JPH11150325A - Measurement of lasing wavelength of distributed reflection type laser and method of design - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of designing a DBR laser, which considers relation of reflection characteristics of a DBR (Bragg reflector) mirror to gain characteristics of an active medium from a design stage of the DBR laser. SOLUTION: A method of designing a distributed reflection type laser of a structure is provided, wherein a resonator is constituted into such a structure that an active layer is provided between first and second distributed reflection type mirrors provided in opposition to each other, and a laser beam is outputted via the first distributed reflection type mirror and in the reflection spectrum of the first distributed reflection type mirror. More than one wavelength to reduce the reflectivity to a prescribed level exist (short broken lines) and the gain of the active layer in at least one wavelength out of the wavelengths in which a reduction in the reflectivity is generated and the reflectivity (long broken lines) of the second distributed reflection type mirror are set to that they respectively become higher than a prescribed gain and a prescribed reflectivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed Bragg reflector (DBR) laser having a DBR (Distributed Bragg reflector) structure, and more particularly, to forming an active layer between opposed Bragg reflectors. To form a resonator, and a surface emitting laser (SEL: surface emitting laser) in which laser output is performed through one Bragg reflector.
(Laser) lasing wavelength measurement method and design method.

Here, lasing refers to a laser operation in which electrons transition to a high-energy state and light of almost a single wavelength is generated by stimulated emission. The lasing wavelength refers to the possibility of laser oscillation in the resonator. Wavelength.

[0003]

2. Description of the Related Art In recent years, a surface emitting laser (SEL) has received much attention for the following reasons.

(1) Since SEL can emit light in a direction perpendicular to the wafer surface, a two-dimensional array of lasers is possible.

(2) A semiconductor laser that emits light from an end face emits an elliptical beam due to its structure, whereas an SEL emits a circular beam. Therefore, fiber coupling can be easily realized.

(3) Laser two-dimensional (2D) array of SELs is possible, which is useful for high-density optical interconnection.

(4) SELs can operate in the ultraviolet to near-infrared range, depending on the quantum well material, and can be a versatile source.

(5) Since the SEL has a resonator length as short as the radiation wavelength, it can emit the shortest optical pulse among semiconductor lasers, and can perform optical communication, optical drive line switch, and photoconductive sampler module. It can also be applied to other applications.

This SEL requires high precision in assembling the SEL in order to obtain an optimized output with a low threshold value.

[0010]

There has been no detailed study on the relationship between the reflection characteristic of the DBR mirror and the gain characteristic of the active medium in the SEL, and these relationships are considered from the design stage of the SEL. There was no idea. Therefore, conventionally, D having various reflection characteristics
A plurality of SELs having BR mirrors are manufactured, and these SELs
Inefficient work such as checking whether or not to obtain a good laser oscillation by actually operating the device has been performed.

In order to efficiently manufacture the SEL, the inventors conducted a detailed study on the relationship between the reflection characteristic of the DBR mirror and the gain characteristic of the active medium. It was found that the wavelength greatly affected. For example, in the SEL, the reflection characteristic of the DBR mirror on the light output side (the change in the reflectance with respect to the wavelength; here, the wavelength at which the reflectance sharply decreases becomes important) and the gain curve of the active medium (with respect to the wavelength) It is found that the relationship between the change in gain and the wavelength having a peak becomes important) greatly affects the lasing wavelength of the SEL.

As can be seen from the above research results, SEL
Considering the relationship between the reflection characteristics of the DBR mirror and the gain characteristics of the active medium from the design stage of
Can be realized. Furthermore, SEL
SEL before the package without actually operating
Can be known, and thereby the throughput can be improved.

The present invention has been made in view of the above results, and provides a lasing wavelength measuring method capable of knowing a lasing wavelength before a package without actually operating the SEL. DB from stage
It is an object of the present invention to provide a method of designing a DBR laser in consideration of a relationship between a reflection characteristic of an R mirror and a gain characteristic of an active medium.

[0014]

In order to achieve the above object, a lasing wavelength measuring method according to the present invention is characterized in that an active layer is provided between first and second distributed reflection mirrors provided opposite to each other, and a resonance is provided. A measuring device for measuring the lasing wavelength of the distributed reflection type laser in which the laser beam is outputted via the first distributed reflection type mirror, wherein the first and second distributed reflection type mirrors are respectively provided. A first step of measuring the reflection spectrum of the first distributed reflection type mirror and comparing the reflection spectrum of the first distributed reflection type mirror with a gain characteristic indicating a change in gain with respect to a wavelength of the active layer obtained in advance, A second step of obtaining a wavelength at which the reflectance of the distributed reflection type mirror falls to a predetermined reflectance and the gain of the active layer is equal to or more than a predetermined gain; and
A wavelength at which the reflectance of the second distributed reflection type mirror is equal to or higher than a predetermined reflectance among the wavelengths determined in the step (c).

According to the design method of the present invention, a resonator is formed by providing an active layer between first and second distributed reflection mirrors provided opposite to each other, and a resonator is formed via the first distributed reflection mirror. A method of designing a distributed-reflection laser in which laser light is output, wherein one or more wavelengths at which the reflectance falls to a predetermined reflectance are present in the reflection spectrum of the first distributed-reflection mirror. The gain of the active layer and the reflectance of the second distributed-reflection mirror at at least one wavelength among the wavelengths causing a decrease in reflectance are respectively equal to or higher than a predetermined gain and a predetermined reflectance. I do.

In the above case, at least one of the wavelengths at which the reflectance of the first distributed reflection mirror causes a decrease in the reflectance and a gain curve indicating a change in gain with respect to the wavelength of the active layer obtained in advance. May be made to substantially coincide with the peak wavelength.

