MXPA97006479A - Optical communication system that uses spectralme divided optical source - Google Patents

Abstract

The present invention relates to an apparatus and method of multiple-wavelength wavelength signals using a single broad-band optics, such as an LED, for generating many independent optical wavelength channels. An optical transmitter includes a wavelength channel that defines the assembly that resolves the wide-spectrum pulse outputs by the source in discrete wavelength bands that constitute the respective pulses (ie, wavelength channels) and that insert a delay between the bands to define a sequence of individually steerable channels. According to one embodiment of the invention, the spectral division is achieved by means of a multiple channel filter, and the insertion of the respective delays is achieved by individual fiber sections, each section having a selected length to introduce a particular delay, coupled to the output ports of the router. The inserted delays can be conveniently selected to separate adjacent wavelength channels and thus reduce the likelihood of crosstalk to a minimum. The pulses of the so-resolved channels arrive at different times at a multiplexer which can be configured, for example, as a passive WDM multiplexer or as a star combiner. The resulting sequence of steerable wavelength channels can be supplied to one or more high-speed broadband modulators, with each modulator being operable to modulate some or all of the channels

Description

OPTICAL COMMUNICATION SYSTEM THAT USES SPECTRALLY DIVIDED OPTICAL SOURCE FIELD OF THE INVENTION The present invention relates generally to optical communication systems and, more particularly, to improvements in optical communication systems employing wide spectrum, spectrally divided optical sources.

BACKGROUND OF THE INVENTION The transmission capacity of optical communication systems is currently limited by the modulation bandwidth of the optical source and the dispersed and non-linear propagation effects. Although a fiber optic section has a very wide optical bandwidth (10-20 THz), the speed of data transmitted on such sections is currently limited to approximately 2.5 Gbits / sec in single channel communication systems. Wavelength division multiplexing (WDM) generally increases the capacity of the optical system by simultaneously transmitting data on various optical carrier signals at different wavelengths. REF: 25171 The total capacity of the system is increased by a factor equal to the number of different wavelength channels. Another advantage of the WDM is realized in the systems of communications from one point to multiple points such as fiber to the home. In this case, the provision of improved power decomposition, security, update capacity, service flexibility, and lower component speed requirements compared to time division multiplexed point-to-point (TDM) links make the WDM attractive . The WDM systems which until now had been proposed generally include a separate optical modulation source for each channel or individual transmission wavelength. For example, an array of laser diodes can be used - with each laser diode being tuned to a different and individually modulated frequency. The laser frequencies are combined as, for example, by means of an optical coupler and then thrown towards one end of an optical fiber. At the other end of the fiber, the wavelength channels are separated from each other and directed towards the corresponding receivers. Due to the number of technical problems, the WDM systems proposed so far are not considered commercially viable for mass market applications as well as fiber distribution to the home. One such problem is the small number of channels currently accommodated. Especially, although a WDM system could be considered cheap if a large number of channels were made available (32-64 or even 128), the current multi-channel laser diodes are very difficult to manufacture with acceptable performance even with as few channels as 8. . Further. The passive WDM dividers currently available have a large temperature variation of their passband channels, thus requiring a continuous tuning capability in the multi-channel sources that has not yet been achieved. Therefore, although the WDM offers an elegant solution to increase the capacity and transparency of optical networks, the WDM for fiber distribution networks as they are currently conceived are not considered cost competitive with simple point-to-point schemes. (one fiber per user), and cheaper packages are needed. For fiber optic home communications systems, low cost methods of providing optical signals in and out of the home is a challenging problem. Although time domain multiplexing (TDM) of data streams could be another method to increase transmission capacity, it is not desirable to build a specific network with expensive high frequency electronic components that are difficult to update in the future. For example, to free or provide data speeds of 50 Mbits / sec in a single home, a 32 channel system could require transmitters, routers, amplifiers, receivers and modulators with a capacity of 1.5 Gbits / sec and greater. It is not desirable to place such expensive state-of-the-art components in every home. In addition, it is desirable to have both the system in the field and in the home transparent and passive, that is, regardless of the speed of the line that does not require an electrical power supply. In addition to the low data rate systems required for local access (50 - 155 MHz), high-speed data systems (622 MHz - 2.5 Gbits / sec) can also benefit from the WDM. In such a case, similar problems are caused by the difficulty of obtaining a source of multiple frequencies with proper channel tuning, stability and modulation bandwidth. As is clear from the foregoing, there is a continuing need for an efficient and inexpensive WDM system that is capable of transmitting a large number of spectral channels.

