Abstract:
A system and method for producing a multiple optical channel source (MOCS). The method includes producing the SC in a medium using at least one femto-second or pico-second optical input pump pulse; splitting input pump pulse or resultant output SC pulse(s) into a plurality of collinear pulses; applying a time delay τ between the least one of input pump pulse or SC pulses; and producing a MOCS by the spectral interference of the plurality of SC pulses. The system includes a laser producing femto-second or pico-second pump pulses, a medium with a high value of the χ (3)  nonlinear response to produce spectrally coherent SC, an optical system for delivery of laser pump pulses into the SC producing medium, an optical system for splitting the input pump pulses or output SC pulses into a plurality of collinear pulses, and a means for applying a time delay τ between the plurality of pump or SC pulses.

Description:
PRIORITY 
   The present application claims priority to a U.S. Provisional Patent Application entitled “Method And Apparatus For Producing Multiple Optical Channel Source From A Supercontinuum Generation For WDM Communication,” filed on Mar. 23, 2004, and assigned Ser. No. 60/555,312, the contents of which are hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a supercontinuum generator for producing a multiple optical channel source, and more particularly, to a supercontinuum (SC) generator to provide a multiple optical channel source for a wave division multiplexing (WDM) communication system. 
   2. Description of the Related Art 
   SC generation refers to the generation of intense ultra-fast broadband “white light” pulses spanning from the ultraviolet (UV) to the near-infrared (near-IR) wavelength regions. SC generation is one of the key requirements necessary for developing ultra-fast laser and nonlinear optics technologies. One method of generating an SC includes inputting a high-power light pulse into a non-linear optical medium wherein the light pulse undergoes a broadening and emerges as an SC. This broadening is due to non-linear interactions between the light and the medium. 
   When applied to communication systems, SC wavelength-sliced sources have many advantages, chief of which are being background-noise free and having a high-bit rate capacity. Additionally, SC derived sources can reduce the hardware complexity of optical communication systems by replacing many light sources with a single SC source, which would result in commensurate savings in hardware design and testing, and reduce system maintenance and cost. 
   For example, in conventional wave division multiplexing (WDM) communication systems, a large number of optical sources such as laser diodes are used as a multiple channel source. Additionally, each laser diode must be independently controlled by a controller. This increases the complexity and cost of the WDM communication system and decreases the system&#39;s reliability. Moreover, it is difficult to construct existing WDM sources having more than 50 channels. Additionally, it is difficult to provide uniform channel spacing using the existing WDM sources. 
   SC&#39;s based on self phase modulation (SPM) and cross phase modulation (XPM) in bulk fiber mediums were discovered and pioneered by Dr. R. R. Alfano. 
   SC generation can be used to obtain multiple wavelength channels, as it can easily produce more than 100 optical longitudinal modes, while maintaining the coherency between the frequency modes. An advantage of using longitudinal (frequency) modes of the SC spectrum is that the resultant fixed channel spacing has the accuracy of a microwave oscillator. This means that entire wavelength channels can be fixed to grid frequencies by adjusting just one wavelength. 
   Other applications for SC-based sources and systems include WDM/TDM optical communication systems and other types of communications systems, optical frequency comb generators, high-resolution spectroscopy, optical metrology and optical tomography. 
   The SC arises from the propagation of intense pico-second (ps) or femto-second (fs) pulses through condensed matter, fibers, waveguides, or gaseous media (see, R. R. Alfano and S. L. Shapiro: Phys. Rev. Lett. 24, 584, (1970); Phys. Rev. Lett. 24, 592–594, (1970); Phys. Rev. Lett. 24, 1219, (1970) and U.S. Pat. No. 3,782,828, entitled “Picosecond Spectrometer Using Picosecond Continuum,” to Alfano et al.). Various processes are responsible for the generation of SC&#39;s, including self-, induced-, and cross-phase modulations and four-photon parametric processes, and soliton generation. When an intense laser pulse propagates through a medium, it changes the refractive index of the medium, which, in turn, changes the phase, amplitude, and frequency of the pulse. However, when two laser pulses having different wavelengths propagate simultaneously through a condensed medium, coupled interactions (i.e., cross-phase modulation) occur through the nonlinear susceptibility coefficients. These coupled interactions of two different wavelengths, can introduce phase modulation, amplitude modulation, and spectral broadening in each of the pulses due to the other pulse using cross-effects (see, U.S. Pat. No. 5,150,248, entitled “Terahertz Repetition Rate Optical Computing Systems, And Communication Systems And Logic Elements Using Cross-Phase Modulation Based Optical Processors,” to Alfano et al.). Dispersion plays a critical role in the SC, and in particular, about the zero group velocity dispersion region. 
