CN110596918B - Method and device for controlling bias working point of modulator - Google Patents
Method and device for controlling bias working point of modulator Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 57
- 230000003287 optical effect Effects 0.000 claims description 40
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 23
- 229910052710 silicon Inorganic materials 0.000 claims description 23
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 2
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
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Abstract
The embodiment of the application discloses a control method of a bias working point of a modulator, which comprises the following steps: determining a disturbance signal to be applied to a phase modulation electrode of the modulator based on an intrinsic characteristic of the modulator; wherein the disturbance signal is a voltage signal with a specific time-varying periodicity; detecting a signal component having the same frequency as the disturbance signal from an output signal of an output terminal of the modulator; the initial bias voltage is adjusted based on the amplitude of the signal component to determine a bias operating point of the modulator. The embodiment of the application also provides a control device for the bias working point of the modulator.
Description
Technical Field
The application belongs to the technical field of optical fiber communication, and in particular relates to a method and a device for controlling a bias working point of a modulator.
Background
The requirements of modern communication on transmission capacity, speed and performance are greatly improved, and coherent optical communication has a high spectrum utilization rate, so that the coherent optical communication becomes an important research direction of modern optical communication research. The modulator is a key device for realizing a high-order modulation code pattern, is easily influenced by environmental factors such as temperature, pressure and the like in actual use, so that a static working point of the modulator shifts, the quality and the stability of an optical modulation signal are influenced, and the error code performance of a transmission system is deteriorated.
Most of the existing researches are directed to bias voltage control of a lithium niobate (LiNbO 3) modulator, and a common method is to introduce a sinusoidal disturbance signal on a phase modulation electrode to detect a first harmonic signal of the sinusoidal disturbance signal so as to achieve the purposes of detecting working point drift and controlling. And LiNbO 3 The modulator is based on linear electro-optic effect, i.e. the optical phase varies linearly with the amplitude of the applied electric field, whereas the modulation characteristics of silicon-based modulators are equivalent to LiNbO 3 Complete differentiation of modulators, the bias operating point of silicon-based modulatorsThe phase change is a silicon-based thermo-optic effect, a nonlinear electro-optic effect, i.e., the modulator phase change is proportional to the square of the bias voltage. In a silicon-based optical modulator, when a normal sinusoidal disturbance signal is used, the lock of the off-point (Null point) and the quadrature point (Quad point) cannot be performed according to the first harmonic of the signal. Therefore, the bias voltage locking method based on the conventional LiNbO3 modulator cannot be directly applied to the silicon-based optical modulator.
Disclosure of Invention
In view of this, embodiments of the present application provide a method and apparatus for controlling a bias operating point of a modulator to solve at least one problem existing in the related art.
The technical scheme of the embodiment of the application is realized as follows:
in a first aspect, an embodiment of the present application provides a method for controlling a bias operating point of a modulator, where the method includes:
determining a disturbance signal to be applied to a phase modulation electrode of the modulator based on an intrinsic characteristic of the modulator; wherein the disturbance signal is a time-varying periodic voltage signal;
detecting a signal component having the same frequency as the disturbance signal from an output signal of an output terminal of the modulator;
and adjusting the bias voltage of the phase modulation electrode according to the amplitude of the signal component to determine the bias working point of the modulator.
In a second aspect, an embodiment of the present application provides a control apparatus for a bias operating point of a modulator, where the apparatus includes: the device comprises a first determining module, a detecting module and a second determining module, wherein:
the first determining module is used for determining the amplitude of a disturbance signal to be applied to the phase modulation electrode according to the initial bias voltage of the phase modulation electrode of the modulator;
the detection module is used for detecting a signal component with the same frequency as the disturbance signal from an output signal of the output end of the modulator;
the second determining module is used for adjusting the bias voltage of the phase modulation electrode according to the amplitude of the signal component so as to determine the bias working point of the modulator.
The embodiment of the application provides a method and a device for controlling bias working points of a modulator. Firstly, determining a disturbance signal to be applied to the phase modulation electrode according to the inherent characteristic of the modulator; then, detecting a signal component having the same frequency as the disturbance signal from an output signal of an output terminal of the modulator; finally, according to the amplitude of the signal component, regulating the bias voltage of the phase modulation electrode to determine the bias working point of the modulator; in this way, by applying the disturbance signal related to the bias voltage to the phase modulation electrode of the silicon-based optical modulator, the amplitude of the signal component with the same frequency as the applied disturbance signal is detected in the output signal of the modulator, so that the bias working point of the silicon-based optical modulator can be simply and rapidly locked and maintained, the control difficulty is reduced, and the control precision is improved.
