JP2001033513A - Characteristic measuring method of semiconductor optical element and recording medium in which characteristic measuring program is recorded - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method excellent in measuring precision and reproducibility of measurement. SOLUTION: A step current power source circuit 3 applies a current which is gradually increased or decreased stepwise to a semiconductor laser diode(LD) 1 in the forward direction through measuring terminals 2a, 2b. A voltage measuring circuit 4 measures a forward direction voltage of the LD 1. An operation/ control circuit 5 calculates twice differentiated value of a forward direction voltage E to a current I, and makes the value of a current I which has been applied to the LD 1 when the twice differentiated value becomes maximum a threshold current of the LD 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring characteristics of a semiconductor optical device which is easy to measure, and has excellent measurement accuracy and reproducibility, and a recording medium on which a characteristic measurement program is recorded.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser diode (hereinafter, referred to as a semiconductor laser diode) has been disclosed.
In general, the threshold current (hereinafter referred to as LD) is derived from the characteristics of the light output with respect to the current (hereinafter, referred to as IL characteristics). FIG. 10 is a block diagram of a conventional measuring device for measuring the IL characteristics of an LD. The measuring device shown in FIG. 10 includes measuring terminals 22a and 22b for connecting a semiconductor laser diode (hereinafter, referred to as LD) 1 and an LD that gradually increases or decreases in a stepwise manner through the measuring terminals 22a and 22b.
1, a step current power supply circuit 23 applied in the forward direction, and a photodetector (hereinafter referred to as PD) 24 such as a photodiode.
And an optical coupling medium 25 composed of a space, an optical fiber, etc., for the LD 1 and the PD 24, a PD light receiving circuit 26 for obtaining the optical output of the LD 1 from the output of the PD 24, and a control circuit 27 for controlling the entire measuring apparatus. I have. In addition, the measuring device includes
A computer 28 is connected, and the computer 28 has an interface circuit 29 and a CPU 30.

There are four methods for deriving a threshold current using the measuring apparatus shown in FIG. 10, and in each case, the threshold current is derived from the IL characteristic of the LD 1 taken into the CPU 30. Illustrating these derivation methods is the IL characteristic in FIGS. 11 to 14, reference numeral 14 denotes a spontaneous emission light characteristic region of the IL characteristic, reference numeral 15 denotes a stimulated emission light characteristic region of the IL characteristic, and Ith denotes a threshold current. In FIG. 14, reference numeral 16 denotes a one-time differential (external differential quantum efficiency, hereinafter referred to as luminous efficiency) characteristic of the light output Po with respect to the current I, and reference numeral 17 denotes the light output P with respect to the current I.
This is a second derivative (differentiation of luminous efficiency) characteristic of o.

A conventional threshold current deriving method will be described below with reference to FIGS. (A) The threshold current deriving method shown in FIG. 11 is a method in which a current value corresponding to a constant low-level stimulated emission (laser oscillation) light output value 18 is defined as a threshold current Ith. (B) The threshold current deriving method shown in FIG. 12 is a method of determining, as the threshold current Ith, a value (intercept) at which a straight line 19 obtained by extrapolating the characteristic 15 of the stimulated emission light in the IL characteristic is in contact with the current axis. (C) The threshold current deriving method shown in FIG. 13 uses a straight line 19 obtained by extrapolating the characteristic 15 of the stimulated emission light in the IL characteristic and an I-L characteristic.
Straight line 2 extrapolating the characteristic 14 of spontaneous emission light in the L characteristic
In this method, a current value corresponding to an intersection with 0 is determined as a threshold current Ith. (D) The threshold current deriving method shown in FIG. 14 is a method in which the current value when the second derivative 17 of the optical output Po with respect to the current I takes the maximum value is defined as the threshold current Ith.

[0005]

The threshold current deriving methods shown in FIGS. 11 to 14 are widely used. However, near the boundary between the original spontaneous emission light and the stimulated emission light (threshold current in the current axis), competition between the luminescence recombination current and the non-emission recombination current, competition between the spontaneous emission light and the stimulated emission light in the emission recombination current And an unstable region where some modes of the multi-wavelength mode of the stimulated emission compete with each other. Therefore, there is an accuracy limit in deriving the threshold current Ith from the IL characteristics of such an unstable and minute light output region, and there is a problem in the reproducibility of the derived value in each threshold current detection method. there were.

