JP5622239B2 - Optical transmitter and drive condition setting device for optical transmitter - Google Patents

Description

  The present invention relates to an optical transmitter that generates an optical signal used in an optical fiber communication system.

  In order to increase the transmission distance in the optical access network, it is necessary to improve dispersion tolerance. In general, in an optical access network, an optical signal is intensity-modulated according to data to be transmitted. In modulation including intensity modulation, the optical frequency width of signal light is expanded by the modulation sideband. Further, when a direct modulation semiconductor laser (DML: Directly Modulated Laser) or a semiconductor electroabsorption (EA) modulator is used, intensity modulation involves phase modulation.

  In a modulator that involves phase modulation in intensity modulation, frequency chirp is generated in the signal light generated by the modulation. For example, in the case of an EA modulator, the frequency chirp is caused by a change in the refractive index of the modulator according to a voltage applied for modulation. That is, when the refractive index changes, the phase of light passing through the modulator is modulated. Then, since the time derivative of the phase is the optical frequency, the frequency of the output light changes. This frequency change is called frequency chirp. This is shown in Non-Patent Document 1, for example.

  When the optical frequency width including the frequency chirp increases, the optical fiber transmission characteristics are adversely affected. In general, as one of the characteristics of an optical fiber, there is a property that the propagation speed varies depending on the frequency of the propagating light. For this reason, the signal light whose optical frequency width is widened includes a component that advances fast and a component that advances slowly in one bit. As a result, the signal waveform after propagating through the optical fiber is broken. Due to the collapse of the signal waveform, inter-symbol interference (ISI) occurs and transmission characteristics deteriorate. This is shown in Non-Patent Document 2, for example.

  In view of this, a method has been proposed in which deterioration of transmission characteristics due to dispersion is suppressed by adjusting phase modulation and intensity modulation to improve dispersion tolerance. As such a method, a method combining a DML and an optical filter and a method combining a DML and an EA modulator have been proposed. The method of combining DML and an optical filter is realized by extracting light chirped at a predetermined timing of modulation with an optical filter. In the method combining the DML and the EA modulator, the DML is used as a light source and a phase modulator, the EA modulator is used as an intensity modulator, and the modulation degree of the synchronized phase modulation and intensity modulation is adjusted. As a result, single sideband amplitude modulation (SSB) modulation is performed, the amount of rising and falling of the bit is adjusted so that the bit does not spread, and the amount of chirp in FSK (Frequency Shift Keying) The dispersion tolerance is improved by using MSK (Minimum Shift Keying) modulation in which the transmission rate is half the transmission rate.

F. Koyama and K.K. Iga, “Frequency Chirping in External Modulators”, Journal of Lightwave Technology, vol. 6, no. 1, pp. 87-93, January 1988. B. Wedding, “New Method for Optical Transmission Beyond Dispersion Limit”, Electronics Letters, vol. 28, no. 14, pp. 1298-1300, July 1992.

  In the optical access network, it is important to reduce the cost of the apparatus and reduce the power consumption. For this reason, it is necessary to adjust the temperature of the optical transmitter. However, the above-described system requires temperature control. This is because, if the method combines the DML and the optical filter, if the oscillation wavelength of the semiconductor laser changes as the environmental temperature changes, the relationship between the timing to be extracted and the wavelength collapses. In the method combining the DML and the EA modulator, the oscillation intensity of the semiconductor laser and the extinction characteristic of the EA modulator change as the environmental temperature changes, and the relationship between the adjusted phase modulation and the modulation degree of the intensity modulation collapses accordingly. It is.

  Therefore, in order to solve the above-described problems, the present invention operates an optical transmitter that is designed to be long in temperature-free operation, thereby reducing the cost and power consumption of the device and facilitating application to an optical access network. For the purpose.

  In order to achieve the above object, the optical signal of the optical signal is not affected by the temperature change in the modulation unit, so that the frequency fluctuation in the modulation unit satisfies a predetermined condition, or regardless of the temperature change in the modulation unit. The driving conditions in the modulation section at each temperature in the modulation section are set so that the error rate after propagation satisfies a predetermined condition.

Specifically, the present invention provides a modulation unit that outputs a modulated optical signal, a temperature measurement unit that measures a temperature in the modulation unit, and a modulation in the modulation unit regardless of a temperature change in the modulation unit. A drive condition setting table storage unit for storing a table in which the drive condition in the modulation unit at each temperature in the modulation unit is set so that the frequency fluctuation accompanying the modulation including the sideband satisfies a predetermined condition; A modulation control unit that controls the modulation unit based on a temperature measured by the temperature measurement unit and a driving condition at the temperature set by the table, and the modulation unit includes a semiconductor electroabsorption modulator. the drive condition includes a bias voltage and a driving voltage amplitude of the previous SL semiconductor electroabsorption modulator is an optical transmitter.

According to this configuration, since the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation unit satisfies the predetermined condition regardless of the temperature change in the modulation unit, the optical transmitter can be operated without temperature control. Can do.

  Further, according to the present invention, the drive condition setting table storage unit is configured to detect the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation unit and the error after propagation of the optical signal regardless of the temperature change in the modulation unit. The optical transmitter stores a table in which driving conditions in the modulation unit at each temperature in the modulation unit are set so that a rate satisfies a predetermined condition.

According to this configuration, the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation unit satisfies the predetermined condition regardless of the temperature change in the modulation unit, and the error after propagation of the optical signal Since the rate satisfies a predetermined condition, the optical transmitter can be operated without temperature control.

