Abstract:
A method and an optical transmitter utilizing the same are provided. The method, adopted by an optical transmitter, transmitting data signal and control signal to an optical receiver of an target device, including: providing a data signal in a first frequency band; providing a control signal in a second frequency band; combining the data signal in the first frequency band and the control signal in the second frequency band to generate a combined signal; and converting the combined signal into an outgoing optical signal to be transmitted to the optical receiver; wherein the control signal is arranged for controlling the target device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to a high-speed serial data link communication system, and in particular relates to a method of transmitting data and control signal over an optical cable and an optical transmitter utilizing the same. 
         [0003]    Description of the Related Art 
         [0004]    An active optical cable (AOC) is an optical fiber cable that is terminated on each end with a plug that contains an optical transceiver module that converts electrical signals into optical signals and optical signals into electrical signals. 
         [0005]    Increasing number of communication networks now adopt AOCs to extend the transmission distance. However, the communication networks typically employ a number of control signals and data signals to operate connections and communications between network components. The control signals are typically transmitted via an additional copper wire or optical fiber, such that the cost for build communication network using AOCs has become considerable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
         [0007]    An embodiment of a method is disclosed, adopted by an optical transmitter, transmitting data signal and control signal to an optical receiver of a target device, including: providing a data signal in a first frequency band; providing a control signal in a second frequency band; combining the data signal in the first frequency band and the control signal in the second frequency band to generate a combined signal; and converting the combined signal into an outgoing optical signal to be transmitted to the optical receiver; wherein the control signal is arranged for controlling the target device. 
         [0008]    Another embodiment of an optical transmitter is disclosed, transmitting data signal and control signal to an optical receiver of a target device, including: a control data converter, a combiner circuit and an electrical-to-optical device. The control data converter is configured to convert a control signal into continuous wave (CW) signals with different predetermined frequencies respectively according to different states of the control signal. The combiner circuit, coupled to the control data converter, is configured to combine a data signal variously transmitted in a first frequency band and the CW signals to generate a combined signal. The electrical-to-optical device, coupled to the combiner circuit, is configured to convert the combined signal into an outgoing optical signal to be transmitted to the optical receiver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a block diagram of an optical communication system  1  according to an embodiment of the invention; 
           [0011]      FIG. 2A  is a schematic diagram for an optical transmission device  2  according to an embodiment of the invention; 
           [0012]      FIG. 2B  is a schematic diagram for an optical transmission device  2  according to another embodiment of the invention; 
           [0013]      FIG. 3  is a block diagram of an optical receiver  3  according to an embodiment of the invention; and 
           [0014]      FIG. 4  is a flowchart of an optical transmission method according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0016]    Various aspects are described herein in connection with an optical communication system, which can be a Universal Serial Bus (USB) system, a Peripheral Component Interconnect Express (PCIe) system, a High-Definition Multimedia Interface (HDMI) system, a Display Port (DP) system, an Accelerated Graphics Port (AGP) system, or any communication system which adopts optical fibers as a transmission medium. 
         [0017]      FIG. 1  is a block diagram of an optical communication system  1  according to an embodiment of the invention, including a host device  16 , a target device  18 , and two optical transmission devices  10  and  12 , coupled thereto by optical cables  14   a  and  14   b.  The optical transmission device  10  is coupled to the host device  16 . The optical transmission device  12  is coupled to the target device  18 . The optical transmission devices  10  and  12  and the optical cables  14   a  and  14   b  are formed as an AOC (Active Optical Cable) for example. The host device  10  can be in communication with the target device  12  at a distance using the AOC cable to carry communication information. The host device  10  may be, but not limited to, an USB host device or a PCIe host device. The target device  12  may be, but not limited to, an USB device or a PCIe device. The optical cables  14   a  and  14   b  may be constructed in form of separate cables or a combined cable. 