<Operation> As will be described in detail in the embodiment, an active layer is provided between first and second distributed reflection mirrors provided opposite to each other to form a resonator, and a first distribution mirror is formed. In a distributed reflection laser in which laser light is output via a reflection mirror, the gain of the active layer is sufficient at a wavelength at which the reflectance of the first distributed reflection mirror on the light output side sharply decreases, and The condition for obtaining laser oscillation is that the reflectance of the second distributed reflection mirror is sufficiently high. In the design method of the present invention, since the design is performed so as to satisfy these conditions, good laser oscillation can be obtained, and the inefficient work as in the related art is not performed.

Further, the wavelength at which the reflectance of the first distributed-reflection type mirror rapidly falls and the peak wavelength of the gain curve of the active layer coincide with each other, and the reflectance of the second distributed-reflection type mirror is sufficiently high. By doing so, a higher laser output can be obtained. In the design method of the present invention, a design is performed so as to satisfy this condition, so that a laser having a higher laser output can be obtained.

Since laser oscillation can be obtained in the relationship between the reflection characteristics of the first and second distributed reflection mirrors and the gain characteristics of the active layer as described above, the reflection of the first and second distributed reflection mirrors can be improved. By knowing the characteristics and the gain characteristics of the active layer, the lasing wavelength can be known. In the lasing wavelength measurement method of the present invention, since the gain characteristics of the active medium used for the active layer are obtained in advance, the reflection spectra are measured for the first and second distributed reflection mirrors, respectively. You can know the lasing wavelength. As described above, the lasing wavelength can be known by measuring the reflection spectrum of each of the first and second distributed reflection type mirrors. Therefore, even before the package, the lasing wavelength can be obtained without actually operating the SEL. Can be measured.

[0020]

Next, embodiments of the present invention will be described with reference to the drawings.

First, a specific configuration of the SEL will be described. FIG. 9 is a cross-sectional view showing a schematic configuration of an SEL applicable to the present invention. This SEL is composed of a plurality of layers of a pair of AlAs / AlGaAs on an n-type substrate 100.
DBR mirror 101, active layer 102, AlAs / Al
A p-type DBR mirror 103 composed of a plurality of layers of GaAs, an SiO 2 layer 104, a p-electrode 105, and an n-electrode 106 are sequentially stacked.
The mirror 103 side is an emission surface.

In the SEL having the above configuration, a resonator is formed between the n-type DBR mirror 101 and the p-type DBR mirror 103, and the reflectance increases at a wavelength that matches the periodic structure of these mirrors, and laser oscillation occurs. In this SEL, the reflection characteristics of the p-type DBR 103 on the light output side (the change in the reflectance with respect to the wavelength; here, the wavelength at which the reflectance sharply decreases are important) and the gain curve of the active layer 102 (the wavelength (The wavelength having a peak becomes important due to the change in gain with respect to the above) greatly affects the lasing wavelength of the SEL.

Hereinafter, the relationship between the reflection characteristic of the p-type DBR mirror 103 and the gain curve of the active layer 102 with respect to the performance of the SEL will be described.

EXPERIMENTAL EXAMPLE 1 The SEL used here has the same structure as the SEL shown in FIG. 9. Both the n-type DBR mirror and the p-type DBR mirror each have 20 AlAs / AlGaAs pairs.
The thickness of the AlAs / AlGaAs layer is 71.2 / 59.
8 nm, number of quantum wells (QW) is 4, QW thickness is 9n
The distance between m and QW is 7 nm, the thickness of the spacer / self-confinement heterostructure (SCH) is 359/150 nm, and the resonator length is 4λ (850 nm). 8 of this SEL
FIG. 1 shows the reflectance characteristics of the DBR mirror in the range of 00 to 900 nm. In the figure, the solid line indicates the calculated value of the reflectance of an ideal DBR mirror, the short broken line indicates the measured value of the reflectance of an n-type DBR mirror, and the long broken line indicates the measured value of the reflectance of a p-type DBR mirror. Here, the range of 800 to 900 nm is D
This is selected according to the gain curve of the GaAs quantum well constituting the BR mirror.

Referring to FIG. 1, AlAs / AlGaAs
For a DBR mirror with 20 pairs of s, ideally 81
A reflection spectrum exceeding 99% can be achieved in the range of 0 to 890 nm. In the case of the p-type DBR mirror, the reflectance decreases to about 45% around 858 nm,
It decreases to about 55% around 4 nm. On the other hand, these 858
The reflectivity of the n-type DBR mirror at around nm and 884 nm exceeds 99%.

The lasing spectrum of this SEL (Ga
FIG. 2 shows a gain curve of a quantum well of As. Comparing the reflectance characteristic shown in FIG. 1 with the lasing spectrum in FIG. 2, the vicinity of 884 nm where the reflectance sharply drops in the p-type DBR mirror deviates from the peak wavelength of the lasing spectrum, and the gain near 884 nm shows the gain. It turns out that it cannot be obtained. Therefore, laser output cannot be expected around 884 nm.

On the other hand, although the vicinity of 858 nm does not coincide with the peak wavelength of the lasing spectrum, it is near the peak wavelength, and it can be seen that a certain gain can be obtained. Therefore, if the laser oscillation wavelength is satisfied around 858 nm, light output can be obtained at this wavelength around 858 nm. However, in this case, the reflectance is about 4
Since it is reduced to 5%, a high output cannot be expected because the cavity loss increases.

