Patent Publication Number: US-2003235415-A1

Title: Optical communication devices and optical communication methods

Description:
TECHNICAL FIELD  
       [0001] The invention relates to optical communication devices and optical communication methods.  
       BACKGROUND OF THE INVENTION  
       [0002] Networking has become increasingly popular as a way to exchange information between different devices such as computer systems and telephony devices, for example. Voice and data networks are advancing in sophistication to meet increasing demands for communication of voice and other data.  
       [0003] Parallel optical communication networks are utilized to communicate relatively large amounts of data between sources and destinations. Such parallel optical communication networks may be coupled with central offices, implemented as computer interconnects between source and destination devices as well as utilized in a wide variety of other applications.  
       [0004] Some parallel optical communications applications require very high aggregate bandwidth. In such applications, the number of channels including fibers and detectors can become relatively large requiring significant space. Further, these networks are also relatively expensive to construct and maintain. As the demand for voice and data communications services continues to increase, the demand for networks capable of handling increased bandwidth also increases.  
       [0005] Accordingly, there exists a need to provide improved devices and methodologies to accommodate such demands while minimizing or avoiding problems associated with conventional arrangements.  
       SUMMARY OF THE INVENTION  
       [0006] Aspects of the invention relate to optical communication devices and optical communication methods. Aspects of the invention may be implemented in parallel optical communication applications to provide enhanced bandwidth. Aspects of the invention may be used in applications other than communication applications.  
       [0007] According to one aspect of the invention, an optical communication device is provided. An exemplary device according to this aspect includes an optical communication device which comprises a plurality of light sources configured in an array and individually adapted to communicate information with respect to an optical communication medium, wherein individual light sources are configured to emit light having at least three different and distinct levels to communicate the information with respect to the optical communication medium. The device of this aspect further includes a controller configured to provide a plurality of control signals to control respective ones of the light sources to individually communicate respective information using the at least three different and distinct levels to implement multi-level coding.  
       [0008] Another aspect of the invention provides an optical communication method. The method includes providing an array comprising a plurality of light sources emitting light having at least three different and distinct levels using individual ones of the light sources. The method of this aspect further includes controlling the light sources to individually emit light between the at least three different and distinct levels to implement multi-level coding to communicate information and optically coupling the light having the at least three different and distinct levels with an optical communication medium after the controlling.  
       [0009] Another aspect of the present invention also relates to an optical communication method. This method includes receiving a plurality of electrical data signals providing a plurality of control signals responsive to the electrical data signals. The method also includes emitting light comprising a plurality of optical signals individually having at least three distinct and different levels using a plurality of light sources configured in an array and individually comprising a plurality of discrete light emission devices individually having a light emission intensity corresponding to a single one of the at least three different and distinct levels. The method of this aspect also includes controlling the at least three different and distinct levels of the optical signals by controlling the discrete light emission devices using the control signals to implement multi-level coding to communicate information of the electrical data signals and optically coupling the optical signals individually having the at least three distinct and different levels with a plurality of respective optical fibers after the controlling.  
       [0010] According to additional aspects of the invention, a plurality of light emission devices may be implemented upon a monolithic substrate, such as a single semiconductive die. In one operational aspect, plural ones of the monothically implemented lasers may be used to provide redundant communications.  
       [0011] Other aspects of the invention are provided, at least some of which are described in detail below.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] Preferred embodiments of the invention are described below with reference to the following accompanying drawings depicting examples embodying the best mode for practicing the invention.  
     [0013]FIG. 1 is a functional block diagram of an exemplary optical communication system.  
     [0014]FIG. 2 is a functional block diagram of an exemplary source optical communication device of the optical communication system.  
     [0015]FIG. 3 is a functional block diagram of an exemplary light source of the source optical communication device.  
     [0016]FIG. 4 is an illustrative representation of an exemplary source optical communication device and exemplary optical communication media.  
     [0017]FIG. 5 is a graphical representation of an exemplary optical signal communicated by a source optical communication device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0018] Referring to FIG. 1, an exemplary optical communication system  10  comprises a source optical communication device  12 , an optical communication media  16  and a destination optical communication device  18 . The depicted exemplary system  10  is implemented in a highly parallel channel environment. Other configurations are possible.  
