CN114034468A - Wavelength calibration method of multi-channel interference laser - Google Patents
Wavelength calibration method of multi-channel interference laser Download PDFInfo
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Abstract
The invention relates to a wavelength calibration method of a multi-channel interference laser, which is characterized by comprising the following steps: 1) acquiring the relation between the hot electrode injection current and the heating power; 2) measuring the gain spectrum red shift of the laser under small current and normal working current, and offsetting the red shift through the compensation of the temperature controller; 3) setting the injection current of the active region as a small current, selecting any one arm as a reference, adjusting the heating power of the hot electrodes of other N-1 arms to the top point of a power curve by utilizing an optimization algorithm, and measuring the lasing wavelength lambda0(ii) a 4) Extracting the heating power required by generating pi phase shift in each phase region; 5) calculating the relationship between the heating power and the lasing frequency of the common phase region and the hot electrodes at the phase regions of the arms; 6) setting the heating power of the hot electrode in the public phase area in the middle of the non-hysteresis interval, 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 region; 8) and stopping calibrating the wavelength meeting the wavelength error.
Description
Technical Field
The invention relates to the optical communication technology, in particular to a wavelength calibration method of a multi-channel laser.
Background
Tunable lasers have found wide application in the fields of optical sensing, optical inspection and optical communications because of their tunable wavelength. Tunable semiconductor lasers are more attractive to research and market because of their small size, high reliability, low cost, and ease of integration with other devices. Compared with a fixed wavelength laser, the tunable laser needs time-consuming wavelength calibration and complex wavelength locking to ensure accurate wavelength, high side mode suppression ratio and long-term stability. Therefore, the control and packaging costs of tunable lasers are higher.
The monolithic integrated tunable semiconductor lasers commonly available in the market are mainly classified into two types: 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. A plurality of distributed feedback lasers with different center wavelengths are integrated on the same chip in a parallel connection mode, and therefore wide-range wavelength tuning can be achieved. Because the wavelength tuning of the distributed feedback laser array is realized 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 three tuning regions to be controlled simultaneously to achieve wavelength tuning: two reflective regions, a phase region. The wavelength calibration is generally performed by scanning the tuning region control to obtain the tuning spectrum of the feedback signal. The feedback signal may be output optical power, optical spectrum, or active area junction voltage, etc.
The multichannel interference laser is a large-range wavelength tunable laser for mode selection based on multi-cavity interference enhancement. Since the wavelength tuning principle thereof is different from that of other tunable lasers, eight tuning sections need to be controlled simultaneously, so that it is difficult to acquire the tuning spectrum of the feedback signal by scanning the tuning section control. The wavelength characterization method based on the optimization algorithm can be used for performing wavelength characterization on the multi-channel interference laser at the specified wavelength, and 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 tunable optical filter, the wavelength calibration range is limited by the wavelength range of the tunable optical filter, and meanwhile, the variation relationship of tuning region control cannot be obtained, which is not favorable for establishing the wavelength locking algorithm. Therefore, the multichannel interference laser needs a set of wavelength calibration method depending on the tuning principle of the multichannel interference laser.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a wavelength calibration method of a multi-channel interference laser aiming at the defects in the prior art, and the calibration is carried out by depending on the self-tuning principle, thereby being beneficial to establishing a wavelength locking algorithm.
The technical scheme adopted by the invention for solving the technical problems is as follows: a wavelength calibration method of a 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 respectively heated by a hot electrode; the method is characterized in that: the method comprises the following steps:
1) measuring PIV curves of a thermode at a common phase area and an arm phase area of the laser to obtain a relation between thermode injection current and heating power;
2) measuring gain spectrum red shift of the laser caused by a thermal effect under low current and normal working current, and offsetting the gain spectrum red shift through 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 the injection current of the active region as a small current, selecting any one arm as a reference, adjusting the heating power of the hot electrodes of other N-1 arms to the top point of a power curve by utilizing an optimization algorithm, and measuring the lasing wavelength lambda0And will be0As an initial wavelength;
4) respectively scanning the heating power of the hot electrodes at the common phase area and each arm phase area, measuring the output light power of the laser, and extracting the heating power required by pi phase shift generated by each phase area;
5) calculating the relationship between the heating power and the lasing frequency of the common phase region and the thermodes at the phase regions of the arms by using the relationship between the phase change and the wavelength of the N arms with different lengths of the laser;
6) setting the injection current of an active area as a normal working current, scanning the heating power of the hot electrode at the public phase area in the active area under a small current from large to small and from small to large in two pi phase shift periods in sequence, monitoring the output light power or the output wavelength, determining a hysteresis interval, setting the heating power of the hot electrode at the public phase area 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 under the normal working current into the target wavelength, carrying out wavelength calibration under the active region small current again, and updating a wavelength lookup table under the active region small current;
8) and stopping calibrating the wavelength which meets the wavelength error, and repeating the steps 7) and 8) for the wavelength which does not meet the wavelength error until the wavelength error requirement is met.
