JP3727136B2 - Distortion compensation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a distortion compensation apparatus, and more particularly to a distortion compensation apparatus that compensates for distortion generated when optically modulating a frequency-multiplexed signal using a predistortion method.
[0002]
[Prior art]
In optical communication, in general, a transmission side transmits an optical modulation signal in which light intensity or the like is modulated by a signal to be transmitted, and a reception side demodulates the optical modulation signal to obtain an original signal.
By the way, in a light emitting element such as a semiconductor laser, when the applied current is changed, the light output power is also changed. The optical modulation signal is generated using such a phenomenon. However, the optical modulation signal is distorted by the nonlinearity of the semiconductor laser. The influence of this distortion is relatively small when a digital signal is transmitted, but is noticeable when an analog signal is transmitted, and there is a problem that the transmission quality of data is deteriorated.
[0003]
One method for solving this problem is a predistortion method. In this method, a distortion signal that cancels distortion caused by a semiconductor laser or the like is added to the transmission signal. Therefore, when optical modulation is performed, the distortion signal cancels the distortion caused by the nonlinearity. Thus, the data transmission quality is prevented from deteriorating. Hereinafter, an optical transmission device using a predistortion method will be described with reference to FIG.
[0004]
In FIG. 5, a branching unit 100 branches a transmission signal (main signal) into two by an optical modulation unit 600 made of a semiconductor laser or the like. One of the two branched main signals propagates through the first path and is input to the phase inversion multiplexing unit 500, and the other is output to the second path. On the second path, a distortion generating unit 200, an amplitude adjusting unit 300, and a delay amount adjusting unit 400 are arranged.
When the main signal is input, the distortion generation unit 200 generates a signal (distortion signal) that cancels the distortion generated in the optical modulation unit 600. The amplitude adjustment unit 300 adjusts the amplitude level of the distortion signal so that the amplitude level is the same as the distortion generated when the optical modulation unit 600 generates the optical modulation signal. The delay amount adjustment unit 400 adjusts the delay amount of the distortion signal so that the delay amount is the same as that of the main signal propagating through the first path. The phase inversion multiplexing unit 500 adds the main signal and the distortion signal so as to have a phase difference of 180 degrees. Therefore, the output signal from the phase inversion multiplexing unit 500 has the same amplitude level as the main signal and the distortion generated when the optical modulation signal is generated by the optical modulation unit 600 based on the main signal, and the distortion having the opposite phase. Signal. Therefore, in the optical modulation unit 600, distortion caused by the non-linearity of the semiconductor laser is canceled by the distortion signal, so that no distortion occurs in the optical modulation signal.
[0005]
However, in the optical transmission device shown in FIG. 5, the non-linear circuit constituting the distortion generating unit 200 is not a constant delay amount over a wide band, but the delay amount differs for each frequency component. Therefore, when transmitting a wideband signal, for example, a frequency multiplexed signal, the delay amount adjusting unit 400 transmits the delay amount of the distorted signal over the entire frequency band to the main signal (frequency multiplexed signal) that propagates on the first path. ), It is difficult to eliminate the frequency deviation. Therefore, the optical transmission apparatus shown in FIG. 5 has a problem that a considerable difference is produced in the effect of distortion compensation for each frequency component such as a frequency multiplexed signal.
[0006]
Therefore, a method of applying a phase equalization unit to the optical transmission apparatus shown in FIG. Hereinafter, an optical transmission device using a phase equalization unit will be described with reference to FIG. In FIG. 6, the optical transmission device is the same as the configuration shown in FIG. 5 except that it includes a phase equalization unit 601. Accordingly, the corresponding configuration is denoted by the same reference numeral, and Description is omitted. The phase equalization unit 601 includes a coil, a resistor, and a capacitor, and equalizes the frequency deviation of the delay amount in the low, middle, and high frequencies of the distortion signal generated by the distortion generation unit 200. Thus, the frequency deviation of the delay amount of the distortion signal is corrected.
[0007]
[Problems to be solved by the invention]
However, in the optical transmission device shown in FIG. 6, it is difficult to completely equalize the frequency deviation of the delay amount generated in the nonlinear circuit constituting the distortion generator 200, and the circuit configuration of the phase equalizer itself is complicated. There were problems such as the need for fine adjustment. Therefore, in the present invention, when optically modulating a frequency multiplexed signal by a predistortion method, the distortion can be uniformly compensated without variation for each frequency component, and the circuit configuration and the distortion can be easily adjusted. An object is to provide a compensation device.