     [0019] Source optical communication device  12  is configured to generate a plurality of optical signals  14  having data or information encoded thereon for communication. As shown, optical communication system  10  comprises a plurality of channels  15  intermediate source optical communication device  12  and destination optical communication device  18 . As described in detail below, source optical communication device  12  is configured to output optical signals  14  corresponding to channels  15  and which individually implement a multi-level coding scheme according to aspects of the present invention. Optical signals  14  are provided to optical communication media  16  for communication to the appropriate destination optical communication device  18 . In the described exemplary embodiment, respective optical signals  14  outputted from device  12  are maintained within respective channels  15  throughout optical communication media  16  and before application to destination optical communication device  18 . Alternatively, optical signals  14  may be switched from one channel to another as desired.  
     [0020] Optical communication media  16  comprises a plurality of optical waveguides implemented as optical fibers in one embodiment. In the described exemplary embodiment, the number of optical waveguides corresponds to the number of channels  15 . Optical communication media  16  may be implemented in any appropriate configuration including free space for communicating optical signals  14 .  
     [0021] Destination optical communication device  18  is configured to receive the optical signals  14 . Device  18  is configured to distinguish between the plural different and distinct levels within optical signals  14  to receive the multi-level coded data. Destination optical communication device  18  is configured to convert the optical signals  14  into respective electrical signals including the data encoded thereon for further communication of the data.  
     [0022] Referring to FIG. 2, components of an exemplary source optical communication device  12  are depicted. The illustrated source optical communication device  12  includes a buffer  20 , a controller  22 , and a parallel array  23  comprising a plurality of light sources  24  in the illustrated exemplary configuration. Controller  22  is coupled with buffer  20  and individual light sources  24 .  
     [0023] Source optical communication device  12  is configured to couple with external data sources (not shown) which provide information or data to be communicated within optical communication system  10 . In the depicted embodiment, buffer  20  is coupled with a bus  26  and is configured to receive data in one or more electrical signal. The received data to be communicated within system  10  is received from appropriate sources, such as the data sources. Bus  26  may be implemented as a plurality of parallel connections, or alternatively, bus  26  is implemented to provide serial communication of data from one or more data source. Electrical data signals may be multiplexed, using for example, time division multiplexing (TDM) within bus  26 . Buffer  20  operates as a temporary storage device for received data prior to communication of such data to optical communication media  16 .  
     [0024] The array  23  of light sources  24  is coupled with optical communication media  16 . In the depicted arrangement, light sources  24  are individually configured to communicate information with respect to optical communication media  16 . The number of light sources  24  corresponds to the number of channels  15  provided within optical communication system  10  in one exemplary embodiment. In such an embodiment, light sources  24  communicate optical signals  14  to respective optical fibers or other waveguides of optical communication media  16  corresponding to channels  15 .  
     [0025] According to aspects of the present invention, source optical communication device  12  and individual light sources  24  are configured to implement multi-level coding to communicate information received from one or more external data source. Multi-level coding schemes provide a log  2 (n) enhancement to information bandwidth of channels  15  where n is the number of levels used in the coding scheme. As described in further detail below, individual light sources  24 , responsive to control from controller  22 , emit light having at least three different and distinct levels to communicate the received data with respect to optical communication media  16  and to implement multi-level coding. Light sources  24  are configured to emit optical signals  14  having at least three different and distinct levels in an exemplary embodiment. Additional different and distinct levels may also be provided if additional bandwidth is desired.  
     [0026] In the described exemplary embodiment, controller  22  is configured to provide a plurality of control signals to respective light sources  24  to control or modulate the emission of light therefrom (comprising optical signals  14 ) at the different and distinct levels. Controller  22  is configured as processing circuitry configured to execute executable instructions to control light sources  24  in the described exemplary embodiment. Controller  22  configured as processing circuitry executes appropriate executable instructions stored within a memory device (not shown). Executable instructions include, for example, software and/or firmware instructions. Controller  22  implemented as processing circuitry comprises a microprocessor in one exemplary embodiment. Controller  22  may be implemented in hardware configurations in other embodiments.  
