JP2014078545A - Device for driving semiconductor optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a pattern effect of a semiconductor optical device while performing high-frequency emphasis.SOLUTION: A multi-valuing device (12) makes a binary data signal multivalued. An HPF (14) extracts a high-frequency component of a multivalued data signal. A variable amplifier (18) amplifies an output of the HPF (14). A pattern determination device (16) determines a temporal change pattern of the multivalued data signal. A gain control device (20) references a gain table (21) and controls a gain of the variable amplifier (18) according to the determination results of the pattern determination device (16). A gain value to be applied to a possible pattern change of the multivalued data signal is stored in the gain table (21). A delay device (22) delays the multivalued data signal by the time equivalent to the processing time of the HPF (14) and the variable amplifier (18). An adder (24) adds an output of the variable amplifier (18) to an output of the delay unit (22).

Description

  The present invention relates to a semiconductor optical device driving apparatus that multi-level drives a semiconductor optical device.

  In order to realize high-speed data transmission using optical signals, it is necessary to drive semiconductor optical devices such as semiconductor lasers, light emitting diodes (LEDs), semiconductor optical amplifiers, reflective semiconductor optical amplifiers, EA modulators, and LN modulators at high speed. .

  The signal waveform of an optical signal is generally deteriorated by transmission and increases the transmission error rate. As a method for improving such waveform deterioration, a pre-emphasis process in which a drive signal of a semiconductor optical device is emphasized in advance in a high frequency region is known.

  In Patent Documents 1 and 2, a binary data signal to be transmitted is delayed for a predetermined time and inverted to generate or extract a high frequency component, and this high frequency component is added to a current signal corresponding to the binary data signal. Thus, there is described a configuration in which the drive current of the laser diode is used.

JP 2010-099788 A JP 2012-043932 A

  Multi-level modulation is also effective for increasing the data rate. However, when the semiconductor optical device is driven by the multi-value intensity modulation method, the pre-emphasis technology as described in Patent Documents 1 and 2 is applied because the pulse rise and fall of the generated optical signal are not uniform. Even if it does, the optical signal which performed appropriate high region emphasis cannot be obtained as it is.

  In addition, since optical signals generated by many semiconductor optical devices depend on the excitation state during driving, a high-quality optical signal cannot be generated simply by high-frequency enhancement of the driving signal in advance.

  An object of the present invention is to provide a semiconductor optical device driving apparatus that eliminates these disadvantages.

  A semiconductor optical device driving apparatus according to the present invention is a semiconductor optical device driving apparatus that drives a semiconductor optical device in accordance with a data signal, the high-frequency extracting means for extracting a high-frequency component of the data signal, and the high-frequency extracting means Level adjusting means for adjusting the level of the output according to the level adjustment value, pattern determining means for determining a temporal change pattern of the data signal, and the level adjustment value of the level adjusting means according to the determination result of the pattern determining means And a control means for controlling the data signal, and an adding means for adding the data signal and the output of the level adjusting means.

  According to the present invention, it is possible to generate a drive signal in consideration of the pattern effect of the semiconductor optical device to be driven, and therefore it is possible to generate a good quality optical signal by the semiconductor optical device.

It is a schematic block diagram of the first embodiment of the present invention. It is an example of a waveform of a present Example. It is an example of the gain value of a variable amplifier. It is a schematic block diagram of the structure which added the means to determine a gain and a cut-off frequency. 5 is an operation explanatory example of the configuration shown in FIG. 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of the present invention, and FIG. 2 shows examples of waveforms in each part of FIG.

  A binary data signal to be carried by an optical signal is input to the input terminal 10. The multi-value quantization apparatus 12 multi-values the binary data signal from the input terminal 10. Specifically, the multi-value quantization apparatus 12 converts an input binary data signal into a four-value data signal having four values in one time slot. FIG. 2A shows an output waveform example of the multi-value quantization apparatus 12. The output of the multi-value quantization device 12 is input to a high-pass filter (HPF) 14 for high-frequency extraction, a pattern determination device 16 that detects a level change of the multi-value signal, and a time adjustment delay device 22.

  The HPF 14 extracts the high-frequency component, more specifically, the edge component (or the rising component and the falling component) of the level transition from the multi-value data signal output from the multi-value quantization device 12. The cutoff frequency of the HPF 14 is appropriately set or adjusted according to the transmission rate of the multilevel data signal. FIG. 2B shows an output waveform example of the HPF 14 for the multi-value data signal shown in FIG. As shown in FIG. 2B, the amplitude of the output signal of the HPF 14 increases as the level transition of the output waveform of the multi-value quantization apparatus 12 increases. The output signal of the HPF 14 is supplied to the variable amplifier 18.