BRIEF DESCRIPTION OF THE INVENTION The aforementioned deficiencies were addressed, and an advance of the technique was made, by spectral division of the output spectrum of an optical source into a sequence of individually steerable length channels. According to an illustrative embodiment of the present invention, the spectral division is achieved by a multi-channel filter such as, for example, an optical waveguide grating router, and the sequence defined by a plurality of optical delay lines. coupled to the outputs of the multi-channel filter. According to the invention, each delay line is associated with a respective wavelength channel and provides a delay of that channel, which differs from the delay introduced in all other channels so that a repeated sequence of channels or channels is provided. pulses of discrete wavelength. The pulse current thus formed can then be multiplexed, modulated and transmitted on an optical medium such as, for example, one or more fibers in a single mode to a remote receiver. Advantageously, a high-speed single-channel modulator can be used to separately modulate each of the wavelength channels - obviating the need for large arrays of modulators, wherein one modulator is used for each wavelength, associated with the previous configurations. Illustratively, each delay line can be configured as a fiber section coupled to a corresponding output port of the waveguide grating router, with the length of each respective fiber section determining the magnitude of its corresponding delay. The lengths of the adjacent delay line fibers can be selected so that the wavelength pulse series are re-ordered before transmission to the remote receivers. Linear crosstalk due to spectral superposition between channels has been identified as a significant problem in WDM systems that employ spectrally divided sources. According to a particularly preferred embodiment of the present invention, the arrival times of the spectrally adjacent divided channels, as observed by a remote receiver, are rearranged in such a way as to reduce such overlap between channels. An optical multiple wavelength communication system is formed using the multiple wavelength apparatus in conjunction with a multiple wavelength receiver to demultiplex the coded optical signal received in the plurality of modulated optical wavelength channels.