     [0027] Referring to FIG. 3, further details of an individual light source  24  are described according to one exemplary aspect. Light source  24  comprises a plurality of discrete light emission elements  30  according to one exemplary embodiment. Other light source  24  configurations are possible including configurations having additional discrete light emission elements  30  or a single light emission element  30 . In one exemplary embodiment, the light emission elements  30  are implemented as lasers, such as vertical cavity surface emitting lasers (VCSELs).  
     [0028] Light emission elements  30  are individually configured to communicate optical signals  32  which are combined to collectively form an optical signal  14  which is communicated within a respective channel  15  through optical communication media  16  of optical communication system  10 . Light emission elements  30  of a single light source  24  are configured to couple light into a single optical waveguide of the optical communication media  16 . According to aspects of the present invention, light emission elements  30  are configured to communicate respective optical signals  32  individually having a light emission power or intensity equivalent to a single one of the different and distinct levels of optical signals  14 . Further details regarding different and distinct levels of optical signals  14  are described below with reference to FIG. 5.  
     [0029] Referring to FIG. 4, an exemplary implementation of optical communication system  10  is illustrated. Source optical communication device  12  comprises a plurality of light sources  24  as shown. The individual light sources  24  comprise a plurality of light emission elements  30  in the embodiment shown in FIG. 4 and as described above. Light emission elements  30  emit light to form optical signals  14  having different and distinct levels to implement multi-level coding and for communication within optical communication media  16 .  
     [0030] Optical communication media  16  is implemented as a plurality of optical waveguides  28  comprising optical fibers in the depicted exemplary embodiment. Individual optical waveguides  28  correspond to a single communication channel  15  within optical communication system  10 . Individual light sources  24  output the optical signals  14  for communication within the respective channels  15 . At any given moment in time, one or more of channels  15  may not be utilized. In addition, during peak usage, all channels  15  may be utilized to implement communications intermediate source optical communication device  12  and destination optical communication device  18  (FIG. 1).  
     [0031] Controller  22  (FIG. 2) is configured to control the individual light sources  24 . More specifically, controller  22  is configured to turn on or off individual light emission elements  30  of light sources  24  to provide a plurality of different and distinct levels within optical signals  14  responsive to data signals received via bus  26 . In the described implementation, data signals are provided via bus  26  and controller  22  generates respective control signals for individual respective light sources  24  and channels  15  associated therewith responsive to received respective data signals.  
     [0032] In certain embodiments, two light emission elements  30  may be utilized to provide three different and distinct levels within optical signals  14 . As mentioned above, additional (e.g., three or more) light emission elements  30  may be provided within a single light source  24  to provide additional different and distinct levels within optical signals  14  to further enhance bandwidth if desired.  
     [0033] In another embodiment, individual light sources  24  comprise a single light emission element  30 . Controller  22  is configured to control such individual light emission element  30  to emit light at a plurality of intensities corresponding to at least three different and distinct levels. According to one embodiment, controller  22  is configured to adjust the control signal applied to the respective light emission element  30 . Responsive to an adjustment of the control signal, light emission element  30  is configured to adjust the intensity of the emitted light comprising optical signal  14  to provide corresponding different and distinct levels.  
     [0034] For example, controller  22  may adjust a bias of the control signal to enable light emission element  30  to output the different and distinct levels within optical signals  14 . Controller  22  may adjust the bias by adjusting the current of respective control signals responsive to respective data signals according to one exemplary embodiment. Other bias adjustments may be implemented.  
     [0035] Some light emission elements  30 , such as vertical cavity surface emitting lasers (VCSELs), are typically not sufficiently linear with current. Thus, in some configurations, it is desired to characterize the non-linearity of the intensity relative to the control signal bias current to provide proper distinct and different levels which are discernable in destination optical communication device  18  if one light emission element  30  is utilized as light source  24 . It is preferred to provide the spacing between adjacent levels within accurate tolerances for reception within device  18 . If the relationship of bias of the control signal and the corresponding level of the outputted signal is not linear, the relationship may be mapped between the bias and the responsive light intensity outputted from device  30  in order to enable controller  22  to provide control of appropriate spacing between distinct levels within optical signal  14 .  
     [0036] Such can be implemented in a map or logic table accessible by controller  22  in one exemplary configuration. For example, responsive to a data signal indicating a desired level of optical signal  14 , controller  22  accesses a logic table to retrieve the appropriate bias of the control signal to provide the desired level within optical signal  14 . Other configurations are possible.  