In addition, the present invention provides a temperature setting unit that sets a temperature in a modulation unit that outputs a modulated optical signal, and a frequency variation acquisition unit that acquires information on frequency variation accompanying modulation including a modulation sideband in the modulation unit And the modulation unit at each temperature in the modulation unit so that the frequency variation accompanying modulation including the modulation sideband in the modulation unit satisfies a predetermined condition regardless of the temperature change in the modulation unit. A driving condition setting table creating unit that creates a table in which the driving conditions are set , wherein the modulation unit includes a semiconductor electroabsorption modulator, and the driving condition includes a bias voltage of the semiconductor electroabsorption modulator. And a driving condition setting device for an optical transmitter including a driving voltage amplitude .

According to this configuration, since the frequency variation accompanying the modulation including the modulation sideband in the modulation section at each temperature is created in advance, a table for setting that satisfies the predetermined condition is used. Can be operated without temperature control.

  Further, according to the present invention, the frequency variation acquisition unit acquires information on a frequency variation accompanying modulation including a modulation sideband in the modulation unit and an error rate after propagation of the optical signal, and creates the drive condition setting table The unit, regardless of temperature change in the modulation unit, so as to satisfy a predetermined condition for the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation unit and the error rate after propagation of the optical signal, It is a drive condition setting device for an optical transmitter that creates a table in which drive conditions in the modulation unit at each temperature in the modulation unit are set.

According to this configuration, in addition to creating a setting table in which the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation unit at each temperature satisfies the predetermined condition , the error after propagation of the optical signal Since a table for setting the rate satisfying a predetermined condition is created in advance, the optical transmitter can be operated without temperature control by using this table.

The present invention also provides a temperature setting step for setting a temperature in a modulation unit that outputs a modulated optical signal, and information on frequency fluctuations accompanying modulation including modulation sidebands in the modulation unit, and the modulation unit The drive condition in the modulation section at the temperature in the modulation section is set so that the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation section satisfies a predetermined condition regardless of the temperature change in the modulation section A driving condition setting table creating step for creating a table , wherein the modulation unit includes a semiconductor electroabsorption modulator, and the driving condition includes a bias voltage and a driving voltage amplitude of the semiconductor electroabsorption modulator. including a driving condition setting method of the optical transmitter.

According to this configuration, since the frequency variation accompanying the modulation including the modulation sideband in the modulation section at each temperature is created in advance, a table for setting that satisfies the predetermined condition is used. Can be operated without temperature control.

  Further, in the present invention, the drive condition setting table creating step acquires information on frequency fluctuations accompanying modulation including modulation sidebands in the modulation unit and error rate after propagation of the optical signal, and the modulation unit The temperature at the modulation unit is such that the frequency fluctuation accompanying modulation including the modulation sideband at the modulation unit and the error rate after propagation of the optical signal satisfy a predetermined condition regardless of the temperature change of the modulation unit. This is an optical transmitter drive condition setting method for creating a table in which the drive condition in the modulation section is set.

According to this configuration, in addition to creating a setting table in which the frequency fluctuation accompanying the modulation including the modulation sideband in the modulation unit at each temperature satisfies the predetermined condition , the error after propagation of the optical signal Since a table for setting the rate satisfying a predetermined condition is created in advance, the optical transmitter can be operated without temperature control by using this table.

  According to the present invention, an optical transmitter that is intended to be lengthened can be operated without temperature control, thereby reducing the cost and power consumption of the apparatus and facilitating application to an optical access network.

It is a figure which shows the structure of the optical transmitter of this invention. It is a figure which shows the example of a structure of the drive condition setting system of the optical transmitter of this invention. It is a figure which shows the structure of the drive condition setting apparatus of the optical transmitter of this invention. It is a figure which shows the content of the drive condition setting table of this invention. It is a figure which shows the flow of the drive condition setting method of this invention. It is a figure which shows the flow of the drive condition setting method of this invention. It is a figure which shows the flow of the drive condition setting method of this invention. It is a figure which shows the verification result of the optical transmitter of this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Optical transmitter)
The configuration of the optical transmitter of the present invention is shown in FIG. The optical transmitter 1 includes a transmission signal output unit 11, a DML 12, an EA modulator 13, a temperature measurement unit 14, a drive condition setting table storage unit 15, and a modulation control unit 16. In the present embodiment, the DML 12 and the EA modulator 13 are disposed as the modulation unit. However, the DML 12 alone may be disposed, and the DML 12 and the EA modulator 13 are disposed as the intensity modulator and the phase modulator, respectively. Alternatively, other modulators may be arranged.

  The DML 12 and the EA modulator 13 output a modulated optical signal as a modulation unit. Specifically, the DML 12 outputs modulated light modulated based on the current signal (average current value I1 and current amplitude Ipp) from the modulation control unit 16 to the EA modulator 13, and the EA modulator 13 performs modulation control. The signal light modulated based on the voltage signal (average voltage value V2 and voltage amplitude Vpp) from the unit 16 is output to an optical fiber N1 described later. Here, it is preferable that the DML 12 and the EA modulator 13 are integrally formed in a state where they are electrically separated from each other, in order to achieve miniaturization of the optical transmitter 1.

