JP2003298186A - Surface emitting laser element, transceiver using surface emitting laser element, optical transceiver, and optical communication system - Google Patents

Abstract

(57) [Problem] To provide a surface emitting laser element having a low threshold current, high reliability, and capable of single transverse mode oscillation. SOLUTION: It has a structure in which a lower reflective layer 2 is laminated on a substrate 1. The upper region of the lower reflective layer 2 is formed in a mesa shape, and the lower clad layer 3, the active layer 4, the upper clad layer 5, and the upper reflective layer 6 are sequentially laminated on the mesa-shaped region. The mesa shape is formed such that the horizontal cross-sectional shape is circular. A contact layer 7 is laminated on the upper reflective layer 6, and on the contact layer 7,
An annular p-side electrode 8 having a current injection region in the center is arranged, and an n-side electrode 9 is arranged on the lower surface of the substrate 1. Then, in the mirror layer of the first period from the active layer side of the upper reflection layer 6, a current injection region 19a which is disposed near the center of the mesa and has a circular horizontal cross section and a current injection region 19a are formed. Adjacently disposed selective oxidation region 1
The current confinement layer 20 formed by 9b is arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting laser having a structure in which a lower reflection layer, a lower clad layer, an active layer, an upper clad layer and an upper reflection layer are sequentially laminated and which oscillates in a direction perpendicular to a substrate. The present invention relates to an element, a surface emitting laser element capable of single transverse mode oscillation even in a long wavelength band and capable of long-distance transmission, a transceiver using the surface emitting laser element, an optical transceiver, and an optical communication system.

[0002]

2. Description of the Related Art In recent years, vertical cavity surface emitting lasers (VCSE
L: Vertical Cavity Surface Emitting Laser. Less than,
It is called a "surface emitting laser device". ), As the name implies, has a direction in which light resonates perpendicularly to the substrate surface, and is attracting attention as a light source for communication including optical interconnection, and as a device for various other applications. The surface emitting laser device has a structure of 1
Since the ultrashort resonator having a wavelength of about the wavelength is provided, only the fundamental wave can exist in the oscillating laser light. Therefore, D
It is easier to stably maintain a single longitudinal mode than edge-emitting lasers such as FB (Distributed Feedback) lasers. In addition, FFP (Far Field Pattern)
Is obtainable as a laser element which is essentially suitable for optical communication or the like than the DFB laser or the like because it can obtain a narrow value in isotropic direction and has a low relative intensity noise.

When used as a signal light source, 0.8 μm to 1.
A surface emitting laser device having an emission wavelength of 65 μm is required. In the surface emitting laser of this wavelength band, long wavelength band,
For example, a surface emitting laser that oscillates a laser beam having a wavelength of 1.2 μm or more has been impossible to realize for a long time because of difficulty in crystal growth. However, recently, the present inventors have realized a surface emitting laser element that oscillates a laser beam having a wavelength of 1.2 to 1.3 μm (Japanese Patent Application No. 2001-124300).

FIG. 10 shows the structure of the surface emitting laser element described in Japanese Patent Application No. 2001-124300. This surface-emitting laser device has a structure in which a buffer layer 102, a lower reflection layer 103, a lower cladding layer 104, a quantum well layer 105, and an upper cladding layer 106 are sequentially laminated on a substrate 101. Further, on the upper clad layer 106, the current confinement layer 108 and the upper reflection layer 10 processed into a mesa shape.
9 has a laminated structure of the contact layer 110. The current confinement layer 108 is formed by a current injection region 107a made of an AlAs layer in the central portion and a selective oxidation region 107b formed by selectively oxidizing the end portion of the AlAs layer. An n-side electrode 114 is arranged on the lower surface of the substrate 101. Then, in the quantum well layer 105, GaInNA
By adding a small amount of Sb to s, the quantum well layer 10
5 improved the crystallographic quality. As described above, the laser oscillation of the surface emitting laser device in the 1.3 μm band has been recently performed by utilizing the structure improvement of the quantum well layer and the selective oxidation technique of the AlAs layer.

[0005]

However, there are still problems to be solved when the surface emitting laser device is used for signal light sources and the like. First, it is necessary to unify the transverse modes of the oscillating laser light. When the lateral mode has a higher-order mode in the lateral direction, it causes significant deterioration of the signal waveform in proportion to the transmission distance during optical transmission, particularly during high-speed modulation. Therefore, in order to realize long distance transmission, it is necessary to realize single transverse mode oscillation.

The surface emitting laser element is originally difficult to stabilize the transverse mode due to its structure. for that reason,
In a surface emitting laser device having a selective oxidation region, a single transverse mode oscillation is realized by adjusting the diameter of a current injection region sandwiched between the selective oxidation regions, but conventionally, in the 1300 nm band (about 1260 nm to 1360 nm). It has been difficult to realize single transverse mode oscillation by adjusting only the diameter of the current injection region in the surface emitting laser device of the range).

Even if the single transverse mode oscillation can be realized, when the value of the threshold current increases, there arises a problem that the power consumption increases. Therefore, it is necessary to realize single transverse mode oscillation while suppressing an increase in the value of the threshold current. Furthermore, the reliability of the surface emitting laser element must be ensured. This is because it is necessary to have sufficient reliability in order to use the surface emitting laser element for a signal light source or the like.

When used as a signal light source or the like, 10 G
It must be possible to directly modulate at the bit / s level.
This is the minimum number required for actual use as a signal light source with the increase in communication capacity in recent years.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has a low threshold current, high reliability, single transverse mode oscillation is possible, and direct modulation at 10 Gbit / s is possible. Another object of the present invention is to provide a surface emitting laser device, a transceiver using the surface emitting laser device, an optical transceiver, and an optical communication system.

[0010]

In order to achieve the above object, a surface emitting laser element according to claim 1 is provided on a substrate.
A surface emitting laser device having a structure in which a lower reflective layer, a lower clad layer, an active layer, an upper clad layer, and an upper reflective layer are sequentially stacked, and which oscillates in a direction perpendicular to the substrate, wherein the lower reflective layer or Inside the upper reflective layer, 370 nm or more and 780 nm from the center of the active layer
An effective refractive index of a stacking direction region including a selective oxidation region arranged in a region separated by the following distance in the stacking direction and a current injection region sandwiched by the selective oxidation region, And the effective refractive index of the stacking direction region including the selective oxidation region is 0.038 or less.

According to the first aspect of the present invention, since the position of the selective oxidation region in the stacking direction and the difference in effective refractive index are optimized, single transverse mode oscillation is possible and long-distance transmission is possible. A surface emitting laser device that emits light can be realized.

In the surface emitting laser element according to a second aspect of the present invention, in the above invention, the upper reflection layer and the lower reflection layer have a low refractive index layer and a high refractive index each having an optical length of ¼ of an emission wavelength. Formed by stacking a plurality of mirror layers each having a two-layer structure of a refractive index layer, and the selective oxidation region is disposed in the vicinity of a position where the electric field intensity distribution in any one of the mirror layers has a minimum electric field strength distribution. It is characterized by being.

According to a third aspect of the present invention, in the surface emitting laser element according to the above invention, the active layer has a thickness of 1260 nm.
As described above, the optical resonator that emits laser light having a wavelength of 1360 nm or less and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length that is twice the wavelength of the laser light. In the upper or lower reflective layer, the selective oxidation region is first from the active layer side.
It is characterized in that it is arranged in a mirror layer laminated at the cycle.

According to a fourth aspect of the present invention, in the surface emitting laser element according to the above invention, the active layer has a thickness of 1260 nm.
As described above, the optical resonator that emits laser light having a wavelength of 1360 nm or less and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length equal to the wavelength of the laser light. The selective oxidation region is formed on the upper or lower reflection layer from the second side of the active layer side.
It is characterized in that it is arranged in the mirror layer adjacent to the mirror layer laminated in the cycle.

