WO2015159528A1

WO2015159528A1 - Optical transmission device and power supply voltage control method

Info

Publication number: WO2015159528A1
Application number: PCT/JP2015/002026
Authority: WO
Inventors: 山本　浩史
Original assignee: 日本電気株式会社
Priority date: 2014-04-17
Filing date: 2015-04-10
Publication date: 2015-10-22
Also published as: JP2017125867A

Abstract

Provided is an optical transmission device capable of achieving a reduction in power consumption. The optical transmission device comprises: a light source; an optical modulator for modulating light from the light source; a feedback unit for outputting feedback information representing the deviation in a bias voltage from the operating point of the optical modulator; a power supply circuit for outputting a power supply voltage; a bias supply circuit operating responsive to the power supply voltage to supply the optical modulator with a bias voltage; and a control unit for controlling the operation supplying the bias voltage from the bias supply circuit and the operation outputting the power supply voltage from the power supply circuit. The control unit changes the bias voltage on the basis of the feedback information, while changing the power supply voltage in accordance with the value of the bias voltage.

Description

Optical transmitter and power supply voltage control method

The present invention relates to an external optical modulation type optical transmission apparatus and a power supply voltage control method thereof.

Recent optical transmitters, for example, digital coherent optical transmitters, often employ an external optical modulation method. The external light modulation method is a method in which light from a light source (for example, a laser light source) is modulated by an optical modulator.

In an optical transmitter of an external light modulation system, as an optical modulator, a modulator using an electro-optic effect by a dielectric material such as LiNbO ₃ (lithium niobate: abbreviation LN), or a semiconductor such as InP (indium phosphide) A modulator using an electroabsorption effect of a material is used. A device using LiNbO ₃ is called an LN modulator, and a device using InP is called an InP modulator.

The LN modulator can perform high-speed modulation. However, as a phenomenon peculiar to the LN modulator, a drift phenomenon is known in which the operating point of the LN modulator changes due to a temperature change or a change with time. A phenomenon caused by a pyroelectric effect caused by a temperature change is called a thermal (temperature) drift, and a thing caused by a change with time is called a DC drift.

Usually, in an optical transmission apparatus equipped with an LN modulator, feedback control is performed so that the operating point of the LN modulator becomes constant in order to compensate for the influence of the drift phenomenon.

FIG. 4 shows a configuration of an optical transmission apparatus that performs feedback control. Referring to FIG. 4, the optical transmission apparatus includes a light source 101, an optical modulator 102, an RF (Radio Frequency) drive circuit 103, a power supply circuit 104, a bias supply circuit 105, a light detection unit 106, and a control unit 100.

The light source 101 is a laser light source and outputs laser light according to the control signal S1.
The optical modulator 102 is an LN phase modulator. In the LN phase modulator, one optical waveguide is formed on an LN substrate, and an RF driving electrode and a bias adjusting electrode are formed in the vicinity of the optical waveguide.

The light detection unit 106 detects the light intensity of the output light (monitor light) of the light modulator 102, and outputs an electric signal corresponding to the magnitude of the light intensity to the control unit 100 as a monitor light detection signal S3. The RF drive circuit 103 converts a digital signal corresponding to the input information into an analog drive signal and supplies the analog drive signal to the optical modulator 102. Specifically, the RF drive circuit 103 converts an RF electric signal (high frequency signal) that is an input modulation signal (digital signal) into an analog signal, and supplies the drive signal to the optical modulator 102. .

The power supply circuit 104 supplies a power supply voltage to the bias supply circuit 105. The bias supply circuit 105 operates by receiving the power supply voltage from the power supply circuit 104 and supplies the bias voltage V _B to the optical modulator 102 in accordance with the drive control signal S2.