         [0018]    When the optical transmission devices  10 ,  12  and the optical cables  14   a  and  14   b  are formed an AOC (Active Optical Cable) for example, the plugs on the ends of the AOC have housings that are configured to be received within sockets on circuit boards of the host device  16  and the target device  18 . 
         [0019]    The host device  16  can send data information and control information in electrical form to the target device  12  via the two optical transmission device  10 ,  12  and the optical cable  14   a  coupled thereto. The target device  18  may send data information and control information in electrical form to the host device  16  via the two optical transmission device  10 ,  12  and the optical cable  14   b  coupled thereto. The control information from the host device  16  is used to regulate data transmission between the host device  16  and the target device  18 , or manage the state of the target device  18 . In one embodiment, the control information and the data information belong to the same communication protocol. The control information may include, but is not limited to, clock signals, reset signals, and power status signals. Preferably, the control information from the host device  16  may be the remote wake up signal for resuming the target device  18 , or a state switch signal for switching the state of a state machine of the target device  18   
         [0020]    The data information and control information are taken in form of electrical signals, which in turn are encoded and converted into an optical signal for optical transmission in the optical transmission device  10 ,  12 . For example, the optical transmission device  10  may transmit an optical signal S opt1  which contains the data information D t1  and the control information S ca  over the cable  14   a  to the optical transmission device  12 , and the optical transmission device  12  may transmit an optical signal S opt2  which contains the data information D t2  and the control information S cb  over the cable  14   b  to the optical transmission device  10 . 
         [0021]    In operation, the optical transmission device  10  and the optical transmission device  12  can exchange data in each transmission direction by transmitting a data signal in a first frequency band and a control signal in a second frequency band of the common optical signal S opt1  or S opt2  over the optical cable  14   a  or  14   b.  That is, the optical transmission device  10  may transmit data signal in a first frequency band and the control signal in a second frequency band to the optical transmission device  12  via the optical fiber  14   a.  Similarly, the optical transmission device  12  may transmit data signal in the first frequency band and the control signal in the second frequency band to the optical transmission device  10  via the optical fiber  14   b.  Furthermore, the protocol used to communicate the host device  16  and the target device  18  is, but is not limited to, USB 3.0 standard. In USB 3.0 system, a data burst may be transmitted at a rate of 5 Gbps, or in a frequency band between 500 MHz and 2.5 GHz after encoding in a normal mode, and communicates to each other via a Low Frequency Periodic Signaling (LFPS) at 10 to 50 MHz in an idle mode. As a result, the control signals may be sent in a frequency band other than the frequency bands between 500 MHz and 2.5 GHz and between 10 MHz to 50 MHz. For instance, the control signal may be, but not limited to, transmitted at any frequency below 10 MHz without causing interference to transmission of the data signal. Since the data information and the control information can be encapsulated and transmitted in one optical signal, it is no longer required to adopt separate copper wires or optical fibers for transferring the control information between the optical transmission device  10  and the optical transmission device  12 , instead, a common optical cable can be utilized to perform the optical transmission. As a result, the implementation cost can be reduced. 
         [0022]    The optical transmission device  10  contains an optical transmitter  100 , an optical receiver  102 , and a controller  104 . The controller  104 , coupled to the optical transmitter  100  and the optical receiver  102 , is configured to control the data flow and operations of the optical transmitter  100  and the optical receiver  102 . For a transmission path, the controller  104  receives the data information and the control information from the host device  16  and provides the data information and the control information in the form of the data D t1  and S ca  (i.e., data signal D t1  and control signal S ca ) respectively to the optical transmitter  100 . The data D t1  may be variously transmitted in a first frequency band between 500 MHz and 2.5 GHz in a normal mode or 10 to 50 MHz in an idle mode. In turn, the control information is processed by the controller  104  to form the data S ca , a CW (continuous wave) signal with a second frequency which is non-overlapping with the first frequency band. The optical transmitter  100  combines the data D t1  and S ca  to output a combined signal, and then converts the combined signal to the optical signal S opt1  to be transmitted to the optical receiver  120  of the optical transmission device  12  over the optical cable  14   a.  For a reception path, the optical receiver  102  receives the optical signal S opt2  from the optical transmission device  12 , converts the optical signal S opt2  back to an electrical signal, and separates and recovers the data information and the control information in the form of data D t2  and S cb  from the electrical signal. The controller  104  can acquire the recovered data D t2  and S cb  and operate according to the recovered data D t2  and S cb . 
