Semiconductor laser evaluation method, device, and program

Abstract

According to a semiconductor laser evaluating method of the present invention, in a current-to-optical output characteristic, which is a relationship between an injection current of a semiconductor laser and an optical output thereof, wherein the injection current is represented by an X-axis and the optical output is represented by a Y-axis: the intersection between an approximate straight line, which is acquired by linear approximation about predetermined measurement points, and the X-axis is acquired; and then the smallest value of the maximums of such intersections obtained by shifting the measurement points is determined as a threshold value current of the semiconductor laser.　In this way, the present invention can provide the semiconductor laser evaluating method that can precisely evaluate the threshold value currents of semiconductor lasers.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser evaluation method, device, and program for evaluating the threshold current of a semiconductor laser. [Background technology]

[0002] In the research and development of semiconductor lasers, it is necessary to evaluate the characteristics of various semiconductor lasers and provide feedback to the design. An important parameter of semiconductor laser characteristics is the injection current at which laser oscillation begins, i.e., the threshold current. Typically, the threshold current is experimentally obtained from the optical output characteristics (IL characteristics) obtained when a current is injected into a semiconductor laser. Conventionally, the following methods have been used to evaluate the threshold current (for example, Non-Patent Document 1).

[0003] (1) In the IL characteristics, the threshold current is obtained from the intersection of the X-axis and a line passing through two measurement points (IL characteristics data) corresponding to different optical outputs P1 and P2 after laser oscillation (hereinafter referred to as "conventional method 1").

[0004] (2) The threshold current is obtained from the intersection of a line passing through two measurement points (IL characteristic data) corresponding to optical outputs P3 and P4 that are lower than the optical output at the threshold current obtained by Conventional Method 1 with the line obtained by Conventional Method 1 (hereinafter referred to as "Conventional Method 2").

[0005] (3) At each measurement point of the IL characteristics, the differential coefficient dL / dI is calculated, and the threshold current is obtained from the current corresponding to half the peak value of dL / dI (hereinafter referred to as "conventional method 3").

[0006] (4) At each measurement point of the IL characteristic, the second-order differential coefficient d 2 L / dI 2 Find d 2 L / dI 2 The threshold current is obtained from the current corresponding to the peak value (hereinafter referred to as "conventional method 4").

[0007] Furthermore, Non-Patent Document 2 discloses a method for evaluating the threshold current based on the relaxation oscillation frequency. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] “The Differences Between Threshold Current Calculation Methods,” Newport Application Notehttps: / / www.newport.com.cn / medias / sys_master / images / images / hc9 / hd1 / 9680121757726 / AN-12-REV03-Differences-Between-Threshold-Current-Calculations.pdf [Non-patent document 2] DM Kane and Joshua P. Toomey, “Precision Threshold Current Measurement for Semiconductor Lasers Based on Relaxation Oscillation Frequency,” Journal of Lightwave Technology, Vol. 27, No. 15, pp. 2949-2953 (2009). Summary of the Invention [Problem to be solved by the invention]

[0009] However, with the conventional method described above, when evaluating multiple semiconductor lasers with significantly different optical outputs or when the IL characteristics near the threshold are different from the normal form, it is difficult to accurately evaluate the threshold current using the same algorithm or the same parameters.

[0010] Therefore, when semiconductor lasers having various characteristics are evaluated collectively using the same algorithm or the same parameters, there is a problem that after the evaluation, it becomes necessary to separately check whether the threshold current has been accurately evaluated by drawing a graph of the IL characteristics, etc. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, a semiconductor laser evaluation method according to the present invention is a method for evaluating a semiconductor laser, which is characterized by: calculating an intersection between an injection current of a semiconductor laser and the optical output of the semiconductor laser in a current-optical output characteristic in which the injection current is represented on the X axis and the optical output is represented on the Y axis; and calculating an intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis; The injection current increases sequentially Shift First thing to do The maximum value of the intersection obtained Or, the maximum value of the intersection point finally obtained when the measurement point is sequentially shifted in the decreasing direction of the injection current. is determined as the threshold current of the semiconductor laser.

[0012] A semiconductor laser evaluation method according to the present invention includes the steps of: obtaining a current-optical output characteristic showing the relationship between an injection current of a semiconductor laser and the optical output of the semiconductor laser, the current-optical output characteristic being represented on the X-axis and the optical output on the Y-axis; obtaining an approximate line by linear approximation for a predetermined measurement point on the current-optical output characteristic; obtaining an intersection point between the approximate line and the X-axis; and The injection current is sequentially increased or decreased in either direction. shifting the image to obtain the maximum value of the intersection; The first maximum value of the intersection when one direction is an increasing direction The maximum value The threshold current of the semiconductor laser is determined, and the maximum value of the intersection point that is last obtained when the one direction is a decreasing direction is determined. determining a threshold current of the semiconductor laser;

