches available from Sony, Hitachi, and Philips, and Osicom, or fast network hubs and switches, available from 3Com, Cisco, Osicom. FIG. 2 shows a channelizer 18 constructed according to the present invention. The channelizer 18 has an electronic input 26 and an optical input 28, so as to accept both electronic and optical input. Optical signals, from the optical input 28 are converted into an electronic signal by an electro-optical converter such as photo detector 32. Photo detector 32 can comprise any number of commercially available electro-optical converter, such as those sold by Lucent, Epitaxx, Fujitsu, and Hewlett-Packard. That electronic signal is then amplified by a preamplifier and then a main amplifier, such as preamplifier 34 and main amplifier 36. The resulting amplified information-bearing electronic signal is used to control a laser driver 38 (shown in FIG. 2 within broken lines). If the original information-bearing signal is an electronic signal, it passes through a signal conditioning circuit where it is filtered and amplified, and the resultant amplified information-bearing electronic signal is used to control the laser driver 38. The laser driver 38 is commercially available and includes a modulator controller 46, a laser bias controller 48, a laser power monitor 52 and a laser modulator 54. The laser modulator 54 modulates the current powering the laser 56 in accordance with the amplified information-bearing electronic signal. The modulator controller 46 controls the magnitude of the variation in electrical current transmitted to the laser 56. The laser bias controller 48 provides the required laser bias current. An automatic temperature controller 62, which typically includes a temperature sensing device such as a thermister 64, and heating/cooling device, typically a thermoelectric cooler 66, is included to provide a stable operating temperature for the laser 56, thereby insuring greater precision in the operating wavelength of the optical output 58. The laser 56 may be selected from a number of commercially lasers, and semiconductor lasers have been found to be particularly useful. The laser 56 produces an optical signal at a predetermined channel wavelength, corresponding to multiplexer 68 and demultiplexer 98 channels (see FIGs. 1 and 3-6). Typically, wavelengths emitted by channelizers are selected to be within the 1500 nanometer range, the range in which the minimum signal attenuation occurs for silica-based fibers. The wavelengths can also be selected in 1300 nanometer range, the range in which the minimal signal dispersion occurs for the silica- based fibers. Other wavelength band may be also selected according to user requirements. FIG. 1 shows a plurality of channelizers (18, 22 and 24) feeding their respective optical output (58a, 58b and 58d) into a single multiplexer 68. Showing a single multiplexer 68 in FIG. 1 is purely for drafting convenience. In a preferred embodiment, any number of multiplexers may be used. For instance, FIG. 3 shows four multiplexers, multiplexer 68, multiplexer 72, multiplexer 74 and multiplexer 76. Just as with the single multiplexer 68 in FIG. 1 , the four multiplexers in FIG. 3 are merely illustrative of the fact that the number of multiplexers is variable. As can be seen from multiplexer 68 in FIG. 3, the optical output from many channelizers (shown as optical output 58a, optical output 58b, optical output 58c and optical output 58d) can be processed by a single multiplexer 68. FIG. 6 shows how multiplexer 68 combines plural information- bearing optical signals at selected wavelengths, such as optical output 58a, optical output 58b, optical output 58c and optical output 58d, onto a single waveguide, typically at a low loss. Such an information-bearing signal at a DWDM wavelength from a channelizer, for example optical output 58a, is feed into a multiplexer input port 78a. Other information- bearing signals from different channelizers (and at different DWDM wavelengths) are fed into different multiplexer input ports (e.g., optical output 58b is fed into multiplexer input port 78b, optical output 58c is fed into multiplexer input port 78c, and optical output 58d is fed into multiplexer input port 78d). All of these information-bearing optical signals are combined by the multiplexer 68 into a single information-bearing optical signal which is