         [0023]    Similarly, the optical transmission device  12  contains an optical receiver  120 , an optical transmitter  122  and a controller  124 . The controller  124 , coupled to the optical receiver  120  and the optical transmitter  122 , is configured to control the data flow and operations of the optical receiver  120  and the optical transmitter  122 . For a reception path, the optical receiver  120  receives the optical signal S opt1  on the optical cable  14   a  from the optical transmission device  10 , converts the optical signal S opt1  back to an electrical signal, and separates and recovers the data information and the control information in the form of data D t1  and S ca  from the electrical signal. The controller  124  then can acquire the recovered data D t1  and S ca  and operate according to the recovered data D t1  and S ca . For a transmission path, the controller  124  receives the data information and the control information from the target device  18  and provides the data information and the control information in the form of the data D t2  and S cb  (i.e., data signal D t2  and control signal S cb ) to the optical transmitter  122 . Similarly, the data D t2  may be transmitted in the first frequency band between 500 MHz and 2.5 GHz in a normal mode or 10 to 50 MHz in an idle mode. In turn, the control information is processed by the controller  124  to form the data S cb , a CW (continuous wave) signal with the second frequency which is non-overlapping with the first frequency band, the optical transmitter  122  combines the data D t2  and S cb  to output a combined signal, and then converts the combined signal to the optical signal S opt2  for transmission over the optical cable  14   b  to the optical transmission device  10 . 
         [0024]    The optical communication system  1  allows the optical transmission device  10  and optical transmission device  12  to transmit the data information and control information on non-overlapping frequency manner via the optical signal, That is to say, there is no need to build dedicated optical signal for transmitting the control information. In this way, the implementation cost of building the optical communication system  1  is reduced. 
         [0025]      FIG. 2A  is a schematic diagram of an optical transmission device  2  according to an embodiment of the invention. The optical transmission device  2  may serve as the optical transmission device  10  or optical transmission device  12  in  FIG. 1 . 
         [0026]    The optical transmission device  2  contains the controller  22 , a combiner circuit  20 , and an optical transmitter  24 . The combiner circuit  20  includes control data converters  206  and  207  and a combiner  204 . The optical transmitter  24  includes an electrical-to-optical (E/O) device  208 . In one embodiment, the combiner circuit  20  may be an independent circuit, or may be integrated into the controller  22 . In one embodiment, the combiner  204  may be merged into the optical transmitter  24 , while the two control data converters  206  and  207  are merged into the controller  22 . 
         [0027]    The data D t  is a high-speed data with a data frequency between 500 MHz and 2.5 GHz (in other word, a data is provided in a first frequency band). In one embodiment, the data is compliance with the USB 3.0 standard. In  FIG. 2A , two control data converters  206  and  207  are configured to convert electrical control signals into two different CW signals with different frequencies, respectively. The frequencies of the two different CW signals are non-overlapping with the data frequency of the data D t . In one embodiment, the control data converter converts a control signal into a CW signal with a predetermined frequency according to the state of the control signal. In one embodiment, the electrical control signal D c1  has two valid states. One state is “1” represented logic high, the other state is “0” represented logic low for example. The control data converter  206  converts the control signal D c1  into a CW signal with a first predetermined frequency if the control signal D c1  is logic high. Similarly, the control data converter  206  converts the control signal D c1  into another CW signal with a second predetermined frequency if the control signal D c1  is logic low. In an alternative embodiment, the first predetermined frequency may represent that the electrical control signal is in the one valid state, while the predetermined frequency absent may represent that the electrical control signal is in the other valid state. In addition, the first predetermined frequency and the second predetermined frequency are both lower than the frequency band of the data signal. 
