Abstract:
A transmission device includes a first optical modulator configured to modulate, based on a packet signal for each of packets, input light into an optical packet signal and to output an optical packet signal for each of the packets; a generation circuit configured to generate an adjustment signal that adjusts slopes of a rise and a fall of a waveform of the optical packet signal; and a second optical modulator configured to modulate the optical packet signal from the first optical modulator and adjust, based on the adjustment signal, the slopes of the rise and the fall of the waveform of the optical packet signal.

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. 2015-245672, filed on Dec. 16, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a transmission device and a phase adjustment method. 
       BACKGROUND 
       [0003]    For example, an optical path transmission device is a transmission device that uses a wavelength division multiplex (WDM) line to transmit an optical path signal. 
         [0004]    However, in the wavelength division multiplex (WDM) line, because the refractive index of an optical fiber changes due to the changes in light intensities of a subject wavelength and other wavelengths by self phase modulation (SPM) and cross phase modulation (XPM), for example, phase modulation of the optical path signal occurs. 
         [0005]    As a result, the transmission characteristics of the optical path signal degrade due to the phase modulation. 
         [0006]    Accordingly, as a method of reducing the phase modulation of the optical path signal, a function has been known that reduces the steepness of slopes of a rise (Tr) and a fall (Tf) of an optical signal wave in the optical path signal and may thereby reduce the phase modulation of the optical path signal. 
         [0007]    The optical path signals transmitted by the optical path transmission device have characteristics that those are temporally continuous signals and have fixed destinations. 
         [0008]    As a result, in the optical path transmission device, the destination is fixed, and the parameters for reducing the steepness of the slopes of Tr and Tf of the optical path signal are thus fixed. Accordingly, processing thereof is easy. 
         [0009]    Thus, in the optical path transmission device, the steepness of the slopes of Tr and Tf of the optical signal wave in the optical path signal is reduced, and the phase modulation of the optical path signal may thereby be reduced. 
         [0010]    Further, an optical packet transmission device is a transmission device that uses the WDM line to transmit an optical packet signal. 
         [0011]    The optical packet signals have characteristics that those are temporally burst signals and have different destinations. 
         [0012]    The signal characteristics are different between the optical packet signal and the optical path signal. 
         [0013]    Japanese Laid-open Patent Publication No. 2004-198461 and Japanese Laid-open Patent Publication No. 2009-213160 are examples of related art. 
         [0014]    In an optical packet transmission device, it is possible that a method of reducing phase modulation of an optical path signal is applied and the steepness of slopes of Tr and Tf of an optical signal wave in an optical packet signal may thereby be reduced. 
         [0015]    However, in the optical packet transmission device, the destination may be different among each of the optical packet signals, so a transmission path to the destination may be different among each of the optical packet signals. Thus, the parameters for reducing the steepness of the slopes of Tr and Tf of the optical signal wave in the optical packet signal are largely different. 
         [0016]    Accordingly, in the optical packet transmission device, it is difficult to simply apply the method of reducing the steepness of the slopes of Tr and Tf for the optical path transmission device. 
         [0017]    As a result, in the optical packet transmission system, the cross phase modulation of the optical packet signals that correspond to different transmission paths may not be reduced, and degradation of transmission characteristics may thus not be reduced. 
         [0018]    It is desirable to provide a transmission device and a phase adjustment method that may reduce the phase modulation of the optical packet signals. 
       SUMMARY 
       [0019]    According to an aspect of the embodiments, a transmission device includes a first optical modulator configured to modulate, based on a packet signal for each of packets, input light into an optical packet signal and to output an optical packet signal for each of the packets; a generation circuit configured to generate an adjustment signal that adjusts slopes of a rise and a fall of a waveform of the optical packet signal; and a second optical modulator configured to modulate the optical packet signal from the first optical modulator and adjust, based on the adjustment signal, the slopes of the rise and the fall of the waveform of the optical packet signal. 
         [0020]    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. 
         [0021]    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 
         [0022]      FIG. 1A  and  FIG. 1B  illustrate one example of an optical transmission system of a first embodiment; 
           [0023]      FIG. 2  is an explanatory diagram that illustrates one example of a table configuration in a control voltage table; 
           [0024]      FIG. 3  is an explanatory diagram that illustrates one example of decomposition and assembly of packet signals; 
           [0025]      FIG. 4  is an explanatory diagram that illustrates one example of output timings of the packet signal, decomposed data, and optical packet signals; 
           [0026]      FIG. 5  is an explanatory diagram that illustrates examples of configurations of an E/O converter and an optical waveform shaper in a first MDL; 
           [0027]      FIG. 6A  is an explanatory diagram that illustrates examples of the optical packet signal of a third waveguide, the optical packet signal (with no application of a control voltage signal) of a fourth waveguide, and an electric field intensity waveform (with no optical phase difference) of a combined optical packet signal in the optical waveform shaper; 
           [0028]      FIG. 6B  is an explanatory diagram that illustrates examples of the optical packet signal of the third waveguide, the optical packet signal (with application of a control voltage signal) of the fourth waveguide, and the electric field intensity waveform (with an optical phase difference) of a combined optical packet signal in the optical waveform shaper; 
           [0029]      FIG. 7  is an explanatory diagram that illustrates examples of the optical packet signals which are yet to be input, control voltage signals, the optical packet signals whose optical phases have been adjusted, and the optical packet signals resulting from optical multiplexing in the optical waveform shaper; 
           [0030]      FIG. 8  is a flowchart that illustrates one example of a processing operation of a transmission device which is related to an adjustment process; 
           [0031]      FIG. 9  is a flowchart that illustrates one example of a processing operation of a setting circuit which is related to a setting process; 
           [0032]      FIG. 10  is an explanatory diagram that illustrates one example of a configuration of an MDL of a second embodiment; and 
           [0033]      FIG. 11  is an explanatory diagram that illustrates one example of a configuration of an optical modulator. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0034]    Embodiments of a transmission device and an optical phase adjustment method that are disclosed by the present application will hereinafter be described in detail with reference to drawings. 
         [0035]    The techniques of the present disclosure are not limited by the embodiments. 
         [0036]    Further, the embodiments described below may appropriately be combined in the scope in which a contradiction does not occur. 
         [0037]      FIG. 1A  and  FIG. 1B  illustrate one example of an optical transmission system  1  of a first embodiment. 
