JP3964397B2 - Optical transmitter - Google Patents

Description

  The present invention relates to an optical transmitter that modulates an optical signal in accordance with an electric signal and transmits the optical signal in an optical communication system, particularly, a long-distance optical amplification repeater transmission system using optical amplification transmission technology.

  In a long-distance optical amplification repeater transmission system, it is known that the optical S / N ratio is deteriorated or fluctuated due to polarization hole burning of an optical amplification repeater or polarization dependent loss of a transmission path. In order to improve this, polarization scrambling is performed. In particular, in order to average the latter optical S / N ratio fluctuation (signal fading), it is necessary to perform polarization scrambling at least at a speed equal to or higher than the signal bit rate. A lithium niobate optical phase modulator is generally used for this polarization scrambling.

  This lithium niobate optical phase modulator has a feature that phase modulation occurs simultaneously with polarization modulation, and for example, Patent Document 1 discloses that it can be used for the purpose of compensating for waveform deterioration due to dispersion in a transmission path. According to it, it is discussed that driving the polarization scrambler with a data clock synchronized with the bit of data modulation has a significant code error rate improvement effect in ultra-long distance optical amplification repeater transmission systems such as transoceanic oceans. Has been. In other words, by setting the drive phase of the polarization scrambler in a predetermined relationship with the data, the eye is more open so that the amplitude fluctuation at the receiving end caused by optical fiber dispersion or nonlinear refractive index change can be distinguished. You can set the direction to be.

  FIG. 24 is a block diagram showing a conventional optical transmitter disclosed in Patent Document 1. In FIG. In the figure, 1 is a light source, 2 is a light intensity modulator, 3 is a polarization scrambler, 4 is a data signal input terminal, 5 is a clock signal input terminal, 6 is a discriminator, 7 is a light intensity modulator drive circuit, 8 Is a delay device, 9 is a polarization scrambler driving circuit, and 10 is an optical transmitter output terminal.

Next, the operation will be described.
The discriminator 6 generates a light intensity modulator driving signal from the data signal and clock signal input from the data signal input terminal 4 and the clock signal input terminal 5, and the light intensity modulator driving circuit 7 amplifies the signal. Input to the light intensity modulator 2. On the other hand, the clock signal input from the clock signal input terminal 5 is branched and input to the delay unit 8 as a polarization scrambler drive signal to give a delay. The polarization scrambler drive signal delayed by the delay unit 8 is amplified by the polarization scrambler drive circuit 9 and drives the polarization scrambler 3. The light signal output from the light source 1 is subjected to light intensity modulation according to the data signal by the light intensity modulator drive signal in the light intensity modulator 2 and then input to the polarization scrambler 3 to reduce the degree of polarization to zero. Polarized and scrambled and output from the optical transmitter output terminal 10.

Next, the operation of the polarization scrambler 3 will be described with reference to FIG.
Here, FIG. 25A shows a configuration of a lithium niobate optical phase modulator used as the polarization scrambler 3, and FIG. 25B shows a drive waveform of the polarization scrambler 3. 25 (c) shows the locus of the polarization state of the optical signal output from the polarization scrambler 3 on the Poincare sphere. In the Poincare sphere shown in FIG. 25 (c), L is counterclockwise circularly polarized light, R is clockwise circularly polarized light, H is horizontal polarized light, V is vertical polarized light, Q is 45 degree linearly polarized light, and P is -45 degree. Each represents linearly polarized light.

Polarization scrambling means that the degree of polarization is zero. In order for the degree of polarization to be zero, on the Poincare sphere,
(A) The probability of existing in the L hemisphere and the probability of existing in the R hemisphere within a certain time are equal (B) The probability of existing in the Q hemisphere and the probability of existing in the P hemisphere within a certain time (C) It is necessary to satisfy the three conditions that the probability of existing in the H-side hemisphere and the probability of existing in the V-side hemisphere are equal within a certain time.

  As shown in FIG. 25A, 45-degree linearly polarized light is input to the polarization scrambler 3. When the drive signal is zero, the polarization scrambler 3 is output as it is. When a drive signal is applied to the polarization scrambler 3, the degree of phase modulation with respect to the two linearly polarized light components is different. Therefore, as shown in FIG. 25 (b), the polarization state varies on the Poincare sphere according to the drive signal. → L → A → L → Q → R → B → R → Q When the optical signal intensity input from the optical intensity modulator 2 to the polarization scrambler 3 is constant, the polarization state draws a locus indicated by a thick line on the surface of the Poincare sphere. At this time, since the above three conditions (a) to (c) are satisfied, the degree of polarization can be made zero.

  When the drive waveform shown in FIG. 25B is applied to the polarization scrambler 3, the polarization is scrambled, and at the same time, phase modulation proportional to the drive waveform in FIG. 25B is applied. This is because the in-phase component of the phase modulation superimposed on the two linearly polarized light components becomes the residual phase modulation of the output light.

Next, signal waveforms of respective parts of the circuit shown in FIG. 24 will be described with reference to FIG.
The light signal output from the light source 1 is light intensity modulated by the light intensity modulator 2. FIG. 26A shows a waveform example of the output signal of the light intensity modulator. In general, a digital signal is represented by “1” when an optical signal exists within a specified time and “0” when it does not exist. FIG. 26B shows the phase modulation waveform of the optical signal output from the polarization scrambler 3. As described above, when a lithium niobate optical phase modulator is used as the polarization scrambler 3, the phase modulation as shown in FIG. 26B remains simultaneously with the polarization scrambler operation. At this time, the phase of the phase modulation can be adjusted by the delay unit 8.

  Here, phase modulation and frequency modulation are essentially the same, and a frequency modulation waveform is shown in FIG. The phase modulation shown in FIG. 26 (b) is equivalent to the frequency modulation shown in FIG. 26 (c). The time for the optical signal to propagate through the optical fiber varies depending on the frequency. Therefore, as shown in FIGS. 26D and 26E, the waveform after propagation through the optical fiber changes. FIG. 26 (d) shows the state of waveform change, and FIG. 26 (e) shows the waveform after optical fiber transmission. As shown in FIGS. 26D and 26E, when the pulse is compressed, the eye is opened, which is advantageous for identification. On the other hand, when the sign of phase modulation is reversed, the pulse spreads and the eye opening deteriorates, which is disadvantageous for identification.

  Thus, by synchronizing the polarization scrambler drive signal for driving the polarization scrambler 3 with the optical intensity modulator drive signal and optimizing the drive position, the eye opening ratio at the receiving end can be improved. . Similarly, the eye opening improvement effect at the receiving end can be obtained by replacing the polarization scrambler 3 with an optical phase modulator.

Japanese Patent Laid-Open No. 8-111162

  Since the conventional optical transmitter is configured as described above, a large-amplitude signal is generally required to drive the polarization scrambler 3 or the optical phase modulator, and the polarization scrambler driving circuit 9 or There has been a problem that the power consumption of the optical phase modulator driving circuit is increased.

  When the extinction ratio of the light intensity modulator 2 is finite, a slight optical signal remains even when the data signal is “0”. At this time, the residual light is phase-modulated. When a pulsed phenomenon occurs after transmission through an optical fiber and pulsed light is generated when the data signal is “0”, a code error may occur because the receiving end identifies this as “1”. There was also a problem.

  Also, when a return-to-zero signal is used as the light intensity modulator drive signal, the degree of polarization cannot be made zero if the drive phase of the polarization scrambler 3 is set so that the eye opening ratio is optimal. There was a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an optical transmitter with low power consumption of a polarization scrambler driving circuit or an optical phase modulator driving circuit.

  It is another object of the present invention to provide an optical transmitter capable of preventing residual light from being phase-modulated and causing a code error even when the extinction ratio of intensity modulation is finite.

  It is another object of the present invention to provide an optical transmitter capable of making the degree of polarization zero even under conditions where the polarization scrambler maximizes the eye opening in a return-to-zero signal.

An optical transmitter according to the present invention has an optical intensity modulator driving signal as an input, an optical intensity modulator that modulates an optical signal from a light source, and an optical signal that is substantially sinusoidal and synchronized with the optical intensity modulator driving signal. An optical phase modulator that optically modulates an optical signal that has undergone optical intensity modulation based on an optical phase modulator drive signal having a waveform whose polarity is inverted by one period in one data signal section of the intensity modulator drive signal; Are connected in cascade, and the optical phase modulator drive signal to this optical phase modulator is supplied via a switch that is turned on / off by a switch control signal synchronized with the optical intensity modulator drive signal. .

  An optical transmitter according to the present invention is a switch that turns on / off an optical phase modulator drive signal to an optical phase modulator cascaded to an optical intensity modulator by a switch control signal synchronized with the optical intensity modulator drive signal Since the optical phase modulator operates only when an optical signal is input to the optical phase modulator, the power consumption of the optical phase modulator drive circuit can be saved. In addition, when no optical signal is input to the optical phase modulator, phase modulation is not applied. Therefore, when the extinction ratio of the optical intensity modulation is finite, the optical signal remaining when the data signal is “0”. There is an effect that an optical transmitter can be obtained that can prevent the occurrence of a code error due to pulsing after fiber transmission.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an optical transmitter according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes a light source that generates an optical signal, and reference numeral 2 denotes an optical intensity modulator that modulates the optical signal output from the light source 1 in accordance with a data signal. 4 is a data signal input terminal to which a data signal is input, and 5 is a clock signal input terminal to which a clock signal is input. An identifier 6 generates a light intensity modulator drive signal based on the data signal input from the data signal input terminal 4 and the clock signal input from the clock signal input terminal 5. A light intensity modulator drive circuit 7 amplifies the light intensity modulator drive signal output from the discriminator 6 and applies it to the light intensity modulator 2 to drive it. An optical transmitter output terminal 10 outputs an optical signal modulated by the optical transmitter to an optical fiber transmission line. Note that these are portions corresponding to those of the related art shown with the same reference numerals in FIG.