  The temperature measurement part 14 measures the temperature in DML12 and the EA modulator 13 as one form. Specifically, when the difference in temperature between the DML 12 and the EA modulator 13 is negligible, the temperature measurement unit 14 may measure the temperature of both or one of the DML 12 and the EA modulator 13, The temperature of both or one of the surroundings of the EA modulator 13 may be measured. When the difference in temperature between the DML 12 and the EA modulator 13 cannot be ignored, the temperature is measured. When the DML 12 and the EA modulator 13 are mounted on a single substrate, the temperature measurement unit 14 may measure the temperature of the substrate, or measure the ambient temperature around the substrate. Also good. Further, when the temperature is measured at a site away from the DML 12 and the EA modulator 13, the temperature measurement unit 14 is based on the temperature gradient from the temperature measurement point to the DML 12 and the EA modulator 13. What is necessary is just to calculate the temperature of 13.

  As another form, the temperature measurement unit 14 estimates the temperatures at the DML 12 and the EA modulator 13 based on the output intensity and the driving conditions at the DML 12 and the EA modulator 13. Here, the temperature measurement unit 14 may estimate the temperatures at the DML 12 and the EA modulator 13 based on the output intensity at the DML 12 and the applied current. In this case, since the output intensity at the DML 12 decreases as the temperature increases, the temperature can be simply estimated from the relationship between the output intensity at the DML 12 and the applied current. Then, the temperature measuring unit 14 may estimate the temperatures at the DML 12 and the EA modulator 13 based on the output intensity and applied voltage at the EA modulator 13 and the applied current at the DML 12. In this case, the output intensity of the DML 12 decreases as the temperature increases, and the extinction characteristic of the EA modulator 13 deteriorates as the temperature decreases. Therefore, the output intensity and applied voltage in the EA modulator 13 and the applied current in the DML 12 The temperature can be estimated from the combination. The temperature measurement unit 14 desirably estimates the temperatures at the DML 12 and the EA modulator 13 based on the former method. In any method, since the optical transmitter 1 is already provided with output intensity measuring means for the purpose of making the output intensity normally constant, the temperature is newly measured for temperature control. There is no need to add additional parts.

  As one form, the drive condition setting table storage unit 15 does not depend on the temperature change in the DML 12 and the EA modulator 13, so that the frequency variation in the DML 12 and the EA modulator 13 satisfies a predetermined condition. A table in which driving conditions in the DML 12 and the EA modulator 13 at each temperature in the EA modulator 13 are set is stored. Therefore, the frequency variation in the DML 12 and the EA modulator 13 satisfies the predetermined condition regardless of the temperature change in the DML 12 and the EA modulator 13, so that the optical transmitter 1 can be operated without temperature control.

Here, the frequency fluctuation is a frequency fluctuation accompanying the modulation including the modulation sideband and the frequency chirp. The predetermined condition regarding the overall frequency fluctuation including modulation sideband and frequency chirp is, for example, the relationship between the wavelength dispersion of the transmission line at the assumed transmission distance and the error rate or eye opening penalty due to the dispersion of the transmission line. Satisfying a predetermined value. The predetermined value of the error rate or eye opening penalty due to the dispersion of the transmission path is, for example, an error rate of 10 ⁻¹² or 1 dB.

  For example, if the wavelength of the signal light is on the long wavelength side of the zero dispersion wavelength, the frequency decreases and the wavelength increases at the rising edge of the signal light, and the frequency increases and the wavelength decreases at the falling edge of the signal light. The signal light is narrowed and compressed at a leading edge, and the signal light is narrowed and compressed. When this continues, the leading edge and the trailing edge are reversed, and the width of the signal light begins to expand. Therefore, it is desirable that the predetermined condition is set according to the width and compression of the signal light according to the wavelength of the signal light, the assumed transmission distance, and the transmission path dispersion.

  Moreover, it is good also as a predetermined condition that a frequency width is simply below a predetermined value, without considering the frequency fluctuation in each rise and fall of signal light. In this case, setting is easy, but in order for the error rate or eye opening penalty due to dispersion in the transmission path to satisfy a predetermined value, frequency fluctuations at the rise and fall of the signal light are considered. It is desirable to set a smaller value, for example, about half the value.

  Further, as a predetermined condition, when the frequency chirp is small and the frequency fluctuation due to the modulation sideband is main, the frequency spread due to the modulation sideband may be reduced. For example, SSB modulation may be used, and the sideband suppression ratio may be 20 dB or more, or the relationship between intensity modulation and frequency modulation for establishing MSK modulation may be used.

For example, the drive condition setting table storage unit 15 may be predetermined so that the error rate after propagation of the optical signal satisfies a predetermined condition regardless of temperature changes in the DML 12 and the EA modulator 13. A table in which the driving conditions in the DML 12 and the EA modulator 13 at each temperature in the DML 12 and the EA modulator 13 are set so as to be equal to or less than the error rate threshold value. Therefore, since the error rate after propagation of the optical signal satisfies a predetermined condition regardless of the temperature change in the DML 12 and the EA modulator 13, for example, since the error rate is equal to or lower than a predetermined error rate threshold, optical transmission is performed. The device 1 can be operated without temperature control. The predetermined error rate threshold is, for example, an error rate of ^10-12 .

  The drive condition setting table storage unit 15 is a combination of the two forms described above, regardless of temperature changes in the DML 12 and the EA modulator 13, and after the frequency fluctuations in the DML 12 and the EA modulator 13 and the propagation of the optical signal. A table in which driving conditions in the DML 12 and EA modulator 13 at each temperature in the DML 12 and EA modulator 13 are set so that the error rate satisfies a predetermined condition is stored. Therefore, regardless of the temperature change in the DML 12 and the EA modulator 13, the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal satisfy the predetermined conditions. It can be operated without temperature control.