[0013] Furthermore, a semiconductor laser evaluation method according to the present invention is a method for evaluating a semiconductor laser, which is characterized by: expressing a relationship between an injection current of a semiconductor laser and an optical output of the semiconductor laser on a current-optical output characteristic in which the injection current is represented on an X-axis and the optical output is represented on a Y-axis; obtaining an intersection of an approximation line obtained by linear approximation for a predetermined measurement point with the X-axis; and The injection current is sequentially increased or decreased in either direction. Shift the axis to get the maximum value of the intersection, and set it to the origin of the X axis. 、 The aforementioned When one direction is an increasing direction, the first maximum value of the intersection is obtained. local maximum, Alternatively, when the one direction is a decreasing direction, the maximum value of the intersection point that is last obtained among the maximum values ​​of the intersection points.and obtain another approximate straight line by linear approximation for another predetermined measurement point between the When one direction is an increasing direction, the first maximum value of the intersection point is obtained. The current value corresponding to the intersection of the approximation line and the other approximation line is determined as the threshold current of the semiconductor laser. When the one direction is a decreasing direction, a current value corresponding to an intersection between the approximate straight line corresponding to the maximum value of the intersection point last obtained and the other approximate straight line is determined as the threshold current of the semiconductor laser. It is characterized by:

[0014] A semiconductor laser evaluation method according to the present invention includes the steps of: obtaining a current-optical output characteristic showing the relationship between an injection current of a semiconductor laser and the optical output of the semiconductor laser, the current-optical output characteristic being represented on the X-axis and the optical output on the Y-axis; obtaining an approximate line by linear approximation for a predetermined measurement point on the current-optical output characteristic; obtaining an intersection point between the approximate line and the X-axis; and The injection current is sequentially increased or decreased in either direction. a step of shifting the X-axis origin and obtaining a maximum value of the intersection point; 、 The aforementioned When one direction is an increasing direction, the first maximum value of the intersection is obtained. local maximum, Alternatively, when the one direction is a decreasing direction, the maximum value of the intersection point that is last obtained among the maximum values ​​of the intersection points. and obtaining another approximate straight line by linear approximation for another predetermined measurement point between the When one direction is an increasing direction, the first maximum value of the intersection point is obtained. The current value corresponding to the intersection of the approximation line and the other approximation line is determined as the threshold current of the semiconductor laser. When the one direction is a decreasing direction, a current value corresponding to an intersection between the approximate straight line corresponding to the maximum value of the intersection point last obtained and the other approximate straight line is determined as the threshold current of the semiconductor laser. and a step of:

[0015] The semiconductor laser evaluation device according to the present invention includes a driver that supplies an injection current to a semiconductor laser, a detector that detects the optical output of the semiconductor laser, and a current-optical output characteristic that shows the injection current on the X axis and the optical output on the Y axis, and obtains an intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis, and calculates the measurement point. The injection current increases sequentially Shift First thing to do The maximum value of the intersection obtained Or, the maximum value of the intersection point finally obtained when the measurement point is sequentially shifted in the decreasing direction of the injection current. and a calculation unit that determines the threshold current of the semiconductor laser.

[0016] Furthermore, a semiconductor laser evaluation device according to the present invention includes a driver that supplies an injection current to a semiconductor laser, a detector that detects the optical output of the semiconductor laser, and a current-optical output characteristic diagram that shows the relationship between the injection current input from the driver and the optical output input from the detector, where the injection current is represented on the X axis and the optical output is represented on the Y axis. The current-optical output characteristic diagram shows the injection current on the X axis and the optical output, and the intersection of the X axis and an approximation line obtained by linear approximation for a predetermined measurement point is obtained, and the measurement point is The injection current is sequentially increased or decreased in either direction. Shift the axis to get the maximum value of the intersection, and set it to the origin of the X axis. 、 The aforementioned When one direction is an increasing direction, the first maximum value of the intersection is obtained. local maximum Alternatively, when the one direction is a decreasing direction, the maximum value of the intersection point that is last obtained among the maximum values ​​of the intersection points. and obtain another approximate straight line by linear approximation for another predetermined measurement point between the When one direction is an increasing direction, the first maximum value of the intersection point is obtained. The current value corresponding to the intersection of the approximation line and the other approximation line is determined as the threshold current of the semiconductor laser. When the one direction is a decreasing direction, a current value corresponding to an intersection between the approximate straight line corresponding to the maximum value of the intersection point last obtained and the other approximate straight line is determined as the threshold current of the semiconductor laser. and a calculation unit for performing the calculation.

[0017] Further, a semiconductor laser evaluation program according to the present invention is for evaluating the threshold current of a semiconductor laser by causing a computer to calculate a relationship between an injection current of the semiconductor laser and an optical output of the semiconductor laser, the relationship being expressed by plotting the injection current on the X axis and the optical output on the Y axis of a current-optical output characteristic, and obtaining an intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis, and The injection current increases sequentially Shift First thing to do The maximum value of the intersection obtained Or, the maximum value of the intersection point finally obtained when the measurement point is sequentially shifted in the decreasing direction of the injection current. is executed to determine the threshold current of the semiconductor laser.