  Further, reference numeral 8a designates a first step for branching the clock signal input from the clock signal input terminal 5 as an optical phase modulator drive signal for driving an optical phase modulator, which will be described later, and delaying the optical phase modulator drive signal. 1 delay device. Reference numeral 8b denotes a second delay device that branches the optical intensity modulator drive signal output from the discriminator 6 as a switch control signal for controlling a switch to be described later, and delays the switch control signal. The light 11 is cascade-connected to the optical intensity modulator 2, performs optical phase modulation on the optical signal modulated by the optical intensity modulator 2, and outputs the obtained optical signal to the optical transmitter output terminal 10. It is a phase modulator.

  An optical phase modulator driving circuit 12 amplifies the optical phase modulator driving signal branched from the clock signal and given a delay by the first delay unit 8 a and drives the optical phase modulator 11. 13 is controlled by the switch control signal delayed by the second delay unit 8b, and is delayed by the first delay unit 8a only when the optical signal is input to the optical phase modulator 11. This is a switch for inputting a clock signal to the optical phase modulator driving circuit 12 as an optical phase modulator driving signal.

  Here, a semiconductor laser diode can be used as the light source 1, and a lithium Niobate Mach-Zehnder modulator, a semiconductor optical modulator, or the like can be used as the light intensity modulator 2. It goes without saying that a modulator integrated semiconductor laser diode in which the light source 1 and the light intensity modulator 2 are integrated can be used. The optical phase modulator 11 is generally a lithium niobate modulator. As the first delay device 8a and the second delay device 8b, a microwave band phase modulator, a phase shifter using a varactor diode, a delay device having a variable path length, or the like can be used. As the light intensity modulator drive circuit 7 and the optical phase modulator drive circuit 12, high-power amplifiers can be procured from the market.

Next, the operation will be described.
The data signal input from the data signal input terminal 4 and the clock signal input from the clock signal input terminal 5 are respectively input to the discriminator 6, and the discriminator 6 generates a light intensity modulator drive signal based on them. . This light intensity modulator drive signal is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2. On the other hand, the clock signal input from the clock signal input terminal 5 is branched and input to the first delay device 8a as an optical phase modulator drive signal. The optical phase modulator drive signal delayed by the first delay unit 8 a is input to the switch 13. The optical phase modulator drive signal output from the switch 13 is sent to the optical phase modulator drive circuit 12 and amplified by the optical phase modulator drive circuit 12 to drive the optical phase modulator 11.

  The optical intensity modulator drive signal generated by the discriminator 6 is also branched and input to the second delay unit 8b as a switch control signal. The switch 13 is controlled to be turned on / off by a switch control signal input via the second delay unit 8b. The delay amount of the second delay unit 8b is set such that the switch 13 is turned on only when the optical signal is input from the optical intensity modulator 2 to the optical phase modulator 11, and the optical phase modulator drive signal is converted into the optical phase. It is set to input to the modulator driving circuit 12.

  The light signal output from the light source 1 is subjected to light intensity modulation according to the data signal by the light intensity modulator drive signal amplified by the light intensity modulator drive circuit 7. In general, a digital signal is represented by “1” when an optical signal exists within a specified time and “0” when it does not exist. Here, FIG. 2 shows signal waveforms of respective parts of the optical transmitter configured as described above. 2A shows an example of a data signal sequence input from the data signal input terminal 4, FIG. 2B shows an example of a waveform of an optical signal modulated by the optical intensity modulator 2, and FIG. ) Shows an example of the waveform of the optical phase modulator drive signal input to the optical phase modulator 11 when the switch 13 is always turned on, and FIG. 2D shows that the switch 13 is turned on by the output of the second delay device 8b. An example of the waveform of the optical phase modulator drive signal input to the optical phase modulator 11 when turned off. FIG. 2 (e) is optical phase modulated with the optical phase modulator drive signal shown in FIG. 2 (c). FIG. 2F shows an example of the waveform of the optical signal after the optical fiber transmission, and FIG. 2F shows an example of the waveform of the optical signal optically phase-modulated with the optical phase modulator drive signal shown in FIG. ing.

  When the data signal series shown in FIG. 2 (a) is input from the data signal input terminal 4, the waveform of the output signal of the light intensity modulator 2 is as shown in FIG. 2 (b). Since the extinction ratio of the light intensity modulator 2 is finite, a slight amount of light remains even when the data signal is “0”. Here, when the switch 13 is always turned on, that is, when the switch 13 is not provided, the optical phase modulator drive signal shown in FIG. 2C is input to the optical phase modulator 11. At this time, the phase of the phase modulation can be adjusted by the delay amount of the first delay device 8a.

  Here, phase modulation and frequency modulation are essentially the same. The fact that the propagation time of an optical wave propagating in an optical fiber differs depending on the frequency (wavelength) is generally called dispersion, and the waveform of a frequency-modulated optical signal changes due to this dispersion. Therefore, the waveform of the optical signal modulated by the optical phase modulator 11 to which the optical phase modulator drive signal shown in FIG. 2C is input becomes the waveform shown in FIG. 2E after the optical fiber transmission. Change. As shown in the figure, even when the data signal is “0”, a slight optical signal remains, and this residual optical signal may be pulsed via optical fiber dispersion by optical phase modulation. obtain. When such a phenomenon occurs, “0” of the data signal may be erroneously determined as “1” on the receiving side.

  Therefore, when the data signal is “0”, the switch 13 is turned off by the switch control signal branched from the light intensity modulator driving signal generated by the discriminator 6. As a result, the waveform of the optical phase modulator drive signal input to the optical phase modulator 11 is as shown in FIG. The optical signal modulated by the optical phase modulator 11 to which the optical phase modulator drive signal as shown in FIG. 2 (d) is input has the waveform shown in FIG. The aforementioned problems are avoided. The timing for driving the switch 13 can be controlled by the delay amount of the second delay device 8b as necessary.

  Although the transmission waveform collapses due to the dispersion of the optical fiber, it is possible to compensate for the waveform collapse due to the dispersion of the optical fiber to some extent by applying optical phase modulation. In order to control the waveform at the receiving end, the depth and phase of optical phase modulation may be controlled. As shown in FIG. 2 (f), when optical phase modulation is performed so that the pulse is return-to-zero at the receiving end, there is an advantage that the reception eye sensitivity is increased and the reception identification sensitivity is increased. is there.

  The optical phase modulator driving circuit 12 uses a high-power amplifier as described above. Depending on the configuration of the amplifier, it is possible to reduce the power consumption when the input is turned off. For example, there are methods such as DC coupling input configuration, class B operation, class C operation and the like.

  In the above description, the optical intensity modulator 2 and the optical phase modulator 11 are directly connected. However, an optical amplifier is provided between the optical intensity modulator 2 and the optical phase modulator 11 as necessary. May be provided. FIG. 3 is a block diagram showing such an optical transmitter according to the first embodiment of the present invention, in which an optical amplifier 14 is arranged between the optical intensity modulator 2 and the optical phase modulator 11. It is. Although the basic operation is the same as that of the optical transmitter shown in FIG. 1, the optical amplifier 14 can set the light intensity level high and suppress the deterioration of the optical S / N ratio. Become. Here, when the optical amplifier 14 is provided, it is desirable to control the path length by using the first and second delay devices 8a and 8b.

As described above, according to the first embodiment, the light source that generates the optical signal and the identification that outputs the signal corresponding to the ON / OFF state of the data signal as the optical intensity modulator drive signal in synchronization with the clock signal. , An optical intensity modulator that modulates the optical signal output from the light source based on the optical intensity modulator drive signal, and an optical phase that optically modulates the optical signal modulated by the optical intensity modulator. A modulator and a clock signal are input, and a signal having a waveform that is a substantially sine wave and whose polarity is inverted by one period in the section of one data signal in the optical intensity modulator drive signal, the peak of the waveform is an optical phase modulator. A first delay unit that outputs an optical phase modulator drive signal delayed so as to be positioned at substantially the center of a section corresponding to one data signal in the optical signal input to the optical signal, and an optical intensity modulator drive signal Light intensity on the optical phase modulator The modulator drive signals such that the optical signal corresponding to the ON state is turned on only in the section to be input, a second delay unit for outputting a switching control signal obtained by delaying the optical intensity modulator drive signal, the second The optical phase modulator includes a switch that is controlled by the switch control signal output from the delay unit and inputs the optical phase modulator drive signal to the optical phase modulator only in a section in which the switch control signal is turned on. Since optical phase modulation is performed based on the optical phase modulator drive signal given via the optical phase modulator, when no optical signal is input to the optical phase modulator, phase modulation is not applied and optical intensity modulation is performed. When the extinction ratio of the optical signal is finite, it is possible to prevent a phenomenon in which the optical signal remaining when the data signal is “0” is pulsed after fiber transmission and becomes a code error. Since you are running an optical phase modulator only when the optical signal to the phase modulator is input, effects such as can save power consumption of the optical phase modulator drive circuit can be obtained.

  Further, since the discriminator is configured to use a signal obtained by branching the light intensity modulator driving signal generated from the data signal and the clock signal as the switch control signal, the switch control signal synchronized with the light intensity modulator driving signal is used. The optical phase modulator can be operated only when the optical signal is input to the optical phase modulator, and the phase when no optical signal is input to the optical phase modulator. Since no modulation is applied, there are effects such as saving power consumption of the optical phase modulator driving circuit and preventing occurrence of a code error.

  In addition, since the optical phase modulator driving signal is delayed using the first delay device and the optical intensity modulator driving signal is delayed using the second delay device, the optical signal output from the phase modulator is used. The phase modulation phase and the on / off timing of the switch can be easily adjusted by the delay amounts of the first and second delay units, and further between the optical intensity modulator and the optical phase modulator. By inserting an optical amplifier into the optical path and controlling the path length by the delay amounts of the first delay device and the second delay device, the light intensity level can be set high, and the optical S / N ratio is degraded. The effect that it becomes possible to suppress is obtained.

