Abstract:
A transceiving system includes: a transmitter; and a receiver coupled to the transmitter via optical transmission lines, the transmitter includes: a first processor configured to generate division data obtained by dividing data; a modulator configured to modulate wavelengths of transport lights, which transport the division data, based on setting information including a correspondence relationship between identification information identifying each of the optical transmission lines and wavelength information indicating a wavelength, and output lights, each of which is superimposed with the respective division data, to the optical transmission lines; and a second processor configured to transmit changed setting information, which is obtained by changing the setting information, to the receiver, and the receiver includes: a de-multiplexer configured to separate lights from the optical transmission lines into de-multiplexed lights of a wavelengths, based on the changed setting information; and a third processor configured to convert the de-multiplexed lights into division data.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-149979, filed on Jul. 29, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to optical wavelength-multiplexing communication. 
       BACKGROUND 
       [0003]    In recent years, the computing speed of, for example, supercomputers has been increased. In order to realize the increased computing speed, a large-capacity data transmission technology is required to input/output large-capacity data from a Central Processing Unit (CPU). In an electrical interconnect technology using, for example, a copper wire, a circuit area, the number of transmission lines, and power consumption are remarkably increased with the increase of data capacity, which may make it difficult to realize a high computing speed. Thus, an optical interconnect technology is known which interconnects CPUs with light. In the optical interconnect technology, an optical transceiver using a silicon photonics (SiPH) technology is being developed which is compact to be suitable for large-scale integration and enables a fusion of electricity and light. 
         [0004]    Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 10-028106, Japanese Laid-Open Patent Publication No. 2000-236299, and Japanese Laid-Open Patent Publication No. 2005-341529. 
       SUMMARY 
       [0005]    According to one aspect of the embodiments, A transceiving system includes: a transmitter; and a receiver coupled to the transmitter via optical transmission lines using optical wavelength multiplexing communication, wherein the transmitter includes: a first processor configured to generate a plurality of division data obtained by dividing data, and transmit the plurality of division data; and a modulator configured to modulate wavelengths of transport lights, which transport the plurality of division data, respectively, based on setting information including a correspondence relationship between identification information identifying each of the optical transmission lines and wavelength information indicating a wavelength, and output lights, each of which is superimposed with the respective division data, to the optical transmission lines, respectively; a second processor configured to transmit changed setting information, which is obtained by changing the setting information, to the receiver, and wherein the receiver includes: a de-multiplexer configured to separate lights input from the optical transmission lines into de-multiplexed lights of a plurality of wavelengths, respectively, based on the changed setting information; and a third processor configured to convert the plurality of de-multiplexed lights into division data, respectively. 
         [0006]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  is a view for explaining an exemplary transceiving system using an optical interconnect technology according to an embodiment; 
           [0008]      FIG. 2  is a view for explaining an exemplary configuration of a SiPH transmitter; 
           [0009]      FIG. 3  is a view for explaining an exemplary configuration of a SiPH receiver; 
           [0010]      FIG. 4  is a view for explaining an exemplary relationship between a wavelength and absorption spectrum in a wavelength division multiplexing mode; 
           [0011]      FIG. 5  is a table for explaining an exemplary method of selecting a combination for minimizing power consumption; 
           [0012]      FIG. 6  is a table for explaining an exemplary method of selecting a combination for improving reliability while reducing power consumption; 
           [0013]      FIG. 7A  is a flowchart for explaining an exemplary process of a transmitter; 
           [0014]      FIG. 7B  is a flowchart for explaining an exemplary process of a transmitter; 
           [0015]      FIG. 8A  is a flowchart for explaining an exemplary process of a receiver; 
           [0016]      FIG. 8B  is a flowchart for explaining an exemplary process of a receiver; 
           [0017]      FIG. 9  is a flowchart for explaining an exemplary process of selecting an optimal combination; 
           [0018]      FIG. 10  is a view for explaining another example of communication between control units; and 
           [0019]      FIG. 11  is a flowchart for explaining another example of communication between control units. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    A transmitter of an optical transceiver includes a light source which emits a light, and an optical modulator which modulates a transport light that carries data in the light. The optical modulator includes a ring modulator advantageous for low power consumption and compactness. The ring modulator has an absorption spectrum in a predetermined free spectral range. The absorption spectrum of the ring modulator has an error due to a production tolerance of optical modulators. Therefore, in the transmitter of the optical transceiver, the ring modulator is heated by a heater to allocate an absorption spectrum of the ring modulator to a wavelength of modulated light. Hereinafter, a wavelength of modulated light may be sometimes referred as a “wavelength of a light to be modulated.” The data carried on a light is an electrical signal. The optical modulator varies a refractive index by generating carriers in a PN junction in the resonator with a voltage of the electrical signal as a bias. 
         [0021]    Wavelength Division Multiplex (WDM) refers to a method of transmitting a light obtained by superimposing a plurality of wavelength to a single transmission line. When wavelength-multiplexed lights are transmitted between transceivers using the SiPH technology as in the WDM, optical transmission lines (lanes), of which the number corresponds to the number of kinds of wavelengths, are preset between the transceivers. For example, when the lights of four kinds of wavelengths are transmitted/received between the transceivers, four optical transmission lines are preset between the transceivers. While the wavelength-multiplexed lights are transmitted for all of the optical transmission lines, any one of multiplexed wavelengths is modulated and transmitted in each optical transmission line. Meanwhile, it is assumed that a wavelength to be modulated is preset for each optical transmission line. 