According to a fifth aspect of the present invention, in the above surface-emitting laser element, the selective oxidation region has a thickness of 6 nm.
As described above, it is characterized by having a film thickness of 32 nm or less.

According to a sixth aspect of the present invention, there is provided the surface emitting laser element according to the above invention, wherein the selective oxidation region is 10 n.
It is characterized by having a film thickness of not less than m and not more than 13 nm.

According to a seventh aspect of the present invention, in the surface emitting laser element according to the above-mentioned invention, the active layer has a thickness of 1260 nm.
As described above, the optical resonator that emits laser light having a wavelength of 1360 nm or less and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length that is twice the wavelength of the laser light. In the upper or lower reflective layer, the selective oxidation region is located second from the active layer side.
It is characterized in that it is arranged in a mirror layer laminated at the cycle.

According to an eighth aspect of the present invention, in the surface emitting laser element according to the above invention, the active layer has a thickness of 1260 nm.
As described above, the optical resonator that emits laser light having a wavelength of 1360 nm or less and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length equal to the wavelength of the laser light. The selective oxidation region is arranged in the mirror layer stacked in the third period from the active layer side in the upper or reflective layer.

According to a ninth aspect of the present invention, in the above surface-emitting laser element, the selective oxidation region has a thickness of 6 nm.
As described above, it is characterized by having a film thickness of 46 nm or less.

According to a tenth aspect of the present invention, in the surface emitting laser element according to the above-mentioned invention, the selective oxidation region is 10
It is characterized in that it has a film thickness of not less than 20 nm and not more than 20 nm.

According to an eleventh aspect of the present invention, in the surface emitting laser element according to the above invention, the substrate is made of GaAs, and the low refractive index layer is made of Al _x Ga _1-x As (0.
5 ≦ x ≦ 1), and the high refractive index layer is Al _x Ga _1-x A
s (0 ≦ x ≦ 0.2), and the selective oxidation region is Al
It is characterized in that it is formed by selectively oxidizing _x Ga _1-x As (0.97 ≦ x ≦ 1).

According to a twelfth aspect of the present invention, there is provided a transceiver according to any one of the first to eleventh aspects, and a current value injected into the surface-emission laser element based on an input electric signal. And a light receiving section having a photoelectric conversion element that receives an optical signal incident from the outside and converts the optical signal into an electric signal.

The optical transceiver according to claim 13 is
A surface-emitting laser device according to claim 1, a signal multiplexing circuit for multiplexing a plurality of electric signals,
A control circuit for controlling the surface emitting laser element based on an electric signal output from the signal multiplexing circuit, a photoelectric conversion element for receiving an optical signal incident from the outside and converting the optical signal into an electric signal, and the photoelectric conversion element And a signal separation circuit for separating the output electric signal into a plurality of electric signals.

An optical communication system according to a fourteenth aspect is the surface emitting laser element according to any one of the first to eleventh aspects, and a control circuit for controlling the surface emitting laser element.
A transmission optical fiber that receives and transmits the optical signal emitted from the surface emitting laser element from one end, and a photoelectric conversion that receives the optical signal that enters from the other end of the transmission optical fiber and converts it into an electrical signal. And an element.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a surface emitting laser device, a transceiver using the surface emitting laser device, an optical transceiver and an optical communication system according to the present invention will be described below with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. It should be noted that the drawings are schematic, and the relationship between the thickness and width of each layer, the ratio of each layer, and the like are different from the actual ones. Even between drawings
As a matter of course, there are included portions having different dimensional relationships and ratios.

(First Embodiment) First, a surface emitting laser element according to the first embodiment will be described. Embodiment 1
In the surface emitting laser device according to the second aspect, the structure of the selective oxidation region is optimized for the surface emitting laser device in the 1300 nm band. FIG. 1 is a sectional view showing the structure of the surface emitting laser device according to the first embodiment. Hereinafter, the structure of the surface emitting laser device according to the first embodiment will be described with reference to FIG. 1 as appropriate.

The surface emitting laser device according to the first embodiment has a structure in which the lower reflective layer 2 is laminated on the substrate 1. The upper region of the lower reflective layer 2 is formed in a mesa shape, and the lower clad layer 3, the active layer 4, the upper clad layer 5, and the upper reflective layer 6 are sequentially laminated on the mesa-shaped region. The mesa shape is formed so that the horizontal cross section is circular. Furthermore, the upper reflective layer 6
A contact layer 7 is stacked on the contact layer 7. On the contact layer 7, a p-side electrode 8 having a ring shape with a current injection region in the center is arranged, and an n-side electrode 9 is arranged on the lower surface of the substrate 1. ing. Then, in the upper reflection layer 6, a current confinement layer 20 that is disposed near the center of the mesa and has a current injection region 19a having a circular horizontal cross section and a selective oxidation region 19b adjacent to the current injection region 19a. Are arranged. The specific structure of the selective oxidation region 19b will be described in detail later.

The substrate 1 is an n-type GaAs substrate.
In addition, the substrate 1 usually has a (100) plane as a main plane, and the thin film structure above the lower reflective layer 2 is laminated on the (100) plane. The lower reflection layer 2 is for reflecting the light of the emission wavelength of the light generated in the active layer 4 and feeding it back. Specifically, the lower reflective layer 2 has a structure in which a large number of mirror layers 12 formed by a laminated structure of a high refractive index layer 10 and a low refractive index layer 11 are laminated.

The high refractive index layer 10 is formed of an n-type GaAs layer, and the low refractive index layer 11 is an n-type Al _0.9 Ga layer.
It is formed by a _0.1 As layer. The film thicknesses of the high-refractive index layer 10 and the low-refractive index layer 11 are adjusted so that the optical length thereof is ¼ of the emission wavelength λ in order to reflect only the light of the emission wavelength. Specifically, since the emission wavelength of the surface emitting laser device according to the first embodiment is 1300 nm,
In consideration of the refractive index of each layer, the film thickness of the high refractive index layer 10 is 94
The thickness of the low refractive index layer 11 is about 110 nm. By having such a structure, the mirror layer 12 is
The combination of the high-refractive index layer 10 and the low-refractive index layer 11 has a function of reflecting light having an emission wavelength at a constant rate. In order to increase the reflectance of the lower reflective layer 2 as a whole, the lower reflective layer 2 is formed by laminating 34.5 mirror layers 12. The fraction below the decimal point is due to the layer formed of only the high refractive index layer 10.

The active layer 4 has a structure including a quantum well layer. Specifically, as shown in FIG. 1, the active layer 4 includes a barrier layer 13a, a quantum well layer 14a, a barrier layer 13b, a quantum well layer 14b, a barrier layer 13c, and a quantum well layer, which are sequentially stacked on the lower cladding layer 3. 14c and the barrier layer 13d. That is, it has a structure in which the three quantum well layers 14a to 14c are sandwiched by the four barrier layers 13a to 13d.

The quantum well layers 14a to 14c are for efficiently confining carriers by the quantum confinement effect, and are formed of GaInNAsSb layers. The quantum well layers 14a to 14c have good crystallinity because Sb is added in a minute amount. Also, the quantum well layer 1
4a to 14c are required to have an extremely thin film thickness in order to exhibit the quantum confinement effect, and the film thickness of each layer in the first embodiment is set to about 7 nm.

The barrier layers 13a to 13d are the quantum well layers 14
The barrier layers 13a and 13d have a thickness of about 30 nm, and the barrier layers 13b and 13c have a thickness of about 20 nm.