         [0028]    Please reference  FIG. 2A , two switches  200  and  202  can be served as the control data converters described above. The control signals D c1  and D c2  serves as switch control signals SW 1  and SW 2 , respectively, for controlling the switches  200  and  202 , respectively. The frequencies freq c10 , freq c11 , freq c20 , and freq c21  are different from the data frequency of the data D t , and may be in a low-frequency range, for example, less than 20 MHz, but not limited to. The four frequencies freq c10 , freq c11 , freq c20 , and freq c21  may be generated from a single source, or may be generated from different sources. Further, the frequencies freq c10 , freq c11 , freq c20 , and freq c21  are different to one another, and freq c10  and freq c11  represent two states of the control signal D c1  respectively, freq c20  and freq c21  represent two states of the control signal D c2  respectively. For example, the frequencies freq c10 , freq c11  may be 4 MHz and 5 MHz respectively. When the control signal D c1  is a first logic state, the switch  200  selects to output the frequency freq c10  as the electrical control signal S c1 , which is 4 MHz to the combiner  204 . When the control signal D c1  is a second logic state, the switch  200  selects to output the frequency freq c11  as the electrical control signal S c1 , which is 5 MHz to the combiner  204 . The switch  202  is operated in the same way. When the control signal D c2  is a first logic state, the switch  202  selects to output the frequency freq c20  as the electrical control signal S c2  to the combiner  204 . When the control signal D c2  is a second logic state, the switch  202  selects to output the frequency freq c21  as the electrical control signal S c2  to the combiner  204 . In addition, data D t  is filtered by a high-pass filter  210  to generate a filtered data signal D tf  prior to the combiner  204  to ensure the data D t  is more precisely. The switches  200  and  202  select frequencies freq c10 , freq c11 , freq c20 , and freq c21  by the control signals D c1  and D c2 , respectively to output the selected frequencies (electrical control signals S c1  and S c2 ) to the combiner  204 , which combine the selected frequencies and the filtered data signal D tf  to generate the combined signal S comb . Because the frequencies freq c10 , freq c11 , freq c20 , and freq c21  and the frequency of the data D t  are non-overlapping to each other, they will not cause interference to one another in the combined signal S comb . 
         [0029]    The E/O device  208  contains a laser diode (not shown), or any other suitable laser device that could be substituted therefor. The laser diode generates an optical carrier signal with a predetermined carrier frequency and a wideband bandwidth. The E/O device  208  receives the combined signal S comb  from the combiner  204 , modulates the combined signal S comb  with the optical carrier signal to output an optical signal S opt  for communicating over the optical fibers (not shown). In one embodiment, the E/O device  208  simply receives the combined signal S comb  and transforms to an optical signal S opt  for subsequent transmission in any manner. 