  The parameters of the table may be parameters that control the degree of modulation and the chirp amount in each modulator. When the DML 12 and the EA modulator 13 are arranged, the parameters are the average current value and modulation amplitude applied to the DML 12 and the average voltage value and modulation amplitude applied to the EA modulator 13 at each temperature. It is. When the DML 12 alone is arranged, the parameters are the average current value and the modulation amplitude applied to the DML 12 at each temperature. If other modulators are in place, the parameters are the other modulators, such as the average current value and modulation amplitude or average voltage value and modulation amplitude applied to the respective modulator at each temperature. Is a parameter for determining the degree of modulation and the amount of chirp. Since the voltage value and the current value are related by a conversion formula of voltage value = current value × resistance, the parameter may be voltage display or current display. The parameter may be an average value or an upper limit value or a lower limit value.

  The modulation control unit 16 controls the DML 12 and the EA modulator 13 based on the temperature measured by the temperature measurement unit 14 and the driving condition at the temperature set by the table. Specifically, the modulation control unit 16 acquires a transmission signal from the transmission signal output unit 11 and acquires temperature information from the temperature measurement unit 14. Then, the modulation control unit 16 refers to the table stored in the drive condition setting table storage unit 15 and acquires information on the drive condition at the temperature. Further, the modulation control unit 16 outputs a current signal (average current value I1 and current amplitude Ipp) to the DML 12 based on the transmission signal and driving conditions, and a voltage signal (average voltage value V2 and voltage amplitude) to the EA modulator 13. Vpp) is output.

  Here, each output has a predetermined phase relationship. The predetermined phase relationship is, for example, that a phase of modulation applied to light output as modulated light by the DML 12 and a phase of modulation applied to light output as signal light by the EA modulator 13 are propagation delays. Is a phase relationship in which the phase difference is zero. In order to adjust the phase relationship, the phase of the modulation applied to the DML 12 and the phase of the modulation applied to the EA modulator 13 may be adjusted, or the phase of the propagation light between the DML 12 and the EA modulator 13 may be The adjustment may be performed by providing a phase adjustment unit (not shown) that adjusts the amount of current applied and the like, and changing the amount of current applied to the phase adjustment unit. Then, even if the measured temperature is not described in the table, the modulation control unit 16 may obtain the driving condition at the measured temperature from the driving condition at the described temperature using the interpolation process. .

  The following conditions etc. are mention | raise | lifted as a predetermined condition which the frequency fluctuation | variation in DML12 and EA modulator 13 should satisfy | fill. The first condition is to adjust the relationship between the intensity fluctuation and the frequency fluctuation so that the SSB modulation is realized when the frequency fluctuation due to the modulation sideband is the main frequency fluctuation. The second condition is that when the frequency fluctuation due to chirp is the main frequency fluctuation, the amount of chirp at the rise and fall of the bit is adjusted to be a predetermined chirp amount. The third condition is to adjust the relationship between the intensity fluctuation and the frequency fluctuation so that the MSK modulation is realized when the frequency fluctuation due to the modulation sideband is the main frequency fluctuation.

  The first condition will be described in detail below. The first condition is effective when the spread of the optical frequency width due to the modulation sideband is the main cause of the deterioration of the transmission characteristics rather than the spread of the optical frequency width due to the chirp. The first condition is that Δf = MB, where Δf is the total frequency chirp amount in the DML 12 and EA modulator 13, M is the total intensity modulation degree in the DML 12 and EA modulator 13, and B is the transmission band. / 2.

  For example, the DML 12 is modulated using an inverted transmission signal, and the EA modulator 13 is modulated using an uninverted transmission signal. The frequency chirp amount Δf1 in the DML 12 is expressed as Δf1 = α1 (1 / P1) (dP1 / dt + LP1). Here, α1, P1, dP1 / dt, and L are the chirp parameter, light intensity, time derivative of the light intensity, and nonlinear coefficient in the DML 12, respectively. The frequency chirp amount Δf2 in the EA modulator 13 is expressed as Δf2 = α2 (1 / P2) (dP2 / dt). Here, α2, P2, and dP2 / dt are the chirp parameter, light intensity, and time derivative of the light intensity in the EA modulator 13, respectively.

  In order to satisfy Δf = MB / 2, α1 (1 / P1) (dP1 / dt + LP1) + α2 (1 / P2) (dP2 / dt) = B (k1I1-k2V2) / 2 may be satisfied. Here, I1 is the modulation amplitude of the applied current in the DML 12, and V2 is the modulation amplitude of the applied voltage in the EA modulator 13. K1 is a proportional coefficient when the frequency chirp amount is proportional to the applied current value in the DML 12, and k2 is a proportional coefficient when the frequency chirp amount is proportional to the applied voltage value in the EA modulator 13. Here, the proportionality coefficient may not depend on the temperature, and may depend on the temperature. When it is constant regardless of the temperature, a constant value is used regardless of the temperature, and when it changes depending on the temperature, a value corresponding to the temperature is used. The frequency chirp amount is exemplified as being proportional to the applied current value and the applied voltage value, but may be set according to the relationship even if not proportional.

(Optical transmitter drive condition setting device)
An example of the configuration of the optical transmitter drive condition setting system of the present invention is shown in FIG. The drive condition setting system N includes an optical fiber N1, an optical amplifier N2, a bandpass filter N3, an optical attenuator N4, an optical coupler N5, a frequency chirp measuring instrument N6, an optical receiver N7, an error detector N8, a DML12, and an EA modulator. 13, a temperature setting unit 21, a pulse pattern generator 111, and phase shifters 112 and 113. The DML 12 and the EA modulator 13 are the same as those shown in FIG. The temperature setting unit 21 includes a temperature adjusting element such as a Peltier element, and is the same as that shown in FIG.