[0008]
[Means for Solving the Problems and Effects of the Invention]
  A first invention is a distortion compensation apparatus that compensates for distortion generated when a frequency-multiplexed signal is modulated by a predetermined method using a predistortion method,
  The frequency-multiplexed electrical signal is converted into first and second frequency-multiplexed signals.BranchA first branch,
  A distortion generator that generates and outputs a distortion signal using the second frequency multiplexed signal;
  A delay amount frequency deviation adjusting unit that gives the first frequency multiplexed signal the same characteristics as the frequency deviation of the delay amount of the distortion generating unit;
  A first phase-inversion multiplexing unit that multiplexes the distortion signal and the first frequency multiplexed signal output from the delay amount frequency deviation adjustment unit so as to have a phase difference of 180 degrees;
[0009]
When the predistortion method is used, if a distortion signal is generated from a frequency multiplexed signal, a frequency deviation of the delay amount occurs. However, according to the first invention, the delay amount frequency deviation adjusting unit gives the frequency deviation of the delay amount to the first frequency multiplexed signal. The first phase inversion multiplexing unit combines the first frequency multiplexed signal and the distortion signal as described above so as to have a phase difference of 180 degrees. When modulation is performed using the output signal from the first phase-inversion multiplex unit using the predetermined method, the amount of distortion compensation for one wave and one wave of the frequency multiplexed signal can be made uniform.
[0010]
According to a second invention, in the first invention, an amplitude adjusting unit for adjusting the amplitude level of the distortion signal is further provided.
[0011]
According to the second invention, since the amplitude level of the distortion signal can be adjusted, the frequency multiplexed signal is modulated when modulated by the above-mentioned predetermined method by the output signal from the first phase inversion multiplexing unit. The amount of distortion compensation for each wave can be made more uniform.
[0012]
According to a third invention, in the first or second invention, a delay amount adjusting unit for adjusting a delay amount of the distortion signal is further provided.
[0013]
According to the third invention, the absolute value of the delay amount of the distortion signal can be adjusted. The adjustment of the absolute value is simple as is well known. This facilitates the circuit configuration of the distortion compensation device and its fine adjustment.
[0014]
  In a fourth invention according to any one of the first to third inventions, the distortion generator is
  The second frequency multiplexed signal isA phase-inversion branching section for branching into the first and second signals so that the amplitude levels are equal and opposite in phase;
  First and second nonlinear circuits that give the first and second signals the same characteristics as the frequency deviation;
  A multiplexing unit for multiplexing the output signals from the first and second nonlinear circuits,
  The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
  The output signal from the multiplexing unit is characterized by comprising only the second-order distortion component of the input signal.
[0015]
According to the fourth aspect of the invention, when the output signal from the first phase inversion multiplexing unit is modulated by the predetermined method, the amount of compensation for the secondary distortion of one wave and one wave of the frequency multiplexed signal is made uniform. can do.
[0016]
  In a fifth aspect based on the first to third aspects, the strain generator is
  Input signal from the first branchBifurcateA second branch,
  Either one of the signals branched in the second branch, So that the amplitude level is equal and out of phaseBranch to first and second branch signalsA phase inversion branch,
  1 and 2 branch signalsFirst and second nonlinear circuits that give the same characteristics as the frequency deviation;
  A second phase inversion multiplexing unit that combines the output signals from the first and second nonlinear circuits in opposite phases;
  First branch signalAnd a third phase inversion multiplexing unit that combines the output signals from the second phase inversion multiplexing unit in opposite phases,
  The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
  The output signal from the second phase-inversion multiplexer is composed of the main signal of the input signal and its third-order distortion component;
  The output signal from the third phase inversion multiplexing unit is characterized by consisting only of the third-order distortion component of the input signal.
[0017]
According to the fifth aspect of the invention, when the output signal from the first phase inversion multiplexing unit is modulated by the predetermined method, the compensation amount of the third-order distortion of one wave and one wave of the frequency multiplexed signal is made uniform. can do.
[0018]
The sixth invention is characterized in that, in the fourth or fifth invention, the same nonlinear circuit is used for the delay amount frequency deviation adjusting section and the first and second nonlinear circuits.
[0019]
According to the sixth aspect of the invention, the distortion compensation amount of one wave and one wave of the frequency multiplexed signal can be easily made uniform.