The control unit 100 supplies the control signal S1 to the light source 101 and supplies the drive control signal S2 to the bias supply circuit 105. The control unit 100 controls the bias supply circuit 105 so that the bias voltage V _B becomes a voltage value (optimum value) that is the operating point of the optical modulator 102 based on the monitor light detection signal S 3 from the light detection unit 106. (ABC control: Auto Bias Control). As an ABC operation at the time of phase modulation, for example, the control unit 100 inserts a pilot signal into the drive control signal S2 and extracts a pilot signal inserted from the monitor light detection signal S3 input from the light detection unit 106. Then, the inserted pilot signal and the extracted pilot signal are synchronously detected, and the bias supply circuit 105 is controlled so that the synchronous detection signal becomes 0V. Details of ABC operation during phase modulation are disclosed in, for example,

Patent Documents

1 and 2.

FIG. 5 is a diagram for explaining a modulation curve and an operating point of the optical modulator 102. The modulation curve of the optical modulator 102 is shown in a two-dimensional coordinate system in which the vertical axis represents the light intensity and the horizontal axis represents the bias voltage value.

The modulation curve of the optical modulator 102 is a COS square function curve, and the operating point of the optical modulator 102 is set on this modulation curve. The operating point of the optical modulator 102 is appropriately set according to the modulation method. Here, since it is phase modulation, the minimum point on the modulation curve is set as an operating point (a point indicated by a circle).

The optical modulator 102 performs phase modulation based on the drive signal from the RF drive circuit 103 with the operating point as a reference. Specifically, when the RF electric signal is “0”, the driving voltage V ₁ is supplied to the RF driving electrode, and when the RF electric signal is “1”, the driving voltage V ₂ is for RF driving. Supplied to the electrode. Here, each of the drive voltages V ₁ and V ₂ is a voltage value based on the operating point, and is set to a voltage value at a maximum point located on the left and right of the operating point on the modulation curve. The drive voltage V ₁ is −Vπ, and the drive voltage V ₂ is + Vπ. “Vπ” is a half-wave voltage that changes the phase of light propagating in the waveguide by a half wavelength. For example, a phase change amount of 2π occurs between the phase of light when the drive voltage V ₁ (−Vπ) is supplied and the phase of light when the drive voltage V ₂ (+ Vπ) is supplied.

However, as shown in FIG. 5, the operating point of the optical modulator 102 drifts (changes) over time.

A curve indicated by a solid line is a modulation curve when the power is turned on, and the voltage value at the operating point A is V _B 1. The control unit 100 controls the bias supply circuit 105 so that the bias voltage V _B becomes the voltage value V _B 1. As a result, the optical modulator 102 performs phase modulation based on the drive signal from the RF drive circuit 103 with the operating point A as a reference.

A curve indicated by a broken line is a modulation curve after a certain time has elapsed since the power was turned on, and the voltage value V _B 2 at the operating point _B is different from the voltage V _B 1 at the operating point A. That is, the voltage value of the operating point is shifted from V _B 1 to V _B 2. In this case, in the state where a bias voltage V _B to the voltage value V _B 1, since the bias voltage V _B deviates from the voltage value V _B 2 is the optimum value, waveform distortion occurs in the output waveform of the optical modulator 102.

When the bias voltage V _B is an optimum value, the synchronous detection signal described above becomes 0V. The control unit 100 changes the bias voltage V _B so that the synchronous detection signal becomes 0V. As a result, the bias voltage V _B is set to the optimum voltage value V _B 2, and as a result, the optical modulator 102 uses the operating point B as a reference and the phase based on the drive signal from the RF drive circuit 103. Modulation is performed.

In the optical transmitter shown in FIG. 4, in order to ensure long-term reliability, it is necessary to cope with a wide range of operating point fluctuations, for example, ± 50V. For this reason, the power supply circuit 104 outputs a fixed power supply voltage of 50 V so that the upper limit value of the bias voltage specification of the optical modulator 102 can be covered.

Here, techniques relating to bias voltage control of an optical transmitter of an external modulation type are described in Patent Documents 3-7 and the like in addition to

Patent Documents

1 and 2 described above.

