JPH025587A - Characteristic measurement of semiconductor laser and device therefor - Google Patents

Abstract

PURPOSE:To measure the characteristic of an LD element easily at a low cost by a method wherein a waveform is obtained by detecting the change with time of the intensity distribution of an interference fringe formed through an interferometer, whose sharp phase discontinuous point is detected to measure an oscillating wavelength property, which is dependent on an injection current under a specified condition, of a semiconductor laser element. CONSTITUTION:Laser rays, projected from an interferometer, are detected by a photodetector 9 such as a photodiode or the like to obtain an intensity change signal (fringe change signal) 10 of an interference fringe formed through an interferometer 8 at the position of the photodetector 9, the change signal 10 is inputted into a computer 11, and a signal process is performed to detect a mode hopping. The computer 11, composed of a microprocessor, a memory and others, controls an LD drive circuit 1 corresponding to the fringe change signal 10, detects a mode hopping, and perform a measurement control as an interferometer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for measuring characteristics of a semiconductor laser, and more particularly to a method and apparatus for measuring characteristics of a semiconductor laser for measuring oscillation wavelength characteristics of a semiconductor laser element.

[Prior Art] Semiconductor lasers (hereinafter referred to as LDs) are simpler, cheaper, smaller, and lighter in device configuration than gas lasers, and are suitable for use as light sources for optical communication, audio, or video optical disks, etc.
It is widely used in Further, recently, research has been actively conducted on its application to light sources for optical interferometers.

[Problem to be solved by the invention] In an LD element, the oscillation wavelength changes depending on the current injected into the element, but the relationship between the two is not linear, and the oscillation wavelength changes after a certain injection current value. It has a so-called mode hopping characteristic that changes discontinuously.

Interferometers perform measurements by observing interference fringes formed by wavelength scanning, but if the mode hopping described above occurs, the oscillation wavelength will change.
It must be used to avoid dry hopping points. Furthermore, mode hopping does not always occur at a constant injection current value, and the mode hopping point varies depending on temperature conditions, etc., so to avoid mode hopping, consider the injection current, temperature, and other conditions and the characteristics of the oscillation wavelength in advance. Must be measured.

For this purpose, it is necessary to measure the oscillation wavelength of the LD element using a spectrometer using a diffraction grating, an interferometer, or the like.

However, the method using a spectroscope has the following problem.

1) A diffraction grating or an interferometer reflecting mirror is used as a laser beam. 2) A complicated device is required, especially when the LD element is used as a light source in order to be evaluated when it is mounted on a device such as an interferometer. A structure is required to introduce a device into the system under test, making the entire equipment complicated and large. Furthermore, this is not a practical method if it is necessary to calibrate each device one by one before shipping.

An object of the present invention is to solve the above-mentioned problems and to make it possible to easily and inexpensively measure the characteristics of an LD element.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a semiconductor laser characteristic measurement method and apparatus for measuring the oscillation wavelength characteristics of a semiconductor laser element. The LED light from the semiconductor laser element, whose conditions can be controlled as desired, was introduced into an interferometer to form interference fringes, and the temperature of the semiconductor laser element was controlled to a predetermined value. The injected current of the semiconductor laser element under a predetermined temperature condition is determined by detecting the sharp phase discontinuity point of the waveform obtained by changing the intensity distribution of the interference fringes formed by the interferometer. According to the above configuration, the time-varying signal of the interference fringe intensity can be observed using a photodetector, which requires less equipment than using a measurement spectrometer. The configuration is simple and measurements can be performed in a short time. In particular, when the device is constructed as an interferometer, measurements can be made using the hardware of the interferometer itself, and the device can be constructed easily, inexpensively, small and lightweight.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings. Here, we will show an example of an interferometer and show the L of its light source.
A configuration for measuring the oscillation characteristics of a D element will be illustrated.

FIG. 1 shows the configuration of an interferometer employing the present invention.

The laser light source is a single mode oscillation LD element 3, and the ATM
(Temperature control circuit) 2 receives temperature control.

ATM 2 controls the temperature of the I and D elements 3 to a desired constant value. This control temperature value is determined by the computer 11.