   Currently, existing optical multiplexing systems such as wavelength/time division multiplexing (WDM/TDM) have limitations which are caused by the number of optical channels which can be provided by an optical channel source. Moreover, many optical channel generators require an individual laser for each optical channel which increases the complexity of the optical channel generator. Therefore, it is difficult to construct a WDM optical channel source that can provide more than 100 optical communication channels. For this reason, SC optical channel sources are a desirable means for providing multiple optical carriers (see, H. Takara. Optics &amp; Photonics news, p. 48–51, March 2002). The advantages of using an SC source include its super-broadband spectrum to simultaneously generate more than 100 channels with fixed spectral channel spacing. 
   As a result of space-time self-focusing, multi-photon absorption and self-steeping, an “optical shock” wave forms inside the medium that gives rise to an even broader blue-shifted pedestal in the transmitted pulse spectrum. 
   There are several important applications of the SC pulse, such as a white-light probe pulse to study the fundamental temporal dynamics of elementary excitations in the fields of chemistry, biology and condensed matter. Additionally SC pulses can be used as a multi-wavelength optical source for optical fiber communication systems, and as an optical source for optical coherence tomography (OCT) to detect cells. 
   Shaping, signal processing, and time-space conversion of fs pulses can be achieved by linear and nonlinear manipulation of the spatially dispersed optical frequency spectrum within a grating pair and lens pulse shaper. This approach can be used for processing of information in ultra high-speed optical communications networks. 
   An ultrafast coherence cross-correlation technique can be used for the detection of coherence data streams as well as photon echo signals on an fs time scale. 
   Throughout this document, the term SC fiber is used to refer to SC fibers or other suitable SC producing mediums. 
   The high degree of spatial coherence of an SC source is highly desirable for use in wireless communication systems and for a frequency comb generation. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide an improved SC optical channel source for producing between 200 and 1000 optical channels using a phase stabilized pump laser having a wavelength of 1550 nm, 850 nm or 1300 nm. 
   It is a further object of the present invention to provide an SC optical channel source having a fixed channel spacing with the accuracy of a microwave oscillator. 
   Moreover, it is a further object of the present invention to provide an SC optical channel source wherein entire wavelength channels can be fixed to grid frequencies by adjusting a single wavelength. 
   It is another object of the present invention to provide an SC optical channel source that can be used in WDM optical communication systems, optical frequency comb generators, high-resolution spectroscopy systems, optical metrology systems and optical tomography systems. 
   In the present invention a method for producing multiple optical frequency channels from an SC generator includes the steps of producing an SC in a medium using at least one femento-second (fs) or at least one pico-second (ps) optical pump pulse, splitting either the optical pump pulse (before it is converted into an SC pulse) or an output SC pulse (after the optical pump pulse has been converted into an SC pulse) into the at least two collinear pulses, applying a time delay between the at least two pump pulses or SC pulses (dependent upon which type of pulse has been split as described above), and producing a plurality of optical frequency channels through spectral interference of the at least two SC pulses. 
   A method according to an embodiment of the present invention includes the steps of applying at least a single optical pump pulse to an SC medium so as to generate an SC pulse output, splitting the output SC pulse into at least two SC pulses, and collinearly combining SC pulses with a desired time delay so as to produce a plurality of optical frequency channels. 
   Suitable mediums for producing an SC include fibers and waveguides or bulk materials with third order susceptibility (χ (3) )—(nonlinear susceptibility) nonlinear material characteristics. 
   Moreover, in some embodiments of the present invention, the SC medium can include an SC-producing fiber having a zero-dispersion wavelength λ D  where
 
