JP5939925B2 - Optical output device and optical output method - Google Patents

Description

  The present invention relates to an optical output device and an optical output method.

  As an apparatus capable of outputting two RZ (Return-to-Zero) pulse trains having different duty ratios, there is an optical pulse generator disclosed in Patent Document 1.

  This optical pulse generator exhibits a periodic transmittance characteristic that is an even function with respect to a drive voltage in which an operating bias voltage (DC voltage) and an AC voltage having a frequency f are combined, and the value of the applied drive voltage. And an optical modulator that modulates the input light according to the transmittance by changing the transmittance according to the above. The optical pulse generator enables output of two RZ pulse trains having a frequency of 2 × f with different duty ratios by switching the drive voltage applied to the optical modulator.

  That is, the optical pulse generator modulates the input light by applying a drive voltage with the voltage that minimizes the transmittance as the operation bias voltage to the optical modulator, and the duty ratio is, for example, 66%. RZ pulse train is output. Also, the optical pulse generator modulates the input light by applying a driving voltage with the voltage that maximizes the transmittance as the operating bias voltage to the optical modulator, and the duty ratio is, for example, 33%. RZ pulse train is output.

  In this way, the optical pulse generator is configured such that the operation bias voltage of the drive voltage applied to the optical modulator is a voltage that minimizes the transmittance of the optical modulator, a voltage that maximizes the transmittance of the optical modulator, By switching to either of these, it is possible to output two RZ pulse trains with different duty ratios.

JP 2000-89176 A

  As described above, the optical pulse generation device described in Patent Document 1 is a voltage that minimizes the transmittance of the optical modulator, or a voltage that maximizes the transmittance of the optical modulator. Either. Therefore, when the drive voltage changes from the operation bias voltage → the maximum value → the operation bias voltage → the minimum value, if the operation bias voltage that minimizes the transmittance is applied to the optical modulator, the transmittance of the optical modulator Shows the change from local minimum value (minimum value) → local maximum value (maximum value) → local minimum value (minimum value) → local maximum value (maximum value), and an operating bias voltage that maximizes the transmittance is applied to the optical modulator. If so, the transmittance of the optical modulator shows a change from a maximum value (maximum value) → a minimum value (minimum value) → a maximum value (maximum value) → a minimum value (minimum value).

  Therefore, when the operating bias voltage is set to a voltage that minimizes the transmittance and to a voltage that maximizes the transmittance, the amplitude of each RZ pulse train output from the optical modulator has a peak (maximum). (Maximum) and minimum (minimum)) timings do not match.

  Therefore, the operation bias voltage of the drive voltage is switched between a voltage that minimizes the transmittance and a voltage that maximizes the transmittance, and the apparatus is configured to switch the duty ratio of the RZ pulse train output from the optical modulator. For example, when synchronizing the output RZ pulse train and the data signal, the following is necessary to achieve correct synchronization with the data signal. That is, it is necessary to match the timings at which two RZ pulse trains having different duty ratios show peak values (maximum value (maximum value) and minimum value (minimum value)). Here, the RZ pulse train output from the optical modulator has a frequency twice the frequency f of the drive voltage. That is, the frequency is higher than the drive voltage. Therefore, there is a problem that it is difficult for RZ pulse trains having different duty ratios, in other words, light having different degrees of modulation to coincide with the timing at which the peak values (maximum value (maximum value) and minimum value (minimum value)) coincide. there were.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical output device and an optical output method that can easily match the timings at which lights having different degrees of modulation exhibit a minimum value and a maximum value. To do.

In order to achieve the above object, an optical modulation unit of an optical output device according to the present invention is configured to periodically apply an applied voltage obtained by combining an AC voltage applied to an AC voltage terminal and a bias voltage applied to a bias voltage terminal. In response to such changes, the transmittance is periodically changed, and the input light is modulated according to the transmittance. The bias switching unit switches the bias voltage to either a predetermined voltage for setting the transmittance to a predetermined value or a specified voltage for setting the transmittance to a specified value different from the predetermined value. The phase control unit modulates the light modulated by the optical modulation unit when the bias voltage switched by the bias switching unit is a predetermined voltage, and modulates by the optical modulation unit when the bias voltage switched by the bias switching unit is a specified voltage. The phase of the AC voltage changes when the bias voltage is switched from the specified voltage to the specified voltage and when the specified voltage is switched from the specified voltage to the specified voltage so that the timing at which the measured light matches the minimum and maximum values is the same. Ru is.

