JP2010093123A - Optical transmission apparatus and control method of optical transmission signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a quenching ratio without using a pilot signal. <P>SOLUTION: An optical transmission apparatus 10 includes: an LDD 12 for generating a driving current on the basis of a modulation current modulated in accordance with transmission information; an LD 14 for receiving an input of the driving signal and transmitting an optical signal; an MPD 16 for receiving the optical signal transmitted from the LD 14; a filter for extracting a certain frequency band from a voltage signal obtained on the basis of the optical signal received by the MPD 16; and a means for controlling an amplitude of a modulation current on the basis of comparing an amplitude of the voltage signal extracted by the filter with a reference amplitude. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical transmitter and an optical transmission signal control method.

  Some use a laser diode (LD) in a transmission module of an optical transmission device. For data communication of such an optical transmission apparatus, a baseband communication system that supplies a bias current to an LD and modulates the amount of the current according to transmission data may be used.

The LD changes the IL characteristics that represent the relationship between the drive current and the optical output due to temperature changes and deterioration over time. Therefore, in order to stabilize the communication quality, the output intensity ratio of the optical signal of 0/1 must be set. A circuit for controlling the extinction ratio (ER) to be constant is required. Therefore, conventionally, as described in Patent Document 1 below, a transmission signal is combined with a pilot signal having a sufficiently lower frequency and smaller amplitude than the transmission signal, and an optical signal is transmitted from the LD. Some of them are provided with a circuit that receives a transmitted optical signal, detects a pilot signal from the received optical signal, and controls an extinction ratio according to the amplitude intensity of the detected pilot signal.
JP 2003-169022 A

  However, with the conventional technology, if the amplitude of the pilot signal combined with the transmission signal is reduced, the amplitude of the pilot signal cannot be accurately detected near the changing point of the LD characteristic of the LD due to the change in the amplitude of the optical signal. On the other hand, if the amplitude of the pilot signal is increased, the transmission signal is disturbed, and the extinction ratio cannot be controlled accurately.

  The present invention has been made in view of the above problems, and one of the objects of the present invention is to provide an optical transmission apparatus and an optical transmission signal control method capable of controlling the extinction ratio without using a pilot signal. It is in.

  In order to achieve the above object, an optical transmission apparatus according to the present invention transmits a drive circuit that generates a drive current based on a modulation current modulated according to transmission information, and receives an input of the drive current and transmits an optical signal. A light transmitting element, a light receiving element that receives an optical signal transmitted from the light transmitting element, and a filter that extracts a part of a frequency band from a voltage signal obtained based on the optical signal received by the light receiving element And control means for controlling the amplitude of the modulation current based on a comparison between the amplitude of the voltage signal extracted by the filter and a reference amplitude.

  In the aspect of the invention, the control unit controls the amplitude of the modulation current based on a difference between the amplitude of the voltage signal extracted by the filter and a reference amplitude.

  In one aspect of the present invention, the control means limits amplification of the amplitude of the modulation current when the difference between the amplitude of the voltage signal extracted by the filter and a reference amplitude exceeds a threshold value.

  In one aspect of the present invention, the information processing apparatus further includes transmission information detection means for detecting presence / absence of the transmission information, and the control means detects the modulation current when the transmission information is not detected by the transmission information detection means. Limit the change of amplitude.

  In one aspect of the present invention, the control means may control the modulation current when the rate of change of the difference between the amplitude of the voltage signal extracted by the filter and a reference amplitude is not within a predetermined range. Limit amplitude changes.

  In one aspect of the present invention, it further includes means for detecting the temperature of the optical transmission element, and the control means controls the amplitude of the modulation current based on the detected temperature.

  In the aspect of the invention, the filter extracts a part of a low frequency band from the voltage signal obtained based on the optical signal.

  In one aspect of the present invention, the modulation current is modulated by encoding a signal per frame.

  The optical transmission signal control method according to the present invention includes a step of generating a drive current based on a modulation current modulated according to transmission information, a step of receiving an input of the drive current, and a step of transmitting an optical signal; Receiving the transmitted optical signal; extracting a part of a frequency band from a voltage signal obtained based on the received optical signal; and an amplitude and a reference amplitude of the extracted voltage signal; And controlling the amplitude of the modulation current based on the comparison.