In the lower clad layer 3, the active layer 4, and the upper clad layer 5, the total optical length of the film thicknesses of the layers is 2 at the emission wavelength λ.
It is formed to be doubled and functions as an optical resonator. Therefore, in the following, the lower clad layer 3, the active layer 4, and the upper clad layer 5 are collectively referred to as a 2λ resonator 15. In the first embodiment, the lower clad layer 3 is made of an n-type GaAs layer and the upper clad layer 5 is made of a p-type GaAs layer, and the respective film thicknesses thereof are about 297 nm.

The upper reflective layer 6 is similar to the lower reflective layer 2 in that
Among the lights generated in the active layer 4, the light having an emission wavelength is reflected and fed back. In particular,
The upper reflective layer 6 has a structure in which a large number of mirror layers 18 formed by pairs of a low refractive index layer 16 and a high refractive index layer 17 that are sequentially stacked are stacked. The low refractive index layer 16 is p-type Al
_{It has a 0.9} Ga _0.1 As layer, and the high refractive index layer 17 is a p-type Ga layer.
It has an As layer. Since the laser light generated in the active layer 4 is fed back, the upper reflective layer 6 has a high reflectance. Since the surface-emission laser device according to the first embodiment emits laser light vertically upward with respect to the substrate 1,
The upper reflective layer 6 needs to have a lower reflectance than the lower reflective layer 2. Therefore, the upper reflective layer 6 has a structure including 25 mirror layers 18 less in number than the lower reflective layer 2.
In the following description, the 25 mirror layers 12 or the mirror layers 18 constituting the lower reflective layer 2 or the upper reflective layer 6 will be referred to as the mirror layer disposed closest to the active layer 4 in the first cycle, if necessary. The second mirror layer is in contact with the first mirror layer and the first mirror layer is in the second cycle, and the second mirror layer is in contact with the second mirror layer in the third cycle. These are referred to as eye mirror layers and the like, respectively.

Further, among the low refractive index layers 16 constituting the upper reflection layer 6, the lower refractive index layer 16 constituting the lowermost layer, that is, the mirror layer of the first period laminated adjacent to the upper clad layer 5 is , P-type Al _0.9 Ga _0.1 As layer and p-type Al
It has a structure in which an As layer is sequentially laminated. And AlA
In the region near the center of the s layer, the current injection region 1
9a is formed, and the current confinement layer 20 is formed by the selective oxidation region 19b formed by selective oxidation near the end.

The selective oxidation region 19b is for confining the current injected from the p-side electrode 8 to increase the current density flowing into the active layer 4 and reduce the oscillation threshold. The refractive index of the selective oxidation region 19b is to have a value different from the current injection region 19a and Al _0.9 Ga _{0 .1} As layer exists around affects the confinement horizontal direction of the light. That is, since the selective oxidation region 19b is present, the surface emitting laser element according to the first embodiment has a refractive index waveguide type waveguide.

The selective oxidation region 19b has a thickness of 13 nm in the first embodiment. In addition, the current injection region 19a defined by the width of the selective oxidation region 19b.
Has a diameter of 5.3 μm. The reason for adopting such a structure will be described below.

In the surface emitting laser device according to the first embodiment, the oscillation characteristics are improved by optimizing the structure of the selective oxidation region 19b. Specifically, the selective oxidation region 19b
It is necessary to consider the position of the film in the mirror layer, the mirror layer in which the selective oxidation region 19b is arranged, and the width and film thickness of the selective oxidation region 19b. The optimization of these requirements will be described below.

First, the position in the mirror layer to be arranged will be described. The current injection region 19a adjacent to the selective oxidation region 19b has a refractive index close to that of an Al _0.9 Ga _0.1 As layer. Therefore, the AlAs layer forming the selective oxidation region 19b and the current injection region 19a is the low refractive index layer 1
1 or in the low refractive index layer 16 is required. Further, in order to suppress the loss of light generated in the active layer 4, a position close to the node of the standing wave (a position where the electric field intensity distribution is minimum), that is, the low refractive index layer 11 or the low refractive index layer. 1
6 is preferably arranged in a region separated from the active layer 4, that is, near the lower surface of the low refractive index layer 11 or near the upper surface of the low refractive index layer 16.

Next, a description will be given of which mirror layer the selective oxidation region 19b is arranged in. As described above, the selective oxidation region 19b has a current confinement function. From the viewpoint of confining the current and increasing the density of the current flowing into the active layer 4, the selective oxidation region 19b is preferably arranged in a position close to the active layer 4. When the selective oxidation region 19b is arranged at a position separated from the active layer 4, the selective oxidation region 1
This is because the current confined by 9b diffuses again before the current flows into the active layer 4 and the current density decreases. Therefore, from the viewpoint of suppressing the oscillation threshold value to be low, it is preferable to dispose the selective oxidation region 19b close to the active layer 4.

On the other hand, when it is arranged close to the active layer 4, another problem occurs. The selective oxidation region 19b is formed by laminating an AlAs layer or the like once and processing it into a mesa,
It is formed by introducing oxygen atoms from the outside by heating in a steam atmosphere to selectively oxidize. By introducing oxygen atoms from the outside, the initial crystal order is damaged, so that dislocations occur in the selective oxidation region 19b. Therefore, when the selective oxidation region 19b is too close to the active layer 4, dislocations in the selective oxidation region also affect the crystal structure of the active layer 4, and the reliability as a surface emitting laser device is reduced. Therefore, from the viewpoint of ensuring the reliability of the surface emitting laser element, the selective oxidation region 19b is formed.
Is preferably separated from the active layer 4.

As described above, since there is a trade-off relationship between the suppression of the oscillation threshold value and the securing of the reliability of the surface emitting laser element, there is an optimum value for the position of the selective oxidation region 19b in the stacking direction. Therefore, the inventors of the present application have determined the optimum value by changing the position of the selective oxidation region 19b in the stacking direction of the surface emitting laser element and examining its characteristics.

Specifically, in a surface emitting laser device having an emission wavelength of about 850 nm (hereinafter referred to as "850 nm band surface emitting laser device"), the position where the selective oxidation region is arranged is changed in the stacking direction to set the threshold value. The current value and the reliability of the surface emitting laser device were measured. The measurement target is a 850 nm surface emitting laser device,
This is because the m-band surface emitting laser device has been extensively studied and its characteristics have been well understood. Therefore, it is possible to eliminate the influence of the portion other than the selective oxidation region on the measurement result, and to understand the influence of the selective oxidation region on the characteristics of the surface emitting laser device. 850 nm used for measurement
The structure of the band-emission laser device is the same as that of the first embodiment except the part corresponding to the wavelength such as the optical length of the optical resonator.
It has the same structure as the surface-emitting laser device according to the present invention.

As shown in FIGS. 2 (a) to 2 (c), the inventors of the present invention have selectively oxidized regions on the mirror layer of the first period, the mirror layer of the third period and the mirror layer of the fifth period, respectively. 1
9b-1, 19b-2, 19b-3 and the threshold current and reliability of the 850 nm band surface emitting laser device having the λ resonator having the current injection regions 19a-1, 19a-2, 19a-3 formed therein. Was done. As a result, when the selective oxidation region 19b-1 was arranged in the mirror layer in the first cycle, there was a problem in reliability, and it was found that it was not suitable for practical use. When the selective oxidation region 19b-2 was arranged in the mirror layer of No. 3, the reliability was high and the threshold current was low. Furthermore, the fifth
When the selective oxidation region 19b-3 was arranged in the mirror layer of the cycle, the reliability was secured, but the threshold current was the third.
There was a tendency to increase compared with the case where it was arranged on the mirror layer at the cycle. Since the increase of the threshold current in the case of being arranged in the mirror layer of the fifth period is within the allowable range, the inventors of the present application have found that for the 850 nm band surface emitting laser element, the mirror layer of the third period to the fifth period It was concluded that it is preferable to place a selective oxidation region in the.