∂(υ g   −1 )/∂ω=0 at λ D  
 
   υ g  is group velocity, ω is angular frequency, and the pump laser can include a variable output wavelength having a zero-dispersion wavelength, and a pump wavelength difference that is less than 100 nm. Furthermore, the SC-producing fiber can optionally have a variable length. Suitable mediums for producing the SC include fibers, waveguides or other bulk materials having non-linear material characteristics. For example, such materials can include photonic crystal fibers, highly nonlinear fibers, hollow fibers, crystals, glasses, gases. In yet other embodiments of the present invention, an output of the SC-producing fiber can be coupled to a variable-length polarization-maintaining (PM) fiber. 
   In still other embodiments of the present invention, an input or an output of the SC-producing fiber is coupled to an interferometer having a variable path difference. 
   In yet further embodiments of the present invention, an output of the SC-producing fiber can be coupled to an interferometer having a variable path difference and the interferometer&#39;s output can be coupled to an imaging spectrograph or an optical spectrum analyzer. 
   In other embodiments of the present invention, a method for producing multiple optical channels from an SC generator includes the step of adjusting a variable frequency distance between optical channels, by varying the optical time delay between the at least two optical pump or SC pulses. 
   In still further embodiments of the present invention, a method for producing two collinear pump pulses includes the step of placing a variable thickness glass plate into the path of the optical pump pulse such that at least part of the pump pulse is incident upon the variable thickness glass plate. The variable thickness glass plate is placed such that a part of the optical sources&#39; pump pulse passes through the variable thickness glass plate. 
   In additional embodiments of the present invention, a method for producing at least two collinear pump pulses includes the steps of beam-splitting and delaying the optical pump pulse into at least two pulses having a desired time delay, and collinearly combining the beam-split pulses with a predetermined optical delay. 
   In yet other embodiments of the present invention, suitable methods for producing multiple collinear pump pulses include transmitting the original pump pulse through a Fabry-Perot etalon. 
   Moreover, in one embodiment of the present invention, an apparatus for producing a multiple-optical-channels source from an SC generator includes a laser for producing at least one fs or ps optical pump pulse, a medium having a χ (3)  nonlinear response for producing a spectrally coherent SC pulse, an optical guide for delivering at least one optical pulse into the SC producing medium, an optical splitter for splitting the at least one optical pump pulse or SC pulse into at least two collinear pulses, and a time delay system for applying a delay between the at least two optical pump or SC pulses. 
   In other embodiments of the present invention, an optical pump source with a variable wavelength may also be used. 
   In other preferred embodiments of the present invention, an interferometer with a variable path difference is coupled to either or both an input and an output of an SC-producing fiber. Suitable interferometers include those with a variable path difference, such as a fiber-optic-based interferometer with a path difference produced by a piezo-electric transducer. In yet other preferred embodiments of the present invention, a multiple optical channel source is coupled with an optical communication system for increasing the data transmission rates and bandwidth capacity of the communication system. This embodiment can be used with both new and/or existing optical-fiber transmission systems. 
   A means for producing at least two collinear pump pulses can include a beam-splitter for splitting a pump pulse into the at least two pulses, and a combiner (e.g., a collinear combiner) for collinearly combining the at least two pulses having a desired optical delay. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
       FIG. 1A  is an illustration which shows the spectral broadening of an fs pulse within a non-linear fiber medium resulting in an SC pulse output; 
       FIG. 1B  is a graph which illustrates the spectral broadening of the narrow frequency pulse after it has passed through the SC fiber; 