BRIEF DESCRIPTION OF THE DRAWINGS The features and benefits of the invention mentioned above will be better understood from a consideration of the following detailed description taken in conjunction with the accompanying drawings, in which: FIGURE 1 is a block diagram of a communication system of multiple wavelength constructed in accordance with the present invention; FIGURE 2A is a graphical representation of an illustrative sequence of broad spectrum pulses of which a plurality of discrete wavelength channels are derived according to one aspect of the present invention; FIGURE 2B is a graphical representation of channels of discrete wavelength after the spectral direction; FIGURE 3 is a schematic diagram of a multiple wavelength communication system in which a wavelength channel is used that defines the assembly constructed in accordance with an illustrative embodiment of the present invention; FIGURE 4 describes the ideal transmission function of a multiple wavelength filter that can be used in the wavelength channel that defines the assembly of FIGURE 3; FIGURE 5A shows an integrated optical WDM device conventionally used to implement the waveguide grating router (WGR) used as a multi-channel filter in the embodiment of FIGURE 3; FIGURE 5B shows the periodic step band transmission characteristic of the router device of FIGURE 5A; FIGURE 6A is an exemplary frequency spectra of a light emitting diode (LED) that can be employed as a wide spectrum optical source in accordance with the present invention; FIGURE 6B describes the frequency spectrum of FIGURE 6A after spectral amplification and division to produce a number of discrete wavelength channels according to the present invention; FIGURE 7 shows the measured, delayed pulse current of eight wavelength channels produced by the wavelength grid router used in the illustrative embodiment of FIGURE 3, after the insertion of delays and the consequent rearrangement; FIGURE 8A shows the signals of FIGURE 7 after transmission, demultiplexing, and detection of a remote receiver; FIGURE 8B shows the ocular pattern, with data modulation, at -32 dBm of energy received from one of the received and detected channels provided during the operation of the illustrative configuration described in FIGURE 3; FIGURE 9A is a schematic diagram of a wavelength channel defining the assembly constructed in accordance with another embodiment of the present invention; and FIGURE 9B is a schematic diagram describing a wavelength channel defining the assembly constructed in accordance with a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, the wide spectrum output of a suitable optical source - illustratively, a light emitting diode (LED) having an output centered at a typical telecommunications wavelength such as, for example, 1550 nm - it is divided spectrally and therefore processed in such a way that it allows it to serve a larger number of subscribers than what had hitherto been considered practicable. An illustrative multiple wavelength optical communication system 10 constructed in accordance with the present invention is shown schematically in FIGURE 1. As seen in FIGURE 1, the system 10 includes a transmitter 12 and a receiver 14. wide-spectrum optical pulse 16, of the optical source 18, is amplified by the amplifier 20 and supplied to the channel defining the assembly 22. A pulse generator 23 determines the width and speed of repetition of the broad-spectrum pulses which, illustratively, they can be 2.5 ns and 20 ns, respectively (FIGURE 2A). As will be explained in more detail below, the wavelength channel defining the assembly 22 is operable to the spectral division of the output pulses provided by the optical source 18 in a plurality of discrete wavelength bands in the form of pulses. Individuals? -? n and, as indicated conceptually in FIGURE 2B, insert a time delay between them so that they are individually steerable. That is, the wide-spectrum source is divided spectrally and processed to form a series of pulses of modulated data, each at different wavelengths. Each different wavelength (referred to herein as a wavelength channel) is modulated with the information to be transmitted on that particular channel. The transmitter 12 of the present invention provides a method of transmitting data over many separate wavelength channels, using only a single broadband modulator. Optionally, a frequency-dependent filter (not shown) may be connected such as, for example, a coating discharge fiber grating or a multilayer interference filter at the output of the wavelength channel defining the assembly 22 to equalize the energy spectrum or power of some or all of the optical wavelength channels. In the embodiment of FIGURE 1, a data generator 24 generates multiple low frequency data signals (illustratively 8-16 channels at 50 Mbits / sec per channel, for local access applications) that are multiplexed by time division (TDM) up to a high data rate (400-800 Mbits / sec), in this example) by an electronic TDM unit (not shown). The resulting wavelength channels are encoded by the modulator 26 using the output of the high-speed data signal over the wavelength channel that defines the assembly and amplified by the amplifier 25. As will be readily appreciated by those skilled in the art. In the technique, the high-speed data signal should have a data rate that is at least equal to the speed (?) of the wide-spectrum pulse rate multiplied by the number of wavelength channels used.

Advantageously, the high-speed data signal contained can be encoded on the multiple-channel optical signal by passing it through a wide-band optical modulator 26. This modulator 26 is capable of modulating the optical signals over a range of length Wide wave (50 nm bandwidth), typically) and has low polarization dependence. A bulky InGaAsP waveguide modulator is the preferred modulator 26 of this embodiment, however, any broadband optical modulator could be used. The output of the modulator 26 is transmitted on an optical medium 28 (e.g., a single-mode optical fiber) to a multiple wavelength receiver 14 comprising, for example, a passive WDM divider router 30 which demultiplexes the signal optical received in a plurality of modulated optical wavelength channels 32 (e.g., 50 MHz WDM channels) which is intended to be for the optical network unit 34 (ONU) of a particular subscriber. Although the receiver 14 has been described as using a passive WDM divider or router, it should be understood that a waveguide grating router, diffraction grating, interference filter array or other apparatus can be used to demultiplex the received optical signal. in the plurality of modulated optical wavelength channels.