  According to one aspect of the present invention, the extinction ratio of an optical signal transmitted based on transmission information can be controlled without using a pilot signal.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments (hereinafter referred to as embodiments) for carrying out the invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of an optical transmission device 10 according to the present embodiment. As shown in FIG. 1, the optical transmission device 10 includes an LDD (LD driver) 12, an LD (laser diode) 14, an MPD (monitor photodiode) 16, an APC circuit 18, and an AMC circuit 20.

  The LD 14 is an optical transmission element for optically converting electrons according to the amount of input current. The optical transmission apparatus 10 according to the present embodiment may use a direct modulation type LD.

  The LDD 12 is a drive circuit that supplies current to the LD 14, and is a modulation current (pulse current) that is modulated with “0” being Low and “1” being High based on digital transmission information including “0” and “1”. It also functions as a circuit that generates In the present embodiment, an LDD of a coupling drive method of either a DC drive method (DC coupling drive method) or an AC drive method (AC coupling drive method) may be used. In the DC drive system, a drive current generated by combining a base current (bias current) generated by a DC current supply circuit inside the LDD and the modulation current (pulse current) inside the LDD is directly applied to the LD. The AC drive method is a base current (bias current) generated by a DC current supply circuit called a bias tee after an AC capacitor (AC capacitor) is passed through a modulation current (pulse current). ) And drive the LD. Note that a single-phase input or a differential input may be used to input the transmission signal. The LDD 12 drives the LD 14 as described above to generate an optical signal for optical communication. In the present embodiment, a circuit configuration is used in which the light emission of the LD 14 is received by the MPD 16 so that the operation status of the LD 14 can be monitored.

  2A shows an IL characteristic representing the relationship between the drive current input to the LD 14 and the light output, and FIG. 2B shows the input light intensity and output current of the MPD 16. In FIG. 2A, the horizontal axis represents drive current, the vertical axis represents light output, and in FIG. 2B, the horizontal axis represents MPD output current, and the vertical axis represents MPD input light (intensity). .

  As shown in FIG. 2A, when the drive current input to the LD 14 exceeds the threshold value, the LD 14 starts to emit light, and thereafter emits an optical signal having an output proportional to the input drive current. And the optical signal transmitted from LD14 is received by MPD16 mentioned later.

  FIG. 2B shows the relationship between the input light intensity to the MPD 16 and the current output from the MPD 16. As shown in FIG. 2B, the input light intensity of the MPD 16 and the current output from the MPD 16 are in a proportional relationship.

  FIG. 2A shows the IL characteristics of the LD 14 when the temperature of the LD 14 is different. The IL curve shown in FIG. 2A is the case where the temperature of the LD 14 is T1 and T2, respectively, and T1 <T2. As shown in FIG. 2A, when the temperature of the LD 14 rises, the conversion efficiency of the input drive current into an optical signal deteriorates. That is, in order to obtain a constant light output and light amplitude, it is necessary to control the output and amplitude of the drive current in accordance with the temperature of the LD 14. Such deterioration of the conversion efficiency is caused not only by the temperature change of the LD 14 but also by aging. Hereinafter, a configuration for controlling the optical output and amplitude from the LD 14 will be described.

  The MPD 16 is a light receiving element that receives a transmission signal emitted from the LD 14. The MPD 16 converts the received optical signal into a current corresponding to its intensity.

  The current sensor 28 includes a resistor 28a and an error amplifier 28b. The current sensor 28 detects a potential difference of current flowing between the resistors and converts it as a voltage signal.

  The APC (Auto Power Control) circuit 18 is a control circuit that controls the drive current so that the average amount of light emitted from the LD 14 is constant. The driving method of the LD 14 by the LDD 12 in the present embodiment indicates AC driving (AC driving method). The APC circuit 18 controls the amount of light emitted from the LD 14 by controlling the magnitude of the base current that is the direct current component of the drive current.

