Wavelength map data acquisition apparatus and acquisition method

Abstract

The present invention provides a wavelength map data acquisition device comprising: an optical spectrum analyzer or wavelength meter (308) that measures the oscillation wavelengths of a DBR laser (100) when a first current having a first fixed value is injected into a DBR region and a second current injected into a phase adjustment region is varied, and when a second current having a second fixed value is injected into the phase adjustment region and the first current is varied; a boundary approximation unit (312) that uses a quadratic function to approximate the boundary where mode hop occurs on a wavelength map representing the oscillation wavelengths generated by combinations of the first and second currents; and a wavelength determination unit (313) that determines data of oscillation wavelengths for positions other than the boundary where mode hop occurs on the wavelength map.

Description

Technical Field

[0001] The present invention relates to a wavelength map data acquisition device and an acquisition method for acquiring wavelength map data representing the oscillation wavelength characteristics of a distributed feedback wavelength tunable semiconductor laser.

Background Art

[0002] Wavelength tunable lasers are useful light sources used in a wide range of fields such as wavelength division multiplexing transmission, optical measurement, optical frequency swept OCT (Optical Coherence Tomography), laser light spectroscopy, and optical sensitivity measurement. Among them, wavelength tunable semiconductor lasers using a semiconductor as a gain medium are widely used in various fields because they have low power consumption, are small in size, and are easy to handle.

[0003] Wavelength tunable semiconductor lasers are mainly classified into three types according to their structures: distributed feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers, and external resonator lasers.

[0004] DFB lasers employ a simple structure in which a grating is formed on an active layer, and wavelength tunability is achieved by adjusting the injection current amount or the temperature of the chip. DBR lasers do not have a grating disposed on the active region, but have DBR gratings disposed on both sides or one side of the active region. Also, usually, a phase adjustment region is provided to perform phase matching. DBR lasers achieve wavelength tunability by using the carrier plasma effect that occurs when current is injected into a DBR region independent of the active region. External resonator lasers have a mirror disposed outside the active region, and wavelength tunability is achieved by mechanically moving the mirror. In the case of semiconductor lasers, MEMS (Micro Electro Mechanical Systems) mirrors are usually used to reduce the footprint.

[0005] Of the three types of tunable semiconductor lasers described above, DBR lasers have the characteristics of being high-speed and having a certain degree of tunability. When controlling a DBR laser, acquiring oscillation wavelength map data is extremely important. However, acquiring oscillation wavelength map data takes an enormous amount of time, as described below, which has resulted in a significant decrease in the productivity of DBR lasers.

[0006] To explain the conventional challenges, we will first describe the structure of the DBR laser. Figure 7 shows an example of the configuration of the DBR laser 100. On the semiconductor substrate 101, an active region 105 consisting of multiple quantum wells, an SOA (Semiconductor Optical Amplifier) ​​region 109 consisting of multiple quantum wells, a forward DBR region 106 consisting of bulk material, a backward DBR region 107 consisting of bulk material, and a phase adjustment region 108 consisting of bulk material are formed. Furthermore, an overcladding 104 is formed on top of these regions.

[0007] A lower electrode 110 is formed beneath the semiconductor substrate 101. Additionally, on the overclad 104, an active region electrode 111 is formed above the active region 105, an SOA region electrode 115 is formed above the SOA region 109, a front DBR region electrode 112 is formed above the front DBR region 106, a rear DBR region electrode 113 is formed above the rear DBR region 107, and a phase adjustment region electrode 114 is formed above the phase adjustment region 108.

[0008] Next, we will explain the role of each region in laser oscillation and wavelength control. The forward DBR region 106, the phase adjustment region 108, and the rear DBR region 107 constitute a resonator. The light generated in the active region 105 becomes a laser oscillation by the resonator, is amplified by the SOA region 109, and is emitted from the right side of Figure 7. The resonator determines the oscillation wavelength. In Figure 7, I1 is the current applied to the active region electrode 111, I2 is the DBR current applied to the forward DBR region electrode 112 and the rear DBR region electrode 113, I3 is the phase adjustment current applied to the phase adjustment region electrode 114, and I4 is the current applied to the SOA region electrode 115.

[0009] Next, the wavelength map will be explained. Figure 8 shows an example of a wavelength map for the DBR laser 100. The wavelength map uses the DBR current injected into the DBR region on the horizontal axis and the phase adjustment current injected into the phase adjustment region 108 on the vertical axis. The oscillation wavelength of the DBR laser 100 generated by the combination of these two currents is represented by a single color or a closed region color filled with hatching. The DBR current is the total amount of current that flows when the front DBR region 106 and the rear DBR region 107 are electrically connected.

[0010] Mode hopping does not occur in regions where the color changes continuously in the wavelength map (closed regions filled with a single color or hatching in Figure 8), but it does occur when the oscillation wavelength changes discontinuously beyond a boundary. The boundary where mode hopping occurs is called a boundary. From the wavelength map, it can be seen that some degree of wavelength tuning can be achieved by injecting current only into the DBR regions 106 and 107 without injecting current into the phase adjustment region 108, and also by injecting current only into the phase adjustment region 108 without injecting current into the DBR regions 106 and 107. However, since mode hopping occurs immediately, the method of injecting current into only one of the DBR regions 106 and 107 or the phase adjustment region 108 only allows for continuous changes in the oscillation wavelength within a range of about 1 nm at best.