(A) In the threshold current deriving method shown in FIG. 11, the corresponding current value changes depending on the level 18 of the guide light to be set, so the derived threshold current becomes a provisional value,
There is a problem that the derived value does not accurately reflect the original threshold current. (B) In the threshold current deriving method shown in FIG. 12, the current value varies depending on the gradient of the stimulated emission light characteristic 15 and the spontaneous emission light level. Therefore, there is a problem that the derived value does not accurately reflect the original threshold current. (C) In the threshold current deriving method shown in FIG. 13, the derived value accurately reflects the original threshold current due to a derivation error due to the nonlinearity or instability of the spontaneous emission light among the measured emission light. There was no problem. (D) In the threshold current deriving method shown in FIG.
Is used, the derived value relatively accurately reflects the original threshold current. However, due to competition between minute spontaneous emission light, stimulated emission light, multiple wavelength modes, and the like, a plurality of local maxima are generated in the second differential characteristic 17 of the optical output Po, so that the maximum value fluctuates every measurement, and the derived value There is a problem that subtle variations occur. The present invention has been made to solve the above problems,
An object of the present invention is to provide a method for measuring characteristics of a semiconductor optical device and a recording medium on which a characteristic measurement program is recorded, which has excellent measurement accuracy and reproducibility of measurement.

[0007]

According to a method of measuring the characteristics of a semiconductor optical device according to the present invention, a threshold current of the semiconductor optical device is derived from a differential value of a differential resistance characteristic with respect to a current of the semiconductor optical device. In addition, the method for measuring the characteristics of a semiconductor optical device according to the present invention includes an application procedure of applying a current gradually increasing or decreasing stepwise or pulsewise in a forward direction of the semiconductor optical device, and a measurement for measuring a forward voltage of the semiconductor optical device. Instructions,
It has a calculation procedure for calculating a second derivative of the forward voltage with respect to the current, and a derivation procedure for deriving a threshold current of the semiconductor optical device based on a singular value of the calculated second derivative.
In the above derivation procedure, the current value applied to the semiconductor optical device when the second derivative of the voltage takes the maximum value is set as the threshold current. Further, the second derivative characteristic of the optical output with respect to the current of the semiconductor optical element is obtained in advance, the current range to be measured is determined from the current range of the convex second derivative characteristic including the maximum value, and the above-described application is performed in the determined current range. The procedure, the measurement procedure, the calculation procedure, and the derivation procedure are performed.

The recording medium on which the characteristic measuring program of the present invention is recorded has a computer for deriving a threshold current of a semiconductor optical device from a differential value of a differential resistance characteristic with respect to a current of the semiconductor optical device. It is.
Further, the recording medium on which the characteristic measurement program of the present invention is recorded measures an application procedure of applying a current gradually increasing or decreasing stepwise or pulsewise in the forward direction of the semiconductor optical device, and measuring a forward voltage of the semiconductor optical device. The computer causes the computer to execute a measurement procedure, a calculation procedure for calculating a second derivative of the forward voltage with respect to the current, and a derivation procedure for deriving a threshold current of the semiconductor optical device based on a singular value of the calculated second derivative. It is like that. In the above derivation procedure, the current value applied to the semiconductor optical device when the second derivative of the voltage takes the maximum value is used as the threshold current. Further, the second derivative characteristic of the optical output with respect to the current of the semiconductor optical element is obtained in advance, the current range to be measured is determined from the current range of the convex second derivative characteristic including the maximum value, and the above-described application is performed in the determined current range. It performs a procedure, a measurement procedure, a calculation procedure, and a derivation procedure.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Next, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram of a measuring apparatus used in the characteristic measuring method according to the first embodiment of the present invention. The measuring device shown in FIG. 1 includes a measuring terminal 2a, 2b for connecting a semiconductor laser diode (hereinafter, referred to as an LD) 1 and an LD 1 which gradually increases or decreases in a stepwise manner through a measuring terminal 2a, 2b.
, A step current power supply circuit 3 applied in the forward direction, a voltage measurement circuit 4 connected in parallel with the step current power supply circuit 3 to measure the forward voltage of the LD 1, and a threshold current of the LD 1 An arithmetic / control circuit 5 for deriving
An interface circuit 6 for interfacing the step current power supply circuit 3 and the voltage measurement circuit 4 with the operation / control circuit 5; a control signal from the operation / control circuit 5 to the step current power supply circuit 3; A D / A / A / D conversion circuit 7 for converting a current value applied from the step current power supply circuit 3 to the LD 1 into a digital value, and a control signal from the arithmetic / control circuit 5 to the voltage measurement circuit 4 as an analog signal. It has a D / A / A / D conversion circuit 8 for converting the voltage value measured by the voltage measurement circuit 4 into a digital value, and a characteristic display device 9 for displaying the measurement result.