  APC-ref (APC reference voltage) and the output value of the averaging filter 18b are input to an error amplifier 18a that performs differential amplification calculation, and a voltage corresponding to the difference calculation result is input to a current source (voltage controlled current source) 26. The The APC circuit 18 is a closed-loop circuit, and in the first round, the output value of the averaging filter 18b is infinitely close to 0 V with respect to the set voltage of APC-ref, and in some cases, the maximum set value is supplied to the current source 26. Sent. Therefore, an RC filter so-called integration circuit may be provided between the APC-ref and the error amplifier 18a or between the error amplifier 18a and the current source 26 to control the response speed of the voltage value input to the current source 26.

  The current source 26 sends current through the bias tee, causing the LD 14 to emit light. The MPD 16 receives the light, and the current output generated by the received light passes through the current sensor 28 and then is input to the error amplifier 18a through the averaging filter 18b. The second and subsequent rounds are controlled by the feedback result and the constant difference calculation result of APC-ref. Therefore, a desired light output can be obtained by controlling the set value of APC-ref.

  The AMC (Auto Modulation Control) circuit 20 is a control circuit that controls the amplitude of the optical signal transmitted from the LD 14 to be constant. In the present embodiment, the AMC circuit 20 is a circuit that controls the amplitude of the modulation current that is the alternating current component of the drive current based on the optical signal received by the MPD 16, and includes a filter 30, an amplitude detector 32, and an error amplifier 34. It is composed. The details of the signal processing in the AMC circuit 20 will be described below with reference to specific examples of signal waveforms shown in FIGS.

  The optical transmission device 10 according to the present embodiment may use a transmission method such as SONET / SDH or Ethernet (registered trademark) as a method of optical communication. According to these methods, the transmission signal is divided into small chunks, and the divided chunks (frames) are encoded and modulated, so that the transmission signal shows a continuous and wide band constant pattern.

  The AMC circuit 20 is a circuit similar to the APC circuit 18. A voltage corresponding to the difference calculation result of the AMC-ref (AMC reference voltage) and the amplitude detector 32 is input to the error setting terminal of the LDD 12 to the error amplifier 34 that performs differential amplification calculation. Based on the voltage input from the error amplifier 34, the LDD 12 generates a modulation current at a constant conversion rate of the output modulation current with respect to the set voltage included in the LDD 12. The high / low level of the modulation current is set based on a digital communication signal input to the LDD 12. Since the present embodiment uses AC driving (AC driving method), it is combined with a base current generated by the APC circuit 18 via an AC capacitor (AC capacitor), and is generated as an optical communication signal.

  The AMC circuit 20 is a closed loop circuit, and in the first round, the output value of the amplitude detector 32 is as close to 0V as possible with respect to the set voltage of AMC-ref, so that the maximum set value is sent to the LDD 12 in some cases. Therefore, an RC filter so-called integration circuit is installed between the AMC-ref and the error amplifier 18a, or between the error amplifier 18a and the current source 26, and the response speed of the voltage value input to the current source 26 is controlled to make transient and abnormal input. The set value may be avoided.

  The LDD 12 supplies a modulation current to the LD 14 with respect to the set voltage. In this embodiment, the APC circuit 18 is set to operate with a constant light output, and the generation probability of a High / Low level signal input to the LDD 12 is 1: 1.

  FIG. 3 shows the characteristics of the signal input to the LD 14. 3A shows a waveform of a signal input to the LD 14, and FIG. 3B shows a signal pattern obtained by enlarging a part 100 of the waveform of the signal. FIG. 3C shows the frequency characteristics of the input signal. In FIG. 3C, the vertical axis represents output intensity and the horizontal axis represents frequency. As shown in FIG. 3, the input signal has a constant pattern with a continuous and wide band.

  The LD 14 is controlled in amplitude by the LDD 12 in accordance with the input signal, and oscillates an optical signal. The oscillated optical signal is received by the MPD 16. The MPD 16 may have a low frequency characteristic (for example, one having a frequency characteristic about 1/50 times that of an optical signal). The light receiving current of the MPD 16 is converted into a voltage signal by the current sensor 28 as in the APC circuit 18.

  FIG. 4A shows the waveform of the signal output from the MPD 16, and FIG. 4B shows the frequency characteristics of the signal output from the MPD 16. The solid line in FIG. 4B indicates the output waveform from the MPD 16 and the broken line indicates the frequency characteristic of the input signal to the MPD 16. As shown in FIG. 4B, the frequency band of the output signal from the MPD 16 is narrower than the input signal to the MPD 16.