Drawings
Fig. 1 is a schematic flow chart of implementation of a method for controlling a bias operating point of a modulator according to an embodiment of the present application;
FIG. 2 is a schematic flow chart of another implementation of a method for controlling a bias operating point of a modulator according to an embodiment of the present disclosure;
FIG. 3 is a schematic flow chart of another implementation of a method for controlling a bias operating point of a modulator according to an embodiment of the present disclosure;
FIG. 4 is a signal transmission characteristic of an MZ modulator according to the embodiment of the present application;
FIG. 5 is a FFT simulation result of Null point in the embodiment of the present application;
FIG. 6 is a FFT simulation result of the Quad point in the embodiment of the present application;
FIG. 7 is a functional block diagram of a method of controlling a bias operating point of a modulator according to an embodiment of the present application;
FIG. 8 is a schematic diagram of a method for controlling a bias operating point of a modulator according to an embodiment of the present application
FIG. 9 is a schematic flow chart of another implementation of a method for controlling a bias operating point of a modulator according to an embodiment of the present disclosure;
fig. 10 is a schematic diagram of a composition structure of a control device for a bias operating point of a modulator according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.
Example 1
An embodiment of the present application provides a method for controlling a bias operating point of a modulator, and fig. 1 is a schematic implementation flow diagram of the method for controlling a bias operating point of a modulator according to the embodiment of the present application, as shown in fig. 1, where the method includes the following steps:
step S101 of determining a disturbance signal to be applied to a phase modulation electrode of the modulator based on an intrinsic characteristic of the modulator.
Here, the modulator may be various modulators, and in one embodiment, may be a Mach-Zehnder (MZ) modulator, or may be an in-phase quadrature (IQ, in phase and Quadrature phase) modulator composed of a plurality of MZ modulators. The modulator is made of silicon light, hereinafter referred to as a silicon-based light modulator.
The inherent characteristics of the modulator here refer to the fact that the phase modulation principle of a silicon-based optical modulator is realized by thermal modulation, and the phase change of the silicon-based optical modulator is proportional to the square of the bias voltage.
Here, the disturbance signal is a time-varying periodic voltage signal, the disturbance signal applied to the phase modulation electrode is generally a small-amplitude low-frequency perturbation signal, the frequency selection of the disturbance signal should be smaller than the 3dB cut-off frequency of the thermo-optic phase shifter of the modulator, the disturbance amplitude is about 10% of the half-wave voltage of the thermo-optic phase shifter, in this embodiment of the present application, the disturbance signal is determined according to the inherent characteristics of the modulator in step S101, and in a specific implementation, the disturbance signal may be directly customized and generated by the DAC of the single chip microcomputer. In order not to affect the correct demodulation of the modulation information, the amplitude of the disturbance signal applied to the phase modulation electrode of the modulator is much smaller than the modulation signal.
Step S102, detecting a signal component with the same frequency as the disturbance signal from the output signal of the output end of the modulator.
Here, the output end of the modulator outputs a modulated optical signal, which needs to be converted into an electrical signal through photoelectric conversion, and this step can be implemented by a Monitor Photodiode (MPD) built in the modulator.
Here, since the disturbance signal is added, the output optical power may have a jitter in the form of a sinusoidal signal, and the frequency of such sinusoidal signal is the same as the frequency of the added disturbance signal, the same signal component as the frequency of the disturbance signal may be detected by a filter or a data processing unit.
Step S103, according to the amplitude of the signal component, the bias voltage of the phase modulation electrode is adjusted to determine the bias working point of the modulator.
Here, a signal component having the same frequency as the disturbance signal is detected, and the amplitude of the signal component is further extracted.
Here, the bias operating point of the modulator refers to a special operating point on a transmission curve of the MZ modulator, such as a Null point and a Quad point, and in actual use, the modulator needs to be biased at a suitable operating point.
It should be noted that, although the amplitude of the disturbance signal is small, the disturbance signal still has an influence on light. At different bias operating points, the optical power amplitude effects of the perturbation signal are different. The offset voltage can be judged whether to drift or not by detecting the amplitude of the disturbance signal output by the modulator, and the offset voltage of the phase modulation electrode can be accurately controlled to be stabilized at an optimal working point.
According to the control method for the bias working point of the modulator, firstly, a disturbance signal to be applied to the phase modulation electrode is determined according to the inherent characteristic of the modulator; then, detecting a signal component having the same frequency as the disturbance signal from an output signal of an output terminal of the modulator; finally, according to the amplitude of the signal component, regulating the bias voltage of the phase modulation electrode to determine the bias working point of the modulator; therefore, the amplitude of the signal component with the same frequency as the added disturbance signal in the output light of the modulator is detected in real time by applying the disturbance signal related to the bias voltage to the phase modulation electrode of the modulator, and the bias working point is locked accordingly, so that the bias working point of the silicon optical modulator can be simply and rapidly locked and maintained, the control difficulty is reduced, and the control precision is improved.