Preferably, in step 2), the compensation method of the temperature controller is as follows: when the injection current of the active region is set at a small current, the temperature controller sets the temperature higher than a normal value during normal operation, and when the injection current of the active region is set at a normal operation current, the temperature controller sets the normal value.
Preferably, in step 3), the arm with the shortest length is taken as a reference.
Preferably, in step 3), the optimization algorithm is a hill climbing algorithm based on parabolic fitting: selecting the heating power of a hot electrode at a certain arm, changing a plurality of preset phase shift points near an initial value, monitoring the output light power of the laser, fitting the relation between the heating power and the output light power through a parabola, and selecting the maximum value of the output light power as an updated phase shift point, wherein the phase shift point is optimized once, and the phase regions of N-1 arms are completely optimized once; and (5) iterating the loop until the maximum phase shift deviation in two adjacent wheels is smaller than a specified value, and jumping out of the loop, wherein the phase regions of the arms are considered to be in the same phase state at the moment.
Preferably, the calculation mode in step 5) is as follows:
5.1) according to the actual heating power provided by the hot electrode, converting the theoretical required value into a plurality of pi phase shifts within the range of the heating power provided by the hot electrode: at an initial wavelength λ0As an origin, interpolating in the long and short wavelength directions at specified frequency intervals, each interpolated wavelength requiring a common wavelength to be tuned first by the quasi-continuous tuning capability of the longitudinal modesMoving the heating power of the hot electrode in the phase area to the maximum value of an output power curve, adjusting the heating power of the hot electrode in the phase area of the N-1 arms to the top point of the power curve by utilizing an optimization algorithm, and measuring the real-time lasing wavelength;
5.2) fitting the relationship between the heating power of the hot electrode and the lasing frequency of the common phase area and the phase areas of the arms again according to the measured real-time lasing wavelength; then returning to the 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 value lambda of the wavelength range of the laser which can be actually tunedminAnd maximum value λmaxAnd a wavelength lookup table for a certain frequency interval at the active cell small current.
Compared with the prior art, the invention has the advantages that: by utilizing the self-tuning principle (relation of thermode heating) of the laser, the wavelength calibration can be carried out without the help of a high-precision external adjustable optical filter, 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 invention;
FIG. 2-1 is a schematic diagram of the alignment of the lasing longitudinal mode and the reflection peak;
FIG. 2-2 is a schematic diagram of a lasing longitudinal mode deviating from a reflection peak;
FIG. 3 is a schematic diagram of an asymmetric gain curve and mirror 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 power with the increase and decrease of the heating power of the hot electrode in the common phase region when the active region injects a current of 30mA, 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 power with the increase and decrease of the heating power of the hot electrode in the common phase region when 70mA current is injected into the active region, wherein the ordinate is the SOA photocurrent (mA) and the abscissa is the heating power (mW);
4-3 are graphs showing the variation of the laser output power with the increase and decrease of the heating power of the hot electrode in the common phase region when the active region injects 120mA current, wherein the ordinate is SOA photocurrent (mA) and the abscissa is heating power (mW);
5-1 to 5-9 are graphs showing the change of the output optical power of the laser with the heating power of the hot electrode in the common phase region and the arm phase region in a small range when the active region injects a current of 30mA, wherein FIG. 5-1 is a graph showing the change of the common phase region; FIGS. 5-2 to 5-9 are graphs showing the variation of the arm phase regions, which are sequentially arranged in increasing arm lengths; the ordinate is the SOA photocurrent (mA) and the abscissa is the heating power (mW).
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like 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 invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present invention and to simplify the description, but are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and that the directional terms are used for purposes of illustration and are not to be construed as limiting, for example, because the disclosed embodiments of the present invention may be oriented in different directions, "lower" is not necessarily limited to a direction opposite to or coincident with the direction of gravity. Furthermore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.
