# US 2014/0153077 A1 · Optical modulation device and bias voltage control method

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2014/0153077 A1
- Document ID: US20140153077A1
- Status: Published application
- Kind: A1
- Application number: 14/122,687
- Filed: 2012-08-21
- Published: 2014-06-05
- Earliest claimed: 2011-08-22
- Assignees: Nippon Telegraph and Telephone Corporation
- Inventors: Hiroto Kawakami; Eiji Yoshida; Yutaka Miyamoto
- Web page: https://patentgrep.com/patent/US20140153077A1

## CPC

- G02F 1/0123: {Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops}
- G02F 1/21: by interference
- H04B 10/5053: {using a parallel, i.e. shunt, combination of modulators}
- H04B 10/50575: {to control the modulator DC bias}
- H04B 10/541: {Digital intensity or amplitude modulation}
- H04L 27/3411: {reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set}
- H04L 27/364: {Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels}
- G02B 6/28: having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02F 1/212: {Mach-Zehnder type}
- H04B 10/50595: {to control the modulator DC bias}
- H04B 10/548: Phase or frequency modulation
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An optical modulation device including: bias power supplies that output a signal having a bias voltage corresponding to the null point of an optical modulation unit to the optical modulation unit; and synchronous detection circuits that determine whether an intensity of a QAM signal at a drift non-occurrence time where no drift occurs in the bias voltage becomes larger or smaller than the intensity of the QAM signal at a drift occurrence time where a drift occurs in the bias voltage, adjust the bias voltage to maximize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time, and adjust the bias voltage to minimize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time.

## Claims

### Claim 1

An optical modulation device, comprising:
an I-component optical modulation unit that modulates a continuous optical signal for an I-component of a QAM signal;
a Q-component optical modulation unit that modulates a continuous optical signal for a Q-component of the QAM signal;
a phase shift unit that shifts a phase of an optical signal on an input side and/or an output side for the I-component optical modulation unit and/or the Q-component signal optical modulation unit to adjust a phase difference between an output of the I-component optical modulation unit and an output of the Q-component optical modulation unit after the phase shift to π/2;
a QAM signal generation unit that multiplexes the output of the I-component optical modulation unit and the output of the Q-component optical modulation unit after the phase shift to generate the QAM signal;
an I-component data signal output unit that outputs an I-component data signal to the I-component optical modulation unit to cause the I-component optical modulation unit to modulate a continuous optical signal using the I-component data signal;
a Q-component data signal output unit that outputs a Q-component data signal to the Q-component optical modulation unit to cause the Q-component optical modulation unit to modulate a continuous optical signal using the Q-component data signal;
an I-component bias voltage signal output unit that outputs a signal having an I-component bias voltage corresponding to a null point of the I-component optical modulation unit to the I-component optical modulation unit;
a Q-component bias voltage signal output unit that outputs a signal having a Q-component bias voltage corresponding to a null point of the Q-component optical modulation unit to the Q-component optical modulation unit;
an I-component bias voltage signal adjustment unit that
determines whether an intensity of the QAM signal at a drift non-occurrence time where no drift occurs in the I-component bias voltage becomes larger or smaller than the intensity of the QAM signal at a drift occurrence time where a drift occurs in the I-component bias voltage,
adjusts the I-component bias voltage to maximize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time, and
adjusts the I-component bias voltage to minimize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time; and
a Q-component bias voltage signal adjustment unit that
determines whether the intensity of the QAM signal at a drift non-occurrence time where no drift occurs in the Q-component bias voltage becomes larger or smaller than the intensity of the QAM signal at a drift occurrence time where a drift occurs in the Q-component bias voltage,
adjusts the Q-component bias voltage to maximize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time, and
adjusts the Q-component bias voltage to minimize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time.