  The pulse pattern generator 111 receives an external device that supplies the transmission signal not shown in FIG. 1 to the transmission signal output unit 11 and the external transmission signal shown in FIG. The transmission signal output unit 11 that outputs a signal or current signal and the partial control function of the modulation control unit 16 are the same. However, the signal output from the pulse pattern generator 111 is a signal that mimics the signal output from the external device. For example, if the external device outputs an 8B / 10B signal, it corresponds to 8B / 10B. If a 64B / 66B signal is output, a signal corresponding to 64B / 66B is output. The corresponding signal may be a pseudo-random pattern in which the same code continuation condition is more severe. A part of the function of the modulation control unit 16 that the pulse pattern generator 111 serves is an adjustment function of the average voltage amount and the voltage amplitude.

  The phase shifters 112 and 113 have the remaining functions of the modulation control unit 16 shown in FIG. The remaining functions of the phase shifters 112 and 113 are functions for adjusting the phase of the voltage signal to be applied. Although an example is shown in which a voltage signal in which 0 and 1 bits are inverted from each other is output from the pulse pattern generator 111 to the DML 12 and the EA modulator 13, the pulse pattern generator 111 outputs to the DML 12 and the EA modulator 13. On the other hand, a voltage signal in which the 0 and 1 bits are not inverted may be output. When only the voltage signal that does not invert the 0 and 1 bits is used, an inverter may be connected to one of the outputs to invert the 0 and 1 bits as necessary.

Although the output of the pulse pattern generator 111 is two outputs, a single output may be branched and input to each, or one of the branched outputs may be inverted by an inverter or the like. The pulse pattern generator 111 may output a sine wave signal without considering the code length of the transmission signal. In this case, a synthesizer may be used instead of the pulse pattern generator 111. In the case of the output of a sine wave signal, since the influence of the pattern effect such as the same sign continuation does not appear, the predetermined condition is strictly set to the error rate 10 ⁻¹³ instead of the error rate 10 ⁻¹² for the effect. . Further, an AWG (Arrayed Waveguide Grating) may be used instead of the pulse pattern generator 111. The pattern output from the pulse pattern generator 111 may be a PRBS (Pseudo Random Binary Sequence) signal. The number of stages is desirably set according to the assumed modulation format.

  The frequency fluctuation measurement using the frequency chirp measuring device N6 and the error rate measurement using the error detector N8 may be measured in parallel or in any one of them. When the transmission line loss is sufficiently small, the optical amplifier N2 and the bandpass filter N3 need not be provided. When the nonlinear phenomenon in the transmission line can be ignored, the optical amplifier N2 or the optical amplifier N2 and the band pass filter N3 may be disposed in front of the optical fiber N1. When the ASE is negligible or when a sufficiently large signal is amplified by the optical amplifier N2, the band pass filter N3 may not be provided. The band pass filter N3 may be provided in front of the optical receiver N7.

  The frequency chirp measuring instrument N6 is assumed to measure after transmission, but may be measured without transmission. That is, the optical coupler N5 may be installed in front of the optical fiber N1, and the input to the frequency chirp measuring device N6 and the optical fiber N1 may be branched and measured. When measuring only the frequency fluctuation, the output of the EA modulator 13 is directly input to the frequency chirp measuring device N6, and the optical fiber N1, the optical amplifier N2, the bandpass filter N3, the optical attenuator N4, the optical coupler N5, and the optical receiving device. N7 and error detector N8 may not be provided.

  The configuration of the optical transmitter drive condition setting apparatus of the present invention is shown in FIG. The drive condition setting device 2 includes a temperature setting unit 21, a frequency variation / error rate acquisition unit 22, and a drive condition setting table creation unit 23. The optical transmitter 1 and the drive condition setting device 2 may be partially disposed in the same device, or all may be disposed as different devices. At least the optical transmitter 1 includes a pulse pattern generator 111, phase shifters 112 and 113, an optical fiber N1, an optical amplifier N2, a bandpass filter N3, an optical attenuator N4, an optical coupler N5, a frequency chirp measuring device N6, and an optical receiver. N7 and error detector N8 are not included.

  The temperature setting unit 21 sets temperatures in the DML 12 and the EA modulator 13 that output the intensity-modulated optical signal. The frequency fluctuation / error rate acquisition unit 22 acquires frequency fluctuation information in the DML 12 and the EA modulator 13 from the frequency chirp measuring instrument N6, or error rate information after propagation of the optical signal as an error detector N8. Get from.

  When the optical transmitter 1 and the drive condition setting device 2 are arranged in the same device, the temperature setting unit 21 is a device such as a thermostatic chamber that adjusts the temperatures of the optical transmitter 1 and the drive condition setting device 2. If the DML 12 and the EA modulator 13 are provided with temperature control such as a Peltier element instead of a device such as a thermostat, the temperature control may be used. In this case, it is desirable that the temperature setting unit 21 includes a driver that drives the temperature adjustment provided in the DML 12 and the EA modulator 13.

  Most desirably, the DML 12 and the EA modulator 13 are not provided with temperature control. In this case, the temperature adjustment and the cost of installing the driver are reduced. Next, it is desirable to provide temperature control but not the driver. This is because the cost of installing a temperature-controlled driver is reduced in this case. Next, it is desirable to provide temperature control and its driver, but not to control temperature and its driver.