Referring to fig. 1, a multichannel interference wavelength tunable laser includes an active region 1, a common phase region 2, and a multichannel interference region 3, where the multichannel interference region 3 includes a 1 × N beam splitter 31 and N arms 32, where N is a natural number (N ≧ 2) which is not less than 2, and the lengths of the arms 32 may be the same or different, and the following description will be made with respect to the case of different arm lengths.
The common phase region 2 and the multi-channel interference region 3 are 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 optical gain required by laser lasing; the common phase section 2 is used to fine tune the position of the longitudinal mode of the laser. The multi-channel interference region 3 is used for mode selection. The 1 XN branch region is used for dividing an input light field into N output light fields and can be composed of structures such as a multimode interferometer, a Y branch or a star coupler. In this embodiment, N is 8.
The front facet of the laser may be a broadband reflective structure such as a cleaved facet or a dual-port multimode interference reflector. The semiconductor optical amplifier 4 can be simply integrated by means of a dual-port multimode interference reflector for amplifying the output optical power of the laser. A multimode interference reflector 33 is integrated at the end of each arm to reflect light back into the cavity. In order to adjust the phase of each arm 32, an arm phase region 321 is provided on each arm 32. By adjusting the phase of the arm phase area 321, the phases of the eight arms 32 can be in phase at a specified wavelength, and a reflection spectrum with a single reflection peak dominant is formed to realize mode selection.
The structure of each region of the laser is the prior art, and can be seen in the Chinese patent with the application number of 201611039594.2 of the applicant.
In general, adjusting the phase of the common phase region 2 and the arm phase region 321 can be achieved by both electrical injection and heating. The free carrier absorption introduced by the electrical injection causes extra loss, so that the output optical power of the laser is influenced by the magnitude of the injected current. The phase regions are heated without additional losses, while the phase changes and the heating power changes approximately linearly. Therefore, the heating method is described below as an example, and the phase region is generally heated by fabricating a micro thermode.
When the lasing longitudinal mode (dashed line in the longitudinal direction) and the reflection peak (curve) are aligned, the reflection corresponding to this lasing mode is maximum, see fig. 2-1, and when the lasing longitudinal mode deviates from the reflection peak, see fig. 2-2, the reflection corresponding to this lasing mode becomes small. Affected by the nonlinear effect, mainly the carrier density pulse effect, the gain near the lasing mode is asymmetric, i.e. the gain at long wavelengths near the lasing mode is higher than the gain at short wavelengths, as shown in fig. 3.
When the longitudinal lasing mode and the reflection peak are completely aligned, the heating power of the common phase region 2 thermode is increased, the longitudinal lasing mode moves to a long wavelength, and the lasing wavelength increases. Because of the lower gain corresponding to the short wavelength mode, mode hopping does not occur when the reflection of the adjacent short wavelength longitudinal mode is slightly larger than the reflection of the lasing longitudinal mode. The longitudinal lasing mode continues to move toward the longer wavelength until the reflection of the adjacent longitudinal short-wavelength mode increases such that the gain of its corresponding threshold mode decreases to be the same as the gain, and the mode jumps to the adjacent longitudinal short-wavelength mode. On the contrary, when the lasing longitudinal mode and the reflection peak are completely aligned, the heating power of the common phase region 2 hot electrode is reduced, the laser 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 variation of the laser output optical power curve with the heating power of the common phase region 2 hot electrode is similar to a downward opening parabola, and simultaneously, the hysteresis phenomenon that the heating power of the common phase region 2 hot electrode is increased and decreased is different from the corresponding mode hopping point is shown.
The change curves of the actually tested output light power of the multi-channel interference laser along with the increase and decrease of the heating power of the hot electrode in the common phase area are shown in FIGS. 4-1 to 4-3. The output optical power was tested as a detector by means of an inverted bias semiconductor optical amplifier. The heating power of the hot electrode 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 mode hopping is not easy to occur when the heating power of the common phase area 2 hot electrode is increased on the basis of the optimal working point, and mode hopping is easy to occur when the heating power of the common phase area 2 hot electrode is decreased. The interval in which the output optical powers do not coincide is a hysteresis interval. If the heating power of the common phase section 2 hot electrode is set within the hysteresis interval, mode hopping is liable to occur at the time of wavelength switching. Therefore, in order to avoid the occurrence of mode hopping, it is necessary to set the heating power of the common phase section 2 hot electrode in a non-hysteresis section, such as a region with an abscissa of 3 to 6 as shown in FIG. 4-1 and a region with an abscissa of 4 to 6 as shown in FIG. 4-2.