Patent Document 1 describes an optical transmission device including a Mach-Zehnder type LN modulator. In this optical transmitter, a Mach-Zehnder LN modulator is driven by a drive signal on which a low-frequency dither signal is superimposed. Then, based on the phase comparison result between the dither signal extracted from the output signal of the Mach-Zehnder LN modulator and the dither signal before superposition, a bias voltage for compensating for the operating point drift of the Mach-Zehnder LN modulator is generated.

Patent Document 2 describes feedback control in which output light (monitor light) of a Mach-Zehnder LN modulator is detected by a photodetector and a bias voltage is controlled based on the output value of the photodetector. Patent Document 3 discloses that training is performed to calculate an intermediate point from the minimum and maximum values of the operating point bias set value, and the calculated intermediate value is set as an appropriate operating point of the external modulator. Has been.

JP 2004-37647 A JP 2003-233047 A JP 2006-31003 A JP 2011-221370 A JP 2008-282057 A JP 2003-233042 A JP-A-4-337707

However, in the optical transmission device shown in FIG. 4, the power supply circuit 104 outputs a voltage (V _{max in} FIG. 5) that can cover the upper limit value of the bias voltage specification of the optical modulator 102. For example, the power supply circuit 104 always supplies a power supply voltage of 50 V to the bias supply circuit 105. In this case, the following problems occur.

In the short-term period (several hours or several days) after the power is turned on, the optical modulator shown in FIG. A power supply voltage V _max that can cover the upper limit value of the bias voltage specification 102 is supplied to the bias supply circuit 105. That is, in the optical transmission device shown in FIG. 4, a power supply voltage larger than necessary with respect to the bias voltage supplied to the optical modulator 102 is supplied to the bias supply circuit 105. For this reason, the problem that power consumption increases arises.

The optical transmission devices described in Patent Documents 1-3 also have the above-described problem of increased power consumption because the power supply voltage is fixed.

An object of the present invention is to provide an optical transmission apparatus and a power supply voltage control method thereof that can solve the above-described problems and can reduce power consumption.

To achieve the above object, an optical transmission apparatus according to the present invention receives light output means for outputting light, a drive signal and a bias voltage as inputs, and modulates light from the light output means according to the drive signal. A light modulation means for changing the intensity of the output light in accordance with the bias voltage, and a feedback indicating a deviation amount of the bias voltage with respect to an operating point of the light modulation means set to a predetermined value based on the intensity of the output light. Feedback means for generating information; power supply means for outputting a power supply voltage; bias supply means that operates in response to the power supply voltage and supplies the bias voltage to the light modulation means; and the bias of the bias supply means Control means for controlling the supply operation of the voltage and the output operation of the power supply voltage of the power supply means. Based on Dobakku information, along with changing the bias voltage, to vary the power supply voltage according to the value of the bias voltage.

In order to achieve the above object, a power supply voltage control method according to the present invention receives a drive signal and a bias voltage as input, modulates light from a light source according to the drive signal, and outputs light intensity according to the bias voltage. A power supply voltage control method for an optical transmission device, comprising: an optical modulator that changes, and a bias supply circuit that operates by receiving a power supply voltage and supplies the bias voltage to the optical modulator, The bias voltage is changed based on feedback information indicating a deviation amount of the bias voltage with respect to the operating point of the optical modulator that is generated based on the intensity and is set to a predetermined value, and according to the value of the bias voltage The power supply voltage is changed.

According to the present invention, since the minimum power supply voltage necessary for supplying the bias voltage is supplied to the bias supply circuit, the power consumption can be reduced.

It is a block diagram which shows the structure of the optical transmitter by one Embodiment of this invention. FIG. 2 is a diagram for explaining a relationship among an operating point drift, a bias voltage, and a power supply voltage when the optical modulator of the optical transmission device shown in FIG. 1 is turned on. FIG. 2 is a diagram for explaining a relationship between an operating point drift, a bias voltage, and a power supply voltage when a certain time has elapsed after the optical modulator of the optical transmission device shown in FIG. 1 is turned on. FIG. 2 is a diagram for explaining an optimum value of a bias voltage and a change in power supply voltage in the optical transmission device shown in FIG. 1. It is a block diagram which shows the structure of the optical transmitter with which feedback control is performed. FIG. 5 is a diagram for explaining a modulation curve and an operating point of an optical modulator of the optical transmission device shown in FIG. 4.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an optical transmission apparatus according to an embodiment of the present invention. Referring to FIG. 1, the optical transmission apparatus includes a light source 1, an optical modulator 2, an RF drive circuit 3, a power supply circuit 4, a bias supply circuit 5, a light detection unit 6, and a control unit 10.

