JP4629949B2 - Surface emitting laser element, transceiver using surface emitting laser element, optical transceiver, and optical communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface emitting laser element 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, and lasing in a direction perpendicular to a substrate. The present invention relates to a surface emitting laser element capable of oscillating in a single transverse mode and capable of long-distance transmission, a transceiver using the surface emitting laser element, an optical transceiver, and an optical communication system.
[0002]
[Prior art]
In recent years, vertical cavity surface emitting lasers (VCSELs) are referred to as “surface emitting laser elements”, and the direction in which light resonates is perpendicular to the substrate surface. It is attracting attention as a light source for communication, including optical interconnection, and as a device for various other applications. Since the surface emitting laser element includes an ultrashort resonator of about one wavelength due to its structure, the wavelength that can exist in the oscillating laser beam is only the fundamental wave. Therefore, it is easier to stably maintain the single longitudinal mode than an edge-emitting laser such as a DFB (Distributed Feedback) laser. In addition, the FFP (Far Field Pattern) is isotropic and narrow values can be obtained, and the relative intensity noise is low, so that it is attracting attention as a laser element that is essentially suitable for optical communication and the like than a DFB laser or the like.
[0003]
When used as a signal light source, a surface emitting laser element having an emission wavelength of 0.8 μm to 1.65 μm including a low loss wavelength band of an optical fiber as a transmission medium is required. In a surface emitting laser of this wavelength band, a surface emitting laser that oscillates a laser beam having a long wavelength band, for example, a wavelength of 1.2 μm or more, has not been realized for a long time due to difficulty in crystal growth. However, recently, the present inventors have realized a surface emitting laser element that oscillates laser light having a wavelength of 1.2 to 1.3 μm (Japanese Patent Application No. 2001-124300).
[0004]
The structure of the surface emitting laser element described in Japanese Patent Application No. 2001-124300 is shown in FIG. This surface-emitting laser element has a structure in which a buffer layer 102, a lower reflective layer 103, a lower cladding layer 104, a quantum well layer 105, and an upper cladding layer 106 are sequentially stacked on a substrate 101. Further, the upper clad layer 106 has a laminated structure of a current confinement layer 108 processed into a mesa shape, an upper reflective layer 109, and a contact layer 110. The current confinement layer 108 is formed by a current injection region 107a made of an AlAs layer at the center and a selective oxidation region 107b formed by selectively oxidizing the end of the AlAs layer. An n-side electrode 114 is disposed on the lower surface of the substrate 101. In the quantum well layer 105, the crystallographic quality of the quantum well layer 105 is improved by adding a small amount of Sb in GaInNAs. As described above, the laser oscillation of the 1.3 μm band surface emitting laser element has recently been performed using the improvement of the structure of the quantum well layer and the selective oxidation technique of the AlAs layer.
[0005]
[Problems to be solved by the invention]
However, problems to be solved remain when surface emitting laser elements are used for applications such as signal light sources. First, it is necessary to unify the transverse mode of the oscillating laser beam. When the transverse mode has a high-order mode in the transverse direction, it causes a 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.
[0006]
The surface emitting laser element is inherently difficult to stabilize the transverse mode due to its structure. Therefore, in a surface emitting laser element having a selective oxidation region, single transverse mode oscillation is realized by adjusting the diameter of the current injection region sandwiched between the selective oxidation regions, but conventionally, the 1300 nm band (1260 nm to 1360 nm). In a surface-emitting laser element of a range of a certain extent, it is difficult to realize single transverse mode oscillation by adjusting only the diameter of the current injection region.
[0007]
Even if single transverse mode oscillation can be realized, if the value of the threshold current increases, problems such as increased power consumption occur. 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 a surface emitting laser element for a signal light source or the like.
[0008]
Furthermore, when used for a signal light source or the like, it is necessary to be able to directly modulate at a 10 Gbit / s level. This is a minimum number necessary for actual use as a signal light source with an increase in communication capacity in recent years.
[0009]
The present invention has been made in view of the above disadvantages of the prior art, and has a low threshold current, a high reliability, a single transverse mode oscillation, and a surface emission capable of direct modulation at 10 Gbit / s. It is an object of the present invention to provide a laser element, a transceiver using a surface emitting laser element, an optical transceiver, and an optical communication system.