The optimal working point of the laser is that when the longitudinal lasing mode and the reflection peak are completely aligned, the reflection is maximum, and the output light power is highest. In order to obtain 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 severe the hysteresis effect. As shown in fig. 4-1 and 4-2, when the injection current of the active region 1 of the laser 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 becomes obviously smaller, and the optimal operating point of the laser is already positioned at the edge of the non-hysteresis interval. The hysteresis effect becomes more severe by continuing to increase the active region 1 injection current, and the optimum operating point is outside the non-hysteresis interval. At this time, if the heating power of the common phase section 2 hot electrode is set at the optimum operating point, mode hopping of the laser occurs very easily.
In addition, the laser is affected by self-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 hopping, the heating power of the hot electrode in the common phase region 2 needs to be set in the middle of the non-hysteresis interval, as shown by the dotted line in fig. 4-3. Although setting the operating point of the laser at the very middle of the non-hysteresis interval (on the long wavelength side of the reflection peak) reduces a portion of the output optical power, the detuned loading effect (detuned loading effect) is beneficial for reducing the intrinsic linewidth of the laser.
The shape of the reflection spectrum is determined by the difference in length and phase 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 hot electrode heating power of one arm phase region 321 is individually adjusted, the phase of the arm 32 is deviated, and the laser output power is reduced. Since the longer arm 32 has a larger influence on the reflection spectrum, the phase shift becomes larger, and mode hopping is more likely to occur in the longer arm 32. Therefore, on the basis of the same phase of the eight arms, the heating power of the hot electrode in the phase area of the arms is changed within a certain range, and the change of the output light power of the laser is similar to a downward opening parabola.
In fig. 5-1 to 5-9, the upper curve is a power curve when the longitudinal lasing mode is aligned with the reflection peak, and the lower curve is a power curve when the longitudinal lasing mode is shifted from the reflection peak in the long wavelength direction, wherein in fig. 5-2, the curve with the vertex on the right is a power curve when the longitudinal lasing mode is aligned with the reflection peak, and the curve with the vertex on the left is a power curve when the total lasing mode is shifted from the reflection peak in the long wavelength direction. As shown in the power curve when the lasing longitudinal mode and the reflection peak are aligned, when the eight arms 32 are in phase and the longitudinal mode and the reflection peak are aligned, the heating powers of the common phase zone 2 and the arm phase zone 321 thermodes are scanned in a small range, respectively, and the heating power of each phase zone thermode is substantially located at the apex of the power curve. In the scanning process, only the heating power of the hot electrode in one phase area is changed, and the heating power of the hot electrodes in other phase areas is kept unchanged. Since the hot electrode heating power of the laser common phase region 2 needs to be set at the middle of the non-hysteresis interval due to the hysteresis effect, 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 the heating power of the hot electrode of the arm phase region 321 deviates from the apex of the power curve when the longitudinal mode deviates from the reflection peak in the long wavelength direction. In the arm length increasing arrangement, the heating power of the hot electrode of the arm phase area 321 in fig. 5-2 to 5-6 (1 to 5, respectively) deviates to the right of the parabola, while the heating power of the hot electrode of the arm phase area 321 in fig. 5-7 to 5-9 (6 to 8, respectively) deviates to the left of the parabola. Each arm 32 is of a different length and thus has a different corresponding free spectral range. The heating power of the common phase area 2 hot electrode is increased, the phase is increased, and the longitudinal mode of the laser moves to long wavelength. At the same time, the cavity corresponding to each arm 32 is equivalently phased in the same way, and the longitudinal mode corresponding to each arm 32 is also shifted in the longer wavelength. Under the condition of the same phase change amount, the free spectrum range of the No. 1-5 arm 32 is larger than that of the laser, so that the longitudinal mode corresponding to the No. 1-5 arm 32 moves more. If realignment with the longitudinal mode of the laser is required, the hot electrode heating power in phase area 321 of arm No. 1-5 needs to be reduced to shift the longitudinal mode of its corresponding cavity to a short wavelength. Therefore, the heating power of the No. 1-5 arm thermode 321 is located at the right side of the parabola. On the contrary, in the case of the same phase change amount, the free spectrum range of arm No. 6-7 32 is smaller than that of the laser, so that the longitudinal mode shift corresponding to arm No. 6-7 32 is less. If realignment with the longitudinal mode of the laser is required, the hot electrode heating power in arm phase region # 6-7 321 needs to be increased to shift the longitudinal mode of its corresponding cavity toward longer wavelengths. Therefore, the heating power of the hot electrode of arm No. 6-7 321 is located at the left side of the parabola. The greater the difference between the free spectral range of each arm 32 and the free spectral range of the laser, the greater the deviation from the power curve vertex. The amount by which the heating power of the hot electrode of each arm 32 deviates from the apex of the power curve is related to the amount by which the lasing longitudinal mode deviates from the reflection peak.