Hereinafter, the characteristic measuring method of the present invention using the measuring apparatus of FIG. 1 will be described. FIG. 2 shows the current-
It is a figure which shows a voltage characteristic (it is hereafter called IV characteristic).
In FIG. 2, reference numeral 11 denotes an actually measured IV characteristic of the LD 1;
Is a one-time differential (differential resistance) characteristic of the voltage E with respect to the current I,
Reference numeral 13 denotes a twice differential characteristic of the voltage E with respect to the current I.

Usually, most of the energy components (voltage / heat, photons, phonons) when the current I is applied to the LD are reflected in the forward voltage E of the LD 1. Therefore, the characteristics of the LD with respect to the current I are measured more stably and reproducibly at the voltage E than at the optical output Po. In particular, the range up to the vicinity of the threshold current where the luminous efficiency is small is a region where voltage measurement is superior to light measurement.

In FIG. 2, the threshold current Ith of LD1
Can be derived as a singular value (maximum value) in the twice differential characteristic of the forward voltage E. This is because the change in the luminous efficiency between the spontaneous emission light region and the stimulated emission light region is reflected on the voltage E. In the differential resistance characteristic 12 shown in FIG. 2, the position of the threshold current Ith corresponds to a position slightly before the value is clamped at a substantially constant value.

Next, the characteristic measuring method of the present invention using the measuring apparatus of FIG. 1 will be described more specifically. FIG. 3 is a flowchart showing a characteristic measuring method of the present invention using the measuring device of FIG. First, the arithmetic / control circuit 5
A control signal for instructing D1 to apply a current I of a predetermined start value (a value smaller than the threshold current) is sent to the interface circuit 6. Interface circuit 6, D / A / A
The step current power supply circuit 3 receiving the control signal via the / D conversion circuit 7 applies a current I of a predetermined start value to the LD 1 (step 101).

Subsequently, the arithmetic / control circuit 5 sends a control signal for instructing to measure the forward voltage E of the LD 1 to the interface circuit 6. Interface circuit 6, D
The voltage measurement circuit 4 that has received the control signal via the / A / A / D conversion circuit 8 measures the forward voltage E of the LD 1 (Step 102).

The arithmetic / control circuit 5 calculates the value of the current I applied from the step current power supply circuit 3 to the LD 1 by D / A · A /
The value of the voltage E measured by the voltage measuring circuit 4 is taken in through the D / A / A / D converting circuit 8 and the interface circuit 6 while being taken in through the D conversion circuit 7 and the interface circuit 6, and the voltage with respect to the current I is taken. The second derivative of E is calculated (step 103).

Next, the arithmetic / control circuit 5 determines whether or not the second derivative of the calculated voltage E is valid (step 1).
04). If the second derivative of the voltage E is not valid (is a very large value unsuitable for deriving a threshold current described later), the arithmetic / control circuit 5 sets the value of the current I applied to the LD 1 to a fixed amount. Interface circuit 6,
A control signal is sent to the step current power supply circuit 3 via the D / A / A / D conversion circuit 7. Accordingly, the step current power supply circuit 3 increases the current I applied to the LD 1 (Step 105).

The voltage measuring circuit 4 measures the forward voltage E of the LD 1 according to the instruction of the arithmetic / control circuit 5 (step 10).
2) The arithmetic / control circuit 5 calculates a second derivative of the voltage E with respect to the current I (step 103), and calculates the calculated voltage E
It is determined whether the second derivative of is valid (step 10).
4). Thus, the operations of steps 102 to 105 are repeated until the second derivative of the voltage E becomes valid.

Next, the arithmetic / control circuit 5 executes step 10
If it is determined in step 4 that the second derivative of the voltage E is valid, it is determined whether the second derivative is a local maximum (step 106). If the second derivative of the voltage E is not the local maximum, the arithmetic / control circuit 5 determines whether the second derivative is 0 (step 107).