[0010]
[Means for Solving the Problems]
To achieve the above objective, This invention The surface emitting laser device according to the present invention has 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 a surface that oscillates in a direction perpendicular to the substrate. A selective oxidation region disposed in a region separated from the active layer center by a distance of not less than 370 nm and not more than 780 nm inside the lower reflective layer or the upper reflective layer, the light emitting laser element; A difference value between the effective refractive index of the stacking direction region including the current injection region and the effective refractive index of the stacking direction region including the selective oxidation region. Is 0.038 or less.
[0011]
This invention According to the present invention, since the position of the selective oxidation region in the stacking direction and the effective refractive index difference are optimized, a surface emitting laser element that emits a laser beam capable of single transverse mode oscillation and capable of long-distance transmission is provided. Can be realized.
[0012]
Also, This invention In the surface emitting laser element according to the present invention, the upper reflective layer and the lower reflective layer have 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. The selective oxidation region is arranged 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 minimized. .
[0013]
Also, This invention In the surface emitting laser element according to the present invention, the active layer emits laser light having a wavelength of 1260 nm or more and 1360 nm or less, and is formed by the lower cladding layer, the active layer, and the upper cladding layer. The optical resonator has an optical length twice as long as the wavelength of the laser beam, and the selective oxidation region is in the mirror layer laminated in the first period from the active layer side in the upper or lower reflection layer. It is characterized by being arranged in.
[0014]
Also, This invention In the surface emitting laser element according to the present invention, the active layer emits laser light having a wavelength of 1260 nm or more and 1360 nm or less, and is formed by the lower cladding layer, the active layer, and the upper cladding layer. The optical resonator has an optical length equal to the wavelength of the laser beam, and the selective oxidation region is adjacent to a mirror layer stacked in a second period from the active layer side in the upper or lower reflective layer. It is arranged in the mirror layer.
[0015]
Also, This invention In the surface emitting laser element according to the present invention, the selective oxidation region has a thickness of 6 nm or more and 32 nm or less.
[0016]
Also, This invention The surface emitting laser element according to the present invention is characterized in that, in the above invention, the selective oxidation region has a thickness of 10 nm or more and 13 nm or less.
[0017]
Also, This invention In the surface emitting laser element according to the present invention, the active layer emits laser light having a wavelength of 1260 nm or more and 1360 nm or less, and is formed by the lower cladding layer, the active layer, and the upper cladding layer. The optical resonator has an optical length that is twice as long as the wavelength of the laser beam, and the selective oxidation region is in the mirror layer laminated in the second period from the active layer side in the upper or lower reflective layer. It is characterized by being arranged in.
[0018]
Also, This invention In the surface emitting laser element according to the present invention, the active layer emits laser light having a wavelength of 1260 nm or more and 1360 nm or less, and is formed by the lower cladding layer, the active layer, and the upper cladding layer. The optical resonator has an optical length equal to the wavelength of the laser beam, and the selective oxidation region is disposed in a mirror layer stacked in a third period from the active layer side in the upper or reflective layer. It is characterized by.
[0019]
Also, This invention In the surface emitting laser element according to the present invention, the selective oxidation region has a thickness of 6 nm to 46 nm.
[0020]
Also, This invention In the surface emitting laser element according to the present invention, the selective oxidation region has a thickness of 10 nm or more and 20 nm or less.
[0021]
Also, This invention In the surface emitting laser element according to the present 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), the high refractive index layer is made of Al _x Ga _1-x As (0 ≦ x ≦ 0.2), and the selective oxidation region is Al _x Ga _1-x It is formed by selectively oxidizing As (0.97 ≦ x ≦ 1).
[0022]
Also, This invention The transceiver The above invention An optical transmitter having the surface-emitting laser element according to any one of the above, a control circuit that controls a current value injected into the surface-emitting laser element based on an input electric signal, and light incident from the outside And an optical receiver having a photoelectric conversion element for receiving a signal and converting it into an electrical signal.
[0023]
Also, This invention The optical transceiver The above invention A surface-emitting laser element according to any one of the above, a signal multiplexing circuit that multiplexes a plurality of electrical signals, and a control that controls the surface-emitting laser element based on the electrical signals output from the signal multiplexing circuit A circuit, a photoelectric conversion element that receives an optical signal incident from the outside and converts it into an electrical signal, and a signal separation circuit that separates the electrical signal output from the photoelectric conversion element into a plurality of electrical signals. Features.