[0018] Further, a semiconductor laser evaluation program according to the present invention is for evaluating the threshold current of a semiconductor laser by causing a computer to calculate a relationship between an injection current of the semiconductor laser and an optical output of the semiconductor laser, the relationship being expressed by plotting the injection current on the X axis and the optical output on the Y axis of a current-optical output characteristic, and obtaining an intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis, and The injection current is sequentially increased or decreased in either direction. Shift the axis to get the maximum value of the intersection, and set it to the origin of the X axis. 、 The aforementioned When one direction is an increasing direction, the first maximum value of the intersection is obtained. local maximum, Alternatively, when the one direction is a decreasing direction, the maximum value of the intersection point that is last obtained among the maximum values ​​of the intersection points.and obtain another approximate straight line by linear approximation for another predetermined measurement point between the When one direction is an increasing direction, the first maximum value of the intersection point is obtained. The current value corresponding to the intersection of the approximation line and the other approximation line is determined as the threshold current of the semiconductor laser. When the one direction is a decreasing direction, a current value corresponding to an intersection between the approximate straight line corresponding to the maximum value of the intersection point last obtained and the other approximate straight line is determined as the threshold current of the semiconductor laser. The process is executed. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a semiconductor laser evaluation method, apparatus, and program that can accurately evaluate the threshold current of a semiconductor laser. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a block diagram showing the configuration of a semiconductor laser evaluation device according to a first embodiment of the present invention. [Figure 2A] FIG. 2A is a diagram for explaining the concept of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 2B] FIG. 2B is a diagram for explaining the concept of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 2C] FIG. 2C is a diagram for explaining the concept of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 2D] FIG. 2D is a diagram for explaining the concept of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 2E] FIG. 2E is a diagram for explaining the concept of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 2F] FIG. 2F is a diagram for explaining the concept of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a flowchart illustrating the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 5A]FIG. 5A is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 5B] FIG. 5B is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 5C] FIG. 5C is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 6A] FIG. 6A is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 6B] FIG. 6B is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 7A] FIG. 7A is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 7B] FIG. 7B is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 7C] FIG. 7C is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 8A] FIG. 8A is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 8B] FIG. 8B is a diagram for explaining the effect of the semiconductor laser evaluation method according to the first embodiment of the present invention. [Figure 9A] FIG. 9A is a diagram for explaining the concept of a semiconductor laser evaluation method according to a second embodiment of the present invention. [Figure 9B] FIG. 9B is a diagram for explaining the concept of the semiconductor laser evaluation method according to the second embodiment of the present invention. [Figure 9C] FIG. 9C is a diagram for explaining the concept of the semiconductor laser evaluation method according to the second embodiment of the present invention. [Figure 10] FIG. 10 is a flowchart illustrating a semiconductor laser evaluation method according to the second embodiment of the present invention. [Figure 11A]FIG. 11A is a diagram for explaining the effect of the semiconductor laser evaluation method according to the second embodiment of the present invention. [Figure 11B] FIG. 11B is a diagram for explaining the effect of the semiconductor laser evaluation method according to the second embodiment of the present invention. [Figure 12] FIG. 12 is a diagram illustrating an example of the configuration of a computer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] First Embodiment A semiconductor laser evaluation device, method, and program according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 8B.

[0022] <Configuration of semiconductor laser evaluation device> The semiconductor laser evaluation device 10 according to this embodiment includes a drive unit 11, a detection unit 12, a calculation unit 13, a storage unit 14, and an output unit (display unit) 15, as shown in FIG.

[0023] The driver 11 injects a current into the semiconductor laser 1 to be measured.

[0024] The detector 12 receives the laser light from the semiconductor laser 1 and measures the optical output.

[0025] The storage unit 14 stores the relationship between the injection current value by the drive unit 11 and the optical output value by the detection unit 12 as a current-light (IL) characteristic.

[0026] The calculation unit 13 reads out the IL characteristic data from the storage unit 14 and evaluates the threshold current based on the IL characteristic data (described later). Here, the threshold current may be evaluated directly from the measured IL characteristic data without reading out the IL characteristic data from the storage unit 14.

[0027] The output unit (display unit) 15 outputs (displays) IL characteristic data, threshold current, and the like.

[0028] <Semiconductor laser evaluation method> First, the concept of the semiconductor laser evaluation method according to the present embodiment will be explained.

[0029] In the semiconductor laser evaluation method according to this embodiment, the threshold current is evaluated based on the IL characteristics, which represent the injection current of the semiconductor laser and the optical output of the semiconductor laser on the X and Y axes, respectively.

[0030] In the IL characteristics assumed in this embodiment, as shown in FIG. 2A, the optical output increases as the injection current increases, and the injection current becomes lower than the threshold current I th Above this value, the optical output power increases rapidly. If the injection current increases further, the optical output power decreases.