### Claim 2 (depends on 1)

The optical modulation device according to claim 1, further comprising:
an I-component calculation unit that calculates a value shown in Equation 25 when a voltage of the I-component data signal is Vmi (where mi=0, 1, . . . , ni/2−1 when a number of the I-component data signal level is ni) and a half wavelength voltage of the I-component optical modulation unit is Vπi; and
∑
m
i
=
0
n
i
/
2
-
1

cos

(
V
m


i
V
π


i

π
)
(
Equation


25
)
a Q-component calculation unit that calculates a value shown in Equation 26 when a voltage of the Q-component data signal is Vmq (where mq=0, 1, . . . , nq/2−1 when a number of the Q-component data signal level is nq) and a half wavelength voltage of the Q-component optical modulation unit is Vπq,
∑
m
q
=
0
n
q
/
2
-
1

cos

(
V
mq
V
π


q

π
)
(
Equation


26
)
wherein
the I-component bias voltage signal adjustment unit
determines that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time when the value shown in Equation 25 and calculated by the I-component calculation unit is negative and
determines that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time when the value shown in Equation 25 and calculated by the I-component calculation unit is positive, and
the Q-component bias voltage signal adjustment unit
determines that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time when the value shown in Equation 26 and calculated by the Q-component calculation unit is negative and
determines that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time when the value shown in Equation 26 and calculated by the Q-component calculation unit is positive.

### Claim 3 (depends on 1)

The optical modulation device according to claim 1, further comprising:
an I-component data signal voltage adjustment unit that adjusts, when the I-component bias voltage signal adjustment unit determines that the intensity of the QAM signal at the drift non-occurrence time becomes equal to the intensity of the QAM signal at the drift occurrence time, the voltage of the I-component data signal such that the I-component bias voltage signal adjustment unit determines that the intensity of the QAM signal at the drift non-occurrence time does not become equal to the intensity of the QAM signal at the drift occurrence time; and
a Q-component data signal voltage adjustment unit that adjusts, when the Q-component bias voltage signal adjustment unit determines that the intensity of the QAM signal at the drift non-occurrence time becomes equal to the intensity of the QAM signal at the drift occurrence time, the voltage of the Q-component data signal such that the Q-component bias voltage signal adjustment unit determines that the intensity of the QAM signal at the drift non-occurrence time does not become equal to the intensity of the QAM signal at the drift occurrence time.

### Claim 4

An optical modulation device that generates a QAM signal whose order is set to be constant, the device comprising:
an I-component optical modulation unit that modulates a continuous optical signal for an I-component of the QAM signal;
a Q-component optical modulation unit that modulates a continuous optical signal for a Q-component of the QAM signal;
a phase shift unit that shifts a phase of an optical signal on an input side and/or an output side for the I-component optical modulation unit and/or the Q-component signal optical modulation unit to adjust a phase difference between an output of the I-component optical modulation unit and an output of the Q-component optical modulation unit after the phase shift to π/2;
a QAM signal generation unit that multiplexes the output of the I-component optical modulation unit and the output of the Q-component optical modulation unit after the phase shift to generate the QAM signal;
an I-component data signal output unit that outputs an I-component data signal whose amplitude is controlled to be constant to the I-component optical modulation unit to cause the I-component optical modulation unit to modulate a continuous optical signal using the I-component data signal;
a Q-component data signal output unit that outputs a Q-component data signal whose amplitude is controlled to be constant to the Q-component optical modulation unit to cause the Q-component optical modulation unit to modulate a continuous optical signal using the Q-component data signal;
an I-component bias voltage signal output unit that outputs a signal having an I-component bias voltage corresponding to a null point of the I-component optical modulation unit to the I-component optical modulation unit;
a Q-component bias voltage signal output unit that outputs a signal having a Q-component bias voltage corresponding to a null point of the Q-component optical modulation unit to the Q-component optical modulation unit;
an I-component bias voltage signal adjustment unit that maximizes or minimizes an intensity of the QAM signal to adjust the I-component bias voltage to an optimum value; and
a Q-component bias voltage signal adjustment unit that maximizes or minimizes the intensity of the QAM signal to adjust the Q-component bias voltage to an optimum value.