  The drive condition setting table creation unit 23, as one form, allows the DML 12 and the EA modulator 13 so that the frequency variation in the DML 12 and the EA modulator 13 satisfies a predetermined condition regardless of the temperature change in the DML 12 and the EA modulator 13. A table in which driving conditions in the DML 12 and the EA modulator 13 at each temperature in the EA modulator 13 are set is created. Then, the driving condition setting table creation unit 23 registers the table in the driving condition setting table storage unit 15.

  For example, the drive condition setting table creating unit 23 may be predetermined so that the error rate after propagation of the optical signal satisfies a predetermined condition regardless of temperature changes in the DML 12 and the EA modulator 13. A table in which the driving conditions in the DML 12 and the EA modulator 13 at the respective temperatures in the DML 12 and the EA modulator 13 are set so as to be equal to or lower than the error rate threshold value. Then, the driving condition setting table creation unit 23 registers the table in the driving condition setting table storage unit 15.

  The integrally shaped DML 12 and EA modulator 13 are installed in the drive condition setting device 2 and a drive condition setting table is created in the drive condition setting device 2, and then the integrally shaped DML 12 and EA modulator 13 are set to drive conditions. The drive condition setting table may be stored in the optical transmitter 1 by being removed from the device 2 and installed in the optical transmitter 1.

  The contents of the drive condition setting table of the present invention are shown in FIG. At each temperature, the bias Ibias and drive amplitude Ipp related to the current applied to the DML 12 and the bias Vbias and drive amplitude Vpp related to the voltage applied to the EA modulator 13 are optimized.

  Regardless of the temperature change in the DML 12 and the EA modulator 13, a setting table is created at which the frequency fluctuation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal satisfy predetermined conditions. FIG. 5 shows a flow of the driving condition setting method of the present invention. The temperature measurement unit 21 sets the temperature in the DML 12 and the EA modulator 13 (step S1). The modulation control unit 16 outputs the drive amplitude Ipp and the bias current Ibias to the DML 12, and outputs the drive amplitude Vpp and the bias voltage Vbias to the EA modulator 13 (Step S2). The frequency variation / error rate acquisition unit 22 acquires information on the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal from the frequency chirp measuring device N6 and the error detector N8 (step S3). .

  If the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal satisfy the predetermined conditions (YES in step S4), the drive condition setting table creation unit 23 outputs in step S2. The drive amplitude Ipp, bias current Ibias, drive amplitude Vpp, and bias voltage Vbias are written to the temperature set in step S1 (step S5). If the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal do not satisfy the predetermined condition (NO in step S4), the drive condition setting table creation unit 23 performs steps S2 to S4. Repeat. The processing described above is executed at each temperature.

  Regardless of the temperature change in the DML 12 and the EA modulator 13, the frequency fluctuation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal are made to satisfy a predetermined condition at each temperature. An example of the flow of the driving condition setting method of the present invention is shown in FIGS. The temperature measurement unit 21 sets the temperature in the DML 12 and the EA modulator 13 (step S11). In the following processing, values to be written in the table are determined in the order of the drive amplitude Ipp in the DML 12, the drive amplitude Vpp in the EA modulator 13, the bias current Ibias in the DML 12, and the bias voltage Vbias in the EA modulator 13.

  The modulation control unit 16 outputs the drive amplitude Ipp to the DML 12 (Step S12). The frequency variation / error rate acquisition unit 22 acquires information on the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal from the frequency chirp measuring device N6 and the error detector N8 (step S13). . The drive condition setting table creating unit 23 satisfies a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13 and satisfies a predetermined error rate after propagation of the optical signal, for example, a predetermined condition. If it is equal to or less than the error rate threshold value set (YES in step S14), the drive amplitude Ipp is stored. The drive condition setting table creating unit 23 does not satisfy a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13, or an error rate after propagation of an optical signal does not satisfy a predetermined condition, for example, If it is not less than the predetermined error rate threshold (NO in step S14), drive amplitude Ipp is changed and steps S12 to S14 are repeated. The drive condition setting table creation unit 23 may store the optimum drive amplitude Ipp if step S13 is repeated a predetermined number of times (YES in step S14).

  The modulation control unit 16 outputs the drive amplitude Vpp to the EA modulator 13 (step 15). The frequency variation / error rate acquisition unit 22 acquires information on the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal from the frequency chirp measuring device N6 and the error detector N8 (step S16). . The drive condition setting table creating unit 23 satisfies a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13 and satisfies a predetermined error rate after propagation of the optical signal, for example, a predetermined condition. If it is equal to or less than the error rate threshold value set (YES in step S17), the drive amplitude Vpp is stored. The drive condition setting table creating unit 23 does not satisfy a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13, or an error rate after propagation of an optical signal does not satisfy a predetermined condition, for example, If not below the predetermined error rate threshold value (NO in step S17), drive amplitude Vpp is changed and steps S15 to S17 are repeated. Drive condition setting table creation unit 23 may store optimum drive amplitude Vpp if step S16 is repeated a predetermined number of times (YES in step S17).

  The modulation control unit 16 outputs the bias current Ibias to the DML 12 (Step S18). The frequency variation / error rate acquisition unit 22 acquires information on the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal from the frequency chirp measuring device N6 and the error detector N8 (step S19). . The drive condition setting table creating unit 23 satisfies a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13 and satisfies a predetermined error rate after propagation of the optical signal, for example, a predetermined condition. If it is less than or equal to the error rate threshold value set (YES in step S20), the bias current Ibias is stored. The drive condition setting table creating unit 23 does not satisfy a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13, or an error rate after propagation of an optical signal does not satisfy a predetermined condition, for example, If not below the predetermined error rate threshold value (NO in step S20), the bias current Ibias is changed and steps S18 to S20 are repeated. The drive condition setting table creating unit 23 may store the optimum bias current Ibias if step S19 is repeated a predetermined number of times (YES in step S20).