         [0022]    As a transmission system which conducts optical communication by the wavelength division multiplexing mode, for example, signal light transmission/reception is performed while making transmission characteristics constant among signal lights. The signal lights output from a signal light output unit are multiplexed and some of the multiplexed signal lights are extracted. Signal light power is detected for each wavelength corresponding to a signal light wavelength. Based on the detected signal light power for each wavelength, a signal light output of an optical amplifier for use in amplifying the corresponding wavelength signal light is controlled. 
         [0023]    As a technique related to wavelength dispersion, for example, a wavelength dispersion compensation is performed by outputting a light of a wavelength, which has a transmission characteristic optimal to the wavelength dispersion into an optical transmission line, to the optical transmission line without using a wavelength-variable laser. A plurality of light sources outputting lights of different wavelengths is provided, and, before starting the operation of an optical transmission system, a wavelength of a light output to the optical transmission line is varied in order to detect a wavelength having a transmission characteristic optimal to the wavelength dispersion into an optical transmission line. During the operation of the optical transmission system, the light of the detected optimal wavelength is output to the optical transmission line. 
         [0024]    In an optical transmission system, for example, a channel is allocated by automating each order of wavelength detection, wavelength setting, and wavelength selection of a plurality of single wavelength lights in an optical transmission system. Based on the power of single wavelengths individually sweep-output from a transmitter which individually outputs the single-wavelength lights, wavelength information of each single-wavelength light is notified to the transmitter. The wavelengths of single wavelength lights output by the transmitter are controlled based on the notified wavelength information. 
         [0025]    In an optical transmission line in which wavelength-multiplexed lights obtained by superimposing lights having different wavelengths are transmitted, a wavelength to be modulated in the transmitted lights is preset. Each ring modulator in a transmitter is heated in order to adjust its own absorption spectrum to a wavelength to be modulated. Here, since a combination of a wavelength to be modulated in the wavelength-multiplexed light and an optical transmission line is preset, an amount of power to be used for the heating by a heater may not be considered. 
         [0026]    The combination of a wavelength to be modulated in the wavelength-multiplexed light and an optical transmission line may also be changed. However, when the transmitter arbitrarily changes the setting of the wavelength of light to be modulated, the receiver may not restore the modulated wavelength to the original wavelength. 
         [0027]    Hereinafter, embodiments will be described in detail with reference to the drawings. 
         [0028]      FIG. 1  is a view for explaining an exemplary transceiving system using an optical interconnect technology according to an embodiment. A transceiving system  1000  includes a transmitter  100 , a receiver  200 , and optical transmission lines  300  ( 300   a  to  300   d ). The transmitter  100  and the receiver  200  are interconnected by the optical transmission lines  300  used for communication using optical wavelength-multiplexing communication. 
         [0029]    The transmitter  100  includes a chip  110  and a modulating unit  120 . The receiver  200  includes a de-multiplexing unit  220  and a chip  210 . The chip  110  and the chip  210  are, for example, CPUs. In the transceiving system  1000  of this embodiment, large capacity data communication and high speed communication are realized by using an optical interconnect for communication between the chip  110  and the chip  210 . In order to realize the optical interconnect, the transmitter  100  includes the modulating unit  120  and the receiver  200  includes the de-multiplexing unit  220 . 
         [0030]    The chip  110  includes a generating unit  111  and a transmitting unit  112 . The generating unit  111  generates a plurality of division data obtained by dividing data to be transmitted from the transmitter  100  to the receiver  200 . The respective division data are denoted by A to D. The transmitting unit  112  transmits the division data A to D generated in the generating unit  111  to the modulating unit  120 . Processes of the generating unit  111  and the transmitting unit  112  are implemented with an operation of a CPU. The process of the generating unit  111  is a process executed in a logic layer of the CPU. A process of the transmitting unit  112  is a process executed in a physical layer of the CPU. 
         [0031]    The modulating unit  120  includes a control unit  121 . The modulating unit  120  is, for example, a SiPH transmitter. The control unit  121  holds wavelength information indicating a wavelength to be modulated in wavelength-multiplexed lights, and setting information defining a correspondence relationship with identification numbers identifying optical transmission lines. The control unit  121  is, for example, a microcomputer. The control unit  121  holds power consumption information corresponding to a combination of an identification number identifying each optical transmission line and a wavelength to be modulated in each optical transmission line (for more information, see, e.g.,  FIGS. 5 and 6 ). The “power consumption” used herein refers to electric energy used for heating by a heater in a ring modulator. Based on the power consumption information, the control unit  121  selects a combination of an identification number identifying each optical transmission line whose power consumption by the heater becomes smaller and a wavelength to be modulated in each optical transmission line, and updates the setting information. Based on the combinations of optical transmission lines and wavelengths to be modulated, which is selected by the control unit  121 , the modulating units  120  modulate transport lights of wavelengths carrying division data, respectively, and output lights, each of which is superimposed with division data, to the optical transmission lines, respectively. Meanwhile, a light resonant to the ring modulator is separated and modulated. 