Example two
An embodiment of the present application provides a method for controlling a bias operating point of a modulator, and fig. 2 is a schematic flow chart of another implementation of the method for controlling a bias operating point of a modulator in the embodiment of the present application, as shown in fig. 2, where the method includes the following steps:
step S201, determining a disturbance signal to be applied to a phase modulation electrode of the modulator according to an intrinsic characteristic of the modulator.
Step S202, detecting a signal component with the same frequency as the disturbance signal from the output signal of the output terminal of the modulator.
And step S203, carrying out feedback adjustment on the bias voltage of the phase modulation electrode according to the amplitude of the signal component so that the amplitude of the signal component is smaller than a first threshold value.
Here, the first threshold is set to be a minimum value on a transmission curve of the MZ modulator, and the initial bias voltage of the phase modulation electrode is feedback-adjusted by detecting the magnitude of the signal component having the same frequency as the disturbance signal in the output optical signal in real time until the magnitude of the signal component is minimum.
And S204, determining the offset voltage corresponding to the extracted disturbance signal with the amplitude smaller than a first threshold value as an offset working point of the phase modulation electrode.
Here, the offset voltage when the amplitude of the disturbance signal obtained in step S203 is the minimum value is determined as the offset operating point of the phase modulation electrode.
According to the control method for the offset working point of the modulator, the disturbance signal related to the offset voltage is applied to the phase modulation electrode of the silicon-based light modulator, the signal component with the same frequency as the disturbance signal in the output signal of the modulator is detected in real time, the initial offset voltage is fed back and regulated according to the signal component, and the offset voltage corresponding to the minimum amplitude of the signal component is used as the offset working point, so that the offset working point of the silicon-based light modulator can be simply and rapidly locked and maintained, the control difficulty is reduced, and the control precision is improved.
Example III
In coherent optical communication, a multi-level amplitude-phase modulation plus polarization multiplexing technology is a research hot spot. In the technology of multi-level amplitude phase modulation and polarization multiplexing, an IQ modulator formed based on a dual parallel mach-Zehnder (DPMZ, dual Parallel Mach-Zehnder) modulator structure is widely focused as a core optical device of a coherent optical communication system.
In practical operation, it is generally required to bias the IQ modulator at a suitable operating point, that is, two sub-intensity modulators of the upper and lower arms need to be biased at the lowest point of the transmission curve to implement carrier suppression, and the sub-phase modulators need to be controlled at the quadrature point to generate an accurate 90 ° phase shift, so as to ensure orthogonality of the two IQ branches. In practical use, the I-path and Q-path offset operating points of the IQ modulator are affected by thermal crosstalk, so that the I-path and Q-path cannot be locked in a single control manner.
For the convenience of understanding the above technical solution, the embodiments of the present application will be described by taking IQ modulator as an example.
As shown in fig. 3, the embodiment of the present application provides a method for controlling a bias operating point of a modulator, and as can be seen from the figure, the implementation process specifically includes the following steps:
step S301, according to the bias voltage V of the electrode I I A first perturbation signal to be applied on the electrode I is determined.
Here, the first disturbance signal is a time-varying periodic voltage signal, according to the formula
Determining the amplitude Φ of a first perturbation signal to be applied to the electrode I 1, wherein ,VI For the bias voltage of the phase modulation electrode I, the value of A is 1 to 10 percent of V π Taking the square root of the magnitude, V π For half-wave voltage of the modulator, f 1 The frequency of the first disturbance signal and t is time.
Step S302, according to the bias voltage V of the electrode Q Q A second perturbation signal to be applied to the electrode Q is determined.
Here, the second disturbance signal is a voltage signal different from the first disturbance signal in step S201, according to the formula
Determining the amplitude Φ of the second perturbation signal to be applied to the electrode Q 2, wherein ,VQ For the initial bias voltage of the phase modulation electrode Q, the value of A is 1 to 10 percent of V π Taking the square root of the magnitude, V π For half-wave voltage of the modulator, f 2 Is the frequency of the second disturbance signal, t is time, wherein the frequency f 2 And the frequency f in step S301 1 Are not identical.
Here, the first disturbance signal is applied to the phase modulation electrode I of the IQ modulator, and the second disturbance signal is applied to the phase modulation electrode Q of the IQ modulator, so that the phase modulation electrode I and the phase modulation electrode Q can be simultaneously adjusted.
Step S303, detecting the frequency f from the output signals of the output end of the IQ modulator 1 Is of frequency f 2 Is of frequency f 1 +f 2 Is included in the signal component of the signal(s).
The output end of the IQ modulator outputs an optical signal, which is subjected to photoelectric conversion and FFT (Fast Fourier Transformation) spectral analysis to extract a frequency f 1 Is of frequency f 2 Is of frequency f 1 +f 2 Is included in the signal component of the signal(s).
Step S304, adjusting the bias voltage V I The frequency is f 1 V when the amplitude of the signal component of (2) is smaller than the first threshold I As a biased operating point for the electrode I.