  According to the present invention, it is easy to match the timing at which lights having different modulation degrees exhibit a minimum value and a maximum value.

It is a figure which shows the structure of the optical pulse generator which concerns on Embodiment 1 of this invention. It is a figure which shows the transmittance | permeability and drive signal of an optical modulator. It is a figure which shows a RZ pulse train. It is a figure which shows the structure of the optical pulse generator which concerns on Embodiment 2 of this invention.

(Embodiment 1)
Hereinafter, as shown in FIG. 1, an optical pulse generator 10 (optical output device) according to Embodiment 1 of the present invention includes a semiconductor laser element 11, an optical modulator 12, an oscillator 13, an amplifier 14, A bias switching circuit 15 and a phase shifter 16 are provided.

  The semiconductor laser element 11 is a laser diode that outputs a sinusoidal laser beam at a predetermined wavelength. The output terminal of the semiconductor laser element 11 is connected to one end of a waveguide (not shown). The other end of the waveguide is connected to the input terminal of the optical modulator 12.

  The optical modulator 12 responds to a periodic change in a drive voltage (applied voltage) obtained by combining an AC voltage having a frequency f applied to the AC voltage terminal and a DC bias voltage applied to the bias voltage terminal. The transmittance is periodically changed, and the input laser light is modulated according to the transmittance. For this reason, the optical modulator 12 outputs laser beams having different degrees of modulation, in other words, RZ pulse trains having different duty ratios, when drive voltages having different bias voltages are applied. The input terminal of the optical modulator 12 is connected to one end of the waveguide. The other end of the waveguide is connected to the output terminal of the semiconductor laser element 11.

  The optical modulator 12 has a bias voltage terminal electrically connected to the bias switching circuit 15 and an AC voltage terminal electrically connected to the phase shifter 16. With this connection, a bias voltage that is a DC voltage output from the bias switching circuit 15 and an AC voltage having a frequency f output from the phase shifter 16 are applied to the optical modulator 12. The optical modulator 12 has a transmittance according to a combined voltage of the applied bias voltage and the applied AC voltage, that is, a drive voltage (applied voltage having a frequency f with the bias voltage as a node) as shown in FIG. (The minimum transmittance is zero). Examples of the optical modulator 12 include a Mach-Zehnder interferometer type optical modulator and a directional coupler type optical modulator. The light modulator 12 exhibits a transmittance characteristic that varies with a function depending on the driving voltage.

  The oscillator 13 outputs an AC voltage having a frequency f. As shown in FIG. 1, one end of the oscillator 13 is connected to the input terminal of the amplifier 14, and the other end of the oscillator 13 is grounded. The AC voltage output from the oscillator 13 is input to the amplifier 14.

  The amplifier 14 changes the amplitude of the input AC voltage to such an amplitude Va that the transmittance of the optical modulator 12 changes from the minimum value to the maximum value (that is, the transmittance changes from the maximum value to the minimum value). Amplify (see FIG. 2). In other words, the amplifier 14 amplifies the amplitude of the input AC voltage to an amplitude Va such that the transmittance of the optical modulator 12 changes from a minimum value to a maximum value adjacent to the minimum value, for example.

  Thus, the amplifier 14 amplifies the amplitude of the input AC voltage so that the peak-to-peak of the AC voltage becomes 2Va. The output terminal of the amplifier 14 is connected to the input terminal of the phase shifter 16. Therefore, the input AC voltage after amplification, that is, the AC voltage having the frequency f and the amplitude Va is input to the phase shifter 16. A bias switching circuit 15 is connected to the phase shifter 16.

  The bias switching circuit 15 corresponds to, for example, a switching signal from a computer, and sets the voltage value of the bias voltage to a voltage that minimizes the transmittance of the optical modulator 12 (the voltage at which the optical modulator 12 exhibits the minimum transmittance). Alternatively, a voltage that maximizes the transmittance of the optical modulator 12 (a voltage at which the optical modulator 12 exhibits the maximum transmittance) is switched and output. The bias switching circuit 15 is connected to each voltage terminal of the phase shifter 16 and the optical modulator 12. Therefore, the bias voltage output from the bias switching circuit 15 is input to the phase shifter 16 and the optical modulator 12.

  The output terminal of the phase shifter 16 is connected to the optical modulator 12. When the voltage value of the bias voltage output from the bias switching circuit 15 is a voltage that maximizes the transmittance of the optical modulator 12, the phase shifter 16 advances the phase of the input AC voltage by π / 2 (or , Delayed by π / 2), and outputs an alternating voltage whose phase is changed. On the other hand, when the voltage value of the bias voltage output from the bias switching circuit 15 is a voltage that minimizes the transmittance of the optical modulator 12, the phase shifter 16 does not change the phase of the input AC voltage, The input AC voltage is output as it is.