         [0038]    The optical transmission system  1  illustrated in  FIGS. 1A and 1B  is an optical packet transmission system that is configured by connecting plural transmission devices  2  such as optical packet transmission devices which transmit temporally burst optical packet signals together by a wavelength division multiplexer (WDM) ring line  3 , for example. 
         [0039]    The optical packet signals have characteristics that those are temporally burst signals and have different destinations and packet lengths compared to an optical path signal which has a fixed destination and is temporally continuous, for example. 
         [0040]    The transmission device  2  performs parallel processing of the optical packet signals, divides the optical packet signals into plural optical wavelengths, and transmits those in order to improve line usage efficiency by shortening a line occupancy time in a case of transmitting the optical packet signals on the WDM ring line  3 . 
         [0041]    The transmission device  2  has a client interface (CLIF)  10 , plural modules (MDLs)  20 , an optical switch  30 , a line IF  40 , a decision circuit  50 , and a generation circuit  60 . 
         [0042]    For convenience of description, as for the CLIF  10  and the MDL  20 , a function of transmitting the optical packet signal from the client (CL) line  4  to the WDM ring line  3  will be exemplified. However, it goes without saying that a function of transmission from the WDM ring line  3  to the CL line  4  is also provided. 
         [0043]    The CLIF  10  is a communication IF that conducts the communication with the CL line  4 . 
         [0044]    The CLIF  10  has a decomposition circuit  11 , a buffer  12 , a determination circuit  13 , and an extraction circuit  14 . 
         [0045]    The decomposition circuit  11  is a processing circuit that decomposes a packet signal into plural decomposed data for the parallel processing of the packet signal from the CL line  4 . 
         [0046]    The decomposition circuit  11  decomposes the packet signal into the decomposed data that are allocated to each optical wavelength λ in the WDM ring line  3 . 
         [0047]    The buffer  12  is an area that temporarily stores the decomposed data resulting from the decomposition by the decomposition circuit  11 . 
         [0048]    The decomposition circuit  11  and the buffer  12  are a division circuit that performs time division of the packet signal into the optical wavelengths in the WDM ring line  3 , for example. 
         [0049]    The determination circuit  13  determines whether or not the packet signal from the CL line  4  is present. 
         [0050]    The extraction circuit  14  extracts destination information and packet length information from header information of the packet signal from the CL line  4 . 
         [0051]    The destination information is information that indicates the destination of the packet signal. 
         [0052]    The packet length information is information that indicates the signal length of the packet signal. 
         [0053]    The plural MDLs  20  are optical modules that convert the decomposed data stored in the buffer  12  into the optical packet signals of the optical wavelengths λ of used lines in the WDM ring line  3 . 
         [0054]    The MDLs  20  are a first MDL  20 A to an Xth MDL  20 X. 
         [0055]    Each of the MDLs  20  has a laser diode (LD)  21 , an E/O circuit  22 , an E/O converter  23 , a shaping circuit  24 , and an optical waveform shaper  25 . 
         [0056]    The LD  21  inputs continuous wave (CW) light with the optical wavelength λ of a narrow band that is specified to each of the MDLs  20  to the E/O converter  23 . 
         [0057]    The E/O circuit  22  is a driver that drives and controls the E/O converter  23 . 
         [0058]    The E/O circuit  22  inputs the decomposed data that are stored in the buffer  12  and allocated to each of the optical wavelengths λ to the E/O converter  23 . 
         [0059]    The E/O converter  23  is a ferroelectric modulator such as a lithium niobate modulator (LN modulator) of a Mach-Zehnder type, for example, which performs optical conversion of the decomposed data from the E/O circuit  22  into the optical packet signal by the CW light from the LD  21 . 
         [0060]    The shaping circuit  24  is an adjustment signal generation circuit that applies a control voltage signal, which is an adjustment signal and will be described later, to the optical packet signal which is transmitted through the optical waveform shaper  25 , for example. 
         [0061]    The optical waveform shaper  25  is a ferroelectric modulator such as the LN modulator of the Mach-Zehnder type, for example. 
         [0062]    The optical waveform shaper  25  is a slope adjustment modulator, for example. 
         [0063]    The optical waveform shaper  25  has a third waveguide  25 A and a fourth waveguide  25 B, which will be described later, and performs optical branching of the optical packet signal from the E/O converter  23  into the third waveguide  25 A and the fourth waveguide  25 B. 
         [0064]    The third waveguide  25 A transmits and outputs the optical packet signal resulting from the optical branching. 
         [0065]    The fourth waveguide  25 B applies the control voltage signal from the shaping circuit  24  to the optical packet signal resulting from the optical branching and thereby outputs the optical packet signal whose optical phase has been adjusted. 
         [0066]    The optical packet signal that is an output of the fourth waveguide  25 B is the optical packet signal whose optical phase has been adjusted and which has an optical phase difference compared to the optical packet signal that is an output of the third waveguide  25 A. 
         [0067]    The optical switch  30  is a switch that switches and outputs the optical packet signals between the MDLs  20  and the line IF  40 . 
         [0068]    The optical switch  30  has a switch MDL  31 , a line monitoring circuit  32 , and a switch control circuit  33 . 
         [0069]    The switch MDL  31  is a switch that switches and outputs the optical packet signals of the respective optical wavelengths λ between the MDLs  20  and the line IF  40 . 
         [0070]    The line monitoring circuit  32  monitors a line use situation of each of the optical wavelengths λ in the WDM ring line  3 . 
         [0071]    The switch control circuit  33  controls the switch MDL  31 . 
         [0072]    The line IF  40  is a communication IF that conducts the communication with the WDM ring line  3 . 
         [0073]    The line IF  40  has an optical multiplexer  41  and an optical demultiplexer  42 . 
         [0074]    The optical multiplexer  41  is, for example, an output section that performs combined output of the decomposed optical packet signals of the respective optical wavelengths λ to the WDM ring line  3 . 
         [0075]    The optical demultiplexer  42  performs demultiplexed input of the optical packet signals that are received from the WDM ring line  3 . 
         [0076]    The line monitoring circuit  32  monitors a line situation of each of the optical wavelengths λ in the WDM ring line  3  from the optical demultiplexer  42 . 
         [0077]    The decision circuit  50  is a processing circuit that decides the control voltage value of the control voltage signal which is applied to the optical waveform shaper  25 . 
         [0078]    The decision circuit  50  has a control voltage table  51 , a control voltage acquisition circuit  52 , and a setting circuit  53 . 