sent on a single optical waveguide, such as optical waveguide 82. Optical waveguide 82 extends from the output port 80 of multiplexer 68. Thus the combination of the optical output 58a-d of the various channelizers (18, 22 and 24), forms the multiplexed optical signal which is the output of the multiplexer 68. The optical waveguide 82 is typically a single mode optical fiber, and is the principle transmission medium. In an optical communications system 10 (FIG. 1 ) with but a single multiplexer, such as multiplexer 68, the optical waveguide 82 is the link between "sender" and "receiver." However, as can be seen from FIG. 3, any number of multiplexers (e.g., multiplexer 68, multiplexer 72, multiplexer 74 and multiplexer 76) may form the inputs to another multiplexer 84. This is also shown in FIG. 7, in which multiplexer 84 is receiving optical waveguide 82 from multiplexer 68 at multiplexer input port 78a; optical waveguide 86 from multiplexer 72; optical waveguide 88 from multiplexer 74 and optical waveguide 92 from multiplexer 76. Of course, a multiplexer is not limited to receiving either all optical waveguides from multiplexers or all optical outputs from channelizers; the user is free to "mix and match." For example, the user could alter the configurations shown in FIGs. 6-7 and used multiplexer input port 78a of multiplexer 84 to receive optical output 58a from channelizer 18 (FIG.2), while using the remaining input ports (e.g., multiplexer input ports 78b-d) for optical waveguide 86, optical waveguide 88, and optical waive guide 92 (FIG. 3), from other multiplexers. The combinations are limitless. Referring to FIG. 1 , in describing the manner in which data travels from the transmitting station 94 (shown within broken lines) to the receiving station 96 (also shown within broken lines), only the simple model in which a single multiplexer 68 receives the optical output (58a, 58b and 58d) of three channelizers (18, 22 and 24) will be discussed. Again it should be emphasized that virtually any number of channelizers and multiplexers could be employed in an infinite number of combinations. Optical waveguide 82 extends from multiplexer 68 at one end of the optical waveguide 82 and from demultiplexer 98 at its other end. Thus the multiplexed optical signal from multiplexer 68 is brought to demultiplexer 98. The demultiplexer 98 is structurally identical to the multiplexer 68. By sending a multiplexed optical signal into the demultiplexer 98 in what would be the output port 80 of the multiplexer 68, the process of the multiplexer 68 is reversed and it becomes a demultiplexer 98, a device separating a information-bearing signals from a single waveguide into plural information-bearing optical signals at selected wavelengths and routing them onto separate waveguides, typically at low loss. To view the process in greater detail, FIG. 6 shows multiplexer 68 and a demultiplexer 98. Multiplexer 68 has a plurality of reflectors, one for each multiplexer input port, such as reflector 102, reflector 104, reflector 106 and reflector 108. Each reflector is coated with a wavelength- selective dielectric thin-film filter. These consist of high and low refractive index dielectric films in alternating layers, which pass information-bearing optical signals of a predetermined wavelength, but reflect all other wavelengths. By changing composition of the dielectric films, the desired wavelength can be selected. Thus optical output 58a has been transmitted by channelizer 18 (FIG. 1 ) at the predetermined wavelength noted in FIG. 3 as λ1. The dielectric filter of reflector 102 is thus designed to pass only optical signals at wavelength λ1. Theoretically, optical output 58a is only at wavelength λ1. However, any errant optical signal at some other wavelength would not pass into multiplexer 68, providing an extra assurance of signal quality. Optical output 58a is thus passed through reflector 102, and to the interior side of reflector 104. Similarly, reflector 104 will only pass an optical signal at wavelength λ2 from optical output 58b, which is joined with the signal from optical output 58a and passed to the interior side of reflector 106. The process repeats itself until all incoming optical signals are joined (in this example, λ1 , λ2, λ3 and λ4) onto optical waveguide 82. Viewing FIG. 6 along side FIG. 1 , optical waveguide 