CN114034468B - Wavelength calibration method of multichannel interference laser - Google Patents
Wavelength calibration method of multichannel interference laser Download PDFInfo
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- CN114034468B CN114034468B CN202111310647.0A CN202111310647A CN114034468B CN 114034468 B CN114034468 B CN 114034468B CN 202111310647 A CN202111310647 A CN 202111310647A CN 114034468 B CN114034468 B CN 114034468B
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Abstract
The application relates to a wavelength calibration method of a multichannel interference laser, which is characterized by comprising the following steps of: 1) Acquiring the relation between the injection current of the thermode and the heating power; 2) Measuring the gain spectrum red shift of the laser under the small current and normal working current, and counteracting the red shift through the compensation of the temperature controller; 3) Setting injection current of the active region as small current, selecting any one arm as reference, adjusting heating power of the hot electrodes of other N-1 arms to the peak of a power curve by using an optimization algorithm, and measuring the lasing wavelength lambda 0 The method comprises the steps of carrying out a first treatment on the surface of the 4) Extracting heating power required by generating pi phase shift of each phase region; 5) Calculating the relation between the heating power and the lasing frequency of the hot electrode at the common phase region and each arm phase region; 6) Setting the heating power of the hot electrode at the public phase region at the middle of the non-hysteresis region, measuring the real-time lasing wavelength and calculating the deviation from the target lasing wavelength; 7) Updating a wavelength lookup table under the small current of the active area; 8) And stopping calibrating the wavelength which meets the wavelength error.
Description
Technical Field
The application relates to an optical communication technology, in particular to a wavelength calibration method of a multichannel laser.
Background
Tunable lasers are widely used in the fields of optical sensing, optical inspection and optical communications because of their wavelength tuning. Tunable semiconductor lasers are favored for research and market because of their small size, high reliability, low cost, and ease of integration with other devices. Tunable lasers require time-consuming wavelength calibration and complex wavelength locking to ensure accurate wavelength, high side-mode rejection ratio, and long-term stability compared to fixed wavelength lasers. Thus, the control and packaging costs of the tunable laser are higher.
Monolithically integrated tunable semiconductor lasers commonly found in the market today are mainly divided into two categories: one type is a distributed bragg feedback laser array. Typically a single distributed feedback laser can achieve a tuning range of 3-5 nanometers by varying the temperature. Multiple distributed feedback lasers with different center wavelengths are integrated on the same chip in parallel, so that wide-range wavelength tuning can be realized. Because the distributed feedback laser array realizes wavelength tuning by changing the temperature of the laser, the wavelength calibration is relatively simple; another class is widely tunable lasers based on distributed bragg reflection. Such tunable lasers typically require simultaneous control of three tuning zones to achieve wavelength tuning: two reflection regions, one phase region. The wavelength calibration is generally performed by scanning tuning area control to obtain a tuning spectrum of the feedback signal. The feedback signal may be output optical power, optical spectrum, or active area junction voltage, etc.
The multi-channel interference laser is a large-range wavelength tunable laser that performs mode selection based on multi-cavity interference enhancement. Because the wavelength tuning principle is different from that of other tunable lasers, eight tuning zones need to be controlled simultaneously, so it is difficult to acquire the tuning spectrum of the feedback signal by scanning the tuning zone control. The wavelength characterization of the multichannel interference laser can be performed by a wavelength characterization method based on an optimization algorithm with a specified wavelength, so that the characterization speed is high. However, the wavelength characterization method based on the optimization algorithm needs to perform wavelength calibration by means of a high-precision external adjustable optical filter, the wavelength calibration range is limited by the wavelength range of the adjustable optical filter, and meanwhile, the change relation of tuning area control cannot be acquired, so that the establishment of the wavelength locking algorithm is not facilitated. Therefore, the multichannel interference laser needs a set of wavelength calibration methods relying on its tuning principle.