         [0032]    In this way, the modulating units  120  are able to reduce the power consumption of the transmitter  100  by selecting a combination of an optical transmission line whose power consumption becomes smaller and a wavelength of light to be modulated and modulating the selected wavelength of light to be modulated. Meanwhile, a combination of an optical transmission line and a wavelength of light to be modulated, which is selected by the control unit  121 , may be selected in such a way that the maximum of power consumption in the combination is decreased, or may be optimized in various ways. 
         [0033]    However, when a wavelength different from a wavelength provided in the receiver  200  is modulated in the transmitter  100 , the receiver  200  may not be able to restore data normally. With this problem, the control unit  121  transmits changed setting information to a control unit  221  of the receiver  200 . The control unit  121  and the control unit  221  conduct wireless or wired data communication with each other. Thus, the receiver  200  may be able to determine which wavelength is set for each optical transmission line, and may be able to restore data from received light. 
         [0034]    The de-multiplexing unit  220  of the receiver  200  separates a light having a resonating wavelength from the wavelength-multiplexed lights input via the optical transmission lines  300 , based on changed setting information (a correspondence relationship between a wavelength of light to be modulated and an optical transmission line). The de-multiplexing unit  220  is implemented with a SiPH receiver. A converting unit  211  converts light output from the de-multiplexing unit  220  into division data. An assembly unit  212  assembles the division data into the original data. 
         [0035]    In this way, by selecting the optimal combination of an optical transmission line and a wavelength of light to be modulated, under the control of the control unit  121 , the power consumption of the transmitter  100  side may be reduced. Meanwhile, a changing process of the setting information, based on which the control unit  121  selects a combination of an optical transmission line and a wavelength of light to be modulated, may be performed, for example, when the transceiving system  1000  is powered on. In this case, the transceiving system  1000  operates with the same setting until the transceiving system  1000  is powered off. In addition, the changing process of the setting information, based on which the control unit  121  selects a combination of an optical transmission line and a wavelength of light to be modulated, may be regularly performed. 
         [0036]      FIG. 2  is a view for explaining an exemplary configuration of a SiPH transmitter. A SiPH transmitter  310  operates as the modulating unit  120  of  FIG. 1 . The SiPH transmitter  310  includes a microcomputer  301 , an array laser  302 , a wavelength division multiplexing-type multiplexer (WDMMUX)  303 , a ring modulator  304  (e.g., ring modulators  304   a  to  304   d ), a heater  305 , a monitor photodiode  306 , a driver  307 , and a lane  308  (e.g., lanes  308   a  to  308   d ). The microcomputer  301  operates as the control unit  121  of  FIG. 1 . The array laser  302  is a light source that outputs lights of different wavelengths, the number of which is the same as that number of the lanes  308   a  to  308   d.  The array laser  302  is installed to be oscillated at different wavelengths by a diffraction grating (distribution feedback). The WDMMUX  303  is a device which collects input lights of different wavelengths into a single waveguide so as to transmit the input lights. The ring modulator  304  separates a light of a wavelength to be modulated from the wavelength-multiplexed lights, generates a carrier in a PN junction in the modulator with a voltage of an electrical signal as a bias, and modulates the separated light by varying a refractive index. The heater  305  is used to heat the ring modulator  304  in order to match a ring modulation wavelength and a light wavelength in the waveguide to each other. The monitor photodiode  306  is used to determine whether or not the ring modulation wavelength and the light wavelength in the waveguide are matched to each other. The driver  307  is an amplifier which converts an electrical signal, which is data transmitted from the chip  110 , into a bias voltage of the ring modulator  304 . The microcomputer  301  controls the power of the heaters  305  such that the output of the monitor photodiode  306  becomes constant by adjusting the oscillation wavelength of the ring modulator  304 . In addition, the microcomputer  301  initializes various devices in the SiPH transmitter  310 . The division data A to D of  FIG. 1  are transmitted to the receiver via the lanes  308   a  to  308   d,  respectively. 
         [0037]      FIG. 3  is a view for explaining an exemplary configuration of a SiPH receiver. A SiPH receiver  400  operates as the de-multiplexing unit  220  of  FIG. 1 . The SiPH receiver  400  includes a de-multiplexer  401  (e.g., de-multiplexers  401   a  to  401   d ), a heater  402 , a monitor photodiode  403 , a photodiode  404 , a TIA/LIM (Trans Impedance Amp/Limiting Amp)  405 , and a microcomputer  406 . The microcomputer  406  operates as the control unit  221  of  FIG. 1 . The de-multiplexer  401  separates a light having a wavelength to be modulated from the wavelength-multiplexed optical signals and inputs the separated light to the photodiode  404 . The heater  402  may be the same as the heater  302  illustrated in  FIG. 2 . The monitor photodiode  403  may be the same as the monitor photodiode  303  illustrated in  FIG. 2 . The photodiode  404  converts the modulated light into an electrical signal. The TIA of the TIA/LIM  405  refers to a pre-amplifier that converts a photodiode current into a voltage. The LIM of the TIA/LIM  405  refers to a post-amplifier which sets an output amplitude to fit the chip of the reception side. 