[0011] Currently, continuous wavelength tuning of 5 nm or more is achieved by injecting current into both the DBR regions 106, 107 and the phase adjustment region 108 (see Non-Patent Literature 1). In the method disclosed in Non-Patent Literature 1, the same power supply is divided by resistors to synchronously inject current into the DBR regions 106, 107 and the phase adjustment region 108, achieving wavelength tuning of 5.6 nm. In the method disclosed in Non-Patent Literature 2, control is performed by using separate power supplies that synchronize the current injected into the DBR regions 106, 107 and the current injected into the phase adjustment region 108. The methods disclosed in Non-Patent Literature 1 and Non-Patent Literature 2 are essentially the same control methods.

[0012] Thus, according to the control methods disclosed in Non-Patent Documents 1 and 2, the oscillation wavelength of a DBR laser can be continuously changed in a range of 5 nm or more. However, in order to realize this control method, it is necessary to acquire wavelength map data.

[0013] Here, we will explain the specific method for acquiring wavelength map data. As mentioned above, the oscillation wavelength of a DBR laser is determined by applying separate currents to two types of regions: the DBR regions 106 and 107 and the phase adjustment region 108. Therefore, in order to control a desired DBR laser, it is necessary to acquire the oscillation wavelength of the DBR laser in advance for each combination of the DBR current value and the phase adjustment current value.

[0014] Figure 9 is a block diagram showing the configuration of a conventional wavelength map data acquisition device. The wavelength map data acquisition device consists of a current source 302 for injecting current into the active region 105 of the DBR laser 100, a current source 303 for injecting current into the SOA region 109, a current source 304 for injecting current into the DBR regions 106 and 107, a current source 305 for injecting current into the phase adjustment region 108, wiring 306a connecting the electrode 111 of the DBR laser 100 to the current source 302, wiring 306b connecting the electrode 115 to the current source 303, wiring 306c connecting the electrodes 112 and 113 to the current source 304, wiring 306d connecting the electrode 114 to the current source 305, an optical cable 307 for guiding light from the DBR laser 100, and an optical spectrum analyzer or wavelength meter 308.

[0015] Current sources 302-305 are connected to the four regions of the DBR laser 100 (active region 105, SOA region 109, DBR regions 106, 107, and phase adjustment region 108), respectively. A constant current is applied to the active region 105 and the SOA region 109. For the DBR regions 106, 107 and the phase adjustment region 108, the current is applied while varying by a small amount. The spectral shape of the laser light emitted from the DBR laser 100 is measured using an optical spectrum analyzer or wavelength meter 308.

[0016] In this way, wavelength map data can be acquired by measuring the oscillation wavelength of the DBR laser 100 while changing the combination of DBR current value and phase adjustment current value. The time required for measurement varies depending on the model and settings of the optical spectrum analyzer or wavelength meter 308, as well as the current range and current interval being measured, but it usually takes several hours or more to acquire the wavelength map data. [Prior art documents] [Non-patent literature]

[0017] [Non-Patent Document 1] Takuya Kanai,et al.,“First Demonstration of 2μm Wavelength Tunable Distributed Bragg Reflector Laser Diode”,The Proceedings of the 25th International Semiconductor Laser Conference,Kobe,Japan,TuB4,Sep.2016 [Non-Patent Document 2] M.Abe,et al.,“4-nm continuous rapid sweeping spectroscopy in 2 m band using distributed Bragg reflector laser”,Applied Physics B,123:260,2017 [Overview of the project] [Problems that the invention aims to solve]

[0018] The present invention was made to solve the above problems and aims to provide a wavelength map data acquisition device and acquisition method that can significantly reduce the acquisition time of wavelength map data. [Means for solving the problem]

[0019] The wavelength map data acquisition apparatus of the present invention comprises a current source configured to inject current into a distributed reflection type tunable semiconductor laser; a measurement unit configured to measure the oscillation wavelength of the semiconductor laser when a first current of a first fixed value is injected into the DBR region of the semiconductor laser and a second current injected into the phase adjustment region of the semiconductor laser is changed, and the oscillation wavelength when a second current of a second fixed value is injected into the phase adjustment region and the first current injected into the DBR region is changed; and a wavelength map representing the oscillation wavelength generated by the combination of the first and second currents, wherein the first current is set to the first fixed value axis. The present invention is characterized by comprising: a mode-hop point extraction unit configured to extract pairs of the first current value and the second current value for each axis at points where a mode-hop occurs on an axis where the second current is set to the second fixed value; a boundary approximation unit configured to approximate the boundary where a mode-hop occurs on the wavelength map using a quadratic function based on the processing results of the mode-hop point extraction unit; and a wavelength determination unit configured to determine the oscillation wavelength data for positions on the wavelength map other than the boundary where a mode-hop occurs, based on the measurement results of the measurement unit and the processing results of the boundary approximation unit.

[0020] Further, the method for obtaining wavelength map data of the present invention injects a first current of a first fixed value into the DBR region of a distributed reflection type wavelength-variable semiconductor laser, and changes the oscillation wavelength of the semiconductor laser when changing the second current injected into the phase adjustment region of the semiconductor laser, and a first step of measuring the oscillation wavelength when injecting a second current of a second fixed value into the phase adjustment region and changing the first current injected into the DBR region; in the wavelength map representing the oscillation wavelength generated by the combination of the first and second currents, on the axis with the first current as the first fixed value and on the axis with the second current as the second fixed value, a second step of extracting the pair of the first current value and the value of the second current at the point where a mode hop appears for each axis; a third step of approximating the boundary where the mode hop occurs on the wavelength map by a quadratic function based on the processing result of the second step; and a fourth step of determining the data of the oscillation wavelength at positions other than the boundary where the mode hop occurs on the wavelength map based on the measurement result of the first step and the processing result of the third step.