A research system that uses a LED centered at 1550 nm as an optical source to serve up to 64 subscribers is described in FIGURE 2. It should be noted that although an output spectrum centered at approximately 1550 nm is shown and described in detail here, nevertheless it was contemplated that the output spectrum of the optical source may alternatively be centered around some other wavelength of interest such as, for example, 1,300 nm, and reference is made here to any particular wavelength band is by way of example Illustrative only. It should be readily appreciated by those skilled in the art that the number of subscribers that can be served by a single optical source depends on the output power. In the exemplary arrangement of FIGURE 3, in which the optical source is a focused LED at 1550 nm, the amplifier 20 is preferably configured as a conventional erbium-adulterated fiber amplifier (EDFA). Fiber amplifiers are not currently available, however, for many other wavelength bands, such as those around 1300 nm. In such cases, a semiconductor optical amplifier may be used. The semiconductor optical amplifier can, if desired, be integrated with an optical LED source to obtain a monolithically integrated amplifier LED structure. It is believed that the manufacture of such devices is within the experience of those familiar with the art. For a detailed description of an integrated LED-amplifier suitable for 1300b nm, however, reference may be made to an article by K. -Y. Liou et al., Entitled "LED-Monolithically Integrated Semiconductor Amplifier for Applications as a Transceiver in Fiber Access Systems", IEEE Photonics Technology Letters, Vol. 8, p. 800-802. In any case, and continuing with reference to the illustrative embodiment of FIGURE 3, it should be noted that the channel defining the assembly 16 includes a multiple channel filter device (e.g., a waveguide grating router 36) that selects and routes each successive wavelength channel to a corresponding optical delay line (e.g., fiber optic sections 38a-38h) with as little crosstalk between the adjacent channels as possible. The transmission spectrum (wavelength comb) of an ideal multiple channel filtering device which can be employed as shown in FIGURE 4. FIGURE 5A shows an integrated optical WDM device conventionally used to implement a fiberglass grating router. spectral division waveguide (WGR). FIGURE 5B shows the periodic passband transmission characteristic for the router device 36. Within the band center, there is a number of desired transmission channels. Outside that region, the integrated optical WGR components exhibit a periodic bandpass behavior. For a detailed description of the construction and operation of such a router, reference may be made to an article by C. Dragone et al., Entitled "Integrated Optical NXN Multiplexer on Silicon" IEEE Photonics Technology Letters, Vol. 3. Pp. 896-899 , 1991. To release an exemplary data rate of 50 Mb / sec per channel, the LED comprises the illustrative optical source 18 was directly modulated, at a peak power of -7.9 dBm, with 2.5 nsec pulses at a repetition rate of 20 nsec. Such modulation results in a wide spectrum pulse such as that shown in FIGURE 6A. In the arrangement described in FIGURE 3, the amplifier 20 was configured as a two-stage fiber amplifier and was observed to increase the spectrally divided output at a peak power of -7 dBm per channel. The measured signal gain provided by the fiber amplifier was 22 dB. The 200 GHz channel spacing of the spectral division WGR 36 filtered the amplified spontaneous emission noise of the fiber amplifier 20. FIGURE 6B shows the spectrally divided output spectrum, amplified, of the wavelength channel 4. The repetition peaks in FIGURE 4 are separated by the free spectral range of 128 Á of the WGR. All other channels exhibit optical spectra similar to those in FIGURE 4, except that they are equally separated by the channel separation of 16 Á of the WGR employed. It should be readily appreciated by those skilled in the art from the comparison of FIGURES 2 and 4 that the amplified and divided spectrum is modified by the optical gain spectrum of the fiber amplifier adulterated with erbium 18. The measured total insertion loss The WGR for each channel, including the loss of spectral division, was approximately 21 dB. Returning to FIGURE 3, it should be noted that in addition to the multiple channel filter such as the WGR 36 and the delay l 30a-30h, the illustrative wavelength channel defining the assembly 22 further includes the multiple output port, optical coupler of multiple output port 40. In a form that will now be described, the delay l and the coupler serve collectively to multiplex the output of the spectrally divided LED of the multiple channel filter into a sequence of individually steerable wavelength channels indicated generally as channels 1-8. According to the present