         [0079]    The control voltage table  51  is a table that stores control voltage values which are set for respective pieces of destination information of the packet signals. 
         [0080]      FIG. 2  is an explanatory diagram that illustrates one example of a table configuration in the control voltage table  51 . 
         [0081]    The control voltage table  51  illustrated in  FIG. 2  is a table that stores an optical wavelength  51 B used in the WDM ring line  3  and a control voltage value  51 C which are associated with each other with respect to each piece of destination information  51 A. 
         [0082]    The control voltage acquisition circuit  52  is, for example, an acquisition circuit that acquires the control voltage value for each of the optical wavelengths λ which corresponds to the destination information from the control voltage table  51 . 
         [0083]    The control voltage acquisition circuit  52  then notifies the generation circuit  60  of the acquired control voltage value. 
         [0084]    The setting circuit  53  sets and registers the voltage value of the optical wavelength λ with respect to each of the pieces of destination information in the control voltage table  51 . 
         [0085]    The setting circuit  53  uses a test optical packet signal under the communication environment of the transmission path that corresponds to the destination information and thereby acquires a lower limit voltage value and an upper limit voltage value of each of the optical wavelengths λ. 
         [0086]    In addition, the setting circuit  53  specifies an arbitrary voltage value for each of the optical wavelengths λ from the voltage range between the lower limit voltage value and the upper limit voltage value with respect to each of the optical wavelengths λ and registers the specified arbitrary voltage value as the control voltage value in the control voltage table  51 . 
         [0087]    The control voltage values for the same destination information are specified so as to be different among each of the optical wavelengths λ. 
         [0088]    The generation circuit  60  is a processing circuit that controls an output timing of the packet signal in accordance with the line use situation of the optical wavelength λ which is used in the WDM ring line  3 , for example. 
         [0089]    The generation circuit  60  has an information optical demultiplexer  61 , an available line monitoring circuit  62 , an output control circuit  63 , and a control circuit  64 . 
         [0090]    The information optical demultiplexer  61  decomposes information from the extraction circuit  14  into the destination information and the packet length information. 
         [0091]    The available line monitoring circuit  62  monitors an available situation of an optical line of each of the optical wavelengths λ in the WDM ring line  3  based on monitoring results from the line monitoring circuit  32 . 
         [0092]    The output control circuit  63  controls the output timing of the buffer  12  in order to output the decomposed data that correspond to the optical wavelength λ in an available state in a case where the optical line of the optical wavelength λ to be used is in the available state, based on the monitoring results of the available line monitoring circuit  62 . 
         [0093]    The output control circuit  63  has an application time acquisition circuit  63 A. 
         [0094]    In a case where the application time acquisition circuit  63 A acquires the packet length information from the information optical demultiplexer  61 , the application time acquisition circuit  63 A adds a shortest packet interval to the packet length of the decomposed data as an application target and thereby calculates the line occupancy time of the decomposed data in the WDM ring line  3 . 
         [0095]    The packet length of the decomposed data as the application target is the signal length that corresponds to the decomposed data allocated to each of the optical wavelengths λ. 
         [0096]    For example, the line occupancy time of the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9  that are allocated to an optical wavelength λ 1  in a packet signal P 1  illustrated in  FIG. 3  is the packet lengths of the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9 +the shortest packet interval σ 2. 
         [0097]    The shortest packet interval÷2 is a margin of the application time that corresponds to the packet length and may thus be “0”. 
         [0098]    The application time acquisition circuit  63 A sets the line occupancy time as the application time of the control voltage signal and sets the application time for the control circuit  64 . 
         [0099]    The control circuit  64  generates the control voltage signal based on the control voltage value that is acquired by control voltage acquisition circuit  52  and the application time that is acquired by the application time acquisition circuit  63 A. 
         [0100]    The control circuit  64  sets, for the shaping circuit  24 , the control voltage signal to be applied to the optical packet signal that passes through the fourth waveguide  25 B in the optical waveform shaper  25  in each of the MDLs  20 . 
         [0101]      FIG. 3  is an explanatory diagram that illustrates one example of decomposition and assembly of the packet signals.  FIG. 4  is an explanatory diagram that illustrates one example of output timings of the packet signal, decomposed data, and optical packet signals. 
         [0102]    For convenience of description, it is assumed that the packet signal P 1  illustrated in  FIG. 3  is the packet signal from a CL 1  to a CL 2  and a packet signal P 2  is the packet signal from the CL 1  to a CL 3 . 
         [0103]    Further, it is assumed that a packet signal P 3  is the packet signal from the CL 1  to the CL 3 . 
         [0104]    It is assumed that the CL 1  is a CL on the CL line  4  side and the CL 2  and the CL 3  are the CLs on the sides of CL lines that are connected with the other transmission devices  2  connected with WDM ring line  3 . 
         [0105]    The packet signal P 1 , the packet signal P 2 , and the packet signal P 3  are input in this order from the CL line  4  to the decomposition circuit  11 . 
         [0106]    The decomposition circuit  11  decomposes the packet signal P 1  into decomposed data P 1 - 1  to P 1 - 10 . 
         [0107]    For example, among optical wavelengths λ 1 , λ 2 , λ 3 , and λX, the decomposition circuit  11  sequentially allocates the decomposed data P 1 - 1  to the optical wavelength λ 1 , the next decomposed data P 1 - 2  to the optical wavelength λ 2 , the next decomposed data P 1 - 3  to the optical wavelength λ 3 , and the next decomposed data P 1 - 4  to the optical wavelength λX and sequentially stores those decomposed data P 1 - 1  to P 1 - 4  in the buffer  12 . 
         [0108]    In addition, the decomposition circuit  11  sequentially allocates the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9  to the optical wavelength λ 1 , the decomposed data P 1 - 2 , P 1 - 6 , and P 1 - 10  to the optical wavelength λ 2 , the decomposed data P 1 - 3  and P 1 - 7  to the optical wavelength λ 3 , and the decomposed data P 1 - 4  and P 1 - 8  to the optical wavelength λX. 
         [0109]    Then, the decomposition circuit  11  sequentially stores those decomposed data P 1 - 1  to P 1 - 10  in the buffer  12 . 
         [0110]    For example, the first MDL  20 A converts the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9  into the optical packet signal of the optical wavelength λ 1 . 
         [0111]    The second MDL  20 B converts the decomposed data P 1 - 2 , P 1 - 6 , and P 1 - 10  into the optical packet signal of the optical wavelength λ 2 . 