Disclosure of Invention
The technical problem to be solved by the application is to provide a wavelength calibration method of a multichannel interference laser, which aims at the defects existing in the prior art and is calibrated by means of a self tuning principle, thereby being beneficial to the establishment of a wavelength locking algorithm.
The technical scheme adopted for solving the technical problems is as follows: the wavelength calibration method of the multichannel interference laser comprises an active region, a common phase region and a multichannel interference region, wherein the multichannel interference region comprises N arms, N is a natural number not less than 2, each arm is provided with an arm phase region, and the common phase region and the arm phase region are heated by a hot electrode respectively; the method is characterized in that: the method comprises the following steps:
1) Measuring PIV curves of the hot electrodes at the public phase area and the arm phase area of the laser to obtain the relation between the injection current of the hot electrodes and the heating power;
2) Measuring the gain spectrum red shift of the laser caused by the thermal effect under the small current and the normal working current, and counteracting the gain spectrum red shift through the compensation of a temperature controller of the laser; the small current is adjacent to and greater than a current minimum threshold of the laser;
3) Setting injection current of the active region as small current, selecting any one arm as reference, adjusting heating power of the hot electrodes of other N-1 arms to the peak of a power curve by using an optimization algorithm, and measuring the lasing wavelength lambda 0 And lambda is taken as 0 As an initial wavelength;
4) The heating power of the hot electrode at the common phase area and the phase areas of each arm is scanned respectively, the output optical power of the laser is measured, and the heating power required by generating pi phase shift of each phase area is extracted;
5) Calculating the relation between the heating power and the lasing frequency of the common phase region and the hot electrode at each arm phase region by utilizing the relation between the phase change and the wavelength of N arms with different lengths of the laser;
6) Setting the injection current of an active region as the current of normal operation, sequentially scanning the heating power of a hot electrode at a public phase region under the condition that the active region is small current from large to small and from small to large in two pi phase shift periods, monitoring the output optical power or the output wavelength, determining a hysteresis interval, setting the heating power of the hot electrode at the public phase region in the middle of a non-hysteresis interval, measuring the real-time lasing wavelength, and calculating the deviation from the target lasing wavelength;
7) Compensating the wavelength deviation of the active region obtained under the normal working current into a target wavelength, calibrating the wavelength under the small current of the active region again, and updating a wavelength lookup table under the small current of the active region;
8) Stopping calibrating the wavelength which meets the wavelength error, and repeating the steps 7) and 8) until the wavelength which does not meet the wavelength error meets the requirement of the wavelength error.
Preferably, in step 2), the temperature controller compensates for the following: when the injection current of the active region is set at a small current, the temperature controller sets a higher temperature than a normal value in normal operation, and when the injection current of the active region is set at a normal operation current, the temperature controller sets a return normal value.
Preferably, in step 3), the arm with the shortest length is used as a reference.
Preferably, in step 3), the optimization algorithm is a hill climbing algorithm based on parabolic fit: selecting heating power of a thermode at a certain arm, changing a plurality of preset phase shift points near an initial value, simultaneously monitoring the output optical power of a laser, fitting a relation between the heating power and the output optical power through parabola, selecting an updated phase shift point at the maximum value of the output optical power, wherein the phase shift point is optimized once, and all N-1 arm phase areas are optimized once; and (3) iterating the loop until the maximum phase shift deviation in two adjacent rounds is smaller than a specified value, and jumping out of the loop, wherein the phase areas of the arms are considered to be in the same phase state at the moment.