[0031] 2B to 2E show the threshold current I th In this embodiment, the measurement point (data) is sequentially shifted (incremented) in the direction of increasing the injection current in the IL characteristics, thereby obtaining the threshold current I th Get.

[0032] Here, the black circle in the figure indicates the nth measurement point, and the arrow in the figure is an approximation line obtained by linearly approximating the nth measurement point using 2k+1 pieces of measurement data from the nkth to the (n+kth) measurement points, and the tip of the arrow indicates the intersection with the X-axis (X-intercept).

[0033] First, the measurement point is the threshold current I th When the shift occurs in the current region significantly lower than , the slope of the fitted line is almost zero, and the X-intercept is near the origin (Fig. 2B).

[0034] Next, the measurement point is the threshold current I th When the injection current shifts in the direction of increasing in the lower current region, the X-intercept of the fitted line becomes positive, and the distance between the origin and the threshold current I th It is located between (Figure 2C).

[0035] Next, the measurement point is the threshold current Ith When the IL characteristic shifts to the linear region at higher currents, the X-intercept of the approximation line becomes the threshold current I th (Figure 2D).

[0036] Next, the measurement point is further increased to the threshold current I th When the linearity of the IL characteristics is maintained in the higher current region, the X-intercept of the approximation line also shifts with the threshold current I th (Figure 2E).

[0037] Finally, when the measurement point shifts to a region where the rate of increase of the optical output, i.e., the slope of the IL characteristic, decreases in the region where the injection current is higher, the X-intercept of the approximation line becomes the threshold current I th lower values ​​(Fig. 2F).

[0038] In this way, when the measurement point of the IL characteristics is shifted (incremented) in the direction of increasing injection current, the intersection (X-intercept) of the approximation line at the measurement point with the X-axis increases in the X-axis (injection current) direction, and the threshold current I th It reaches a maximum value and then decreases.

[0039] Therefore, by sequentially shifting (incrementing) the measurement point in the IL characteristics in the direction of increasing injection current and extracting the maximum value of the X-intercept, the threshold current I th can be obtained.

[0040] Here, when multiple maximum values ​​of the X-intercept are extracted, the first maximum value of the X-intercept obtained, that is, the minimum value among the multiple maximum values ​​of the X-intercept, is used as the threshold current I th (see below).

[0041] FIG. 3 is a flowchart illustrating an example of a semiconductor laser evaluation method according to this embodiment.

[0042] In measuring the IL characteristics, the driver 11 supplies an injection current to the semiconductor laser 1, and the detector 12 detects the optical output of the semiconductor laser 1. The relationship between the injection current and the optical output output from the driver 11 and the detector 12 is measured as the IL characteristics.

[0043] The measured IL characteristics are stored in the storage unit 14.

[0044] First, the calculation unit 13 acquires the IL characteristics from the storage unit 14 (step S11). Alternatively, the calculation unit 13 may directly acquire the measured IL characteristics.

[0045] Next, the variable (index) n of the IL characteristic data is initialized with the index of the array initial value (step S12). Here, the variable (index) n of the IL characteristic data is the number (a numerical value indicating the order) of the IL characteristic data. The index of the array initial value is the number of the first data of the IL characteristic data used for threshold current evaluation. For example, if the index of the array initial value is 1, it is initialized as n=1.

[0046] Next, for the nth measurement point in the IL characteristics, an approximate line is obtained by linear approximation of 2k+1 pieces of measurement data from the nkth to the n+kth measurement point (step S13). Hereinafter, k will be referred to as the "averaging parameter." Here, the least squares method or the like is used for the linear approximation.

[0047] Next, the intersection (X-intercept) of the approximation line with the X-axis is found and set as the array element X(n) (step S14).

[0048] Next, the X-intercept (X(n)) at the n-th measurement point is compared with the X-intercept (X(n-1)) at the previous (n-1) measurement point (step S15).

[0049] Here, if X(n) is equal to or greater than X(n-1), the next data (n+1th data) is selected (step S16), and the same steps are carried out (steps S13 to S15).

[0050] On the other hand, when X(n) indicates a value lower than X(n - 1), X(n - 1) is determined as the threshold current, and the evaluation is terminated (step S17). Thus, the maximum value of the X intercept is determined as the threshold current.

[0051] Here, an example where X(n - 1) is determined as the threshold current when X(n) indicates a value lower than X(n - 1) has been shown, but it is not limited to this. When X(n) indicates a value lower than a plurality of data measured before X(n), any one of the plurality of data may be determined as the threshold current.

[0052] For example, when X(n) indicates a value lower than X(n - 1) and X(n - 2), that is, when X(n) < X(n - 1) and X(n) < X(n - 2), if X(n - 1) < X(n - 2), X(n - 2) which is the maximum value may be determined as the threshold current.

[0053] Thereby, the influence of experimental errors such as noise can be suppressed, and an accurate threshold current can be obtained.