         [0112]    The third MDL  20 C converts the decomposed data P 1 - 3  and P 1 - 7  into the optical packet signal of the optical wavelength λ 3 . 
         [0113]    The Xth MDL  20 X converts the decomposed data P 1 - 4  and P 1 - 8  into the optical packet signal of the optical wavelength λX. 
         [0114]    In a case where the output control circuit  63  detects the available states of the optical lines of the optical wavelengths λ 1 , λ 2 , λ 3 , and λX of the WDM ring line  3 , the output control circuit  63  controls the output of the buffer  12  in order to output the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9  to the first MDL  20 A. 
         [0115]    Further, the output control circuit  63  controls the output of the buffer  12  in order to output the decomposed data P 1 - 2 , P 1 - 6 , and P 1 - 10  to the second MDL  20 B, the decomposed data P 1 - 3  and P 1 - 7  to the third MDL  20 C, and the decomposed data P 1 - 4  and P 1 - 8  to the Xth MDL  20 X. 
         [0116]    The first MDL  20 A converts the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9  into the optical packet signal of the optical wavelength λ 1  and outputs those to the optical switch  30 . 
         [0117]    The second MDL  20 B converts the decomposed data P 1 - 2 , P 1 - 6 , and P 1 - 10  into the optical packet signal of the optical wavelength λ 2  and outputs those to the optical switch  30 . 
         [0118]    The third MDL  20 C converts the decomposed data P 1 - 3  and P 1 - 7  into the optical packet signal of the optical wavelength λ 3  and outputs those to the optical switch  30 . 
         [0119]    The Xth MDL  20 X converts the decomposed data P 1 - 4  and P 1 - 8  into the optical packet signal of the optical wavelength λX and outputs those to the optical switch  30 . 
         [0120]    Then, the optical multiplexer  41  of the line IF  40  performs multiplexed output of the optical packet signal of the optical wavelength λ 1  from the first MDL  20 A to the line of the optical wavelength λ 1  in the WDM ring line  3  and multiplexed output of the optical packet signal of the optical wavelength λ 2  from the second MDL  20 B to the line of the optical wavelength λ 2 . 
         [0121]    Further, the optical multiplexer  41  performs multiplexed output of the optical packet signal of the optical wavelength λ 3  from the third MDL  20 C to the line of the optical wavelength λ 3  and multiplexed output of the optical packet signal of the optical wavelength λX from the Xth MDL  20 X to the line of the optical wavelength λX. 
         [0122]    That is, the optical multiplexer  41  performs the multiplexed output of the optical packet signals of the optical wavelengths λ 1 , λ 2 , λ 3 , and λX at the same timing. 
         [0123]    The optical packet signal from the first MDL  20 A is the signal resulting from the optical conversion of the decomposed data P 1 - 1 , P 1 - 5 , and P 1 - 9 . 
         [0124]    The optical packet signal from the second MDL  20 B is the signal resulting from the optical conversion of the decomposed data P 1 - 2 , P 1 - 6 , and P 1 - 10 . 
         [0125]    The optical packet signal from the third MDL  20 C is the signal resulting from the optical conversion of the decomposed data P 1 - 3  and P 1 - 7 . 
         [0126]    The optical packet signal from the Xth MDL  20 X is the signal resulting from the optical conversion of the decomposed data P 1 - 4  and P 1 - 8 . 
         [0127]    Further, the decomposition circuit  11  similarly decomposes the packet signal P 2  and the packet signal P 3  and stores the decomposed data of the packet signals in the buffer  12 . 
         [0128]    In addition, the output control circuit  63  controls the output of the buffer  12  in order to sequentially output the decomposed data that are stored in the buffer  12  to the MDLs  20  of the respective optical wavelengths λ based on a line available situation of the WDM ring line  3 . 
         [0129]    Further, the other transmission device  2  connected with the CL 2  sequentially extracts optical packet signals P 1 - 1  to P 1 - 10  of the optical wavelengths λ 1 , λ 2 , λ 3 , and λX of the CL 2  from the WDM ring line  3  and assembles the optical packet signal P 1  from those extracted optical packet signals P 1 - 1  to P 1 - 10 . 
         [0130]    Further, the other transmission device  2  connected with the CL 3  sequentially extracts optical packet signals P 2 - 1  to P 2 - 7  of the respective optical wavelengths λ of the CL 3  from the WDM ring line  3  and assembles the optical packet signal P 2  from those extracted optical packet signals P 2 - 1  to P 2 - 7 . 
         [0131]    Further, the other transmission device  2  connected with the CL 3  sequentially extracts optical packet signals P 3 - 1  to P 3 - 11  of the respective optical wavelengths λ of the CL 3  from the WDM ring line  3  and assembles the optical packet signal P 3  from those extracted optical packet signals P 3 - 1  to P 3 - 11 . 
         [0132]    It is assumed that the transmission device  2  has to receive the optical packet signals of the respective optical wavelengths at the same timing in consideration of assembling the optical packet signals on the reception side and thus transmits the optical packet signals at the same timing. 
         [0133]      FIG. 5  is an explanatory diagram that illustrates examples of configurations of the E/O converter  23  and the optical waveform shaper  25  in the first MDL  20 A. 
         [0134]    For convenience of description, the first MDL  20 A will be exemplified. However, the second MDL  20 B, the third MDL  20 C, and the Xth MDL  20 X have the same configuration as the first MDL  20 A, and descriptions of configurations and operations thereof will thus not be made. 
         [0135]    The E/O converter  23  in the first MDL  20 A has a first waveguide  23 A and a second waveguide  23 B and performs optical branching of the CW light from the LD  21  into the first waveguide  23 A and the second waveguide  23 B. 
         [0136]    The E/O circuit  22  applies the decomposed data (data patterns) P 1 - 1 , P 1 - 5 , and P 1 - 9  to the CW light that passes through the first waveguide  23 A and the second waveguide  23 B. 
         [0137]    As a result, the E/O converter  23  performs optical conversion into the optical packet signals P 1 - 1 , P 1 - 5 , and P 1 - 9  by the first waveguide  23 A and the second waveguide  23 B. 
         [0138]    The E/O converter  23  combines the optical packet signals that are outputs of the first waveguide  23 A and the optical packet signals that are outputs of the second waveguide  23 B and outputs the combined optical packet signals to the optical waveform shaper  25 . 