Advantages of the Invention

[0021] According to the present invention, by providing a measurement unit, a mode hop point extraction unit, a boundary approximation unit, and a wavelength determination unit, wavelength map data of a distributed reflection type wavelength-variable semiconductor laser can be obtained in a short time. As a result, in the present invention, the productivity of the wavelength-variable semiconductor laser can be significantly improved.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a block diagram showing the configuration of a wavelength map data acquisition apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining a method of obtaining wavelength map data of an embodiment of the present invention. [Figure 3] FIG. 3 is a flowchart for explaining the operation of a wavelength map data acquisition apparatus according to an embodiment of the present invention. [Figure 4]FIG. 4 is a flowchart for explaining the operation of the wavelength map data acquisition device according to an embodiment of the present invention. [Figure 5] FIG. 5 is a flowchart for explaining the operation of the wavelength map data acquisition device according to an embodiment of the present invention. [Figure 6] FIG. 6 is a block diagram showing a configuration example of a computer that realizes the wavelength map data acquisition device according to an embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing an example of the configuration of a DBR laser. [Figure 8] FIG. 8 is a diagram showing an example of the wavelength map of a DBR laser. [Figure 9] FIG. 9 is a block diagram showing the configuration of a conventional wavelength map data acquisition device.

MODE FOR CARRYING OUT THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the wavelength map data acquisition device according to an embodiment of the present invention, and the same components as those in FIG. 9 are denoted by the same reference numerals. The configuration of the DBR laser 100 is as shown in FIG. 7.

[0024] The wavelength map data acquisition device of this embodiment includes a current source 302 that injects current into the active region 105 of the DBR laser 100, a current source 303 that injects current into the SOA region 109, a current source 304 that injects current into the DBR regions 106 and 107, a current source 305 that injects current into the phase adjustment region 108, a wiring 306a that connects the electrode 111 of the DBR laser 100 and the current source 302, a wiring 306b that connects the electrode 115 and the current source 303, a wiring 306c that connects the electrodes 112 and 113 and the current source 304, a wiring 306d that connects the electrode 114 and the current source 305, an optical cable 307 that guides the light from the DBR laser 100, and an optical spectrum analyzer or wavelength meter 308 (measurement unit) that measures the wavelength of the laser light emitted from the DBR laser 100.

[0025] Furthermore, the wavelength map data acquisition device includes a control unit 309 that controls current sources 302 to 305, a storage unit 310 that stores measurement results, a mode hop point extraction unit 311 that extracts pairs of DBR current values ​​and phase adjustment current values ​​at points where mode hops occur in the wavelength map, a boundary approximation unit 312 that approximates the boundary where a mode hop occurs on the wavelength map using a quadratic function, and a wavelength determination unit 313 that determines the oscillation wavelength data of the DBR laser 100 for positions on the wavelength map other than the boundary where a mode hop occurred.

[0026] Figure 2 is a diagram illustrating the method for acquiring wavelength map data in this embodiment, and Figures 3 to 5 are flowcharts illustrating the operation of the wavelength map data acquisition device. In this embodiment, for example, the minimum and maximum values ​​of the current applied to the DBR regions 106 and 107 are known values ​​depending on the specifications of the DBR laser 100 from which the wavelength map data is to be acquired, and the minimum and maximum values ​​of the current injected into the phase adjustment region 108 are also known values. The control unit 309 controls the current sources 302 and 303 to inject predetermined currents into the DBR laser 100 and the SOA region 109, respectively.

[0027] First, the control unit 309 controls the current source 304 to inject a specified minimum value of DBR current into the DBR regions 106 and 107 of the DBR laser 100, and controls the current source 305 to change the phase adjustment current injected into the phase adjustment region 108 of the DBR laser 100 from a specified minimum value to a specified maximum value (Figure 3, step S100). The optical spectrum analyzer or wavelength meter 308 measures the wavelength of the laser light when the phase adjustment current changes from a minimum value to a maximum value (Figure 3, step S101). The processes in steps S100 and S101 measure the change in wavelength along the y1 axis in Figure 2, and the measurement result (201 in Figure 2) is stored in the storage unit 310.

[0028] Next, the control unit 309 controls the current source 304 to inject a predetermined maximum value of DBR current into the DBR regions 106 and 107, and controls the current source 305 to change the phase adjustment current injected into the phase adjustment region 108 from a predetermined minimum value to a predetermined maximum value (Figure 3, step S102). The optical spectrum analyzer or wavelength meter 308 measures the wavelength of the laser light when the phase adjustment current changes from the minimum value to the maximum value (Figure 3, step S103). The processes in steps S102 and S103 measure the change in wavelength on the y2 axis in Figure 2, and the measurement result (202 in Figure 2) is stored in the storage unit 310.

[0029] Next, the control unit 309 controls the current source 305 to inject a specified minimum value of phase adjustment current into the phase adjustment region 108, and controls the current source 304 to change the DBR current injected into the DBR regions 106 and 107 from a specified minimum value to a specified maximum value (Figure 3, step S104). The optical spectrum analyzer or wavelength meter 308 measures the wavelength of the laser light when the DBR current changes from a minimum value to a maximum value (Figure 3, step S105). The processes in steps S104 and S105 measure the change in wavelength along the x1 axis in Figure 2, and the measurement result (203 in Figure 2) is stored in the storage unit 310.