In the 850 nm band surface emitting laser device used for the measurement, the film thickness of the upper cladding layer and the film thicknesses of the low refractive index layer and the high refractive index layer are the surface emitting laser according to the first embodiment due to the difference in the emission wavelength. Different from the element. Therefore, in optimizing the position of the selective oxidation region 19b in the stacking direction in the first embodiment, the distance from the center of the active layer was referred to in the above measurement result. In the 850 nm surface emitting laser device used for the measurement, the distance from the center of the active layer to the lower end of the mirror layer in the third period is 390 nm, and the distance to the lower end of the mirror layer in the fifth period is 660 nm. With reference to this value, in the surface-emission laser device according to the first embodiment, the lower end of the mirror layer in which the selective oxidation region 19b is arranged is 370 nm to the center of the active layer 4.
It was determined to exist in the range of 680 nm.

In the first embodiment, the mirror layer of the first period is selected as the mirror layer suitable for this numerical range. This is because the first mirror layer has a distance of 375 nm from the center of the active layer 4. Regarding the position in the mirror layer, when it is provided in the upper reflection layer as described above, it is preferable that the selective oxidation region 19b is arranged near the upper surface of the low refractive index layer. Therefore, from these viewpoints, the position of the selective oxidation region 19b in the stacking direction is determined to be the position shown in FIG.

Next, optimization of the horizontal width of the selective oxidation region 19b and the film thickness in the stacking direction will be described in order from the viewpoint of realizing single transverse mode oscillation. Since the horizontal width of the selective oxidation region 19b is determined by optimizing the diameter of the current injection region 19, the optimization of the diameter of the current injection region 19a will be mainly described below.

First, optimization of the diameter of the current injection region 19a determined by the width of the selective oxidation region 19b will be described. In general, it is possible to realize single transverse mode oscillation by reducing the diameter of the current injection region 19a. On the other hand, as the diameter of the current injection region 19a becomes smaller, there arises a problem that the threshold current increases due to diffraction loss,
In order to suppress the increase of the threshold current, the current injection region 19a
It is necessary to increase the diameter of. Therefore, there is a trade-off relationship between the threshold current suppression and the single transverse mode oscillation enable condition, and the diameter of the current injection region 19a has an optimum value.

Therefore, the inventors of the present application measured the oscillation transverse mode of the 850 nm band-emission laser device when the diameter of the current injection region was changed, and examined the optimum value of the diameter of the current injection region. Specifically, FIG.
As shown in (b), the selective oxidation region is inserted in the mirror layer of the third period, the thickness of the selective oxidation region is fixed to 20 nm, the diameter of the current injection region 19a is changed, and the threshold current and the lateral current are changed. The mode was measured.

As a result of the measurement, the maximum value of the diameter of the current injection region in which single transverse mode oscillation was possible was 3.5 μm. Further, when the diameter was 3.5 μm, the value of the threshold current could be suppressed to be within the allowable range. Regarding the effective refractive index difference described later, this surface emitting laser element has a difference of 0.
It was 0165.

On the basis of this result, the inventors of the present application have found that the current injection region 19a of the surface emitting laser device according to the first embodiment.
The condition was that the diameter was 3.5 μm or more. This is because the suppression of the increase in the threshold current has a poor correlation with the emission wavelength of the surface emitting laser element,
This is because when the threshold current is suppressed within the allowable range in the m-band surface emitting laser element, it is considered that the threshold current can be suppressed within the allowable range even at 1300 nm. However,
The inventors of the present application consider that it is more preferable to increase the diameter of the current injection region 19a in accordance with the ratio of emission wavelengths, and the optimum value of the diameter of the current injection region 19a is 3.5 μm (13
00/850) and 5.3 μm.

Next, under the conditions relating to the diameter of the current injection region 19a, the optimum value of the film thickness of the selective oxidation region 19b necessary for realizing the single transverse mode oscillation will be examined. For transverse mode oscillation, the current injection region 19a
This is because the effective refractive index difference in the refractive index waveguide type waveguide has an influence as well as the diameter. In the following, first, the effective refractive index difference will be briefly described, the optimum value of the effective refractive index difference will be derived, and then the condition of the film thickness of the selective oxidation region 19b necessary to realize the optimum value will be derived.

As described above, due to the presence of the selective oxidation region 19b, the surface emitting laser device according to the first embodiment has a refractive index waveguide type waveguide. For example, as shown in FIG. 3, the index-guided waveguide is formed in a first region 21 that is a stacking direction region including a current injection region 19a and second regions 22 and 23 that include a selective oxidation region 19b. The structure in which the first region 21 functions as a waveguide due to the difference in effective refractive index which is the difference in equivalent refractive index of The structure of the index-guided waveguide is explained by the refractive index distribution of the surface emitting laser device. Specifically, the optical confinement in the horizontal direction is equivalently replaced by the planar waveguide having the equivalent refractive index of the first region 21, and the second regions 22 and 23, and is evaluated. The structure and transverse modes can be analyzed.

For example, in the surface emitting laser device according to the first embodiment, the refractive index of the selective oxidation region 19b has a smaller value than the refractive index of AlAs forming the current injection region 19a. Therefore, the equivalent refractive index of the second regions 22 and 23 has a smaller value than the equivalent refractive index of the first region 21, and the light generated from the active layer 4 is guided in the first region 21 and emitted to the outside. It The structure of the refractive index waveguide type waveguide corresponds to the effective refractive index difference which is the difference between the equivalent refractive index of the first region 21 and the equivalent refractive index of the second regions 22 and 23. The manner in which light is guided varies.

The relationship between the diameter Φ _c of the current injection region 19a capable of realizing single transverse mode oscillation and the effective refractive index difference Δn is Φ _c ∝λ / (Δn) using the emission wavelength λ. It is known that it can be approximated as ^1/2 ... (1). Therefore, 850
To determine the horizontal width and the film thickness of the selective oxidation region 19b in the surface emitting laser device according to the first embodiment by using the measurement result obtained for the nm band surface emitting laser device and the formula (1). You can

First, in order to suppress an increase in the threshold current, the conditional expression of the effective refractive index difference Δn when the diameter of the current injection region 19a is at least 3.5 μm is the measurement result and (1).
From the formula, Φ _c (λ = 1.3 μm) / Φ _c (λ = 0.85 μm) = {1.3 / (Δn) ^1/2 } / {0.85 / (0.0165) ^1/2 } ... (2 ) Is required. Where Φ _c (λ = 0.85 μm) = 3.5
Since the value is 1 μm or more on the right side of the equation (2), the diameter of the current injection region 19a is 3.5 μm or more even in the surface emitting laser element according to the first embodiment. When the equation (2) is calculated for Δn, Δn ≦ 0.038 may be satisfied for the effective refractive index difference Δn in order to satisfy the above condition. Since the value of the effective refractive index difference Δn can be controlled by the film thickness of the selective oxidation region 19b, the maximum value of the film thickness of the selective oxidation region 19b can be obtained from this condition. Further, from the equation (1), the effective refractive index difference Δn is 850n.
As with the measurement result of the m-band surface emitting laser device, 0.0165
If so, the diameter of the current injection region 19a also becomes 1.5 times as large as the wavelength ratio, which is more preferable.