[0054] In the present embodiment, an example where n is sequentially increased has been shown, but n may be sequentially decreased. In this case, for example, X(n) and X(n + 1) are compared, and when X(n) < X(n + 1), X(n + 1) is determined as the threshold current. Thus, by changing (shifting) n, the maximum value of X(n) may be obtained.

[0055] Also, in the semiconductor laser evaluation method according to the present embodiment, when a plurality of maximum values of the X intercepts are obtained when n is sequentially increased, the maximum value of the X intercept obtained first is set as the threshold current I th . Also, when a plurality of maximum values of the X intercepts are obtained when n is sequentially decreased, the maximum value of the X intercept obtained last is set as the threshold current I th . That is, the minimum value among the maximum values of the plurality of X intercepts is determined as the threshold current I th .

[0056] As described above, in the semiconductor laser evaluation method according to the present embodiment, the minimum value of the maximum values ​​at the intersection of the IL characteristics between the approximate line obtained by linear approximation for a predetermined measurement point and the X-axis is determined as the threshold current of the semiconductor laser.

[0057] <Effects> The effects of the semiconductor laser evaluation method according to this embodiment will be described with reference to FIGS. 4 to 8B.

[0058] FIG. 4 shows the IL characteristics (dotted line in the figure) and the change in X(n) (solid line in the figure), which is the X-intercept, in this embodiment.

[0059] X(n) is nearly zero when the injection current I(n) is low, and then increases sharply as the injection current I(n) increases, after which it remains almost constant.Furthermore, as the injection current I(n) increases, X(n) decreases and becomes negative.

[0060] From this change in X(n), the maximum value of X(n) is the threshold current I th is determined as follows.

[0061] Next, the semiconductor laser evaluation method according to this embodiment will be compared with conventional method 1.

[0062] In Conventional Method 1, as shown in Figure 5A, the threshold current I th Determine.

[0063] However, as shown in FIG. 5B, when multiple kinks occur in the IL characteristics (dotted line in the figure), the threshold current cannot be accurately evaluated even if the line connecting the two measured points is extended (solid arrow in the figure).

[0064] On the other hand, according to the semiconductor laser evaluation method of this embodiment, as shown in FIG. 5C, X(n) (solid line in the figure) shows multiple maximum values ​​corresponding to multiple kinks in the IL characteristics (dotted line in the figure). Among these maximum values, X(n) corresponding to the first maximum value obtained, that is, the smallest X(n) among the multiple maximum values, is used as the threshold current I th This allows the threshold current to be accurately evaluated.

[0065] Furthermore, in Conventional Method 1, it may not be possible to evaluate the threshold current using the same parameters for all of a plurality of semiconductor lasers each having different IL characteristics. For example, when evaluating the threshold current between two predetermined points, it may not be possible to obtain measurement data for the two points for the IL characteristics of all of a plurality of semiconductor lasers.

[0066] For example, in the case shown in Figure 6A, measurement data can be obtained from two points corresponding to optical outputs P1 and P2 of the IL characteristics (dotted lines in the figure) 162 and 163, respectively, and the threshold current can be accurately evaluated by extending the line connecting these two points (solid arrow in the figure).

[0067] However, measurement data corresponding to the optical output P2 cannot be obtained for the IL characteristics (dotted line in the figure) 161, and measurement data for two points cannot be obtained. As a result, the threshold current cannot be accurately evaluated for all of the semiconductor lasers.

[0068] On the other hand, according to the semiconductor laser evaluation method of this embodiment, as shown in FIG. 6B, the maximum value of X(n) (solid line in the figure) can be obtained for each of the laser IL characteristics (dotted lines in the figure) 161, 162, 163 of the plurality of semiconductors. Therefore, each of the maximum values ​​of X(n) can be calculated by multiplying the threshold current I th1 , I th2 , I th3 Therefore, the threshold current can be accurately evaluated.

[0069] Next, the semiconductor laser evaluation method according to this embodiment will be compared with conventional method 4.

[0070] In Conventional Method 4, as shown in Figure 7A, the second-order differential coefficient d 2 L / dI 2 The threshold current I th Therefore, if the IL characteristics change sharply near the threshold current, the steep d 2 L / dI 2 Since the peak of th can be determined.

[0071] However, as shown in FIG. 7B, when the IL characteristic (dotted line in the figure) changes gradually near the threshold current, d 2 L / dI 2 Since the steep peak (solid line in the figure) cannot be obtained, the threshold current I th cannot be determined.

[0072] On the other hand, according to the semiconductor laser evaluation method of the present embodiment, as shown in FIG. 7C, X(n) (solid line in the figure) clearly shows a maximum value, so that it is easy to obtain an accurate threshold current I th can be determined.

[0073] Next, experimental results obtained by the semiconductor laser evaluation method according to this embodiment will be described with reference to FIGS. 8A and 8B.