[0024]
Also, This invention The optical communication system related to The above invention A surface emitting laser element according to any one of the above, a control circuit that controls the surface emitting laser element, an optical fiber for transmission that transmits an optical signal emitted from the surface emitting laser element from one end, and And a photoelectric conversion element that receives the optical signal incident from the other end of the transmission optical fiber and converts it into an electrical signal.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of a surface emitting laser element, a transceiver using the surface emitting laser element, an optical transceiver, and an optical communication system according to the present invention will be described below with reference to the drawings. In the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic, and it should be noted that the relationship between the thickness and width of each layer, the ratio of each layer, and the like are different from the actual ones. Of course, the drawings include portions having different dimensional relationships and ratios.
[0026]
(Embodiment 1)
First, the surface emitting laser element according to the first embodiment will be described. In the surface emitting laser element according to the first embodiment, the structure of the selective oxidation region is optimized with respect to the 1300 nm band surface emitting laser element. FIG. 1 is a sectional view showing the structure of the surface emitting laser element according to the first embodiment. Hereinafter, the structure of the surface emitting laser element according to the first embodiment will be described with reference to FIG. 1 as appropriate.
[0027]
The surface emitting laser element according to the first embodiment 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 cladding layer 3, the active layer 4, the upper cladding layer 5, and the upper reflective layer 6 are sequentially stacked on the region formed in the mesa shape. In addition, this mesa shape is formed so that a horizontal cross-sectional shape may be circular. Further, a contact layer 7 is laminated on the upper reflective layer 6, and a p-side electrode 8 having a ring shape having a current injection region in the center is disposed on the contact layer 7, and n on the lower surface of the substrate 1. Side electrodes 9 are arranged. In the upper reflective layer 6, a current confinement layer 20 is disposed near the center of the mesa and includes a current injection region 19a having a circular horizontal cross section and a selective oxidation region 19b adjacent to the current injection region 19a. Is arranged. The specific structure of the selective oxidation region 19b will be described in detail later.
[0028]
The substrate 1 is made of an n-type GaAs substrate. 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 reflective layer 2 is for reflecting and feeding back the light having the emission wavelength among the light generated in the active layer 4. 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.
[0029]
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 _0.1 It is formed by the 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 is ¼ of the output wavelength λ in order to reflect only the light having the output wavelength. Specifically, since the emission wavelength of the surface emitting laser element according to the first embodiment is 1300 nm, the film thickness of the high refractive index layer 10 is about 94 nm in consideration of the refractive index of each layer. The film thickness of 11 is about 110 nm. By having such a structure, the mirror layer 12 has a function of reflecting light having an emission wavelength at a certain ratio in the combination of the high refractive index layer 10 and the low refractive index layer 11. 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. Note that the fraction after the decimal point is attributed to a layer made of only the high refractive index layer 10.
[0030]
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 sequentially stacked on the lower cladding layer 3. 14c and the barrier layer 13d. That is, it has a structure in which three quantum well layers 14a to 14c are sandwiched between four barrier layers 13a to 13d.
[0031]
The quantum well layers 14a to 14c are for confining carriers with high efficiency by the quantum confinement effect, and are formed of GaInNAsSb layers. The quantum well layers 14a to 14c have good crystallinity by adding a small amount of Sb. Further, the quantum well layers 14a to 14c need to have a very 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.
[0032]
The barrier layers 13a to 13d are for separating the quantum well layers 14a to 14c from each other. The thickness of the barrier layers 13a and 13d is about 30 nm, and the thickness of the barrier layers 13b and 13c is 20 nm. Degree.
[0033]
The lower clad layer 3, the active layer 4, and the upper clad layer 5 are formed so that the total optical length of the film thickness of each layer is twice the emission wavelength λ, and functions as an optical resonator. Therefore, hereinafter, 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 cladding layer 3 is an n-type and the upper cladding layer 5 is a p-type GaAs layer, and each film thickness is about 297 nm.
[0034]
Similar to the lower reflective layer 2, the upper reflective layer 6 is for reflecting and feeding back the light having the emission wavelength among the light generated in the active layer 4. Specifically, the upper reflective layer 6 has a structure in which a 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. _0.9 Ga _0.1 The As layer is provided, and the high refractive index layer 17 is a p-type GaAs layer. In order to feed back the laser light generated in the active layer 4, the upper reflective layer 6 has a high reflectance. Note that the surface-emitting laser element according to the first embodiment emits laser light in a vertically upward direction with respect to the substrate 1, so that 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 composed of 25 mirror layers 18 that are fewer than the lower reflective layer 2. In the following description, the mirror layer disposed on the most active layer 4 side of the 25 mirror layers 12 or 18 constituting the lower reflective layer 2 or the upper reflective layer 6 is set to the first period as necessary. The mirror layer arranged in contact with the mirror layer in the first period, the mirror layer arranged in contact with the mirror layer in the first period, the mirror layer in the second period, and the mirror layer arranged in contact with the mirror layer in the second period in the third period They are called eye mirror layers, respectively.