EXPERIMENTAL EXAMPLE 2 The SEL used here is the same as that of Experimental Example 1 except that the thickness of the spacer / self-confinement heterostructure (SCH) is 1125/150 nm and the resonator length is 10λ (850 nm). It has the same structure as SEL. FIGS. 3 and 4 show a reflectance characteristic diagram and a lasing spectrum diagram of the DBR mirror of this SEL, respectively. In FIG. 3, a solid line indicates a calculated value of the reflectance of an ideal DBR mirror, a short broken line indicates a measured value of the reflectance of an n-type DBR mirror, and a long broken line indicates a measured value of the reflectance of a p-type DBR mirror.

Referring to FIG. 3 and FIG. 4, there are a plurality of peaks in the lasing spectrum, and three wavelengths of 814 nm, 834 nm, and 840 nm correspond to the peaks at which the reflectance of the p-type DBR mirror decreases. There is a wavelength.

The first peak of the lasing spectrum is 8
The reflectance of the p-type DBR mirror and the n-type DBR mirror at this wavelength is about 70%, respectively.
And about 90%. Here, since the first peak of the lasing spectrum is small and the gain is not so remarkable, a high laser output cannot be expected.

The second and third peaks of the lasing spectrum are 834 nm and 840 nm, respectively, and these peaks overlap. The reflectivity of the p-type DBR mirror near the wavelengths of these second and third peaks is both 1
It has dropped to the 0% range. Here, the second and third peaks of the lasing spectrum are large and a sufficient gain can be obtained, but a high laser output cannot be expected because the reflectance of the p-type DBR mirror is as low as 10%.

Although there are some sharp drops in the reflectance of the p-type DBR mirror near 860 nm and further above, there is no peak in the lasing spectrum at these wavelengths, and laser output cannot be expected.

Experimental Example 3 The SEL used here has a spacer / self-confinement heterostructure (SCH) thickness of 104.3 / 150 nm,
The structure is the same as that of the SEL of Experimental Example 1 except that the resonator length is 2λ (850 nm). FIGS. 5 and 6 show a reflectance characteristic diagram and a lasing spectrum diagram of the DBR mirror of this SEL, respectively. In FIG. 5, the solid line indicates the calculated value of the theoretical reflectance of the SEL DBR mirror, the short broken line indicates the measured value of the reflectance of the n-type DBR mirror, and the long broken line indicates the measured value of the reflectance of the p-type DBR mirror.

Referring to FIGS. 5 and 6, the lasing spectrum has a first peak near 818 nm,
There is a second peak near 850 nm, and these 818n
There is a sharp decrease in the reflectance of the p-type DBR mirror near m and around 850 nm. The reflectivity of the p-type DBR mirror and the n-type DBR mirror near 818 nm exceeds 85% and 95%, respectively, and the reflectivity of the p-type DBR mirror and the n-type DBR mirror near 850 nm exceeds 40% and 99%, respectively. Therefore, in the SEL in this experimental example, the SEL around 818 nm and 850 nm
A laser output can be expected in the vicinity.

There are several wavelengths at which the reflectivity of the p-type DBR mirror rapidly decreases, except for around 818 nm and 850 nm. At these wavelengths, there is no peak in the lasing spectrum, and it is expected that a laser output will be obtained. Can not.

Experimental Example 4 The SEL used here has a spacer / self-confinement heterostructure (SCH) thickness of 104.3 / 150 nm,
The structure is the same as that of the SEL of Experimental Example 1 except that the resonator length is 2λ (850 nm). FIGS. 7 and 8 show a reflectance characteristic diagram and a lasing spectrum diagram of the DBR mirror of this SEL, respectively. In FIG. 7, the solid line shows the calculated value of the reflectance of an ideal DBR mirror, the short broken line shows the measured value of the reflectance of an n-type DBR mirror, and the long broken line shows the measured value of the reflectance of a p-type DBR mirror.

Referring to FIGS. 7 and 8, the lasing spectrum has a peak near 814 nm.
At around 14 nm, the reflectance of the p-type DBR mirror is 15
%, And the reflectance of the n-type DBR mirror is 60%. Therefore, the SEL in this experimental example
Then, it can be expected that a laser output is obtained at around 814 nm.

There are several wavelengths at which the reflectivity of the p-type DBR mirror rapidly decreases except around 814 nm. However, at these wavelengths, there is no peak in the lasing spectrum, and it cannot be expected to obtain a laser output.

As can be seen from the above experimental examples 1 to 4, in order to obtain a laser output, there is a sharp drop in the reflectance in the reflection spectrum of the DBR mirror on the light output side, and the wavelength of the drop is determined by the lasing of the active medium. It is necessary that the reflectivity of the DBR mirror on the other side at this wavelength is at least equal to or higher than the reflectivity at which laser oscillation is possible, and that the peak wavelength substantially coincides with the peak wavelength of the spectrum, and that the reflectivity of the DBR mirror at this wavelength is at least higher. is there.

Next, a method for measuring the lasing wavelength of a DBR laser and a method for designing the DBR laser using the conditions for obtaining the above laser output will be described.

<Lasing Wavelength Measuring Method> As described above, in a SEL having a Bragg reflector structure, if the gain curve of the active medium is known in advance, the reflection spectrum of each DBR mirror constituting the SEL must be measured. Thus, the lasing wavelength can be accurately known without operating the SEL.

Hereinafter, taking the SEL shown in FIG. 9 as an example, the procedure of measuring the lasing wavelength will be specifically described.

