JPWO2012137280A1 - Optical transmitter and method for controlling optical transmitter - Google Patents

Abstract

An optical transmitter 1 of the present invention includes a light source 3 that outputs continuous light, a modulator 4 that modulates continuous light based on a modulation signal, and an optical signal modulated by the modulator 4 into monitor light and output light. A light branching unit 8 that branches, a light intensity detecting unit 5 that receives monitor light and generates an electrical signal according to the intensity of the monitor light, and a light that receives the monitor light and generates an electrical signal according to the wavelength of the monitor light A wavelength detection unit 6; and a control unit 12 that controls the light source based on the electrical signals generated by the light intensity detection unit 5 and the optical wavelength detection unit 6 so that the light intensity of the output light and the center wavelength of the output light are constant. .

Description

  The present invention relates to an optical transmitter and a method for controlling the optical transmitter.

  Wavelength division WDM (Wavelength Division Multiplexing) transmission schemes using RZ-DQPSK (Return to Zero Differential Quadrature Phase Shift Keying) are used as optical signal modulation schemes for long-distance and large-capacity optical communications ( Non-patent document 1 below).

  In order to perform RZ-DQPSK modulation, it is necessary to connect the modulators in multiple stages, and the number of components to be mounted is large, which causes an increase in cost and mounting area. In order to reduce the size and cost of an optical transmitter that performs RZ-DQPSK modulation, it is effective to integrate a light source and a modulator.

  Since high wavelength stability is required in the WDM transmission system, high wavelength stability is also required in an optical transmitter (integrated optical transmitter) in which a light source and a modulator are integrated (for example, Non-Patent Document 2 below). reference). In the conventional optical transmitter, it is possible to control the wavelength of the light source alone (for example, see Patent Document 1 below). When the optical wavelength and light intensity monitor are arranged at the point where the output of the light source and the modulator is branched as an integrated optical transmitter, the intensity of light input to the monitor changes due to the loss of the modulator. Control of the light wavelength of the light source becomes an issue.

  As a method for controlling the integrated optical transmitter, for example, Patent Literature 2 discloses a method for obtaining monitor light having an appropriate intensity. In Patent Document 2 below, in an optical transmitter in which a light source, a modulator, and a bandpass filter are connected in cascade, the output of the modulator is branched into monitor light and output light by a coupler, and attenuated before the monitor light is input to the monitor unit. It is the structure which lets a part pass. Thereby, the monitor light of appropriate intensity can be obtained by controlling the attenuation amount of the attenuation unit.

Japanese Examined Patent Publication No. 62-55318 JP 2003-233047 A

A. Ehrhardt, et al. “Field Trial to Upgrade an Existing 10Gbps DWDM Link by 40Gbps RZ-DQPSK Channels,” ICTON07. 9th, pp34-38, 2007. B. Villeneuve, et al. “High-stability wavelength-controlled DFB laser sources for dense WDM applications” OFC 1998, pp 381-382, 1998.

  As described above, when the light source and the modulator are integrated, the intensity of the light input to the monitor changes due to the loss of the modulator, so that the control of the light wavelength of the light source becomes a problem. However, Non-Patent Document 1, Non-Patent Document 2, and Patent Document 1 do not show a solution to this problem.

  Further, with the method of Patent Document 2, it is possible to obtain monitor light with an appropriate intensity. However, Patent Document 2 does not disclose a method of stabilizing the wavelength of the light source. For this reason, the method of Patent Document 2 has a problem that it is insufficient for stable operation of the integrated optical transmitter.

  The present invention has been made in view of the above, and an object of the present invention is to obtain an optical transmitter capable of controlling the wavelength constant in an optical transmitter in which a modulator and a light source are integrated, and a method for controlling the optical transmitter. And

  In order to solve the above-described problems and achieve the object, the present invention provides a light source that outputs continuous light, a modulation unit that modulates the continuous light based on a modulation signal, and an optical signal output from the modulation unit. A light branching part for branching into at least two branched lights including monitor light and output light, a light intensity detecting part for receiving the monitor light and generating an electrical signal according to the intensity of the monitor light, and the monitor An optical wavelength detector that receives light and generates an electrical signal according to the wavelength of the monitor light; and the optical intensity of the output light based on the electrical signal generated by the optical intensity detector and the optical wavelength detector And a controller that controls the light source so that the center wavelength of the output light is constant.

  The optical transmitter and the optical transmitter control method according to the present invention have an effect that the wavelength can be controlled to be constant in the optical transmitter in which the modulator and the light source are integrated.