[0030] Next, the control unit 309 controls the current source 305 to inject a phase adjustment current of a predetermined maximum value into the phase adjustment region 108, and controls the current source 304 to change the DBR current injected into the DBR regions 106 and 107 from a predetermined minimum to a predetermined maximum value (Figure 3, step S106). The optical spectrum analyzer or wavelength meter 308 measures the wavelength of the laser light when the DBR current changes from the minimum to the maximum value (Figure 3, step S107). The processes in steps S106 and S107 measure the change in wavelength on the x2 axis in Figure 2, and the measurement result (204 in Figure 2) is stored in the storage unit 310.

[0031] Next, the control unit 309 controls the current source 304 to inject a DBR current that is the midpoint between a specified minimum and maximum value into the DBR regions 106 and 107, and controls the current source 305 to change the phase adjustment current injected into the phase adjustment region 108 from a specified minimum to a specified maximum value (Figure 3, step S108). The optical spectrum analyzer or wavelength meter 308 measures the wavelength of the laser light when the phase adjustment current changes from the minimum to the maximum value (Figure 3, step S109). The processes in steps S108 and S109 measure the change in wavelength along the y3 axis in Figure 2, and the measurement results are stored in the storage unit 310.

[0032] Next, the control unit 309 controls the current source 305 to inject a phase adjustment current that is the midpoint between a specified minimum and maximum value into the phase adjustment region 108, and controls the current source 304 to change the DBR current injected into the DBR regions 106 and 107 from a specified minimum to a specified maximum value (Figure 3, step S110). The optical spectrum analyzer or wavelength meter 308 measures the wavelength of the laser light when the DBR current changes from the minimum to the maximum value (Figure 3, step S111). The processes in steps S110 and S111 measure the change in wavelength on the x3 axis in Figure 2, and the measurement results are stored in the storage unit 310.

[0033] Next, the mode-hop point extraction unit 311 extracts pairs of DBR current values ​​and phase adjustment current values ​​for each axis at points on the y1 axis, y2 axis, x1 axis, x2 axis, y3 axis, and x3 axis where mode-hops with discontinuous changes in wavelength occur, based on the measurement results stored in the memory unit 310 (Figure 4, step S112).

[0034] The boundary approximation unit 312 initializes the variable i, which is used to count mode hops appearing on the y1 axis, to 1, and the variable p, which is used to count mode hops appearing on the x3 axis, to 1 (Figure 4, step S113). Based on the extraction results by the mode hop point extraction unit 311, if the boundary approximation unit 312 determines that it cannot utilize the p-th closest point among the mode hops appearing on the x3 axis to the minimum value of the DBR current (NO in Figure 4, step S114), it calculates a quadratic function connecting the i-th closest point among the mode hops appearing on the y1 axis to the maximum value of the phase adjustment current and the i-th closest point among the mode hops appearing on the x2 axis to the minimum value of the DBR current (Figure 4, step S115).

[0035] Furthermore, if the boundary approximation unit 312 determines that it can utilize the point that is the p-th closest to the minimum value of the DBR current among the mode hops appearing on the x3 axis (YES in step S114), it calculates a quadratic function connecting three points: the point that is the i-th closest to the maximum value of the phase adjustment current among the mode hops appearing on the y1 axis, the point that is the i-th closest to the minimum value of the DBR current among the mode hops appearing on the x2 axis, and the point that is the p-th closest to the minimum value of the DBR current among the mode hops appearing on the x3 axis (Figure 4, step S116).

[0036] If the y-coordinate of the i-th point among the mode hops appearing on the x2 axis that is closest to the minimum DBR current exceeds (maximum phase adjustment current - minimum phase adjustment current) ÷ 2, the determination in step S114 is NO. If the y-coordinate of the i-th point among the mode hops appearing on the x2 axis that is closest to the minimum DBR current is less than or equal to (maximum phase adjustment current - minimum phase adjustment current) ÷ 2, the determination in step S114 is YES.

[0037] The boundary approximation unit 312 repeatedly performs the process in step S115, increasing the variable i by 1 each time (Figure 4, step S118) until there are no more points on the y1 axis where mode hopping occurs (YES in Figure 4, step S117). The boundary approximation unit 312 also repeatedly performs the process in step S116, increasing the variables i and p by 1 each time (Figure 4, step S120) until there are no more points on the y1 axis where mode hopping occurs (YES in Figure 4, step S119).

[0038] The boundary approximation section 312 initializes the variable j, which counts mode hops that appear on the x1 axis, to 1 after there are no more points on the y1 axis where mode hops have appeared (YES in steps S117 and S119) (Figure 4, step S121).

[0039] If the boundary approximation unit 312 determines, based on the extraction results by the mode hop point extraction unit 311, that it cannot utilize the p-th closest point to the minimum DBR current among the mode hops appearing on the x3 axis (NO in step S122 of Figure 4), it calculates a quadratic function connecting the j-th closest point to the minimum DBR current among the mode hops appearing on the x1 axis and the i-th closest point to the minimum DBR current among the mode hops appearing on the x2 axis (step S123 of Figure 4).

[0040] Furthermore, if the boundary approximation unit 312 determines that it can utilize the p-th closest point to the minimum DBR current among the mode hops appearing on the x3 axis (YES in step S122), it calculates a quadratic function connecting three points: the j-th closest point to the minimum DBR current among the mode hops appearing on the x1 axis, the i-th closest point to the minimum DBR current among the mode hops appearing on the x2 axis, and the p-th closest point to the minimum DBR current among the mode hops appearing on the x3 axis (Figure 4, step S124).