       FIG. 2A  is an illustration which shows the use of two time-delayed pump pulses to produce two spectrally-broadened SC pulses in an SC fiber; 
       FIG. 2B  is a graph which illustrates the frequency domain of a multiple channel generation of the SC pulses shown in  FIG. 2A ; 
       FIG. 3  is a block diagram of a laser source coupled to a Michelson Interferometer which can be used as a time-delay system, according to an embodiment of the present invention; 
       FIG. 4  is a block diagram illustrating a basic configuration of an SC source according to an embodiment of the present invention; 
       FIG. 5A  is a block diagram illustrating a basic configuration of an SC source for producing multiple optical channels according to an embodiment of the present invention; 
       FIG. 5B  is a block diagram illustrating a basic configuration of an alternative SC source for producing multiple optical channels according to an alternative embodiment of the present invention; 
       FIG. 6  is a block diagram illustrating the use of a time-delay system including a fiber-optic-based Mach-Zender Interferometer according to an embodiment of the present invention; 
       FIG. 7  is a block diagram illustrating a multiple optical channel generator including an optic-based Michelson Interferometer as a time-delay system, according to an embodiment of the present invention; 
       FIG. 8  is an illustration of a multiple optical channel generator including a variable thickness plate as a time-delay system, according to an embodiment of the present invention; 
       FIG. 9  is a graph which illustrates an SC spectrum produced in a 5-km telecom fiber by a single 90 fs pulse with a 50-MHz repetition rate; 
       FIG. 10  is a graph which illustrates the generation of multiple optical channels, having a frequency distance between channels of 600 GHz, from an SC source using two pump pulses separated by a time delay τ=3.3 ps, according to an embodiment of the present invention; 
       FIG. 11  is a graph which illustrates a multiple optical channel generation from an SC source where the frequency distance between channels is 75 GHz and the SC source uses two pump pulses separated by a time delay τ=26.4 ps, according to an embodiment of the present invention; 
       FIG. 12  is a graph which shows an expanded area of the graph shown in  FIG. 11 , wherein the channels are expanded; and 
       FIG. 13  is a block diagram which illustrates a setup of an optical WDM communication system according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention provides a novel and useful method for the generation of multiple optical channels which can be used in communication systems and other systems as desired. 
   An illustration which shows the conventional spectral broadening of an fs pulse within a non-linear fiber medium resulting in an SC pulse output is shown in  FIG. 1A . An optical pulse  10  enters an SC fiber medium  12  and undergoes spectral broadening and is converted into an SC pulse  10 ′. 
   A graph illustrating the spectral broadening of the narrow frequency pulse after it has passed through the SC fiber is seen in  FIG. 1B . Comparison of the SC pulse  10 ′ with the initial optical pulse  10  illustrates the broad flattening of the spectrum of the initial pulse  10  as it is converted into the SC pulse  10 ′. 
   An illustration which shows the use of two time-delayed pump pulses to produce two spectrally broadened SC pulses in an SC fiber is seen in  FIG. 2A . Pulses  20  and  22  are delayed by a time delay τ and then inserted into an SC fiber  24 . The pulses  20  and  22  undergo spectral broadening within the SC fiber  24 , and emerge as SC pulses  20 ′ and  22 ′ which are separated by time delay τ′ (where τ and τ′ are equal). Pulses  20 ′ and  22 ′ can then be used to generate multiple optical frequency channels as will be described below. 
   A graph illustrating the frequency domain of a multiple channel generation of the SC pulses shown in  FIG. 2A , is shown in  FIG. 2B . The theoretical background for the SC multiple frequency channels generation will be described below. 
   Two pump pulses (e.g., pulses  20  and  22 ) produce two independent SC pulses (e.g., pulses  20 ′ and  22 ′). The amplitudes of the generated SC are E(t) and E(t−τ) and are separated in time by interval τ′. Additionally, G(ω) and G(ω)exp(−i ωτ) are the respective Fourier transformed spectral amplitudes of these pulses. At the spectral output, the pulses produce a spectral interference pattern with a spectral intensity distribution as defined by Equation 1 below.
 