The arithmetic / control circuit 5 controls the step current power supply circuit 3 to increase the value of the current I applied to the LD 1 by a certain amount when the second derivative of the voltage E is neither the maximum value nor 0. Send a signal. Accordingly, the step current power supply circuit 3 increases the current I applied to the LD 1 (Step 105).

As shown in FIG. 2, the second derivative 13 of the voltage E
Decreases sharply with an increase in the current I, then turns to increase, reaches a maximum value, and then decreases again to reach zero. Therefore, steps 102 to 104, 106, 107, 1
When the operation of Step 05 is repeated, the second derivative of the voltage E reaches the maximum value. The arithmetic / control circuit 5 determines that the second derivative of the voltage E has a maximum value (YE
S), the value of the current I applied to the LD 1 is changed to a threshold current It
h (step 108).

Thereafter, steps 102 to 104, 10
When the operations 6, 107 and 105 are repeated, the second derivative of the voltage E decreases and reaches zero. Arithmetic / control circuit 5
When the second derivative of the voltage E first becomes 0 (YES in step 107), the step current is controlled via the interface circuit 6 and the D / A / A / D conversion circuits 7 and 8 to stop the measurement. A control signal is sent to the power supply circuit 3 and the voltage measurement circuit 4. Thereby, the step current power supply circuit 3 and the voltage measurement circuit 4 end the measurement.

As described above, according to the characteristic measuring method of the present invention, the IV characteristic can be measured without measuring the IL characteristic of the LD 1.
Only by measuring the characteristics, the threshold current Ith of the LD 1 can be easily derived. Further, according to the characteristic measuring method of the present invention, the threshold current I excellent in measurement accuracy and measurement reproducibility is obtained.
th can be derived.

FIG. 4 shows a second differential characteristic 13 of the voltage E in FIG. 2 and a second differential characteristic 17 of the light output Po in FIG.
Are superimposed on each other. Similarly, the second differential characteristic 1 for each LD obtained by changing the LD to be measured
3 and 17 are shown in FIGS. 4 to 6, in the second differential characteristic 17 of the optical output Po, since a plurality of maximum values appear, there is a possibility that the derived threshold current varies.

On the other hand, the second derivative 13 of the voltage E
Indicates a single maximum value at all times, even if the LD to be measured changes or the measurement is repeated. Therefore, according to the present invention, a stable threshold current Ith without variation can be derived.

In the conventional threshold current deriving method for deriving the threshold current from the IL characteristic of the LD, it may be difficult to derive the threshold current. In other words, in the measurement of the IL characteristic, as shown in FIG. 10, an LD 1 to be measured and an electrical and optical connection provided with a three-dimensional optical coupling space for taking in the light emitted from the LD 1 into the PD 24. A measurement system is required.

However, L measured by the device shape or the like
If the optical coupling between D1 and PD24 is difficult, the threshold current I
th cannot be detected. For example, in checking an optical module or an integrated optical device equipped with an LD, if the optical output is reduced or lost from a waveguide such as an optical fiber, the reduction or loss of the optical output is caused by the internal LD and the waveguide between the LD. It is caused by deterioration or loss of optical coupling, or L
In some cases, it was not easy to determine whether D was caused by a failure.

Similarly, when the LD is mounted on a large device or the like and the mounting space is narrow, the PD cannot be installed in the mounting space of the LD, so that the IL measurement of the LD cannot be performed. On the other hand, in the present invention, it is only necessary to connect two lead wires to the LD and measure the IV characteristics. Therefore, the LD or the closed resonator in a narrow space mounted on an integrated device or the like is required. The threshold current Ith of the ring LD can be derived.

[Second Embodiment] FIG. 7 shows a second embodiment of the present invention.
It is a flowchart figure which shows the characteristic measuring method which becomes embodiment of FIG. Also in the present embodiment, the configuration of the measuring apparatus is the same as that of the first embodiment, and thus the description will be given with reference to FIG. 1 together with FIG. First, the step current power supply circuit 3 applies a current I of a predetermined start value (a value larger than the threshold current) to the LD 1 according to an instruction of the arithmetic / control circuit 5 (step 201).