The light source 1, the RF drive circuit 3, and the bias supply circuit 5 are the same as the light source 101, the RF drive circuit 103, and the bias supply circuit 105 shown in FIG. That is, the light source 1 outputs laser light according to the control signal S1 input from the control unit 10. The RF drive circuit 3 converts a digital signal corresponding to the input information into an analog drive signal and supplies the analog drive signal to the optical modulator 2. Bias supply circuit 5 operates receiving the power supply voltage from the power supply circuit 4 supplies a bias voltage V _B to the optical modulator 2 according to the driving control signal S2.

The light modulator 2 is an LN modulator and modulates light from the light source 1. LN modulators include modulation schemes such as intensity modulation, phase modulation, and polarization modulation, and the optical modulator 2 can employ any modulation scheme. Here, an LN phase modulator is used as the optical modulator 2.

In the LN phase modulator, one optical waveguide is formed on an LN substrate, and an RF driving electrode and a bias adjusting electrode are formed in the vicinity of the optical waveguide. Light from the light source 1 enters from one end of the optical waveguide. The incident light propagates in the optical waveguide and is emitted from the other end of the optical waveguide. A phase change corresponding to the drive voltage supplied to the RF drive electrode is caused to the light propagating in the optical waveguide.

The light detection unit 6 detects the output light of the light modulator 2 and includes, for example, a PD (photodiode). The output light of the optical modulator 2 is branched into two using a Y-branch waveguide or a 3 dB directional coupler, and one of the branched lights is supplied to the PD as monitor light. The PD supplies an electrical signal corresponding to the light intensity of the input monitor light to the control unit 10 as a monitor light detection signal S3. Note that the light detection unit 6 may be incorporated in the light modulator 2.

The power supply circuit 4 supplies a power supply voltage to the bias supply circuit 5, and is configured to increase or decrease the power supply voltage according to the power supply control signal S4. Such a power supply circuit 4 with a variable power supply voltage can be constituted by, for example, a DC-DC converter with a variable output voltage.

The control unit 10 supplies the control signal S 1 to the light source 1, supplies the drive control signal S 2 to the bias supply circuit 5, and supplies the power control signal S 4 to the power circuit 4. The control unit 10 performs ABC control based on the monitor light detection signal S 3 from the light detection unit 6 so that the bias voltage V _B becomes the voltage value of the operating point of the optical modulator 2. The control unit 10 according to the present embodiment further performs power supply voltage control so that a necessary minimum power supply voltage corresponding to the determined voltage value is supplied to the bias supply circuit 5.

For example, the control unit 10 inserts a pilot signal into the drive control signal S2 and extracts the inserted pilot signal from the monitor light detection signal S3 input from the light detection unit 6. Then, the inserted pilot signal and the extracted pilot signal are synchronously detected, and the bias supply circuit 5 is controlled so that the synchronous detection signal becomes 0V.

Here, the power supply voltage supplied to the bias supply circuit 5 is adjusted to the voltage value at the operating point if a voltage (for example, V _B + α) that is slightly larger than the voltage value at the operating point of the optical modulator 2 can be supplied. I can do it. The application of the RF signal from the RF drive circuit 3 is performed by AC (Alternating Current) coupling from the outside, so that it is not necessary to apply a bias voltage considering the AC amplitude.

That is, the minimum power supply voltage V ₀ necessary for the bias supply circuit 5 to supply the bias voltage V _B is given by V ₀ = V _B + α. Here, “α” is a margin (fixed value) set in advance in consideration of the configuration of the bias supply circuit 5 and the like. For example, when the power supply circuit 4 supplies the power supply voltage V ₀ (= V _B + α) to the bias supply circuit 5, when the bias voltage V _B is changed by ΔV, the power supply voltage V ₀ is also changed by ΔV. . Thereby, it is possible to supply the minimum power supply voltage V ₀ necessary for the bias supply circuit 5 to supply the bias voltage V _B.