         [0139]    The optical waveform shaper  25  has the third waveguide  25 A and the fourth waveguide  25 B and performs optical branching of the optical packet signal from the E/O converter  23  into the third waveguide  25 A and the fourth waveguide  25 B. 
         [0140]    The third waveguide  25 A transmits the optical packet signal resulting from the optical branching. 
         [0141]    The fourth waveguide  25 B applies the control voltage signal that corresponds to the application time to the optical packet signal resulting from the optical branching and outputs the optical packet signal to which the control voltage signal is applied, that is, the optical packet signal whose optical phase has been adjusted. 
         [0142]    An optical phase difference occurs between the optical packet signal that is the output of the fourth waveguide  25 B and the optical packet signal that is the output of the third waveguide  25 A. 
         [0143]    The optical waveform shaper  25  then outputs the optical packet signal which results from combining of the optical packet signal as the output of the third waveguide  25 A and the optical packet signal with the adjusted optical phase as the output of the fourth waveguide  25 B and in which an optical phase interference occurs. 
         [0144]    As a result, as illustrated in  FIG. 5 , the steepness of the slopes of Tr and Tf of an optical signal wave is reduced in the optical signal wave of the optical packet signal whose optical phase has been adjusted. 
         [0145]      FIG. 6A  is an explanatory diagram that illustrates examples of an optical packet signal OP 1  of the third waveguide  25 A, an optical packet signal (with no application of the control voltage signal) OP 2  of the fourth waveguide  25 B, and the electric field intensity waveform (with no optical phase difference) of a combined optical packet signal OP 3  in the optical waveform shaper  25 . 
         [0146]    The optical waveform shaper  25  combines the optical packet signal OP 1  that is the output of the third waveguide  25 A and the optical packet signal OP 2  that is the output of the fourth waveguide  25 B and outputs the combined optical packet signal OP 3 . 
         [0147]    An envelope L 1  of the combined optical packet signal OP 3  is illustrated in  FIG. 6A . 
         [0148]      FIG. 6B  is an explanatory diagram that illustrates examples of the optical packet signal OP 1  of the third waveguide  25 A, an optical packet signal (with application of the control voltage signal) OP 4  of the fourth waveguide  25 B, and the electric field intensity waveform (with an optical phase difference) of a combined optical packet signal OP 5  in the optical waveform shaper  25 . 
         [0149]    The optical waveform shaper  25  combines the optical packet signal OP 1  that is the output of the third waveguide  25 A and the optical packet signal OP 4  of the fourth waveguide  25 B, to which the control voltage has been applied, and outputs the combined optical packet signal OP 5 . 
         [0150]    An envelope L 2  of the combined optical packet signal OP 5  has a mild slope compared to the envelope L 1 . 
         [0151]    As a result, the slope of the envelope becomes milder in a case where the optical phase difference is present, and the steepness of the slopes of Tr and Tf of the optical signal wave of the optical packet signal OP 5  is thereby reduced. 
         [0152]      FIG. 7  is an explanatory diagram that illustrates examples of the optical packet signals P 1  to P 3  which are yet to be input, the control voltage signals, the optical packet signals P 1  to P 3  whose optical phases have been adjusted, and the optical packet signals P 1  to P 3  resulting from optical combining in the optical waveform shaper  25 . 
         [0153]    The optical packet signals P 1 , P 2 , and P 3  have different destinations. 
         [0154]    The optical waveform shaper  25  applies a control voltage signal V 1  based on the destination information and the packet length information of the optical packet signal P 1  to the optical packet signal P 1  from the E/O converter  23 . 
         [0155]    In addition, the optical waveform shaper  25  outputs an optical packet signal P 1 A that is an output of the third waveguide  25 A and an optical packet signal P 1 B as an output of the fourth waveguide  25 B, to which the control voltage signal V 1  has been applied, that is, whose optical phase has been adjusted. 
         [0156]    The optical waveform shaper  25  combines the optical packet signal P 1 A and the optical packet signal P 1 B whose optical phase has been adjusted and outputs a combined optical packet signal P 1 C. 
         [0157]    The combined optical packet signal P 1 C is in a state where the steepness of the slopes of Tr and Tf is reduced. 
         [0158]    Further, the optical waveform shaper  25  applies a control voltage signal V 2  based on the destination information and the packet length information of the optical packet signal P 2  to the optical packet signal P 2  from the E/O converter  23 . 
         [0159]    In addition, the optical waveform shaper  25  outputs an optical packet signal P 2 A that is an output of the third waveguide  25 A and an optical packet signal P 2 B as an output of the fourth waveguide  25 B, to which the control voltage signal V 2  has been applied, that is, whose optical phase has been adjusted. 
         [0160]    The optical waveform shaper  25  combines the optical packet signal P 2 A and the optical packet signal P 2 B whose optical phase has been adjusted and outputs a combined optical packet signal P 2 C. 
         [0161]    The combined optical packet signal P 2 C is in a state where the steepness of the slopes of Tr and Tf is reduced. 
         [0162]    Further, the optical waveform shaper  25  applies a control voltage signal V 3  based on the destination information and the packet length information of the optical packet signal P 3  to the optical packet signal P 3  from the E/O converter  23 . 
         [0163]    In addition, the optical waveform shaper  25  outputs an optical packet signal P 3 A that is an output of the third waveguide  25 A and an optical packet signal P 3 B as an output of the fourth waveguide  25 B, to which the control voltage signal V 3  has been applied, that is, whose optical phase has been adjusted. 
         [0164]    The optical waveform shaper  25  combines the optical packet signal P 3 A and the optical packet signal P 3 B whose optical phase has been adjusted and outputs a combined optical packet signal P 3 C. 
         [0165]    The combined optical packet signal P 3 C is in a state where the steepness of the slopes of Tr and Tf is reduced. 
         [0166]    A description will next be made about an operation of the optical transmission system  1  of the first embodiment. 
         [0167]      FIG. 8  is a flowchart that illustrates one example of a processing operation of the transmission device  2  which is related to an adjustment process. 
         [0168]    The adjustment process illustrated in  FIG. 8  is a process for reducing the steepness of the slopes of Tr and Tf of the optical signal wave in the optical packet signal by the optical phase interference between the same optical packet signals with respect to each of the optical packet signals. 
         [0169]    In  FIG. 8 , the determination circuit  13  in the transmission device  2  determines whether or not the packet signal from the CL line  4  is present (step S 11 ). 