         [0038]      FIG. 4  is a graph for explaining an exemplary relationship between a wavelength and an absorption spectrum in a wavelength division multiplexing mode. In the graph illustrated in  FIG. 4 , a vertical axis represents absorption strength of an absorption spectrum and a horizontal axis represents a wavelength. In the graph illustrated in  FIG. 4 , four wavelengths A to D output from the array laser  302  of the SiPH transmitter  310  in a wavelength division multiplexing mode are illustrated. The wavelengths A to D are exemplary wavelengths to be modulated. The wavelengths A to D to be modulated are wavelengths selected based on the electrical signals of the division data A to D. The graph illustrated in  FIG. 4  also illustrates an exemplary a relationship between a wavelength and absorption strength of each of an absorption spectrum  501  and an absorption strength  502  of the ring modulators  304 . For example, the absorption spectrum  501  is an exemplary relationship between a wavelength and absorption strength of the ring modulator  304   a.  The absorption spectrum  502  is an exemplary relationship between a wavelength and absorption strength of the ring modulator  304   b.    
         [0039]    For example, when the light having the wavelength A is to be modulated in the ring modulator  304   a,  the microcomputer  301  controls the heater to heat the ring modulator  304   a.  Then, the rightmost peak of the absorption spectrum  501  of the ring modulator  304   a  is adjusted to be matched to the wavelength A. When the absorption spectrum  501  of the ring modulator  304   a  is matched to the wavelength A, the light having the wavelength A is separated from the wavelength-multiplexed lights and modulated. Likewise, when the light having the wavelength B is to be modulated in the ring modulator  304   b,  the microcomputer  301  controls the heater to heat the ring modulator  304   b.  Then, the second peak from the right of the absorption spectrum  502  of the ring modulator  304   b  is adjusted to be matched to the wavelength B. A combination of the absorption spectrum  501  of the ring modulator  304   a  and the wavelength A to be modulated and a combination of the absorption spectrum  502  of the ring modulator  304   b  and the wavelength B to be modulated are indicated by a case  503 . Arrows in the case  503  indicates adjustment widths of the absorption spectrum  501  and the absorption spectrum  502  each of which is adjusted by the heating of the heater. The adjustment widths correspond to power consumption. 
         [0040]    As another example, when the light having the wavelength A is to be modulated in the ring modulator  304   b,  the microcomputer  301  controls the heater to heat the ring modulator  304   b.  Then, the rightmost peak of the absorption spectrum  502  of the ring modulator  304   b  is adjusted to match the wavelength A. When the light having the wavelength B is to be modulated in the ring modulator  304   a,  the microcomputer  301  controls the heater to heat the ring modulator  304   a.  Then, the second peak from the right of the absorption spectrum  501  of the ring modulator  304   a  is adjusted to be matched to the wavelength B. A combination of the absorption spectrum  502  of the ring modulator  304   b  and the wavelength A and a combination of the absorption spectrum  501  of the ring modulator  304   a  and the wavelength B are indicated by a case  504 . Arrows in the case  504  indicate adjustment widths of the absorption spectrum  501  and the absorption spectrums  502  each of which is adjusted by the heating of the heater. The adjustment widths correspond to power consumption. 
         [0041]    As illustrated in the case  503 , when the light of the wavelength A is to be modulated in the ring modulator  304   a  and the light having the wavelength B is to be modulated in the ring modulator  304   b,  the power consumption is large. By changing this setting to a setting in which the light having the wavelength A is to be modulated in the ring modulator  304   b  and the light having the wavelength B is to be modulated in the ring modulator  304   a,  as illustrated in the case  504 , the power consumption is capable of being reduced. 
         [0042]      FIG. 5  illustrates tables for explaining an exemplary method of selecting a combination for minimizing power consumption. A power consumption table  601  represents exemplary power consumption in each of combinations of ring modulators  304   a  to  304   d  of the modulating unit  120  and wavelengths A to D to be modulated. Numbers 1 to 4 of the modulating unit  120  correspond to the ring modulators  304   a  to  304   d  of  FIG. 2 , respectively. Power consumption in a case where an absorption spectrum of No. 1 of the modulating unit  120  (e.g., the ring modulator  304   a ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  601 . In order to adjust the absorption spectrum of No. 1 of the modulating unit  120  to the wavelength A, for example, power of 30 mW is used. In order to adjust the absorption spectrum of No. 1 of the modulating unit  120  to the wavelength B, for example, power of 14 mW is used. In order to adjust the absorption spectrum of No. 1 of the modulating unit  120  to the wavelength C, for example, power of 28 mW is used. In order to adjust the absorption spectrum of No. 1 of the modulating unit  120  to the wavelength D, for example, power of 1 mW is used. Likewise, power consumption in a case where an absorption spectrum of No. 2 of the modulating unit  120  (e.g., the ring modulator  304   b ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  601 . Power consumption in a case where an absorption spectrum of No. 3 of the modulating unit  120  (e.g., the ring modulator  304   c ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  601 . Power consumption in a case where an absorption spectrum of No. 4 of the modulating unit  120  (e.g., the ring modulator  304   d ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  601 . In this way, the control unit  121  generates the power consumptions in all the combinations of the absorption spectrums of the modulating unit  120  and the wavelengths A to D when the transmitter  100  is powered on. 