[0020]
In a seventh aspect based on the sixth aspect, the nonlinear circuit of the delay amount frequency deviation adjusting unit operates in a linear region,
The frequency deviation given by the delay amount frequency deviation adjustment unit does not deviate from the frequency deviation of the delay amount generated by the nonlinear circuit included in the distortion generation unit, and is distorted in the output signal from the nonlinear circuit of the delay amount frequency deviation adjustment unit. It is characterized by not producing any components.
[0021]
According to the seventh aspect of the present invention, when the signal modulated from the output signal from the first phase inversion multiplexing unit is modulated by the predetermined method, the distortion compensation amount of one wave and one wave of the frequency multiplexed signal can be made more uniform. it can.
[0022]
In an eighth aspect based on the second aspect, the delay amount frequency deviation adjusting unit is configured by a non-linear circuit,
The distortion generator
A phase inversion branching unit that branches the input signal from the first branching unit into first and second signals so that the amplitude levels are equal and have opposite phases;
First and second nonlinear circuits that give the first and second signals the same characteristics as the frequency deviation;
A multiplexing unit for multiplexing the output signals from the first and second nonlinear circuits,
The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
The output signal from the multiplexing unit consists of only the second-order distortion component of the input signal,
When the output signal from the nonlinear circuit includes a distortion component, the amplitude adjustment unit adjusts the amplitude level of the distortion signal so that the distortion component is canceled by the distortion signal.
[0023]
According to the eighth aspect, even if distortion is generated by the delay amount frequency deviation adjusting unit, the distortion is compensated by the distortion signal. This facilitates setting of the operating condition of the delay amount frequency deviation adjusting unit. Further, when the output signal from the first phase inversion multiplexing unit is modulated by the above-described predetermined method, the compensation amount of the secondary distortion of one wave and one wave of the frequency multiplexed signal can be made uniform.
[0024]
  In a ninth aspect based on the second aspect, the delay amount frequency deviation adjusting unit is configured by a non-linear circuit,
  The distortion generator
    Input signal from the first branchBifurcateA second branch,
    Either one of the signals branched in the second branch, So that the amplitude level is equal and out of phaseBranch to first and second branch signalsA phase inversion branch,
    1 and 2 branch signalsFirst and second nonlinear circuits that give the same characteristics as the frequency deviation;
    A second phase inversion multiplexing unit that combines the output signals from the first and second nonlinear circuits in opposite phases;
    The first branch signal andA third phase inversion multiplexing unit that combines the output signal from the second phase inversion multiplexing unit with an opposite phase,
  The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
  The output signal from the second phase-inversion multiplexer is composed of the main signal of the input signal and its third-order distortion component;
  The output signal from the third phase-inversion multiplexer is composed of only the third-order distortion component of the input signal;
  When the output signal from the nonlinear circuit includes a distortion component, the amplitude adjustment unit adjusts the amplitude level of the distortion signal so that the distortion component is canceled by the distortion signal.
[0025]
According to the ninth aspect, even if distortion is generated by the delay amount frequency deviation adjusting unit, the distortion is compensated by the distortion signal. This facilitates setting of the operating condition of the delay amount frequency deviation adjusting unit. Further, when the output signal from the first phase inversion multiplexing unit is modulated by the predetermined method, the compensation amount of the third-order distortion of one wave and one wave of the frequency multiplexed signal can be made uniform.
[0026]
  A tenth aspect of the invention is a distortion compensation apparatus that compensates for distortion generated when a frequency-multiplexed signal is modulated by a predetermined method using a predistortion method,
  The frequency-multiplexed electrical signal is converted into first and second frequency-multiplexed signals.BranchA first branch,
  A distortion generator that generates and outputs a distortion signal using the second frequency multiplexed signal;
  A delay amount frequency deviation adjusting unit that gives the first frequency multiplexed signal the same characteristics as the frequency deviation of the delay amount of the distortion generating unit;
  A first phase inversion multiplexing unit that combines the distortion signal and the first frequency multiplexed signal output from the delay amount frequency deviation adjustment unit so as to have a phase difference of 180 degrees;
  The distortion generator
  A second frequency multiplexed signal propagating along the second pathFirst 1 And bifurcate into second branch signalA second branch,
  Has the same delay amount frequency characteristics as the delay amount frequency deviation adjustment unit,1 branch signalA nonlinear circuit that outputs distortion components in
  2 branch signalA second amplitude adjustment unit that adjusts and outputs the amplitude level of
  2 branch signalA second delay amount adjustment unit for adjusting and outputting the delay amount of
  First and second branch signalsAnd a second phase inversion multiplexing unit that multiplexes the signals in the opposite phase.