[0074] The semiconductor lasers used for evaluation were semiconductor laser a and semiconductor laser b, which have different IL characteristics. Figures 8A and 8B show the experimental results (IL characteristics) for semiconductor laser a and semiconductor laser b, respectively. The experiment (evaluation) was performed with the averaging parameter k set to 5.

[0075] The IL characteristics of semiconductor laser a (dotted line in the figure) were evaluated. As a result, as shown in Figure 8A, X(n) reached a maximum value at n = 17 (corresponding to an injection current of 1.7 mA), and the threshold current I th The approximated line at this time is shown by the solid line 171 in the figure.

[0076] Furthermore, the IL characteristics of semiconductor laser b (dotted line in the figure) were evaluated, and as a result, as shown in Figure 8B, X(n) reached a maximum value at n = 26 (corresponding to an injection current of 2.6 mA), and the threshold current I th was obtained at 1.60 mA. The approximate line at this time is shown by the solid line 172 in the figure.

[0077] <Second embodiment> A semiconductor laser evaluation apparatus, method, and program according to a second embodiment of the present invention will be described with reference to Figures 9A to 11B. The configuration of the semiconductor laser evaluation apparatus according to this embodiment is similar to that of the first embodiment.

[0078] <Semiconductor laser evaluation method> 9A to 9C show the concept of the semiconductor laser evaluation method according to this embodiment, and Fig. 10 shows a flowchart of an example of the semiconductor laser evaluation method according to this embodiment.

[0079] In this embodiment, it is assumed that the change in optical output near the threshold value in the IL characteristics is gradual, as shown in FIG. 9A.

[0080] First, as in the first embodiment, the maximum value of X(n) is obtained from the intersection (X-intercept) of the linear approximation line and the X-axis in the IL characteristic (dotted line in the figure). This maximum value of X(n) is used as the tentative threshold current I th The approximate line at this time (hereinafter referred to as "approximate line A") is indicated by a solid line 211 in the drawing.

[0081] In detail, in the IL characteristic, the approximation line is k A n+kth to n+kth A 2k up to the th A +1 measurement data. The maximum value of X(n), which is the intersection point (X-intercept) of this approximation line with the X-axis, is taken as the tentative threshold current I th The approximate line at this time is set as approximate line A (steps S21 to S27).

[0082] Next, from the origin of the IL characteristic th ' to the specified measurement point (n B An approximate line (hereinafter referred to as "approximate line B"; solid line 212 in the figure) is determined by linear approximation for the nth measurement point (FIG. 9C, step S28). B For the nth measurement point, B -k B th to n B +k B 2k up to the th B +1 measurement data is obtained by linear approximation.

[0083] Here, the predetermined measurement points (n B th measurement point), the origin and I th The midpoint between the measurement point n' corresponding to the ' (the n' / 2nd measurement point) and the measurement point n' corresponding to the ' is used. In addition to the n' / 2nd measurement point, the n' / 3rd or n' / 4th measurement point may also be used. th Alternatively, the measurement point several times before the measurement point corresponding to ' (the n'-k0th measurement point) may be used.

[0084] Finally, the current value corresponding to the intersection of approximate lines A and B (black circle in the figure) is the threshold current I th (FIG. 9C, step S29).

[0085] In addition, in the semiconductor laser evaluation method according to the present embodiment, when the maximum values ​​of a plurality of X-intercepts (X(n)) are acquired, the minimum value among the maximum values ​​of the plurality of X(n) is used as the provisional threshold current I th 'Let's say.

[0086] <Effects> In the IL characteristics of a semiconductor laser, the spontaneous emission light from the semiconductor laser is very strong, so the change in optical output near the threshold may be gradual. Also, light may be detected even in the current region below the threshold due to noise or dark current in the photodetector of the measurement system.

[0087] When evaluating the threshold current for such IL characteristics using the conventional method and the semiconductor laser evaluation method according to the first embodiment, a value lower than the actual threshold current corresponding to the change in IL characteristics is determined as the threshold current, and as a result, the threshold current cannot be evaluated accurately.

[0088] According to the semiconductor laser evaluation method of the present embodiment, as described above, the threshold current can be accurately evaluated in response to changes in the IL characteristics.

[0089] Next, experimental results obtained by the semiconductor laser evaluation method according to this embodiment will be described with reference to FIGS. 11A and 11B.

[0090] The semiconductor lasers to be evaluated were semiconductor laser a and semiconductor laser b, which have different IL characteristics, as in the first embodiment. Figures 11A and 11B show the experimental results for semiconductor laser a and semiconductor laser b, respectively.

[0091] The averaging parameter k for the IL characteristics of semiconductor laser a (dotted line in the figure) A As a result of evaluation with n set to 5, as shown in FIG. 11A, X(n) showed a maximum value at n=17 (corresponding to an injection current of 1.7 mA), and the tentative threshold current I th The approximated line A at this time is shown by the solid line 221 in the figure.

[0092] Also, the origin and the tentative threshold current I th The measurement point (n B The nth measurement point B = 5), k B = 5 and linear approximation was performed to obtain approximate line B (solid line 222 in the figure).