2A and 2B are diagrams for explaining the relationship between the operating point drift of the optical modulator 2, the optimum value of the bias voltage, and the minimum required power supply voltage. 2A shows the time when the power is turned on, and FIG. 2B shows the time when a certain time has passed after the power is turned on. The modulation curve of the optical modulator 2 is shown in a two-dimensional coordinate system in which the vertical axis represents the light intensity and the horizontal axis represents the bias voltage value. In FIG. 2B, the modulation curve at power-on is shown by a broken line. The upper limit value of the bias voltage specification of the optical modulator 2 is V _max .

The modulation curve of the optical modulator 2 is a COS square function curve, and the operating point of the optical modulator 2 is set on this modulation curve. The operating point of the optical modulator 2 is appropriately set according to the modulation method. Here, since it is phase modulation, the minimum point on the modulation curve is set as an operating point (a point indicated by a circle).

In the optical modulator 2, phase modulation based on the drive signal from the RF drive circuit 3 is performed with the operating point as a reference. Specifically, when the RF electric signal is “0”, the driving voltage V ₁ is supplied to the RF driving electrode, and when the RF electric signal is “1”, the driving voltage V ₂ is for RF driving. Supplied to the electrode. Here, each of the drive voltages V ₁ and V ₂ is a voltage value based on the operating point, and is set to a voltage value at a maximum point located on the left and right of the operating point on the modulation curve. The drive voltage V ₁ is −Vπ, and the drive voltage V ₂ is + Vπ. “Vπ” is a half-wave voltage that changes the phase of light propagating in the waveguide by a half wavelength. For example, a phase change amount of 2π occurs between the phase of light when the drive voltage V ₁ (−Vπ) is supplied and the phase of light when the drive voltage V ₂ (+ Vπ) is supplied.

When the power is turned on, the voltage value of the operating point of the optical modulator 2 (the operating point A in FIG. 2A) is V _B 1. The minimum power supply voltage value required for the bias supply circuit 5 to supply the bias voltage V _B having the voltage value V _B 1 to the optical modulator 2 is V _min 1 = V _B 1 + α.

The controller 10 controls the bias supply circuit 5 so that the bias voltage V _B becomes the voltage value V _B 1, and at the same time controls the power supply circuit 4 so that the power supply voltage V ₀ becomes the voltage value V _min 1. Thereby, the bias supply circuit 5 can secure a necessary voltage control range, and the optical modulator 2 performs phase modulation based on the drive signal from the RF drive circuit 3 with the operating point A as a reference. In this case, compared with the example shown in FIG. 5, the power supply voltage is lower by [V _max −V _min 1], so that the power consumption by the bias supply circuit 5 can be reduced.

After the power is turned on, the operating point of the optical modulator 2 changes from the operating point A to the operating point B over time. In FIG. 2B, the voltage value at the operating point B is V _B 2 (> V _B 1). The minimum power supply voltage value required for the bias supply circuit 5 to supply the bias voltage V _B having the voltage value V _B 2 to the optical modulator 2 is V _min 2 = V _B 2 + α.

The control unit 10 controls the power supply circuit 4 so that the power supply voltage V ₀ becomes the voltage value V _min 2 at the same time as controlling the bias supply circuit 5 so that the bias voltage V _B becomes the voltage value V _B 2. Thereby, the bias supply circuit 5 can secure a necessary voltage control range, and the optical modulator 2 performs phase modulation based on the drive signal from the RF drive circuit 3 with the operating point B as a reference. In this case, compared with the example shown in FIG. 5, the power supply voltage is lower by [V _max −V _min 2], so that the power consumption by the bias supply circuit 5 can be reduced.