Embodiment 2. FIG.
FIG. 4 is a block diagram showing an optical transmitter according to Embodiment 2 of the present invention. In the figure, 1 is a light source, 2 is a light intensity modulator, 4 is a data signal input terminal, 5 is a clock signal input terminal, 6 is a discriminator, 7 is a light intensity modulator drive circuit, 8a is a first delay device, 8b is a second delay device, 10 is an optical transmitter output terminal, 11 is an optical phase modulator, 12 is an optical phase modulator drive circuit, and 13 is a switch, and these are denoted by the same reference numerals in FIG. Since they are equivalent to those in the first embodiment, detailed description thereof is omitted. An optical demultiplexer 15 demultiplexes part of the optical signal input from the optical intensity modulator 2 to the optical phase modulator 11. Reference numeral 16 denotes a photodiode as a light receiver that converts the optical signal demultiplexed by the optical demultiplexer 15 into a switch control signal by an electric signal. Reference numeral 17 denotes an amplifier that amplifies the switch control signal photoelectrically converted by the photodiode 16 and inputs it to the second delay device 8b.

  As described above, the optical transmitter according to the second embodiment does not branch the switch control signal for turning on / off the switch 13 from the optical intensity modulator driving signal generated by the discriminator 6, but the optical phase. It differs from that of the first embodiment in that a part of the optical signal input to the modulator 11 is demultiplexed by the optical demultiplexer 15 and converted into an electric signal by the photodiode 16. Is different.

Next, the operation will be described.
The data signal input from the data signal input terminal 4 and the clock signal input from the clock signal input terminal 5 are input to the discriminator 6, and a light intensity modulator drive signal is generated. This light intensity modulator drive signal is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2. The clock signal input from the clock signal input terminal 5 is branched as an optical phase modulator drive signal and input to the first delay unit 8a. The optical phase modulator drive signal delayed by the first delay unit 8 a is input to the optical phase modulator drive circuit 12 via the switch 13 and is amplified there to drive the optical phase modulator 11. This operation is the same as in the first embodiment.

  On the other hand, a part of the optical signal sent from the optical intensity modulator 2 to the optical phase modulator 11 is demultiplexed by the optical demultiplexer 15 and photoelectrically converted by the photodiode 16 to become a switch control signal by an electric signal. . The switch control signal output from the photodiode 16 is amplified by the amplifier 17. The switch control signal amplified by the amplifier 17 is proportional to the intensity of the optical phase modulator drive signal input to the optical phase modulator 2. The switch 13 is turned on / off by a switch control signal output from the amplifier 17. That is, the switch 13 is turned on only when an optical signal is input to the optical phase modulator 11. As shown in the figure, the control accuracy can be improved by providing the second delay device 8b between the amplifier 17 and the switch 13.

  Further, by replacing the photodiode 16 with an avalanche photodiode, it may be possible to reduce the gain of the amplifier 17 or to omit the amplifier 17.

  Thus, since the optical phase modulator drive signal is supplied to the optical phase modulator 11 only when the optical signal is input, an effect of reducing the power consumption of the optical phase modulator drive circuit 12 can be expected. . Further, when the data signal is “0”, the optical signal that remains slightly is phase-modulated, so that it can be prevented from being pulsed through dispersion of the optical fiber and causing a code error. .

  In the optical transmitter having the configuration shown in FIG. 4, the light intensity modulation component input to the optical phase modulator 11 is extracted from the optical signal input to the optical phase modulator 11. Even if the length of the optical fiber connecting the optical phase modulator 11 varies, it can operate stably.

  Further, it is assumed that an optical amplifier is inserted between the light intensity modulator 2 and the optical phase modulator 11 for the purpose of increasing the S / N ratio of the output light of the optical transmitter. The length of the optical fiber constituting the optical amplifier is considered to be several tens of meters or more, and the fiber length may vary due to a change in environmental temperature. It is known that the propagation delay time of the optical amplifier becomes a maximum of several picoseconds due to a temperature change of 1 ° C. In such a case, the second embodiment described later which is not affected by the delay time fluctuation due to the temperature fluctuation. This is particularly effective for the optical transmitter.

That is, according to the second embodiment, a light source that generates an optical signal, a discriminator that outputs a signal corresponding to an on / off state of a data signal in synchronization with a clock signal, as a light intensity modulator drive signal, and a light source An optical signal output from the optical intensity modulator that modulates the optical intensity based on the optical intensity modulator drive signal, an optical phase modulator that optically modulates the optical signal modulated by the optical intensity modulator, A clock signal is input, and a signal having a waveform that is a substantially sine wave and whose polarity is inverted by one period in the section of one data signal in the optical intensity modulator drive signal is input to the optical phase modulator. A first delay unit that outputs an optical phase modulator drive signal delayed so as to be positioned at substantially the center of a section corresponding to one data signal in the optical signal, and is input to the optical phase modulator from the optical intensity modulator Demultiplexing part of an optical signal A demultiplexer, a photoreceiver that converts the optical signal demultiplexed by the optical demultiplexer, and an output signal of the photoreceiver are input, and the optical intensity is modulated from the optical intensity modulator to the optical phase modulator. A second delayer for outputting a switch control signal obtained by delaying the output signal of the optical receiver so that the optical signal is turned on only during a period in which an optical signal corresponding to the on state of the optical device driving signal is input; The optical phase modulator is provided with a switch that inputs the optical phase modulator drive signal to the optical phase modulator only during a period when the switch control signal is turned on. Since the optical phase modulation is performed on the basis of the optical phase modulator driving signal given by the optical intensity modulator, the switch for turning on / off the optical phase modulator driving signal is controlled from the optical intensity modulator to the optical phase modulator. Input light intensity modulation Since it is executed using a signal extracted from the optical signal, there is an effect that it operates stably without being affected by the fluctuation of the propagation time due to the temperature of the optical fiber connecting the optical intensity modulator and the optical phase modulator. .

Embodiment 3 FIG.
FIG. 5 is a block diagram showing an optical transmitter according to the third embodiment of the present invention. The same reference numerals as those in FIG. In the figure, reference numeral 18 denotes a second clock signal extracted from the output signal of the photodiode 16 amplified by the amplifier 17 and input it to the switch 13 via the first delay unit 8a as an optical phase modulator drive signal. A clock extraction circuit. Reference numeral 19 denotes a branch circuit which branches the output signal of the amplifier 16 into two, one of which is input to the clock extraction circuit 18 and the other as a switch control signal to the second delay device 8b.

As described above, the difference between the third embodiment and the second embodiment is that an optical phase modulator drive signal is branched by the branch circuit 19 instead of the first clock signal input from the clock signal input terminal 5. The second clock signal extracted by the clock extraction circuit 18 from the output signal of the photodiode 16 is used.

Next, the operation will be described.
The optical signal input from the optical intensity modulator 2 to the optical phase modulator 11 is demultiplexed by the optical demultiplexer 15, photoelectrically converted by the photodiode 16, and amplified by the amplifier 17. The output signal of the amplifier 17 is sent to the branch circuit 19 and branched, one of which is input to the second delay unit 8b and the other is input to the clock extraction circuit 18. The signal input to the second delay unit 8b is given a delay as a switch control signal to control on / off of the switch 13. A second clock signal is extracted from the signal input to the clock extraction circuit 18. This second clock signal is input to the first delay unit 8a as an optical phase modulator drive signal, and is sent to the switch 13 with a delay if necessary. As the clock extraction circuit 18, a non-linear clock extraction circuit using a frequency multiplier is generally used.

  As described above, also in the third embodiment, the optical phase modulator drive signal is supplied to the optical phase modulator 11 only when the optical signal is input. Can be expected to be small. Further, when the data signal is “0”, it is possible to prevent a slight residual optical signal from being pulsed through dispersion of the optical fiber and causing a code error by being phase-modulated, Further, since the optical intensity modulation component input to the optical phase modulator 11 is extracted from the optical signal input to the optical phase modulator 11, the optical fiber connecting the optical intensity modulator 2 and the optical phase modulator 11 is extracted. Even if the length of the lens fluctuates, it can operate stably.

  As described above, according to the second and third embodiments, the switch for turning on / off the optical phase modulator driving signal is extracted from the optical signal input to the optical phase modulator and photoelectrically converted. Since it is controlled by the switch control signal, when the extinction ratio of the light intensity modulation is finite, the phenomenon that the optical signal remaining when the data signal is “0” is pulsed after fiber transmission and becomes a code error does not occur. In addition to saving power consumption of the optical phase modulator drive circuit, it is not affected by variations in propagation time due to the temperature of the optical fiber connecting the optical intensity modulator and optical phase modulator. An effect is obtained.

In the third embodiment, the second clock signal is extracted by the clock extraction circuit from the signal obtained by converting the optical signal demultiplexed by the optical demultiplexer into the electric signal by the light receiver, and the second clock signal is extracted from the second clock signal. Since it is configured to be input to the switch as a drive signal, there is an effect that it operates stably without being affected by fluctuations in propagation time due to the temperature of the optical fiber connecting the optical intensity modulator and the optical phase modulator.

Embodiment 4 FIG.
FIG. 6 is a block diagram showing an optical transmitter according to Embodiment 4 of the present invention. The same reference numerals are assigned to the corresponding parts, and the description thereof is omitted. In the figure, reference numeral 20 denotes an optical phase modulator which removes the high frequency component from the output signal of the photodiode 16 amplified by the amplifier 17 and drives the optical phase modulator 2 only when the optical signal is input thereto. It is a low-pass filter as an optical phase modulator drive signal generation circuit that generates a drive signal. Thus, the fourth embodiment is different from the third embodiment in that the output signal of the amplifier 17 is directly connected to the optical phase modulator driving circuit 12 via the low-pass filter 20.

Next, the operation will be described.
Here, FIG. 7 is an operation explanatory view showing signal waveforms of respective parts of the optical transmitter configured as described above. FIG. 7A shows an example of a data signal sequence inputted from the data signal input terminal 4, FIG. 7B shows an example of the waveform of an optical signal modulated by the optical intensity modulator 2, and FIG. ) Shows an example of the waveform of the optical phase modulator drive signal output from the low-pass filter 20.

