JP2001075062A - Optical modulation device and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC bias setting circuit shortening a time when an optical modulator is converged to an optimum operationg point by preliminarily setting the initial value of the DC bias while predicting an optimum operating point. SOLUTION: In an optical modulation device 10 which is provided with a light source for optical communication LD1, an optical modulator 2 intensity modulating the output light of the light source LD1, a branching circuit 3 branching an optical signal for monitor from an optical signal whose intensity is modulated, a PD 4 converting the branched optical signal into an electric signal and a DC bias setting circuit 5 which sets a DC bias based on this electric signal and outputs it to the modulator 2, the circuit 5 predicts an operating point most suitable to the intesity modulation to set the initial value of the DC bias based on this operating point and it calculates the mean intensity of the optical signal at the operating point to adjust the setting value of the DC bias by comparing this mean intensity with the electric signal from the PD 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a DC bias setting circuit for controlling an operating point in an optical modulation device and a storage medium therefor.

[0002]

2. Description of the Related Art In recent years, a Mach-Zehnder type optical modulator has been used in an optical communication system for transmitting a large amount of data through an optical fiber. However, in this Mach-Zehnder type optical modulator, there is a DC drift in which the operating point for performing optical modulation shifts as shown in FIG. There is a problem that light is not intensity-modulated accurately. Therefore, conventionally, control has been performed such that the operating point is optimized.

In Japanese Patent Laid-Open No. 6-67128, a monitoring optical signal branched from output light of an optical modulator is compared with a predetermined reference voltage to control a bias voltage applied to the optical modulator. Operating point control.

[0004]

However, in the above control, the initial value of the bias voltage is set to a certain constant, the output signal of the optical modulator is monitored, and the bias voltage is changed in accordance with the output signal. Since feedback is provided to the optical modulator, it takes time to converge to the optimum operating point.

In some cases, the time required to converge to the optimum operating point varies greatly due to a change in the operating point or the like, or the operation point converges to an erroneous half-period or one-period operating point.

SUMMARY OF THE INVENTION An object of the present invention is to predict an optimal operating point and obtain a D
An object of the present invention is to provide a DC bias setting circuit that sets the initial value of the C bias in advance to shorten the time required for convergence to the optimum operating point.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention according to claim 1 comprises a light source for optical communication, an optical modulator for intensity-modulating an optical signal output from the light source, and an optical modulator. A branching unit for branching an optical signal for monitoring from an optical signal intensity-modulated by the modulation unit, a conversion unit for converting the optical signal branched by the branching unit into an electric signal, and an electric signal converted by the conversion unit And a DC bias setting unit for setting a DC bias in the optical modulation unit by detecting and referring to the DC bias setting unit, wherein the DC bias setting unit sets a plurality of reference points for measuring an average intensity of the optical signal. An average intensity measuring unit (for example, corresponding to steps S1 and S2 in the flowchart shown in FIG. 5) for measuring the average intensity of the optical signal at each of the set reference points, and the average intensity measuring unit Measured operating point predicting means for predicting the operating point is optimum for the intensity modulation based on the average intensity (e.g., step S3~ of the flowchart shown in FIG. 5
Corresponds to S5. ), Wherein the DC bias is set based on the operating point predicted by the operating point predicting means.

According to the first aspect of the present invention, the DC bias setting section measures the average intensity of the optical signal at a plurality of reference points by the average intensity measuring means, and based on the average intensity by the operating point estimating means. An operating point that is optimal for the intensity modulation of the optical signal is predicted, and a DC bias is set based on the predicted operating point, so that the operating point converges to an incorrect operating point that is not the optimal operating point for the intensity modulation of the optical signal. Can be prevented.

According to a second aspect of the present invention, in the optical modulator according to the first aspect, the DC bias setting section sets an initial value of the DC bias based on the operating point predicted by the operating point predicting means. Initial value setting means (corresponding to, for example, steps S5 and S7 in the flowchart shown in FIG. 5) to be output to the optical modulation section, and averaging of the optical signal based on the operating point predicted by the operating point predicting means. An average intensity calculating means for calculating the intensity (corresponding to, for example, step S6 of the flowchart shown in FIG. 5), the electric signal converted by the conversion unit, the average intensity calculated by the average intensity calculating means, DC bias adjusting means for adjusting the set value of the DC bias and outputting the adjusted value to the optical modulator (for example, corresponds to step S8 in the flowchart shown in FIG. 5). ) Is further provided.