invention, fiber delay l of different lengths are used at each of the output ports of the waveguide grating router 36 to delay a pulse width per channel and then multiplex, via the coupler. multiple port 40, the respective pulses in a sequence of repeated pulses. In the illustrative eight channel system described in FIGURE 3, in which it is desirable to obtain a data rate per channel of 50 Mb / s, the optical source 18 is pressed with 1 / (8 X 50 Mb / s), producing a pulse width of 2.5 nsec at a repetition frequency of 400 MHz. The delay l are passive and easy to implement. Illustratively, for the single-mode fiber used at 1.3 μm with an index n of about 1.5, the delay time is 20.5 cm / nsec. Consequently, a delay of 2.5 nsec is obta for each 0.51 meters of fiber. According to an especially preferred embodiment of the present invention, the different length delay l are arranged in such a way (not shown) that they reorder the monotonic sequence of the output of the channels by the router 36 in a different order in the which adjacent wavelengths are separated to minimize the effects of crosstalk due to spectral superposition. By way of illustrative example, channels 1-8 can be rearranged as shown in FIGURE 3 to obtain the sequence of channels 1, 4, 7, 2, 5, 8, 3 and 6 by the use of delay llengths fiber of 0.51 meters, 2.04 meters, 3.57 meters, 1.02 meters, 2.55 meters, 4.08 meters, 1.53 meters, and 3.06 meters, respectively. Such an arrangement therefore provides a separation between the wavelength channels which is sufficient to overcome the disadvantages associated with the spectrally divided systems of the prior art. Of course, the delay l 38a to 38h employed can be arranged to achieve any desired sequence of wavelength channels and the specific arrangements shown and described herein are by way of illustrative example only. FIGURE 7 shows the measured pulse current of the eight wavelength channels -produced by the waveguide grating router 18 after the insertion of the delays and the consequent rearrangement to obtain the sequence mentioned in the previous example. The variation of power or output power of the channel, determ from the peak intensities in FIGURE 7, was 1.6 dB. As noted above, the multiplexing of the plurality of wavelength channels thus created or variable delay pulses is achieved by the optical coupler 40. In the 8-channel mode shown in FIGURE 3, up to 64 subscribers can be served from a single optical source using a star coupler that has eight input ports and eight output ports to combine the respective delayed pulse channels into a single eight-channel sequence that is then evenly divided among the eight output ports of the coupler. The star coupler 40 used in the arrangement of FIGURE 3 combines the pulse current in the desired order that had a measured insertion loss of 9.5 dB. A single modulator, such as one of the modulators 26a-26h coupled to a respective output port of the optical coupler 40, can be operated to modulate some or all of the channels present in the multiple channel sequence. As will be readily appreciated by those skilled in the art, the multiple channel filter and optical coupler of the wavelength channel defining the assembly 22 introduces considerable insertion loss. Consequently, care should be taken to ensure that the output power of the optical source is sufficient for the number of subscribers that will be served. In the exemplary system described in FIGURE 3, each modulator such as M1 through Mn was configured as a structure independent of polarization and was integrated monolithically with a semiconductor amplifier to ensure a suitable signal level for transmission to the receiver 14. Any arrangement of optical receiver capable of receiving and demultiplexing an optical signal comprising a plurality of wavelength channels for subsequent distribution to the respective subscribers. In the illustrative example of FIGURE 3, a passive WDM receiver using a multi-channel filter 42 similar to that used in the wavelength channel defining assembly 22. The integrated optical versions of the WDM filtering device 42 have been provided. been made on silica-on-silicon substrates and with InGaAsP guides including microcircuit amplifiers. Bulky components, consisting of arrays and fiber grids, or multiple interference filter components could also be used to provide a passive WDM receiver. Using a second WGR 42 at receiver 14 for the passive WDM demultiplexing of the eight channels, an insertion loss of 12.5 dB was observed. The received demultiplexed signals, detected using a p-i-n receiver, are shown in FIGURE 8A. With data modulation, the ocular pattern in the received power of -321 dBm of a typical channel is shown in FIGURE 8B. According to the invention, if a WDM divider in the receiver 14 is updated or changed (causing changes in the wavelength channels), the TDM source in the transmitter 