[0093] From the intersection of the above approximate lines A and B, the threshold current I th was obtained at 0.98mA.

[0094] Next, the IL characteristics of semiconductor laser b (dotted line in the figure) are calculated using the averaging parameter k A As a result of evaluation with n set to 5, as shown in FIG. 11B, X(n) showed a maximum value at n=26 (corresponding to an injection current of 2.6 mA), and the tentative threshold current I th The approximate line A at this time is shown by the solid line 223 in the figure.

[0095] Also, the origin and the tentative threshold current I th The measurement point (n B The nth measurement point B = 9), k B = 5 and linear approximation was performed to obtain approximate line B (solid line 224 in the figure).

[0096] From the intersection of the above approximate lines A and B, the threshold current I th was obtained at 1.74mA.

[0097] 12 shows an example of the configuration of a computer for executing a semiconductor laser evaluation method according to an embodiment of the present invention. This semiconductor laser evaluation method can be realized by a computer including a CPU (Central Processing Unit) in an arithmetic unit 13, a storage device (storage unit) 14, and an interface device 18, and a program for controlling these hardware resources. Here, a driver 11, a detector 12, and an output unit 15 are connected to the interface device 18. The CPU executes the processing according to the embodiment of the present invention in accordance with the semiconductor laser evaluation program stored in the storage device 14. In this way, the semiconductor laser evaluation program causes the semiconductor laser evaluation method according to the embodiment of the present invention to be executed.

[0098] In the semiconductor laser evaluation apparatus 10 according to the embodiment of the present invention, a computer may be provided inside the apparatus, or at least a part of the functions of the computer may be realized using an external computer. Furthermore, the storage unit 14 may also use a storage medium 14_2 external to the apparatus, and the semiconductor laser evaluation program stored in the storage medium 14_2 may be read and executed. The storage medium 14_2 may include various magnetic recording media, magneto-optical recording media, CD-ROMs, CD-Rs, and various memories. Furthermore, the semiconductor laser evaluation program may be supplied to the computer via a communication line such as the Internet.

[0099] In the embodiments of the present invention, examples of algorithms, parameters, and structures of components in the semiconductor laser evaluation method, device, and program are shown, but the present invention is not limited to these. Anything that can demonstrate the functions and effects of the semiconductor laser evaluation method, device, and program may be used. [Industrial Applicability]

[0100] The present invention relates to a method, an apparatus and a program for evaluating the threshold current of a semiconductor laser, and can be applied to improving the characteristics of a semiconductor laser. [Explanation of symbols]

[0101] 1. Semiconductor laser 10. Semiconductor laser evaluation equipment 11 Drive unit 12 Detector 13 Arithmetic section

Claims

1. A semiconductor laser evaluation method for determining a threshold current of the semiconductor laser, the method comprising: obtaining an intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X-axis in a current-optical output characteristic in which the injection current of the semiconductor laser is represented on the X-axis and the optical output of the semiconductor laser is represented on the Y-axis; and determining, as a threshold current of the semiconductor laser, either the maximum value of the intersection obtained first when the measurement point is sequentially shifted in the direction of increasing the injection current or the maximum value of the intersection obtained last when the measurement point is sequentially shifted in the direction of decreasing the injection current.

2. obtaining a current-optical output characteristic showing the relationship between an injection current of a semiconductor laser and an optical output of the semiconductor laser, the injection current being plotted on the X axis and the optical output being plotted on the Y axis; obtaining an approximate straight line by linear approximation for predetermined measurement points in the current-light output characteristics; obtaining an intersection point between the approximation line and the X-axis; a step of sequentially shifting the measurement point in either an increasing direction or a decreasing direction of the injection current to obtain a maximum value of the intersection point; determining the first-obtained maximum value of the intersection points as the threshold current of the semiconductor laser when the one direction is an increasing direction, and determining the last-obtained maximum value of the intersection points as the threshold current of the semiconductor laser when the one direction is a decreasing direction; A semiconductor laser evaluation method comprising:

3. A relationship between an injection current of a semiconductor laser and an optical output of the semiconductor laser is represented by a current-optical output characteristic in which the injection current is represented on the X axis and the optical output is represented on the Y axis, and an intersection point between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis is obtained, and the measurement point is sequentially shifted in either an increasing direction or a decreasing direction of the injection current to obtain a maximum value of the intersection point; obtaining another approximate straight line by linear approximation for another predetermined measurement point between the origin of the X-axis and the first maximum value of the intersection point obtained when the one direction is an increasing direction, or the last maximum value of the intersection point obtained when the one direction is a decreasing direction; a current value corresponding to the intersection of the approximate straight line corresponding to the maximum value of the intersection point obtained last and the other approximate straight line is determined as the threshold current of the semiconductor laser when the one direction is an increasing direction, and when the one direction is a decreasing direction, a current value corresponding to the intersection of the approximate straight line corresponding to the maximum value of the intersection point obtained last and the other approximate straight line is determined as the threshold current of the semiconductor laser.