  A signal photoelectrically converted by the photodiode 16 and output from the amplifier 17 is a light intensity modulator driving signal as shown in FIG. When this signal is input to the low-pass filter 20 and its high-frequency component is removed, a signal as shown in FIG. 7C is obtained. The waveform of the output signal of the low-pass filter 20 is similar to the phase modulation waveform when the switch 13 shown in FIG. 2D is turned on / off. The signal from which the high-frequency component is removed by the low-pass filter 20 is sent to the optical phase modulator driving circuit 12 as an optical phase modulator driving signal, where it is amplified and drives the optical phase modulator 11. The signal output from the optical phase modulator driving circuit 12 is proportional to the intensity of the optical signal input from the optical intensity modulator 2 to the optical phase modulator 11.

  Note that the optical phase modulator drive signal shown in FIG. 7C is different from that shown in FIG. 2D when “1” is continuous, but is relatively inter-symbol when “1” is continuous. Since there is little interference, an effect close to that of the optical transmitter according to the third embodiment shown in FIG. 5 can be obtained.

  Further, if the output signal of the amplifier 17 is input to the low-pass filter 20 via a delay device, the phase of the optical phase modulator drive signal can be set more accurately.

  As described above, according to the fourth embodiment, since the output signal of the amplifier is directly input to the optical phase modulator driving circuit via the low-pass filter, the optical phase modulator driving signal is band-limited. Since the optical phase modulator operates only when the optical intensity modulator driving signal is used and the optical signal is input to the optical phase modulator, the power consumption of the optical phase modulator driving circuit can be saved. The optical signal remaining at the time of data “0” when the extinction ratio of the light intensity modulation is finite can be prevented from being pulsed after fiber transmission and causing a sign error. Compared to the optical transmitter of aspect 3, there is an effect that an optical transmitter that is less affected by propagation time variation due to the temperature of the optical fiber connecting the optical intensity modulator and the optical phase modulator can be realized with fewer parts. is there.

Embodiment 5 FIG.
FIG. 8 is a block diagram showing an optical transmitter according to Embodiment 5 of the present invention. The same reference numerals are assigned to the corresponding parts, and the description thereof is omitted. In the figure, 8c gives a delay to the signal branched from the light intensity modulator drive signal generated based on the data signal and the clock signal, which is input from the data signal input terminal 4 and the clock signal input terminal 5 by the discriminator 6. It is a delay device. The fifth embodiment is different from the fourth embodiment in that not the output signal of the amplifier 17 but the output signal of the delay unit 8 c is input to the low-pass filter 20.

Next, the operation will be described.
The discriminator 6 generates a light intensity modulator drive signal for driving the light intensity modulator 2 based on the data signal input from the data signal input terminal 4 and the clock signal input from the clock signal input terminal 5. To do. This light intensity modulator drive signal is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2. The light intensity modulator drive signal output from the discriminator 6 is branched and also input to the delay unit 8c. The delay unit 8 c gives a delay to the light intensity modulator drive signal and inputs it to the low-pass filter 20. The low-pass filter 20 removes the high frequency component of the output signal of the delay unit 8 c to generate an optical phase modulator drive signal, and sends it to the optical phase modulator drive circuit 12. The optical phase modulator driving circuit 12 amplifies the optical phase modulator driving signal and drives the optical phase modulator 11. The signal output from the optical phase modulator driving circuit 12 is proportional to the intensity of the optical signal input from the optical intensity modulator 2 to the optical phase modulator 11.

  Also in the fifth embodiment, the waveform of the data signal when “1” is continuous is different from that shown in FIG. 2D, but when “1” is continuous, the intersymbol interference is relatively small. An effect close to that of the optical transmitter according to the first embodiment shown can be obtained.

  As described above, according to the fifth embodiment, the output signal of the discriminator delayed by the delay unit is directly input to the optical phase modulator driving circuit via the low-pass filter. The optical phase modulator drive circuit uses the band-limited optical intensity modulator drive signal as the optical drive signal, and the optical phase modulator operates only when the optical signal is input to the optical phase modulator. Power consumption can be saved, and when the extinction ratio of the light intensity modulation is finite, it is possible to prevent the phenomenon that the optical signal remaining at the time of data “0” is pulsed after fiber transmission and becomes a code error. In addition, as compared with the optical transmitter of the first embodiment, the number of components is less, and the light is not affected by the fluctuation of the propagation time due to the temperature of the optical fiber connecting the optical intensity modulator and the optical phase modulator. The effect of realizing a transmitter A.

Embodiment 6 FIG.
FIG. 9 is a block diagram showing an optical transmitter according to the sixth embodiment of the present invention. The same reference numerals are assigned to the corresponding parts, and the description thereof is omitted. In the figure, reference numeral 21 denotes a branch circuit that branches from the clock signal input to the clock signal input terminal 5 and branches the optical phase modulator drive signal delayed by the first delay unit 8a into two. This is an inverter circuit that inverts one polarity of the signal branched by the branch circuit 21. 23 is branched from the optical intensity modulator driving signal output from the discriminator 6, and the signal delayed by the second delay unit 8b is used as a switching control signal, and the two lights having different polarities are controlled by the signal. This is a 2-input 1-output selector switch that selects one of the phase modulator drive signals and inputs the selected signal to the optical phase modulator drive circuit 12. Reference numeral 24 denotes an optical phase modulator drive signal inversion means which is formed by the branch circuit 21, the inverter circuit 22, and the changeover switch 23 and inverts the polarity of the optical phase modulator drive signal.

Next, the operation will be described.
The discriminator 6 generates a light intensity modulator drive signal for driving the light intensity modulator 2 based on the data signal input from the data signal input terminal 4 and the clock signal input from the clock signal input terminal 5. To do. This light intensity modulator drive signal is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2. Further, the optical intensity modulator drive signal output from the discriminator 6 is branched and input to the second delay unit 8b and delayed, and becomes a switching control signal for controlling the changeover switch 23.

  On the other hand, the optical phase modulator drive signal branched from the clock signal input from the clock signal input terminal 5 is input to the first delay unit 8a and given a delay. The optical phase modulator drive signal delayed by the first delay unit 8a is input to the branch circuit 21 and branched into two. One of the output signals of the branch circuit 21 is input to one input terminal of the changeover switch 23, and the other is input to the inverter circuit 22. The inverter circuit 22 inverts the polarity of the optical phase modulator drive signal from the branch circuit 21 and inputs it to the other input terminal of the changeover switch 23. The selector switch 23 is switched by a switching control signal from the second delay unit 8b, selects an optical phase modulator driving signal input from one of the input terminals, and outputs the selected signal from the output terminal. The optical phase modulator drive signal output from the changeover switch 23 is sent to the optical phase modulator drive circuit 12 and amplified to drive the optical phase modulator 11.

  Here, the optical signal output from the light source 1 is subjected to optical intensity modulation in accordance with the data signal in the optical intensity modulator 2 by the optical intensity modulator driving signal amplified by the optical intensity modulator driving circuit 7. The optical signal modulated by the optical intensity modulator 2 is input to the optical phase modulator 11. The optical phase modulator 11 has a polarity of an optical phase modulator drive signal output from the changeover switch 23 when light is present (when “1”) and when light is not present (when “0”). Is controlled to reverse.

  The optical phase modulator drive signal inversion means 24 formed by the branch circuit 21, the inverter circuit 22, and the changeover switch 23 outputs the optical phase by the switching control signal synchronized with the optical intensity modulator drive signal as described above. An operation of inverting the polarity of the modulator drive signal is performed. A device that realizes the same function as the optical phase modulator drive signal inverting means 24 alone includes a microwave phase modulator. The inverter circuit 22 can be replaced with a suitable delay device.

  Here, FIG. 10 is an operation explanatory diagram showing signal waveforms of respective parts of the optical transmitter configured as described above. FIG. 10A shows an example of a data signal sequence input from the data signal input terminal 4, FIG. 10B shows an example of the waveform of an optical signal modulated by the optical intensity modulator 2, and FIG. ) Is an example of a waveform of an optical phase modulator driving signal input to the optical phase modulator 11, and FIG. 10D is an optical signal that is optical phase modulated by the optical phase modulator driving signal shown in FIG. The example of a waveform after optical fiber transmission is shown.

  When the data signal series shown in FIG. 10A is input from the data signal input terminal 4, the waveform of the optical signal output from the light intensity modulator 2 is as shown in FIG. Since the extinction ratio of the light intensity modulator 2 is finite, a slight amount of light remains even when the data signal is “0”. When the optical signal having the waveform shown in FIG. 10B is output from the optical intensity modulator 2, the optical phase modulator driving signal having the waveform shown in FIG. 10C is input to the optical phase modulator 11. In the optical signal modulated by the optical phase modulator 11 with the optical phase modulator driving signal having the waveform shown in FIG. 10C, the waveform after the optical fiber transmission is caused by the dispersion of the optical fiber. It changes as shown in d).

  Here, the optical signal slightly remaining when the data signal is “0” is optically phase-modulated in the opposite direction to that when the data signal is “1”. It will not be converted. Therefore, the possibility of erroneously determining “0” of the data signal as “1” on the receiving side is small.

  As described above, according to the sixth embodiment, when the optical signal is input to the optical phase modulator using two types of optical phase modulator drive signals of the normal phase and the reverse phase, the optical phase modulator is input. Since the optical phase modulator is driven with the optical phase modulator drive signal of different polarity, the data signal is “0” when the extinction ratio of the light intensity modulation is finite. The phenomenon that the residual optical signal is pulsed after fiber transmission to generate a code error can be prevented, and the eye opening ratio can be increased.

  Further, according to the sixth embodiment, the optical phase modulator drive signal inverting means includes a branch circuit for branching the optical phase modulator drive signal in two, an inverter circuit for inverting one of the polarities, and an output of the branch circuit Since one of the other signal and one of the output signals of the inverter circuit is constituted by a changeover switch that is selected in accordance with a changeover control signal branched from the light intensity modulator drive signal generated by the discriminator, prevention of code errors And an optical transmitter capable of improving the eye opening ratio can be easily realized.