  The modulation control unit 16 outputs the bias voltage Vbias to the EA modulator 13 (Step 21). The frequency variation / error rate acquisition unit 22 acquires information on the frequency variation in the DML 12 and the EA modulator 13 and the error rate after propagation of the optical signal from the frequency chirp measuring device N6 and the error detector N8 (step S22). . The drive condition setting table creating unit 23 satisfies a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13 and satisfies a predetermined error rate after propagation of the optical signal, for example, a predetermined condition. If it is equal to or less than the error rate threshold value set (YES in step S23), the bias voltage Vbias is stored. The drive condition setting table creating unit 23 does not satisfy a predetermined condition for frequency fluctuations in the DML 12 and the EA modulator 13, or an error rate after propagation of an optical signal does not satisfy a predetermined condition, for example, If it is not below the predetermined error rate threshold (NO in step S23), the bias voltage Vbias is changed and steps S21 to S23 are repeated. The drive condition setting table creating unit 23 may store the optimum bias voltage Vbias if step S22 is repeated a predetermined number of times (YES in step S23).

  The drive condition setting table creation unit 23 uses the drive amplitude Ipp, drive amplitude Vpp, bias current Ibias, and bias voltage Vbias stored in steps S14, S17, S20, and S23, respectively, for the temperatures set in step S11. Write (step S24). The processing described above is executed at each temperature.

  Changes in the error rate when the drive amplitude Ipp in the DML 12 and the drive amplitude Vpp in the EA modulator 13 are changed occur when the bias current Ibias in the DML 12 and the bias voltage Vbias in the EA modulator 13 are changed. Less than change in error rate. Therefore, in this embodiment, first, the drive amplitude Ipp in the DML 12 and the drive amplitude Vpp in the EA modulator 13 are changed, and then the bias current Ibias in the DML 12 and the bias voltage Vbias in the EA modulator 13 are changed. ing. However, in another embodiment, first, the bias current Ibias in the DML 12 and the bias voltage Vbias in the EA modulator 13 are changed, and then the drive amplitude Ipp in the DML 12 and the drive amplitude Vpp in the EA modulator 13 are changed. You may let them. Furthermore, when the frequency variation and the error rate become higher in the current step than in the previous step, the previous step may be repeated without proceeding to the previous step. In FIGS. 5 to 7, it is determined whether or not both the frequency fluctuation and the error rate satisfy a predetermined condition. However, whether or not one of the frequency fluctuation and the error rate satisfies a predetermined condition is determined. You may judge.

(Verification result of optical transmitter)
A verification result of the optical transmitter 1 will be described. The DML 12 and the EA modulator 13 are respectively used for the 10 Gbit / s NRZ (Non Return to Zero) data signal of the pulse pattern generator 111 by using a signal that is not inverted 01 and an inverted signal of 01. Drove. The number of stages of the PRBS (Pseudo Random Binary Sequence) signal at this time was 31.

  For verification after transmission of 100 km, transmission of 100 km is performed using an ordinary SMF (Single Mode Fiber) having a dispersion characteristic of 17 ps / nm / km as the optical fiber N1 with respect to the optical output signal of the optical transmitter 1. The propagation loss was compensated for using an EDFA (Erbium Doped Fiber Amplifier) as the optical amplifier N2, the filtering was performed using the bandpass filter N3, and the error rate was measured using the error detector N8. For verification after transmission of Back to Back, the optical fiber N1, the optical amplifier N2, and the bandpass filter N3 are not used.

  The verification result of the optical transmitter of the present invention is shown in FIG. The white triangle indicates the error rate after transmission of Back to Back at a temperature of 30 ° C. using the driving conditions optimized for the temperature of 30 ° C., and the black triangle is optimized for the temperature of 30 ° C. The error rate after transmission of 100 km at a temperature of 30 ° C. using the determined driving conditions is shown. The black circle shows the error rate after transmission of 100 km at a temperature of 55 ° C. using the driving conditions optimized for a temperature of 30 ° C., and the white circle shows the driving conditions optimized for a temperature of 55 ° C. The error rate after transmission of 100 km at a temperature of 55 ° C. is shown.

When the back-to-back transmission is performed at a temperature of 30 ° C. using the driving conditions optimized for the temperature of 30 ° C., the minimum receiving sensitivity when the error rate is 10 ⁻¹² is −14.2 dBm. It was. When transmission of 100 km was performed at a temperature of 30 ° C. using the driving conditions optimized for the temperature of 30 ° C., the minimum receiving sensitivity was −12.8 dBm when the error rate was 10 ⁻¹² . When transmission of 100 km was performed at a temperature of 55 ° C. using a driving condition optimized for a temperature of 30 ° C., the minimum receiving sensitivity when the error rate was 10 ⁻¹² was −11.1 dBm. When transmission of 100 km was performed at a temperature of 55 ° C. using a driving condition optimized for a temperature of 55 ° C., the minimum receiving sensitivity was −13.2 dBm when the error rate was 10 ⁻¹² . Thus, when transmission of 100 km was performed at a temperature of 55 ° C., the minimum reception sensitivity improved by (−11.1 dBm) − (− 13.2 dBm) = 2.1 dBm before and after optimization of the driving conditions.