[0027]
According to the tenth invention, when the output signal from the first phase inversion multiplexer is modulated by the predetermined method, the compensation amount of one wave and one wave of the frequency multiplexed signal can be made uniform. .
[0028]
According to an eleventh aspect, in the tenth aspect, the same nonlinear circuit is used as the delay amount frequency deviation adjusting unit and the nonlinear circuit.
[0029]
According to the eleventh aspect, the distortion compensation amount of one wave and one wave of the frequency multiplexed signal can be easily made uniform.
[0030]
In a twelfth aspect based on the tenth aspect, the delay amount frequency deviation adjusting unit is composed of a nonlinear circuit,
The output signal from the second phase inversion multiplexing unit consists only of the second and third order distortion components of the first frequency multiplexed signal,
The non-linear circuit constituting the delay amount frequency deviation adjusting unit is set with operating conditions so that the third-order distortion component is canceled by the first phase-inversion multiplexing unit from the output signal from the second phase-inversion multiplexing unit. It is characterized by that.
[0031]
According to the twelfth aspect, even when distortion is caused by the delay amount frequency deviation adjusting unit, the distortion is compensated by the distortion signal. This facilitates setting of the operating condition of the delay amount frequency deviation adjusting unit. Further, when the output signal from the first phase inversion multiplexing unit is modulated by the above-described predetermined method, the compensation amount of the secondary distortion of one wave and one wave of the frequency multiplexed signal can be made uniform.
[0032]
In a thirteenth aspect based on the tenth aspect, the delay amount frequency deviation adjusting unit is composed of a nonlinear circuit,
The output signal from the second phase inversion multiplexing unit consists only of the second and third order distortion components of the first frequency multiplexed signal,
The non-linear circuit constituting the delay amount frequency deviation adjustment unit is set with operating conditions so that the second-order distortion component is canceled by the first phase-inversion multiplexing unit from the output signal from the second phase-inversion multiplexing unit. It is characterized by that.
[0033]
According to the thirteenth aspect, even if distortion occurs by the delay amount frequency deviation adjusting unit, the distortion is compensated by the distortion signal. This facilitates setting of the operating condition of the delay amount frequency deviation adjusting unit. Further, when the output signal from the first phase inversion multiplexing unit is modulated by the predetermined method, the compensation amount of the third-order distortion of one wave and one wave of the frequency multiplexed signal can be made uniform.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram illustrating a configuration of an optical transmission apparatus to which a distortion compensation apparatus (refer to a dotted line inside) according to the first embodiment of the present invention is applied. In FIG. 1, the distortion compensator includes a first branching unit 100, a distortion generating unit 200, a first amplitude adjusting unit 300, a first delay amount adjusting unit 400, and a first phase inversion multiplexing unit. 500 and a delay amount frequency deviation adjusting unit 700.
The first branching unit 100 branches a main signal (frequency multiplexed signal), which is input from the outside and is to be optically modulated by an optical modulation unit 600 made of a semiconductor laser or the like, into first and second frequency multiplexed signals. The first frequency multiplexed signal is output to the first path, and the second frequency multiplexed signal is output to the second path. On this first path, there is a delay amount frequency deviation adjusting unit 700, and on the second path, there is a distortion generating unit 200, a first amplitude adjusting unit 300, and a first delay amount adjusting unit 400. Arranged.
When the second frequency-multiplexed signal is input, the distortion generator 200 generates a signal (hereinafter referred to as “distortion signal”) that cancels the distortion generated in the optical modulator 600. The distortion signal has a different delay amount (frequency deviation of the delay amount) for each frequency component. The first amplitude adjustment unit 300 adjusts the amplitude level of the distortion signal so that the signal has the same amplitude as the distortion generated when the optical modulation unit 600 disposed in the subsequent stage of the distortion compensation apparatus generates the optical modulation signal. adjust. The first delay amount adjusting unit 400 adjusts the delay amount of the distortion signal so that the delay amount is the same as that of the first frequency multiplexed signal propagating through the first path.
The delay amount frequency deviation adjustment unit 700 gives the same frequency deviation of the delay amount of the distortion signal propagating through the second path to the first frequency multiplexed signal propagating through the first path.
The first phase inversion multiplexing unit 500 adds and outputs the first frequency multiplexed signal to which the frequency deviation of the delay amount is given and the distortion signal so as to have a phase difference of 180 degrees. Therefore, the output signal from the first phase inversion multiplexing unit 500 is a distortion generated when the optical modulation unit 600 generates an optical modulation signal using the first frequency multiplexing signal and the first frequency multiplexing signal. And a distortion signal having the same amplitude level as the above and having a phase opposite to that of the distortion. Accordingly, in the optical modulation unit 600, distortion caused by the nonlinearity of the semiconductor laser is canceled by the distortion signal, so that the optical modulation signal does not cause distortion.