[0041] If the y-coordinate of the i-th point closest to the minimum DBR current among the mode hops appearing on the x2 axis is less than or equal to (maximum phase adjustment current - minimum phase adjustment current) ÷ 2, the determination in step S122 is NO. If the y-coordinate of the i-th point closest to the minimum DBR current among the mode hops appearing on the x2 axis is greater than (maximum phase adjustment current - minimum phase adjustment current) ÷ 2, the determination in step S122 is YES.

[0042] The boundary approximation unit 312 repeatedly performs the process in step S123, increasing the variables i and j by 1 each time (Figure 4, step S126) until there are no more points on the x2 axis where mode hopping occurs (YES in Figure 4, step S125). The boundary approximation unit 312 also repeatedly performs the process in step S124, increasing the variables i, j, and p by 1 each time (Figure 4, step S128) until there are no more points on the x2 axis where mode hopping occurs (YES in Figure 4, step S127).

[0043] The boundary approximation unit 312 initializes the variable k, which is used to count mode hops that have appeared on the y2 axis, to 1 after there are no more points on the x2 axis where mode hops have appeared (YES in steps S125 and S127) (Figure 5, step S129).

[0044] If the boundary approximation unit 312 determines, based on the extraction results by the mode hop point extraction unit 311, that it cannot utilize the p-th closest point among the mode hops appearing on the x3 axis to the minimum value of the DBR current (NO in step S130 of Figure 5), it calculates a quadratic function connecting the k-th closest point among the mode hops appearing on the y2 axis to the maximum value of the phase adjustment current and the j-th closest point among the mode hops appearing on the x1 axis to the minimum value of the DBR current (step S131 of Figure 5).

[0045] Furthermore, if the boundary approximation unit 312 determines that it can utilize the p-th closest point to the minimum DBR current among the mode hops appearing on the x3 axis (YES in step S130), it calculates a quadratic function connecting three points: the k-th closest point to the maximum value of the phase adjustment current among the mode hops appearing on the y2 axis, the j-th closest point to the minimum DBR current among the mode hops appearing on the x1 axis, and the p-th closest point to the minimum DBR current among the mode hops appearing on the x3 axis (Figure 5, step S132).

[0046] If the y-coordinate of the j-th point closest to the minimum DBR current among the mode hops appearing on the x1 axis exceeds (maximum phase adjustment current - minimum phase adjustment current) ÷ 2, the determination in step S130 is NO. If the y-coordinate of the j-th point closest to the minimum DBR current among the mode hops appearing on the x1 axis is less than or equal to (maximum phase adjustment current - minimum phase adjustment current) ÷ 2, the determination in step S130 is YES.

[0047] The boundary approximation unit 312 repeatedly performs the process in step S131, increasing the variables j and k by 1 each time (Figure 5, step S134) until there are no more points on the y2 axis where mode hopping occurs (YES in Figure 5, step S133). The boundary approximation unit 312 also repeatedly performs the process in step S132, increasing the variables j, k, and p by 1 each time (Figure 5, step S126) until there are no more points on the y2 axis where mode hopping occurs (YES in Figure 5, step S135). In this way, the boundaries where mode hopping occurs on the wavelength map can be approximately represented by a single quadratic function or by multiple intersecting quadratic functions.

[0048] In the example above, we described a case where mode hop points appearing on the x3 axis can be utilized. However, if mode hop points appearing on the y3 axis can be utilized instead of those appearing on the x3 axis, then mode hop points appearing on the x3 axis may be used instead.

[0049] Next, the wavelength determination unit 313 determines the oscillation wavelength of the DBR laser 100 for positions on the wavelength map other than the boundary where mode hopping occurred, based on the measurement results stored in the memory unit 310 and the processing results of the boundary approximation unit 312 (Figure 5, step S137). As described above, the processing in steps S100 to S111 has already obtained the relationship between the phase adjustment current and the oscillation wavelength of the DBR laser 100 at the minimum, intermediate, and maximum values ​​of the DBR current, and the relationship between the DBR current and the oscillation wavelength of the DBR laser 100 at the minimum, intermediate, and maximum values ​​of the phase adjustment current. Therefore, if the horizontal axis of the wavelength map is I_dbr and the vertical axis is I_phase, the oscillation wavelength λ of the DBR laser 100 at the position (I_dbr, I_phase) on the wavelength map can be determined using the obtained relationships.

[0050] The change in oscillation wavelength λ when the DBR current I_dbr is changed can be approximated by a simple quadratic function within the range where mode hopping does not occur. Therefore, a finite number of quadratic functions λ(I_dbr) are calculated for the x1, x2, and x3 axes, respectively.

[0051] Specifically, the wavelength determination unit 313 calculates a quadratic function λ_x1(I_dbr) on the x1 axis based on the measurement results of steps S104 and S105 (203 in Figure 2). Since the measurement results are discontinuous at the points where mode hopping occurs, the change in wavelength λ when the DBR current I_dbr is changed is expressed by multiple quadratic functions λ_x1(I_dbr). For example, in the example of measurement result 203 in Figure 2, there are six discontinuities in wavelength λ, so the changes in wavelength λ before and after the discontinuities are approximated by different quadratic functions λ_x1(I_dbr), and a total of seven quadratic functions λ_x1(I_dbr) are calculated.

[0052] Furthermore, the wavelength determination unit 313 calculates a quadratic function λ_x2(I_dbr) on the x2 axis based on the measurement results of steps S106 and S107 (204 in Figure 2). For example, in the case of measurement result 204 in Figure 2, there are 5 discontinuities in the wavelength λ, so 6 quadratic functions λ_x2(I_dbr) are calculated. The wavelength determination unit 313 also calculates a quadratic function λ_x3(I_dbr) on the x3 axis based on the measurement results of steps S110 and S111.