82 transmits the joined optical signals to demultiplexer 98, entering at input port 110 which is an exact duplicate of output port 80 of multiplexer 68. Reflector 112, just like reflector 102 of multiplexer 68, is adapted to allow only optical signals of wavelength λ1 to pass (which are passed out of the demultiplexer 98 and to an optional receiver 122 which will covert the optical signals back to their original form and format, and then to a receiving element 124), and to reflect all other wavelengths. Unlike reflector 102 of the multiplexer 68, such reflection is in the interior side of reflector 112, and such signals (at wavelengths λ2, λ3 and λ1 ) are reflected to reflector 114. Reflector 114, similarly, will pass only signals at wavelength λ2, and reflect to reflector 116 the remaining wavelengths (A3 and λ4). As can be seen, this process repeats itself any number of times for any number of wavelengths. The above discussion focused upon an embodiment in which only a single multiplexer 68 and a single demultiplexer 98 are employed. In a preferred embodiment, they can consist of plural sub units, arranged in any number of ways. FIGs. 3-5 show three such configurations: parallel cascade (FIG. 3), serial cascade (FIG. 4), and hybrid cascade (FIG. 5). In the parallel cascade configuration, depicted in FIG. 3, output ports of plural sub units of multiplexer (68, 72, multiplexer 74 and 76), as a group of information-bearing optical signals from a group of channelizers are fed into input ports of multiplexer 84. That combination of signals forms a multiplexed optical signal which is output to optical waveguide 126. In the serial cascade configuration, depicted in FIG. 4, output ports of plural sub units of multiplexers (72, 74 and 76) are connected serially to multiplexer 68, which outputs the combined signal to optical waveguide 82. In the parallel cascade configuration, depicted in FIG. 5, the output port of multiplexer 68 is connected to an input port of multiplexer 72, and the output port of multiplexer 76 is connected to an input port of multiplexer 74. Outputs of multiplexer 72 and multiplexer 74 are fed into multiplexer 84 which in turn combines all channels onto optical waveguide 126. The same configurations can be used with demultiplexers. For instance, FIG. 3 shows demultiplexer 98, demultiplexer 128, demultiplexer 132, demultiplexer 134 and demultiplexer 136 in parallel cascade, while FIG. 4 shows the same demultiplexers in serial cascade, and FIG. 5 shows them in a hybrid cascade configuration. Although in FIGs. 3-5 all show multiplexers in the same configuration as demultiplexers, users are free to mix configurations. For example, although not shown, a user could arrange multiplexers in a hybrid cascade configuration and demultiplexers in parallel cascade. Other combinations are limited only by the inventiveness of the user. Providing a optical communications system 10 without long distance specific equipment such as amplifiers, external modulators and clock recovery systems allows complete bi-directional operation. Thus, without any set-up or alteration of the system, if for example, information-bearing signals are fed into demultiplexer 128, demultiplexer 132, demultiplexer 134 and demultiplexer 136 (FIGs. 3-5) then these demultiplexers act as multiplexers, and similarly multiplexer 68, multiplexer 72, multiplexer 74 and multiplexer 76 function as demultiplexers. A further advantage of the optical communications system 10 of the present invention is a modularity of the multiplexers and demultiplexers. Referring to FIG. 3, if usage changes, such that for example, multiplexer 68 and demultiplexer 128 are no longer necessary, or require servicing or repair, they can be removed without disruption to the rest of the system. Conversely, if additional channels are required, additional multiplexer(s) (not shown) can be added in any number of ways, such as attaching the optical waveguide from an additional multiplexer to the multiplexer input ports, such as multiplexer input port 78a of multiplexer 68 (FIG. 3). Corresponding demultiplexers can be added (also not shown). Having now described the invention in accordance with the requirements of the patent statutes, those skilled in the art will understand how to make changes and modifications in the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.