Preferably, the calculation in step 5) is as follows:
5.1 According to the actual heating power provided by the thermode, converting the theoretical required value into a plurality of pi phase shifts to the heating power range provided by the thermode: at an initial wavelength lambda 0 As an origin, interpolation is carried out in the directions of long wavelength and short wavelength at a specified frequency interval, each interpolated wavelength needs to firstly utilize the quasi-continuous tuning capability of a longitudinal mode to move the heating power of the hot electrode in the public phase region to the maximum value of an output power curve, and then utilizes an optimization algorithm to adjust the heating power of the hot electrode at N-1 arm phase regions to the peak of the power curve and measure the real-time lasing wavelength;
5.2 Then re-fitting the relation between the heating power of the thermodes at the common phase region and the phase regions of each arm and the lasing frequency according to the measured real-time lasing wavelength; then returning to step 5.1), repeating the process until the difference between the interpolated wavelength and the expected wavelength exceeds a preset value, and stopping interpolation;
thereby obtaining the minimum lambda of the wavelength range in which the laser is actually tunable min And a maximum value lambda max And a wavelength lookup table of certain frequency intervals under the small current of the active area.
Compared with the prior art, the application has the advantages that: the wavelength calibration can be carried out by utilizing the self tuning principle (each relation of hot electrode heating) of the laser without using an external adjustable optical filter with high precision, so that the wavelength calibration range is not limited by the wavelength range of the adjustable optical filter any more, the change relation of tuning area control can be obtained, and the establishment of a wavelength locking algorithm is facilitated.
Drawings
FIG. 1 is a schematic diagram of a laser according to an embodiment of the present application;
FIG. 2-1 is a schematic illustration of alignment of lasing longitudinal mode and reflection peak;
FIG. 2-2 is a schematic diagram of the longitudinal lasing mode as it deviates from the reflection peak;
FIG. 3 is a graph of asymmetric gain curves and specular loss due to nonlinear effects near the lasing mode of a laser, where the ordinate is normalized gain/loss and the abscissa is wavelength;
FIG. 4-1 is a graph showing the variation of the laser output optical power with increasing and decreasing heating power of the thermodes in the common phase region when a 30mA current is injected into the active region, wherein the ordinate is the SOA photocurrent (mA) and the abscissa is the heating power (mW);
FIG. 4-2 is a graph showing the variation of the laser output optical power with increasing and decreasing heating power of the thermodes in the common phase region when 70mA current is injected into the active region, wherein the ordinate is SOA photocurrent (mA) and the abscissa is heating power (mW);
FIGS. 4-3 are graphs showing the variation of the laser output optical power with increasing and decreasing heating power of the thermodes in the common phase region when 120mA current is injected into the active region, wherein the ordinate represents the SOA photocurrent (mA) and the abscissa represents the heating power (mW);
FIGS. 5-1 to 5-9 are graphs showing small-range changes in laser output optical power with heating power of the thermodes in the common phase region and the arm phase region when current is injected into the active region by 30mA, wherein FIG. 5-1 is a graph showing the changes in the common phase region; FIGS. 5-2 through 5-9 are graphs showing the variation of the arm phase region and are sequentially arranged with increasing arm length; where the ordinate is the SOA photocurrent (mA) and the abscissa is the heating power (mW).
Detailed Description
Embodiments of the present application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions.
In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for purposes of describing the present application and simplifying the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and because the disclosed embodiments of the present application may be arranged in different orientations, these directional terms are merely for illustration and should not be construed as limitations, such as "upper", "lower" are not necessarily limited to orientations opposite or coincident with the direction of gravity. Furthermore, features defining "first", "second" may include one or more such features, either explicitly or implicitly.
Referring to FIG. 1, a multi-channel interference wavelength tunable laser includes an active region 1, a common phase region 2, and a multi-channel interference region 3, where the multi-channel interference region 3 includes a 1 XN beam splitter 31 and N arms 32, where N is a natural number (N. Gtoreq.2) not smaller than 2, and the lengths of the arms 32 may be the same or different, and will be described below with reference to the case of different arm lengths.
Wherein the common phase region 2 and the multi-channel interference region 3 are of passive structures. The common phase region 2 is between the active region 1 and the multi-channel interference region 3. The active region 1 is used for providing the optical gain required by laser lasing; the common phase region 2 is used to fine tune the position of the longitudinal modes of the laser. The multichannel interference region 3 is used for mode selection. The 1 XN branch area is used for dividing an input light field into N output light fields and can be composed of a multimode interferometer, a Y branch or a star coupler and other structures. In this embodiment, n=8.