FIG. 1 is a diagram illustrating a functional configuration example of the optical transmitter according to the first embodiment. FIG. 2 is a diagram illustrating an example of a light output spectrum in each step. FIG. 3 is a diagram illustrating a functional configuration example of the optical transmitter according to the second embodiment.

  Embodiments of an optical transmitter and an optical transmitter control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating an example of a functional configuration of an optical transmitter according to a first embodiment of the present invention. As shown in FIG. 1, the optical transmitter 1 of this embodiment includes an integrated optical transmission module 2, a light source 3, a modulator (modulator) 4, a light intensity detector 5, an optical wavelength detector 6, and a variable temperature. Elements 7a and 7b, an optical branching unit 8, a light source control unit 9, an electric signal amplification unit 10, temperature control units 11a and 11b, a control unit 12, and a memory 13 are provided.

  Hereinafter, the function of each part of the optical transmitter 1 of the present embodiment will be described. The integrated optical transmission module 2 is a module in which a light source 3, a modulator 4, a light intensity detector 5, an optical wavelength detector 6, an optical branching unit 8, a temperature variable element 7a, and a temperature variable element 7b are integrated. is there.

  The light source 3 outputs CW (Continuous Wave) light, the light wavelength can be adjusted by the temperature of the light source 3, and the light intensity is adjusted by the current supplied to the light source 3.

  The modulator 4 modulates the CW light input from the light source 3 based on the modulation signal input from the electric signal amplification unit 10 and outputs the modulated CW light to the optical branching unit 8. The optical branching unit 8 branches the optical signal output from the modulator 4 into output light and monitor light. In the present embodiment, the optical branching unit 8 branches the optical signal output from the modulator 4 into two parts, that is, output light and monitor light, but includes output light and monitor light 3 You may branch into two or more.

  The light intensity detector 5 generates an electrical signal having a level corresponding to the intensity of the monitor light branched by the light splitter 8, and outputs the generated electrical signal to the controller 12. The optical wavelength detection unit 6 generates an electrical signal having a level corresponding to the wavelength of the monitor light branched by the optical branching unit 8 and outputs the generated electrical signal to the control unit 12.

  The temperature variable element 7 a controls the temperatures of the light source 3 and the modulator 4. The temperature variable element 7 b controls the temperatures of the light intensity detector 5 and the light wavelength detector 6. The light source controller 9 controls the current supplied to the light source 3 based on the control signal input from the controller 12.

  The electric signal amplifying unit 10 amplifies an externally input modulation signal (a signal modulated based on a clock signal, data to be transmitted, etc.) based on a control signal input from the control unit 12 and modulates 4 is output.

  The temperature control unit 11a controls the current supplied to the temperature variable element 7a based on the control signal input from the control unit 12. The temperature control unit 11b controls a current supplied to the temperature variable element 7b based on a control signal input from the control unit 12.

  The control unit 12 is based on the electrical signals output from the light intensity detection unit 5 and the optical wavelength detection unit 6 and information in the memory 13, and the light source control unit 9, the electrical signal amplification unit 10, the temperature control unit 11a, and the temperature control unit. The control signal for controlling each of 11b is output. The memory 13 stores various information used by the control unit 12.

  Next, the operation of the optical transmitter 1 of the present embodiment will be described. FIG. 2 is a diagram illustrating an example of a light output spectrum in each step. The operation for each step will be described below.

・ Step # 1
First, when power is supplied to the optical transmitter 1, the control unit 12 is activated. The control unit 12 reads the setting information corresponding to the wavelength to be set from the memory 13, and outputs a control signal to the light source control unit 9 so as to set the current according to the wavelength to be set based on the read setting information. Then, a control signal is output to the first temperature control unit 11a and the temperature control unit 11b so as to set the temperature according to the wavelength to be set. Note that the setting information stored in the memory 13 stores, for each wavelength to be set, a current set in the light source control unit 9, a target temperature to be set in the temperature control units 11a and 11b, and the like. To do.

  The light source control unit 9 activates the light source 3 and supplies current to the light source 3 based on a control signal from the control unit 12. The light source 3 outputs CW light having a wavelength corresponding to the supplied current. Further, the temperature control unit 11 a activates the temperature variable element 7 a and controls the temperatures of the light source 3 and the modulator 4 based on a control signal from the control unit 12. The temperature control unit 11 b activates the temperature variable element 7 b and controls the temperatures of the light intensity detection unit 5 and the light wavelength detection unit 6 based on a control signal from the control unit 12.