  Since the voltage signal output from the current sensor 28 may be noise on the high frequency side from the cutoff frequency, noise is removed by passing through the filter 30 and a part of the frequency band is extracted from the voltage signal.

  The filter 30 is a filter that extracts a part of the frequency band of the input voltage signal, and may be constituted by a band pass filter or a low pass filter. The frequency band of the portion where the signal intensity is stable in the voltage signal is extracted by the filter 30, and this is used for amplitude control by the AMC circuit 20.

  5A and 5B show the waveforms of signals output from the filter 30. FIG. By passing through the filter, it is shown that the frequency band is limited to a part of the frequency band.

  The voltage signal that has passed through the filter 30 is transmitted to the amplitude detector 32. The amplitude detector 32 is a circuit that detects the amplitude of an input signal, converts the detected amplitude to a voltage level at a constant magnification, and outputs the voltage level.

  As shown in FIG. 6A, the amplitude detector 32 holds the peak of the intensity of the input signal, smoothes the peak-held signal as shown in FIG. 6B, and converts it to a constant voltage level. Process. The amplitude detector 32 may have a function of inserting a noise removal filter before peak hold, or inserting an amplifier after smoothing to offset to a desired voltage level.

  The signal of the amplitude detector 32 is input to the error amplifier 34, and the error calculation is performed between the AMC-ref and the output signal of the amplitude detector 32. It is controlled by the feedback result after the second round and the constant difference calculation result of AMC-ref. Therefore, a desired light amplitude can be obtained by controlling the set value of AMC-ref.

  Next, a second embodiment according to the present invention will be described. In the second embodiment, a control unit (transient response control) 36 provided between the error amplifier 34 and the LDD 12 performs the following processing.

  The control unit 36 receives the input from the error amplifier 34, generates a control signal, and outputs the generated control signal to the LDD 12. The control signal may be represented by a voltage, for example. In the present embodiment, the control unit 36 may be configured by a microcomputer. The control unit 36 converts the voltage level input from the error amplifier 34 from analog data to digital data by the A / D conversion unit 38. The control unit 36 has a function of an output controller 40 that receives the converted digital data as input and determines an output based on the input. The output controller 40 may be realized by the central processing unit of the control unit 36 operating according to a program stored in the control unit 36.

FIG. 7 shows the relationship between input and output in the output controller 40 of the control unit 36. As shown in FIG. 7, in the present embodiment, the output controller 40 outputs in proportion to the input until the input reaches the threshold value, but when the input exceeds the threshold value, the output is constant (O _limit ). I have to. The reason why the upper limit is set for the output is as follows.

  A non-amplitude signal in which “1” or “0” continues in the transmission signal or a signal having a frequency that is too high to be detected by the amplitude detector 32 is detected as substantially no signal. In this case, the signal from the amplitude detector 32 is infinitely close to 0V. Since the error amplifier 34 is used in the closed loop circuit of this embodiment, there is a possibility that the maximum output value is input to the LDD 12 as a result of error calculation with AMC-ref. The LDD 12 generates a modulation current with a constant conversion rate. A large modulation current is set for generation. After that, when returning from a state detected as a no-signal state to a signal such as a pseudo random number binary sequence (PRBS), the LDD 12 is already set to generate a large modulation current. Proper amplitude control cannot be performed in a transient response. In order to avoid such a risk, an upper limit is set for the output from the control unit 36. The upper limit value set as the output value in the control unit 36 may be determined according to the LDD 12 or LD 14 to be driven.

  The control unit 36 converts the data value output from the output controller 40 according to the input voltage from digital data to analog data (signal) by the D / A conversion unit 42 and outputs the converted data value to the LDD 12. The LDD 12 generates a modulation current in accordance with the signal input from the control unit 36.