 I=|G (ω)+ G (ω)exp(− i  ωτ)| 2 =2 |G (ω)| 2 (1+cos(ωτ))  Equation (1)
 
   Moreover, in the spectral domain, the period of the spectral interference fringes is defined by Equation 2.
 
Ω=1/τ  Equation (2)
 
   The frequency interval between generated multiple optical channels can be changed by varying the time delay τ. The number of the generated frequency channels can be expressed by N as shown in Equation 3.
 
 N=Δν/Ω   Equation (3)
 
where Δν is a spectral bandwidth of the SC source, and the number of the channels N is in the range of 100 to 2000. In alternative embodiments, N is in the range of 2000 to 7000.
 
   A block diagram of a laser source coupled to a Michelson Interferometer which can be used as a time delay system, according to an embodiment of the present invention, is seen in  FIG. 3 . The Michelson Interferometer acts as a pulse delay device. An fs laser  30  generates an fs pulse  32 , which is incident upon a beam-splitter  34  and is subsequently split into two pulses  32 ′ and  32 ″ by beam-splitter  34 . Pulse  32 ″ is not reflected by mirror  34 , and subsequently is incident upon mirror  36 , whereupon it is reflected back to the beam-splitter  34  and is then reflected so that it is incident upon optional mirror  31 . Pulse  32 ′, after being redirected by beam-splitter  34 , is incident upon mirror  38  and reflected back through the beam-splitter  34 . By adjusting the distance that pulses  32 ′ and  32 ″ travel, the pulses can be delayed by desired time τ. Moreover, the pulses can also be delayed by optical mediums such as glass which will be described below. The pulses  32 ′ and  32 ″ are then incident upon optional mirror  31 , then enter SC fiber  33 , and are then spectrally broadened and converted into SC pulses  32 ′″ and  32 ″″ separated by time delay τ′. It should be noted that pulses  32 ′ and  32 ″ have been arbitrarily chosen and either can precede the other. Moreover, the pulses can be optically amplified by an optical amplifier (e.g., an erbium-doped fiber amplifier (EDFA) or any other suitable optical or IR repeater that amplifies a modulated laser beam directly, without opto-electronic and electro-optical conversion) which is not shown. 
   A block diagram illustrating a basic configuration of an SC source according to an embodiment of the present invention is shown in  FIG. 4 . The optical pump laser  40  is coupled to an SC fiber  42  so that one or more optical pulses (not shown) generated by the laser are converted to SC pulses (not shown). The generated SC pulses are then input to a fiber amplifier  44  which amplifies the one or more SC pulses (not shown) and outputs the resultant one or more SC pulses at end  46 . 
   A block diagram illustrating a basic configuration of an SC source for producing multiple optical channels according to an embodiment of the present invention is shown in  FIG. 5A . A laser pump  50  generates a plurality of pump pulses (e.g.,  51  and  53 ) separated by a time delay τ′. The pump pulses are then fed to SC fiber  52 , which converts the pump pulses into SC pulses (not shown). The SC pulses are then amplified by a fiber amplifier  54 , and emerge as multiple optical channel pulses  51 ′ and  53 ′, having a time delay τ. At the spectral output, these two spectrally broadening SC pulses produce spectral interference patterns with the distance between frequency channels equal to a distance which is defined by Ω=1/τ. It should also be noted that by causing multiple delays an optical pump pulse can be split into a plurality of pulses. For illustration only, only two pump pulses are shown. 
   A block diagram illustrating a basic configuration of an alternative SC source for producing multiple optical channels according to an alternative embodiment of the present invention is shown in  FIG. 5B . In this embodiment, a pump laser  56  is coupled to SC fiber  58 , which is further coupled to a time delay system  60  which is coupled to an fiber amplifier  59 . In use, the pump laser  56  generates a single pulse, which is incident upon the SC fiber  58  and converted into an SC pulse (not shown). This SC pulse is then input to the time delay system  60  which splits the single SC pulse into at least two SC pulses  55  and  57  having a time delay τ between each of them. For illustration, only two SC pulses are shown. SC pulses  55  and  57  are then amplified by the fiber amplifier  59 . SC pulses  55  and  57  produce a spectral interference pattern with the distance between the channels equal to Ω. 
   A block diagram illustrating the use of a time-delay system including a fiber-optic-based Mach-Zender Interferometer to produce a multiple optical channel generation according to an embodiment of the present invention is shown in  FIG. 6 . The fiber-optic-based Mach-Zender Interferometer (MZI)  62  is used as a time-delay system. The input pulse is split into the two pulses by the input beam splitter (not shown) of the MZI. A time delay between two pulses is produced by the different fiber lengths of the MZI. The time delay can vary, changing the length of the MZI fiber by a piezo-electric transducer (PZT) which is not shown. The two pulses are combined with a predetermined time delay by the MZI output combiner. The system includes a pump laser  62  which is coupled to the MZI  64 , which is coupled to SC fiber  66 , and subsequently coupled to amplifier  68 . This system is similar to the embodiments as described above, and therefore an operational description is not provided. 
   A block diagram illustrating a multiple optical channel generator including an optic-based Michelson Interferometer as a time delay system, according to an embodiment of the present invention, is shown in  FIG. 7 . In this embodiment, a Michelson Interferometer (MI)  74  is used as a time-delay system. In use, an optical pulse (not shown) generated by pump laser  70  is incident upon SC fiber  72  and is then split into at least two pulses by an input beam splitter of the MI  74 . A time delay between two pulses is produced by different lengths of optical fibers  77  and  79  of the MI  74 , respectively. The pulses are then reflected back by mirrors  73  and  75  placed at the ends of the optical fibers  77  and  79 , respectively. The induced time delay can be varied by changing the length of the MI&#39;s  74  optical fibers (e.g., either or both of the optical fibers  77  and  79 ) by the PZT. The two pulses are combined with a predetermined time delay by the MI&#39;s  74  input beam splitter. 
   An illustration of a multiple optical channel generator including a variable thickness plate as a time-delay system, according to an embodiment of the present invention, is shown in  FIG. 8 . One or more of variable thickness plate  82  may be used as a time-delay system. The light transmission plate is placed into a portion of the pump laser&#39;s output beam  81  so that preferably substantially half of the pump laser&#39;s output beam is delayed by a time delay τ, where τ is defined by Equation 4.
 