[0053] Similarly, the change in oscillation wavelength λ when the phase adjustment current I_phase is changed can be approximated by a simple quadratic function within the range where mode hopping does not occur. Therefore, a finite number of quadratic functions λ(I_phase) are calculated for the y1, y2, and y3 axes, respectively.

[0054] Specifically, the wavelength determination unit 313 calculates a quadratic function λ_y1(I_phase) on the y1 axis based on the measurement results of steps S100 and S101 (201 in Figure 2). For example, in the case of measurement result 201 in Figure 2, there are two discontinuities in the wavelength λ, so three quadratic functions λ_y1(I_phase) are calculated.

[0055] Furthermore, the wavelength determination unit 313 calculates a quadratic function λ_y2(I_phase) on the y2 axis based on the measurement results of steps S102 and S103 (202 in Figure 2). For example, in the case of measurement result 202 in Figure 2, there are two discontinuities in the wavelength λ, so three quadratic functions λ_y2(I_phase) are calculated. The wavelength determination unit 313 also calculates a quadratic function λ_y3(I_phase) on the y3 axis based on the measurement results of steps S108 and S109.

[0056] In this way, the quadratic functions λ_x1(I_dbr), λ_x2(I_dbr), λ_x3(I_dbr), λ_y1(I_phase), λ_y2(I_phase), and λ_y3(I_phase) can be calculated.

[0057] Here, the coordinates of the position on the wavelength map other than the boundary where mode hopping occurred are defined as I_dbr=x and I_phase=y. The wavelength determination unit 313 calculates the wavelength λ corresponding to the position (x,y) on the wavelength map based on the quadratic functions λ_x1(I_dbr), λ_x2(I_dbr), λ_x3(I_dbr), λ_y1(I_phase), λ_y2(I_phase), and λ_y3(I_phase) for each of the four axes closest to the position (x,y), and sets the representative value of the four calculated wavelengths λ as the wavelength λ(x,y) at position (x,y).

[0058] For example, if the position (x,y) is in a region enclosed by the x2 axis, x3 axis, y1 axis, and y3 axis, the wavelength determination unit 313 calculates the wavelength λ_x2(x) from a quadratic function λ_x2(I_dbr) with respect to the x2 axis, the wavelength λ_x3(x) from a quadratic function λ_x3(I_dbr) with respect to the x3 axis, the wavelength λ_y1(y) from a quadratic function λ_y1(I_phase) with respect to the y1 axis, and the wavelength λ_y3(y) from a quadratic function λ_y3(I_phase) with respect to the y3 axis.

[0059] The wavelength determination unit 313 sets the wavelength λ(x,y) at position (x,y) as a representative value for the four wavelengths λ_x2(x), λ_x3(x), λ_y1(y), and λ_y3(y). A representative value could be, for example, the average value. Note that if I_dbr=x is a discontinuity point in the quadratic function λ_x2(I_dbr), the wavelength λ_x2(x) will be an indeterminate value and will be excluded from the calculation of the representative value. If I_dbr=x is a discontinuity point in the quadratic function λ_x3(I_dbr), the wavelength λ_x3(x) will be an indeterminate value and will be excluded from the calculation of the representative value. If I_phase=y is a discontinuity point in the quadratic function λ_y1(I_phase), the wavelength λ_y1(y) will be an indeterminate value and will be excluded from the calculation of the representative value. If I_phase=y is a discontinuity point in the quadratic function λ_y3(I_phase), the wavelength λ_y3(y) will be an indeterminate value and will be excluded from the calculation of the representative value.

[0060] In this way, the wavelength λ(x,y) can be determined for each position (x,y) on the wavelength map other than the boundary where mode hopping occurs, and wavelength map data (x,y,λ(x,y)) can be obtained. The wavelength map data (x,y,λ(x,y)) is stored in the storage unit 310. If the position (x,y) lies on the boundary determined by the boundary approximation unit 312, an undefined value is stored as the wavelength λ(x,y). In this embodiment, wavelength map data, which represents the wavelength characteristics of DBR lasers and similar lasers, can be acquired in a short time.

[0061] The following describes specific examples of the effects of this embodiment. First, we will describe the case when the conventional method is used. A current of 100 mA is applied to the active region 105 and the SOA region 109 of the DBR laser 100, respectively. In addition, currents of 0 mA to 20 mA are applied to the DBR regions 106, 107 and the phase adjustment region 108 at intervals of 0.05 mA, 0.10 mA, and 0.25 mA, respectively.

[0062] As shown in Table 1, with the conventional method, acquiring wavelength λ data at current intervals of 0.25 mA results in 6561 measurement points, and since each measurement takes 4 seconds, the total measurement time is 7.3 hours. Similarly, acquiring wavelength λ data at current intervals of 0.1 mA takes 44.9 hours, and acquiring wavelength λ data at current intervals of 0.05 mA takes a staggering 178.7 hours.

[0063] [Table 1]

[0064] Next, we will describe the case when the wavelength map data acquisition device of this embodiment is used. As shown in Table 1, when the wavelength map data acquisition device of this embodiment is used, the number of measurement points when wavelength λ data is acquired at current intervals of 0.25 mA is 486, and the measurement time per measurement is 4 seconds, so the total measurement time is 0.54 hours. Similarly, the measurement time when wavelength λ data is acquired at current intervals of 0.1 mA is 1.34 hours, and the measurement time when wavelength λ data is acquired at current intervals of 0.05 mA is 2.67 hours, showing that the measurement time can be significantly reduced compared to conventional methods. In reality, it is necessary to calculate the wavelength map data based on the measured data, but the calculation processing time is at most about 30 minutes, so the productivity of the DBR laser can be improved by more than 7 times compared to conventional methods.