FIG. 3 is a diagram for explaining the change in the optimum value (voltage at the operating point) of the bias voltage and the change in the power supply voltage supplied to the bias supply circuit 5. The vertical axis represents the bias voltage, and the horizontal axis represents time. A graph G1 shows a change in the optimum value (voltage at the operating point) of the bias voltage. A graph G2 shows a change in the power supply voltage. A hatched area S indicates a reduction amount of the power supply voltage. As the power supply voltage reduction amount increases, the power consumption reduction amount increases.

As shown in the graph G1, the bias voltage V _B gradually increases as the operating point changes. Further, as shown in the graph G2, the power supply voltage V ₀ gradually increases as the bias voltage V _B changes. The difference between the bias voltage V _B and the power supply voltage V ₀ corresponds to the above “α”. As can be seen from the hatched area S, the power consumption reduction effect is greatest when the power is turned on, and then gradually decreases with time.

A method of gradually increasing the power supply voltage at a fixed rate is also conceivable. However, in this method, the speed of the operating point drift of the optical modulator 2 is not constant, and varies depending on the operating conditions and the characteristics (inherent characteristics) of the optical modulator 2, so that the bias voltage V _B is set to an optimum value. However, there are cases where the power supply voltage necessary for this cannot be obtained. In the present embodiment, since by changing the power supply voltage V ₀ in accordance with a change in the bias voltage V _B, it is possible to reliably secure the power supply voltage required to the optimum value bias voltage V _B.

As described above, according to the optical transmission device of the present embodiment, the bias voltage V _B can be maintained at an optimum value even when the operating point of the optical modulator 2 fluctuates. There is no problem of distortion.

In addition, since the bias supply circuit 5 is operated at a power supply voltage (minimum required power supply voltage) slightly higher than the voltage value at the operating point of the optical modulator 2, power consumption can be reduced. As described above, since the drive voltage based on the RF electrical signal is applied by AC coupling, it is not necessary to apply the bias voltage in consideration of the AC amplitude.

Although the effect of reducing power consumption differs depending on the configuration of the optical modulator 2, for example, the power consumption can be reduced to half or less as compared with the specification considering long-term reliability. For example, when a modulator with a bias voltage specification of ± 50 V is used, the specification with consideration for long-term reliability needs to set the power supply voltage to 50 V, whereas in this embodiment, the operating point is If it is about 10V, the power supply voltage of the bias supply circuit 5 may be about 12V (about 1/4). That is, when the power supply voltage can be lowered by about 38 V and the power consumption can be considered to be proportional to the power supply voltage, the power consumption can be reduced to about ¼.

In addition, due to the characteristics of the optical modulator 2, the operating point may drift once in the minus direction and then drift in the plus direction. According to this embodiment, the bias voltage V _B is changed according to the monitor light detection signal S3, and the power supply voltage V ₀ is changed according to the change of the bias voltage V _B. For this reason, even if the operating point moves in either the plus direction or the minus direction, it is possible to follow the bias voltage V _B and the power supply voltage V ₀ .

Here, the optical modulator 2 is not limited to the LN phase modulator. For example, the optical modulator 2 may be an LN intensity modulator. Hereinafter, as a modification, an optical transmission device in which the optical modulator 2 is configured by an LN intensity modulator will be described.

The LN intensity modulator is formed with first and second optical waveguides constituting a Mach-Zehnder interferometer on an LN substrate, and in addition to the first and second optical waveguides, an RF driving electrode In addition, a bias adjusting electrode is formed.

One end of the first and second optical waveguides is coupled to the first Y branch waveguide, and the other end is coupled to the second Y branch waveguide. Light from the light source 1 is supplied to the first and second optical waveguides via the first Y branch waveguide. The light propagated through each of the first and second optical waveguides is multiplexed by the second Y branch waveguide. The light detection unit 6 detects a part of the output light output through the second Y-branch waveguide as monitor light.

The operating point of the optical modulator 2 is set between the maximum point and the minimum point of the modulation curve shown in FIG. 2A and the like. The drive voltage V ₁ when the RF electrical signal is “0” is a minimum voltage value, and the drive voltage V ₂ when the RF electrical signal is “1” is a maximum voltage value.