     [0037] In some configurations of the present invention, a plurality of lasers, such as vertical cavity surface emitting lasers (VCSELs), may be provided in a monolithic arrangement. For example, a plurality of lasers may be fabricated upon a single monolithic semiconductive substrate, such as a single silicon die, using semiconductor processing techniques.  
     [0038] One or more waveguide  28  may be optically coupled with a monolithic arrangement of the lasers to communicate optical signals  14  generated using the lasers. The waveguide(s)  28  may be individually arranged and configured to communicate optical signals  14  and/or  32  received from one of the lasers or a plurality of the lasers.  
     [0039] The plurality of lasers of a single die may be utilized to provide one or more light source  24  configured to generate a plurality of optical signals  14  individually having a plurality of levels. Depending upon the configuration of lasers and control scheme being utilized, one die may include a plurality of lasers comprising a plurality of light emission elements  30  of one or more light source  24 . For example, at least some of the lasers of the die may be configured to provide signals  30  of one or more optical signal  14  individually having a plurality of levels.  
     [0040] In another arrangement, one or all of the plurality of lasers of the die could individually correspond to a light source  24  and be controlled (e.g., via control signal bias adjustment as described above) to output an optical signal  14  having at least three different and distinct levels for one channel  15 . In such a configuration, other lasers formed upon the same monolithic die could output another optical signal  14  and/or  32  for another channel  15  and having at least three different and distinct levels.  
     [0041] Accordingly, a plurality of lasers upon a given monolithic die may comprise a plurality of light emission elements  30  utilized to generate a single optical signal  14  as described above and/or one or more other laser of the die may be utilized to form another optical signal  14  either directly or by generating plural optical signals  32  as described above.  
     [0042] Additional aspects of the present invention provide redundancy operations which can be implemented using standard binary communications or multi-level coding schemes described herein. For example, light emission elements  30  of a light source  24  could be utilized in a binary communication scheme wherein all of the elements  30  are controlled to be provided in either an on or off emission state to implement redundant communications (i.e., if one element  30  fails, communications can continue to occur using the remaining elements  30 ).  
     [0043] Redundancy can also be provided in multi-level communication systems if an adequate number of redundant light emission elements  30  are provided or using a common control signal with appropriate biasing to control a plurality of the lasers in parallel. The elements  30  configured to provide redundant operations may be implemented as discrete configurations (e.g., upon a plurality of respective semiconductive substrates) or upon a single monolithic substrate (e.g., die). The lasers may be configured to simultaneously emit the optical signals to provide redundancy, or alternatively, the lasers may be configured to emit signals at different moments in time (e.g., upon failure of one laser, another laser could be utilized) to provide redundant operations.  
     [0044] Referring to FIG. 5, an exemplary graphical representation of an optical signal  14  is depicted. The graphical representation of FIG. 5 depicts intensity of the optical signal  14  versus a time relationship. The depicted graphical representation includes a plurality of levels of optical signal  14  represented by references  40 - 43 . The graphical representation of FIG. 5 corresponds to a light source  24  having three light emission elements  30  configured to emit an optical signal  14  having four different and distinct levels  40 - 43  in one exemplary multilevel coding scheme. More or less levels may be provided.  
     [0045] The intensity level of optical signal  14  corresponding to reference  40  corresponds to controller  22  controlling all light emission elements  30  of light source  24  to be in an off condition. Reference  41  corresponds to controller  22  controlling only one of the three light emission elements  30  to output a respective light signal  32  (FIG. 3) and the other elements  30  are off. Reference  42  corresponds to controller  22  controlling two of the three light emission elements  30  to output respective optical signals  32  while the other element  30  is off. Reference  43  corresponds to controller  22  controlling all three of light emission elements  30  to output respective optical signals  32 . Optical signals  32  are combined to form optical signal  14  depicted in FIG. 5.  
     [0046] As mentioned above, the exemplary graphical representation of optical signal  14  refers to light source  24  including three light emission elements  30  to provide the four different and distinct levels. Alternatively, the light source  24  comprises a single light emission element  30  and controller  22  controls the appropriate bias of a control signal applied to the light emission element  30  to provide the four different and distinct levels. Other configurations are possible.