         [0043]    A power consumption table  602  represents an exemplary power consumption in each of the combinations of de-multiplexers  401   a  to  401   d  of the de-multiplexing unit 220 and the wavelengths A to D. For example, numbers 1 to 4 of the de-multiplexing unit  220  may correspond to the de-multiplexers  401   a  to  401   d  of  FIG. 3 , respectively. Power consumption in a case where an absorption spectrum of No. 1 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   a ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  602 . In order to adjust the absorption spectrum of No. 1 of the de-multiplexing unit  220  to the wavelength A, for example, power of 15 mW is used. In order to adjust the absorption spectrum of No. 1 of the de-multiplexing unit  220  to the wavelength B, for example, power of 7 mW is used. In order to adjust the absorption spectrum of No. 1 of the de-multiplexing unit  220  to the wavelength C, for example, power of 27 mW is used. In order to adjust the absorption spectrum of No. 1 of the de-multiplexing unit  220  to the wavelength D, for example, power of 10 mW is used. Likewise, power consumption in a case where an absorption spectrum of No. 2 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   b ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  602 . Power consumption in a case where an absorption spectrum of No. 3 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   c ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  602 . Power consumption in a case where an absorption spectrum of No. 4 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   d ) is adjusted to each of the wavelengths A to D is actually measured and stored in the power consumption table  602 . In this way, the control unit  221  generates the power consumptions in all the combinations of the absorption spectrums of the de-multiplexing unit  220  and the wavelengths A to D when the receiver  200  is powered on. 
         [0044]    Each of a power consumption table  603  and a power consumption table  604  represents exemplary power consumption in each of combinations of lane numbers and the wavelengths A to D. For example, lane numbers 1 to 4 may correspond to the optical transmission lines  300   a  to  300   d  of  FIG. 1 , respectively. Lane No. 1 (the optical transmission line  300   a ) is used for optical communication between No. 1 of the modulating unit  120  and No. 1 of the de-multiplexing unit  220 . In each of the power consumption table  603  and the power consumption table  604 , power consumption in a combination of lane No. 1 and the wavelengths A to D is the sum of power consumption of the modulating unit  120   a  and power consumption of the de-multiplexing unit  220   a  corresponding to the lane number. For example, the sum of the power consumption to adjust No. 1 of the modulating unit  120  to the wavelength A and the power consumption to adjust No. 1 of the de-multiplexing unit  220  to the wavelength A is stored, as the power consumption corresponding to the wavelength A of lane No. 1, in each of the power consumption table  603  and the power consumption table  604 . Likewise, in each of the power consumption table  603  and the power consumption table  604 , power consumption in a combination of lane No. 2 and the wavelengths A to D is the sum of power consumption of the modulating unit  120   b  and power consumption of the de-multiplexing unit  220   b  corresponding to the lane number. In each of the power consumption table  603  and the power consumption table  604 , the power consumption in a combination of lane No. 3 and the wavelengths A to D is the sum of power consumption of the modulating unit  120   c  and power consumption of the de-multiplexing unit  220   c  corresponding to the lane number. In each of the power consumption table  603  and the power consumption table  604 , power consumption in a combination of lane No. 4 and the wavelengths A to D is the sum of power consumption of the modulating unit  120   d  and power consumption of the de-multiplexing unit  220   d  corresponding to the lane number. 
         [0045]    In the exemplary power consumption table  604 , it is preset that the light of wavelength A is transmitted in lane No. 1, the light of wavelength B is transmitted in lane No. 2, the light of wavelength C is transmitted in lane No. 3, and the light of the wavelength D is transmitted in lane No. 4. In this example, the total power consumption of the transmitter  100  and the receiver  200  is 128 mW, which is obtained by summing 45, 26, 18, and 39. 
         [0046]    The power consumption table  603  is an exemplary case where a combination of minimizing power consumption is selected from all the power consumptions of the power consumption table  603 . The combination minimizing the power consumption is selected by the control unit  121  from all the combinations of the power consumption table  603 . In the exemplary power consumption table  603 , the control unit  121  selects a transmission lane for each wavelength in such a way that the light of wavelength A is transmitted in lane No. 3, the light of wavelength B is transmitted in lane No. 1 of the lane, the light of wavelength C is transmitted in lane No. 4, and the light of wavelength D is transmitted in the lane No. 2. In this case, the total power consumption of the transmitter  100  and the receiver  200  is 67 mW that is obtained by summing 2, 21, 29, and 15. 
         [0047]    In this way, the control unit  121  selects the optimal (minimal) combination with low power consumption from all the combinations of wavelengths to be modulated and lanes when the power of the transmitter  100  and the receiver  200  is on. Thus, the combination selected by the control unit  121  in operation may be used to conduct communication between the transmitter  100  and the receiver  200 , thereby reducing the power consumptions of the transmitter  100  and the receiver  200 . The information of the power consumption table  601  and the power consumption table  602  is shared by the control unit  121  and the control unit  221 . 