According to the second aspect of the present invention, the DC bias setting section sets the initial value of the DC bias by the initial value setting means based on the predicted operating point, and sets the operating point by the average intensity calculating means. Is calculated by comparing the average intensity of the optical signal at step (1) with the electric signal converted by the conversion unit by the DC bias adjusting means, and adjusting the set value of the DC bias. Thus, the time required to converge to the operating point can be reduced.

[0011] The invention according to claim 3 is the invention according to claim 1 or 2.
In the optical modulator according to the aspect, the average intensity measurement unit includes:
The DC bias value of the plurality of reference points is set near zero.

According to the third aspect of the present invention, the plurality of reference points are set to have DC bias values near zero by the average intensity measuring means provided in the DC bias setting section, so that the reference point is optimal for intensity modulation of an optical signal. The prediction of the operating point can be easily executed.

According to a fourth aspect of the present invention, there is provided a storage medium, comprising: a light source for optical communication; an optical modulator for intensity-modulating an optical signal output from the light source; A branching unit for branching the optical signal, a conversion unit for converting the optical signal branched by the branching unit into an electric signal, and detecting and referencing the electric signal converted by the conversion unit to the optical modulation unit for DC. A storage medium storing a computer-executable program in an optical modulation device including a DC bias setting unit for setting a bias, wherein a plurality of reference points for measuring an average intensity of an optical signal are set, and the set reference points are set. A computer-executable program code for measuring the average intensity of the optical signal at each reference point, and for predicting an operating point that is optimal for intensity modulation based on the measured average intensity. And computer executable program code, and characterized by storing a program comprising a program code executable computer for setting the DC bias based on a predicted operating point.

According to the storage medium of the present invention, a light source for optical communication, an optical modulator for intensity-modulating an optical signal output from the light source, and an optical signal intensity-modulated by the optical modulator A branching unit for branching an optical signal for monitoring from, a converting unit for converting the optical signal branched by the branching unit into an electric signal, and detecting the electric signal converted by the converting unit,
A storage medium storing a computer-executable program in an optical modulation device including a DC bias setting unit for setting a DC bias in the optical modulation unit, and executing the program stored in the storage medium. By doing so, the computer (corresponding to, for example, the DC bias setting circuit 5 shown in FIG. 1) sets a plurality of reference points for measuring the average intensity of the optical signal, and sets the optical signal at each of the set reference points. Since the average intensity is measured, the operating point that is optimal for the intensity modulation is predicted based on the measured average intensity, and the DC bias is set based on the predicted operating point, so that it is optimal for the intensity modulation of the optical signal. It is possible to prevent convergence to an erroneous operating point that is not a proper operating point.

According to a fifth aspect of the present invention, there is provided a storage medium, comprising: a light source for optical communication; an optical modulator for intensity-modulating an optical signal output from the light source; A branching unit for branching the optical signal, a conversion unit for converting the optical signal branched by the branching unit into an electric signal, and detecting and referencing the electric signal converted by the conversion unit to the optical modulation unit for DC. A storage medium storing a computer-executable program in an optical modulation device having a DC bias setting unit for setting a bias, wherein an initial value of a DC bias is set based on a predicted operating point. And computer-executable program code for calculating an average intensity of an optical signal based on a predicted operating point And a computer-executable program code for comparing the electric signal converted by the conversion unit with the calculated average intensity, adjusting the set value of the DC bias, and outputting the adjusted DC bias to the light modulation unit. Is stored.