Here, the first threshold is set to the minimum value on the transmission curve of the MZ modulator, and since the minimum value on the transmission curve is fixed, it is easy to distinguish, and this value is generally taken as a detection criterion in detection.
Here, the frequency is f 1 The signal component of (2) has a minimum amplitude, i.e. a frequency f 1 Bias voltage V corresponding to the minimum first harmonic component of (2) I As a bias operating point for electrode I, i.e., null point.
Step S305, adjusting the bias voltage V Q The frequency is f 2 V when the amplitude of the signal component of (2) is smaller than the first threshold Q As a biased operating point for the electrode Q.
Here, the frequency is f 2 Corresponding bias voltage V when the amplitude of the signal component is at a minimum Q As the bias operating point of the electrode Q, i.e., null point.
Step S306, adjusting the initial bias voltage V corresponding to the Phase modulation electrode Phase P The frequency is f 1 +f 2 V when the amplitude of the signal component of (2) is smaller than the first threshold P As a biased operating point for the electrode Phase.
Here, the frequency is f 1 +f 2 The minimum amplitude, i.e. frequency, of the signal component of (2) is f 1 +f 2 Bias voltage V corresponding to second harmonic component of (2) P As a bias operating point for electrode Phase, i.e., the Quad point.
It should be noted that, the amplitudes of the first harmonic component and the second harmonic component of the disturbance signal are different according to different operating points on the transmission curve: the amplitude of the first harmonic component is the largest at the Quad point, the amplitude of the second harmonic component is the smallest, the amplitude of the second harmonic component is the largest at the Null point, and the amplitude of the first harmonic component is the smallest.
The bias voltage V is adjusted in the steps S304 to S306 I 、V Q and VP To determine the offset operating point of each phase modulation electrode of the IQ modulator, i.e. by fine tuning the initial offset voltage of each phase modulation electrodeThe bias voltages of the I path, the Q path and the Phase path of the IQ modulator are adjusted to the optimal bias working point.
The embodiment of the application provides a control method for the bias working point of a modulator, and simultaneously utilizes the first harmonic component and the second harmonic component of a disturbance signal to control the bias voltage, so that the bias working point of the silicon-based optical IQ modulator, namely a Null point and a Quad point, is locked, the control difficulty is reduced, and the control precision is improved. Meanwhile, the locking of the I path and the Q path is realized in a single control mode, and the influence of thermal crosstalk between bias working points of the I path and the Q path is reduced.
Example IV
Currently, in coherent optical communication systems, materials for fabricating optical modulators can be mainly divided into three main categories: lithium niobate (LiNbO 3), indium phosphide (InP), and silicon light. Among them, liNbO3 and InP are more mature schemes, and silicon optical schemes are under research and exploration. LiNbO3 is used for ultra-long distance transmission networks because of its advantages such as linear electro-optic modulation effect and excellent optical performance, but is limited by the characteristics of LiNbO3 material itself, and cannot be applied to the fabrication of integrated coherent devices. InP modulators have complex processes and high costs that limit their range of applications. With the rapid development of silicon-based photoelectronic technology, by means of the existing Complementary Metal Oxide Semiconductor (CMOS) technology, silicon-based light modulators have the advantages of smaller size, higher integration density of optical units, higher modulation efficiency, lower cost and the like, so that silicon-based IQ light modulators are receiving more and more attention in coherent light modules.
Since the IQ-modulator is a combination of a plurality of MZ (Mach-Zehnder) modulators. The MZ modulator is composed of two waveguide arms and two Y-shaped branches, and the electric fields on the two waveguide arms are adjusted to enable the transmission speeds of light beams on the two waveguide arms to be different so as to generate optical path difference, so that the two light beams are interfered, and the modulation of optical signals is realized. Fig. 4 is a signal transmission characteristic curve of the MZ modulator according to the embodiment of the present application, as shown in fig. 4, a curve 41 is a transmission characteristic curve of the output optical power of the MZ modulator with bias voltage, and there are 4 special positions on the curve 41: minimum point 411 (Null point), negative positive intersection 412 (Quad-point), positive intersection 413 (Quad + point) and Peak point 414 (Peak point). To operate properly, the IQ modulator needs to maintain the MZ at a specific operating point, such as the Quad point and the Null point, i.e., a specific bias voltage needs to be applied to the MZ modulator.
Due to the self structure of the MZ modulator, such as environmental stability, mechanical vibration and the like, and environmental temperature and the like, the transmission characteristic curve can change along with time, so that the working point of the modulator is drifted, unstable operation of the modulator is caused, and great influence is brought to practical application. Therefore, it is necessary to adjust the bias voltage applied to the MZ modulator according to the deviation of the MZ modulator operation curve and track and lock the bias voltage so as to stably operate at a specific operation point.