Further, the driving current of the LD element 3 is controlled by the LD ffi dynamic circuit 1, and the oscillation wavelength of the LD element 3 is adjusted by changing this driving current. In the i, D element 3, the refractive index of the waveguide changes due to a change in the injection current, and the oscillation wavelength changes.

The diverging light emitted from the LD element 3 is passed through the collimating lens 4.
is converted into parallel light by The collimated laser beam is guided into the interferometer 8. Here, the structure of a Michelson type interferometer is illustrated.

The laser beam incident on the interferometer 8 is split into two by the beam splitter 5.
It is divided into two luminous fluxes. The two light beams each have a fixed mirror 6.
The beams are reflected by the movable mirror 7 with an optical path difference, and are combined again into one beam by the beam splitter 5 to interfere with each other, and are emitted in a direction perpendicular to the direction of incidence.

The laser beam emitted from the interferometer 8 is received by a light receiving element 9 such as a photodiode, and an intensity change signal (fringe change signal) 1 of interference fringes created by the interferometer 8 at the position of the light receiving element 9 is generated.
0 is obtained, this signal waveform is imported into the computer 11, and signal processing is performed to detect mode hopping.
The computer 11 is composed of a microprocessor, a memory, etc., and controls the X and D drive circuits 1 according to the fringe change signal 10 as described later, and performs detection of 1,000-degree hopping and measurement with an interferometer. control.

The operation of the apparatus of the present invention constructed as described above will be described below.

There is an optical path difference between the reflected light from the fixed mirror 6 and the reflected light from the movable mirror 7, which are obtained by inputting a laser beam of wavelength λ into the interferometer 8!
, then 2 π a−Aexpj (X+φ0)−(1)λ which are respectively expressed by the following equations.The interference fringes obtained by interfering the two reflected lights are expressed by the following equations.

In Figure 2, from equation (3), the vertical axis represents the light intensity! , a graph in which the oscillation wavelength λ is plotted on the horizontal axis.

Here, the LD element 3 has an injected current t as shown in FIG.
From o to 11, the wavelength of the laser light increases monotonically from λO to λ,1, and at 11 the wavelength jumps from λ,1 to λ,2,
After that, suppose that the injection current i has a characteristic (one mode hopping) that increases monotonically with the injection current from λ2, and the injection current i is increased at a constant rate of change with respect to time. The changes in the interference fringes at this time are as shown in FIG. 4, and it can be seen that the jump in the wavelength of the laser beam can be detected by the jump in the phase (discontinuity) of the cosine change of the interference fringes in the injected current 11. In FIG. 4, the horizontal axis represents the injection current i.

Detection of phase jumps in cosine changes in interference fringes can be performed by first-order differentiation of this signal waveform.

FIG. 5 shows a waveform obtained by first-order differentiation of the waveform in FIG. 4. As shown in the figure, the cosine change only changes to a sine change due to the -th differentiation, but the waveform takes very unnatural values where the phase jumps, so this causes the phase jump, that is, the mode hopping point. can be detected.

The object of measurement in the present invention is a semiconductor laser with East mode oscillation and a variable wavelength. FIG. 6 shows the injection current-oscillation wavelength characteristics of a single mode oscillation semiconductor laser. As shown in the figure, in an actual device, there is a linear relationship between the injection current and the oscillation wavelength within a certain injection current range, but the oscillation wavelength jumps significantly due to mode hops at several locations. Mode hopping depends on the temperature and injection current of the semiconductor laser, as well as the oscillation wavelength. When measuring mode hopping for this purpose, either the temperature or the injection current must be kept constant.

Next, with reference to FIG. 13, a procedure for measuring the sod hobbing of a semiconductor laser according to the present invention will be explained. The procedure shown in FIG. 13 is executed by the computer 11.

First, in step S1 of FIG. 13, the temperature of the LD element 3 is made constant at an arbitrary value by the ATM 2.

Subsequently, in step S2, the oscillation flow of the y-D element 3 is changed at a constant rate with respect to time, and wavelength scanning is performed at a constant rate.