### Claim 5 (depends on 4)

The optical modulation device according to claim 4, wherein
Vmi is a constant at all times when a voltage of the I-component data signal is Vmi (where mi=0, 1, . . . , ni/2−1 when a number of the I-component data signal level is ni),
Vmq is a constant at all times when a voltage of the Q-component data signal is Vmq (where mq=0, 1, . . . , nq/2−1 when a number of the Q-component data signal level is nq),
the I-component bias voltage signal adjustment unit
adjusts the I-component bias voltage to maximize the intensity of the QAM signal at all times when a constant set by Equation 27 is negative and
adjusts the I-component bias voltage to minimize the intensity of the QAM signal at all times when the constant set by Equation 27 is positive, and
∑
m
i
=
0
n
i
/
2
-
1

cos

(
V
m


i
V
π


i

π
)
(
Equation


27
)
the Q-component bias voltage signal adjustment unit
adjusts the Q-component bias voltage to maximize the intensity of the QAM signal at all times when a constant set by Equation 28 is negative and
adjusts the Q-component bias voltage to minimize the intensity of the QAM signal at all times when the constant set by Equation 28 is positive.
∑
m
q
=
0
n
q
/
2
-
1

cos

(
V
mq
V
π


q

π
)
(
Equation


28
)

### Claim 6 (depends on 1)

The optical modulation device according to claim 1, further comprising:
an I-component dither voltage signal output unit that outputs a signal, which is superposed on the signal having the I-component bias voltage and has an I-component dither voltage having a frequency ωd, to the I-component optical modulation unit; and
a Q-component dither voltage signal output unit that outputs a signal, which is superposed on the signal having the Q-component bias voltage and has a Q-component dither voltage having a phase difference π/2 between the frequency ωd and the I-component dither voltage, to the Q-component optical modulation unit, wherein
the I-component bias voltage signal adjustment unit performs synchronous detection of the QAM signal with the signal having the I-component dither voltage and adjusts the I-component bias voltage such that a result of the synchronous detection becomes 0 to optimize the intensity of the QAM signal to an extreme value, and
the Q-component bias voltage signal adjustment unit performs synchronous detection of the QAM signal with the signal having the Q-component dither voltage and adjusts the Q-component bias voltage such that a result of the synchronous detection becomes 0 to optimize the intensity of the QAM signal to an extreme value.

### Claim 7 (depends on 6)

The optical modulation device according to claim 6, further comprising:
a phase shift unit bias voltage signal output unit that outputs a signal having a phase shift unit bias voltage, which is used to adjust the phase difference between the output of the I-component optical modulation unit and the output of the Q-component optical modulation unit after the phase shift to π/2, to the phase shift unit; and
a phase shift unit bias voltage signal adjustment unit that performs synchronous detection of the QAM signal with a signal having a frequency 2ωd twice the frequency ωd and adjusts the phase shift unit bias voltage such that a result of the synchronous detection becomes 0 to adjust the phase difference between the output of the I-component optical modulation unit and the output of the Q-component optical modulation unit after the phase shift to π/2.

### Claim 8 (depends on 7)

The optical modulation device according to claim 7, further comprising:
an I-component bias voltage signal sweeping unit that sweeps the I-component bias voltage in a range of 2 Vπi or larger at an initializing operation of the optical modulation device when the half wavelength voltage of the I-component optical modulation unit is Vπi;
a Q-component bias voltage signal sweeping unit that sweeps the Q-component bias voltage in a range of 2 Vπq or larger at the initializing operation of the optical modulation device when the half wavelength voltage of the Q-component optical modulation unit is Vπq;
a phase shift unit bias voltage signal initialization unit that
performs synchronous detection of the QAM signal with the signal having frequency 2ωd twice the frequency ωd while causing the I-component bias voltage signal sweeping unit and the Q-component bias voltage signal sweeping unit to perform the sweeping operation at the initializing operation of the optical modulation device and
initializes the phase shift unit bias voltage such that a result of the synchronous detection becomes 0 or becomes the closest to 0 at all times in a range of the sweeping operation of I-component bias voltage signal sweeping unit and the Q-component bias voltage signal sweeping unit; and
a post-initialization adjustment unit that causes the I-component bias voltage signal adjustment unit, the Q-component bias voltage signal adjustment unit, and the phase shift unit bias voltage signal adjustment unit to perform adjustment after the initialization of the phase shift unit bias voltage by the phase shift unit bias voltage signal initialization unit.