4. obtaining a current-optical output characteristic showing the relationship between an injection current of a semiconductor laser and an optical output of the semiconductor laser, the injection current being plotted on the X axis and the optical output being plotted on the Y axis; obtaining an approximate straight line by linear approximation for predetermined measurement points in the current-light output characteristics; obtaining an intersection point between the approximation line and the X-axis; a step of sequentially shifting the measurement point in either an increasing direction or a decreasing direction of the injection current to obtain a maximum value of the intersection point; obtaining another approximate straight line by linear approximation for another predetermined measurement point between the origin of the X-axis and the first maximum value of the intersection point obtained when the one direction is an increasing direction, or the last maximum value of the intersection point obtained when the one direction is a decreasing direction; determining, when the one direction is an increasing direction, a current value corresponding to an intersection between the approximate straight line corresponding to the maximum value of the first-obtained intersection and the other approximate straight line as the threshold current of the semiconductor laser, and, when the one direction is a decreasing direction, determining, when the one direction is a decreasing direction, a current value corresponding to an intersection between the approximate straight line corresponding to the maximum value of the last-obtained intersection and the other approximate straight line as the threshold current of the semiconductor laser; A semiconductor laser evaluation method comprising:

5. a driver for supplying an injection current to the semiconductor laser; a detector for detecting an optical output of the semiconductor laser; a calculation unit that obtains an intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X-axis in a current-optical output characteristic that represents the relationship between the injection current output from the driving unit and the optical output output from the detection unit, where the X-axis represents the injection current and the Y-axis represents the optical output, and determines, as the threshold current of the semiconductor laser, either the maximum value of the intersection that is first obtained when the measurement point is sequentially shifted in the direction of increasing the injection current or the maximum value of the intersection that is last obtained when the measurement point is sequentially shifted in the direction of decreasing the injection current; A semiconductor laser evaluation device comprising:

6. a driver for supplying an injection current to the semiconductor laser; a detector for detecting an optical output of the semiconductor laser; The relationship between the injection current input from the driver and the optical output input from the detector is represented by a current-optical output characteristic in which the injection current is plotted on the X axis and the optical output is plotted on the Y axis. A point of intersection between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis is obtained, and the measurement point is sequentially shifted in one of the directions of increasing or decreasing the injection current to obtain a maximum value at the intersection. The origin of the X axis and the first maximum value at the intersection are obtained when the direction is increasing, or when the direction is decreasing. a calculation unit that obtains another approximate straight line by linear approximation for a predetermined other measurement point between the maximum value of the intersection point and the maximum value of the intersection point that is obtained last, and determines, when the one direction is an increasing direction, a current value corresponding to the intersection point between the approximate straight line corresponding to the first obtained maximum value of the intersection point and the other approximate straight line as the threshold current of the semiconductor laser, and when the one direction is a decreasing direction, determines, when the one direction is a decreasing direction, a current value corresponding to the intersection point between the approximate straight line corresponding to the last obtained maximum value of the intersection point and the other approximate straight line as the threshold current of the semiconductor laser; A semiconductor laser evaluation device comprising:

7. To evaluate the threshold current of a semiconductor laser, a current-optical output characteristic representing the relationship between an injection current of a semiconductor laser and the optical output of the semiconductor laser, the current-optical output characteristic being represented on the X-axis and the optical output of the semiconductor laser being represented on the Y-axis; obtaining an intersection between the X-axis and an approximation line obtained by linear approximation for a predetermined measurement point; and determining, as a threshold current of the semiconductor laser, either the maximum value of the intersection obtained first when the measurement point is sequentially shifted in the direction of increasing the injection current or the maximum value of the intersection obtained last when the measurement point is sequentially shifted in the direction of decreasing the injection current.

8. To evaluate the threshold current of a semiconductor laser, A relationship between an injection current of a semiconductor laser and an optical output of the semiconductor laser is represented by a current-optical output characteristic in which the injection current is represented on the X axis and the optical output is represented on the Y axis, and an intersection point between an approximation line obtained by linear approximation for a predetermined measurement point and the X axis is obtained, and the measurement point is sequentially shifted in either an increasing direction or a decreasing direction of the injection current to obtain a maximum value of the intersection point; obtaining another approximate straight line by linear approximation for another predetermined measurement point between the origin of the X-axis and the first maximum value of the intersection point obtained when the one direction is an increasing direction, or the last maximum value of the intersection point obtained when the one direction is a decreasing direction; a current value corresponding to the intersection of the approximate straight line corresponding to the maximum value of the intersection point obtained last and the other approximate straight line as the threshold current of the semiconductor laser when the one direction is an increasing direction, and when the one direction is a decreasing direction, the current value corresponding to the intersection of the approximate straight line corresponding to the maximum value of the intersection point obtained last and the other approximate straight line as the threshold current of the semiconductor laser.

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