  Here, when the voltage value of the bias voltage output from the bias switching circuit 15 is a voltage that minimizes the transmittance of the optical modulator 12, the drive voltage applied to the optical modulator 12 is the drive shown in FIG. The voltage becomes PB. That is, when the voltage value of the bias voltage is a voltage that minimizes the transmittance of the optical modulator 12, that is, the bias voltage A, the drive voltage PB saves a voltage value that minimizes the transmittance of the optical modulator 12. Represents a sine wave having an amplitude Va and a frequency f.

  On the other hand, when the voltage value of the bias voltage output from the bias switching circuit 15 is a voltage that maximizes the transmittance of the optical modulator 12, the drive voltage applied to the optical modulator 12 is the drive voltage shown in FIG. Become QB. That is, when the voltage value of the bias voltage is a voltage that maximizes the transmittance of the optical modulator 12, that is, the bias voltage B, the drive voltage QB saves the voltage value that maximizes the transmittance of the optical modulator 12. Represents a sine wave having an amplitude Va and a frequency f.

  Here, as shown in FIG. 2, the optical modulator 12 that changes with the drive voltage QB and the timing at which the transmittance of the optical modulator 12 that changes with the drive voltage PB peaks (maximum (maximum) and minimum (minimum)). 12 coincides with the timing at which the transmittance shows a peak.

  This is because the difference between the bias voltage value of the drive voltage PB and the bias voltage value of the drive voltage QB corresponds to a half cycle of the transmittance, and therefore the phase difference between the drive voltage PB and the drive voltage QB is π / 2 (by setting the phase difference between the drive voltage PB and the drive voltage QB to a quarter of the drive voltage PB (or drive voltage QB)), the transmittance is the minimum value (minimum value). This is because the timing at which the transmissivity coincides with the timing at which the transmittance shows the maximum value (maximum value).

  For reference, when the voltage value of the bias voltage output from the bias switching circuit 15 is a voltage that maximizes the transmittance of the optical modulator 12 (in the case of the bias voltage B), the voltage is output from the amplifier 14. A waveform when an AC voltage is directly input to the optical intensity amplifier 12 without passing through the phase shifter 16 is shown as a drive voltage QB ′. The drive voltage QB 'is a sine wave having an amplitude Va and a frequency f, where the voltage value that maximizes the transmittance of the optical modulator 12 is a node. Here, the drive voltage QB ′ does not change the phase of the AC voltage by the phase shifter 16 (the phases of the drive voltage QB ′ and the drive voltage PQ match). Therefore, the timing at which the transmittance of the optical modulator 12 that changes according to the driving voltage QB ′ reaches a peak does not coincide with the timing at which the transmittance of the optical modulator 12 that changes according to the driving voltage PB reaches a peak.

  When the drive voltage PB described above is applied to the optical modulator 12, when the drive voltage QB is applied to the optical modulator 12, and when the drive voltage QB ′ is applied to the optical modulator 12, the optical modulator FIG. 3 shows the RZ pulse train output from the Twelve.

  In any of the three cases described above, the optical modulator 12 outputs an RZ pulse train having a frequency of 2 × f, specifically, a frequency twice the drive voltage. Here, the reason why the RZ pulse train having a frequency twice the drive voltage is output is as follows. That is, since the amplitude Va of the drive voltages PB, QB, QB ′ is set to a value that changes the transmittance of the optical modulator 12 from, for example, a minimum value to a maximum value, the drive voltages PB, QB, QB ′ are half This is because the transmittance of the optical modulator 12 changes, for example, from the minimum value to the maximum value and changes to the minimum value again while changing by the period. That is, while the drive voltages PB, QB, and QB 'change by half a cycle, the transmittance of the optical modulator 12 changes by one cycle.

  When the drive voltage PB is applied to the optical modulator 12, the optical modulator 12 changes the transmittance according to the value of the drive voltage PB, modulates the input laser light, and the duty ratio is, for example, about A 66% RZ pulse train is output. When the drive voltage QB is applied to the optical modulator 12, the optical modulator 12 modulates the input laser light by changing the transmittance according to the value of the drive voltage QB, and the duty ratio is, for example, about A 33% RZ pulse train is output.