The front facet of the laser may be a broadband reflective structure such as a cleaved facet and a dual-port multimode interference reflector. The semiconductor optical amplifier 4 can be simply integrated by a dual-port multimode interference reflector for amplifying the output optical power of the laser. The end of each arm incorporates a multimode interference reflector 33 for reflecting light back into the cavity. To adjust the phase of each arm 32, an arm phase section 321 is provided on each arm 32. By adjusting the phase of the arm phase region 321, the phases of the eight arms 32 can be in phase at a specified wavelength, forming a reflection spectrum with a single reflection peak dominant, and realizing mode selection.
The structure of each area of the laser is the prior art, and can be seen in China patent application number 201611039594.2 of the inventor.
In general, the adjustment of the phases of the common phase region 2 and the arm phase region 321 can be achieved by both electric injection and heating. The free carrier absorption introduced by the electrical injection brings about additional losses, so that the laser output optical power is affected by the magnitude of the injection current. The phase regions are heated without additional loss, and the phase change and the heating power change approximately linearly. Therefore, the following description will take a heating mode as an example, and the phase region is generally heated by manufacturing a micro-scale thermode.
When the lasing mode (dashed longitudinal line) is aligned with the reflection peak (curved line), see fig. 2-1, the reflection corresponding to the lasing mode is maximum, and when the lasing mode deviates from the reflection peak, see fig. 2-2, the reflection corresponding to the lasing mode is small. The gain around the lasing mode is asymmetric, i.e. the gain around the lasing mode is higher for long wavelengths than for short wavelengths, as shown in fig. 3, due to nonlinear effects, mainly carrier density pulse effects.
When the lasing longitudinal mode and the reflection peak are completely aligned, the heating power of the hot electrode of the common phase region 2 is increased, the lasing wavelength is increased by moving the lasing longitudinal mode towards the long wavelength. Because the short wavelength mode corresponds to a lower gain, mode hops do not occur when the reflection of adjacent short wavelength longitudinal modes is slightly greater than the reflection of lasing longitudinal modes. The lasing longitudinal mode continues to shift toward longer wavelengths until the reflection of the adjacent short wavelength longitudinal mode increases such that its corresponding threshold mode gain decreases to the same gain, and the mode does not jump to the adjacent short wavelength longitudinal mode. In contrast, when the lasing longitudinal mode and the reflection peak are completely aligned, the heating power of the hot electrode of the common phase region 2 is reduced, the lasing longitudinal mode is shifted to a short wavelength, and the lasing wavelength is reduced. Since the gain corresponding to the long wavelength mode is higher, mode hopping occurs when the reflection of the adjacent long wavelength longitudinal mode and the reflection of the lasing longitudinal mode are close.
Therefore, the change of the output optical power curve of the laser along with the heating power of the hot electrode of the common phase region 2 is similar to a parabola with a downward opening, and the hysteresis phenomenon is shown, namely, the increase and the decrease of the heating power of the hot electrode of the common phase region 2 are different in corresponding mode jump points.
The variation curves of the output optical power of the actually tested multichannel interference laser along with the increase and decrease of the heating power of the thermodes in the common phase region are shown in figures 4-1 to 4-3. The output optical power is tested as a detector by a reverse biased semiconductor optical amplifier. The heating power of the thermode corresponding to the dotted line is the optimal working point, namely the longitudinal lasing mode is aligned with the reflection peak. It can be seen that the increase of the heating power of the hot electrode of the common phase region 2 on the basis of the optimal operating point is not easy to cause the mode jump, and the decrease of the heating power of the hot electrode of the common phase region 2 is easy to cause the mode jump. The section where the output light power does not overlap is a hysteresis section. If the heating power of the common phase region 2 thermodes is set within the hysteresis region, mode hopping is liable to occur at the time of wavelength switching. Therefore, in order to avoid the occurrence of the mode skip, it is necessary to set the heating power of the hot electrode of the common phase region 2 in a non-hysteresis region, such as a region having an abscissa of 3 to 6 as shown in fig. 4-1, and a region having an abscissa of 4 to 6 as shown in fig. 4-2.