         [0170]    In a case where the packet signal is present (Yes in step S 11 ), the extraction circuit  14  in the transmission device  2  extracts the destination information and the packet length information from the header information of the packet signal (step S 12 ). 
         [0171]    In a case where the destination information and the packet length information are extracted in step S 12 , the transmission device  2  executes processing operations of step S 13  and step S 16 , which will be described later. 
         [0172]    The decomposition circuit  11  decomposes the packet signal from the CL line  4  and stores the decomposed data from the decomposition in the buffer  12 . 
         [0173]    The control voltage acquisition circuit  52  in the transmission device  2  determines whether or not the control voltage value that corresponds to the acquired destination information is present in the control voltage table  51  (step S 13 ). 
         [0174]    In a case where the control voltage value that corresponds to the destination information is present (Yes in step S 13 ), the control voltage acquisition circuit  52  acquires the control voltage value that corresponds to the destination information and sets the acquired control voltage value for the control circuit  64  (step S 14 ). 
         [0175]    Further, in a case where the control voltage value that corresponds to the destination information is not present (No in step S 13 ), the control voltage acquisition circuit  52  acquires the control voltage value that is an initial value and sets the acquired control voltage value for the control circuit  64  (step S 15 ). 
         [0176]    Further, the application time acquisition circuit  63 A in the transmission device  2  calculates the line occupancy time that corresponds to the decomposed data of the optical wavelength λ of the optical packet signal based on the acquired packet length information and the shortest optical packet signal interval. 
         [0177]    In addition, the application time acquisition circuit  63 A sets the calculated line occupancy time as the application time for the control circuit  64  (step S 16 ). 
         [0178]    The packet length information corresponds to the signal length of the decomposed data of each of the optical wavelengths in a case where the decomposed data of the packet signal from the CL line  4  are allocated to four optical wavelengths, for example. 
         [0179]    The control circuit  64  generates the control voltage signal to be applied to the optical waveform shaper  25  of the MDL  20  that corresponds to the optical wavelength λ based on the control voltage value and the application time (step S 17 ). 
         [0180]    The output control circuit  63  in the transmission device  2  determines whether or not the line of the optical wavelength λ that is used in the WDM ring line  3  is in the available state via the available line monitoring circuit  62  (step S 18 ). 
         [0181]    The output control circuit  63  makes a determination about the available state of the line of the optical wavelength λ that is used for transmission of the optical packet signal related to the decomposed data. 
         [0182]    In a case where the line of the optical wavelength λ that is used for transmission of the optical packet signal is in the available state (Yes in step S 18 ), the output control circuit  63  outputs the decomposed data of the optical wavelength λ from the buffer  12  to the E/O converter  23  in the MDL  20  that corresponds to each of the optical wavelengths λ (step S 19 ). 
         [0183]    The E/O converter  23  performs optical conversion of the decomposed data from the buffer  12  and outputs the optical packet signal. 
         [0184]    The optical waveform shaper  25  in the transmission device  2  performs optical branching of the optical packet signal from the E/O converter  23  and outputs the optical packet signal resulting from the optical branching to the third waveguide  25 A and the fourth waveguide  25 B (step S 20 ). 
         [0185]    The control circuit  64  applies the control voltage signal to the optical packet signal that passes through the fourth waveguide  25 B (step S 21 ). 
         [0186]    Then, because the control voltage signal is applied to the optical packet signal that passes therethrough, the refractive index of the optical packet signal as the output of the fourth waveguide  25 B changes in the fourth waveguide  25 B, an optical phase delay thereby occurs, and the optical packet signal whose optical phase has been adjusted is thus obtained. 
         [0187]    The optical waveform shaper  25  combines the optical packet signal as the output of the third waveguide  25 A and the optical packet signal with the adjusted optical phase as the output of the fourth waveguide  25 B and outputs the combined optical packet signal to the optical line of the specified optical wavelength λ in the WDM ring line  3  (step S 22 ). 
         [0188]    Then, the optical waveform shaper  25  finishes the processing operation illustrated in  FIG. 8 . 
         [0189]    In the combined optical packet signal, the steepness of the slopes of Tr and Tf in the optical packet signal is reduced, and the phase modulation of the optical packet signal may thereby be reduced. 
         [0190]    The transmission device  2  generates the control voltage signals based on the control voltage values for the respective optical wavelengths λ for the respective pieces of destination information of the packet signals. 
         [0191]    The transmission device  2  converts the decomposed data of the packet signal into the optical packet signal and performs optical branching of the optical packet signal into the third waveguide  25 A and the fourth waveguide  25 B. 
         [0192]    The transmission device  2  applies the control voltage signal to the optical packet signal that passes through the fourth waveguide  25 B and outputs the optical packet signal whose optical phase has been adjusted. 
         [0193]    The transmission device  2  combines the optical packet signal of the third waveguide  25 A and the optical packet signal of the fourth waveguide  25 B, whose optical phase has been adjusted, and the steepness of the slopes Tr and Tf of the optical signal wave in the optical packet signal is thereby reduced. 
         [0194]    As a result, the phase modulation of the optical packet signal may be reduced. 
         [0195]      FIG. 9  is a flowchart that illustrates one example of a processing operation of the setting circuit  53  which is related to a setting process. 
         [0196]    The setting process illustrated in  FIG. 9  is a process in which the voltage ranges for the optical wavelengths λ are decided for the respective pieces of destination information by using test optical packet signals and arbitrary voltage values in the voltage ranges are registered as the control voltage values in the control voltage table  51 . 
         [0197]    The setting circuit  53  specifies the communication environment of the transmission path of the destination information of a setting target, for example, a transmission distance and optical fiber conditions (a dispersion coefficient, non-linear characteristics, and so forth) and specifies the MDL  20  to be used for each of the optical wavelengths λ. 
         [0198]    The setting process is a process that is executed in a network construction of the optical transmission system  1 . 
         [0199]    The setting circuit  53  sets the control voltage signal at the voltage value at which the optical phase difference between the optical packet signal as the output of the third waveguide  25 A and the optical packet signal as the output of the fourth waveguide  25 B becomes “0” (step S 31 ). 
         [0200]    The setting circuit  53  specifies the communication environment of the transmission path of the destination information of the setting target and sets the control voltage signal at the voltage value at which the optical phase difference becomes “0” in the transmission path. 
         [0201]    The setting circuit  53  sets an input of the test optical packet signal to the optical waveform shaper  25  for the E/O converter  23  (step S 32 ) and determines whether or not a state where the optical packet signal may be received is provided (step S 33 ). 