         [0030]    Please reference  FIG. 2B , which is a schematic diagram for an optical transmission device  2  according to another embodiment of the invention. The difference of  FIG. 2A  and  FIG. 2B  is that the control data converters are implemented by two programmable frequency dividers  208  and  212 . Two programmable frequency dividers  208  and  212  both received the same frequency source freq. The control signals D c1  and D c2  serves as frequency divider control signals, respectively, for selecting corresponding frequency divider ratio according to the states of the control signals D c1  and D c2 , respectively. When the control signal D c1  is a first logic state, the frequency divider  208  selects a first predetermined frequency divider ratio N DC10  to output the frequency freq c10  as the electrical control signal S c1 , which is 4 MHz to the combiner  204 . When the control signal D c1  is a second logic state, the frequency divider  208  selects a second predetermined frequency divider ratio N DC11  to output the frequency freq c11  as the electrical control signal S c1 , which is 5 MHz to the combiner  204 . The frequency divider  212  is operated in the same way. When the control signal D c2  is a first logic state, the frequency divider  212  selects a third predetermined frequency divider ratio N DC20  to output the frequency freq c20  as the electrical control signal S c2  to the combiner  204 . When the control signal D c2  is a second logic state, the frequency divider  212  selects a fourth predetermined frequency divider ratio N DC21  to output the frequency freq c21  as the electrical control signal S c2  to the combiner  204 . The frequencies freq c10 , freq c11 , freq c20 , and freq c21  are different from the data frequency of the data D t , and may be in a low-frequency range, for example, less than 20 MHz, but not limited to. In addition, data D t  is filtered by a high-pass filter  212  to generate a filtered data signal D tf  prior to the combiner  204  to ensure the data D t  is more precisely. The combiner  204  combines the output frequencies of the control data converters  206  and  207  and the filtered data signal D tf  to generate the combined signal S comb . Because the frequencies freq c10 , freq c11 , freq c20 , and freq c21  and the frequency of the data D t  are non-overlapping to each other, they will not cause interference to one another in the combined signal S comb . Although only two control signals D c1  and D c2  are shown in  FIG. 2A  and  FIG. 2B , those skilled in the art would recognize that more control data may be converted and multiplexed into the optical signal S opt  based on the same principle disclosed in the embodiment. 
         [0031]    The optical transmission devices  10 ,  12  allow the host device  16  and target device  18  to transmit the data information and control information on non-overlapping frequencies via an optical signal, reducing the implementation cost of the optical cable. 
         [0032]      FIG. 3  is a block diagram of an optical receiver  3  according to an embodiment of the invention. The optical receiver  3  may be utilized to serve as the optical receivers  102  and  120  in  FIG. 1 . The optical receiver  3  receives an optical signal S opt  for transmission over the optical cable and recovers electrical data and control signals from the optical signal S opt . 
         [0033]    The optical receiver  3  contains an optical-to-electrical (O/E) device and filters  32 ,  34  and  36 . The O/E device  30  contains a photodetector (not shown) and a transimpedance amplifier (TIA) (not shown). The photodetector detects the light wave of the optical signal S opt  and the TIA transforms the detected optical signal S opt  into a corresponding electrical signal. 
         [0034]    The filter  32  is configured to filter out the electrical data signal D t ′. The filters  34  and  36  are configured for filtering out the frequencies freq c10 , and freq c11 , respectively. The filters  32 ,  34  and  36  may be band-pass filters which allow electrical data and control signals to be separated from the transformed electrical signal. The operating frequency ranges of the filters  32 ,  34  and  36  may be predetermined in compliance with the frequency spectrum design set out in the optical transmission device. Alternatively, the optical receiver  3  may also include a frequency detection circuit (not shown) to actively detect all available frequency components in the optical signal S opt , and configure the operating frequency ranges for the filters  32 ,  34  and  36  accordingly. For example, the filter  32  may be configured to isolate the signal in the frequency band between 500 MHz-2.5 GHz, the filter  34  may be configured to isolate the signal in the frequency band centered at 4 MHz, and the filter  36  may be configured to isolate the signal in the frequency band centered at 5 MHz. In another embodiment, a band-pass filter (not shown in  FIG. 3 ) can be added prior to the filters  34  and  36  to filter out a lower frequency range, for example, below 20 MHz. In addition, since the filter  32  is configured to separate the electrical data signal D t ′ occupying a highest frequency spectrum, the filter  32  may also be a high pass filter. The corresponding filters that filter out the frequencies freq c20 , and freq c21  are not shown in  FIG. 3 . 
         [0035]    The optical receiver  3  allows the host device and target device to identify the data information and control information from an optical signal, reducing the implementation cost of the optical cable. 
         [0036]      FIG. 4  is a flowchart of an optical transmission method according to an embodiment of the invention, incorporating the optical communication system  1  in  FIG. 1  and the optical transmission device  2  in  FIGS. 2A and 2B . The optical transmission method is initiated when the host device  16  or the target device  18  intends to transmit both the data signal and control signal over an AOC cable. 