First, the respective reflection spectra of the n-type DBR mirror 101 and the p-type DBR mirror 103 are measured. Then, the reflection spectrum of the p-type DBR mirror 103 is compared with a gain curve indicating a change in gain with respect to the wavelength of the active layer 102 obtained in advance, and the p-type DBR
A wavelength at which a predetermined gain or more is found on the gain curve of the active medium at a wavelength at which the reflectance sharply drops in the reflection spectrum of the mirror 103 is examined. Further, among the wavelengths on the peak of the gain curve, an n-type DB at a wavelength equal to or higher than a predetermined reflectance (reflectivity capable of laser oscillation) is used.
The wavelength at which the reflection spectrum of the R mirror 101 is equal to or higher than the reflectivity at which laser oscillation is possible is examined. The wavelength thus obtained is the lasing wavelength in the SEL, and laser output is possible at this wavelength.

At the lasing wavelength measured as described above, the laser output is determined by the magnitude of the gain. Therefore, a larger laser output can be obtained as the wavelength at which the reflectance sharply drops in the reflection spectrum of the p-type DBR mirror 103 is closer to the wavelength at the peak of the gain curve.

According to the measurement of the lasing wavelength described above, S
Before actually operating the EL, the lasing wavelength can be accurately known from the reflection spectrum of each DBR mirror and the gain curve of the active medium. Also, from the comparison result between the reflection spectrum and the gain curve, a sharp drop shows a DBR mirror on the light output side (here, the p-type DBR mirror 103).
If the decrease in the wavelength existing in the reflection spectrum is on the gain curve of the active layer and the laser oscillation condition is satisfied, a laser output is generated. However, in order to obtain a high output SEL, at a wavelength where the gain curve of the active layer has a peak, a p-type DBR mirror having a shallow dip in the reflection spectrum and an n having a reflectance of more than 99%
A type DBR mirror is required.

<Design Method of DBR Laser> In order to fabricate a DBR laser, first, there is at least one sharp drop in the reflectance in the reflection spectrum of the DBR mirror on the light output side. It is necessary that the wavelength at which the drop occurs is a wavelength at which a predetermined gain or more is obtained in the active medium. Second, the sharp drop in the reflectance is at least the reflectance at which laser oscillation is possible, and the reflectance of the DBR mirror on the other side at that wavelength needs to be sufficiently high. These first
By satisfying the second condition, the DBR laser can be efficiently manufactured, and the throughput in the manufacturing process can be improved.

Further, under the above first condition, the wavelength at which the reflectance sharply drops in the reflection spectrum of the DBR mirror on the light output side is substantially equal to the peak wavelength of the gain curve of the active medium. Then, a DBR laser having a higher laser output can be efficiently manufactured.

Furthermore, by making the width of the sharp reflectance drop in the reflection spectrum of the DBR on the light output side very narrow, it becomes possible to operate the SEL at a single wavelength.

Further, by extremely shortening the resonator length of the SEL, it is possible to generate a pulse whose pulse length limited by the resonator length is made as short as possible. It is possible to generate a light pulse that is almost one digit shorter than a conventional edge emitting laser.

Although the laser gain shifts to the longer wavelength side as the temperature rises, the reflectivity shifts in the opposite direction at a slower speed, so it is necessary to optimize the position of the sharp drop in the reflection spectrum. Become.

Although the SEL in which the p-type DBR mirror is provided on the light output side has been described above, the SEL applied to the lasing wavelength measuring method and the designing method of the present invention is not limited to this configuration. An n-type DBR mirror may be provided on the light output side.

[0052]

According to the present invention configured as described above, the following effects can be obtained.

According to the design method of the present invention, the gain of the active layer is sufficient at the wavelength where the reflectance of the distributed reflection mirror on the light output side sharply drops, and the reflectance of the second distributed reflection mirror is sufficient. Since the DBR laser is designed to be sufficiently high, the DBR laser can be manufactured efficiently.

In addition, the wavelength at which the reflectivity of the distributed reflection mirror on the light output side sharply falls is matched with the peak wavelength of the gain curve of the active layer, and the reflectance of the distributed reflection mirror on the other side is sufficiently increased. Therefore, a high-power DBR laser can be manufactured.

Further, according to the lasing wavelength measuring method of the present invention, the lasing wavelength can be measured without actually operating the SEL even before the package, so that the throughput in the manufacturing process of the DBR laser can be reduced. Improvement can be achieved.

[Brief description of the drawings]

FIG. 1 shows an ideal reflection spectrum of a DBR mirror of the SEL of the first embodiment, a reflection spectrum of a p-type DBR mirror,
FIG. 4 is a characteristic diagram illustrating a reflection spectrum of an n-type DBR mirror.

FIG. 2 is a gain characteristic diagram relating to an active layer of the SEL of the first embodiment.

FIG. 3 shows an ideal reflection spectrum of a DBR mirror of the SEL of the second embodiment, a reflection spectrum of a p-type DBR mirror,
FIG. 4 is a characteristic diagram illustrating a reflection spectrum of an n-type DBR mirror.

FIG. 4 is a gain characteristic diagram relating to an active layer of the SEL of the second embodiment.

FIG. 5 shows an ideal reflection spectrum of a DBR mirror of the SEL of the third embodiment, a reflection spectrum of a p-type DBR mirror,
FIG. 4 is a characteristic diagram illustrating a reflection spectrum of an n-type DBR mirror.

FIG. 6 is a gain characteristic diagram relating to an active layer of the SEL of the third embodiment.

FIG. 7 shows an ideal reflection spectrum of a DBR mirror of the SEL of the fourth embodiment, a reflection spectrum of a p-type DBR mirror,
FIG. 4 is a characteristic diagram illustrating a reflection spectrum of an n-type DBR mirror.