To simplify the analysis, a single MZ modulator is first considered. To stabilize the bias point of the IQ modulator at the optimal operating point, the characteristics of the input and output signals of the MZ modulator at the optimal bias point must be analyzed.
When a signal is input, the transfer function of the MZ modulator can be written as equation (1):
in the formula (1), t is time, V π For half-wave voltage of modulator, P i For the input intensity of the modulator, P o V for the output intensity of the modulator b and V0 (t) is a DC voltage and a sinusoidal voltage, respectively, applied to the phase modulation electrode of the modulator.
Let the input signal have the form shown in the following formula (2):
in the formula (2), V bias The dc bias voltage, a is a constant, and ω is an angular velocity.
Normalize equation (1) to p=2p 0 /P i Then substituting formula (2) into formula (1) to obtain the following formula (3):
for equation (3), let
Further expansion yields the following equation (4):
P＝1+cosV(t)cosφ T -sinV(t)sinφ T (4)；
expanding the formula (4) by a Taylor series, and reserving three terms to obtain the following formula (5):
will be
Substituting formula (5) for further finishing, let ∈ ->
The following formula (6) is obtained:
reducing the higher term in the formula (6) to be simplified to obtain the following formulas (7) and (8):
for equation (8), the first harmonic component is taken as P (1) The second harmonic component is P (2) The following formulas (9) and (10) are obtained:
thus, by analyzing the 4 best positions along the transmission characteristic curve of the variation of the signal in conjunction with fig. 4, it can be concluded that by the above formulas (9) and (10): the first harmonic component of the Quad point is the largest and the second harmonic component is the smallest. Similarly, the second harmonic component at the Null point is the largest and the first harmonic component is the smallest.
The simulation results of the above theory are shown in fig. 5 and 6. FIG. 5 is a diagram showing FFT simulation results of Null point in the embodiment of the present application, wherein curve 51 is frequency 200H Z The signal transmission curve 52 of (a) is a signal after FFT simulation at Null point, and as can be seen from the curve 52 in FIG. 5, the frequency is 200H Z The first harmonic component (abscissa is 200H) of the signal after FFT processing Z Where) is a minimum value of 0, the second harmonic component (abscissa 400H Z Where) is the peak value. FIG. 6 is a diagram showing FFT simulation results of a Quad point according to an embodiment of the present application, wherein curve 61 is a frequency of 200H Z The curve 62 is a signal obtained by FFT simulation of the Quad point, and as can be seen from the curve 62 in FIG. 6, the frequency is 200H Z The first harmonic component (abscissa is 200H) of the signal after FFT processing Z Where) is peak amplitude, the second harmonic component (abscissa 400H Z Where) is a minimum value of 0.
Fig. 7 is a schematic block diagram of a control method of a bias operating point of a modulator according to an embodiment of the present invention, as shown in fig. 7, the control method of a bias voltage of the modulator according to an embodiment of the present invention adopts a feedback closed-loop control system commonly used in a control system, and the IQ modulator 71 includes an I-path MZ modulator MZMI 711 and a Q-path MZMQ712, which respectively modulate two orthogonal phases of an optical carrier signal output by the laser 72, and a Phase delay Phase 713 ensures orthogonality on the two optical carrier phases.Coupler 731 in photo-conversion module 73 separates a small part of signal from IQ optical modulator 71, and then enters MPD732 to be converted into an electric signal, and then enters ADC733 to be sampled and processed, and then enters data processing unit 74, and respective bias voltages V of MZMI 711, MZMQ712, and Phase 713 are respectively adjusted by DAC741, DAC742, and DAC743 I 、V Q 、V P 。
FIG. 8 is a schematic diagram showing a method for controlling bias operation point of the modulator according to the embodiment of the present application, as shown in FIG. 8, the I-path MZ modulator MZMI 811 of the IQ modulator 81 is loaded in the form of
Is loaded in the form of +.>
Is detected in the output light of the modulator at a frequency f 1 Is of frequency f 2 Is of frequency f 1 +f 2 To lock the bias operating points of the I, Q, and Phase paths, respectively.
Fig. 9 is a flowchart of another implementation of a method for controlling a bias operating point of a modulator according to an embodiment of the present application, as shown in fig. 9, where the method includes the following steps:
step S901, searching bias points in a global range to obtain initial bias voltages V of the phase modulation electrodes I respectively I Initial bias voltage V of phase modulation electrode Q Q Initial bias voltage V of Phase modulation electrode Phase P 。
Here, by searching the bias point in the global range, the most basic method can scan the bias voltage according to a certain step and a curve for one time according to the working curve, and obtain the Null point of the phase modulation electrode I as the initial bias voltage V thereof I The Null point of the phase modulation electrode Q is used as its initial bias voltage V Q The Quad point of Phase modulation electrode Phase is taken as the initial bias voltage V P That is, the bias voltages of the I-path, Q-path, and Phase path are adjusted to the vicinity of the optimum operating point by coarse adjustment.