Here, the selective oxidation region 19 necessary for realizing the above-mentioned effective refractive index difference is calculated by performing a calculation known to those skilled in the art in consideration of the position of the selective oxidation region 19b in the stacking direction.
It is possible to derive the film thickness of b. In conclusion, in the first embodiment, the selective oxidation region 19b is arranged in the first mirror layer, and the thickness of the selective oxidation region 19b is 32 nm in order to set the effective refractive index difference Δn to 0.038 or less.
The following may be done. In addition, the effective refractive index difference is 0.0165.
In that case, the film thickness of the selective oxidation region 19b is 13 nm. Therefore, in order to realize the single transverse mode oscillation in the surface emitting laser device according to the first embodiment, the film thickness of the selective oxidation region 19b needs to be 32 nm or less, and more preferably 13 nm or less.

Next, the minimum value of the film thickness of the selective oxidation region 19b will be examined. As described above, the selective oxidation region 1
9b is formed by first stacking an AlAs layer and then introducing oxygen atoms in a water vapor atmosphere to perform selective oxidation. Here, when the selective oxidation region 19b is formed, Al
If the As layer is too thin, it becomes difficult to introduce oxygen atoms and it becomes difficult to form the selective oxidation region 19b.
The film thickness of the selective oxidation region 19b that is the minimum required for introducing oxygen atoms is 6 nm, and the film thickness of 10 nm or more is more preferable so that the selective oxidation can be easily performed.

From the above discussion, the range of the film thickness d of the selective oxidation region 19b required to realize the single transverse oscillation mode while suppressing the threshold current to a low level is 6 nm ≦ d ≦ 32 nm ... (3 ). Further, a more preferable range of the film thickness d that allows rapid selective oxidation and allows the current injection region 19a to have a large diameter is 10 nm ≦ d ≦ 13 nm (4). Since it is more preferable that the selective oxidation region 19b has a film thickness that satisfies the expression (4), the thickness of the selective oxidation region 19b is 13 nm and the diameter of the current injection region 19a is 5.3 μm in the first embodiment. There is.

The inventors of the present application actually manufactured a surface emitting laser element satisfying the above conditions and examined its characteristics.
Specifically, an n-type GaAs buffer layer of 0.1 μm is laminated on an (100) plane substrate of n-type GaAs,
3 mirror layers made of Al _0.9 Ga _0.1 As and GaAs
The lower reflective layer was formed by stacking 4.5 layers. The active layer has a triple quantum well layer, and the optical resonator including the active layer has an optical length of 2λ. Further, 25 mirror layers made of p-type Al _0.9 Ga _0.1 As and GaAs were laminated to form an upper reflection layer. These semiconductor layers are gas source MBE
(Molecular Beam Epitaxy) method, MBE method, MOCVD
(Metalorganic Chemical Vapor Deposition) method to grow carbon (C) as a p-type impurity,
Silicon (Si) was doped as an n-type impurity. Al
The As layer is the bottom layer of the upper reflection layer (that is, the first period)
The Al _0.9 Ga _0.1 As layer forming the mirror layer of No. 2 was arranged at the upper end portion, and the film thickness was set to 12 nm. Then, the outer diameter of the horizontal cross section of the mesa-shaped portion was set to 40 μm, and after the formation of the mesa, it was held in a steam atmosphere at 420 ° C. for 20 minutes to form a selective oxidation region. AlAs not oxidized
The diameter of the current injection region formed by the layers was 5.2 μm.

When the oscillation characteristics of the surface emitting laser device manufactured as described above were examined, the threshold current value was 0.5 m.
A, the slope efficiency was 0.25 W / A, and continuous oscillation was possible at 100 ° C. or higher. The injection current value is 10
Single transverse mode oscillation is possible at 10 mA or less
When the optical signal directly modulated by it / s was made incident on the optical fiber for transmission, the transmittable distance was 15 km or more,
A good eye pattern of the optical signal after transmission for 15 km was obtained.

(Modification) Next, the structure of the surface emitting laser element according to the modification of the first embodiment will be described. Figure 4
FIG. 8 is a sectional view showing a structure of a surface emitting laser element according to a modification. In the first embodiment, the selective oxidation region 19
Although the mirror layer in which b is arranged is the mirror layer in the first period, it may be arranged in the mirror layer in the second period. Since the distance from the center of the active layer 4 to the lower end of the mirror layer in the second period is 580 nm, it is included in the numerical range of 370 nm to 680 nm defined for the position in the stacking direction, ensuring the reliability and ensuring the threshold current. This is because it can be suppressed.

Since the mirror layer in which the selective oxidation region 19b is arranged becomes the second period, in order to maintain the diameter of the current injection region 19a and maintain the effective refractive index difference, the selective oxidation region 1 is used.
The film thickness of 9b changes. This is because the equivalent refractive index of the second regions 22 and 23 also changes depending on the position of the selective oxidation region 19b in the stacking direction. As a result of calculation, the range of the film thickness d in which the diameter of the current injection region 19a is 3.5 μm or more and the selective oxidation is possible is 6 nm ≦ d ≦ 46 nm (5), The range of the film thickness d in which the diameter of the current injection region 19a is 5.3 μm or more and sufficient selective oxidation is possible is 10 nm ≦ d ≦ 20 nm (6).

(Second Embodiment) Next, a surface emitting laser device according to a second embodiment will be described. Embodiment 2
As shown in FIG. 5, the surface emitting laser device according to
The structure has an emission wavelength of 300 nm, and the optical length of the optical resonator formed by the lower clad layer, the active layer and the upper clad layer is equal to the wavelength of the emitted light. Specifically, the surface emitting laser element according to the second embodiment has a structure in which the lower reflective layer 2 is laminated on the substrate 1. Also,
The upper region of the lower reflective layer 2 is formed in a mesa shape, and the lower clad layer 26, the active layer 4, the upper clad layer 27, and the upper reflective layer 6 are sequentially stacked on the mesa-shaped region. The mesa shape is formed so that the horizontal cross section is circular. Further, a contact layer 7 is laminated on the upper reflective layer 6, a ring-shaped p-side electrode 8 having a current injection region in the center is arranged on the contact layer 7, and an n-side electrode is formed on the lower surface of the substrate 1. The side electrode 9 is arranged. The current confinement layer 30 is disposed inside the upper cladding layer 27 by the selective oxidation region 29b disposed near the center of the mesa and adjacent to the current injection region 29a having a circular horizontal cross section. There is. In addition, in the second embodiment, the parts having the same or similar reference numerals to those of the first embodiment have the same or similar structure and exhibit the same or similar functions unless otherwise specified. To do.

In the second embodiment, the optical length of the λ resonator 28 formed by the lower clad layer 26, the active layer 4 and the upper clad layer 27 is equal to the wavelength of the emitted light.
Therefore, the optimum position of the selective oxidation region 29b in the stacking direction and the film thickness are different from those in the first embodiment. In the following, the emission wavelength is 1300 nm and the λ resonator 28
The optimization of the selective oxidation region 29b of the surface emitting laser device having the above will be described.

First, optimization of the position of the selective oxidation region 29b in the stacking direction will be described. In the first embodiment,
The end surface of the selective oxidation region 29b on the active layer side is the active layer 4
The inventors of the present application have found that it is preferable to dispose it in the mirror layer existing in the range of 370 nm to 680 nm from the center of the. In the second embodiment, the λ resonator 2
It is necessary to determine an appropriate mirror layer in consideration of the difference in optical length of No. 8, and the mirror layer of the second period is selected as a mirror layer suitable for this. This is because the distance from the center of the active layer 4 of the mirror layer in the second period is 392 nm, which meets the above conditions. Also, in the mirror layer in the second period, it is preferable that the selective oxidation region 29b is arranged on the side of the low refractive index layer far from the active layer, as in the first embodiment. As a result, the position of the selective oxidation region 29b in the stacking direction is determined to the position shown in FIG.