FIG. 8 is a gain characteristic diagram relating to the active layer of the SEL of the fourth embodiment.

FIG. 9 is a cross-sectional view illustrating a schematic configuration of an SEL applicable to the present invention.

[Explanation of symbols]

 Reference Signs List 100 n-type substrate 101 n-type DBR mirror 102 active layer 103 p-type DBR mirror 104 SiO 2 layer 105 p-electrode 106 n-electrode

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[Procedure amendment]

[Submission date] January 20, 1998

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DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed Bragg reflector (DBR) laser having a DBR (Distributed Bragg reflector) structure, and more particularly, to forming an active layer between opposed Bragg reflectors. To form a resonator, and a surface emitting laser (SEL: surface emitting laser) in which laser output is performed through one Bragg reflector.
laser), a lasing wavelength measuring method and a designing method.

Here, lasing refers to a laser operation in which electrons transition to a high energy state and light of almost a single wavelength is generated by stimulated emission. The lasing wavelength refers to the possibility of laser oscillation in the resonator. Wavelength.

[0003]

2. Description of the Related Art In recent years, a surface emitting laser (SEL) has received much attention for the following reasons.

(1) Since SEL can emit light in a direction perpendicular to the wafer surface, a two-dimensional array of lasers is possible.

(2) A semiconductor laser that emits light from an end face emits an elliptical beam due to its structure, whereas an SEL emits a circular beam. Therefore, fiber coupling can be easily realized.

(3) Laser two-dimensional (2D) array of SELs is possible, which is useful for high-density optical interconnection.

(4) SELs can operate in the ultraviolet to near-infrared range, depending on the quantum well material, and can be a versatile source.

(5) Since the SEL has a resonator length as short as the radiation wavelength, it can emit the shortest optical pulse among semiconductor lasers, and can perform optical communication, optical drive line switch, and photoconductive sampler module. It can also be applied to other applications.

This SEL requires high precision in assembling the SEL in order to obtain an optimized output with a low threshold value.

[0010]

There has been no detailed study on the relationship between the reflection characteristic of the DBR mirror and the gain characteristic of the active medium in the SEL, and these relationships are considered from the design stage of the SEL. There was no idea. Therefore, conventionally, D having various reflection characteristics
A plurality of SELs having BR mirrors are manufactured, and these SELs
Inefficient work such as checking whether or not to obtain a good laser oscillation by actually operating the device has been performed.

[0011] To produce efficiently SEL, inventors detailed study of the relationship between the gain characteristics of the reflection characteristic and the active medium of the DBR mirror is made by, as a result, these relationships of SEL lasing It was found that the wavelength greatly affected. For example, in the SEL, the reflection characteristic of the DBR mirror on the light output side (the change in the reflectance with respect to the wavelength; here, the wavelength at which the reflectance sharply decreases becomes important) and the gain curve of the active medium (with respect to the wavelength) It is found that the relationship between the gain and the wavelength having a peak becomes important) greatly affects the lasing wavelength of the SEL.

As can be seen from the above research results, SEL
Considering the relationship between the reflection characteristics of the DBR mirror and the gain characteristics of the active medium from the design stage of
Can be realized. Furthermore, SEL
SEL before the package without actually operating
Lasing wavelength can be known, and thereby possible to improve the throughput.

The present invention has been made in view of the above-mentioned results, and provides a lasing wavelength measuring method capable of knowing a lasing wavelength before a package without actually operating the SEL. DB from stage
It is an object of the present invention to provide a method of designing a DBR laser in consideration of a relationship between a reflection characteristic of an R mirror and a gain characteristic of an active medium.

[0014]

In order to achieve the above object, a lasing wavelength measuring method according to the present invention is characterized in that an active layer is provided between first and second distributed reflection mirrors provided opposite to each other, and a resonance is provided. A measuring device for measuring the lasing wavelength of the distributed reflection type laser in which the laser beam is outputted via the first distributed reflection type mirror, wherein the first and second distributed reflection type mirrors are respectively provided. Is measured, and the reflection spectrum of the first distributed reflection type mirror is compared with a gain characteristic indicating a change in gain with respect to a wavelength of the active layer, which is obtained in advance, and the first distributed reflection type mirror is measured. The reflectivity of the mirror drops to the predetermined reflectivity,
And said active layer wavelength <br/> determined Me the gain is more than the predetermined gain, before KiMotomu meta of wavelengths, reflectivity of the second distributed Bragg reflector mirror is equal to or higher than a predetermined reflectivity and Wavelength of the ray
And wherein the managing wavelength and to Turkey.

According to the design method of the present invention, a resonator is formed by providing an active layer between first and second distributed reflection mirrors provided opposite to each other, and a resonator is formed via the first distributed reflection mirror. A method of designing a distributed-reflection laser in which laser light is output, wherein one or more wavelengths at which the reflectance falls to a predetermined reflectance are present in the reflection spectrum of the first distributed-reflection mirror. The gain of the active layer and the reflectance of the second distributed-reflection mirror at at least one wavelength among the wavelengths causing a decrease in reflectance are respectively equal to or higher than a predetermined gain and a predetermined reflectance. I do.

In the above case, at least one of the wavelengths at which the reflectance of the first distributed reflection mirror causes a decrease in the reflectance and a gain curve indicating a change in gain with respect to the wavelength of the active layer obtained in advance. May be made to substantially coincide with the peak wavelength.