  In an optical transmitter having a prior art provided with a temperature adjustment element, the power consumption of the temperature adjustment element when the set temperature is set to 30 ° C. at room temperature is 1.2 W, and when the set temperature is set to 55 ° C. at room temperature The power consumption of was 1.7 W. In the optical transmitter of the present invention, since the temperature adjusting element is unnecessary, it is assumed that the effect of reducing the power consumption can be expected.

  If the frequency variation in the DML 12 or EA modulator 13 has pattern dependence on the modulation bit string, the modulation signal from the modulation control unit 16 to the DML 12 or EA modulator 13 is changed so as to cancel the pattern dependence. It may be deformed. For example, when the frequency chirp amount increases as the continuous length of the same code increases, a low-pass filter having a frequency-transmission intensity characteristic that increases the transmission amplitude of the modulation signal may be used. On the contrary, when the frequency chirp amount decreases as the continuous length of the same code becomes longer, it may be passed through a high-pass filter having a frequency-transmission intensity characteristic in which the transmission amplitude of the modulation signal decreases.

  The optical transmitter and the optical transmitter drive condition setting device according to the present invention can improve dispersion tolerance regardless of environmental temperature without providing temperature control in an optical access network that is intended to be long-lengthened. It can be applied when the cost is reduced and the power consumption is reduced.

1: Optical transmitter 2: Drive condition setting device 11: Transmission signal output unit 12: DML
13: EA modulator 14: temperature measurement unit 15: drive condition setting table storage unit 16: modulation control unit 21: temperature setting unit 22: frequency fluctuation / error rate acquisition unit 23: drive condition setting table creation unit 111: pulse pattern generation Units 112 and 113: Phase shifter N: Drive condition setting system N1: Optical fiber N2: Optical amplifier N3: Band pass filter N4: Optical attenuator N5: Optical coupler N6: Frequency chirp measuring instrument N7: Optical receiver N8: Error detection vessel

Claims (6)

A modulator for outputting a modulated optical signal;
A temperature measurement unit for measuring the temperature in the modulation unit;
Driving in the modulation unit at each temperature in the modulation unit so that a frequency variation accompanying modulation including a modulation sideband in the modulation unit satisfies a predetermined condition regardless of a temperature change in the modulation unit. A drive condition setting table storage unit for storing a table in which conditions are set;
A modulation control unit for controlling the modulation unit based on the temperature measured by the temperature measurement unit and the driving condition at the temperature set by the table;
With
The modulation unit includes a semiconductor electroabsorption modulator,
The drive condition includes a bias voltage and a driving voltage amplitude of the previous SL semiconductor electroabsorption modulator,
Optical transmitter. In the drive condition setting table storage unit, frequency fluctuations accompanying modulation including a modulation sideband in the modulation unit and an error rate after propagation of the optical signal are determined in advance regardless of a temperature change in the modulation unit . The optical transmitter according to claim 1, wherein a table in which a driving condition in the modulation unit at each temperature in the modulation unit is set so as to satisfy a condition is stored. A temperature setting unit for setting the temperature in the modulation unit that outputs the modulated optical signal;
A frequency fluctuation acquisition unit for acquiring information of frequency fluctuations accompanying modulation including modulation sidebands in the modulation unit;
Driving in the modulation unit at each temperature in the modulation unit so that a frequency variation accompanying modulation including a modulation sideband in the modulation unit satisfies a predetermined condition regardless of a temperature change in the modulation unit. A drive condition setting table creating unit for creating a table in which conditions are set;
Equipped with a,
The modulation unit includes a semiconductor electroabsorption modulator,
The driving condition includes a bias voltage and a driving voltage amplitude of the semiconductor electroabsorption modulator.
Drive condition setting device for optical transmitter. The frequency variation acquiring unit acquires information of the error rate after the propagation of the frequency variation and the optical signal due to modulation, including modulation sidebands in the modulation unit,
The drive condition setting table creation unit has predetermined frequency fluctuations associated with modulation including modulation sidebands in the modulation unit and error rate after propagation of the optical signal, regardless of temperature changes in the modulation unit . The drive condition setting device for an optical transmitter according to claim 3, wherein a table is set in which drive conditions in the modulation section at each temperature in the modulation section are set so as to satisfy a condition. A temperature setting step for setting the temperature at the modulation unit that outputs the modulated optical signal;
Obtains information of a frequency variation accompanying modulation, including modulation sidebands in the modulation unit, a frequency variation accompanying the modulation, including modulation sidebands in the modulation section irrespective of the temperature change in the modulation unit is set in advance A drive condition setting table creating step for creating a table in which the drive condition in the modulation unit at the temperature in the modulation unit is set so as to satisfy the following conditions:
In order ,
The modulation unit includes a semiconductor electroabsorption modulator,
The driving condition includes a bias voltage and a driving voltage amplitude of the semiconductor electroabsorption modulator.
Driving condition setting method for optical transmitter. The drive condition setting table creation step acquires information on frequency fluctuations accompanying modulation including modulation sidebands in the modulation unit and error rate after propagation of the optical signal, regardless of temperature changes in the modulation unit. In the modulation unit at the temperature in the modulation unit, the frequency variation accompanying modulation including the modulation sideband in the modulation unit and the error rate after propagation of the optical signal satisfy a predetermined condition. 6. The optical transmitter drive condition setting method according to claim 5, wherein a table in which the drive condition is set is created.

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