         [0037]    Upon startup of the optical transmission method, the host device  16  is in connection with the target device  18  via the AOC cable, ready to send the data and control information over the optical cable  14   a  (S 400 ). 
         [0038]    Next, the electrical data signal D t  in a first frequency band (S 402 ) is provided. In one embodiment, the optical transceiver  100  is configured to transmit the electrical data signal Dt in a first frequency band. The first frequency band may have a range between 500 MHz and 2.5 GHz. Alternatively, data D t  is pre-filtered by a high-pass filter  210  to generate a filtered data signal D tf  to ensure the data D t  is more precisely. 
         [0039]    Meanwhile, the electrical control signal S c  in a second frequency band is provided (S 404 ). The second frequency band is non-overlapping with the first frequency band, and may have a range between 0 Hz and 10 MHz for example. The electrical control signal D c  and data signal D t  belong to the same communication protocol. 
         [0040]    In some embodiments, the optical transceiver  100  is configured to transmit the electrical control signal D c  and convert the electrical control signal D c  to the electrical control signal S c  in a second frequency band according to the state of the electrical control signal D c . Control data converter is implemented in the optical transceiver  100  and configured to convert electrical control signal D c  to the electrical control signal S c  in a second frequency band according to the state of the electrical control signal D c . In one embodiment, the control data converter converts a control signal into a CW signal with a predetermined frequency according to the state of the control signal. In one embodiment, the electrical control signal D c  has two valid states. One state is “1” represented logic high, the other state is “0” represented logic low for example. The control data converter converts the control signal D c  into a CW signal with a first predetermined frequency if the control signal D c  is logic high. Similarly, the control data converter converts the control signal D c  into another CW signal with a second predetermined frequency if the control signal D c  is logic low. In an alternative embodiment, the first predetermined frequency may represent that the electrical control signal is in the one valid state, while the predetermined frequency absent may represent that the electrical control signal is in the other valid state. In addition, the first predetermined frequency and the second predetermined frequency are both lower than the frequency band of the data signal. 
         [0041]    In other embodiments, the optical transceiver  100  converts the electrical control signal D c  to just one electrical control signal S c , which represents a predetermined state of the electrical control signal D c . That is, the optical receiver  120  automatically interprets the electrical control signal D c , as the state other than the predetermined state when the electrical control signal S c  is not received, and considers the electrical control signal D c  as the predetermined state when the electrical control signal S c  is received. 
         [0042]    The combiner circuit  206  then combines the data signal D t  or the filtered data signal D tf  in the first frequency band and the electrical control signal S c  in the second frequency band to generate a combined electrical signal S comb  (S 406 ). Because the data signal and the electrical control signal adopt non-overlapping frequency bands, they will not cause interference to one another in the combined signal S comb . 
         [0043]    Lastly, the E/O device  208  is configured to convert the combined signal S comb  into an outgoing optical signal S opt  (S 408 ) and transmit the outgoing optical signal S opt  over the optical cable to the target device  12 . Because both the data and control signals can be carried on the same optical signal S opt  without causing interference to each other, only one optical cable is needed for the transmission. As a consequence, the implementation cost for building an optical communication network is reduced. 
         [0044]    Although the embodiment explained in the preceding paragraphs employs the host device  16  to illustrate each step in the optical transmission method, it should be recognized that the target device  18  can also adopt the optical transmission method for initiating a transmission from the target device  18  to the host device  16 . 
         [0045]    The optical transmission method allows the host device and target device to transmit the data information and control information on non-overlapping frequency bands via an optical signal, reducing the implementation cost of building the optical communication system  1 . 
         [0046]    As used herein, the term “determining” encompasses calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. 
         [0047]    The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, processor, microprocessor or state machine. 
         [0048]    The operations and functions of the various logical blocks, modules, and circuits described herein may be implemented in circuit hardware or embedded software codes that can be accessed and executed by a processor. 
         [0049]    While the invention has been described by way of example and in terms of the embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.