[0035]
Of the low refractive index layers 16 constituting the upper reflective layer 6, the low refractive index layer 16 constituting the first period mirror layer laminated adjacent to the lowermost layer, that is, the upper cladding layer 5 is p-type. Al _0.9 Ga _0.1 It has a structure in which an As layer and a p-type AlAs layer are sequentially stacked. In the AlAs layer, the current injection region 19a is formed in the region near the center, and the current confinement layer 20 is formed in the vicinity of the end portion by the selective oxidation region 19b formed by selective oxidation.
[0036]
The selective oxidation region 19b is for narrowing the current injected from the p-side electrode 8 to increase the current density flowing into the active layer 4 and to reduce the oscillation threshold. The refractive index of the selective oxidation region 19b is such that the current injection region 19a and Al _0.9 Ga _0.1 Since it has a different value from the As layer, it affects the optical confinement in the horizontal direction. That is, since the selective oxidation region 19b exists, the surface emitting laser element according to the first embodiment includes a refractive index waveguide.
[0037]
The selective oxidation region 19b has a thickness of 13 nm in the first embodiment. The diameter of the current injection region 19a defined by the width of the selective oxidation region 19b is set to 5.3 μm. Hereinafter, the reason why such a structure is adopted will be described.
[0038]
The surface emitting laser element according to the first embodiment improves the oscillation characteristics by optimizing the structure of the selective oxidation region 19b. Specifically, it is necessary to consider the position where the selective oxidation region 19b is disposed in the mirror layer, the mirror layer where the selective oxidation region 19b is disposed, the width and the film thickness of the selective oxidation region 19b. Hereinafter, optimization of these requirements will be described.
[0039]
First, the position in the mirror layer will be described. The current injection region 19a adjacent to the selective oxidation region 19b is made of Al. _0.9 Ga _0.1 It has a refractive index close to the As layer. Therefore, the AlAs layer forming the selective oxidation region 19b and the current injection region 19a needs to be disposed in the low refractive index layer 11 or the low refractive index layer 16. Further, in order to suppress the loss of light generated in the active layer 4, the position close to the node portion of the standing wave (position where the electric field strength distribution is minimized), that is, the low refractive index layer 11 or the low refractive index layer. 16 is preferably disposed in a region separated from the active layer 4, that is, in the vicinity of the lower surface of the low refractive index layer 11 or in the vicinity of the upper surface of the low refractive index layer 16.
[0040]
Next, the mirror layer in which the selective oxidation region 19b is arranged will be described. As already described, the selective oxidation region 19b has a current confinement function. From the viewpoint of increasing the current density flowing into the active layer 4 by confining the current, the selective oxidation region 19b is preferably disposed at a position close to the active layer 4. This is because when the selective oxidation region 19b is arranged at a position separated from the active layer 4, the current confined by the selective oxidation region 19b is diffused again before flowing into the active layer 4 to reduce the current density. Therefore, it is preferable to dispose the selective oxidation region 19b close to the active layer 4 from the viewpoint of suppressing the oscillation threshold value low.
[0041]
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 once laminating an AlAs layer or the like and processing it into a mesa shape, and then selectively oxidizing by introducing oxygen atoms from the outside by heating in a water vapor atmosphere. By introducing oxygen atoms from the outside, the initial crystal order is damaged, so that dislocation occurs in the selective oxidation region 19b. Therefore, when the selective oxidation region 19b is too close to the active layer 4, the dislocation in the selective oxidation region also affects the crystal structure of the active layer 4, and the reliability as the surface emitting laser element is lowered. Therefore, from the viewpoint of ensuring the reliability of the surface emitting laser element, it is preferable to dispose the selective oxidation region 19b away from the active layer 4.
[0042]
As described above, since suppression of the oscillation threshold value and ensuring of the reliability of the surface emitting laser element are in a trade-off relationship, there is an optimum value for the position in the stacking direction of the selective oxidation region 19b. For this reason, the inventors of the present application examine the characteristics of the surface emitting laser element by changing the position of the selective oxidation region 19b in the stacking direction, and derive the optimum value.