  Needless to say, the HPF 14 may be an edge extraction device including a delay circuit and a differential circuit as described in Patent Documents 1 and 2, in addition to an analog filter circuit.

  The pattern determination device 16 determines the level change pattern in the time axis direction of the multilevel data signal output from the multilevel device 12 and outputs the determination result to the gain control device 20. In this embodiment, the pattern determination device 16 determines a change between the current symbol value and the previous symbol value.

The gain control device 20 refers to the gain table 21 and controls the variable amplifier 18 to a gain corresponding to the level transition amount indicated by the determination result of the pattern determination device 16. FIG. 2C shows an example of gain change of the variable amplifier 18. FIG. 3 shows an example of gain control for the waveform example shown in FIG. With respect to the immediately preceding symbol value “00”, the gains for the current symbol values “00”, “01”, “10”, and “11” are g ₀₀ , g ₀₁ , g _02, and g ₀₃ , respectively. The gains for the current symbol values “00”, “01”, “10”, and “11” with respect to the immediately preceding symbol value “01” are g ₁₀ , g ₁₁ , g _12, and g ₁₃ , respectively. For the immediately preceding symbol value “10”, the gains for the current symbol values “00”, “01”, “10”, and “11” are g ₂₀ , g ₂₁ , g _22, and g ₂₃ , respectively. For the immediately preceding symbol value “11”, the gains for the current symbol values “00”, “01”, “10”, and “11” are g ₃₀ , g ₃₁ , g _32, and g ₃₃ , respectively. The gains g ₀₀ , g ₁₁ , g ₂₂ , and g ₃₃ are actually gains for situations where no level transition occurs, and may be indefinite, zero, or the same as the immediately preceding value.

  Semiconductor optical devices generally have a so-called pattern effect that is affected by the preceding drive current waveform even with the same drive current waveform. In the present embodiment, the gain of the variable amplifier 18 is controlled in accordance with the level change pattern of the multilevel data signal that is the source of the drive signal so as to reduce or reduce such a pattern effect.

  Specifically, the semiconductor optical device to be driven (this embodiment) is amplified by how much the high frequency component is amplified with respect to the level change pattern that can be generated by the multilevel data signal generated by the multilevel device 12. Then, whether the pattern effect of the laser diode 30) can be relaxed is measured before the start of use of the present embodiment. The gain table 21 stores table data indicating the correspondence between the level change pattern determined by the pattern determination device 16 based on the measurement result and the gain to be applied to the level change pattern.

  The delay unit 22 delays the output signal of the multi-value quantization apparatus 12 by a time corresponding to the processing time of the HPF 14 and the variable amplifier 18 and supplies the delayed output signal to the adder 24. The adder 24 adds the output signal of the delay device 22 to the output signal of the variable amplifier 18. FIG. 2E shows an example of the output signal waveform of the adder 24. The adder 24 obtains a signal in which the level transition portion of the multilevel data signal is emphasized in a high frequency range. The adder 24 outputs a current signal having a waveform shown in FIG.

  The bias current source 28 outputs a bias current having a current value sufficiently exceeding the laser oscillation threshold of the laser diode 30 to the adder 26. The adder 26 adds the bias current from the bias current source 28 to the current signal output from the adder 24, and drives the laser diode 30 with the current resulting from the addition.

  As can be understood from the above description, the HPF 14, the pattern determination device 16, the variable amplifier 18, the gain control device 20, and the gain table 21 constitute a high-frequency extraction device that extracts high-frequency components for pre-emphasis. However, the pre-emphasis of this embodiment not only compensates for the high frequency reduction that may occur in the transmission path, but also compensates for the pattern effect of the semiconductor optical device to be driven. This is useful not only for value signals but also for driving with binary signals.

In the present embodiment, the gain of the variable amplifier 18 with respect to the current symbol value is controlled according to the immediately preceding symbol value. However, as described above, a pattern that cannot be ignored over a plurality of symbol periods in the semiconductor optical device to be driven. If there is an effect, it is preferable to control the gain of the variable amplifier 18 according to the result of determining such a long-term pattern change. The table of the gain table 21 is expanded according to the length of the symbol period considered retroactively. For example, in the case of an n-value multilevel signal, when considering retroactively up to m symbols, the number of elements in the gain table 21 is ^{nm + 1} .

  A method for determining the gain value of the gain table 21 will be described. FIG. 4 shows a schematic block diagram of a configuration in which a cutoff frequency of the HPF 14 and a means for determining a gain control parameter of the variable amplifier 18 by the gain control device 20 are added.