12 can be easily changed to accommodate the new channel length of wave. This method is attractive since all the high speed TDM electronic devices are in the transmitter 12 which can be located in a central office, and the simple passive WDM 42 (in the receiver 14) is located, literally, in the field in where it is less accessible and where it is more hostile. FIGURES 9A and 9B describe alternative implementations of a wavelength channel defining the assembly that may be employed in accordance with the present invention. By comparing the wavelength channel defining the assembly 22 of FIGURE 9A with the configuration used in the illustrative system of FIGURE 3, it will immediately be apparent that the positions of the optical coupler and the multiple channel filter can be reversed. In the illustrative embodiment of FIGURE 9A, amplified wide spectrum pulses 16 'received from the optical source (not shown) are divided by a star coupler 1 XN 40', with N denoting the number of channels to be spectrally divided. of the wide spectrum pulses, to thereby form a plurality of power split replicas of the input signal. The optical delay lines 38a 'to 38h' delay the respective wide-spectrum pulse sequences in the same way that the spectrally divided pulses were delayed in the modality described above. These delayed pulse sequences are then fed to the respective inputs of a multi-input WDM demultiplexer., multiple outputs, such as, for example, the wavelength grating router MXN 36 ', where N is the number of input wavelength channels and M is the number of output signals containing a sequence of channels of wavelength. Sequentially, the multiplexer spectrally divides into each of the respective wavelength channels of a corresponding delayed wide spectrum pulse to form a plurality of output signals each of which contains a sequence of steerable wavelength channels. or individually treatable. As will be readily understood by those skilled in the art, the order in which the respectively delayed broad-spectrum pulse sequences are released to the WDM multiplexer inputs determines the order of the wavelength channels so that, in one form similar to that described in relation to the illustrative embodiment of FIGURE 3, the wavelength channels can be advantageously rearranged to reduce the crosstalk associated with the spectral superposition. In the wavelength channel defining the assembly 22"of FIGURE 9B, the multi-channel filter is configured as a conventional WDM 1 XN demultiplexer 36", while the optical coupler is configured as a WDM MXN multiplexer, as, for example, the wavelength grating router MXN 38", where N is the number of input wavelength channels, and M is the number of output signals that contain a sequence of wavelength channels As can be seen in FIGURE 9B, the respective output ports of the demultiplexer are coupled by optical delay lines 38a "-38h" to the corresponding output terminals of the multiplexer FIGURE 10 shows an exemplary network in which a system of Spectrally constructed split WDM transmission constructed in accordance with the present invention could be installed.The data enters a switching network 50 from a data source or from another network. ón 50 formats the multi-channel data in a high-speed TDM stream 52 to be used with the WDM transmitter. The modulators (not shown) of the WDM transmitter 12 then encode the high-speed TDM data stream over the individually directed sequence of the spectrally divided wavelength channels and transmit the data through one or more fiber systems. of transmission (illustratively, 10-20 km) - only one of which, generally indicated in reference number 54, is shown - to the remote location where the WDM divider device 56 is located. The individual wavelength channels are then separated in the WDM device 56, and each wavelength signal is directed to a separate ONU (optical network unit) 58, which receives the data with a decoder receiver operation low speed, illustratively, at 50 MHz. Although the above detailed description has described the present invention mainly in terms of particular applications of WDM systems of spectrally divided source, it should be understood that the discussed modes are exemplary only. Many variations can be made in the arrays shown, including the type of optical signaling source, the selection and arrangement of the channel filtering and the optical coupling components within the wavelength channel that defines the assembly, the type of signal lines optical delay, the type of optical modulator, the type of WDM splitter, and the type of network architecture for the implementation of a delay insertion WDM system, spectrally divided. Those and other alternatives and variations will be readily apparent to those skilled in the art, and the present invention is therefore limited only by the appended claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (26)