Subsequently, in step S3, the light from the LD element 3 is applied to the interferometer 8 to obtain interference fringes, the interference fringes are received by the light receiving element 9, and the waveform of the pot acceptance signal 10 is input into the computer 11. FIG. 8 shows an example of the waveform of the pot receiving signal, in which a thousand-degree hopping occurs at the mouth Jf time Mi. When inputting the waveform of the pot reception signal 10 to the computer 11, a quantized data string is actually input at every predetermined sampling time.

Next, in step S4, a first-order differential calculation of the refined signal waveform is performed using Compic and -11. FIG. 9 shows a waveform obtained by firstly differentiating the waveform of FIG. 8. Actually computer 1
1, this waveform is composed of the same data string as above.

Next, in step S5, detection! A novel is set, and a location where the next differential waveform has an extremely large value (a location where the rate of change is large) is detected to detect thousand-degree hopping.

Specifically, mode hopping points are detected by sequentially comparing the first-order differential data string with a predetermined threshold value.

FIG. 10 shows the mode hopping points detected from FIG. 9. Here, the value of the injection current at which mode hopping occurred is calculated in correspondence with FIG. Dohotsubing with a white circle and S decreases by 7! The mode hopping detected in this case is indicated by a black circle.

Subsequently, in step S6, measurements are repeated under the same conditions to calculate the average value of the injection current values at which mode hopping occurs.

Next, in step S7, the ATM 2 shifts the temperatures of the D elements 1 and 3 at regular intervals, and the above process is repeated to detect mode hopping for each temperature in 1 step. 1/Zuru mode hopping point vertically +1 to the different temperature conditions measured! II]
jζ temperature, note on horizontal axis, 1. Here, as in FIG. 10, the mode hopping when the wavelength increases is shown by a white circle, and the mode hopping when the wavelength decreases is shown by a black circle.

As is clear from FIG. 11, the value of the injection current at which mode hopping occurs varies depending on the temperature.

As described above, the mode hopping point can be detected by changing the current injected into the LD element 7-3 over time and detecting a sudden phase jump from the first differential value of the obtained interference fringe change signal. . For example, as shown in FIG. 11, it is possible to measure a thousand-day hopping point depending on the temperature condition, so when operating the interferometer, the ATM 2 is used to control the LD element 3 so that thousand-day hopping does not occur within the desired injection current range. By controlling the temperature of the LD element 3, it is possible to perform measurements only in the region where the injection current/'oscillation wavelength of the LD element 3 linearly corresponds. In addition, the above-mentioned thousand-day hopping measurement is performed at timings such as when the device is started, and an automatic comparison is performed in which various religions are changed during device operation based on the thousand-day hopping conditions obtained by the method. I can also do things.

Characteristic measurements can be performed using the interferometer's own hardware, so there is no need to introduce a new measurement system.
The configuration of the device can be made simple and inexpensive. In particular, measurements can be made in a short time without the need for mechanical control, and moreover, the measurement can be performed continuously over the entire oscillation region of the LD element.
4, the gender can be detected. .

Although FIG. 1 is explained using a Michelson type interferometer, the present invention can also be applied to other interferometers such as a Fizeau type, L. Weiman-Green type, and Matsuhatsu-Ender type.

In addition, if the graph in Figure 11 is folded in the middle as shown in Figure 12, thousand-degree hopping will not occur, such as when it is necessary to increase or decrease the injected current for one or more cycles during interference measurement operation. This is convenient for finding the conditions of temperature and injection current. Such processing is effective when outputting the measurement results in a graph format using a printer or the like.

Note that the method of taking the first-order differential of the refined signal waveform shown in FIG. 5 can also be performed using an analog differentiator circuit.

Further, as the beam splitter 5, a cube beam splitter, a wedged half mirror, or the like is used. A polarizing beam splitter can also be used when a .72 or Fizeau interferometer is applied.