According to the storage medium of the present invention, a light source for optical communication, an optical modulator for intensity-modulating an optical signal output from the light source, and an optical signal intensity-modulated by the optical modulator A branching unit for branching an optical signal for monitoring from, a converting unit for converting the optical signal branched by the branching unit into an electric signal, and detecting the electric signal converted by the converting unit,
A storage medium storing a computer-executable program in an optical modulation device including a DC bias setting unit for setting a DC bias in the optical modulation unit, and executing the program stored in the storage medium. By doing so, the computer (corresponding to, for example, the DC bias setting circuit 5 shown in FIG. 1) sets the initial value of the DC bias based on the predicted operating point, outputs the initial value to the optical modulation unit, and outputs the predicted value. The average intensity of the optical signal is calculated based on the operating point, and the electric signal converted by the conversion unit is compared with the calculated average intensity to adjust the set value of the DC bias and output to the optical modulation unit. For this reason, it is possible to shorten the time required to converge on the operating point as compared with the conventional setting of the DC bias.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical modulator 10 according to the present invention will be described below in detail with reference to FIGS.

FIG. 1 shows an optical modulator 10 to which the present invention is applied.
FIG. 2 is a block diagram showing an internal configuration of the device. In the figure,
The optical modulator includes an LD1, an optical modulator 2, a branch circuit 3, a PD
4 and a DC bias setting circuit 5.

The optical modulator 2 converts the output light output from the LD (Laser Diode) 1 into an input DC bias Vdc.
And intensity-modulated based on the input signal Vs and outputs the intensity-modulated light to the branch circuit 3. Further, as a characteristic of the optical modulator 2, the relationship between the average power P of the modulated light and the applied voltage V is approximated by a cosine wave as shown in the following equation (1). P = Acos (πV / v−φ) + B (1)

In equation (1), A is the amplitude of the wave, v is the half-wave voltage, φ is the phase, and B is the offset value in the P-axis direction (see FIG. 3).

The PD (Photo Diode) 4 detects the average power P of the modulated light branched by the branch circuit 3 and
Output to the C bias setting circuit 5. The DC bias setting circuit 5 outputs a DC bias (Vdc) to the optical modulator 2 to control an optical modulation operating point.

Here, the DC bias setting circuit 5 corresponds to FIG.
As shown in (1), it is composed of a CPU 51, a memory 52, an A / D converter 53, and an I / O 54.

CPU (Central Processing Unit) 51
Executes a “DC bias setting process” (see FIG. 5) described below based on a DC bias setting process program stored in the memory 52, and adjusts a DC bias output to the optical modulator 2 based on the processing result. At the same time, the calculation result related to the DC bias setting is stored in the memory 52.

In the "DC bias setting process" described later, the CPU 51 first sets the DC bias as shown in FIG.
As a reference point near the origin where the bias is “0”, V1,
V2, V3, and V4 are set. Here, V1 is set to 0, V2 is set at a position at an interval ΔV from V1, and V3 and V4 are set at equal intervals ΔV in the same manner. And
The set reference points V1, V2, V3, V4
The average power of the modulated light at P1, P2, P3, P4
Detected as

Next, the CPU 51 calculates the following equations (2) to
Calculate φ by (5). B = (P2 + P3) / 2 + (C^Two/ 2) * ｛(P1-P3)^Two-(P2-P4) ^Two ｝ / (P 2 −P 3) Expression (2) 1 / C = −2 sin (π * ΔV / v) Expression (3) A = √ [｛(P 3 −P 2) / 2 + (C^Two/ 2) * ((P1-P3)^Two-(P2-P4)^Two) / (P2-P3)｝^Two+ C^Two* (P1-P3)^Two] Equation (4) φ = −cos^-1((P1-B) / A) Equation (5)

Then, the CPU 51 selects a desired operating point from a plurality of operating points (marked by x in FIG. 4) by designating m and n, and selects the selected operating point (m, m, n).
The voltage Vm, n in n) is calculated by the following equation (6). Here, when m = 0, the operating point is located at the lower right position, and when m = 1, the operating point is located at the lower left position. Vm, n = (v / π) {(-1) ^m (π / 2 + 2πn) + φ} Equation (6)

Further, the CPU 51 calculates the average power Pm, n at the selected operating point (m, n) by the above equation (1).
Is calculated by Next, the CPU 51 sets Vm, n as the initial value of the DC bias, and thereafter monitors the average power P input from the A / D converter 53.