  Here, the optical pulse generator 10 has an optical modulator that changes with the drive voltage QB, and the timing at which the transmittance of the optical modulator 12 that changes with the drive voltage PB reaches a peak (maximum (maximum) and minimum (minimum)). The timing at which the transmittance of 12 shows a peak is matched. Therefore, the optical pulse generator 10 has the timing at which the RZ pulse train shows the peak value (maximum value (maximum value) and minimum value (minimum value)) when the drive voltage PB is applied to the optical modulator 12, and the optical modulation. The timing when the RZ pulse train when the drive voltage QB is applied to the device 12 shows the peak value can be matched.

  For reference, an RZ pulse train output from the optical modulator 12 when the drive voltage QB ′ is applied is shown. The timing at which the RZ pulse train output at this time exhibits a peak value and the timing at which the RZ pulse train output from the optical modulator 12 when the drive voltage PB is applied do not coincide with each other.

  As described above, the optical pulse generator 10 according to the first embodiment matches the timings at which two RZ pulse trains output from the optical modulator 12 and having different duty ratios show peak values. The optical pulse generator 10 achieves this coincidence by changing the phase of the AC voltage of the drive voltage QB by the phase shifter 16. Here, the drive voltage QB has a frequency that is ½ times the frequency f of the RZ pulse train. In other words, the frequency of the AC voltage is lower than the frequency of the RZ pulse train. Thus, since the optical pulse generator 10 changes the phase of the AC voltage having a lower frequency than the RZ pulse train, two RZ pulse trains having different duty ratios compared to the device that directly changes the phase of the RZ pulse train. It is easy to make the timings at which peak values coincide with each other.

(Embodiment 2)
Next, in the optical pulse generator 20 according to the second embodiment of the present invention, as shown in FIG. 4, a signal optical modulator 17 is newly provided in the optical pulse generator 10 according to the first embodiment. Is. Therefore, in FIG. 4, the same number is attached | subjected to the structure same as the optical pulse generator 10. FIG.

  The signal optical modulator 17 has a signal input terminal connected to the signal generator and a bias voltage terminal connected to the bias switching circuit 15. The input terminal of the signal light modulator 17 is connected to the output terminal of the light modulator 12. The signal generator outputs a data signal having a frequency of 2 × f, which is an AC electrical signal.

  The signal optical modulator 17 is periodically transmitted in accordance with a combined voltage of the data signal input to the signal input terminal and the bias voltage applied to the bias voltage terminal, that is, in accordance with a periodic change of the modulation signal. The rate is changed, and the input RZ pulse train (the RZ pulse train output from the optical modulator 12) is modulated with a baud rate of 2 × f. Thereafter, the signal optical modulator 17 outputs a modulated RZ pulse train (specifically, an RZ pulse train indicating an intensity equal to or higher than a predetermined threshold). The signal optical modulator 17 exhibits a transmittance characteristic that changes with a modulation function with respect to the modulated signal (the minimum value of the transmittance is zero).

  As described above, since the optical pulse generator 20 includes the optical modulator 17 for signals, the RZ pulse train output from the optical modulator 12 can be modulated corresponding to the data signal.

  As described above, similarly to the optical pulse generator 10 of the first embodiment, the optical pulse generator 20 of the second embodiment has two RZ pulse trains output from the optical modulator 12 with different duty ratios having peak values. It is easy to match the timings indicating. This is because the optical pulse generator 20 of the second embodiment changes the phase of the AC voltage of the drive voltage QB by the phase shifter 16 in the same manner as the optical pulse generator 10 of the first embodiment. This is because the timing at which the two RZ pulse trains having different duty ratios output from 12 show peak values is matched.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and applications are possible.

  For example, the optical modulator 12 and the signal optical modulator 17 exhibit transmittance characteristics that change in a function with respect to voltage, but are not limited thereto. That is, the optical modulator 12 and the signal optical modulator 17 may exhibit transmittance characteristics that change in an odd function with respect to the voltage.

  In addition, the amplifier 14 sets the amplitude Va of the drive voltages PB and QB to a value that changes the transmittance of the optical modulator 12 from, for example, a minimum value to a maximum value, but is not limited thereto. That is, the amplifier 14 may set the amplitude Va of the drive voltages PB and QB to be smaller than a value that changes the transmittance of the optical modulator 12 from a minimum value to a maximum value, for example. Even in this case, in the optical pulse generators 10 and 20, the two RZ pulse trains output from the optical modulator 12 and having different duty ratios have peak values (maximum value (maximum value) and minimum value (minimum value)). ) Can be easily matched.