[0035]
By the way, the distortion signal is given a frequency deviation of the delay amount by a non-linear circuit constituting the distortion generator 200. That is, the delay amount differs for each frequency component of the distortion signal. However, the delay amount frequency deviation adjusting unit 700 gives the same characteristic as the frequency deviation characteristic of the delay amount given by the nonlinear circuit to the first frequency multiplexed signal. Therefore, the first delay amount adjustment unit 400 only needs to adjust the absolute value of the delay amount. As a result, even when optically modulating a frequency multiplexed signal, it is possible to provide a distortion compensator that can uniformly compensate for distortion for each frequency component and that can easily adjust the circuit configuration.
[0036]
Note that the branching ratio of the first branching unit 100 does not need to be specified. However, when the amplitude level of the distortion generated in the optical modulation unit 600 is known in advance and the magnitude of the output (distortion signal) with respect to the input (second frequency multiplexed signal) of the distortion generation unit 200 can be grasped, The first amplitude adjusting unit 300 can be omitted by appropriately setting the branching ratio of one branching unit 100.
In addition, the first delay amount adjustment unit 400 can be omitted by setting the first path shown in FIG. 1 to an appropriate length.
[0037]
Further, when the delay amount frequency deviation adjusting unit 700 is configured by a non-linear circuit, it is desirable that the non-linear circuit is operated in a linear region so that the output signal from the delay amount frequency deviation adjusting unit 700 is not distorted. However, even when the output signal is distorted, the distortion generated in the output signal can be canceled by the distortion signal generated by the distortion generator 200. However, in this case, the amplitude level of the distortion signal after canceling out the distortion generated in the nonlinear circuit needs to be the same as the amplitude level of the distortion generated in the optical modulation unit 600.
[0038]
Next, a configuration example of the distortion generator 200 will be described with reference to FIG. 2 or FIG. FIG. 2 is a block diagram illustrating a first configuration example of the distortion generator 200 (see FIG. 1). In FIG. 2, the distortion generator 200 includes a first phase inversion branching unit 201, a first nonlinear circuit 202, a second nonlinear circuit 203, and a multiplexing unit 204, and a distortion signal (2 (Consisting only of the next distortion component).
The phase inversion branching unit 201 splits the second frequency multiplexed signal input from the first branching unit 100 into two branches and outputs them to the primary path and the secondary path. The signals output to the primary path and the secondary path have a phase difference of 180 degrees and are input to the first nonlinear circuit 202 and the second nonlinear circuit 203. Output signals from the first nonlinear circuit 202 and the second nonlinear circuit 203 have a main signal, a second-order distortion component, and a third-order distortion component, respectively. Both main signals and third-order distortion components have a phase difference of 180 degrees, but both second-order distortion components have the same phase. Therefore, when the output signals from the first nonlinear circuit 202 and the second nonlinear circuit 203 are multiplexed by the multiplexing unit 204, the main signal and the third-order distortion component are canceled and only the second-order distortion component is output as a distortion signal. Is done.
[0039]
FIG. 3 is a block diagram showing a second configuration example of the distortion generator 200 (see FIG. 1). In FIG. 3, the distortion generator 200 includes a second branch unit 301, a phase inversion branch unit 302, a first nonlinear circuit 303, a second nonlinear circuit 304, and a second phase inversion multiplexer 305. A second amplitude adjustment unit 306, a second delay amount adjustment unit 307, and a third phase inversion multiplexing unit 308, which generate a distortion signal (consisting only of a third-order distortion component). .
The second branch unit 301 bifurcates the second frequency multiplexed signal input from the first branch unit 100 and outputs it to the first path and the second path. The phase inversion branching unit 302 bifurcates the second frequency multiplexed signal input from the second branching unit 301 via the first path and outputs it to the primary path and the secondary path. The signals output to the primary path and the secondary path have a phase difference of 180 degrees and are input to the first nonlinear circuit 303 and the second nonlinear circuit 304. The output signals from the first nonlinear circuit 303 and the second nonlinear circuit 303 have a main signal, a second-order distortion component, and a third-order distortion component, respectively. Both the main signal and the third-order distortion component have a phase difference of 180 degrees, but the second-order distortion component has the same phase. Therefore, when the output signals from the first nonlinear circuit 202 and the second nonlinear circuit 203 are combined by the second phase inversion multiplexing unit 305 with an antiphase relationship, only the secondary distortion component is canceled, A signal and a third-order distortion component are output. The second amplitude adjustment unit 306 propagates the amplitude level of the main signal included in the output signal from the first phase inversion multiplexing unit 305 through the first path to the third phase inversion multiplexing unit 308. Adjustment is made so as to be the same as the amplitude level of the input second frequency multiplexed signal. The second delay amount adjustment unit 307 makes the delay amount of the output signal from the second amplitude adjustment unit 306 the same as the delay amount of the second frequency multiplexed signal propagating through the first path. adjust.