Subsequently, the voltage measuring circuit 4 measures the forward voltage E of the LD 1 according to the instruction of the arithmetic / control circuit 5 (step 202). The arithmetic / control circuit 5 converts the value of the current I applied from the step current power supply circuit 3 to the LD 1 to D /
The signal is captured via an A / A / D conversion circuit 7 and an interface circuit 6, and the value of the voltage E measured by the voltage measurement circuit 4 is captured via a D / A / A / D conversion circuit 8 and the interface circuit 6. A second derivative of the voltage E with respect to the current I is calculated (step 203).

Next, the arithmetic / control circuit 5 determines whether the second derivative of the calculated voltage E is valid (step 2).
04). When the second derivative of the voltage E is not valid (a very small value that is inappropriate for deriving the threshold current), the arithmetic / control circuit 5 reduces the value of the current I applied to the LD 1 by a certain amount. Interface circuit 6, D / A
A control signal is sent to the step current power supply circuit 3 via the A / D conversion circuit 7. As a result, the step current power supply circuit 3 reduces the current I applied to the LD 1 (Step 205).

The voltage measuring circuit 4 measures the forward voltage E of the LD 1 according to the instruction of the arithmetic / control circuit 5 (step 20).
2) The arithmetic / control circuit 5 calculates the second derivative of the voltage E with respect to the current I (step 203), and calculates the calculated voltage E
It is determined whether or not the second derivative of is valid (step 20).
4). Thus, the operations of steps 202 to 205 are repeated until the second derivative of the voltage E becomes valid.

Next, the arithmetic / control circuit 5 executes step 20
When it is determined in step 4 that the second derivative of the voltage E is valid, it is determined whether the second derivative is a local maximum (step 206). If the second derivative of the voltage E is not the maximum value, the arithmetic / control circuit 5 determines whether the second derivative is in the middle of increasing after the maximum value (step 207).

When the second derivative of the voltage E is not the maximum value and is not increasing after the maximum value, the arithmetic / control circuit 5 reduces the value of the current I applied to the LD 1 by a fixed amount. A control signal is sent to the power supply circuit 3. As a result, the step current power supply circuit 3 reduces the current I applied to the LD 1 (Step 205).

As shown in FIG. 2, the second derivative 13 of the voltage E
Gradually increases with the decrease in the current I, decreases to a local maximum value, and then turns to a sharp increase. Therefore, when the operations of steps 202 to 204, 206, 207, and 205 are repeated, the twice differential value of the voltage E reaches the maximum value. When the second derivative of the voltage E takes the maximum value (YES in step 206), the arithmetic / control circuit 5 outputs the signal LD1.
Is set as the threshold current Ith (step 208).

Thereafter, steps 202 to 204, 20
When the operations of 6, 207 and 205 are repeated, the second derivative of the voltage E decreases and then starts increasing. When the second derivative of the voltage E starts to increase after having reached the maximum value (YES in step 207), the arithmetic / control circuit 5 operates the interface circuit 6 to stop the measurement, and the D / A / A / D
Control signals are sent to the step current power supply circuit 3 and the voltage measurement circuit 4 via the conversion circuits 7 and 8. Thereby, the step current power supply circuit 3 and the voltage measurement circuit 4 end the measurement. As described above, effects similar to those of the first embodiment can be obtained.

[Third Embodiment] FIG. 8 shows a third embodiment of the present invention.
It is a flowchart figure which shows the characteristic measuring method which becomes embodiment of FIG. In the present embodiment, before measuring the IV characteristics of LD1, the IL characteristics of LD1 are measured by a method similar to the conventional method (Step 301).

Subsequently, a second differential characteristic 17 of the light output Po with respect to the current I is obtained. As shown in FIG. 9, the second differential characteristic 17 of the optical output Po with respect to the current I shows a convex characteristic. This convex characteristic gradually increases from 0 with an increase in the current I, decreases after reaching the maximum value, and returns to 0 again.
The current range between the two intersections where the convex characteristic is 0 in contact with the current axis is set as the current range to be measured (step 302).

Next, the arithmetic / control circuit 5 of the measuring apparatus of FIG.
Sends a control signal to the step current power supply circuit 3 to instruct to apply the minimum current I in the current range to be measured. As a result, the step current power supply circuit 3
1 is applied with the minimum current I (step 30).
3). The voltage measuring circuit 4 measures the forward voltage E of the LD 1 according to the instruction of the arithmetic / control circuit 5 (step 30).
4).