Next, optimization of the diameter of the current injection region 29a defined by the horizontal width of the selective oxidation region 29b will be described. As described in the first embodiment, the diameter of the current injection region 29a is determined from the viewpoint of suppressing the increase of the threshold current and realizing the single transverse mode oscillation, and is the optical length of the optical resonator. It is decided independently. Therefore, the same argument as in the first embodiment is established, and the diameter of the current injection region 29a needs to be 3.5 μm or more from the measurement result of the 850 nm band surface emitting laser device. Considering the wavelength ratio, More preferably, it is 5.3 μm.

Finally, optimization of the film thickness of the selective oxidation region 29b will be described. From the viewpoint of realizing single transverse mode oscillation, the first region 21 and the second regions 22 and 23 shown in FIG.
The relationship of the equation (1) is established between the effective refractive index difference and the diameter of the current injection region 29a, and the condition that the single transverse mode oscillation is possible when the diameter of the current injection region 29a is 3.5 μm or more is: The effective refractive index difference needs to be 0.038 or less, and in order to perform single transverse mode oscillation when the diameter of the current injection region 29a is 5.3 μm, the effective refractive index difference is 0.0165.

In determining the film thickness of the selective oxidation region 29b necessary to realize such an effective refractive index difference, the graph shown in FIG. 6 is used in the second embodiment. FIG. 6 is a graph showing the relationship between the film thickness of the selective oxidation region and the effective refractive index difference for each mirror layer in which the selective oxidation region is arranged in the surface emitting laser device having the λ resonator (KDChoquette et. al., Proceedings of SPIE
Vertical-Cavity Surface-Emitting Lasers, vol. 300
3, pp.194-200, 1997.). In FIG. 6, the curve l ₁ shows the case where the selective oxidation layer is arranged in the first cycle, and hereinafter, the curves l ₂ , l ₃ , l ₄ , and ₁₅ are respectively in the second cycle, the third cycle, The case where the selective oxidation regions are arranged in the fourth period and the fifth period is shown. The horizontal axis of the graph shows the film thickness of the selective oxidation region, and the vertical axis of the graph shows the effective refractive index difference.

In the surface-emission laser device according to the second embodiment, the selective oxidation region 29b is arranged in the mirror layer of the second period, so the curve l ₂ is referred to in the graph of FIG. By referring to the curve l ₂ , it can be seen that the film thickness needs to be 32 nm or less in order for the effective refractive index difference to be 0.038 or less. Further, it can be seen that the film thickness becomes 13 nm in order for the effective refractive index difference to be 0.0165.

Since the same discussion as in the first embodiment is established regarding the minimum value of the film thickness, as a result, the selective oxidation region 29b necessary for realizing the single lateral oscillation mode while suppressing the threshold current low. The range of the film thickness d is 6 nm ≦ d ≦ 32 nm (7), which enables rapid selective oxidation, and the current injection region 29a.
The more preferable range of the film thickness d in which the diameter can be increased is 10 nm ≦ d ≦ 13 nm (8). As described above, in the surface emitting laser device according to the second embodiment, the structure of the selective oxidation region 29b is optimized.

(Modification) Next, a surface emitting laser device according to a modification of the second embodiment will be described. FIG. 7 is a cross-sectional view showing the structure of the surface emitting laser element according to the modification, which is different from the second embodiment in that the selective oxidation region 29b is arranged in the mirror layer in the third period.

As described above, also in the second embodiment, it is possible to arrange the selective oxidation region 29b in the mirror layer having the lower end in the range of 370 nm to 680 nm from the center of the active layer 4. The emission wavelength is 1300 nm,
It can be seen that when the optical length of the optical resonator is equal to the wavelength of the emitted light, the lower end of the mirror layer in the third period is separated from the center of the active layer 4 by 596 nm and is included in the above range. Therefore, it is possible to have a structure in which the selective oxidation region 29b-1 is arranged in the mirror layer in the third period.

The conditions of the diameter of the current injection region 29a-1 and the difference in effective refractive index can be considered as in the surface emitting laser device according to the second embodiment. In conclusion, the diameter of the current injection region 29a-1 is 3.5 μm or more, preferably 5.3 μm, and the effective refractive index difference is
It must be 0.038 or less, preferably 0.01
It becomes 65.

The film thickness satisfying the above effective refractive index difference is examined by the graph shown in FIG. In the surface emitting laser element according to the modified example, the selective oxidation region 29b-1 is arranged in the mirror layer in the third period, so that the curve l _{3 in} the drawing is used.
Need to refer to. According to the curve l ₃ , the film thickness needs to be 46 nm or less for the effective refractive index difference to be 0.038 or less, and the film thickness required for the effective refractive index difference to be 0.0165 is 20 nm. Is. With the above, the optimization of the structure of the selective oxidation region 29b-1 according to the modification is completed.

Although the surface emitting laser device according to the present invention has been described with reference to the first and second embodiments and their modifications, structures other than those described above can be adopted. For example, in the first and second embodiments and the modifications thereof, the emission wavelength of the surface emitting laser element is 1300n.
It was m. The present invention is not limited to this, and the structure of the selective oxidation region can be optimized even for a surface emitting laser device having a long wavelength of 850 nm or more. This will be described below.

First, it is preferable that the position of the selective oxidation region in the mirror layer is arranged near the interface of the low refractive index layer on the side far from the active layer regardless of the emission wavelength. The deciding factor regarding which mirror layer is arranged is also from the viewpoint of suppressing an increase in threshold current and ensuring reliability, and these viewpoints have a poor correlation with the emission wavelength. Further, the diameter of the current injection region is also derived from the measurement result for the 850 nm band surface emitting laser device, and as described above, the measurement result is used regardless of the emission wavelength. Regarding the film thickness of the selective oxidation region, the film thickness for obtaining the necessary effective refractive index difference may be derived by a known method. Therefore, 850 nm
Regarding the above long-wavelength surface emitting laser device, Embodiment 1
Alternatively, the method described in 2 can be used to optimize the structure of the selective oxidation region. For the same reason,
The structure of the selective oxidation region can be optimized also for the surface emitting laser device having the optical resonators of different optical lengths. Here, regarding the position of the selective oxidation region in the stacking direction,
The position of the lower end of the mirror layer in which the selective oxidation region is arranged is in the range of 370 nm to 680 nm from the center of the active layer. However, regarding the position of the selective oxidation region itself, the film thickness of the low refractive index layer forming the mirror layer is also taken into consideration. Then, the upper limit of the distance from the center of the active layer is preferably 780 nm.

Besides using carbon as the p-type impurity, zinc (Zn) or beryllium (Be) can be used. The same applies to n-type impurities, and dopants other than silicon may be used.

Although AlAs was used as the semiconductor material for forming the selective oxidation region and the current injection region, Al _x Ga _1-x As (0.97 ≦ x <1) may be used instead of AlAs. It is also possible to form a current injection region.

In the mirror layers constituting the upper reflection layer and the lower reflection layer, the low refractive index layer is made of Al _x Ga _1-x As.
(0.5 ≦ x ≦ 1) and the high refractive index layer is made of Al _x Ga.
_{Even in the case of 1-x} As (0 ≦ x ≦ 0.2), it is possible to reflect light having an emission wavelength and function as a mirror layer. Further, the low-refractive index layer and the high-refractive index layer may have a structure in which a composition gradient layer for relaxing the difference in the refractive index between the low-refractive index layer and the high-refractive index layer is disposed near the boundary between them.

The surface emitting laser device according to the present invention can be realized by using an InP substrate, a GaInAs substrate, or the like as the substrate other than the GaAs substrate.