・ Step # 2
Following step # 1, the control unit 12 sets the operating point of the modulator 4 so that the transmission loss is minimized based on the setting information stored in the memory 13. Here, the transmission loss means the loss of the optical signal in the modulator, and the setting so that the transmission loss is minimized means the modulator that maximizes the output of the optical signal output from the modulator. 4 is an operating point setting. The setting information stored in the memory 13 stores, for each wavelength to be set, operating points set by the control unit 12 in the modulator 4 so that the transmission loss of the modulator 4 is minimized. Suppose that

・ Step # 3
When the operating point of the modulator 4 is set so as to minimize the transmission loss, the controller 12 controls the light source controller 9 so that the light intensity becomes constant based on the electric signal output from the light intensity detector 5. The control signal is output to the temperature control unit 11a so that when the wavelength of the output signal deviates from the desired wavelength based on the electrical signal output from the optical wavelength detector 6, the control signal is output to the temperature control unit 11a. Is output.

・ Step # 4
When the light wavelength and the light intensity are controlled to be constant, the control unit 12 reads setting information corresponding to the wavelength to be set from the memory 13 and outputs the operating point of the modulator 4 based on the setting information. Set according to the wavelength and the modulation method, and control the operating point of the modulator 4 to the optimum point according to the output wavelength and the modulation method based on the electrical signal output from the light intensity detector 5 To do. Here, the optimum point according to the output wavelength and the modulation method is such that when a modulation signal is applied to the modulator 4, a desired optical signal is output according to the wavelength and the modulation method. It is. The setting information stored in the memory 13 includes an operating point set by the control unit 12 in the modulator 4 so that the modulator 4 operates at an optimum point for each wavelength and modulation method to be set, and the like. Is stored.

  In the present embodiment, the light source 3 can adjust the light wavelength according to the temperature and can adjust the light intensity according to the supplied current. Such a function uses, for example, a DFB-LD (Distributed-Feedbak Lazer Diode). Can be realized.

  Further, as the modulator 4, any operating point can be used as long as the operating point can be controlled by the applied voltage and the light can be modulated by adding a modulation signal. This can be realized by a Mach-Zehnder type modulator.

  The light intensity detector 5 only needs to be able to output an electrical signal at a level corresponding to the intensity of the input light. Such a function can be realized by using, for example, a PD (Photo Diode).

  The optical wavelength detector 6 only needs to be able to output an electrical signal at a level corresponding to the wavelength of the input light. In other words, the optical wavelength detector 6 may be configured to change the output electrical signal when the wavelength changes. The optical wavelength detector 6 can be realized by, for example, a configuration in which light that has passed through filters of light having different transmittances according to wavelengths is received by the PD.

  The temperature variable elements 7a and 7b only need to be able to change the temperature based on the input control signal. Such a function can be realized by, for example, a Peltier cooler that can control the temperature by controlling the supplied current.

  The light branching unit 8 only needs to transmit a part of the input light and branch a part thereof. Such a function can be realized by, for example, an optical component such as a beam splitter used for branching normal light.

  The electric signal amplifier 10 only needs to be able to amplify and output the input modulation signal based on the control signal input from the controller 12. Such a function can be realized by a high-frequency electrical component such as a driver amplifier having a gain adjustment function that is usually used for driving a Mach-Zehnder type modulator.

  The control unit 12 may include a plurality of ADCs (Analog to Digital Converters), DACs (Digital to Analog Converters), and I / O (Input / Output) ports, and have a function of performing calculations inside. The control unit 12 can be realized by a microcomputer, for example.

  The memory 13 only needs to have a function capable of storing information therein and reading and writing as necessary. Such a function can be realized by, for example, EEPROM (Electrically Erasable Programmable Read-Only Memory).

  As described above, in the present embodiment, the optical branching unit 8 branches the light modulated by the modulator 4 into the monitor light and the optical signal. Then, the light intensity detector 5 outputs an electrical signal corresponding to the intensity of the monitor light, and the optical wavelength detector 6 outputs an electrical signal corresponding to the wavelength of the monitor light. The control unit 12 controls the intensity and wavelength of the monitor light to be constant based on the electrical signals output from the light intensity detection unit 5 and the light wavelength detection unit 6. For this reason, in an optical transmitter in which a modulator and a light source are integrated (for example, an optical transmitter in which a light source and a modulator are connected in cascade and a part of the optical output is branched and input to a monitoring photodiode), the wavelength is changed. It can be controlled constantly.