         [0202]    The reference for the determination of whether or not the state where the optical packet signal may be received is provided is whether or not a bit error rate (BER) of the optical packet signal is less than a prescribed threshold value. 
         [0203]    In a case where the state where the optical packet signal may be received is not provided (No in step S 33 ), the setting circuit  53  changes the setting of the voltage value in an increasing direction (step S 34 ) and moves to step S 33  in order to determine whether or not the state where the optical packet signal may be received is provided. 
         [0204]    In a case where the state where the optical packet signal may be received is provided (Yes in step S 33 ), the setting circuit  53  stores the present voltage value as the lower limit voltage value (step S 35 ) and changes the setting of the voltage value in the increasing direction (step S 36 ). 
         [0205]    The setting circuit  53  sets the input of the test optical packet signal to the optical waveform shaper  25  for the E/O converter  23  (step S 37 ) and determines whether or not a state where the present optical packet signal may be received is provided (step S 38 ). 
         [0206]    In a case where the state where the present optical packet signal may be received is provided (Yes in step S 38 ), the setting circuit  53  further changes the setting of the voltage value in the increasing direction (step S 39 ) and moves to step S 38  in order to determine whether or not the state where the optical packet signal may be received is provided. 
         [0207]    In a case where the state where the present optical packet signal may be received is not provided (No in step S 38 ), the setting circuit  53  stores the present voltage value as the upper limit voltage value (step S 40 ). 
         [0208]    The setting circuit  53  sets the lower limit voltage value and the upper limit voltage value that are related to the corresponding optical wavelengths λ to the destination information of an examination target as the voltage range, registers an arbitrary voltage value in the voltage range as the control voltage value in the control voltage table  51  (step S 41 ), and finishes the processing operation illustrated in  FIG. 9 . 
         [0209]    The arbitrary voltage value in the voltage range may be specified by an operation by a user, for example. 
         [0210]    As a result, the setting circuit  53  identifies the voltage range between the lower limit voltage value and the upper limit voltage value of one optical wavelength that corresponds to the destination information and registers an arbitrary voltage value in the voltage range as the control voltage value in the control voltage table  51 . 
         [0211]    As a result, the control voltage value for each of the optical wavelengths λ that corresponds to the destination information in the control voltage table  51  may be registered. 
         [0212]    The transmission device  2  may reduce the phase modulation of the optical packet signals even in a case where the destinations are different without requesting a high-speed modulation process because the steepness of the slopes of Tr and Tf is reduced with respect to each of the optical packet signals. 
         [0213]    As a result, the transmission device  2  may handle long distance transmission while reducing degradation of transmission characteristics by reducing the phase modulation of the optical packet signals. 
         [0214]    The control voltage table  51  sets and registers a different control voltage value for each of the optical wavelengths λ in the same destination information and may thus reduce the phase modulation of the optical packet signals with high accuracy. 
         [0215]    Optical path transmission devices may use a dispersion application method that applies a wavelength dispersion by using an optical fiber, a tunable dispersion compensator of a VIPA type, or the like and thereby reduces the steepness of the slopes of Tr and Tf of the optical signal wave in the optical path signal. 
         [0216]    However, in the optical path transmission device, the destination of the optical path signal is fixed, and the applied dispersion amount is thus fixed. 
         [0217]    On the other hand, in the optical packet transmission device, because the destination is different and the applied dispersion amount is different among each of the optical packet signals, the applied dispersion amount may not instantly be set. 
         [0218]    Accordingly, the transmission device  2  reduces the steepness of the slopes of Tr and Tf of the optical signal wave in the optical packet signal of the optical wavelength λ with respect to each of the optical packet signals and may thus reduce the phase modulation of the optical packet signals with high accuracy. 
         [0219]    Further, the optical path transmission devices may use a method of a pre-equalization process that generates an electric signal on which a control signal is superimposed at the stage of electric signal so as to reduce the steepness of the slopes of Tr and Tf of the optical signal wave in the optical path signal resulting from optical conversion. 
         [0220]    However, in the optical path transmission device, the control signals perform control of the waveforms of the slopes of Tr and Tf only at change points of data patterns, that is, perform bitwise control. Thus, the process has to be performed at a higher rate than the bit rate of the data. 
         [0221]    On the other hand, the transmission device  2  does not perform bitwise control but reduces the steepness of the slopes of Tr and Tf with respect to each of the optical packet signals and may thus reduce the phase modulation of the optical packet signals even in a case where the bit rate of the data becomes a higher rate. 
         [0222]    The transmission device  2  performs optical branching of the optical packet signal into the third waveguide  25 A and the fourth waveguide  25 B in the optical waveform shaper  25  and adjusts the optical phase of the optical packet signal that passes through the fourth waveguide  25 B based on the control voltage signal. 
         [0223]    In addition, the transmission device  2  combines the optical packet signal with the adjusted optical phase as the output of the fourth waveguide  25 B and the optical packet signal as the output of the third waveguide  25 A and thereby reduces the steepness of the slopes Tr and Tf of the optical signal wave in the optical packet signal. 
         [0224]    As a result, the phase modulation of the optical packet signal may be reduced. 
         [0225]    The transmission device  2  extracts the destination information from the packet signal, acquires the control voltage value that corresponds to the extracted destination information from the control voltage table  51 , and generates the control voltage signal based on the control voltage value. 
         [0226]    As a result, the transmission device  2  may generate different control voltage signals for the respective pieces of destination information of the packet signals. 
         [0227]    The transmission device  2  extracts the packet length information from the packet signal, calculates the application time of the control voltage signal for the optical packet signal based on the packet length information, and applies the control voltage signal based on the application time to the optical packet signal that passes through the fourth waveguide  25 B. 
         [0228]    As a result, the transmission device  2  may set a different control voltage signal and an application time for each of the packet signals. 
         [0229]    In the above first embodiment, a different control voltage value is registered in the control voltage table  51  with respect to each of the optical wavelengths λ in the same destination information. However, embodiments are not limited to the different control voltage value, but the same control voltage value may be registered in the control voltage table  51  with respect to each of the optical wavelengths λ in the same destination information. 
         [0230]    In the above first embodiment, the optical packet transmission device that transmits the optical packet signal is exemplified. However, similar effects may be obtained by applying the above first embodiment to the optical path transmission device that transmits the optical path signal. 