  According to the optical transmission device 10 according to the first embodiment or the second embodiment described above, the optical amplitude can be controlled based on the optical signal transmitted based on the transmission information without using the pilot signal. By doing so, the accuracy problem caused by the pilot signal can be solved, and the optical amplitude can be controlled with high accuracy. In addition, since it is not necessary to design and mount a pilot signal generation circuit, it contributes to miniaturization of the circuit, and an inexpensive device having low frequency characteristics can be used for the MPD 16 and the amplitude detector 32. The manufacturing cost of the apparatus 10 can also be suppressed.

  Further, for example, a continuous signal such as an international standard SONET / SDH, Ethernet (registered trademark) or pseudo-random binary sequence (PRBS) transmission signal that defines encoding (conversion method) of information transmission in optical communication is provided. The present invention is applied to a device that transmits a signal that is transmitted and has a wide transmission signal bandwidth, and it is possible to optimize the circuit loop time constant (representing the response speed of the circuit) and smooth the signal component. Thus, if a circuit that detects a signal component that is 1/1000 to 1/100 of the fundamental frequency component of the signal is configured, the signal extinction ratio can be suitably controlled by detecting most of the signal amplitude of the transmission signal. In addition, when the fundamental frequency of the signal is 10 Gbit / s, the amplitude can be suitably controlled by detecting most of the signal by using a filter that performs smoothing in the tens of MHz band.

  Next, a third embodiment according to the present invention will be described with reference to FIGS.

  FIG. 8 shows a configuration diagram of an optical transmission apparatus 10 according to the third embodiment. As illustrated in FIG. 8, the optical transmission device 10 includes an LDD 12, an LD 14, an MPD 16, an APC circuit 18, an AMC circuit 20, and a control unit 50. In addition, about the component to which the code | symbol same as the optical transmitter 10 which concerns on 2nd Embodiment was attached | subjected, since it has the function similar to the component mentioned above, description is abbreviate | omitted.

  In FIG. 9, the block diagram of the control part 50 which concerns on 3rd Embodiment is shown. The control unit 50 includes functions of the output controller 40, the difference controller 54, the LOS controller 56, and the temperature controller 58. The order of processing by each function is not limited to the order shown in FIG. 9 and may be another order. Since the output controller 40 has the same function as that used in the second embodiment, the description thereof is omitted.

  The difference controller 54 is a function realized by including a memory that sequentially stores history data of the difference between the signal amplitude and the reference amplitude in the control unit 50. FIG. 10 shows a graph representing the input change rate to the control unit 50 for each hour, which is generated based on the history data managed by the difference controller 54. The vertical axis represents the input change rate. Time is shown on the axis. In the above graph, the input value is sampled every unit time, and the input change rate at each time is calculated as I (n-1) / I (n), where I (n) is a sampling value at time n. Are generated.

  The difference controller 54 determines that there is a sudden change in the light amplitude when the input change rate exceeds a predetermined range (within the range of TH1 and TH2), and the output value at time n is I (n-1). The output value at the time of) shall be maintained. According to the difference controller 54, when an extreme input change occurs, an abnormality such as a signal interruption may have occurred. Therefore, the extinction ratio is not controlled based on the input. Control of the extinction ratio based on this is prevented.

  The LOS controller 56 is a function implemented by including a signal detector 70 that detects the presence or absence of transmission information. When the transmission information is not detected, the signal detector 70 outputs a control signal called Loss Of Signal (hereinafter referred to as LOS) to the LOS controller 56 of the control unit 50. When the LOS signal is input from the signal detector 70, the LOS controller 56 controls to maintain the output from the control unit 50 at the same output as before the transmission of the LOS signal regardless of the input from the output controller 40. . In addition, the LOS controller 56 can acquire information indicating whether transmission information is in a no-signal state or only “0” and “1” are continuous. It is also possible to provide a function for avoiding the problem that the drive current is maximized after returning to the signal state.

  The temperature controller 58 is a function realized by including a temperature detector 60 that detects the temperature of the LD 14. The temperature controller 58 may be activated when the temperature changes while the difference controller 54 or the LOS controller 56 maintains the output. This is because the IL characteristic of the LD 14 changes depending on the temperature. Even if each function maintains the output and controls the setting of the output amplitude, the extinction ratio is not normal when the driving temperature of the LD 14 changes in that state. It is because it may fall into a state. Therefore, as the temperature controller 58, the correspondence relationship between the modulation current amplification factor and the temperature (T) shown in FIG. 11 is stored in advance, so that the temperature changes while the other functions are maintained. If there is, the modulation current amplification factor corresponding to the temperature may be read to change the modulation current amplification factor. By doing so, the extinction ratio can be controlled even when the temperature of the LD 14 changes.