Embodiment 2. FIG.
FIG. 3 is a diagram illustrating a functional configuration example of the second embodiment of the optical transmitter according to the present invention. As shown in FIG. 3, the optical transmitter 1 a according to the present embodiment includes modulators 4 a and 4 b instead of the modulator 4 according to the first embodiment, and electric signal amplifiers 10 a and 10 b instead of the electric signal amplifier 10. Is the same as that of the optical transmitter 1 of the first embodiment. Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted.

  Although a single modulator is used in the first embodiment, the control method of the present invention can be applied to a case where a plurality of modulators are provided. In this embodiment, an example in which two modulators are provided will be described. When such a configuration is adopted, for example, the two modulators are a pulse modulator that modulates with a modulation signal based on a clock signal, and a data modulator that modulates with a modulation signal based on transmission data, respectively. Can be considered.

  The modulator 4a modulates the CW light input from the light source 3 based on the modulation signal input from the electric signal amplifier 10a and outputs the modulated light to the modulator 4b. The modulator 4 b modulates the signal light input from the modulator 4 a based on the modulation signal input from the electric signal amplifier 10 b and outputs the modulated signal light to the optical branching unit 8.

  The electric signal amplifying unit 10a amplifies the input modulation signal based on the control signal input from the control unit 12, and outputs the amplified signal to the modulator 4a. The electric signal amplifying unit 10b amplifies the input modulation signal based on the control signal input from the control unit 12, and outputs the amplified signal to the modulator 4b.

  Next, the operation of the optical transmitter 1a of this embodiment will be described.

Step # 1
Step # 1 is the same as step # 1 in the first embodiment.

Step # 2
After step # 1, the control unit 12 subsequently sets the operating points of the modulator 4a and the modulator 4b based on the setting information stored in the memory 13 so that the transmission loss is minimized.

Step # 3
When the operating points of the modulator 4a and the modulator 4b are set so that the transmission loss is minimized, the control unit 12 outputs the control unit 12 from the light intensity detection unit 5 as in the first embodiment. The temperature control unit outputs a control signal to the light source control unit 9 so that the light intensity is constant based on the electrical signal, and the light wavelength is constant based on the electrical signal output from the light wavelength detection unit 6. A control signal is output to 11a.

Step # 4
When the optical wavelength and the optical intensity are controlled to be constant, the control unit 12 reads out setting information corresponding to the wavelength to be set from the memory 13, and based on the setting information, the operating points of the modulator 4a and the modulator 4b are Set according to the output wavelength and modulation method. Based on the electrical signal output from the light intensity detector 5, the operating point of the modulator 4a and the modulator 4b is controlled to an optimum point according to the output wavelength and the modulation method.

  In the present embodiment, also in the optical transmitter including two modulators, the control unit 12 is based on the electrical signals output from the light intensity detection unit 5 and the optical wavelength detection unit 6 as in the first embodiment. The intensity and wavelength of the monitor light are controlled to be constant. For this reason, an effect similar to that of the first embodiment can be obtained even in an optical transmitter including two modulators.

DESCRIPTION OF SYMBOLS 1 Optical transmitter 2 Integrated optical transmission module 3 Light source 4, 4a, 4b Modulator 5 Light intensity detection part 6 Optical wavelength detection part 7a, 7b Temperature variable element 8 Optical branch part 9 Light source control part 10, 10a, 10b Electric signal Amplifier 11a, 11b Temperature controller 12 Controller 13 Memory

In order to solve the above-described problems and achieve the object, the present invention includes a light source that outputs continuous light, a modulation unit that is integrated with the light source and modulates the continuous light based on a modulation signal, and An optical branching unit that branches the optical signal output from the modulation unit into at least two branched lights including monitor light and output light, and receives the monitor light, and generates an electrical signal according to the intensity of the monitor light An optical intensity detector that receives the monitor light and generates an electrical signal corresponding to the wavelength of the monitor light, and an electrical signal generated by the optical intensity detector and the optical wavelength detector. based on, and a control unit for controlling the light source so that the light intensity and the center wavelength of the output light of the output light becomes constant, the control unit includes a transmission loss the operating point of the modulator portion is minimal And set the output light After the heart wavelength is controlling the light source to a desired wavelength, Settings and in accordance with the modulation scheme operating point of the modulation unit, characterized in that.