Claims: WHAT IS CLAIMED IS: 1. A dense wavelength division multiplexing optical communications system for transmitting a plurality of information-bearing signals between a first station and a second station over a single optical waveguide, said communications system comprising: a plurality of channelizers, each channelizer capable of converting a respective optical or electronic input signal from said first station into a respective modulated optical signal having a respective predetermined wavelength range, independent of the optical and electronic characteristics of the transmission from the first station, and each of said channelizers having a different predetermined wavelength range; an optical waveguide, having a first end and a second end; at least one wavelength multiplexer, having a plurality of input ports, with each of said channelizers transferring a respective said modulated optical signal to a different one of said input ports, and at least one output port adjacent to said first end of the optical waveguide, for combining the modulated optical signals and transferring the combined signals onto the optical waveguide for transmission to the second end of the optical waveguide; at least one wavelength demultiplexer, having at least one input port and a plurality of output ports, said input port being adjacent to the second end of the optical waveguide and receiving said combined signals from the optical waveguide, said demultiplexer isolating the individual respective modulated optical signals and transmitting each of said isolated individual optical modulated signals to respective output port for transmission to the second station; wherein modulated optical signals are combined and transmitted on a single optical waveguide, and after transmission isolated back into respective modulated optical signals without significant loss of signal strength. 2. The optical communications system of Claim 1 wherein each of said plurality of channelizers further comprises: a photo detector for directly converting an optical input signal into a respective electronic signal; an electronic signal amplifier, for amplifying said resulting electronic signal; a laser; and a laser driver for directly modulating the output of the laser according to said resulting electronic signal; wherein each said laser produces a modulated optical signal at a different respective said predetermined wavelength range. 3. The optical communications system of Claim 1 wherein at least one of said multiplexers further comprises an additional input port adapted for receiving the combined signals from the output port of an added multiplexer, allowing said combined signals to be further combined with said modulated optical signals of said at least one of said multiplexers, wherein additional multiplexers may be added without transmission interruption. 4. The optical communications system of Claim 1 wherein said at least one wavelength demultiplexer and said at least one wavelength multiplexer are structurally identical and interchangeable with each other, each of the input ports of the multiplexer serving as an output port of the demultiplexer, the output port of the multiplexer serving as the input port of the demultiplexer, the input port of the demultiplexer serving as the output port of the demultiplexer and the output ports of the demultiplexer serving as input ports of the multiplexer, thereby allowing bidirectional operation of the optical communications system. 5. The optical communications system of Claim 5 wherein said at least one multiplexer further comprises at least one optical film filter for wavelength selection and isolation. 6. The optical communications system of Claim 1 wherein at least one of said plurality of channelizers is capable of converting both optical and electronic input signals into directly modulated optical signals having a respective predetermined wavelength range. 7. The optical communications system of Claim 1 wherein at least one of said plurality of channelizers further comprises a directly modulated laser which produces said modulated optical signal. 8. The optical communications system of all of the above Claims wherein said at least one wavelength multiplexer further comprises at least five wavelength multiplexers, a first wavelength multiplexer, a second wavelength multiplexer, a third wavelength multiplexer, a forth wavelength multiplexer, and a fifth wavelength multiplexer, the outport port of the first wavelength multiplexer transmits its combined signals to one of said plurality of input ports of said fifth wavelength multiplexer, said second wavelength multiplexer transmits its combined signals to another one of said plurality of input ports of said fifth wavelength multiplexer, said third wavelength multiplexer transmits its combined signals to another one of said plurality of input ports of said fifth wavelength multiplexer, and said forth wavelength multiplexer transmits its combined signals to another one of said plurality of input ports of said fifth wavelength multiplexer, whereby said fifth wavelength multiplexer combines said combined signals and transfers the resultant combined signal to the optical waveguide.

Inventors: CHENG XIN, HUANG SHOUHUA, CHENG, XIN, HUANG, SHOUHUA
Applicants: OSICOM TECHNOLOGIES INC, OSICOM TECHNOLOGIES, INC.
Application year: 1999
Main classification: H04J14
IPC codes: H04B10, H04J14