<Operation> As will be described in detail in the embodiment, an active layer is provided between first and second distributed reflection mirrors provided opposite to each other to form a resonator, and a first distribution mirror is formed. In a distributed reflection laser in which laser light is output via a reflection mirror, the gain of the active layer is sufficient at a wavelength at which the reflectance of the first distributed reflection mirror on the light output side sharply decreases, and The condition for obtaining laser oscillation is that the reflectance of the second distributed reflection mirror is sufficiently high. In the design method of the present invention, since the design is performed so as to satisfy these conditions, good laser oscillation can be obtained, and the inefficient work as in the related art is not performed.

Further, the wavelength at which the reflectance of the first distributed-reflection type mirror rapidly falls and the peak wavelength of the gain curve of the active layer coincide with each other, and the reflectance of the second distributed-reflection type mirror is sufficiently high. By doing so, a higher laser output can be obtained. In the design method of the present invention, a design is performed so as to satisfy this condition, so that a laser having a higher laser output can be obtained.

Since laser oscillation can be obtained in the relationship between the reflection characteristics of the first and second distributed reflection mirrors and the gain characteristics of the active layer as described above, the reflection of the first and second distributed reflection mirrors can be improved. By knowing the characteristics and the gain characteristics of the active layer, the lasing wavelength can be known. In the lasing wavelength measurement method of the present invention, since the gain characteristics of the active medium used for the active layer are obtained in advance, the reflection spectra are measured for the first and second distributed reflection mirrors, respectively. You can know the lasing wavelength. As described above, the lasing wavelength can be known by measuring the reflection spectrum of each of the first and second distributed reflection type mirrors. Therefore, even before the package, the lasing wavelength can be obtained without actually operating the SEL. Can be measured.

[0020]

Next, embodiments of the present invention will be described with reference to the drawings.

First, a specific configuration of the SEL will be described. FIG. 9 is a cross section showing a schematic configuration of an SEL applicable to the present invention. This SEL is composed of a plurality of layers of a pair of AlAs / AlGaAs on an n-type substrate 100.
DBR mirror 101, active layer 102, AlAs / Al
A p-type DBR mirror 103 composed of a plurality of layers of GaAs, an SiO 2 layer 104, a p-electrode 105, and an n-electrode 106 are sequentially stacked.
The mirror 103 side is an emission surface.

In the SEL having the above configuration, a resonator is formed between the n-type DBR mirror 101 and the p-type DBR mirror 103, and the reflectance increases at a wavelength that matches the periodic structure of these mirrors, and laser oscillation occurs. In this SEL, the reflection characteristics of the p-type DBR 103 on the light output side (the change in the reflectance with respect to the wavelength; here, the wavelength at which the reflectance sharply decreases are important) and the gain curve of the active layer 102 (the wavelength (The wavelength having a peak becomes important due to the change of the gain with respect to) greatly affects the lasing wavelength of the SEL.

Hereinafter, the relationship between the reflection characteristic of the p-type DBR mirror 103 and the gain curve of the active layer 102 with respect to the performance of the SEL will be described.

EXPERIMENTAL EXAMPLE 1 The SEL used here has the same structure as the SEL shown in FIG. 9. Both the n-type DBR mirror and the p-type DBR mirror each have 20 AlAs / AlGaAs pairs.
The thickness of the AlAs / AlGaAs layer is 71.2 / 59.
8 nm, number of quantum wells (QW) is 4, QW thickness is 9n
The distance between m and QW is 7 nm, the thickness of the spacer / self-confinement heterostructure (SCH) is 359/150 nm, and the resonator length is 4λ (850 nm). 8 of this SEL
FIG. 1 shows the reflectance characteristics of the DBR mirror in the range of 00 to 900 nm. In the figure, the solid line indicates the calculated value of the reflectance of the ideal DBR mirror, the short broken line indicates the measured value of the reflectance of the p- type DBR mirror, and the long broken line indicates the measured value of the reflectance of the n- type DBR mirror. Here, the range of 800 to 900 nm is D
This is selected according to the gain curve of the GaAs quantum well constituting the BR mirror.

Referring to FIG. 1, AlAs / AlGaAs
For a DBR mirror with 20 pairs of s, ideally 81
A reflection spectrum exceeding 99% can be achieved in the range of 0 to 890 nm. In the case of the p-type DBR mirror, the reflectance decreases to about 45% around 858 nm,
It decreases to about 55% around 4 nm. On the other hand, these 858
The reflectivity of the n-type DBR mirror at around nm and 884 nm exceeds 99%.

The lasing spectrum of this SEL (Ga
FIG. 2 shows a gain curve of a quantum well of As. Comparing the reflectance characteristic shown in FIG. 1 with the lasing spectrum in FIG. 2, the vicinity of 884 nm where the reflectivity sharply decreases in the p-type DBR mirror is out of the peak wavelength of the lasing spectrum, and the gain near 884 nm. It turns out that it cannot be obtained. Therefore, laser output cannot be expected around 884 nm.

On the other hand, although the vicinity of 858 nm does not coincide with the peak wavelength of the lasing spectrum, it is near the peak wavelength, and it can be seen that a certain gain can be obtained. Therefore, if the laser oscillation wavelength is satisfied around 858 nm, light output can be obtained at this wavelength around 858 nm. However, in this case, the reflectance is about 4
Since it is reduced to 5%, a high output cannot be expected because the cavity loss increases.

EXPERIMENTAL EXAMPLE 2 The SEL used here is the same as that of Experimental Example 1 except that the thickness of the spacer / self-confinement heterostructure (SCH) is 1125/150 nm and the resonator length is 10λ (850 nm). It has the same structure as SEL. FIGS. 3 and 4 show a reflectance characteristic diagram and a lasing spectrum diagram of the DBR mirror of this SEL, respectively. In FIG. 3, a solid line indicates a calculated value of the reflectance of an ideal DBR mirror, a short broken line indicates a measured value of the reflectance of a p- type DBR mirror, and a long broken line indicates a measured value of the reflectance of an n- type DBR mirror.