         [0048]      FIG. 6  is a table for explaining an exemplary method of selecting a combination for improving reliability while reducing power consumption. In  FIG. 6 , an exemplary method of selecting a combination that is different from a combination in which the power consumption is low will be described by using a power consumption table  701  and a power consumption table  702 . The power consumption table  701  is an exemplary power consumption for each of combinations of the modulating unit  120  and wavelengths A to D. For example, numbers 1 to 4 of the modulating unit  120  may correspond to the ring modulators  304   a  to  304   d  of  FIG. 2 , respectively. The power consumption in a case where an absorption spectrum of No. 1 of the modulating unit  120  (e.g., the ring modulator  304   a ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  701 . When an absorption spectrum of a ring modulator is matched to a wavelength to be modulated, the modulated light is able to be separated from multiplexing-modulated light. Likewise, the power consumption in a case where an absorption spectrum of No. 2 of the modulating unit  120  (e.g., the ring modulator  304   b ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  701 . The power consumption in a case where an absorption spectrum of No. 3 of the modulating unit  120  (e.g., the ring modulator  304   c ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  701 . The power consumption in a case where an absorption spectrum of No. 4 of the modulating unit  120  (e.g., the ring modulator  304   d ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  701 . In this way, the control unit  121  generates the power consumptions in all the combinations of the absorption spectrums of the modulating unit  120  and wavelengths A to D when the transmitter  100  is powered on. 
         [0049]    The power consumption table  702  is an exemplary power consumption for each of combinations of the de-multiplexing unit  220  and wavelengths A to D. For example, numbers 1 to 4 of the de-multiplexing unit  220  may correspond to the de-multiplexers  401   a  to  401   d  of  FIG. 3 , respectively. The power consumption in a case where an absorption spectrum of No. 1 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   a ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  702 . Likewise, the power consumption in a case where an absorption spectrum of No. 2 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   b ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  702 . The power consumption in a case where an absorption spectrum of No. 3 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   c ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  702 . The power consumption in a case where an absorption spectrum of No. 4 of the de-multiplexing unit  220  (e.g., the de-multiplexer  401   d ) is adjusted to each of wavelengths A to D is actually measured and stored in the power consumption table  702 . In this way, the control unit  121  generates the power consumptions in all the combinations of the absorption spectrums of the de-multiplexing unit  220  and wavelengths A to D when the receiver  200  is powered on. 
         [0050]    The control unit  121  selects the optimal combination from the combinations of the modulating unit  120  and wavelengths and the combinations of the de-multiplexing unit  220  and wavelengths. Here, when a combination with high power consumption exists among the combinations selected by the control unit  121 , the modulating unit  120 , the de-multiplexing unit  220 , and a device existing near the units are exposed to a high operation environment temperature for a long time during the product operation. In particular, for example, a semiconductor device or a photonic device is deteriorated in reliability under a high temperature environment. Therefore, in the example of  FIG. 6 , the control unit  121  selects a combination with the smallest maximum power consumption of each heater from the combinations of the modulating unit  120  and wavelengths and the combinations of the de-multiplexing unit  220  and wavelengths. 
         [0051]    The control unit  121  selects a combination with the smallest maximum power consumption of the modulating unit  120  and the de-multiplexing unit  220  from combinations of the power consumption table  701  and the power consumption table  702 . For example, the control unit  121  selects a combination of No. 3 of the modulating unit  120  and wavelength A, a combination of No. 4 of the modulating unit  120  and wavelength B, a combination of No. 2 of the modulating unit  120  and wavelength C, and a combination of No. 1 of the modulating unit  120  and wavelength D from the power consumption table  701 . The control unit  121  selects a combination of No. 3 of the de-multiplexing unit  220  and wavelength A, a combination of No. 4 of the de-multiplexing unit  220  and wavelength B, a combination of No. 2 of the de-multiplexing unit  220  and wavelength C, and a combination of No. 1 of the de-multiplexing unit  220  and wavelength D from the power consumption table  702 . Then, the maximum power consumption of the modulating unit  120  and the de-multiplexing unit  220  becomes 22 mW, thereby decreasing the maximum power consumption in each ring modulator. 
         [0052]    In this way, the control unit  121  selects a combination with decreased maximum power consumption in each ring modulator from all the combinations of wavelengths to be modulated and lanes and then uses the selected combination to conduct communication so that the reliability of a semiconductor device, a photonic device or the like may be prevented from being deteriorated. 