The arithmetic / control circuit 5 converts the value of the current I applied from the step current power supply circuit 3 to the LD 1 to D / A · A /
The value of the voltage E measured by the voltage measuring circuit 4 is taken in through the D / A / A / D converting circuit 8 and the interface circuit 6 while being taken in through the D conversion circuit 7 and the interface circuit 6, and the voltage with respect to the current I is taken. The second derivative of E is calculated (step 305).

Next, the arithmetic / control circuit 5 determines whether or not the twice differential value of the calculated voltage E is a maximum value (step 306). If the second derivative of the voltage E is not the local maximum, the arithmetic / control circuit 5 determines whether or not the current range to be measured has ended (step 307).

The arithmetic / control circuit 5 increases the value of the current I applied to the LD 1 by a certain amount when the second derivative of the voltage E is not the maximum value and the current range to be measured is not over. A control signal is sent to the step current power supply circuit 3. Thereby, the step current power supply circuit 3 increases the current I applied to the LD 1 (Step 308). When the operations of steps 304 to 308 are repeated and the second derivative of the voltage E takes a maximum value (Y in step 306)
ES), the arithmetic / control circuit 5 sets the value of the current I applied to the LD 1 as the threshold current Ith (step 309).

Thereafter, when the value of the current I applied to the LD 1 reaches the maximum value in the current range to be measured (step 3).
(YES in 07), arithmetic / control circuit 5 sends a control signal instructing the end of measurement to step current power supply circuit 3 and voltage measurement circuit 4. Thereby, the step current power supply circuit 3 and the voltage measurement circuit 4 end the measurement.

Some conventional measuring devices for measuring the IL characteristics of an LD have a function of measuring the IV characteristics of the LD. If such a measuring device is used, the characteristic measuring method of the present embodiment can be easily realized only by changing the software of the device. In the present embodiment, the current I is gradually increased in the current range to be measured. However, it is needless to say that the current I may be gradually decreased in the current range to be measured.

[Fourth Embodiment] The arithmetic / control circuit 5 according to the first to third embodiments can be realized by a computer. As is well known, a computer has a CPU, R
OM (Read Only Memory), RAM (Random Access Mem)
ory), an auxiliary storage device such as a floppy disk device, and a large-capacity storage device such as a hard disk device.

A program for realizing the characteristic measuring method of the present invention is provided in a state of being recorded on a recording medium such as a floppy disk, CD-ROM, or memory card. When this recording medium is inserted into the auxiliary storage device, the program recorded on the medium is read. And CPU
Writes the read program in a RAM or a large-capacity storage device, and executes the processing described in FIGS. 3, 7, and 8 according to the program. Thus,
Operations similar to the first to third embodiments can be realized.

In the above embodiment, the IV characteristic of the LD 1 is measured while calculating the second derivative of the voltage E. However, all the IV characteristics in a predetermined current range are measured. After the termination, the second derivative of the voltage E may be calculated to derive the threshold current Ith. Further, in the above embodiment, the IV characteristic of the LD is measured using a current that continuously increases or decreases stepwise, but a current that increases or decreases gradually in a pulsed manner may be used. By using such a pulse current, heat generation of the LD can be suppressed.

[0047]

According to the present invention, the threshold current of the semiconductor optical device is derived from the differential value of the differential resistance characteristic of the semiconductor optical device with respect to the current, that is, the second derivative of the forward voltage with respect to the current. In addition, it is possible to derive a threshold current which is excellent in reproducibility with little variation. As a result, it is possible to easily determine the deterioration / failure of the semiconductor optical device based on the derived threshold current. Further, it is not necessary to measure the current-light output characteristics of the semiconductor optical device, and the threshold current can be derived by connecting two lead wires to the semiconductor optical device. It is possible to derive the threshold current of a semiconductor optical device in a narrow space mounted on an integrated device or the like or a ring-shaped semiconductor optical device of a closed resonator. In addition, it is not necessary to apply a large current required for measuring the current-light output characteristics to the semiconductor optical element to obtain the threshold current. For this reason, if the display device is made compact, such as a liquid crystal display, and the arithmetic / control circuit is replaced by a microprocessor with a memory, the respective circuits of the measuring device are integrated, and a battery is used as a power source for these devices. Thus, a handy threshold current checker (tester) can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a measuring apparatus used in a characteristic measuring method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing current-voltage characteristics of a semiconductor laser diode.