  In addition, the bias switching circuit 15 sets the bias voltage of the drive voltage PB as a voltage that minimizes the transmittance of the optical modulator 12, and sets the bias voltage of the drive voltage QB as a voltage that maximizes the transmittance of the optical modulator 12. However, it is not limited to this. That is, for example, the bias voltage of the drive voltage PB may be a voltage value that makes the transmittance of the optical modulator 12 a predetermined value, and the bias voltage of the drive voltage QB may be a voltage value that makes a specified value different from the predetermined value. In this case, the phase shifter 16 is such that the two RZ pulse trains output from the optical modulator 12 and having different duty ratios coincide with each other in the timing indicating the peak value, in other words, the optical modulator that changes according to the drive voltage PB. The phase difference between the drive voltage PB and the drive voltage QB is controlled so that the timing at which the transmittance of 12 shows a peak coincides with the timing at which the transmittance of the optical modulator 12 that changes according to the drive voltage QB shows a peak. That's fine.

  Various embodiments and modifications can be made to the present invention without departing from the broad spirit and scope of the present invention. The above-described embodiments are for explaining the present invention and do not limit the scope of the present invention. In other words, the scope of the present invention is indicated by the scope of claims, not the embodiment described above. Various modifications within the scope of the claims and within the scope of the equivalent invention are considered to be within the scope of the present invention.

10, 20 Optical pulse generator 11 Semiconductor laser device 12 Optical modulator 13 Oscillator 14 Amplifier 15 Bias switching circuit 16 Phase shifter 17 Optical modulator for signal

Claims (8)

In accordance with the periodic change in the applied voltage, which is a combination of the AC voltage applied to the AC voltage terminal and the bias voltage applied to the bias voltage terminal, the transmittance is periodically changed to change the input light. A light modulator that modulates according to the transmittance;
A bias switching unit that switches the bias voltage to any one of a predetermined voltage for setting the transmittance to a predetermined value and a specified voltage for setting the transmittance to a specified value different from the predetermined value;
Light modulated by the optical modulation unit when the bias voltage switched by the bias switching unit is a predetermined voltage and modulated by the optical modulation unit when the bias voltage switched by the bias switching unit is a specified voltage When the bias voltage is switched from the predetermined voltage to the specified voltage, and when the bias voltage is switched from the specified voltage to the predetermined voltage so that the timing at which the light exhibits a minimum value and a maximum value coincide with each other, a phase control unit which Ru changing the voltage of the phase,
An optical output device comprising: The predetermined voltage is a value indicating the minimum transmittance of the light modulation unit,
The specified voltage is a value indicating the maximum transmittance of the light modulator.
The light output device according to claim 1. An amplitude controller that controls the amplitude of the applied voltage so that the transmittance changes from the minimum to the maximum;
An optical output device according to claim 2. The phase control unit controls the phase difference between an AC voltage when the bias voltage is a predetermined voltage and an AC voltage when the bias voltage is a specified voltage to π / 2.
The light output device according to claim 2 or 3. The phase control unit advances or delays the phase of the AC voltage when the bias voltage is either a predetermined voltage or a specified voltage, and when the bias voltage is the other one different from the one, Do not change the phase of the AC voltage,
The light output device according to claim 4. The light modulator is composed of a Mach-Zehnder interference type light modulator,
The light output device according to any one of claims 1 to 5. In accordance with the periodic change of the data signal that is an alternating current electric signal input to the signal input terminal, the transmittance is periodically changed to further transmit the modulated light output from the light modulation unit. An optical signal modulator that modulates according to the rate,
The light output device according to any one of claims 1 to 6. An optical output method for an optical output device,
The light output device periodically changes the transmittance according to a periodic change of an applied voltage obtained by combining an AC voltage applied to an AC voltage terminal and a bias voltage applied to a bias voltage terminal. A light modulation step for modulating the input light according to the transmittance;
A bias switching step in which the light output device switches the bias voltage to any one of a predetermined voltage for setting the transmittance to a predetermined value and a specified voltage for setting the transmittance to a predetermined value different from the predetermined value. When,
When the bias voltage switched in the bias switching step is a predetermined voltage, the light output device modulates the light modulated in the light modulation step, and the bias voltage switched in the bias switching step is a specified voltage. When the bias voltage is switched from the predetermined voltage to the predetermined voltage, and from the predetermined voltage to the predetermined voltage so that the light modulated in the light modulation step matches the timing indicating the minimum value and the maximum value. when the a phase control step of Ru changing the phase of the AC voltage,
A light output method comprising:

Images