         [0053]      FIGS. 7A and 7B  are flowcharts for explaining an exemplary process performed by a transmitter. The transceiving system  1000  is powered on (Step S 101 ). The control unit  121  performs settings related to the modulating unit  120  (Step S 102 ). The control unit  121  selects a specific wavelength (any of wavelengths A to D) to be output to the array laser  302  (Step S 103 ). The array laser  302  outputs the light of the wavelength selected by the control unit  121  (Step S 104 ). The heater  305  heats the modulating unit  120  to adjust an absorption spectrum (Step S 105 ). The control unit  121  determines whether or not a certain current is detected in the monitor photodiode  306  (Step S 106 ). When it is determined that the certain current is detected in the monitor photodiode  306  (YES in Step S 106 ), the control unit  121  writes power consumption for a combination of a wavelength of the light output from the array laser  302  and the modulating unit  120  in a power consumption table (Step S 107 ). The control unit  121  determines whether or not the process of Steps S 105  to S 107  have been performed for a light of one wavelength for all modulating units  120  (Step S 108 ). When it is determined that the process have not been completed for light of one wavelength for all modulating units  120  (NO in Step S 108 ), the control unit  121  selects another modulating unit  120  and repeats the process from Step  105  (Step S 109 ). When it is determined that the certain current is not detected in the monitor photodiode  306  (NO in Step S 106 ), the control unit  121  determines whether or not power set in the heater is maximal (Step S 110 ). When it is determined that the power set in the heater is maximal (YES in Step S 110 ), the control unit  121  determines that the modulating unit  120  is out of order (Step S 111 ). When the modulating unit  120  is out of order, the process of the transmitter  110  is ended. When it is determined that the power set in the heater is not maximal (NO in Step S 110 ), the control unit  121  repeats the process from Step S 105 . 
         [0054]    The control unit  121  notifies the control unit  221  that the acquisition of power consumption in the combination of light of one wavelength and each modulating unit  120  has been terminated (Step S 112 ). The control unit  121  receives a notification indicating that the process of the control unit  221  has been completed (Step S 113 ). The notifications of Steps S 112  and S 113  are made using a communication method such as, for example, Inter Integrated Circuit (I2C). The control unit  121  determines whether or not the process of Steps S 104  to S 113  has been completed for all the wavelengths (wavelengths A to D of WDM) (Step S 114 ). When it is determined that the process has not been completed for all wavelengths (NO in Step S 114 ), the control unit  121  repeats the process from Step S 103 . 
         [0055]    When it is determined that the process has been completed for all the wavelengths (YES in Step S 114 ), the control unit  121  receives a power consumption table of the receiver  200  from the control unit  221  (Step S 115 ). The control unit  121  selects the optimal combination of a wavelength of light to be modulated and an optical transmission line from the power consumption tables of the transmitter  100  and the receiver  200  (Step S 116 ). The control unit  121  notifies the control unit  221  of the optimal combination (Step S 117 ). The control unit  121  reflects the optimal combination in setting information (Step S 118 ). The control unit  121  terminates the initialization process (Step S 119 ). These processes may be performed at the time of power-on and the used light may not be that subjected to WDM (Wavelength Division Multiplexing). 
         [0056]      FIGS. 8A and 8B  are flowcharts for explaining an exemplary process performed by a receiver. The transceiving system  1000  is powered on (Step S 201 ). The control unit  221  performs settings related to the TIA/LIM  405  (Step S 202 ). The control unit  221  receives a notification indicating that the acquisition of power consumption in the combination of light of one wavelength and each modulating unit  120  has been terminated in the transmitter  100  (Step S 203 ). The notification received by the control unit  221  in Step S 203  is one notified from the control unit  121  of the transmitter  100  in the process of Step S 112 . The heater  402  heats the de-multiplexing unit  220  to adjust an absorption spectrum (Step S 204 ). The control unit  221  determines whether or not a certain current is detected in the monitor photodiode  403  (Step S 205 ). When it is determined that the certain current is detected in the monitor photodiode  403  (YES in Step S 205 ), the control unit  221  writes power consumption for a combination of a wavelength of the light output from the array laser  302  and the de-multiplexing unit  220  in a power consumption table (Step S 206 ). The control unit  221  determines whether or not a process of Steps S 204  to S 206  have been performed for light of one wavelength for all de-multiplexing units  220  (Step S 207 ). When it is determined that the process have not been completed for light of one wavelength for all de-multiplexing units  220  (NO in Step S 207 ), the control unit  221  selects another de-multiplexing unit  220  and repeats the process from Step  204  (Step S 208 ). When it is determined that the certain current is not detected in the monitor photodiode  403  (NO in Step S 205 ), the control unit  221  determines whether or not power set in the heater is maximal (Step S 209 ). When it is determined that the power set in the heater is maximal (YES in Step S 209 ), the control unit  221  determines that the de-multiplexing unit  220  is out of order (Step S 210 ). When the de-multiplexing unit  220  is out of order, the control unit  221  terminates the process. When it is determined that the power set in the heater is not maximal (NO in Step S 209 ), the control unit  221  repeats the process from Step S 204 . 
         [0057]    The control unit  221  notifies the control unit  121  that the acquisition of power consumption in the combination of light of one wavelength and each de-multiplexing unit  220  has been terminated (Step S 211 ). The notification of Step S 211  is made using a communication means such as I2C. The control unit  221  determines whether or not the process of Steps S 203  to S 211  has been completed for all wavelengths (wavelengths A to D of WDM) (Step S 212 ). When it is determined that the process has not been completed for all wavelengths (NO in Step S 212 ), the control unit  221  repeats the process from Step S 204 . 