  In order to adjust the cutoff frequency and determine the gain control parameter of the variable amplifier 18, a light receiver 40, a waveform comparison device 42, a parameter determination device 44, and a cutoff frequency control device 46 are added. In addition to the function of the gain control device 20, the gain control device 20A can control the gain of the variable amplifier 18 to a gain according to an external control signal, and can rewrite the gain table 21.

  The light receiver 40 converts the output optical signal of the laser diode 30 into an electrical signal. Although the details will be described later, the waveform comparison device 42 is configured to calculate each symbol value of the multi-value data signal from the output signal of the light receiver 40 in synchronization with the determination result of the pattern determination device 16 for the low-speed multi-value data signal. The level is determined, and the waveform level of the symbol period is detected and stored. The waveform comparator 42 also detects the difference from the reference level of the optical signal level at each symbol position with respect to the multi-value data signal at the normal speed. When the difference is equal to or greater than the predetermined value, the waveform comparison device 42 supplies the pattern determination result from the pattern determination device 16 and the difference value to the parameter determination device 44.

  The parameter determination device 44 determines the cutoff frequency of the HPF 14 according to the comparison result of the waveform comparison device 42, and controls the cutoff frequency of the HPF 14 via the cutoff frequency control device 46. The parameter determination device 44 also controls the gain of the variable amplifier 18 via the gain control device 20 in accordance with the comparison result of the waveform comparison device 42, and determines the correspondence between the output of the pattern determination device and the gain to be controlled. 20 is stored.

  In the configuration shown in FIG. 4, an operation for optimizing the cutoff frequency and gain control of the HPF 14 offline will be described.

  First, the gain of the variable amplifier 18 with respect to the level change or pattern change of the multilevel data signal is initialized to a constant value. Specifically, the parameter determination device 44 first instructs the gain control device 20A to initialize all gain values stored in the gain table 21 to zero, and the gain control device 20A follows the instruction to obtain the gain table. The gain value of 21 is initialized. Since the gain value becomes zero, the amplitude of the high frequency component output from the variable amplifier 18 becomes zero, and the pre-emphasis is invalidated.

  In this state, a long pattern binary data signal for stabilizing the initial light output and defining the ideal output is input to the input terminal 10. The modulation speed of the long pattern portion is sufficiently slower than the response speed of the laser diode 30. Following this long pattern, a binary data signal of a random pattern with a predetermined modulation rate including all level transitions in the multi-value data signal is input to the input terminal 10. Of course, such a multi-value data signal of a long pattern and a random pattern may be generated and output by the multi-value quantization apparatus 12.

  FIG. 5A shows a waveform example of a multi-value data signal of a long pattern and a random pattern (part) following the long pattern. A part of the random pattern is omitted. FIG. 5B shows an optical output waveform of the laser diode 30 with respect to the multilevel data signal shown in FIG.

The multilevel data signal output from the multilevel device 12 is applied to the adder 26 via the delay unit 22 and the adder 24, and the adder 26 converts the multilevel data signal current from the adder 24 into the bias current source 28. Are added to drive the laser diode 30. At this time, the laser diode 30 outputs an optical signal having a waveform reflecting the multi-value data signal output from the multi-value quantization device 12. In the long pattern, the modulation speed is sufficiently slower than the response speed of the laser diode 30, so that the optical output waveform of the laser diode 30 is almost similar to the waveform of the long pattern. The waveform comparator 42 stores the light output levels I _A , I _B , I _C , and I _D for each symbol from the output level of the light receiver 40 in the long pattern. The light output level for which symbol value can be determined from the output of the pattern determination device 16.

For the random pattern, as shown in FIG. 5B, the deterioration of the optical output waveform becomes remarkable, and the original levels I _A , I _B , I _C , and _ID may not be reached. Since the waveform comparison device 42 can determine which symbol position the output light level of the current light receiver 40 is based on the determination output of the pattern determination device 16, the output level of the light receiver 40 is set to the original levels I _A and I. Compare with _B , I _C and I _D. In the example shown in FIG. 5B, a level difference “a” occurs with respect to the symbol position N, and the waveform comparison device 42 determines the parameter based on this level difference “a” and the determination result of the pattern determination device 16 at this time. Supply to device 44.