If the drive voltage V ₁ is supplied, there is no phase difference between the lights propagated through the respective first and second optical waveguides. In this case, in the second Y-branch waveguide, the light from the first optical waveguide and the light from the second optical waveguide are combined without canceling each other and output from the optical modulator 2.

On the other hand, when the driving voltage V ₂ is supplied, the phase difference of 180 ° between light propagating in the respective first and second optical waveguides is produced. In this case, in the second Y-branch waveguide, the light from the first optical waveguide and the light from the second optical waveguide cancel each other, so that no light is output from the optical modulator 2.

Also in this modification using the LN intensity modulator, the control unit 10 determines that the bias voltage V _B becomes the voltage value of the operating point of the optical modulator 2 based on the monitor light detection signal S3 from the light detection unit 6. Thus, the bias voltage control is performed, and the power supply voltage control for performing the bias voltage supply operation with the minimum necessary power supply voltage is performed.

The control unit 10 inserts a pilot signal into the drive control signal S2 and the pilot signal inserted from the monitor light detection signal S3 input from the light detection unit 6 at the time of intensity modulation as well as at the time of phase modulation. Extract. Then, the inserted pilot signal and the extracted pilot signal are synchronously detected, and the bias supply circuit 5 is controlled so that the synchronous detection signal becomes 0V. Thereby, there exists an effect | action and effect similar to the case where an LN phase modulator is used.

Further, the optical modulator 2 may be formed using a material other than LN, for example, a material having an electro-optic effect such as LiTaO ₃ or KTiOPO ₄ .

Also, a DP-QPSK (Dual Polarization / Quadrature / Phase / Shift / Keying) modulation system that assigns 4-bit data to the optical modulator 2 may be employed. In this case, the effect of reducing power consumption is further increased. For example, assuming that the number of terminals to be controlled is six and the number of ICs (integrated circuits) with a current consumption of about 10 mA, such as an operational amplifier for controlling each terminal, is six, the power consumption reduction amount is 38 V ( (Voltage drop) × 6 (terminal) × 10 (mA) = 2.3 W.

In the optical transmitter and the power supply voltage control method, ABC control may be obtained by any method as long as the operating point of the optical modulator can be stabilized. For example, using the method described in Patent Document 3, training is performed to calculate the intermediate point from the minimum and maximum values of the operating point bias set value, and the calculated intermediate value is used as an appropriate operation of the external modulator. It can also be a point.

In the above optical transmitter, the light source, the optical modulator, the feedback unit, the power supply circuit, the bias supply circuit, and the control unit are the light source 1, the optical modulator 2, the light detection unit 6, the power supply circuit 4, and the bias shown in FIG. It may be configured by the supply circuit 5 and the control unit 10.

It should be noted that the present invention is not limited to the above-described embodiment, and any design change or the like within a range not departing from the gist of the present invention is included in the present invention. Moreover, although a part or all of said embodiment can be described also as the following additional remarks, it is not restricted to the following.

[Appendix 1]
A light source;
An optical modulator that takes a drive signal and a bias voltage as inputs, modulates light from the light source according to the drive signal, and changes the intensity of output light according to the bias voltage;
A feedback unit that outputs feedback information indicating a deviation amount of the bias voltage with respect to an operating point of the optical modulator in which the intensity of the output light is set to a predetermined value;
A power supply circuit that outputs a power supply voltage;
A bias supply circuit that operates by receiving the power supply voltage and supplies the bias voltage to the optical modulator;
A control unit for controlling the supply operation of the bias voltage of the bias supply circuit and the output operation of the power supply voltage of the power supply circuit,
The said control part is an optical transmission apparatus which changes the said power supply voltage according to the value of this bias voltage while changing the said bias voltage based on the said feedback information.

[Appendix 2]
The optical transmitter according to appendix 1, wherein a difference between the power supply voltage and the bias voltage is constant.

[Appendix 3]
The optical transmission device according to

appendix

1 or 2, wherein the power supply circuit includes a DC-DC converter having a variable output voltage.