Further, the active layer is not a structure composed of a triple quantum well layer and a barrier layer separating them,
It may be configured with a single quantum well layer, or may have a structure having other number of quantum well layers. Also, the quantum well layer can be formed of a GaInAs-based or GaAsSb-based semiconductor material. Further, the quantum dots may be formed of (Ga) InAs or the like instead of the quantum well layer. Further, it may be simply a surface emitting laser element having a double hetero structure.

It is also possible to reverse the conductivity type of the semiconductor material forming the surface emitting laser element.
For example, the substrate, the lower clad layer, and the lower reflective layer are formed of p-type semiconductor, and the upper reflective layer and the upper clad layer are n-type.
It may be formed of a mold semiconductor.

Further, the current confinement layer consisting of the selective oxidation region and the current injection region is preferably arranged in the p-type reflection layer, but the same argument can be established even if the current confinement layer is arranged in the n-type reflection layer. It is possible to exert the effect of.

(Third Embodiment) Next, an optical transmitter / receiver according to a third embodiment will be described. FIG. 8 is a block diagram showing the structure of the optical transceiver according to the third embodiment.
The optical transmitter / receiver according to the third exemplary embodiment includes a transceiver 31 having an optical transmitter 34 and an optical receiver 35 for transmitting and receiving an optical signal, a signal multiplexing circuit 32 for inputting an electric signal to the transceiver 31, and a transceiver. 31 has a signal separation circuit 33 for separating an electric signal obtained from the optical signal received.

The optical transmitter 34 is for converting the electric signal inputted from the signal multiplexing circuit 32 into an optical signal and transmitting it. Specifically, the optical transmitter 34 includes a surface emitting laser element 36 that emits an optical signal, and a control circuit 37 that controls the surface emitting laser element 36 based on the input electrical signal.
And an output optical system 38 for outputting the optical signal emitted from the surface emitting laser element 36 to the outside.

As the surface emitting laser element 36 included in the optical transmitter 34, the surface emitting laser element according to the first or second embodiment is used. Therefore, the surface emitting laser element 36 is
It has a low threshold current, high reliability, and single transverse mode oscillation is possible.

The optical receiver 35 is for converting an optical signal received from the outside into an electric signal and outputting it to the signal separation circuit 33. Specifically, the light receiving unit 35 receives the optical signal and converts it into an electric signal.
And an input optical system 40 for guiding an optical signal to the photoelectric conversion element 39, and an amplifier circuit 41 for amplifying an electric signal output from the photoelectric conversion element 39. The photoelectric conversion element 39 is
An electric signal is output based on the intensity of the received optical signal.
As the photoelectric conversion element 39, a photo resistance or the like can be used in addition to the photodiode.

The signal multiplexing circuit 32 serves to multiplex a plurality of electric signals input from the outside into one electric signal. One electric signal obtained by being multiplexed is output to the optical transmission unit 34 included in the transceiver 31.

The signal separation circuit 33, with respect to the electric signal obtained from the optical receiving section 35 constituting the transceiver 31,
It is for separating into a plurality of electric signals. Since the optical signal received by the optical receiver 35 originally includes a plurality of signals, an electrical signal obtained by photoelectrically converting the optical signal also needs to be separated into a plurality of electrical signals in order to extract information. Because there is.

The operation of the optical transmitter / receiver according to the third embodiment will be described. The optical transceiver according to the third embodiment is for transmitting and receiving a plurality of electric signals. First, the transmission operation will be described.

First, a plurality of electric signals input from the outside are converted into a single electric signal by the signal multiplexing circuit 32. Then, this single electric signal is converted into the signal multiplexing circuit 32.
Is input to the control circuit 37, and the control circuit 37 controls the current to be injected into the surface emitting laser element 36 based on this electric signal. Specifically, the control circuit 37 causes the surface emitting laser element 36 to emit an optical signal having a waveform corresponding to the electrical signal waveform. The surface emitting laser device 36
Since is composed of the surface emitting laser device according to the first or second embodiment, direct light modulation is possible at a maximum of 10 Gbit / s. Therefore, a large amount of information can be added to the optical signal and transmitted. The optical signal output from the surface emitting laser element 36 is output to the outside via the output optical system 38. This completes the transmission operation.

Next, the receiving operation will be described. The optical signal transmitted from the outside enters through the input optical system 40 and is received by the photoelectric conversion element 39. The photoelectric conversion element 39 has a function of outputting an electric signal having a waveform corresponding to the intensity change of the received optical signal, and the converted electric signal is input to the amplifier circuit 41. Since the intensity of the optical signal input from the outside is generally weak, the intensity of the electric signal output from the photoelectric conversion element 39 is also weak, and the intensity is amplified by the amplifier circuit 41. Then, the amplified electric signal is input to the signal separation circuit 33 and separated into a plurality of electric signals. This completes the reception operation.

The optical transmitter / receiver according to the third embodiment has the surface emitting laser element according to the first or second embodiment. Therefore, in the third embodiment, the surface emitting laser element 36 has a low threshold current and high reliability. Moreover, it is possible to directly modulate at 10 Gbit / s, and it is possible to output an optical signal having a large amount of information.
Furthermore, when the output optical signal is transmitted by an optical fiber, the transmittable distance becomes 15 km or more, and long-distance transmission becomes possible.

(Fourth Embodiment) Next, an optical communication system according to the fourth embodiment will be described. FIG. 9 is a schematic diagram showing the structure of the optical communication system according to the fourth embodiment. The optical communication system according to the fourth embodiment uses the surface-emission laser device according to the first or second embodiment as a signal light source. Specifically, the surface-emission laser device according to the fourth embodiment includes a signal multiplexing circuit 42, a control circuit 43 connected to the signal multiplexing circuit 42, and a surface-emission laser device connected to the control circuit 43. 44 and optical fiber 4 for transmission
6 and an optical system 45 for optically coupling the surface emitting laser element 44 and one end of the transmission optical fiber 46. Further, a photoelectric conversion element 48 optically coupled to the other end of the transmission optical fiber 46 via an optical system 47, an amplifier circuit 49 connected to the photoelectric conversion element 48, and a signal separation circuit 50 connected to the amplifier circuit 49. Have and.

The single electric signal obtained by the signal multiplexing circuit 42 is input to the control circuit 43, and the control circuit 43 controls the current to be injected into the surface emitting laser element 44 based on this electric signal. As a result, the optical signal output from the surface-emission laser device 44 has a waveform corresponding to the electrical signal obtained by the signal multiplexing circuit 42. The optical signal output from the surface emitting laser element 44 is incident on one end of the transmission optical fiber 46 via the optical system 45 and is transmitted through the transmission optical fiber 46.

The optical signal transmitted through the transmission optical fiber 46 is emitted from the other end of the transmission optical fiber 46,
The light enters the photoelectric conversion element 48 via the optical system 47. The photoelectric conversion element 48 outputs an electric signal based on the received optical signal, and after being amplified by the amplifier circuit 49, the signal separation circuit 50.
Entered in.

The signal separation circuit 50 separates the input electric signal into individual electric signals before being multiplexed by the signal multiplexing circuit 42 to restore information. In this way, the optical communication system according to the fourth embodiment transmits information.

In the optical communication system according to the fourth embodiment, the surface emitting laser element according to the first or second embodiment is used as the signal light source on the transmitting side. Therefore, it is possible to use a signal light source with a low threshold and high reliability. Moreover, since the single transverse mode oscillation is possible, the optical signal can be reliably transmitted without the signal waveform being disturbed during the transmission. Specifically, the transmission optical fiber 46
10 Gbit / s even if the fiber length of 15 km or more
It is possible to transmit an optical signal directly modulated by.