Referring to FIGS. 3 and 4, there are a plurality of peaks in the lasing spectrum, and the peaks corresponding to these peaks at which the reflectivity of the p-type DBR mirror has decreased are 814 nm, 834 nm, There are three wavelengths of 840 nm.

The first peak of the lasing spectrum is 8
The reflectance of the p-type DBR mirror and the n-type DBR mirror at this wavelength is about 70%, respectively.
And about 90%. Here, since the first peak of the lasing spectrum is small and the gain is not so remarkable, a high laser output cannot be expected.

The second and third peaks of the lasing spectrum are 834 nm and 840 nm, respectively, and these peaks overlap. The reflectivity of the p-type DBR mirror near the wavelengths of these second and third peaks is both 1
It has dropped to the 0% range. Here, the second and third peaks of the lasing spectrum are large and a sufficient gain can be obtained, but a high laser output cannot be expected because the reflectance of the p-type DBR mirror is as low as about 10%. .

Note that there are some sharp drops in the reflectance of the p-type DBR mirror near 860 nm and further above, but there is no peak in the lasing spectrum at these wavelengths and the laser No output can be expected.

Experimental Example 3 The SEL used here has a spacer / self-confinement heterostructure (SCH) thickness of 104.3 / 150 nm,
The structure is the same as that of the SEL of Experimental Example 1 except that the resonator length is 2λ (850 nm). FIGS. 5 and 6 show a reflectance characteristic diagram and a lasing spectrum diagram of the DBR mirror of this SEL, respectively. In FIG. 5, the solid line indicates the calculated value of the theoretical reflectance of the SEL DBR mirror, the short broken line indicates the measured value of the reflectance of the p- type DBR mirror, and the long broken line indicates the measured value of the reflectance of the n- type DBR mirror.

Referring to FIGS. 5 and 6, the lasing spectrum has a first peak near 818 nm,
There is a second peak near 850 nm, and these 818n
There is a sharp decrease in the reflectance of the p-type DBR mirror near m and around 850 nm. The reflectivity of the p-type DBR mirror and the n-type DBR mirror near 818 nm exceeds 85% and 95%, respectively, and the reflectivity of the p-type DBR mirror and the n-type DBR mirror near 850 nm exceeds 40% and 99%, respectively. Therefore, in the SEL in this experimental example, the SEL around 818 nm and 850 nm
A laser output can be expected in the vicinity.

[0035] The wavelength at which the reflectance of the p-type DBR mirror suddenly decreases, although there are some other than the vicinity of and around 850 nm 818 nm, beauty in these wavelengths
There is no peak in the power spectrum, and no laser output can be expected.

Experimental Example 4 The SEL used here has a spacer / self-confinement heterostructure (SCH) thickness of 104.3 / 150 nm,
The structure is the same as that of the SEL of Experimental Example 1 except that the resonator length is 2λ (850 nm). FIGS. 7 and 8 show a reflectance characteristic diagram and a lasing spectrum diagram of the DBR mirror of the SEL, respectively. In FIG. 7, the solid line shows the calculated value of the reflectance of an ideal DBR mirror, the short broken line shows the measured value of the reflectance of a p- type DBR mirror, and the long broken line shows the measured value of the reflectance of an n- type DBR mirror.

Referring to FIGS. 7 and 8, the lasing spectrum has a peak near 814 nm.
At around 14 nm, the reflectance of the p-type DBR mirror is 15
%, And the reflectance of the n-type DBR mirror is 60%. Therefore, the SEL in this experimental example
Then, it can be expected that a laser output is obtained at around 814 nm.

There are several wavelengths at which the reflectivity of the p-type DBR mirror rapidly decreases, except for around 814 nm. However, at these wavelengths, there is no peak in the lasing spectrum, and it cannot be expected to obtain a laser output.

[0039] As apparent from the above Experimental Examples 1 to 4, in order to obtain a laser output, there is sharp drop in reflectance in the reflectance spectrum of the DBR mirror of the light output side, the wavelength of the active medium lasing It is necessary that the reflectivity of the DBR mirror on the other side at this wavelength is at least equal to or higher than the reflectivity at which laser oscillation is possible, and that the peak wavelength substantially coincides with the peak wavelength of the spectrum, and that the reflectivity of the DBR mirror at this wavelength is at least higher. is there.

Next, a method of measuring a lasing wavelength of a DBR laser and a method of designing the DBR laser using the conditions for obtaining the laser output will be described.

< Raising Wavelength Measuring Method> As described above, in a SEL having a Bragg reflector structure, if the gain curve of the active medium is known in advance, the reflection spectrum of each DBR mirror constituting the SEL must be measured. Thus, the lasing wavelength can be accurately known without operating the SEL.

Hereinafter, the procedure of measuring the lasing wavelength will be described in detail by taking the SEL shown in FIG. 9 as an example.

First, the respective reflection spectra of the n-type DBR mirror 101 and the p-type DBR mirror 103 are measured. Then, the reflection spectrum of the p-type DBR mirror 103 is compared with a gain curve indicating a change in gain with respect to the wavelength of the active layer 102 obtained in advance, and the p-type DBR
A wavelength at which a predetermined gain or more is found on the gain curve of the active medium at a wavelength at which the reflectance sharply drops in the reflection spectrum of the mirror 103 is examined. Further, among the wavelengths on the peak of the gain curve, an n-type DB at a wavelength equal to or higher than a predetermined reflectance (reflectivity capable of laser oscillation) is used.
The wavelength at which the reflection spectrum of the R mirror 101 is equal to or higher than the reflectivity at which laser oscillation is possible is examined. The wavelength thus obtained is the lasing wavelength in the SEL, and laser output is possible at this wavelength.