FIG. 3 is a flowchart illustrating a characteristic measuring method of the present invention using the measuring device of FIG. 1;

FIG. 4 is a twice differential characteristic diagram illustrating a characteristic measuring method according to the first embodiment of the present invention.

FIG. 5 is a twice differential characteristic diagram showing a characteristic measuring method according to the first embodiment of the present invention.

FIG. 6 is a twice differential characteristic diagram showing a characteristic measuring method according to the first embodiment of the present invention.

FIG. 7 is a flowchart illustrating a characteristic measuring method according to a second embodiment of the present invention.

FIG. 8 is a flowchart illustrating a characteristic measuring method according to a third embodiment of the present invention.

FIG. 9 is a twice differential characteristic diagram illustrating a characteristic measuring method according to a third embodiment of the present invention.

FIG. 10 is a block diagram of a conventional measuring device for measuring current-light output characteristics of a semiconductor laser diode.

FIG. 11 is a current-light output characteristic diagram showing a conventional threshold current deriving method.

FIG. 12 is a graph showing current-current showing another conventional threshold current deriving method.
FIG. 4 is a light output characteristic diagram.

FIG. 13 is a graph showing current-current showing another conventional threshold current deriving method.
FIG. 4 is a light output characteristic diagram.

FIG. 14 is a diagram showing a current-showing another conventional threshold current deriving method.
FIG. 4 is a light output characteristic diagram.

[Explanation of symbols]

1 ... semiconductor laser diode, 2a, 2b ... measurement terminal,
3 Step current power supply circuit 4 Voltage measurement circuit 5 Calculation / control circuit 6 Interface circuit 7, 8 D /
A / A / D conversion circuit, 9: characteristic display device, 11: current-
Voltage characteristic, 12: One-time differential voltage characteristic (differential resistance), 13
... twice differential voltage characteristics, 17 ... twice differential light output characteristics.

Claims (8)

[Claims] 1. A method for measuring characteristics of a semiconductor optical device, wherein a threshold current of the semiconductor optical device is derived from a differential value of a differential resistance characteristic with respect to a current of the semiconductor optical device. A step of applying a current gradually increasing or decreasing stepwise or pulsewise in a forward direction of the semiconductor optical element; a measuring step of measuring a forward voltage of the semiconductor optical element; A method for measuring characteristics of a semiconductor optical device, comprising: a calculation procedure for calculating a second differential value; and a deriving procedure for deriving a threshold current of the semiconductor optical element based on a singular value of the calculated second differential value. 3. The method for measuring characteristics of a semiconductor optical device according to claim 2, wherein the deriving step includes, when the second derivative of the voltage takes a maximum value, a current value applied to the semiconductor optical device as a threshold current. A method for measuring characteristics of a semiconductor optical device. 4. The method for measuring characteristics of a semiconductor optical device according to claim 2, wherein a second differential characteristic of an optical output with respect to a current of the semiconductor optical device is obtained in advance, and a current range of a convex second differential characteristic including a maximum value. A method for measuring characteristics of a semiconductor optical device, comprising: determining a current range to be measured from a current range, and performing the applying, measuring, calculating, and deriving procedures in the determined current range. 5. A recording medium storing a characteristic measurement program for causing a computer to derive a threshold current of a semiconductor optical device from a differential value of a differential resistance characteristic with respect to a current of the semiconductor optical device. 6. An application procedure for applying a current gradually increasing or decreasing stepwise or pulsewise in a forward direction of a semiconductor optical device, a measurement procedure for measuring a forward voltage of the semiconductor optical device, Recording medium for recording a characteristic measurement program for causing a computer to execute a calculation procedure for calculating a second derivative, and a derivation procedure for deriving a threshold current of a semiconductor optical device based on a singular value of the calculated second derivative . 7. The recording medium on which the characteristic measurement program according to claim 6 is recorded, wherein the deriving step includes a step of determining a current value applied to the semiconductor optical element when the second derivative of the voltage has a maximum value, as a threshold current. A recording medium on which a characteristic measurement program is recorded. 8. A recording medium on which the characteristic measurement program according to claim 6 is recorded, wherein a second derivative of an optical output with respect to a current of a semiconductor optical element is obtained in advance, and a current of a convex second derivative including a maximum value is obtained. A recording medium storing a characteristic measurement program, wherein a current range to be measured is determined from the range, and the application procedure, the measurement procedure, the calculation procedure, and the derivation procedure are performed in the determined current range.