The third phase inversion multiplexing unit 308 multiplexes the second frequency multiplexed signal propagating through the first path and the output signal from the second delay amount adjustment unit 307 in an antiphase relationship. Since the second frequency multiplexed signal and the main signal of the output signal from the second delay amount adjustment unit 307 have the same amplitude level and delay amount, only the main signal is canceled and the third-order distortion component is the distortion signal. Is output from the third phase inversion multiplexing unit 308.
[0040]
FIG. 4 is a block diagram showing the overall configuration of the distortion compensation apparatus according to the second embodiment of the present invention, and in particular, a third configuration example of the distortion generator 200 provided in the distortion compensation apparatus. Show. In the distortion compensation apparatus shown in FIG. 4, components corresponding to the configuration shown in FIG. 1 are denoted by the same reference numerals and description thereof is omitted. Here, the distortion generating unit 200 includes a second branching unit 401, a nonlinear circuit 402 having the same frequency deviation characteristic as the nonlinear circuit constituting the delay amount frequency deviation adjusting unit 700, and a second amplitude. It includes an adjustment unit 403, a second delay amount adjustment unit 404, and a second phase inversion multiplexing unit 405, and can generate a distortion signal composed of second-order and third-order distortion.
[0041]
In the distortion generating unit 200, the second branching unit 401 splits the second frequency multiplexed signal input from the first branching unit 100 into two branches and outputs them to the primary path and the secondary path. A nonlinear circuit 402 is arranged on the primary path, and a second amplitude adjusting unit 403 and a second delay amount adjusting unit 404 are arranged on the secondary path. The nonlinear circuit 402 outputs a signal having second and third order distortion components based on the input second frequency multiplexed signal.
Further, the second amplitude adjustment unit 403 makes the amplitude level of the second frequency multiplexed signal propagating through the secondary path the same as the amplitude level of the main signal of the signal output from the nonlinear circuit 402. adjust. The second delay amount adjustment unit 404 adjusts the delay amount of the second frequency multiplexed signal propagating through the secondary path to be the same as the delay amount of the signal output from the nonlinear circuit 402.
The second phase inversion multiplexing unit 405 multiplexes the output signals from the nonlinear circuit 402 and the second delay amount adjustment unit 404 with an antiphase relationship. Therefore, only the main signal of the output signal from the non-linear circuit 402 is canceled out from the output signal from the second phase inversion multiplexing unit 405, and the second-order distortion component and the third-order distortion component are output as distortion signals.
[0042]
However, when the operation condition (bias voltage or the like) of the nonlinear circuit 402 compensates only for the second-order distortion component generated in the optical modulation unit 600 (see FIG. 1), the output signal from the nonlinear circuit 402 is the main signal and the second-order distortion. It is desirable to set so that only the components are present.
Further, when compensating only the third-order distortion component generated in the optical modulation unit 600, it is desirable to set so that the output signal from the nonlinear circuit 402 is only the main signal and the third-order distortion component.
In this way, by inputting the output signal from the nonlinear circuit 402 and the second frequency multiplexed signal whose amplitude level and delay amount are adjusted and propagating through the secondary path to the phase inversion multiplexer 405, From the output signal from the phase inversion multiplexing unit 405, only the distortion component compensated in the optical modulation unit 600 can be obtained in accordance with the operation conditions described above.
[0043]
When the nonlinear circuit constituting the delay amount frequency deviation adjusting unit 700 is operated in the nonlinear region, the first frequency multiplexed signal input to the first phase inversion multiplexing unit 500 includes a distortion component. When the distortion signal output from the distortion generator 200 shown in FIG. 4 includes second-order and third-order distortion components, the first phase-inversion multiplexer 500 completely eliminates the distortion components included in the first frequency multiplexed signal. Do not cancel. As described above, when the distortion generating unit 200 and the delay amount frequency deviation adjusting unit 700 are adjusted, a distortion component remains in the first frequency multiplexed signal input to the optical modulation unit 600. If the distortion component is left, the optical modulation signal generated by the optical modulation unit 600 formed of a non-linear semiconductor laser or the like will not be distorted.