Step S902, applying a phase modulation electrode I in the form of
Is a disturbance signal of (a).
Here, the frequency f of the disturbance signal 1 The 3dB cut-off frequency of the thermo-optic phase shifter of the modulator should be chosen to be less than about 10% of the half-wave voltage of the thermo-optic phase shifter.
Step S503, applying a phase modulation electrode Q in the form of
Is a disturbance signal of (a).
Here, the frequency f of the disturbance signal 2 Following the selection principle in step S902, but the frequency f 2 And the frequency f in step S902 1 Different.
The disturbance signals in the special forms in the steps S902 and S903 can be directly customized and generated by the DAC of the singlechip.
In step S904, the optical signal is converted into an electrical signal by the monitor photodiode MPD at the output end of the modulator, and sent to the data processing unit.
In step S905, the data processing unit detects the frequency as f in real time 1 Is of frequency f 2 Is of frequency f 1 +f 2 Is included in the signal component of the signal(s).
Here, the detection of the respective signal components may be implemented using a filter or a data processing unit.
Step S906, fine tuning V I So that the frequency is f 1 The signal component of the phase modulation electrode I is minimum, and the optimal offset working point of the phase modulation electrode I is achieved.
Here, the initial bias voltage V of the phase modulation electrode I is finely adjusted I Make the output frequency f 1 The minimum of the first harmonic component corresponds to the Null point of the I-path.
Step S907, fine tuning V Q So that the frequency is f 2 The signal component of the phase modulation electrode Q is the smallest, and the best bias working point of the phase modulation electrode Q is achieved.
Here, the initial bias voltage V of the tuning phasing electrode Q is adjusted Q Make the output frequency f 2 The minimum value of the first harmonic component corresponds to the Null point of the Q-path.
Step S908, fine tuning V P So that the frequency is f 1 +f 2 The signal component of (2) is minimum and reaches the optimal bias working point of the Phase modulation electrode Phase.
Here, the initial voltage V of the Phase modulation electrode Phase is finely adjusted P So that the frequency is f 1 +f 2 The sum frequency signal component is smallest, the sum frequency component f 1 +f 2 The second harmonic minimum of (2) corresponds to the Quad point of the Phase path.
For the above steps S906 to S907, in order to eliminate the influence of the thermal crosstalk between the I-path and the Q-path, an iterative locking manner may be adopted to ensure that both the I-path and the Q-path are at the optimal bias working point, that is, after the Q-path is locked, it is necessary to determine whether the I-path bias voltage is offset, and if there is offset, it is necessary to correct again. And the iteration loop is performed until the bias voltages of the I path and the Q path are the optimal bias working points, and finally the bias voltage locking of the modulator is realized.
In the embodiment of the application, the initial bias voltages of the I path and the Q path of the IQ regulator are respectively applied
and />
The amplitude of the first harmonic component and the second harmonic component of the low-frequency disturbance signal is detected, and the initial bias voltage is adjusted according to the amplitude of the first harmonic component and the second harmonic component, so that the modulator can work at an optimal bias point. The purposes of detecting the drift of the bias working point and locking the bias working point are achieved by introducing a disturbance signal in a special form and simultaneously utilizing the first harmonic component and the second harmonic component of the disturbance signal.
Example five
The embodiment of the application provides a control device for a bias working point of a modulator, which comprises all modules and all units included by all modules, and can be realized by specific circuits.
Fig. 10 is a schematic structural diagram of a control device for a bias operating point of a modulator according to an embodiment of the present application, as shown in fig. 10, where the device 10 includes: a first determination module 101, a detection module 102, and a second determination module 103, wherein:
the first determining module 101 is configured to determine a disturbance signal to be applied to the phase modulation electrode according to an intrinsic characteristic of the modulator;
the detection module 102 detects a signal component with the same frequency as the disturbance signal from the output signal of the output end of the modulator;
the second determining module 103 is configured to adjust the bias voltage of the phase modulation electrode according to the amplitude of the signal component, so as to determine a bias operating point of the modulator.
In the above device, the first determining module 101 is configured to determine the amplitude Φ of the disturbance signal to be applied to the phase modulation electrode according to the following formula:
wherein ,Vbais For the bias voltage of the phase modulation electrode, A is a constant, V π And f is the frequency of the disturbance signal, and t is time.
Here, the disturbance signal may be directly customized by the DAC of the single chip microcomputer.
In the above apparatus, the second determining module 104 includes:
the first adjusting unit is used for carrying out feedback adjustment on the bias voltage of the phase modulation electrode according to the amplitude of the signal component so that the amplitude of the signal component is smaller than a first threshold value;
and the first determining unit is used for determining the bias voltage corresponding to the signal component with the amplitude smaller than the first threshold value as the bias working point of the phase modulation electrode.