[Effects of the Invention] As is clear from the above, according to the great invention, in a semiconductor laser characteristic measuring method and apparatus for measuring the oscillation wavelength characteristics of a semiconductor laser element, injection current and temperature conditions during driving can be controlled as desired. The laser light from the semiconductor laser device was introduced into the interferometer to form interference fringes, and the temperature of the semiconductors 1 and 2 was controlled to a predetermined value. By detecting the sharp phase discontinuity point of the waveform obtained by detecting the time change in the intensity distribution of the interference fringes formed by the oscillation that depends on the injected current of the semiconductor tz-the element at a predetermined temperature condition. Since the configuration for measuring wavelength characteristics is adopted, the configuration of the device is simple, inexpensive, small and lightweight, and the oscillation wavelength characteristics can be reliably detected in a short time. In addition, when implementing the present invention in an interferometer that uses a semiconductor laser element as a light source, the hardware of the interferometer itself can be used, so there are advantages such as no need to add a new measurement system to the device. There is.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the structure of an interferometer that adopts the present invention, Figure 2 is a waveform diagram showing the characteristics of the interference fringes in the device j in Figure 1, and Figure 3 is an LD. A diagram showing thousand-day hopping of the element, FIG. 4 is a waveform diagram showing the characteristics of interference fringes when there is thousand-day hopping, and FIG. 5 shows the first-order differential waveform of the waveform in FIG. 4. ? - waveform diagram, Figure 6 is a diagram showing the thousand-degree hopping of the LD element, Figure 7 is a diagram showing the injection current when measuring the characteristics of + and D elements, and Figure 8 is the diagram of Figure 7. Waveform diagram of the wheat refining signal obtained from the drive characteristics, No. 9
The figure is a waveform diagram showing the first-order differential waveform of the waveform in Figure 8.
Figure 0 is an explanatory diagram showing the mode hopping points detected from Figure 9, and Figure 11 is an explanatory diagram showing the mode hopping points detected from Figure 9. Explanatory diagram showing the mode hoppinog points obtained by changing 1, 12th
The figure is an explanatory diagram of 1-1,000-degree hopping by folding back FIG. 11 at the center, and FIG. 13 is a flowchart illustrating the measurement control procedure in the present invention. l...! , D drive shift each foot
2..., to TM3...LD element
4...Collimating lens 5...Beam splitter

Claims (1)

[Scope of Claims] (1) In a semiconductor laser characteristic measurement method for measuring the oscillation wavelength characteristics of a semiconductor laser device, a laser beam of a semiconductor laser device whose injection current and temperature conditions during driving can be controlled as desired is measured using an interferometer. After controlling the temperature of the semiconductor laser element to a predetermined value, the injection current of the semiconductor laser element is changed, and the time change in the intensity distribution of the interference fringes formed by the interferometer is detected. A method for measuring characteristics of a semiconductor laser, comprising: measuring an oscillation wavelength characteristic depending on an injected current of the semiconductor laser element under a predetermined temperature condition by detecting an abrupt phase discontinuity point in the obtained waveform. (2) Semiconductor laser characteristic measurement according to claim 1, characterized in that the temperature conditions during measurement of the oscillation wavelength characteristics are changed and the oscillation wavelength characteristics of the semiconductor laser element are measured under a plurality of temperature conditions. Method (3) A semiconductor laser characteristic measuring device for measuring the oscillation wavelength characteristics of a semiconductor laser device, comprising means for controlling the injection current during driving of the semiconductor laser device to a desired value, and controlling the temperature of the semiconductor laser device to a desired value. an interferometer that introduces laser light from a semiconductor laser element and forms interference fringes according to the wavelength of the laser light; and means that measures the intensity distribution of the interference fringes formed by the interferometer; The temperature control means controls the temperature of the semiconductor laser element to a predetermined value, the injection current control means changes the injection current of the semiconductor laser element, and the measurement means detects a time change in the intensity distribution of the interference fringes. A semiconductor laser characterized in that it is provided with a measurement control means for measuring an oscillation wavelength characteristic depending on the injection current under a predetermined temperature condition of the semiconductor laser element by detecting an abrupt phase discontinuity point of the obtained waveform. Characteristic measuring device. (4) The temperature control means changes the temperature conditions when measuring the oscillation wavelength characteristics, and the oscillation wavelength characteristics of the semiconductor laser element under a plurality of temperature conditions are measured. Semiconductor laser characteristic measurement device.