  When the level difference a detected by the waveform comparison device 42 is equal to or greater than a predetermined threshold value, pre-emphasis is necessary. Therefore, the parameter determination device 44 determines the gain of the variable amplifier 18 according to the level difference a from the waveform comparison device 42, and supplies the determined gain and the determination result of the pattern determination device 16 to the gain control device 20. The gain control device 20 stores the level difference a from the parameter determination device 44 and the determination result of the pattern determination device 16 in a pair in the gain table 21.

The parameter determination device 44 determines the cutoff frequency of the HPF 14 after executing such gain control on a pattern change that can be assumed. Specifically, in the state where the gain is set in the gain table 21, the gain control device 20A reads the gain according to the determination result of the pattern determination device 16 from the gain table 21 and sets it in the variable amplifier 18, so that the waveform comparison The device 42 detects the level of the optical output subjected to the pre-emphasis processing, and calculates a difference value from the reference levels I _A , I _B , I _C , and I _D. The parameter determination device 44 adjusts the cutoff frequency of the HPF 14 via the cutoff frequency control device 46 when the difference value from the waveform comparison device 42 is greater than or equal to a predetermined value.

  In the above description, since the gain and the cut-off frequency are determined by a random pattern with the original modulation degree, the gain cannot be narrowed down to an appropriate range. In response to this, for example, a multi-value data signal having a desired level change pattern is repeatedly output from the multi-value quantization device 12, and the measurement of the difference value a and the adjustment of the gain are repeated, so that the difference value a falls within a preferable range. At this stage, the gain may be finally determined. In addition, if the difference value a does not become less than the threshold value even by adjusting the gain, the cut-off frequency may be adjusted, and the gain adjustment may be restarted if necessary. In the case of sequentially adjusting the gain, for example, the parameter determination device 44 instructs the gain control device 20A to increase (or decrease) a predetermined amount of gain, and the gain control device 20A instructs the gain read from the gain table 21. The variable amplifier 18 may be controlled to a gain increased (or decreased) by the predetermined amount, and the gain table 21 may be overwritten with the changed gain value.

  By dividing the output light of the laser diode 30 into two by a beam splitter and outputting one split light to the light receiver 40 and the other to the optical transmission line, the gain and / or cut-off frequency of the in-line service can be reduced. Sequential adjustment is possible.

  Of course, the gain and / or cut-off frequency may be sequentially adjusted by receiving information such as BER (Bit Error Rate) from the optical signal receiving side.

  Although the embodiment of the driving device for driving the laser diode has been described, the present invention is applied to other semiconductor optical devices such as a light emitting diode (LED), a semiconductor optical amplifier, a reflective semiconductor optical amplifier, an EA modulator, and an LN modulator. The present invention can also be applied to a driving device that drives, and the same effects can be achieved.

  Needless to say, the adder 26 and the bias current source 28 are not required for a semiconductor optical device that does not require a bias current.

  In addition, although the embodiment using the variable amplifier for level adjustment of the extracted high frequency component or pulse edge component has been described, in general, an attenuator capable of changing the attenuation may be used. Obviously, amplification and attenuation may be combined.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

10: Input terminal 12: Multi-level device 14: High-pass filter (HPF)
16: Pattern determination device 18: Variable amplifier 20, 20A: Gain control device 21: Gain table 22: Delay device 24: Adder 26: Adder 28: Bias current source 30: Semiconductor optical device 40: Light receiver 42: Waveform comparison Device 44: Parameter determination device 46: Cut-off frequency control device

Claims (6)

A semiconductor optical device driving apparatus for driving a semiconductor optical device according to a data signal,
High-frequency extraction means for extracting high-frequency components of the data signal;
Level adjustment means for adjusting the level of the output of the high-frequency extraction means according to the level adjustment value;
Pattern determining means for determining a temporal change pattern of the data signal;
Control means for controlling the level adjustment value of the level adjustment means according to the judgment result of the pattern judgment means;
A semiconductor optical device driving apparatus comprising an adding means for adding the data signal and the output of the level adjusting means.   2. The semiconductor optical device driving apparatus according to claim 1, wherein the high-frequency extracting means extracts an edge component of the data signal.   3. The semiconductor optical device driving apparatus according to claim 1, wherein the data signal is a multi-value data signal.   4. The semiconductor optical device driving apparatus according to claim 1, wherein the control unit includes a correspondence table of the change pattern determined by the pattern determination unit and the level adjustment value. .   5. The semiconductor optical device driving apparatus according to claim 1, wherein the level adjusting means is a variable amplifying means capable of controlling a gain.   6. The adding means according to claim 1, further comprising a delay means for delaying the data signal for a time corresponding to a processing time in the high frequency extracting means and the level adjusting means. The semiconductor optical device drive apparatus described in 1.

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