  In addition, although what was applied to the optical transmitter of Embodiment 1 shown in FIG. 1 was shown in the said description, it cannot be overemphasized that it can apply also to the optical transmitter of Embodiment 2 shown in FIG. FIG. 11 is a block diagram showing such an optical transmitter. As a switching control signal for controlling the selector switch 23 of the optical phase modulator driving signal inverting means 24, the optical intensity modulator driving output from the discriminator 6 is shown. The optical signal transmitted from the optical intensity modulator 2 to the optical phase modulator 11 is demultiplexed by the optical demultiplexer 15 and photoelectrically converted by the photodiode 16 instead of being obtained by branching the signal. Using electrical signals. Therefore, the same effects as those of the first embodiment can be obtained, and a stable operation can be performed without being affected by the fluctuation of the propagation time due to the temperature of the optical fiber.

  That is, according to the modification of the sixth embodiment, the optical phase modulator drive signal inverting means includes a branch circuit that divides the optical phase modulator drive signal into two branches, an inverter circuit that inverts one polarity thereof, and a branch. The optical signal sent to the optical phase modulator from the optical intensity modulator demultiplexed by the optical demultiplexer, one of the output signal of the circuit and the output signal of the inverter circuit, is converted into an electrical signal by the photoreceiver. Thus, there is an effect that it is possible to easily realize an optical transmitter that operates stably, can prevent a code error, and can improve the eye opening ratio.

Embodiment 7 FIG.
FIG. 12 is a block diagram showing an optical transmitter according to Embodiment 7 of the present invention. The same reference numerals are assigned to the corresponding parts, and the description thereof is omitted. In the figure, reference numeral 25 denotes a low-pass filter that removes the high-frequency component of the signal branched from the optical intensity modulator drive signal output from the discriminator 6 and inputs the signal to the second delay unit 8b. 26 is an optical phase modulator drive by adding the output signal of the low-pass filter 25 and the signal branched from the clock signal input to the clock signal input terminal 5 and delayed by the first delay unit 8a. An adder that generates a signal. As the adder 26, various analog adders and multiplexers can be used.

Next, the operation will be described.
The data signal and clock signal input from the data signal input terminal 4 and the clock signal input terminal 5 are input to the discriminator 6 to generate a light intensity modulator drive signal. This light intensity modulator drive signal is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2. The light intensity modulator drive signal output from the discriminator 6 is branched and also input to the low-pass filter 25. The signal from which the high-frequency component has been removed by the low-pass filter 25 is input to the second delay unit 8b and given a delay.

  On the other hand, a signal branched from the clock signal input from the clock signal input terminal 5 is input to the first delay unit 8a and given a delay. The signal output from the first delay unit 8 a is input to one input terminal of the adder 26, and the signal output from the second delay unit 8 b is input to the other input terminal of the adder 26. The level of the signals input to the two input terminals of the adder 26 is adjusted as necessary. An attenuator or an amplifier may be used for this signal level adjustment.

  Here, FIG. 13 is an operation explanatory view showing signal waveforms of respective parts of the optical transmitter configured as described above. FIG. 13A shows an example of a data signal sequence input from the data signal input terminal 4, FIG. 13B shows an example of the waveform of an optical signal modulated by the optical intensity modulator 2, and FIG. ) Is a waveform example of a signal input from the second delay unit 8b to the adder 26, FIG. 13D is a waveform example of a signal input from the second delay unit 8b to the adder 26, and FIG. ) Is an example of the waveform of the optical phase modulator drive signal output from the adder 26, and FIG. 13 (f) is an optical fiber transmission of the optical signal phase-modulated with the optical phase modulator drive signal shown in FIG. 13 (e). A later waveform example is shown.

  When the data signal series shown in FIG. 13A is input from the data signal input terminal 4, the waveform of the optical signal output from the light intensity modulator 2 is as shown in FIG. 13B. The signal branched from the optical intensity modulator drive signal output from the discriminator 6 at that time is band-limited by the low-pass filter 25, delayed by the second delay unit 8b, and has the waveform shown in FIG. A signal is input to one of the input terminals of the adder 26. The signal branched from the clock signal is input to the other input terminal of the adder 26 as a signal having the waveform shown in FIG. Here, it is assumed that the amplitude of the signal input from the second delay unit 8b is larger than the amplitude of the signal input from the first delay unit 8a.

  The signal input to the adder 26 from the second delay unit 8b is convex upward when the data signal is "1" as shown in FIG. 13C, but is added from the first delay unit 8a. As shown in FIG. 13D, the signal input to the device 26 is convex downward when the data signal is “1”. Therefore, the waveform of the signal output from the adder 26 obtained by adding them is as shown in FIG. The waveform shown in FIG. 13 (e) is similar to the waveform shown in FIG. 10 (c), and the optical signal is optically phase-modulated with the optical phase modulator drive signal having the waveform shown in FIG. 13 (e). However, as shown in FIG. 13F, the waveform after transmission through the optical fiber is a waveform with a low possibility of erroneously determining “0” of the data signal as “1” on the receiving side.

  Here, in general, it is easy to obtain the adder 26 having an operation band wider than that of the changeover switch 23 in the sixth embodiment shown in FIG. Therefore, the optical transmitter according to the seventh embodiment has an advantage that it is easier to implement.

  As described above, according to the seventh embodiment, when an optical signal is input to the optical phase modulator by adding the optical intensity modulator driving signal and the clock signal as the optical phase modulator driving signal. Therefore, when the extinction ratio of the light intensity modulation is finite, even if the data signal is “0”, the remaining optical signal is An effect is obtained that it is possible to more easily realize an optical transmitter that can prevent a phenomenon that a code error is generated by being pulsed after fiber transmission and can increase an eye opening ratio.

Embodiment 8 FIG.
FIG. 14 is a block diagram showing an optical transmitter according to the eighth embodiment of the present invention. The same reference numerals are assigned to the corresponding parts, and the description thereof is omitted. In the figure, reference numeral 27 denotes a return-to-zero conversion circuit for converting the optical intensity modulator drive signal output from the discriminator 6 into a return-to-zero code. Reference numeral 28 denotes the return-to-zero conversion circuit 27. Andand gate. As described above, the eighth embodiment uses the light intensity modulator driving signal converted from the non-return-to-zero code to the return-to-zero code by the return-to-zero conversion circuit 27, thereby modulating the light intensity. The second embodiment is different from the first embodiment in that the device 2 is driven and the switch 13 is controlled.

Next, the operation will be described.
The data signal and clock signal input from the data signal input terminal 4 and the clock signal input terminal 5 are input to the discriminator 6 to generate a light intensity modulator drive signal. Here, the light intensity modulator drive signal output from the discriminator 6 is a non-return-to-zero code. The light intensity modulator driving signal based on this non-return-to-zero code is input to the return-to-zero conversion circuit 27, and the clock signal input from the clock signal input terminal 5 in the AND gate 28 constituting the non-return-to-zero code. And is converted to a return-to-zero code. The light intensity modulator drive signal based on the return-to-zero code is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2. Accordingly, the optical intensity modulator 2 outputs an optical signal whose optical intensity is modulated in a return-to-zero format to the optical phase modulator 11.

  The light intensity modulator drive signal converted into the return-to-zero code by the return-to-zero conversion circuit 27 is branched and also input to the second delay unit 8b. A delay is given by the device 8b and sent to the switch 13 as a switch control signal. On the other hand, the clock signal input from the clock signal input terminal 5 passes through the first delay unit 8a and is input to the switch 13 as an optical phase modulator drive signal. The switch 13 is controlled to be turned on / off by a switch control signal output from the second delay device 8b. Only when an optical signal is input to the optical phase modulator 11, the switch 13 receives the signal from the first delay device 8a. The output optical phase modulator drive signal is input to the optical phase modulator drive circuit 12.

  In the above description, the return-to-zero conversion circuit 27 uses the AND gate 28. However, the return-to-zero conversion circuit 27 is not limited to this, and for example, a mixer is used. It is also possible to realize this using, for example. As a method for obtaining a return-to-zero modulated optical signal, a second optical intensity modulator driven by a clock signal can also be used.

  As described above, according to the eighth embodiment, a signal obtained by converting the output signal of the discriminator based on the non-return-to-zero code into the return-to-zero code is used as the light intensity modulator driving signal. Therefore, the optical phase modulator can be used only when the optical signal modulated in the return-to-zero format by the optical intensity modulator is input to the optical phase modulator and the optical signal is input to the optical phase modulator. Therefore, the power consumption of the optical phase modulator driving circuit can be saved, and when the extinction ratio of the optical intensity modulation is finite, the optical signal remaining at the time of data “0” is pulsed after the fiber transmission and encoded. Not only is it possible to prevent the occurrence of erroneous phenomena, but the use of return-to-zero modulated optical signals generally has advantages such as reduced intersymbol interference with adjacent pulses. Be used in combination the phase modulation in the return-to-zero modulated optical signal, effects such as eye opening ratio at the receiving end can be improved is obtained.

  In the above description, in the optical transmitter shown in the first embodiment, the optical intensity modulator driving signal output by the discriminator 6 with the non-return-to-zero code is converted into the return-to-zero code. However, the present invention can also be applied to the optical transmitters shown in the second to seventh embodiments, and has the same effect as the case of the description applied to the optical transmitter according to the first embodiment. .

Embodiment 9 FIG.
FIG. 15 is a block diagram showing an optical transmitter according to the ninth embodiment of the present invention. The same reference numerals are assigned to the corresponding parts, and description thereof is omitted. In the figure, 8d is a delay device that gives a delay to the signal branched from the clock signal input from the clock signal input terminal 5, and 29 is the frequency of the clock signal delayed by this delay device 8d. Is a frequency multiplier that inputs the signal to the optical phase modulator drive circuit 12. As the frequency multiplier 29, for example, a doubler using a diode can be used. As described above, the ninth embodiment is different from the eighth embodiment in that the clock signal obtained by multiplying the frequency is used as the optical phase modulator drive signal.

Next, the operation will be described.
The data signal and clock signal input from the data signal input terminal 4 and the clock signal input terminal 5 are input to the discriminator 6 to generate a light intensity modulator drive signal. The light intensity modulator drive signal output from the discriminator 6 is a non-return-to-zero code. The light intensity modulator driving signal based on the non-return-to-zero code is input to the return-to-zero conversion circuit 27 and converted into a return-to-zero code. The light intensity modulator drive signal based on the return-to-zero code is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2, and the return-to-zero signal is output from the light intensity modulator 2. An optical signal whose light intensity is modulated in the form is output to the optical phase modulator 11.