1. An optical multiple wavelength apparatus, characterized in that it comprises a broad spectrum optical source operable at a first rate to generate a sequence of output pulses having a spectral bandwidth covering a plurality of discrete wavelength bands; and a channel defining an optically coupled assembly to the wide spectrum source to resolve the output pulses of the optical source in the plurality of discrete wavelength bands, inserting a delay time between the discrete wavelength bands for thereby defining a sequence of steerable or individually treatable wavelength channels, and combining the discrete wavelength bands in at least one multiplexed output signal.

2. The optical multiple wavelength apparatus according to claim 1, characterized in that it further includes an optical modulator that encodes at least one optical wavelength channel using a data signal operating at a second speed equal to or greater than the first speed to form at least one coded optical channel.

3. The optical multiple wavelength apparatus according to claim 1, characterized in that the second speed is equal to or greater than the first speed multiplexed by the number of optical wavelength channels.

4. The optical multiple wavelength apparatus according to claim 1, characterized in that the optical source is an optically amplified light emitting diode.

5. The optical multiple wavelength apparatus according to claim 1, characterized in that each discrete wavelength channel comprises short optical pulses having a pulse width that is less than or equal to the inverse of the second speed.

6. The optical multiple wavelength apparatus according to claim 1, characterized in that each discrete wavelength channel comprises short optical pulses having a pulse width that is greater than the inverse of the second speed.

7. The optical multiple wavelength apparatus according to claim 1, characterized in that the channel defining the assembly includes a wavelength division demultiplexer having an input port optically coupled to the optical source and a plurality of radio stations. output, the wavelength division multiplexer is operable to resolve each optical input pulse in a plurality of short optical pulses, each short optical pulse corresponds to one of the discrete wavelength bands and is supplied to one of the plurality of exit ports.

8. The optical multiple wavelength apparatus according to claim 6, characterized in that the channel defining the assembly further includes a plurality of fiber optic delay lines, each delay line being optically coupled to one of the output ports of the optical fiber. demultiplexer, to delay the time when the short optical pulses associated with a given wavelength channel arrive at an output of the channel defining the assembly in relation to when the pulses associated with other wavelength channels arrive.

9. The optical multiple wavelength apparatus according to claim 8, characterized in that the assembly defining the channel further includes an optical combiner having a plurality of input ports and at least one output port for receiving delayed optical pulses respectively of delay lines and combine at least some of them for later transmission on a common waveguide.

10. The optical multiple wavelength apparatus according to claim 9, characterized in that the optical combiner is a star coupler.

11. The optical multiple wavelength apparatus according to claim 9, characterized in that the optical combiner is a wavelength division multiplexer.

12. The optical multiple wavelength apparatus according to claim 7, characterized in that the wavelength division demultiplexer includes a waveguide grating router and wherein the optical source is an optically amplified light emitting diode.

13. The optical multiple wavelength apparatus according to claim 1, characterized in that the wavelength channel defining the assembly includes a star coupler having N input ports and M output ports, a plurality of delay lines fiber optic cable each coupled to a corresponding one of the output ports, and a wavelength division multiplexer having input ports each coupled to a respective one of the fiber delay lines, wherein N is a number between or equal to or greater than one, M is an integer equal to a maximum number of optical channels definable by the means defining the wavelength channel, and at least one of the input ports is coupled to the optical source.