[0044]
In the above-described embodiment, the case where the present distortion compensation apparatus is applied to optical communication has been described. However, the present distortion compensation device is not limited to optical communication, and can be applied to all communication using a predistortion method.
In the distortion compensation apparatus, an element having nonlinearity in the relationship between the input signal and the output signal, such as a diode, FET, or transistor, can be used as the nonlinear circuit.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an optical transmission apparatus to which a distortion compensation apparatus according to a first embodiment of the present invention is applied.
FIG. 2 is a block diagram showing a first configuration example of a distortion generator 200 (see FIG. 1).
FIG. 3 is a block diagram showing a second configuration example of the distortion generator 200 (see FIG. 2).
FIG. 4 is a block diagram showing an overall configuration of a distortion compensation apparatus according to a second embodiment of the present invention, and particularly shows a third configuration example of a distortion generator 200;
FIG. 5 is a block diagram showing a configuration of an optical transmission apparatus to which a conventional distortion compensation apparatus (first configuration example) is applied.
FIG. 6 is a block diagram showing a configuration of an optical transmission apparatus to which a conventional distortion compensation apparatus (second configuration example) is applied.
[Explanation of symbols]
100 ... 1st branch part
200 ... distortion generating part
300... First amplitude adjustment unit
400: First delay amount adjustment unit
500 ... 1st phase inversion multiplexing part
600: Light modulation unit
700 ... Delay amount frequency deviation adjustment unit
201, 302... Second phase inversion branching section
202, 303 ... first nonlinear circuit
203, 304 ... second nonlinear circuit
204 ... multiplexing section
305, 405 ... second phase inversion multiplexing unit
306, 403 ... second amplitude adjustment unit
307, 404... Second delay amount adjustment unit
308: Third phase inversion multiplexing unit
401 ... 2nd branch part
402: Non-linear circuit

Claims (13)

A first branching unit that branches the frequency-multiplexed electrical signal into first and second frequency-multiplexed signals;
A distortion generator that generates and outputs a distortion signal using the second frequency-multiplexed signal;
A delay amount frequency deviation adjusting unit that gives the first frequency multiplexed signal the same characteristic as the frequency deviation of the delay amount of the distortion generating unit;
Distortion compensation comprising a first phase-inverted multiplexing unit that combines the distortion signal and the first frequency multiplexed signal output from the delay amount frequency deviation adjustment unit so as to have a phase difference of 180 degrees. apparatus.   The distortion compensation apparatus according to claim 1, further comprising an amplitude adjustment unit that adjusts an amplitude level of the distortion signal.   The distortion compensation apparatus according to claim 1, further comprising a delay amount adjustment unit that adjusts a delay amount of the distortion signal. The distortion generator is
A phase inversion branching unit for branching the second frequency multiplexed signal into first and second signals so that the amplitude levels are equal and opposite in phase;
First and second nonlinear circuits that give the first and second signals the same characteristics as the frequency deviation;
A multiplexing unit that combines the output signals from the first and second nonlinear circuits,
The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
The distortion compensation apparatus according to claim 1, wherein an output signal from the multiplexing unit is composed of only a second-order distortion component of the input signal. The distortion generator is
A second branching unit that splits an input signal from the first branching unit into two branches ;
A phase inversion branching unit that branches one of the signals branched into two by the second branching unit into first and second branched signals so that the amplitude levels are equal and have opposite phases;
First and second nonlinear circuits that give the first and second branched signals the same characteristics as the frequency deviation;
A second phase inversion multiplexing unit that combines the output signals from the first and second nonlinear circuits in opposite phases;
A third phase inversion multiplexing unit that combines the first branch signal and the output signal from the second phase inversion multiplexing unit in opposite phases;
The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
The output signal from the second phase-inversion multiplexer is composed of the main signal of the input signal and its third-order distortion component;
The distortion compensation apparatus according to any one of claims 1 to 3, wherein an output signal from the third phase inversion multiplexing unit is composed of only a third-order distortion component of the input signal.   The distortion compensation apparatus according to claim 4 or 5, wherein the same nonlinear circuit is used for the delay amount frequency deviation adjusting unit and the first and second nonlinear circuits. The nonlinear circuit of the delay amount frequency deviation adjustment unit operates in a linear region,