The best working point of the laser is that when the lasing longitudinal mode and the reflection peak are completely aligned, the reflection is maximum and the output optical power is highest. In order to obtain a high output optical power, the injection current of the active region 1 needs to be increased. However, the nonlinear effect of the laser is affected by the output optical power. The higher the output optical power, the stronger the nonlinear effect, i.e. the more serious the hysteresis effect. As shown in fig. 4-1 and 4-2, the injection current of the laser active region 1 is increased from 30mA to 70mA, the output optical power of the laser is increased, the hysteresis effect becomes more obvious, the non-hysteresis interval is obviously smaller, and the optimal operating point of the laser is already located at the edge of the non-hysteresis interval. The hysteresis effect becomes more serious and the optimum operating point is located outside the non-hysteresis interval by continuing to increase the injection current to the active region 1. At this time, if the heating power of the common phase region 2 thermode is set at the optimum operating point, the laser is very susceptible to mode-hops.
In addition, the laser is affected by aging and external environmental factors during long-time use, and the working state of the laser changes, so in order to enable the laser to stably work for a long time without mode jump, the heating power of the hot electrode of the common phase region 2 needs to be set in the middle of a non-hysteresis region, as shown by the dotted line in fig. 4-3. Although setting the operating point of the laser in the very middle of the non-hysteresis interval (long wavelength side of the reflection peak) reduces a part of the output optical power, the detuning loading effect (detuned loading effect) is beneficial to reduce the intrinsic linewidth of the laser.
The shape of the reflection spectrum is determined by the length differences and phases of the eight arms 32. Each arm phase region 321 affects only the phase of a portion of the light. When the eight arms 32 are in phase at a given wavelength, the thermode heating power of one arm phase region 321 is adjusted separately, the phase of the arm 32 is shifted, and the laser output optical power is reduced. Since the longer arm 32 has a greater influence on the reflection spectrum, the larger the phase deviation is, and the longer arm 32 is more likely to cause mode hops. Therefore, on the basis of eight arms in phase, the heating power of the hot electrode in the arm phase region is changed within a certain range, and the change of the output optical power of the laser is similar to a parabola with a downward opening.
In fig. 5-1 to 5-9, the upper curve is the power curve when the lasing longitudinal mode and the reflection peak are aligned, the lower curve is the power curve when the lasing longitudinal mode deviates from the reflection peak toward the long wavelength direction, wherein in fig. 5-2, the curve with the vertex on the right is the power curve when the lasing longitudinal mode and the reflection peak are aligned, and the curve with the vertex on the left is the power curve when the lasing heald mode deviates from the reflection peak toward the long wavelength direction. As shown by the power curves when the lasing longitudinal modes and reflection peaks are aligned, when the eight arms 32 are in phase and the longitudinal modes and reflection peaks are aligned, the heating power of the common phase region 2 and the arm phase region 321 thermodes, respectively, is scanned over a small range, each of the heating powers of the phase region thermodes being located substantially at the peak of the power curve. In the scanning process, only the heating power of one phase region hot electrode is changed, and the heating power of other phase region hot electrodes is kept unchanged. Because of the influence of the hysteresis effect, the heating power of the thermode of the laser common phase region 2 needs to be set in the middle of the non-hysteresis region, and therefore the alignment state of the arm phase region 321 when the longitudinal mode deviates from the reflection peak in the long wavelength direction is tested, as shown by the power curve when the lasing longitudinal mode deviates from the reflection peak in the long wavelength direction.