### Claim 9 (depends on 1)

The optical modulation device according to claim 1, further comprising:
a controller unit that
stops the Q-component bias voltage signal adjustment unit when operating the I-component bias voltage signal adjustment unit and
stops the I-component bias voltage signal adjustment unit when operating the Q-component bias voltage signal adjustment unit.

### Claim 10 (depends on 1)

The optical modulation device according to claim 1, wherein
a progression {Vmi} becomes an arithmetic progression when the voltage of the I-component data signal is Vmi (where mi=0, 1, . . . , ni/2−1 when the number of the I-component data signal level is ni), and
a progression {Vmq} becomes an arithmetic progression when the voltage of the Q-component data signal is Vmq (where mq=0, 1, . . . , nq/2−1 when the number of the Q-component data signal level is nq).

### Claim 11 (depends on 1)

The optical modulation device according to claim 1, wherein
a progression {sin(Vmi/Vπi×π/2)} becomes an arithmetic progression when the voltage of the I-component data signal is Vmi (where mi=0, 1, . . . , ni/2−1 when the number of the I-component data signal level is ni) and the half wavelength voltage of the I-component optical modulation unit is Vπi, and
a progression {sin(Vmq/Vπq×π/2)} becomes an arithmetic progression when the voltage of the Q-component data signal is Vmq (where mq=0, 1, . . . , nq/2−1 when the number of the Q-component data signal level is nq) and the half wavelength voltage of the Q-component optical modulation unit is Vπq.

### Claim 12

A bias voltage control method, comprising:
I and Q component optical modulation steps of modulating continuous optical signals for I and Q components of a QAM signal;
a phase shift step of shifting a phase of an optical signal on an input side and/or an output side for the I-component optical modulation step and/or the Q-component signal optical modulation step and adjusting a phase difference between an output of the I-component optical modulation step and an output of the Q-component optical modulation step after the phase shift to π/2; and
a QAM signal generation step of multiplexing the output of the I-component optical modulation step and the output of the Q-component optical modulation step after the phase shift to generate the QAM signal, wherein
the I-component optical modulation step sequentially includes
an I-component signal input step of
inputting an I-component data signal used to modulate a continuous modulation signal and
inputting a signal having an I-component bias voltage corresponding to a null point of the I-component optical modulation step and
an I-component bias voltage signal adjustment step of
determining whether an intensity of the QAM signal at a drift non-occurrence time where no drift occurs in the I-component bias voltage becomes larger or smaller than the intensity of the QAM signal at a drift occurrence time where a drift occurs in the I-component bias voltage,
adjusting the I-component bias voltage to maximize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time, and
adjusting the I-component bias voltage to minimize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time, and
the Q-component optical modulation step sequentially includes
a Q-component signal input step of
inputting a Q-component data signal used to modulate a continuous modulation signal and
inputting a signal having a Q-component bias voltage corresponding to a null point of the Q-component optical modulation step and
a Q-component bias voltage signal adjustment step of
determining whether the intensity of the QAM signal at a drift non-occurrence time where no drift occurs in the Q-component bias voltage becomes larger or smaller than the intensity of the QAM signal at a drift occurrence time where a drift occurs in the Q-component bias voltage,
adjusting the Q-component bias voltage to maximize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes larger than the intensity of the QAM signal at the drift occurrence time, and
adjusting the Q-component bias voltage to minimize the intensity of the QAM signal when determining that the intensity of the QAM signal at the drift non-occurrence time becomes smaller than the intensity of the QAM signal at the drift occurrence time.