[Appendix 4]
The feedback unit includes a light detection unit that detects the intensity of the output light and supplies the detection value to the control unit as the feedback information.
The control unit superimposes a predetermined pilot signal on the bias voltage, and changes the bias voltage so that a synchronous detection result between the pilot signal extracted from the detection value and the pilot signal becomes 0. 4. The optical transmission device according to any one of 3.

[Appendix 5]
The optical transmission device according to appendix 4, wherein the light detection unit is incorporated in the optical modulator.

[Appendix 6]
The optical transmitter according to any one of appendices 1 to 5, wherein the optical modulator is made of lithium niobate.

[Appendix 7]
The driving signal and the bias voltage are input, respectively, and the light from the light source is modulated according to the driving signal, and the optical modulator that changes the intensity of the output light in accordance with the bias voltage, operates in response to the power supply voltage, and A power supply voltage control method for an optical transmission device comprising a bias supply circuit for supplying a bias voltage to the optical modulator,
Based on feedback information indicating the amount of deviation of the bias voltage with respect to the operating point of the optical modulator where the intensity of the output light is a predetermined value, the bias voltage is changed, and according to the value of the bias voltage, A power supply voltage control method for changing the power supply voltage.

The present invention can be applied to all optical modulators in which bias voltage control is performed.

This application claims priority based on Japanese Patent Application No. 2014-085223 filed on April 17, 2014, the entire disclosure of which is incorporated herein.

DESCRIPTION OF SYMBOLS 1 Light source 2 Optical modulator 3 RF drive circuit 4 Power supply circuit 5 Bias supply circuit 6 Optical detection part 10 Control part

Claims

Light output means for outputting light;
A light modulation unit that receives a drive signal and a bias voltage as input, modulates the light from the light output unit according to the drive signal, and changes the intensity of the output light according to the bias voltage;
Feedback means for generating feedback information indicating a deviation amount of the bias voltage with respect to an operating point of the light modulation means set to a predetermined value based on the intensity of the output light;
Power supply means for outputting a power supply voltage;
A bias supply means that operates by receiving the power supply voltage and supplies the bias voltage to the light modulation means;
Control means for controlling the supply operation of the bias voltage of the bias supply means and the output operation of the power supply voltage of the power supply means,
The control means changes the bias voltage based on the feedback information, and changes the power supply voltage according to the value of the bias voltage.
Optical transmitter.
The optical transmission device according to claim 1, wherein the control unit changes the power supply voltage so that a difference between the power supply voltage and the bias voltage is constant.
3. The optical transmission device according to claim 1, wherein the power supply means comprises a DC-DC converter with variable output voltage.
The feedback unit includes a light detection unit that detects the intensity of the output light and supplies the detected value to the control unit as the feedback information.
The control means superimposes a predetermined pilot signal on the bias voltage, and changes the bias voltage so that a synchronous detection result between the pilot signal extracted from the detection value and the pilot signal becomes zero. 4. The optical transmission device according to any one of items 1 to 3.
The optical transmission device according to claim 4, wherein the optical detection unit is incorporated in the optical modulation means.
The optical transmitter according to any one of claims 1 to 5, wherein the optical modulation means is configured by a modulator using lithium niobate.
The optical transmission device according to any one of claims 1 to 6, further comprising an RF drive unit that converts a digital signal corresponding to the input information into an analog drive signal and supplies the analog drive signal to the optical modulation unit.
The driving signal and the bias voltage are input, respectively, and the light from the light source is modulated according to the driving signal, and the optical modulator that changes the intensity of the output light in accordance with the bias voltage, operates in response to the power supply voltage, and A power supply voltage control method for an optical transmission device comprising a bias supply circuit for supplying a bias voltage to the optical modulator,
The bias voltage is changed based on feedback information that is generated based on the intensity of the output light and indicates a deviation amount of the bias voltage with respect to the operating point of the optical modulator that is set to a predetermined value. Changing the power supply voltage according to a value;
Power supply voltage control method.