The above is the characteristics of the multi-channel interference laser, and the flow of the wavelength characterization method for the multi-channel interference laser is shown in fig. 6 by combining the above characteristics, specifically as follows:
1) measuring PIV (power-current-voltage) curves of the thermodes in the common phase region 2 and the arm phase region 321 of the laser to obtain the relationship between the thermode injection current and the heating power;
2) measuring the gain spectrum red shift (wavelength shift) of the laser caused by thermal effect under small current (the current of the laser is above and close to the minimum threshold value and is smaller than the normal working current) and normal working current (such as 100 milliamperes), and offsetting the gain spectrum red shift (wavelength shift) by the compensation of a temperature controller of the laser; in this step, specifically, when the injection current of the active region 1 is set at a small current, the temperature controller setting temperature is adaptively higher than a normal value in normal operation, and when the injection current of the active region 1 is set at a normal operation current, the temperature controller sets a return value;
3) setting the injection current of the active region 1 to be a small current (above the current threshold of the laser and adjacent to the threshold), and selecting any one of the arms 32 as a reference, wherein the shortest arm 32 is taken as the reference; the heating power of the hot electrodes of the other seven arms 32 is adjusted to the top of the power curve by using an optimization algorithm and the lasing wavelength lambda is measured0And using it as initial wavelength; the optimization algorithm is a hill climbing algorithm developed for optimizing the arm phase region 321 based on parabolic fitting, the heating power of a 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 micro phase shift points, such as 0.02 pi, the output light power of the laser is monitored at the same time, the relationship between the heating power and the output light power is fitted through a parabola, the maximum value of the output light power is selected as an updated phase shift point, which is one-time optimization, and the seven arm phase regions 321 are completely optimized once; iteration and circulation are carried out, circulation is carried out until the maximum phase shift deviation in two adjacent wheels is smaller than a specified value, and the arm phase regions 321 (eight arm phase regions 321) are considered to be in the same phase state at the moment;
4) respectively scanning the heating power of the hot electrodes at the public phase area 2 and each arm phase area 321, measuring the output light power of the laser, and extracting the heating power required by pi phase shift generated by each phase area;
5) calculating the relationship between the heating power and the lasing frequency of the thermodes in the common phase region 2 and the phase region 321 of each arm theoretically by using the relationship between the phase change and the wavelength of the eight arms with different lengths of the laser;
in this step, the calculation method 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 be within the range of the appropriate heating power provided by the thermode: at an initial wavelength λ0For the origin, interpolating in the long and short wavelength directions at specified frequency intervals, e.g. ITU 50GHz intervals, each interpolated wavelength requires the thermoelectric power of the common phase region by first using the quasi-continuous tuning capability of the longitudinal modesThe heating power of the pole is moved to the maximum value of an output power curve, then the heating power of the hot pole at the seven arm phase regions 321 is adjusted to the top point of the power curve by using an optimization algorithm, and the real-time lasing wavelength is measured;
5.2) then fitting the relation between the heating power of the thermode and the lasing frequency in the common phase region 2 and each arm phase region 321 (eight arm phase regions 321) again according to the measured 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 if the difference exceeds a longitudinal mode interval, stopping interpolation;
in this way a practically tunable wavelength range lambda of the laser can be obtainedminAnd λmaxAnd a wavelength lookup table for a certain frequency interval at a small current in the active region 1;
6) setting the injection current of an active area 1 as a normal working current, scanning the heating power of a hot electrode at a common phase area 2 under the small current of the active area 1 from large to small and from small to large in two pi phase shift periods in sequence, monitoring the output light power or output wavelength, determining a hysteresis interval, setting the heating power of the hot electrode at the common phase area 2 in the middle of a non-hysteresis interval, measuring the real-time lasing wavelength and calculating the deviation from a target lasing wavelength;
7) adding the obtained wavelength deviation and the target wavelength under the normal working current of the active region 1, thereby compensating the target wavelength to the target wavelength, calibrating the wavelength under the low current again, and updating a wavelength lookup table under the low current of the active region 1; because the wavelength has deviation under the normal working current, the deviation is compensated into the target wavelength under the low current for calibration, and the frequency error can be eliminated by switching to the normal working current after calibration;
8) and stopping calibrating the wavelength which meets the wavelength error, and repeating the steps 7) and 8) for the wavelength which does not meet the wavelength error until the wavelength error requirement is met.