         [0231]    In the above first embodiment, a parallel processing configuration is exemplified in which the decomposed data resulting from division of the packet signal are allocated to each of the optical wavelengths λ of the WDM ring line  3 . However, embodiments are not limited to such a configuration, but modifications may appropriately be made. 
         [0232]    In the setting process in the above first embodiment, in steps S 33  and S 38 , a determination is made whether or not the state where the optical packet signal may be received is provided. However, a determination may be made whether or not the state where the optical packet signal may be received is provided based on the BER by an operation by the user. 
         [0233]    As the E/O converter  23  in the above first embodiment, the LN modulator is exemplified, for example. However, the E/O converter  23  is not limited to the LN modulator but may be an electric field absorption type modulator (EA modulator), for example, and may appropriately be changed. 
         [0234]    As the optical waveform shaper  25  in the above first embodiment, the LN modulator is exemplified, for example. However, the optical waveform shaper  25  may be an electro-optic modulator that performs phase modulation by using a phase difference by a change in the refractive index in the third waveguide  25 A and the fourth waveguide  25 B and may appropriately be changed. 
         [0235]    The control voltage signal applied to the optical waveform shaper  25  in the above first embodiment adjusts the optical phase of the optical packet signal by voltage control. However, embodiments are not limited to the voltage control, but the optical phase of the optical packet signal may be adjusted by current control or temperature control, for example. 
         [0236]    In each of the MDLs  20  in the above first embodiment, the E/O converter  23  and the optical waveform shaper  25  are respectively configured with separate optical modulators. However, the E/O converter  23  and the optical waveform shaper  25  may be configured with a single optical modulator. An embodiment in such a case will be described below as a second embodiment. 
         [0237]      FIG. 10  is an explanatory diagram that illustrates one example of a configuration of an MDL  200  of the second embodiment, and  FIG. 11  is an explanatory diagram that illustrates one example of a configuration of an optical modulator  26 . 
         [0238]    The same reference characters will be given to the same configurations as the MDL  20  of the first embodiment, and descriptions of the same configurations and operations will not be made. 
         [0239]    The MDL  200  illustrated in  FIG. 10  has a superimposing circuit  27  and the optical modulator  26  in addition to the LD  21 , the E/O circuit  22 , and the shaping circuit  24 . 
         [0240]    The superimposing circuit  27  superimposes the decomposed data from the E/O circuit  22  and the control voltage signal from the shaping circuit  24  together and inputs the superimposed signal to the optical modulator  26 . 
         [0241]    The optical modulator  26  has a fifth waveguide  26 A and a sixth waveguide  26 B and performs optical branching of the CW light from the LD  21  into the fifth waveguide  26 A and the sixth waveguide  26 B. 
         [0242]    The fifth waveguide  26 A transmits the CW light resulting from the optical branching. 
         [0243]    The sixth waveguide  26 B applies the superimposed signal to the CW light resulting from the optical branching and outputs the optical packet signal whose optical phase has been adjusted. 
         [0244]    The optical modulator  26  combines the CW light as an output of the fifth waveguide  26 A and the optical packet signal with the adjusted optical phase as an output of the sixth waveguide  26 B and outputs the optical packet signal in which an optical phase interference occurs. 
         [0245]    As a result, as illustrated in  FIG. 11 , the steepness of the slopes of Tr and Tf of the optical signal wave of the optical packet signal is reduced. 
         [0246]    As a result, the steepness of the slopes of Tr and Tf of the optical signal wave in the optical packet signal is reduced, and the phase modulation of the optical packet signal may thus be reduced. 
         [0247]    While an E/O converter and an optical waveform shaper are not provided separately, the optical modulator  26  of the second embodiment performs the optical branching of the CW light from the LD  21  into the fifth waveguide  26 A and the sixth waveguide  26 B. 
         [0248]    The optical modulator  26  applies the superimposed signal for superimposing the control voltage signal and the decomposed data to the CW light that passes through the sixth waveguide  26 B and outputs the optical packet signal whose optical phase has been adjusted. 
         [0249]    The optical modulator  26  combines the CW light as the output of the fifth waveguide  26 A and the optical packet signal with the adjusted optical phase as the output of the sixth waveguide  26 B and outputs the optical packet signal in which an optical phase interference occurs. 
         [0250]    As a result, the steepness of the slopes of Tr and Tf of the optical signal wave in the optical packet signal is reduced, and the phase modulation of the optical packet signal may thus be reduced. 
         [0251]    In the second embodiment, the control voltage signal is superimposed on all the decomposed data (data pattern). Accordingly, the optical phase difference in the original data pattern is changed from 0°→180° or 180°→0°. 
         [0252]    Thus, “0” and “1” of the generated optical packet signal are not turning on and turning off but becomes magnitude changes in the light intensity due to degradation of the amplitude of the optical packet signal (extinction ratio degradation of an optical signal). 
         [0253]    Accordingly, because it is possible that the transmission distance and SN strength degrade, application of this embodiment is suitable for short distance transmission. 
         [0254]    The control voltage signal applied to the optical waveform shaper  25  in the above embodiment adjusts the optical phase of the optical packet signal by voltage control. However, embodiments are not limited to the voltage control, but the optical phase of the optical packet signal may be adjusted by current control or temperature control, for example. 
         [0255]    Further, the configuration elements of the sections illustrated in the drawings do not necessarily have to be physically configured as illustrated in the drawings. 
         [0256]    That is, specific modes of distribution and integration of the sections are not limited to the modes in the drawings. All or a portion thereof may be configured by functionally or physically distributing or integrating those by any set in accordance with various kinds of loads, use situations, and so forth. 
         [0257]    In addition, all or any portion of various kinds of circuits provided in the devices may be executed on a central processing unit (CPU), a digital signal processor (DSP), an integrated circuit (IC), a field programmable gate array (FPGA), and so forth. In addition, a plurality of various kinds of circuits may be integrated into one circuit, and all or any portion thereof may be executed on a central processing unit (CPU), a digital signal processor (DSP), an integrated circuit (IC), a field programmable gate array (FPGA), and so forth. 
         [0258]    Further, all or any portion of various kinds of circuits may be executed on a program that is analyzed and executed by a CPU or the like or on hardware by wired logic. 
         [0259]    Areas that store various kinds of information may be configured with a read only memory (ROM) and random access memories (RAM) such as a synchronous dynamic random access memory (SDRAM), a magnetoresistive random access memory (MRAM), and non-volatile random access memory (NVRAM), for example. 
         [0260]    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.