14. A transmitter for use in an optical communication system, characterized in that it comprises: a wide-spectrum optical source operable at a first rate to generate a sequence of output pulses having a spectral bandwidth covering a plurality of bands of length of discrete wave; means defining the channel optically coupled to the wide spectrum source to resolve the output pulses of the optical source in a plurality of short optical pulses corresponding to the discrete wavelength bands, to insert a delay time between the pulses short opticals to thereby define a reordered sequence of individually steerable wavelength channels, and to combine the discrete wavelength bands in at least one multiplexed output signal; and an optical modulator for encoding at least one of the wavelength channels using a data signal operating at a second speed equal to or greater than the first rate to form an encoded optical channel.

15. The transmitter according to claim 14, characterized in that the adjacent wavelength channels are separated in the time domain in the reordered sequence of the wavelength channels to thereby reduce the crosstalk.

16. A method of operating a transmitter in an optical communication system, characterized in that it comprises the steps of: resolving the output pulses of a wide-spectrum optical source in a plurality of discrete wavelength bands; inserting a time delay between the resolved discrete wavelength bands to thereby define a sequence of individually steerable wavelength channels; and combining the discrete wavelength bands in at least one multiplexed output signal.

17. The method according to claim 16, characterized in that it further includes a step of modulating sequentially, using a single modulator after the combining step, a plurality of wavelength channels with data for transmission to a remote receiver.

18. The method according to claim 16, characterized in that the sequence of discrete wavelength bands is rearranged during the insertion step of the time delay.

19. The method according to claim 16, characterized in that it also includes a step of amplifying the output of the optical source before the resolution step.

20. An operating method of a multi-wavelength optical communication system, characterized in that it comprises the steps of: resolving the output pulses of a wide-spectrum optical source in a plurality of discrete wavelength bands; inserting a time delay between the discrete wavelength bands to thereby define a sequence of individually steerable wavelength channels; combining discrete wavelength bands resolved into at least one multiplexed output signal; and modulating sequentially after the combining step, using a single modulator, a plurality of wavelength channels with data for transmission to a remote receiver.

21. The method according to claim 20, characterized in that the insertion step of the time delay is performed before the resolution step.

22. The method according to claim 20, characterized in that it further includes a step of launching the modulated wavelength channel in an optical medium for transmission to a multiple wavelength receiver.

23. The method according to claim 22, characterized in that it further includes a step of receiving the channels launched to the multiple wavelength receiver comprising a waveguide grating router followed by photodetectors.

24. The method in accordance with the claim 22, characterized in that it also includes a step of receiving the channels launched in a multiple wavelength receiver comprising a diffraction grating followed by photodetectors.

25. The method according to claim 22, characterized in that it further includes a step of receiving the channels launched in a multiple wavelength receiver comprising an interference filter array followed by photodetectors.

26. The method in accordance with the claim 22, characterized in that it further includes a step of receiving the channels launched in a multiple wavelength receiver comprising a wavelength division demultiplexer followed by photodetectors. SUMMARY OF THE INVENTION An optical multiple wavelength signal apparatus and method is provided using a single broadband optical source such as, for example, an LED, to generate many independent optical wavelength channels. An optical transmitter includes a wavelength channel that defines the assembly that resolves the wide spectrum pulse outputs by the source into discrete wavelength bands that constitute the respective pulses (ie, wavelength channels) and that insert a delay between the bands to define a sequence of individually steerable channels. According to one embodiment of the invention, the spectral division is achieved by means of a multiple channel filter, and the insertion of the respective delays is achieved by individual fiber sections, each section having a selected length to introduce a particular delay, coupled to the output ports of the router. The inserted delays can be conveniently selected to separate adjacent wavelength channels and thus reduce the likelihood of crosstalk to a minimum. The pulses of the channels thus resolved arrive at different times to a multiplexer which can be configured, for example, as a passive WDM multiplexer or as a star combiner. The resulting sequence of steerable wavelength channels can be supplied to one or more high-speed broadband modulators, with each modulator being operable to modulate some or all of the channels.