Claims (5)
1. A wavelength calibration method of a multi-channel interference laser comprises an active area (1), a common phase area (2) and a multi-channel interference area (3), wherein the multi-channel interference area (3) comprises N arms (32), N is a natural number not less than 2, each arm (32) is provided with an arm phase area (321), and the common phase area (2) and the arm phase areas (321) are respectively heated through a hot electrode; the method is characterized in that: the method comprises the following steps:
1) measuring PIV curves of the thermodes at the common phase region (2) and the arm phase region (321) of the laser, and acquiring the relation between the injection current and the heating power of the thermodes;
2) measuring gain spectrum red shift of the laser caused by a thermal effect under low current and normal working current, and offsetting the gain spectrum red shift through 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 the injection current of the active region (1) as a small current, selecting any one arm (32) as a reference, adjusting the heating power of the hot electrodes of the other N-1 arms (32) to the top point of a power curve by utilizing an optimization algorithm, and measuring the lasing wavelength lambda0And will be0As an initial wavelength;
4) respectively scanning the heating power of the hot electrodes at the public phase area (2) and each arm phase area (321), measuring the output light power of the laser, and extracting the heating power required by pi phase shift generated by each phase area;
5) calculating the relationship between the heating power and the lasing frequency of the common phase region (2) and the thermodes at the phase region (321) of each arm by using the relationship 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 area (1) as the current of normal work, scanning the heating power of the hot electrode at the common phase area (2) in the active area (1) under low current from large to small and from small to large in two pi phase shift periods in sequence, monitoring the output light power or the output wavelength, determining a hysteresis interval, setting the heating power of the hot electrode at the common phase area (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 normal current into a target wavelength, calibrating the wavelength under the low current of the active region (1) again, and updating a wavelength lookup table under the low current of the active region (1);
8) and stopping calibrating the wavelength which meets the wavelength error, and repeating the steps 7) and 8) for the wavelength which does not meet the wavelength error until the wavelength error requirement is met.
2. The method for calibrating the wavelength of a multi-channel interference laser according to claim 1, characterized in that: in step 2), the compensation method of the temperature controller is as follows: when the injection current of the active region (1) is set at a small current, the temperature controller sets the temperature higher than a normal value during normal operation, and when the injection current of the active region (1) is set at a normal operation current, the temperature controller sets the normal value.
3. The method for calibrating the wavelength of a multi-channel interference laser according to claim 1, characterized in that: in step 3), the arm (32) with the shortest length is taken as a reference.
4. The method for calibrating the wavelength of a multi-channel interference laser according to claim 1, characterized in that: in step 3), the optimization algorithm is a hill climbing algorithm based on parabolic fitting: selecting the heating power of a hot electrode at a certain arm (32), changing a plurality of preset phase shift points near an initial value, monitoring the output light power of the laser, fitting the relation between the heating power and the output light power through a parabola, and selecting the maximum value of the output light power as an updated phase shift point, wherein the phase shift point is optimized once, and the N-1 arm phase region (321) is completely optimized once; and (3) iterating the loop until the maximum phase shift deviation in two adjacent wheels is smaller than a specified value, and jumping out of the loop, wherein the phase regions (321) of the arms are considered to be in the same phase state.
5. The method for calibrating the wavelength of a multi-channel interference laser according to claim 1, characterized in that: in step 5), the calculation mode is as follows:
5.1) according to the actual heating power provided by the thermode, the theoretical requirementThe value is transformed into a plurality of pi phase shifts to be within the heating power range provided by the hot electrode: at an initial wavelength λ0Interpolation is carried out in the direction of long wavelength and short wavelength at the appointed frequency interval as the origin, the heating power of the hot electrode in the public phase area is moved to the maximum value of an output power curve by utilizing the quasi-continuous tuning capacity of a longitudinal mode for each interpolated wavelength, then the heating power of the hot electrode in the N-1 arm phase area (321) is adjusted to the top point of the power curve by utilizing an optimization algorithm, and the real-time lasing wavelength is measured;
5.2) then fitting the relation between the heating power of the thermode and the lasing frequency at the common phase area (2) and each arm phase area (321) again according to the measured real-time lasing wavelength; then returning to the 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 value lambda of the wavelength range of the laser which can be actually tunedminAnd maximum value λmaxAnd a wavelength lookup table for a certain frequency interval at a small current of the active region (1).
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