  On the other hand, the clock signal input from the clock signal input terminal 5 is branched and input to the frequency multiplier 29 via the delay unit 8d. The frequency multiplier 29 multiplies the frequency of this clock signal and sends it to the optical phase modulator drive circuit 12 as an optical phase modulator drive signal. The optical phase modulator drive circuit 12 amplifies the input optical phase modulator drive signal, sends it to the optical phase modulator 11, and drives it.

  Here, FIG. 16 is an operation explanatory diagram showing signal waveforms of respective parts of the optical transmitter configured as described above. 16A shows an example of a data signal sequence input from the data signal input terminal 4, and FIG. 16B shows an example of a waveform of an optical signal that has been optical intensity modulated by the optical intensity modulator 2. FIG. (C) is a waveform example of an optical phase modulator drive signal output from the optical phase modulator drive circuit 12 to the optical phase modulator 11, and FIG. 16 (d) is an optical phase modulator drive signal shown in FIG. 16 (c). 4 shows an example of a waveform of an optical signal phase-modulated by the optical fiber after transmission.

  When the data signal sequence shown in FIG. 16A is input from the data signal input terminal 4, the waveform of the optical signal output from the optical intensity modulator 2 that performs optical intensity modulation in a return-to-zero format is shown in FIG. 16 (b). On the other hand, the clock signal input from the clock signal input terminal 5 is sent to the frequency multiplier 29 via the delay unit 8d, and the frequency is multiplied. From this frequency multiplier 29, a sine wave having a period twice that of the data series is input to the optical phase modulator drive circuit 12. The optical phase modulator drive circuit 12 amplifies it, sends it to the optical phase modulator 11 as an optical phase modulator drive signal shown in FIG. 16C, and drives it.

  With the principle described with reference to FIG. 26 for the conventional optical transmitter, the output signal of the optical intensity modulator 2 shown in FIG. 16B is pulse-compressed, and after optical fiber transmission, as shown in FIG. 16D. Thus, the waveform is more advantageous for reception with more open eyes. Here, the degree of pulse compression is determined by the frequency shift amount of frequency modulation resulting from optical phase modulation and the dispersion of the optical fiber. The frequency shift amount is proportional to the frequency of the optical phase modulation signal if the degree of phase modulation is the same. For this reason, when the frequency of the optical phase modulator drive signal for driving the optical phase modulator 11 is doubled, the amplitude of the optical phase modulator drive signal necessary for obtaining the pulse compression effect can be halved, Power consumption can be reduced.

  In order to make the frequency of the optical phase modulator drive signal twice the data modulation frequency, the duty of the light intensity modulated pulse should be ½ or less, and the optical phase modulator drive signal In order to make the frequency three times the data modulation frequency, it is desirable to set the duty of the light intensity modulated pulse to 1/3 or less.

  Further, when the optical signal modulated by the optical intensity modulator 2 is not input to the optical phase modulator 11, the signal input to the optical phase modulator driving circuit 12 as in the eighth embodiment. Providing the switch 13 for turning off the power is further advantageous in improving transmission characteristics and reducing power consumption. In that case, as shown in the above embodiments, the switch 13 is controlled by photoelectrically converting the output signal of the discriminator 6 or the optical signal input to the optical phase modulator 11 with a light receiver such as a photodiode 16. Can be used.

  As described above, according to the ninth embodiment, the optical signal modulated with the return-to-zero code by the optical intensity modulator is input to the optical phase modulator, and the optical phase modulator is driven. As the optical phase modulator drive signal, a signal obtained by multiplying the clock signal is used, so the amplitude of the optical phase modulator drive signal to obtain the required pulse compression effect can be reduced, and the optical phase modulator drive The effect that the power consumption of the circuit can be saved is obtained.

  That is, according to the ninth embodiment, an optical phase modulator drive signal for driving an optical phase modulator to which an optical signal modulated with a return-to-zero code is input is clocked by a frequency multiplier. Since it is configured to use a signal obtained by multiplying the frequency of the signal, the amplitude of the optical phase modulator drive signal can be reduced if the frequency is increased, so that the power consumption of the optical phase modulator drive circuit can be saved. effective.

Embodiment 10 FIG.
FIG. 17 is a block diagram showing an optical transmitter according to the tenth embodiment of the present invention. The same reference numerals as those in FIGS. 12 and 14 denote the same parts, and a description thereof will be omitted. The difference between the tenth embodiment and the seventh embodiment shown in FIG. 12 is that the low-pass filter 25 is removed and the output signal of the discriminator 6 is returned to zero by the return-to-zero conversion circuit 27. It has been converted into a code.

Next, the operation will be described.
The light intensity modulator drive signal generated by the discriminator 6 is converted from a non-return-to-zero code to a return-to-zero code by a return-to-zero conversion circuit 27 and is sent to the light intensity modulator drive circuit 7. Sent. The light intensity modulator drive circuit 7 amplifies it and inputs it to the light intensity modulator 2. Accordingly, the optical signal sent from the optical intensity modulator 2 to the optical phase modulator 11 is optically modulated in a return-to-zero format.

  On the other hand, the signal branched from the output signal of the return-to-zero conversion circuit 27 and the signal branched from the clock signal input to the clock signal input terminal 5 are the second delay unit 8b and the first delay. A delay is given by the unit 8 a to perform phase control, which is input to the adder 26. The signal level of the signal input to the adder 26 is optimized using an attenuator or an amplifier as necessary. These two signals are added by the adder 26. As a result, the optical phase modulator drive signal having the waveform shown in FIG. 13 (e) is input from the adder 26 to the optical phase modulator drive circuit 12. Therefore, as in the case of using a non-return-to-zero code, intersymbol interference does not occur when data signals are “1” continuous.

  As described above, according to the tenth embodiment, the optical phase modulator is driven by the optical phase modulator driving signal obtained by adding the signal converted by the return-to-zero conversion circuit 27 and the clock signal. As in the case of using a non-return-to-zero code, intersymbol interference does not occur when the data signal is “1” continuous, and the transmission characteristics can be improved more effectively.

Embodiment 11 FIG.
18 is a block diagram showing an optical transmitter according to an eleventh embodiment of the present invention. The same reference numerals as those in FIGS. 15 and 17 denote the same parts, and a description thereof will be omitted. In the eleventh embodiment, the clock signal delayed by the first delay unit 8a is not input to the adder 26 as it is, but is frequency-multiplied by the frequency multiplier 29 and then input to the adder 26. This is different from the case of the tenth embodiment shown in FIG.

Next, the operation will be described.
The light intensity modulator drive circuit 7 amplifies the light intensity modulator drive signal converted by the return-to-zero conversion circuit 27 into a return-to-zero code and inputs the amplified signal to the light intensity modulator 2. Accordingly, the optical signal sent from the optical intensity modulator 2 to the optical phase modulator 11 is optically modulated in a return-to-zero format. Further, the output signal of the return-to-zero conversion circuit 27 is branched and sent to the second delay unit 8b, and after delaying and phase adjustment, it is input to the adder 26. On the other hand, the clock signal input to the clock signal input terminal 5 is also branched, delayed by the first delay unit 8 a and subjected to phase adjustment, and then input to the frequency multiplier 29. The frequency of the clock signal is multiplied by the frequency multiplier 29 and then input to the adder 26. The signal level of each signal input to the adder 26 is optimized using an attenuator or an amplifier as necessary. These two signals are added by an adder 26 and input to the optical phase modulator driving circuit 12 as an optical phase modulator driving signal. The optical phase modulator driving circuit 12 amplifies and drives the optical phase modulator 11.

  As described above, according to the eleventh embodiment, when a frequency doubler is used as the frequency multiplier 29, the output of the optical phase modulator driving circuit 12 is the same as in the ninth embodiment shown in FIG. Even if the amplitude is halved, the same frequency shift amount as in the case of the tenth embodiment shown in FIG. 17 can be applied, so that the same transmission characteristics as in the tenth embodiment can be obtained, and the optical Since the output level of the phase modulator driving circuit 12 can be reduced, it is possible to obtain an effect such that power consumption can be reduced.

Embodiment 12 FIG.
FIG. 19 is a block diagram showing an optical transmitter according to the twelfth embodiment of the present invention. The same reference numerals are assigned to the corresponding parts, and the description thereof is omitted. In the figure, 3 is a polarization scrambler for making the polarization state of the optical signal output from the optical transmitter output terminal 10 random on average, and 9 is a delay given by the first delay unit 8a. This is a polarization scrambler drive circuit that amplifies the received signal, inputs it to the polarization scrambler 3 as a polarization scrambler drive signal, and drives it. As described above, in the twelfth embodiment, the polarization scrambler 3 is used as the optical phase modulator 11, and the optical phase modulator drive circuit 12 is replaced by the polarization scrambler drive circuit 9 accordingly. The difference from Embodiment 8 is that a signal delayed by branching is used as a polarization scrambler drive signal.

Next, the operation will be described.
The discriminator 6 generates a light intensity modulator driving signal based on a non-return-to-zero code from the data signal and the clock signal input from the data signal input terminal 4 and the clock signal input terminal 5. This light intensity modulator drive signal is input to the return-to-zero conversion circuit 27 and converted from a non-return-to-zero code to a return-to-zero code. The light intensity modulator drive signal based on the return-to-zero code is amplified by the light intensity modulator drive circuit 7 and input to the light intensity modulator 2, and the light intensity modulator 2 returns the signal in a return-to-zero format. The optical signal whose light intensity has been modulated is output to the polarization scrambler 3. The signal branched from the return-to-zero optical intensity modulator drive signal output from the return-to-zero conversion circuit 27 is also input to the second delay unit 8b to be delayed. , And sent to the switch 13 as a switch control signal.