Here, for the output optical signal of the modulator, spectral analysis may be performed by an FFT algorithm, adjusting the initial bias voltage to observe the amplitude of the FFT-processed signal. And judging whether the bias working point drifts or not by detecting the magnitude of the harmonic component, and controlling the bias of the modulator to be always in a target state by using a feedback closed-loop system.
In the device, the modulator is an IQ modulator, and the phase modulation electrode at least comprises electrodes I and Q;
correspondingly, the first determining module 101 includes:
a second determining unit for determining a bias voltage V according to the electrode I I Determining a first perturbation signal to be applied on the electrode I;
a third determination unit for determining a bias voltage V according to the electrode Q Q Determining a second perturbation signal to be applied on the electrode Q; wherein the frequency of the first disturbance signal is f 1 The frequency of the second disturbance signal is f 2 ，f 1 And f 2 Different;
the detection module 103 includes:
a detection unit for detecting the frequency f from the output signals of the output end of the modulator 1 Is of frequency f 2 Is of frequency f 1 +f 2 Is included in the signal component of the signal(s).
Here, the output optical signal is converted into an electrical signal by the monitor photodiode MPD built in the modulator, and then detection and extraction of each signal component may be implemented using a filter or a data processing unit.
In the above apparatus, the first adjusting unit includes:
a first regulating subunit for regulating the bias voltage V I The frequency is f 1 V when the amplitude of the signal component of (2) is smaller than the first threshold I As a biased operating point for the electrode I;
a second regulating subunit for regulating the bias voltage V Q The frequency is f 2 V when the amplitude of the signal component of (2) is smaller than the first threshold Q As a biased operating point for the electrode Q;
a third regulating subunit for regulating the initial bias voltage V corresponding to the Phase modulation electrode Phase P The frequency is f 1 +f 2 V when the amplitude of the signal component of (2) is smaller than the first threshold P As a biased operating point for the electrode Phase.
Here, the bias voltages corresponding to the electrodes I, Q and Phase can be adjusted by 3 DACs, respectively.
The description of the apparatus embodiments above is similar to that of the method embodiments above, with similar advantageous effects as the method embodiments. For technical details not disclosed in the device embodiments of the present application, please refer to the description of the method embodiments of the present application for understanding.
It should be appreciated that reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be understood that, in various embodiments of the present application, the sequence numbers of the foregoing processes do not mean the order of execution, and the order of execution of the processes should be determined by the functions and internal logic thereof, and should not constitute any limitation on the implementation process of the embodiments of the present application. The foregoing embodiment numbers of the present application are merely for describing, and do not represent advantages or disadvantages of the embodiments.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in other ways. The above-described embodiment of the apparatus is merely illustrative, and for example, the division of the units is merely a logic function division, and there may be other division manners in actual implementation, such as: multiple units or components may be combined or may be integrated into another system, or some features may be omitted, or not performed. In addition, the various components shown or discussed may be coupled or directly coupled or communicatively coupled to each other via some interface, device or unit, whether electrical, mechanical or otherwise.
The units described above as separate components may or may not be physically separate, and components shown as units may or may not be physical units; can be located in one place or distributed to a plurality of network units; some or all of the units may be selected according to actual needs to achieve the purposes of the embodiments of the present application.
In addition, each functional unit in each embodiment of the present application may be integrated in one processing unit, or each unit may be separately used as one unit, or two or more units may be integrated in one unit; the integrated units may be implemented in hardware or in hardware plus software functional units.
Those of ordinary skill in the art will appreciate that: all or part of the steps for implementing the above method embodiments may be implemented by hardware related to program instructions, and the foregoing program may be stored in a computer readable storage medium, where the program, when executed, performs steps including the above method embodiments; and the aforementioned storage medium includes: a mobile storage device, a Read Only Memory (ROM), a magnetic disk or an optical disk, or the like, which can store program codes.
Alternatively, the integrated units described above may be stored in a computer readable storage medium if implemented in the form of software functional modules and sold or used as a stand-alone product. Based on such understanding, the technical solutions of the embodiments of the present application may be essentially or partly contributing to the related art, embodied in the form of a software product stored in a storage medium, including several instructions for causing an apparatus automatic test line to perform all or part of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a removable storage device, a ROM, a magnetic disk, or an optical disk.
The foregoing is merely an embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think about changes or substitutions within the technical scope of the present application, and the changes and substitutions are intended to be covered in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A method of controlling a bias operating point of a modulator, the method comprising:
determining a disturbance signal to be applied to a phase modulation electrode of the modulator based on an intrinsic characteristic of the modulator; wherein the disturbance signal is a time-varying periodic voltage signal; the inherent characteristics refer to the phase modulation principle of the silicon-based optical modulator;
detecting a signal component having the same frequency as the disturbance signal from an output signal of an output terminal of the modulator;
and adjusting the bias voltage of the phase modulation electrode according to the amplitude of the signal component to determine the bias working point of the modulator.