         [0058]    When it is determined that the process has been completed for all wavelengths (YES in Step S 212 ), the control unit  221  transmits the power consumption table to the control unit  121  (Step S 213 ). The control unit  221  receives the optimal combination of a wavelength of light to be modulated and an optical transmission line from the control unit  121  (Step S 214 ). The control unit  221  reflects the optimal combination in setting information (Step S 215 ). The control unit  221  terminates the initialization process (Step S 216 ). 
         [0059]    In this way, by selecting the optimal combination of an optical transmission line and a wavelength of light to be modulated under control of the control unit  121 , it is possible to reduce the power consumption of the transmitter  100 . On the other hand, a process of changing the setting information to allow the control unit  121  to select a combination of an optical transmission line and a wavelength of light to be modulated may be performed, for example, when the transceiving system  1000  is powered on. In this case, the transceiving system  1000  operates with the same setting until the transceiving system  1000  is powered off. Alternatively, this changing process of the setting information in which the control unit  121  selects the combination of the optical transmission line and the wavelength of light to be modulated may be regularly performed. 
         [0060]      FIG. 9  is a flowchart for explaining an exemplary process of selecting the optimal combination. The process of Step S 116  of the control unit  121 , which is illustrated in  FIG. 7B , will be described in more detail with reference to the flowchart of  FIG. 9 . The control unit  121  selects setting information (hereinafter referred to as an initial setting) which is a preset combination of a wavelength of light to be modulated and an optical transmission line (Step S 301 ). The control unit  121  calculates an evaluation value of the initial setting (Step S 302 ). When the sum of power consumptions of the heater in the optimal combination is small, the sum of power consumption of the heater of the transmitter  100  and power consumption of the heater of the receiver  200  of the combination in the initial setting is used as the evaluation value. When the maximum power consumption of the heater is decreased in the optical combination, the maximum power consumption of the heater of the transmitter  100  and the receiver  200  of the combination in the initial setting is used as the evaluation value. 
         [0061]    The control unit  121  generates a substitution matrix of combinations of wavelengths of light to be modulated and optical transmission lines and selects one combination (Step S 303 ). The control unit  121  calculates an evaluation value in the selected combination (Step S 304 ). The control unit  121  compares the evaluation value in Step S 302  with the evaluation value in Step S 304  so as to determine whether or not the evaluation value is improved (Step S 305 ). When it is determined that the evaluation value of the selected combination is better (YES in Step S 305 ), the control unit  121  uses the selected combination and the evaluation value as a comparison object (Step S 306 ). The control unit  121  initializes the substitution matrix and repeats the process from Step S 303  (Step S 307 ). 
         [0062]    When it is determined that the evaluation value of the selected combination is worse (NO in Step S 305 ), the control unit  121  determines whether or not other combinations are included in the substitution matrix (Step S 308 ). When it is determined that other combinations are included in the substitution matrix (YES in Step S 308 ), the control unit  121  repeats the process from Step S 303 . When it is determined that other combinations are not included in the substitution matrix (NO in Step S 308 ), the control unit  121  selects the selected combination as the optimal combination (Step S 309 ). 
         [0063]    In this way, by selecting the optimal combination of an optical transmission line and a wavelength of light to be modulated under control of the control unit  121 , the power consumption of the transmitter  100  may be reduced. 
       Other Examples of Communication between Control Units 
       [0064]      FIG. 10  is a view for explaining another example of communication between the control units. In  FIG. 10 , the same elements of SiPH transmitter  310  and SiPH receiver  400  as those of  FIGS. 2 and 3  are denoted by the same reference numerals. For notifications (e.g., Steps S 112 , S 117 , S 211  and S 213 ) between the microcomputer  301  and the microcomputer  406 , a control signal superimposed on a power line of the array laser  302  is transmitted to the SiPH receiver  400 . 
         [0065]    The microcomputer  301  transmits a control signal for notifying the microcomputer  406  of information to the power line of the array laser  302  (see an arrow  309 ). The control signal is transmitted to the SiPH receiver  400  via an optical transmission line. The SiPH receiver  400  includes a photodiode  407  for transmitting the control signal to the microcomputer  406  in the end of the de-multiplexer  401 . In this communication method, no ring resonator may be used to transmit the control signal. 
         [0066]      FIG. 11  is a flowchart for explaining another example of communication between the control units. The flowchart of  FIG. 11  illustrates a process performed after Step S 108  of  FIG. 7A . The control unit  121  stops light that is being output from the array laser  302  (Step S 401 ). The control unit  121  outputs a laser beam obtained by superimposing a control signal on the light of the array laser  302  (Step S 402 ). The control unit  121  uses the laser beam to notify the control unit  221  that the acquisition of power consumption in a combination of light of one wavelength and each modulating unit  120  has been terminated (Step S 403 ). The control unit  121  controls the array laser  302  to stop the laser beam (Step S 404 ). The control unit  121  resumes the output of the light of the array laser  302  (Step S 405 ). The control unit  121  receives a notification indicating that the process of the control unit  221  has been completed (Step S 406 ). 
         [0067]    In this communication method, no ring resonator may be used in order to transmit the control signal. 
         [0068]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.