[0065] The control unit 309, storage unit 310, mode hop point extraction unit 311, boundary approximation unit 312, and wavelength determination unit 313 of the wavelength map data acquisition device described in this embodiment can be realized by a computer equipped with a CPU (Central Processing Unit), storage device, and interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 6.

[0066] The computer comprises a CPU 400, a storage device 401, and an interface device (I / F) 402. Current sources 302-305 and an optical spectrum analyzer or wavelength meter 308 are connected to the I / F 402. In such a computer, the program for realizing the wavelength map data acquisition method of the present invention is stored in the storage device 401. The CPU 400 executes the processing described in this embodiment according to the program stored in the storage device 401.

[0067] Some or all of the above examples may also be described as follows, but are not limited to the following:

[0068] (Note 1) The wavelength map data acquisition apparatus of the present invention includes a current source configured to inject current into a distributed reflection type tunable semiconductor laser, a measurement unit configured to measure the oscillation wavelength of the semiconductor laser when a first fixed current is injected into the DBR region of the semiconductor laser and a second current injected into the phase adjustment region of the semiconductor laser is changed, and the oscillation wavelength when a second fixed current is injected into the phase adjustment region and the first current injected into the DBR region is changed, and a wavelength map representing the oscillation wavelength generated by the combination of the first and second currents, wherein the first current is The system includes a mode-hop point extraction unit configured to extract pairs of the first current value and the second current value for each axis at points where a mode-hop occurs on an axis with a fixed value of 1 and an axis with a second fixed current value; a boundary approximation unit configured to approximate the boundary where a mode-hop occurs on the wavelength map using a quadratic function based on the processing results of the mode-hop point extraction unit; and a wavelength determination unit configured to determine the oscillation wavelength data for positions on the wavelength map other than the boundary where a mode-hop occurs, based on the measurement results of the measurement unit and the processing results of the boundary approximation unit.

[0069] (Note 2) The wavelength map data acquisition device described in Note 1 further comprises a control unit configured to control the current source, wherein, during measurement by the measurement unit, the control unit sets the first fixed value and the second fixed value to three predetermined values: a minimum value, an intermediate value, and a maximum value, respectively, and when injecting the first current of the first fixed value into the DBR region, it changes the second current injected into the phase adjustment region from the minimum value to the maximum value, and when injecting the second current of the second fixed value into the phase adjustment region, it changes the first current injected into the DBR region from the minimum value to the maximum value.

[0070] (Note 3) In the wavelength map data acquisition device described in Note 1, the boundary approximation unit approximates the boundary where a mode hop occurred on the wavelength map by calculating a quadratic function that connects the mode hop points that appeared on the axis where the first current is set to the first fixed value in the wavelength map and the mode hop points that appeared on the axis where the second current is set to the second fixed value in the wavelength map.

[0071] (Note 4) In the wavelength map data acquisition device described in Note 1, the wavelength determination unit calculates a quadratic function that approximates the change in the oscillation wavelength for each axis on which the first current is set to the first fixed value and the second current is set to the second fixed value in the wavelength map, and determines the data of the oscillation wavelength for positions on the wavelength map other than the boundary where mode hopping occurs based on these quadratic functions.

[0072] (Note 5) The wavelength map data acquisition method of the present invention comprises: a first step of injecting a first fixed value first current into the DBR region of a distributed reflection type tunable semiconductor laser and measuring the oscillation wavelength of the semiconductor laser when a second current injected into the phase adjustment region of the semiconductor laser is changed, and measuring the oscillation wavelength when a second fixed value second current is injected into the phase adjustment region and the first current injected into the DBR region is changed; and in a wavelength map representing the oscillation wavelength generated by the combination of the first and second currents, the first current is the first fixed value The method includes: a second step of extracting pairs of the first current value and the second current value for each axis at points where mode hops occur on an axis with a fixed value and on an axis with the second current set as the second fixed value; a third step of approximating the boundary where mode hops occurred on the wavelength map with a quadratic function based on the processing results of the second step; and a fourth step of determining the oscillation wavelength data for positions on the wavelength map other than the boundary where mode hops occurred, based on the measurement results of the first step and the processing results of the third step.

[0073] (Note 6) In the wavelength map data acquisition method described in Note 5, the first step includes setting the first fixed value and the second fixed value to three predetermined values: a minimum value, an intermediate value, and a maximum value, varying the second current injected into the phase adjustment region from the minimum value to the maximum value when injecting the first current of the first fixed value into the DBR region, and varying the first current injected into the DBR region from the minimum value to the maximum value when injecting the second current of the second fixed value into the phase adjustment region.

[0074] (Note 7) In the wavelength map data acquisition method described in Note 5, the third step includes a step of approximating the boundary where a mode hop occurred on the wavelength map by a quadratic function, by calculating a quadratic function that connects the mode hop points that appeared on the axis where the first current is set as the first fixed value in the wavelength map and the mode hop points that appeared on the axis where the second current is set as the second fixed value in the wavelength map.