In order to solve the above-described problems and achieve the object, the present invention includes a light source that outputs continuous light, a modulation unit that is integrated with the light source and modulates the continuous light based on a modulation signal, and An optical branching unit that branches the optical signal output from the modulation unit into at least two branched lights including monitor light and output light, and receives the monitor light, and generates an electrical signal according to the intensity of the monitor light An optical intensity detector that receives the monitor light and generates an electrical signal corresponding to the wavelength of the monitor light, and an electrical signal generated by the optical intensity detector and the optical wavelength detector. And a control unit that controls the light source so that the light intensity of the output light and the center wavelength of the output light are constant, and the control unit has a minimum passing loss at the operating point of the modulation unit. light output from Do Ri said modulator unit After the output of No. was controlling the light source so that the center wavelength of the output light is maximized such so that setting becomes a desired wavelength, Settings and in accordance with the modulation scheme operating point of the modulator portion, it It is characterized by.

In order to solve the above-described problems and achieve the object, the present invention includes a light source that outputs continuous light, a modulation unit that is integrated with the light source and modulates the continuous light based on a modulation signal, and An optical branching unit that branches the optical signal output from the modulation unit into at least two branched lights including monitor light and output light, and receives the monitor light, and generates an electrical signal according to the intensity of the monitor light An optical intensity detector that receives the monitor light and generates an electrical signal corresponding to the wavelength of the monitor light, and an electrical signal generated by the optical intensity detector and the optical wavelength detector. And a control unit that controls the light source so that the light intensity of the output light and the center wavelength of the output light are constant, and the control unit has a minimum passing loss at the operating point of the modulation unit. Light output from the modulator After the output of No. was controlling the light source so that the center wavelength of the output light by controlling the light source so that the light intensity as a kind of setting the maximum is constant becomes a desired wavelength, the modulation unit The operating point is set according to the modulation method.

Claims (8)

A light source that outputs continuous light;
A modulator for modulating the continuous light based on a modulation signal;
An optical branching unit for branching the optical signal output from the modulation unit into at least two branched lights including monitor light and output light;
A light intensity detector that receives the monitor light and generates an electrical signal according to the intensity of the monitor light;
An optical wavelength detector that receives the monitor light and generates an electrical signal according to the wavelength of the monitor light;
Based on the electrical signal generated by the light intensity detector and the light wavelength detector, a controller that controls the light source so that the light intensity of the output light and the center wavelength of the output light are constant,
An optical transmitter comprising: The intensity of the continuous light changes according to the current supplied to the light source, and the wavelength of the continuous light changes according to the temperature of the light source,
A light source control unit for controlling a current supplied to the light source;
A temperature controller for controlling the temperature of the light source;
With
The control unit instructs the light source control unit to supply a current to the light source, and instructs the temperature control unit to set a target temperature so that the light intensity of the output light and the center wavelength of the output light are The optical transmitter according to claim 1, wherein the light source is controlled to be constant.   3. The optical transmitter according to claim 1, wherein the light source, the modulation unit, the light intensity detection unit, and the optical wavelength detection unit are integrated to form a module.   The modulation unit is either a pulse modulation unit that modulates the continuous light based on a modulation signal based on a clock signal, or a data modulation unit that modulates the continuous light based on a modulation signal based on transmission data The optical transmitter according to claim 1, wherein the optical transmitter is one.   A plurality of the modulation units, and as the modulation unit, a pulse modulation unit that modulates the continuous light based on a modulation signal based on a clock signal, and a data modulation that modulates the continuous light based on a modulation signal based on transmission data The optical transmitter according to claim 1, wherein the optical transmitter includes at least one of the first and second sections.   The optical transmitter according to claim 1, wherein the modulation unit is a Mach-Zehnder optical modulator. A continuous light output step for outputting continuous light;
A modulation step of modulating the continuous light based on a modulation signal;
An optical branching step for branching the optical signal modulated by the modulation step into at least two branched lights including monitor light and output light;
A light intensity detecting step for receiving the monitor light and generating an electrical signal corresponding to the intensity of the monitor light;
An optical wavelength detection step for receiving the monitor light and generating an electrical signal corresponding to the wavelength of the monitor light;
A control step for controlling the light source that outputs the continuous light so that the light intensity of the output light and the center wavelength of the output light are constant based on the electrical signals generated in the light intensity detection step and the light wavelength detection step; ,
An optical transmitter control method comprising: Before the start of the continuous light output step, the setting step of setting the temperature of the light source to a temperature according to the wavelength to be set;
A first operating point setting step for setting the operating point of the modulation unit that performs the modulating step after the start of the continuous light output step so that transmission loss is minimized;
Including
After performing the control step after the first operating point setting step, the operating point of the modulation unit is controlled to an optimum point according to the wavelength of the continuous light output from the light source and the modulation method. The method of controlling an optical transmitter according to claim 7.

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