At the lasing wavelength measured as described above, the laser output is determined by the magnitude of the gain. Therefore, a larger laser output can be obtained as the wavelength at which the reflectance sharply drops in the reflection spectrum of the p-type DBR mirror 103 is closer to the wavelength at the peak of the gain curve.

According to the above measurement of the lasing wavelength, S
Before actually operating the EL, the lasing wavelength can be accurately known from the reflection spectrum of each DBR mirror and the gain curve of the active medium. Also, from the comparison result between the reflection spectrum and the gain curve, a sharp drop shows a DBR mirror on the light output side (here, the p-type DBR mirror 103).
If the decrease in the wavelength existing in the reflection spectrum is on the gain curve of the active layer and the laser oscillation condition is satisfied, a laser output is generated. However, in order to obtain a high output SEL, at a wavelength where the gain curve of the active layer has a peak, a p-type DBR mirror having a shallow dip in the reflection spectrum and an n having a reflectance of more than 99%
A type DBR mirror is required.

<Design Method of DBR Laser> In order to fabricate a DBR laser, first, there is at least one sharp drop in the reflectance in the reflection spectrum of the DBR mirror on the light output side. It is necessary that the wavelength at which the drop occurs is a wavelength at which a predetermined gain or more is obtained in the active medium. Second, the sharp drop in the reflectance is at least the reflectance at which laser oscillation is possible, and the reflectance of the DBR mirror on the other side at that wavelength needs to be sufficiently high. These first
By satisfying the second condition, the DBR laser can be efficiently manufactured, and the throughput in the manufacturing process can be improved.

Further, under the above first condition, the wavelength at which the reflectance sharply drops in the reflection spectrum of the DBR mirror on the light output side is substantially equal to the peak wavelength of the gain curve of the active medium. Then, a DBR laser having a higher laser output can be efficiently manufactured.

Furthermore, by making the width of the sharp reflectance drop in the reflection spectrum of the DBR on the light output side very narrow, it becomes possible to operate the SEL at a single wavelength.

Further, by extremely shortening the resonator length of the SEL, it is possible to generate a pulse whose pulse length limited by the resonator length is made as short as possible. It is possible to generate a light pulse that is almost one digit shorter than a conventional edge emitting laser.

Although the laser gain shifts to the longer wavelength side as the temperature rises, the reflectivity shifts in the opposite direction at a slower speed, so it is necessary to optimize the position of the sharp drop in the reflection spectrum. Become.

Although the SEL in which the p-type DBR mirror is provided on the light output side has been described above, the SEL applied to the lasing wavelength measuring method and the designing method of the present invention is not limited to this configuration. An n-type DBR mirror may be provided on the light output side.

[0052]

According to the present invention configured as described above, the following effects can be obtained.

According to the design method of the present invention, the gain of the active layer is sufficient at the wavelength where the reflectance of the distributed reflection mirror on the light output side sharply drops, and the reflectance of the second distributed reflection mirror is sufficient. Since the DBR laser is designed to be sufficiently high, the DBR laser can be manufactured efficiently.

In addition, the wavelength at which the reflectivity of the distributed reflection mirror on the light output side sharply falls is matched with the peak wavelength of the gain curve of the active layer, and the reflectance of the distributed reflection mirror on the other side is sufficiently increased. Therefore, a high-power DBR laser can be manufactured.

Further, according to the lasing wavelength measuring method of the present invention, the lasing wavelength can be measured without actually operating the SEL even before the package, so that the throughput in the manufacturing process of the DBR laser can be reduced. Improvement can be achieved.

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Claims (3)

[Claims] An active layer is provided between first and second distributed reflection mirrors provided opposite to each other to form a resonator, and a laser beam is output via the first distributed reflection mirror. A method of measuring a lasing wavelength of a distributed reflection type laser, comprising: a first step of measuring respective reflection spectra of the first and second distributed reflection type mirrors; and the first distributed reflection type mirror. Is compared with a gain characteristic indicating a change in gain with respect to the wavelength of the active layer obtained in advance, the reflectance of the first distributed reflection type mirror falls to a predetermined reflectance, and A second step of obtaining a wavelength at which the gain of the layer is equal to or greater than a predetermined gain; and among the wavelengths obtained in the second step, the reflectance of the second distributed reflection type mirror is equal to or greater than a predetermined reflectance. wavelength A third step of setting the lasing wavelength to the lasing wavelength. 2. An resonator is formed by providing an active layer between first and second distributed reflection mirrors provided opposite to each other, and a laser beam is output via the first distributed reflection mirror. A distributed reflection laser design method, wherein the reflection spectrum of the first distributed reflection mirror has one or more wavelengths at which the reflectance decreases to a predetermined reflectance,
Setting the gain of the active layer and the reflectance of the second distributed reflection mirror at at least one wavelength among the wavelengths at which the reflectance has decreased to a predetermined gain and a predetermined reflectance or more, respectively. And a method of designing a distributed reflection laser. 3. The distributed reflection laser designing method according to claim 2, wherein at least one of the wavelengths at which the reflectance of the first distributed reflection mirror causes a decrease in reflectance is obtained in advance. A method of designing a distributed reflection laser, wherein a peak wavelength of a gain curve indicating a change in gain with respect to a wavelength with respect to the active layer is substantially matched.