  According to the optical transmission device 10 according to the second embodiment described above, the extinction ratio can be controlled with higher accuracy by further providing the functions of the difference controller 54, the LOS controller 56, and the temperature controller 58. it can.

  Of course, the present invention is not limited to the above-described embodiment. For example, the control unit is configured by selectively combining some of the output controller 40, the difference controller 54, the LOS controller 56, and the temperature controller 58. It is good to do.

It is a block diagram of an optical transmitter. It is a figure which shows the characteristic of IL characteristic and MPD showing the relationship between the drive current input into LD, and optical output. It is a figure which shows the characteristic of the signal input into LD. It is a figure which shows the characteristic of the signal output from a current sensor. It is a figure which shows the characteristic of the signal output from a filter. It is a figure which shows the characteristic of the signal obtained in an amplitude detector. It is the figure which showed the relationship between the input and output in an output controller. It is a block diagram of the optical transmitter which concerns on 3rd Embodiment. It is a block diagram of the control part which concerns on 3rd Embodiment. It is a graph showing the input change rate for every time. It is a figure which shows the correspondence of the amplification factor of a modulation current, and the inclination of temperature.

Explanation of symbols

  10 optical transmitter, 12 LDD, 14 LD, 16 MPD, 18 APC circuit, 18a error amplifier, 18b averaging filter, 20 AMC circuit, 22 capacitor, 24 inductor, 26 current source, 28 current sensor, 28a resistance, 28b error Amplifier, 30 Filter, 32 Amplitude detector, 34 Error amplifier, 36 Control unit, 38 A / D conversion unit, 40 Output controller, 42 D / A conversion unit, 100 Part of signal waveform, 50 Control unit, 54 Difference Controller, 56 LOS controller, 58 temperature controller, 60 temperature detector, 70 signal detector.

Claims (9)

A drive circuit for generating a drive current based on a modulated current modulated according to transmission information;
An optical transmission element that receives an input of the drive current and transmits an optical signal;
A light receiving element for receiving an optical signal transmitted from the light transmitting element;
A filter for extracting a part of the frequency band from the voltage signal obtained based on the optical signal received by the light receiving element;
And a control means for controlling the amplitude of the modulation current based on a comparison between the amplitude of the voltage signal extracted by the filter and a reference amplitude. The optical transmission device according to claim 1, wherein the control unit controls the amplitude of the modulation current based on a difference between an amplitude of a voltage signal extracted by the filter and a reference amplitude. The control means limits amplification of the amplitude of the modulation current when the difference between the amplitude of the voltage signal extracted by the filter and a reference amplitude exceeds a threshold value. Optical transmitter. Further comprising transmission information detecting means for detecting the presence or absence of the transmission information,
4. The optical transmission according to claim 1, wherein when the transmission information is not detected by the transmission information detection unit, the control unit limits the change in the amplitude of the modulation current. 5. apparatus. The control means limits the change in the amplitude of the modulation current when the change rate of the difference between the amplitude of the voltage signal extracted by the filter and the reference amplitude is not within a predetermined range. The optical transmission device according to claim 1. Means for detecting the temperature of the optical transmitter element;
The optical transmission apparatus according to claim 1, wherein the control unit controls the amplitude of the modulation current based on the detected temperature. The optical transmission device according to claim 1, wherein the filter extracts a part of a low frequency band from a voltage signal obtained based on the optical signal. The optical transmission device according to claim 1, wherein the modulation current is modulated by encoding a signal per frame. Generating a drive current based on a modulation current modulated according to transmission information;
Receiving an input of the drive current and transmitting an optical signal;
Receiving the transmitted optical signal; and
Extracting a part of the frequency band from the voltage signal obtained based on the received optical signal;
Controlling the amplitude of the modulation current based on a comparison between an amplitude of the extracted voltage signal and a reference amplitude. A method for controlling an optical transmission signal, comprising:

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