[0075] (Note 8) In the wavelength map data acquisition device described in Note 5, the fourth step includes calculating a quadratic function that approximates the change in the oscillation wavelength for each axis on which the first current is set to a first fixed value and the second current is set to a second fixed value in the wavelength map, and determining the data of the oscillation wavelength for positions on the wavelength map other than the boundary where a mode hop occurs based on these quadratic functions. [Industrial applicability]

[0076] This invention can be applied to technologies for improving the productivity of semiconductor lasers. [Explanation of Symbols]

[0077] 100...DBR laser, 101...semiconductor substrate, 104...overcladding, 105...active region, 106...forward DBR region, 107...backward DBR region, 108...phase adjustment region, 109...SOA region, 110...bottom electrode, 111...active region electrode, 112...forward DBR region electrode, 113...backward DBR region electrode, 114...phase adjustment region electrode, 115...SOA region electrode, 302~305...current source, 306a~306d...wiring, 307...optical cable, 308...optical spectrum analyzer or wavelength meter, 309...control unit, 310...storage unit, 311...mode hop point extraction unit, 312...boundary approximation unit, 313...wavelength determination unit.

Claims

1. A current source configured to inject current into a distributed reflection type tunable semiconductor laser, A measuring unit configured to measure the oscillation wavelength of the semiconductor laser when a first fixed current is injected into the DBR region of the semiconductor laser and a second current injected into the phase adjustment region of the semiconductor laser is changed, and the oscillation wavelength when a second fixed current is injected into the phase adjustment region and the first current injected into the DBR region is changed. A mode hop point extraction unit is configured to extract pairs of the values ​​of the first current and the second current at points where a mode hop occurs, for each axis, in a wavelength map representing the oscillation wavelength generated by the combination of the first and second currents, on an axis where the first current is set to a first fixed value and on an axis where the second current is set to a second fixed value. A boundary approximation unit is configured to approximate the boundary where a mode hop occurred on the wavelength map using a quadratic function, based on the processing results of the mode hop point extraction unit. A wavelength map data acquisition device comprising: a wavelength determination unit configured to determine the oscillation wavelength data for positions on the wavelength map other than the boundary where a mode hop occurred, based on the measurement results of the measurement unit and the processing results of the boundary approximation unit.

2. In the wavelength map data acquisition apparatus according to claim 1, The system further comprises a control unit configured to control the current source, The wavelength map data acquisition device is characterized in that, when the measurement unit performs a measurement, the control unit sets the first fixed value and the second fixed value to three predetermined values: a minimum value, an intermediate value, and a maximum value, respectively, and when injecting the first current of the first fixed value into the DBR region, it changes the second current injected into the phase adjustment region from the minimum value to the maximum value, and when injecting the second current of the second fixed value into the phase adjustment region, it changes the first current injected into the DBR region from the minimum value to the maximum value.

3. In the wavelength map data acquisition apparatus according to claim 1, The wavelength map data acquisition device is characterized in that the boundary approximation unit approximates the boundary where a mode hop occurs on the wavelength map by calculating a quadratic function that connects the mode hop points that appear on the axis where the first current is set to a first fixed value in the wavelength map and the mode hop points that appear on the axis where the second current is set to a second fixed value in the wavelength map, thereby approximating the boundary where a mode hop occurs on the wavelength map with a quadratic function.

4. In the wavelength map data acquisition apparatus according to claim 1, The wavelength map data acquisition device is characterized in that the wavelength determination unit calculates a quadratic function that approximates the change in the oscillation wavelength for each axis on which the first current is set to a first fixed value and the second current is set to a second fixed value in the wavelength map, and determines the oscillation wavelength data for positions on the wavelength map other than the boundary where mode hopping occurs based on these quadratic functions.

5. A first step of measuring the oscillation wavelength of a distributed reflection type tunable semiconductor laser when a first fixed current is injected into the DBR region of the semiconductor laser and a second current injected into the phase adjustment region of the semiconductor laser is changed, and when a second fixed current is injected into the phase adjustment region and the first current injected into the DBR region is changed, In a wavelength map representing the oscillation wavelength generated by the combination of the first and second currents, the second step is to extract pairs of the values ​​of the first current and the second current at points where mode hopping occurs on an axis where the first current is set to a first fixed value and on an axis where the second current is set to a second fixed value, for each axis. A third step is to approximate the boundary where mode hopping occurred on the wavelength map with a quadratic function based on the processing result of the second step, A method for acquiring wavelength map data, comprising a fourth step of determining the oscillation wavelength data for positions on the wavelength map other than the boundary where a mode hop occurred, based on the measurement results of the first step and the processing results of the third step.

6. In the method for acquiring wavelength map data according to claim 5, A method for acquiring wavelength map data, characterized in that the first step includes the steps of setting the first fixed value and the second fixed value to three predetermined values: a minimum value, an intermediate value, and a maximum value, varying the second current injected into the phase adjustment region from the minimum value to the maximum value when injecting the first current of the first fixed value into the DBR region, and varying the first current injected into the DBR region from the minimum value to the maximum value when injecting the second current of the second fixed value into the phase adjustment region.

7. In the method for acquiring wavelength map data according to claim 5, A method for acquiring wavelength map data, characterized in that the third step includes the step of approximating the boundary where a mode hop occurred on the wavelength map by a quadratic function, by calculating a quadratic function that connects the mode hop points that appear on the axis where the first current is set as the first fixed value in the wavelength map and the mode hop points that appear on the axis where the second current is set as the second fixed value in the wavelength map.

8. In the method for acquiring wavelength map data according to claim 5, A method for acquiring wavelength map data, characterized in that the fourth step includes calculating a quadratic function that approximates the change in the oscillation wavelength on the axis where the first current is set to a first fixed value and on the axis where the second current is set to a second fixed value in the wavelength map, and determining the oscillation wavelength data for positions on the wavelength map other than the boundary where mode hopping occurs based on these quadratic functions.

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