  On the other hand, the signal branched from the clock signal input from the clock signal input terminal 5 is delayed through the first delay unit 8a and input to the switch 13 as a polarization scrambler drive signal. The switch 13 is controlled to be turned on / off by a switch control signal output from the second delay device 8b. Only when an optical signal is input to the polarization scrambler 3, the switch 13 receives the signal from the first delay device 8a. The output polarization scrambler drive signal is input to the polarization scrambler drive circuit 9. The polarization scrambler 3 driven by the polarization scrambler drive signal from the polarization scrambler drive circuit 9 has an average random polarization state of the optical signal output from the optical transmitter output terminal 10. And The polarization scrambler 3 can suppress the effect of deterioration or fluctuation of the optical S / N ratio due to polarization hole burning in the optical amplifier used in the transmission path or polarization dependence loss of the transmission path.

  Here, as the polarization scrambler 3, a lithium niobate optical phase modulator is generally used, and this has the feature that phase modulation occurs simultaneously with polarization modulation, as described with reference to FIG. Therefore, the phenomenon that the receiving side erroneously determines “1” when the data signal is “0” is also shown in FIG. 14 in the optical transmitter according to the twelfth embodiment shown in FIG. It can be avoided as in the case of Embodiment 8, and the power consumption can be reduced in the same manner.

  That is, in all the above embodiments of the present invention, the optical phase modulator 11 can be replaced with the polarization scrambler 3. This is because the polarization scrambler 3 is a kind of optical phase modulator.

  Note that the optical transmitter of the twelfth embodiment shown in FIG. 19 may cause a slight problem in the degree of polarization that can be achieved. Hereinafter, the polarization scrambler operation in the optical transmitter of FIG. 19 will be described with reference to FIG. Here, FIG. 20A shows an example of the trajectory of the polarization state of the optical signal output from the polarization scrambler 3 when optical intensity modulation is performed with a return-to-zero code and the optical signal is polarization scrambled. FIG. 20B shows a waveform example of a polarization scrambler driving signal given to the polarization scrambler 3 at that time, and FIG. 20C shows the polarization scrambler 3 from the light intensity modulator 2 at that time. 2 shows an example of a waveform of an optical signal that is optical intensity modulated with a return-to-zero code input to the.

  Here, the polarization state of the optical signal output when an optical signal that has been optical intensity modulated with a non-return-to-zero code or an optical signal that has not been optical intensity modulated is input to the polarization scrambler 3, Drawing a locus on a great circle on the Poincare sphere is as described with reference to FIG. As shown in FIG. 20 (c), the optical signal input to the polarization scrambler 3 is light intensity modulated with a return-to-zero code, and the polarization scrambler driving circuit 9 outputs the polarization scrambler. 20B, the phase of the polarization scrambler driving signal for driving 3 is as shown in FIG. 20B. The locus of the polarization state of the optical signal output from the polarization scrambler 3 at that time is shown in FIG. As shown in (a). As shown in the figure, the polarization state when the optical signal amplitude is weak is plotted inside the Poincare sphere.

As explained in FIG. 25, in order for the degree of polarization to become zero, on the Poincare sphere,
(A) The probability of existing in the L hemisphere and the probability of existing in the R hemisphere within a certain time are equal (B) The probability of existing in the Q hemisphere and the probability of existing in the P hemisphere within a certain time (C) It is necessary to satisfy the three conditions that the probability of existing in the H-side hemisphere and the probability of existing in the V-side hemisphere are equal within a certain time.

  In this case, as shown in FIG. 20A, the polarization state does not draw a trajectory in the R-side hemisphere, and thus the condition (A) cannot be satisfied. As described above, in the optical transmitter according to the twelfth embodiment using the light intensity modulation with the return-to-zero code, the degree of polarization may not be zero. The degree of polarization that can be achieved depends on the phase relationship between the light intensity modulation waveform and the polarization scrambler driving waveform.

  As described above, in the optical transmitter configured as shown in FIG. 19 according to the twelfth embodiment, the degree of polarization may not be zero. However, the degree of polarization is sufficiently small as compared with the case where the polarization scrambler 3 is not used. In many cases, it is not a serious problem to be able to achieve.

  As described above, according to the twelfth embodiment, since the optical phase modulator is replaced by the polarization scrambler, the degree of polarization of the output optical signal is sufficiently increased as compared with the case where the polarization scrambler is not used. The effect which can be made small is acquired.

  In the above description, the polarization scrambler 3 is used as the optical phase modulator 11 of the eighth embodiment shown in FIG. 14, but the other first to seventh embodiments and the other embodiments are described. The polarization scrambler 3 may be used for the optical phase modulator 11 in the ninth to eleventh embodiments, and the same effects as those applied to the eighth embodiment are achieved.

Embodiment 13 FIG.
FIG. 21 is a block diagram showing an optical transmitter according to the thirteenth embodiment of the present invention. Corresponding portions are denoted by the same reference numerals as those in FIG. 19, and description thereof is omitted. In the figure, reference numeral 30 denotes a λ / 4 plate that rotates the polarization state of the optical signal output from the polarization scrambler 3 by 90 degrees. Reference numeral 31 denotes a Faraday rotator that rotates the polarization state of an optical signal input from the λ / 4 plate 30 in accordance with a drive signal. For example, a device using a magneto-optical effect can be used. Reference numeral 32 denotes a Faraday rotator driving circuit for driving the Faraday rotator 31, which is configured using an amplifier. An oscillator 33 oscillates at a predetermined frequency and supplies an output to the Faraday rotator driving circuit.

  As described above, in the thirteenth embodiment, the λ / 4 plate 30, the Faraday rotator 31, the Faraday rotator drive circuit 32, and the oscillator 33 are added between the polarization scrambler 3 and the optical transmitter output terminal 10. Thus, this is different from the twelfth embodiment.

  As described above, in the optical transmitter of the twelfth embodiment shown in FIG. 19, when the return-to-zero code is used, the polarization scrambler driving signal shown in FIG. 20B and the optical transmitter shown in FIG. Depending on the phase relationship of the light intensity modulation waveform shown, the degree of polarization may not be zero. The thirteenth embodiment having the configuration shown in FIG. 21 shows a method for solving such a problem.

  The operation of the optical transmitter shown in FIG. 21 will be described below with reference to FIG. Here, FIG. 22A shows an example of the locus of the polarization state of the optical signal after optical intensity modulation is performed with the return-to-zero code output from the polarization scrambler 3, and FIG. FIG. 6 shows an example of the locus of the polarization state of the optical signal after the light intensity modulation is performed with the return-to-zero code output from the λ / 4 plate 30 and the state of polarization rotation by the Faraday rotator 31.

  The polarization state of the optical signal output from the polarization scrambler 3 is as shown in FIG. 22A, which is the same as the output of the polarization scrambler 3 in the twelfth embodiment shown in FIG. The same. Light intensity modulation is performed with a return-to-zero code output from the polarization scrambler 3, and the optical signal is input to the λ / 4 plate 30 and its polarization state is as shown in FIG. Rotate 90 degrees. In FIG. 22B, the main axis direction of the λ / 4 plate 30 is set so that the probability of existing in the L-side hemisphere and the probability of existing in the R-side hemisphere within a certain time are equal.

  Here, the Faraday rotator 31 has the property of rotating the polarization state parallel to the equator on the Poincare sphere in accordance with the drive signal oscillated by the oscillator 33 and amplified by the Faraday rotator drive circuit 32. Accordingly, the polarization state of the optical signal output from the Faraday rotator 31 rotates as indicated by the arrow in FIG. At this time, the above three conditions (A), (B), and (C) are satisfied on the Poincare sphere, and even when the return-to-zero code is employed, the degree of polarization is zero.

As described above, according to the thirteenth embodiment, an oscillator that outputs a signal that oscillates at a predetermined frequency, and a predetermined state for rotating the polarization state to reduce the degree of polarization based on the output signal of the oscillator. Since a Faraday rotator driving circuit that outputs a drive signal that oscillates at a frequency of Faraday and a Faraday rotator that is connected to the output of the optical phase modulator and rotates the polarization state of the input optical signal according to the drive signal , The effect that the degree of polarization can be made zero can be obtained even for an optical signal whose light intensity is modulated with a return-to-zero code.

  In the above description, the case where the optical transmitter according to the twelfth embodiment is applied has been described. However, in any of the first to eleventh embodiments other than the twelfth embodiment, the phase modulator is used. It is possible to output the output signal of the (polarization scrambler 3) via the λ / 4 plate and the Faraday rotator, and in either case, the case where the present invention is applied to the twelfth embodiment. The same effect is produced.

Embodiment 14 FIG.
FIG. 23 is a block diagram showing an optical transmitter according to the fourteenth embodiment of the present invention. Corresponding portions are denoted by the same reference numerals as in FIGS. 1 and 19, and description thereof is omitted. In the figure, 8e is a third delay device corresponding to the first delay device 8a shown in FIG. 19, 8f is a fourth delay device corresponding to the second delay device 8b shown in FIG. 19, and 13a Is a first switch corresponding to the switch 13 shown in FIG. 1, and 13b is a second switch corresponding to the switch 13 shown in FIG. The difference between the fourteenth embodiment and the first embodiment is that the polarization scrambler 3, the polarization scrambler driving circuit 9, the third delay device 8e, the fourth delay device 8f, and the second switch 13b are provided. It is in the added point. The first delay unit 8a and the third delay unit 8e receive a clock signal and have a waveform that is substantially sinusoidal and whose polarity is inverted by one period in one data signal section of the optical intensity modulator drive signal. Outputs an optical phase modulator driving signal obtained by delaying the signal so that the peak of the waveform is positioned at approximately the center of the section corresponding to one data signal in the optical signals respectively input to the two optical phase modulators. An optical phase modulator driving signal delay unit is configured, and the second delay unit 8b and the fourth delay unit 8f receive the optical intensity modulator driving signal, and the optical intensity modulators are respectively input to the two optical phase modulators. The switch control signal delay unit is configured to output a switch control signal obtained by delaying the light intensity modulator drive signal so that the light intensity modulator drive signal is turned on only during a period in which the optical signal corresponding to the on state of the drive signal is input. .

Next, the operation will be described.
Here, the operation until the optical phase modulator 11 is driven by the optical phase modulator drive signal that is turned on / off by the first switch 13a and amplified by the optical phase modulator drive circuit 12 and outputs an optical signal. Is the same as in the first embodiment. In addition to the effect of reducing the degree of polarization of the optical signal output from the optical transmitter output terminal 10, the polarization scrambler 3 to which the optical signal from the optical phase modulator 11 is input, A similar pulse compression effect is realized.