It can be seen that when the longitudinal mode deviates from the reflection peak in the long wavelength direction, the heating power of the hot electrode of the arm phase region 321 deviates from the peak of the power curve. According to the arrangement of increasing arm length, the heating power of the hot electrode of the arm phase region 321 in fig. 5-2 to 5-6 (respectively numbered 1 to 5) deviates to the right side of the parabola, and the heating power of the hot electrode of the arm phase region 321 in fig. 5-7 to 5-9 (respectively numbered 6 to 8) deviates to the left side of the parabola. Each arm 32 is of a different length and its corresponding free spectral range is then different. The heating power of the hot electrode in the common phase region 2 is increased, the phase is increased, and the longitudinal mode of the laser is shifted towards long wavelength. At the same time, the cavities corresponding to each arm 32 are equivalently increased by the same phase, and the longitudinal mode corresponding to each arm 32 is shifted at a longer wavelength. In the same phase change amount, the free spectral range of the arms 1 to 5 32 is larger than that of the laser, so that the longitudinal mode corresponding to the arms 1 to 5 moves more. If realignment with the longitudinal mode of the laser is required, the hot electrode heating power of the number 1-5 arm phase region 321 needs to be reduced to shift its longitudinal mode of the corresponding cavity to a short wavelength. The heating power of the No. 1-5 arm heat electrode 321 is located on the right side of the parabola. In contrast, in the case of the same amount of phase change, the free spectral range of the arms No. 6 to No. 7 32 is smaller than that of the laser, so that the longitudinal mode movement corresponding to the arms No. 6 to No. 7 32 is less. If realignment with the laser longitudinal mode is required, the hot electrode heating power of the number 6-7 arm phase region 321 needs to be increased to shift the longitudinal mode of its corresponding cavity to longer wavelengths. The heating power of the hot electrode of the arms No. 6-7 321 is thus located to the left of the parabola. The greater the difference between the free spectral range corresponding to each arm 32 and the free spectral range of the laser, the greater the deviation from the peak of the power curve. The amount by which the heating power of the hot electrode of each arm 32 deviates from the peak of the power curve is related to the amount by which the lasing longitudinal mode deviates from the reflection peak.
The above characteristics of the multi-channel interference laser, in combination with the above characteristics, the flow of the wavelength characterization method for the multi-channel interference laser is shown in fig. 6, and specifically is as follows:
1) Measuring PIV (power-current-voltage) curves of hot electrodes of a common phase region 2 and an arm phase region 321 of the laser, and obtaining the relation between the injection current of the hot electrodes and the heating power;
2) Measuring the gain spectrum red shift (wavelength drift) of the laser caused by the thermal effect under the conditions of small current (the current of the laser is above the minimum threshold value and is smaller than the normal working current near the threshold value) and normal working current (such as 100 milliamperes), and counteracting the gain spectrum red shift (wavelength drift) by the compensation of a temperature controller of the laser; in the step, the specific practice is that when the injection current of the active area 1 is set at a small current, the temperature controller is set at a temperature adaptively higher than a common value in normal operation, and when the injection current of the active area 1 is set at a normal operation current, the temperature controller is set at a return common value;