Then, the CPU 51 adjusts the DC bias so that the monitored average power P becomes the same as the average power Pm, n calculated by the equation (1), and changes the DC bias from the I / O 54. Output to the optical modulator 2 to converge to a desired optimum operating point.

The memory 52 stores a DC bias setting program and the above-described equations (1) to (6), and also stores data of a reference point to be set. Further, the memory 52 stores the calculation result of the DC bias setting by the CPU 51.

The A / D converter 53 is a PD4 (see FIG. 1).
Is converted into a digital signal, and this digital signal is output to the CPU 51.

The I / O 54 transmits and receives data of the reference point and the like set by an external personal computer or the like.
Is an interface for transmitting the DC bias set by. Here, when transmitting the DC bias, the DC bias is transmitted to the optical modulator 2 via an A / D converter (not shown) provided in the I / O 54.

Further, by connecting to an external personal computer or the like via the I / O 54, the setting conditions of the reference point stored in the memory 52 and the change of the formula used in the DC bias setting process by the CPU 51 can be changed. It can be done easily.

Next, the CPU 5 of the DC bias setting circuit 5
The “DC bias setting process” executed by the first control unit 1 will be described with reference to the flowchart shown in FIG.

First, the CPU 51 sets reference points V1, V2, V3, and V4 for the light modulator (step S5).
1) The average power P at each reference point is represented by P
1, P2, P3, and P4 (Step S
2). Next, the CPU 51 calculates φ by the above equations (2) to (5) (step S3).

Then, the CPU 51 selects a desired operating point from a plurality of operating points by designating m and n (step S4), and calculates a voltage Vm, n at the selected operating point (m, n). It is calculated by the above equation (6) (step S5). Further, the CPU 51 calculates the average power Pm, n of the modulated light at the operating point (m, n) using the above equation (1) (step S6).

Next, the CPU 51 sets the calculated Vm, n as the initial value of the DC bias (Step S).
7).

Then, the CPU 51 sets the DC bias so that the average power Pm, n calculated in step S6 is equal to the average power P of the modulated light input from the PD 4 via the A / D converter 53. Is adjusted to converge to the desired optimum operating point (step S8), and the process is terminated.

As described above, in the present embodiment,
Reference points V1 and V set when DC bias is set near "0"
2, the average power P of the modulated light at V3 and V4 was measured, the optimal operating point was predicted based on the measured average power, and the initial value of the DC bias was set. Then, the average power Pm, n at the optimum operating point is calculated,
The DC bias was adjusted so that m and n and the input average power P became the same so as to converge to the optimum operating point.

Accordingly, it is possible to reduce the time required for the bias voltage to converge to the optimum operating point, as compared with the conventional case where the bias voltage is set to a certain constant.

Further, by predicting the optimum operating point based on the measured average power, it is possible to converge on an erroneous operating point, for example, an operating point shifted from the desired operating point by an integral multiple of a half-wave voltage. Can be prevented.

Further, from the plurality of operating points shown in FIG. 4, m and n can be designated to converge on a desired operating point selected.

In the equation (6), since a DC bias at an arbitrary selected operating point can be calculated, a complicated conditional branch is not required in a program for setting and processing an operating point.

[0043]

According to the first aspect of the present invention, there is provided an optical modulator comprising:
According to the storage medium described, the DC bias setting unit predicts an operating point that is optimal for intensity modulation of the optical signal based on the average intensity of the optical signal measured at the plurality of reference points, and based on the operating point. Since the DC bias is set, it is possible to prevent convergence to an erroneous operating point that is not the optimum operating point for intensity modulation of the optical signal.

According to the optical modulation device of the second aspect and the storage medium of the fifth aspect, the DC bias setting unit sets an initial value of the DC bias based on the predicted operating point,
The average intensity of the optical signal at the operating point is calculated, and the average intensity is compared with the electric signal obtained by converting the optical signal to obtain a DC signal.
By adjusting the bias setting, the conventional D
The time required to converge on the operating point can be shorter than the setting of the C bias.

According to the third aspect of the present invention, since the plurality of bias reference points are set near zero by the average intensity measuring means provided in the DC bias setting unit, the optimum operating point for intensity modulation of the optical signal is predicted. Can be easily executed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an internal configuration of a light modulation device 10 to which the present invention is applied.