The frequency deviation given by the delay amount frequency deviation adjusting unit does not deviate from the frequency deviation of the delay amount generated by the nonlinear circuit included in the distortion generating unit, and the output signal from the nonlinear circuit of the delay amount frequency deviation adjusting unit The distortion compensation apparatus according to claim 6, wherein a distortion component is not generated in the distortion compensation apparatus. The delay amount frequency deviation adjustment unit is configured by a nonlinear circuit,
The distortion generator is
A phase inversion branching unit that branches the input signal from the first branching unit into first and second signals so that the amplitude levels are equal and have opposite phases;
First and second nonlinear circuits that give the first and second signals the same characteristics as the frequency deviation;
A multiplexing unit that combines the output signals from the first and second nonlinear circuits,
The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
The output signal from the multiplexing unit consists of only the second-order distortion component of the input signal;
When the output signal from the nonlinear circuit includes a distortion component, the amplitude adjustment unit,
The distortion compensation apparatus according to claim 2, wherein an amplitude level of the distortion signal is adjusted so that the distortion component is canceled by the distortion signal. The delay amount frequency deviation adjustment unit is configured by a nonlinear circuit,
The distortion generator is
A second branching unit that splits an input signal from the first branching unit into two branches ;
A phase inversion branching unit that branches one of the signals branched into two by the second branching unit into first and second branched signals so that the amplitude levels are equal and have opposite phases;
First and second nonlinear circuits that give the first and second branched signals the same characteristics as the frequency deviation;
A second phase inversion multiplexing unit that combines the output signals from the first and second nonlinear circuits in opposite phases;
A third phase inversion multiplexing unit that combines the first branch signal and the output signal from the second phase inversion multiplexing unit in opposite phases;
The first and second nonlinear circuits set operating conditions such that the amplitude levels of the signals output from the first and second nonlinear circuits are the same;
The output signal from the second phase-inversion multiplexer is composed of the main signal of the input signal and its third-order distortion component;
The output signal from the third phase-inversion multiplexer is composed of only the third-order distortion component of the input signal;
When the output signal from the nonlinear circuit includes a distortion component, the amplitude adjustment unit adjusts the amplitude level of the distortion signal so that the distortion component is canceled by the distortion signal. The distortion compensation apparatus according to claim 2. A first branching unit that branches the frequency-multiplexed electrical signal into first and second frequency-multiplexed signals;
A distortion generator that generates and outputs a distortion signal using the second frequency-multiplexed signal;
A delay amount frequency deviation adjusting unit that gives the first frequency multiplexed signal the same characteristic as the frequency deviation of the delay amount of the distortion generating unit;
A first phase inversion multiplexing unit that combines the distortion signal and the first frequency multiplexed signal output from the delay amount frequency deviation adjustment unit so as to have a phase difference of 180 degrees;
The distortion generator is
A second branch section that bifurcates the second frequency-multiplexed signal propagating through the second path to the first and second branch signal,
A non-linear circuit having a frequency characteristic of the same delay amount as that of the delay amount frequency deviation adjusting unit, and outputting a distortion component in the one branch signal ;
A second amplitude adjusting unit for adjusting and outputting the amplitude level of the two branch signals ;
A second delay amount adjustment unit for adjusting and outputting the delay amount of the two branch signals ;
A distortion compensation apparatus comprising: a second phase inversion multiplexing unit that combines the first and second branch signals with opposite phases.   The distortion compensation apparatus according to claim 10, wherein the same nonlinear circuit is used for the delay amount frequency deviation adjusting unit and the nonlinear circuit. The delay amount frequency deviation adjustment unit is configured by a nonlinear circuit,
The output signal from the second phase inversion multiplexing unit consists only of the second and third order distortion components of the first frequency multiplexed signal,
The non-linear circuit constituting the delay amount frequency deviation adjusting unit operates so as to cancel out the third-order distortion component from the output signal from the second phase inversion multiplexing unit by the first phase inversion multiplexing unit. The distortion compensation apparatus according to claim 10, wherein The delay amount frequency deviation adjustment unit is configured by a nonlinear circuit,
The output signal from the second phase inversion multiplexing unit consists only of the second and third order distortion components of the first frequency multiplexed signal,
The non-linear circuit constituting the delay amount frequency deviation adjusting unit operates so as to cancel out the second-order distortion component from the output signal from the second phase inversion multiplexing unit by the first phase inversion multiplexing unit. The distortion compensation apparatus according to claim 10, wherein

Images