Further, since the surface emitting laser device according to the first or second embodiment can change the emission wavelength in the range of 850 nm to 1650 nm, it is possible to select the wavelength with which the transmission optical fiber 46 has a low loss. It is possible. Further, there is an advantage that the existing optical communication system can be used in these wavelength bands. For example, with an emission wavelength of 980 nm, an EDFA (Erbium Doped Fiber Amplifi
er) may be arranged. In this case, EDFA
Since the intensity of the optical signal can be amplified by this, the transmission distance can be further extended. Similarly, TD
FA, Raman amplifier or the like may be used.

[0101]

As described above, according to the inventions of claims 1 to 11, since the structure of the selective oxidation region is optimized,
It is possible to provide a surface emitting laser device that suppresses the threshold current to a low value, has high reliability, can perform single transverse mode oscillation, can directly modulate at 10 Gbit / s, and can transmit over a long distance. Play.

According to the invention of claims 12 to 14,
Since the surface emitting laser having the optimized structure of the selective oxidation region is used, it is possible to provide a transceiver, an optical transceiver, and an optical communication system capable of single transverse mode oscillation and capable of long-distance transmission.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a surface emitting laser device according to a first embodiment.

2A to 2C are cross-sectional views showing the structure of an 850 nm surface-emitting laser device used for measurement.

FIG. 3 is a schematic diagram for explaining an effective refractive index difference.

FIG. 4 is a cross-sectional view showing a structure of a surface emitting laser element according to a modification of the first embodiment.

FIG. 5 is a sectional view showing a structure of a surface emitting laser device according to a second embodiment.

FIG. 6 is a graph showing the relationship between the film thickness of the selective oxidation region and the effective refractive index difference for each mirror layer in which the selective oxidation region is arranged.

FIG. 7 is a sectional view showing a structure of a surface emitting laser element according to a modified example of the second embodiment.

FIG. 8 is a block diagram showing a structure of an optical transceiver according to a third exemplary embodiment.

FIG. 9 is a block diagram showing a structure of an optical communication system according to a fourth exemplary embodiment.

FIG. 10 is a sectional view showing a structure of a conventional surface emitting laser device.

[Explanation of symbols]

1 substrate 2 Lower reflective layer 3, 26 Lower clad layer 4 Active layer 5,27 Upper clad layer 6 Upper reflective layer 7 Contact layer 8 p-side electrode 9 n-side electrode 10,17 High refractive index layer 11, 16 Low refractive index layer 12, 18 Mirror layer 13a to 13d Barrier layer 14a-14d quantum well layer 15 2 λ resonator 19a, 29a, 29a-1 Current injection region 19b, 29b, 29b-1 selective oxidation region 20, 30 Current constriction layer 28 λ resonator 31 transceiver 32, 42 signal multiplexing circuit 33, 50 Signal separation circuit 34 Optical transmitter 35 Optical receiver 36,44 surface emitting laser device 37, 43 Control circuit 38 Output optical system 39, 48 Photoelectric conversion element 40 Input optical system 41, 49 Amplification circuit 45, 47 Optical system 46 Optical fiber for transmission

Claims (14)

[Claims] 1. A surface emitting laser device having a structure in which a lower reflective layer, a lower clad layer, an active layer, an upper clad layer, and an upper reflective layer are sequentially laminated on a substrate, and oscillates in a direction perpendicular to the substrate. Which is inside the lower reflective layer or the upper reflective layer,
The current injection includes: a selective oxidation region arranged in a region separated from the center of the active layer by a distance of 370 nm to 780 nm in the stacking direction; and a current injection region sandwiched between the selective oxidation regions. A surface emitting laser element, wherein a difference value between an effective refractive index of a stacking direction region including a region and an effective refractive index of a stacking direction region including the selective oxidation region is 0.038 or less. 2. The upper reflective layer and the lower reflective layer are formed by laminating a plurality of mirror layers each having a two-layer structure of a low refractive index layer and a high refractive index layer having an optical length of ¼ of an emission wavelength. 2. The surface emitting device according to claim 1, wherein the selective oxidation region is formed and is disposed in the vicinity of a position where the electric field intensity distribution in the low refractive index layer in any one of the mirror layers is minimum. Laser device. 3. The active layer has a thickness of 1260 nm or more, 13
An optical resonator that emits laser light having a wavelength of 60 nm or less, and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length that is twice the wavelength of the laser light; 3. The selective oxidation region is arranged in the mirror layer laminated in the first period from the active layer side in the upper or lower reflective layer.
The surface emitting laser device described in 1. 4. The active layer has a thickness of 1260 nm or more, 13
An optical resonator that emits a laser beam having a wavelength of 60 nm or less, and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length equal to the wavelength of the laser beam, and the selective oxidation is performed. 3. The region is arranged in the upper or lower reflective layer in a mirror layer laminated in a second period from the side of the active layer.
The surface emitting laser device described in 1. 5. The selective oxidation region has a thickness of 6 nm or more and 32.
The surface emitting laser element according to claim 3, which has a film thickness of not more than nm. 6. The selective oxidation region is 10 nm or more, 1
The surface emitting laser element according to claim 3, which has a film thickness of 3 nm or less. 7. The active layer has a thickness of 1260 nm or more, 13
An optical resonator that emits laser light having a wavelength of 60 nm or less, and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length that is twice the wavelength of the laser light; 3. The selective oxidation region is arranged in the mirror layer laminated in the second period from the side of the active layer in the upper or lower reflective layer.
The surface emitting laser device described in 1. 8. The active layer comprises 1260 nm or more, 13
An optical resonator that emits a laser beam having a wavelength of 60 nm or less, and is formed by the lower clad layer, the active layer, and the upper clad layer has an optical length equal to the wavelength of the laser beam, and the selective oxidation is performed. 3. The region is arranged in the upper or lower reflective layer in a mirror layer laminated in a third period from the side of the active layer.
The surface emitting laser device described in 1. 9. The selective oxidation region is 6 nm or more, 46
9. The surface emitting laser element according to claim 7, which has a film thickness of not more than nm. 10. The selective oxidation region is 10 nm or more,
8. A film having a film thickness of 20 nm or less.
Alternatively, the surface emitting laser device according to item 8. 11. The substrate is made of GaAs, and the low refractive index layer is made of Al _x Ga _1-x As (0.5 ≦ x ≦).
1), and the high refractive index layer is formed of Al _x Ga _1-x As (0 ≦
x ≦ 0.2), and the selective oxidation region is Al _x Ga _1-x
The surface emitting laser element according to claim 1, wherein the surface emitting laser element is formed by selectively oxidizing As (0.97 ≦ x ≦ 1). 12. A surface emitting laser element according to claim 1, and a control circuit for controlling a current value injected into the surface emitting laser element based on an inputted electric signal. A transceiver comprising: an optical transmitter; and an optical receiver having a photoelectric conversion element that receives an optical signal incident from the outside and converts the optical signal into an electric signal. 13. The surface emitting laser device according to claim 1, a signal multiplexing circuit for multiplexing a plurality of electrical signals, and an electrical signal output from the signal multiplexing circuit. A control circuit for controlling the surface emitting laser element based on the above, a photoelectric conversion element for receiving an optical signal incident from the outside and converting it into an electric signal, and an electric signal output from the photoelectric conversion element are separated into a plurality of electric signals. An optical transmitter / receiver, comprising: 14. The surface emitting laser element according to claim 1, a control circuit for controlling the surface emitting laser element, and an optical signal emitted from the surface emitting laser element from one end. An optical communication system comprising: a transmission optical fiber which is incident and transmitted; and a photoelectric conversion element which receives the optical signal incident from the other end of the transmission optical fiber and converts the optical signal into an electric signal. .