FIG. 2 is a block diagram showing an internal configuration of a DC bias setting circuit 5 shown in FIG.

FIG. 3 is a diagram showing a set position of a reference point for measuring an average power P of modulated light.

FIG. 4 is a diagram showing a plurality of operating points of an optical modulator executed in the optical modulator 2.

FIG. 5 is a flowchart illustrating “DC bias setting processing” executed by a CPU 51 of the DC bias setting circuit 5;

6A and 6B are diagrams showing setting of a DC bias, wherein FIG. 6A shows that DC modulation is well set and intensity modulation is performed at an optimum operating point, and FIG. 6B shows poor setting of DC bias. FIG. 9 is a diagram showing that an operating point is not optimal.

[Explanation of symbols]

 Reference Signs List 10 light modulator 1 LD 2 light modulator 3 branch circuit 4 PD 5 DC bias setting circuit 51 CPU 52 memory 53 A / D converter 54 I / O

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[Procedure amendment]

[Submission date] September 10, 1999 (1999.9.1
0)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/04 10/06

Claims (5)

[Claims] A light source for optical communication, an optical modulator for intensity-modulating an optical signal output from the light source, and a branch for splitting a monitoring optical signal from the optical signal intensity-modulated by the optical modulator. Unit, a converter for converting the optical signal split by the splitter into an electric signal, and a DC bias setting for detecting and referring to the electric signal converted by the converter and setting a DC bias in the optical modulator by referring to the signal. A DC bias setting unit, which sets a plurality of reference points for measuring the average intensity of the optical signal, and measures the average intensity of the optical signal at each of the set reference points. Measuring means, and an operating point predicting means for predicting an operating point that is optimal for intensity modulation based on the average intensity measured by the average intensity measuring means, and an operating point predicted by the operating point predicting means. Base An optical modulator for setting a DC bias based on the DC bias. 2. An initial value setting means for setting an initial value of a DC bias based on an operating point predicted by the operating point estimating means and outputting the initial value to the optical modulation section; An average intensity calculation unit that calculates an average intensity of the optical signal based on the operating point predicted by the prediction unit, an electric signal converted by the conversion unit, and an average intensity calculated by the average intensity calculation unit. DC compared
D to adjust the set value of the bias and output to the optical modulator
The light modulation device according to claim 1, further comprising: C bias adjusting means. 3. The optical modulator according to claim 1, wherein said average intensity measuring means sets the plurality of reference points at a DC bias value near zero. 4. A light source for optical communication, an optical modulator for intensity-modulating an optical signal output from the light source, and a branch for splitting an optical signal for monitoring from the optical signal intensity-modulated by the optical modulator. Unit, a converter for converting the optical signal split by the splitter into an electric signal, and a DC bias setting for detecting and referring to the electric signal converted by the converter and setting a DC bias in the optical modulator by referring to the signal. And a storage medium storing a computer-executable program in the optical modulation device comprising: a plurality of reference points for measuring the average intensity of the optical signal; Computer executable program code to measure average intensity and computer executable to predict operating point optimal for intensity modulation based on measured average intensity Program codes and the storage medium characterized by storing a program comprising a program code executable computer for setting the DC bias based on a predicted operating point. 5. A light source for optical communication, an optical modulator for intensity-modulating an optical signal output from the light source, and a branch for splitting a monitoring optical signal from the optical signal intensity-modulated by the optical modulator. Unit, a converter for converting the optical signal split by the splitter into an electric signal, and a DC bias setting for detecting and referring to the electric signal converted by the converter and setting a DC bias in the optical modulator by referring to the signal. A storage medium storing a computer-executable program in the light modulation device comprising: a computer for setting an initial value of a DC bias based on a predicted operating point and outputting the initial value to the light modulation unit; An executable program code; a computer-executable program code for calculating an average intensity of the optical signal based on the predicted operating point; A program including a computer-executable program code for adjusting the set value of the DC bias by comparing the electric signal with the calculated average intensity and outputting the adjusted value to the optical modulation unit is stored. Storage media.