  The polarization scrambler 3 delays the signal branched from the clock signal by the third delay unit 8e, and then turns it on / off by the second switch 13b and amplifies it by the polarization scrambler driving circuit 9. It is driven by a wave scrambler drive signal. The second switch 13b is turned on / off by turning on the first switch 13a by a switch control signal branched from the optical intensity modulator drive signal generated by the discriminator 6 and delayed by the second delay unit 8b. It is controlled by a switch control signal branched from the optical intensity modulator drive signal generated by the discriminator 6 and delayed by the fourth delay unit 8f so as to be turned off.

  Thus, according to the fourteenth embodiment, since a plurality of optical phase modulators are used, the waveform at the receiving end can be controlled more precisely, and one of the plurality of optical phase modulators can be controlled. In addition, since the polarization scrambler is used, the effect that the degree of polarization of the output optical signal can be reduced can be obtained.

It is a block diagram which shows one structural example of the optical transmitter by Embodiment 1 of this invention. It is operation | movement explanatory drawing which shows the signal waveform of each part of the optical transmitter in Embodiment 1 of this invention. It is a block diagram which shows the other structural example of the optical transmitter by Embodiment 1 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 2 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 3 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 4 of this invention. It is operation | movement explanatory drawing which shows the signal waveform of each part of the optical transmitter in Embodiment 4 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 5 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 6 of this invention. It is operation | movement explanatory drawing which shows the signal waveform of each part of the optical transmitter in Embodiment 6 of this invention. It is a block diagram which shows the other structural example of the optical transmitter by Embodiment 6 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 7 of this invention. It is operation | movement explanatory drawing which shows the signal waveform of each part of the optical transmitter in Embodiment 7 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 8 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 9 of this invention. It is operation | movement explanatory drawing which shows the signal waveform of each part of the optical transmitter in Embodiment 9 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 10 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 11 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 12 of this invention. It is operation | movement explanatory drawing for demonstrating operation | movement of the optical transmitter in Embodiment 12 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 13 of this invention. It is operation | movement explanatory drawing for demonstrating operation | movement of the optical transmitter in Embodiment 13 of this invention. It is a block diagram which shows the structural example of the optical transmitter by Embodiment 14 of this invention. It is a block diagram which shows the structural example of the conventional optical transmitter. It is operation | movement explanatory drawing for demonstrating operation | movement of the polarization scrambler of the conventional optical transmitter. It is operation | movement explanatory drawing which shows the signal waveform of each part of the conventional optical transmitter.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light source, 2 Optical intensity modulator, 3 Polarization scrambler, 4 Data signal input terminal, 5 Clock signal input terminal, 6 Discriminator, 8a 1st delay device, 8b 2nd delay device, 8c, 8d delay device 8e 3rd delay device, 8f 4th delay device, 11 optical phase modulator, 13 switch, 13a 1st switch, 13b 2nd switch, 14 optical amplifier, 15 optical demultiplexer, 16 photodiode ( Receiver), 18 clock extraction circuit, 20 low-pass filter (optical phase modulator drive signal generation circuit), 21 branch circuit, 22 inverter circuit, 23 changeover switch, 24 optical phase modulator drive signal inversion means, 26 adder , 27 Return-to-zero converter, 29 Frequency multiplier, 30 λ / 4 plate, 31 Faraday rotator, 32 Faraday rotator drive .

Claims (9)

A light source that generates an optical signal;
An identifier that outputs a signal corresponding to the on / off state of the data signal in synchronization with the clock signal as a light intensity modulator drive signal;
A light intensity modulator for modulating the light intensity of the light signal output from the light source based on the light intensity modulator drive signal;
An optical phase modulator that optically modulates an optical signal that has been optical intensity modulated by the optical intensity modulator; and
The clock signal is input, and a signal having a waveform that is a substantially sine wave and whose polarity is inverted by one period in a section of one data signal in the optical intensity modulator driving signal, the peak of the waveform is applied to the optical phase modulator. A first delay unit that outputs an optical phase modulator drive signal delayed so as to be positioned approximately at the center of a section corresponding to one data signal in the input optical signal;
The light intensity modulator drive signal is input, and the light intensity modulator drive is turned on only during a period in which the optical signal corresponding to the ON state of the light intensity modulator drive signal is input to the optical phase modulator. A second delay device for outputting a switch control signal obtained by delaying the signal;
A switch that is controlled by a switch control signal output from the second delay device, and that inputs the optical phase modulator drive signal to the optical phase modulator only in a section in which the switch control signal is turned on.
The optical phase modulator performs optical phase modulation based on the optical phase modulator driving signal given through the switch.   2. The optical transmitter according to claim 1, wherein an optical amplifier is inserted between the optical intensity modulator and the optical phase modulator. A light source that generates an optical signal;
An identifier that outputs a signal corresponding to the on / off state of the data signal in synchronization with the clock signal as a light intensity modulator drive signal;
A light intensity modulator for modulating the light intensity of the light signal output from the light source based on the light intensity modulator drive signal;
An optical phase modulator that optically modulates an optical signal that has been optical intensity modulated by the optical intensity modulator; and
The clock signal is input, and a signal having a waveform that is a substantially sine wave and whose polarity is inverted by one period in a section of one data signal in the optical intensity modulator driving signal, the peak of the waveform is applied to the optical phase modulator. A first delay unit that outputs an optical phase modulator drive signal delayed so as to be positioned approximately at the center of a section corresponding to one data signal in the input optical signal;
An optical demultiplexer for demultiplexing a part of an optical signal input to the optical phase modulator from the optical intensity modulator;
A light receiver for converting the optical signal demultiplexed by the optical demultiplexer into an electrical signal;
An output signal of the photoreceiver is input, and the optical phase modulator is turned on only during a period in which an optical signal corresponding to an on state of the optical intensity modulator driving signal is input from the optical intensity modulator to the optical phase modulator. A second delay device for outputting a switch control signal obtained by delaying the output signal of the light receiver;
A switch that is controlled by a switch control signal output from the second delay device, and that inputs the optical phase modulator drive signal to the optical phase modulator only in a section in which the switch control signal is turned on.
The optical phase modulator performs optical phase modulation based on the optical phase modulator driving signal given through the switch. A light source that generates an optical signal;
A discriminator for outputting a signal corresponding to the on / off state of the data signal in synchronization with the first clock signal as a light intensity modulator drive signal;
A light intensity modulator for modulating the light intensity of the light signal output from the light source based on the light intensity modulator drive signal;
An optical phase modulator that optically modulates an optical signal that has been optical intensity modulated by the optical intensity modulator; and
An optical demultiplexer for demultiplexing a part of an optical signal input to the optical phase modulator from the optical intensity modulator;
A light receiver for converting the optical signal demultiplexed by the optical demultiplexer into an electrical signal;
A clock extraction circuit for extracting a second clock signal from the output signal of the light receiver;
In synchronization with the second clock signal, a signal having a waveform that is a substantially sine wave and whose polarity is inverted by one period in a section of one data signal in the light intensity modulator drive signal is represented by a peak of the waveform. A first delay unit that outputs an optical phase modulator drive signal delayed so as to be positioned at substantially the center of a section corresponding to one data signal in the optical signal input to the phase modulator;
An output signal of the photoreceiver is input, and the optical phase modulator is turned on only during a period in which an optical signal corresponding to an on state of the optical intensity modulator driving signal is input from the optical intensity modulator to the optical phase modulator. A second delay device for outputting a switch control signal obtained by delaying the output signal of the light receiver;
A switch that is controlled by a switch control signal output from the second delay device, and that inputs the optical phase modulator drive signal to the optical phase modulator only in a section in which the switch control signal is turned on.
The optical phase modulator performs optical phase modulation based on the optical phase modulator driving signal given through the switch.   2. A return-to-zero conversion circuit that converts a light intensity modulator drive signal output from the discriminator into a return-to-zero code and sends it to the light intensity modulator. 5. The optical transmitter according to claim 1.   The optical transmitter according to any one of claims 1 to 5, wherein a polarization scrambler is used as the optical phase modulator. An oscillator that outputs a signal that oscillates at a predetermined frequency;
A Faraday rotator drive circuit that outputs a drive signal that oscillates at a predetermined frequency for rotating the polarization state to reduce the degree of polarization based on the output signal of the oscillator;
7. A Faraday rotator, which is connected to the output of the optical phase modulator and rotates the polarization state of the input optical signal in accordance with the drive signal, is provided. Optical transmitter according to item A light source that generates an optical signal;
An identifier that outputs a signal corresponding to the on / off state of the data signal in synchronization with the clock signal as a light intensity modulator drive signal;
A light intensity modulator for modulating the light intensity of the light signal output from the light source based on the light intensity modulator drive signal;
Two or more optical phase modulators connected in cascade for optical phase modulation of the optical signal modulated by the optical intensity modulator,
The clock signal is input, and a signal having a waveform that is a substantially sine wave and whose polarity is inverted by one period in a section of one data signal in the optical intensity modulator driving signal is represented by a peak of the waveform. Delay for two or more optical phase modulator driving signals for outputting an optical phase modulator driving signal delayed so as to be positioned at substantially the center of a section corresponding to one data signal in the optical signal respectively input to the phase modulator And
The light intensity modulator driving signal is input, and the two or more optical phase modulators are turned on only during a period in which an optical signal corresponding to the on state of the light intensity modulator driving signal is input. Two or more switch control signal delay units for outputting a switch control signal obtained by delaying the light intensity modulator drive signal;
Controlled by the switch control signal output from the switch control signal delay unit, the optical phase modulator drive signal is input to each of the two or more optical phase modulators only in a section in which the switch control signal is turned on. Two or more switches to
The two or more optical phase modulators perform optical phase modulation on the basis of the optical phase modulator drive signal respectively given through the two or more switches .   9. The optical transmitter according to claim 8, wherein a polarization scrambler is used for at least one of the two or more optical phase modulators connected in cascade.

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