2. The method of claim 1, wherein said determining a perturbation signal to be applied to the phase modulation electrode based on an intrinsic characteristic of the modulator comprises:
determining the amplitude of the disturbance signal to be applied to the phase modulation electrode according to the following formula
：
wherein ,
for the bias voltage of the phase modulation electrode, A is constant,>
for the frequency of the disturbance signal, +.>
Is time.
3. The method of claim 1, wherein adjusting the bias voltage of the phase modulation electrode based on the magnitude of the signal component to determine the bias operating point of the modulator comprises:
according to the amplitude of the signal component, carrying out feedback adjustment on the bias voltage of the phase modulation electrode to enable the amplitude of the signal component to be smaller than a first threshold value;
and determining the bias voltage corresponding to the signal component with the amplitude smaller than the first threshold value as a bias working point of the phase modulation electrode.
4. The method of claim 1, the modulator being an IQ modulator, the phase modulating electrode comprising at least electrodes I and Q;
correspondingly, said determining a disturbance signal to be applied to said phase modulation electrode according to an intrinsic characteristic of said modulator comprises: according to the bias voltage of the electrode I
Determining a first perturbation signal to be applied on the electrode I; according to the bias voltage of the electrode Q>
Determining a second perturbation signal to be applied on the electrode Q; wherein the frequency of the first disturbance signal is +.>
The frequency of the second disturbance signal is +.>
，/>
And->
Different;
the detecting of the signal component of the same frequency as the disturbance signal from the output signal of the output end of the modulator comprises: from the output signals of the output end of the IQ modulator, respectively detecting the frequency as
Is of the frequency of
Is of frequency +.>
Is included in the signal component of the signal(s).
5. The method according to claim 4, wherein the method further comprises:
adjusting the bias voltage
The frequency is +.>
Is smaller than the first threshold value>
As a biased operating point for the electrode I; />
Adjusting the bias voltage
The frequency is +.>
Is smaller than the first threshold value>
As a biased operating point for the electrode Q;
adjusting the bias voltage corresponding to Phase of Phase modulation electrode
The frequency is +.>
Is smaller than the first threshold value>
As a biased operating point for the electrode Phase.
6. A control device for a bias operating point of a modulator, for use in a silicon-based optical modulator, said device comprising: the device comprises a first determining module, a detecting module and a second determining module, wherein:
the first determining module is used for determining a disturbance signal to be applied to the phase modulation electrode according to the inherent characteristic of the modulator; the inherent characteristics refer to the phase modulation principle of the silicon-based optical modulator;
the detection module is used for detecting a signal component with the same frequency as the disturbance signal from an output signal of the output end of the modulator;
the second determining module is used for adjusting the bias voltage of the phase modulation electrode according to the amplitude of the signal component so as to determine the bias working point of the modulator.
7. The apparatus of claim 6, wherein the first determining module is configured to determine the amplitude of the disturbance signal to be applied to the phase modulation electrode according to the following formula
：
wherein ,
for the bias voltage of the phase modulation electrode, A is constant,>
for the frequency of the disturbance signal, +.>
Is time.
8. The apparatus of claim 6, wherein the second determining module comprises:
the first adjusting unit is used for carrying out feedback adjustment on the bias voltage of the phase modulation electrode according to the amplitude of the signal component so that the amplitude of the signal component is smaller than a first threshold value;
and the first determining unit is used for determining the bias voltage corresponding to the signal component with the amplitude smaller than the first threshold value as the bias working point of the phase modulation electrode.
9. The device of claim 8, the modulator being an IQ modulator, the phase modulating electrode comprising at least electrodes I and Q;
correspondingly, the first determining module includes:
a second determining unit for determining the bias voltage of the electrode I
Determining a first perturbation signal to be applied on the electrode I;
a third determination unit for determining the bias voltage of the electrode Q
Determining a second perturbation signal to be applied on the electrode Q;
wherein the frequency of the first disturbance signal is
The frequency of the second disturbance signal is +.>
, wherein ,/>
And (3) with
Different;
the detection module comprises:
a detection unit for detecting the frequency from the output signals of the output end of the modulator
Is of frequency +.>
Is of frequency +.>
Is included in the signal component of the signal(s).
10. The apparatus of claim 9, wherein the first adjustment unit comprises:
a first adjusting subunit for adjusting the bias voltage
The frequency is +.>
Is smaller than the first threshold value>
As a biased operating point for the electrode I;
a second adjusting subunit for adjusting the bias voltage
The frequency is +.>
Is smaller than the first threshold value>
As a biased operating point for the electrode Q;
a third regulating subunit for regulating the bias voltage corresponding to the Phase modulation electrode Phase
The frequency is set as
Is smaller than the first threshold value>
As a biased operating point for the electrode Phase. />
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