3) Setting the injection current of the active region 1 to a small current (above the current threshold of the laser and adjacent to the threshold), selecting any one of the arms 32 as a reference, here the shortest arm 32 as a reference; the heating power of the hot electrodes of the other seven arms 32 is adjusted to the peak of the power curve by using an optimization algorithm and the lasing wavelength lambda is measured 0 And takes the same as the initial wavelength; the optimization algorithm here refers to the existing hill climbing algorithm developed for optimization of the arm phase region 321 and based on parabolic fit, the heating power of the hot electrode at a certain arm 32 is selected to change a plurality of preset phase shift points near an initial value, the phase shift points are tiny phase shift points, such as 0.02 pi, and the output light power of the laser is monitored at the same time, and the output light power of the laser is obtained through parabolic fitThe relation between the heating power and the output optical power is selected, the maximum value of the output optical power is an updated phase shift point, the phase shift point is optimized once, and all the seven arm phase areas 321 are optimized once to form a round; iterating the loop until the maximum phase shift deviation in two adjacent rounds is smaller than a prescribed value, and jumping out of the loop, wherein each arm phase region 321 (eight arm phase regions 321) is considered to be in the same phase state at the moment;
4) The heating power of the hot electrode at the common phase region 2 and the phase regions 321 of each arm is scanned respectively, the output optical power of the laser is measured, and the heating power required by generating pi phase shift of each phase region is extracted;
5) Calculating the relationship between heating power and lasing frequency of a heating electrode at a theoretical common phase region 2 and each arm phase region 321 by utilizing the relationship between the phase change and the wavelength of eight arms with different lengths of the laser;
in the step, the calculation mode is as follows:
5.1 According to the actual heating power provided by the thermodes, converting the theoretical required value into a plurality of pi phase shifts within the range of the heating power provided by the appropriate thermodes: at an initial wavelength lambda 0 As an origin, interpolation is carried out in the directions of a long wavelength and a short wavelength at a specified frequency interval, such as the interval ITU 50GHz, each interpolated wavelength needs to firstly utilize the quasi-continuous tuning capability of a longitudinal mode to move the heating power of the hot electrode in the common phase region to the maximum value of an output power curve, and then an optimization algorithm is utilized to adjust the heating power of the hot electrode in the seven arm phase regions 321 to the peak of the power curve and measure the real-time lasing wavelength;
5.2 Then re-fitting the relationship between the thermode heating power and the lasing frequency at the common phase region 2 and each arm phase region 321 (eight arm phase regions 321) according to the measured lasing wavelength; then returning to step 5.1), repeating the process until the interpolated wavelength differs from the expected wavelength by more than a preset value, if more than one longitudinal mode interval is exceeded, stopping interpolation;
in this way a practically tunable wavelength range lambda of the laser can be obtained min And lambda (lambda) max And a wavelength lookup table of a certain frequency interval at 1 small current in the active region;
6) Setting the injection current of the active region 1 as the current of normal operation, sequentially scanning the heating power of the hot electrode at the public phase region 2 under the small current of the active region 1 from large to small and from small to large in two pi phase shift periods, monitoring the output optical power or the output wavelength, determining a hysteresis interval, setting the heating power of the hot electrode at the public phase region 2 in the middle of a non-hysteresis interval, measuring the real-time lasing wavelength, and calculating the deviation from the target lasing wavelength;
7) Adding the obtained wavelength deviation and the target wavelength under the normal working current of the active area 1, thereby compensating the target wavelength into the target wavelength, calibrating the wavelength under the small current again, and updating a wavelength lookup table under the small current of the active area 1; because the wavelength has deviation under the normal working current, the deviation is compensated into the target wavelength for calibration under the small current, and the normal working current is switched after the calibration is finished, so that the frequency error can be eliminated;
8) Stopping calibrating the wavelength which meets the wavelength error, and repeating the steps 7) and 8) until the wavelength which does not meet the wavelength error meets the requirement of the wavelength error.