 T =( n− 1) d/c   Equation (4)
 
where n is the index of refraction of the plate  82 , d is the thickness of the plate  82  and c is the speed of light. The plate includes two prisms  83  and  85 , which can be adjustably located relative to each other to vary τ by changing the thickness d of the plate. A lens  84  is provided to focus the resulting pump laser&#39;s output beam  81  so that it can be incident upon the SC fiber  86 .
 
   A working embodiment of the present invention will now be described in detail. A fiber ring laser is used to produce optical pulses centered at 1560 nm with a pulse duration of 90 fs, with a 50-MHz repetition rate and an average power of 10 mW. A 5 km telecom fiber was used to produce the SC output, as is shown in the graph of  FIG. 9 . 
   A graph which illustrates the generation of multiple optical channels, having a frequency distance between channels of 600 GHz, from an SC source using two pump pulses separated by a time delay τ=3.3 ps, according to an embodiment of the present invention, is shown in  FIG. 10 . In this embodiment, the time delay system includes a 1-mm-thick glass plate which is placed so that one-half of the laser&#39;s output pump pulse beam diameter is incident upon the glass plate. The frequency distance between the channels is Ω=1/τ=c/(n−1)d=3×10 11 /0.5×1=600 GHz, and the number of generated frequency channels, n, is 18. 
   A graph which illustrates a multiple optical channel generation from an SC source where the frequency distance between channels is 75 GHz and the SC source uses two pump pulses separated by a time delay τ=26.4 ps, according to an embodiment of the present invention, is shown in  FIG. 11 . A fiber ring laser is used to produce optical pulses centered at 1560 nm with a pulse duration of 90 fs, with a 50-MHz repetition rate and an average power of 10 mW. A 5-km telecom fiber was used to produce the SC output, as shown in the graph of  FIG. 9 . In this embodiment, to decrease the distance between channels, an 8-mm-thick glass plate is placed in the output pulses so that one-half of the laser&#39;s output pump pulse beam diameter is incident upon the glass plate. The frequency distance between the channels is Ω=1/τ=c/(n−1)d=600/8=75 GHz, and the number of generated frequency channels, n, is 66. 
   A graph which illustrates a portion of the frequency channels shown in  FIG. 11 , is shown in  FIG. 12 . The frequency distance between the channels is Ω=1/τ=c/(n−1)d=600/8=75 GHz. 
   A block diagram which illustrates a setup of an optical WDM communication system according to an embodiment of the present invention is shown in  FIG. 13 . The WDM communication system  120  includes an SC multiple optical channel source  122 , which includes a control system (not shown), which is coupled to an input demultiplexer (DEMUX)  124  for wavelength division demultiplexing through the use of Arrayed Waveguide Grating (AWG) device. The AWG separates frequency channels in space. In this case, each channel can be independently coded (by using different type modulators  121 ) and another AWG (multiplexer)  126  transfers all frequency channels into a single optical communication fiber  130  for transmission through transmission line  128 . 
   The SC multiple channel source can generate multiple optical channels simultaneously, and thus provide for an efficient, simple, reliable and cost-effective WDM communication system. Moreover, as the SC multiple channel source can generate multiple optical frequency channels with uniform channel spacing, it is easy to control all the wavelengths on the International Telecommunication Union grids simultaneously. For these and other reasons, it is clearly seen that the current system is superior to existing WDM communication systems which use multiple lasers as an optical source. 
   While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.