Claims (5)
1. A wavelength calibration method of a multichannel interference laser, the laser comprising an active region (1), a common phase region (2) and a multichannel interference region (3), the multichannel interference region (3) comprising N arms (32), N being a natural number not smaller than 2, each arm (32) having an arm phase region (321), the common phase region (2) and the arm phase region (321) being heated by a thermode, respectively; the method is characterized in that: the method comprises the following steps:
1) Measuring PIV curves of hot electrodes at a public phase region (2) and an arm phase region (321) of the laser to obtain the relation between hot electrode injection current and heating power;
2) Measuring the gain spectrum red shift of the laser caused by the thermal effect under the small current and the normal working current, and counteracting the gain spectrum red shift through the compensation of a temperature controller of the laser; the small current is adjacent to and greater than a current minimum threshold of the laser;
3) Active region(1) Is set to a small current, any one arm (32) is selected as a reference, the heating power of the thermodes of the other N-1 arms (32) is adjusted to the peak of a power curve by using an optimization algorithm, and the lasing wavelength lambda is measured 0 And lambda is taken as 0 As an initial wavelength;
4) The heating power of the hot electrode at the common phase region (2) and the phase regions (321) of each arm is scanned respectively, the output optical power of the laser is measured, and the heating power required by generating pi phase shift of each phase region is extracted;
5) Calculating the relation between the heating power and the lasing frequency of the hot electrode at the common phase region (2) and each arm phase region (321) by utilizing the relation between the phase change and the wavelength of N arms (32) with different lengths of the laser;
6) Setting the injection current of the active region (1) as the current of normal operation, sequentially scanning and monitoring the output optical power or the output wavelength from large to small and from small to large in two pi phase shift periods of the heating power of the hot electrode at the public phase region (2) under the condition that the active region (1) is small current, determining a hysteresis interval, setting the heating power of the hot electrode at the public phase region (2) in the middle of a non-hysteresis interval, measuring the real-time lasing wavelength and calculating the deviation from the target lasing wavelength;
7) Compensating the wavelength deviation obtained by the active region (1) under the normal current into a target wavelength, calibrating the wavelength under the small current of the active region (1) again, and updating a wavelength lookup table under the small current of the active region (1);
8) Stopping calibrating the wavelength which meets the wavelength error, and repeating the steps 7) and 8) until the wavelength which does not meet the wavelength error meets the requirement of the wavelength error.
2. The method for calibrating the wavelength of the multichannel interference laser according to claim 1, wherein: in step 2), the compensation method of the temperature controller is as follows: when the injection current of the active area (1) is set at a small current, the temperature controller sets a higher temperature than a normal value in normal operation, and when the injection current of the active area (1) is set at a normal operation current, the temperature controller sets a return normal value.
3. The method for calibrating the wavelength of the multichannel interference laser according to claim 1, wherein: in step 3), the shortest length arm (32) is used as a reference.
4. The method for calibrating the wavelength of the multichannel interference laser according to claim 1, wherein: in step 3), the optimization algorithm is a hill climbing algorithm based on parabolic fit: selecting heating power of a hot electrode at a certain arm (32), changing a plurality of preset phase shift points near an initial value, simultaneously monitoring output optical power of a laser, fitting a relation between the heating power and the output optical power through parabola, selecting an updated phase shift point at the maximum value of the output optical power, wherein the phase shift point is optimized once, and N-1 arm phase areas (321) are completely optimized once; and iterating the loop until the maximum phase shift deviation in two adjacent rounds is smaller than a specified value, and jumping out of the loop, wherein the phase areas (321) of the arms are considered to be in the same phase state.
5. The method for calibrating the wavelength of the multichannel interference laser according to claim 1, wherein: the calculation in step 5) is as follows:
5.1 According to the actual heating power provided by the thermode, converting the theoretical required value into a plurality of pi phase shifts to the heating power range provided by the thermode: at an initial wavelength lambda 0 As an origin, interpolation is carried out in the directions of long wavelength and short wavelength at a specified frequency interval, each interpolated wavelength needs to firstly utilize the quasi-continuous tuning capability of a longitudinal mode to move the heating power of a common phase region hot electrode to the maximum value of an output power curve, and then utilizes an optimization algorithm to adjust the heating power of the hot electrode at N-1 arm phase regions (321) to the peak of the power curve and measure the real-time lasing wavelength;
5.2 Then re-fitting the relation between the heating power of the thermodes at the common phase region (2) and the phase regions (321) of each arm and the lasing frequency according to the measured real-time lasing wavelength; then returning to step 5.1), repeating the process until the difference between the interpolated wavelength and the expected wavelength exceeds a preset value, and stopping interpolation;
thereby obtaining the minimum lambda of the wavelength range in which the laser is actually tunable min And a maximum value lambda max And a wavelength lookup table of a certain frequency interval under the small current of the active region (1).
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