[0043]
Specifically, for a surface emitting laser element having an emission wavelength of about 850 nm (hereinafter referred to as “850 nm band surface emitting laser element”), the position where the selective oxidation region is arranged is changed in the stacking direction, and the threshold current value is set. In addition, the reliability of the surface emitting laser element was measured. The reason why the measurement target is the 850 nm band surface emitting laser element is that the 850 nm band surface emitting laser element has already been extensively studied and its characteristics are well understood. Therefore, it is possible to eliminate the influence on the measurement result by the part other than the selective oxidation region, and the influence of the selective oxidation region on the characteristics of the surface emitting laser element can be grasped. The structure of the 850-nm band surface emitting laser element used for the measurement is the same as that of the surface emitting laser element according to the first embodiment except for the part corresponding to the wavelength such as the optical length of the optical resonator. Shall have.
[0044]
The inventors of the present application, as shown in FIGS. 2A to 2C, selectively oxidized regions 19 b-1 in the first period mirror layer, the third period mirror layer, and the fifth period mirror layer, respectively. , 19b-2, 19b-3 and the 850 nm band surface emitting laser element having the λ resonator formed with the current injection regions 19a-1, 19a-2, 19a-3, the threshold current and reliability were measured. . As a result, when the selective oxidation region 19b-1 was arranged in the mirror layer in the first period, there was a problem in reliability, and a result that was not appropriate for practical use was obtained. When the selective oxidation region 19b-2 was arranged in the mirror layer, the reliability was high and the threshold current was low. Further, when the selective oxidation region 19b-3 is arranged in the fifth period mirror layer, although the reliability can be ensured, the threshold current increases compared to the case where the threshold current is arranged in the third period mirror layer. The tendency to do was seen. Since the increase in the threshold current when it is arranged on the mirror layer in the fifth period is within an allowable range, the inventors of the present application have developed a mirror layer in the third to fifth periods for the 850 nm band surface emitting laser element. It was concluded that it is preferable to place a selective oxidation region in
[0045]
The thickness of the upper cladding layer, the thickness of the low refractive index layer, and the thickness of the high refractive index layer of the 850 nm band surface emitting laser element used for the measurement are different from those of the surface emitting laser element according to the first embodiment. To do. Therefore, in optimizing the position of the selective oxidation region 19b in the stacking direction in the first embodiment, the distance from the active layer center was referred to with respect to the measurement result. In the 850-nm band surface emitting laser element used for the measurement, the distance from the center of the active layer to the lower end of the third period mirror layer is 390 nm, and the distance to the lower end of the fifth period mirror layer is 660 nm. With reference to this value, in the surface-emitting laser device according to the first embodiment, the lower end of the mirror layer in which the selective oxidation region 19b is disposed is in the range of 370 nm to 680 nm from the center of the active layer 4. Determined.
[0046]
In the first embodiment, the first-cycle mirror layer is selected as the mirror layer suitable for this numerical range. This is because the first period mirror layer has a distance of 375 nm from the center of the active layer 4. Further, when the position in the mirror layer is provided in the upper reflective layer as described above, the selective oxidation region 19b is preferably disposed in the vicinity of 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 at the place shown in FIG.
[0047]
Next, optimization of the width in the horizontal direction and the film thickness in the stacking direction of the selective oxidation region 19b 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 following mainly describes optimization of the diameter of the current injection region 19a.
[0048]
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, single transverse mode oscillation can be realized by reducing the diameter of the current injection region 19a. On the other hand, there is a problem that the threshold current increases due to diffraction loss as the diameter of the current injection region 19a decreases. In order to suppress the increase of the threshold current, it is necessary to increase the diameter of the current injection region 19a. . Therefore, a trade-off relationship is also established between the threshold current suppression and the single transverse mode oscillation enabling condition, and there is an optimum value for the diameter of the current injection region 19a.
[0049]
For this reason, the inventors of the present application have measured the oscillation transverse mode when the diameter of the current injection region is changed for the 850 nm band surface emitting laser element, and investigated the optimum value of the diameter of the current injection region. Specifically, as shown in FIG. 2B, the selective oxidation region is inserted into the third-period mirror layer, the thickness of the selective oxidation region is fixed at 20 nm, and the diameter of the current injection region 19a is set. Varying and measuring the threshold current and transverse mode aspects.
[0050]
As a result of the measurement, the maximum value of the diameter of the current injection region capable of single transverse mode oscillation was 3.5 μm. Further, when the diameter was 3.5 μm, the value of the threshold current could be suppressed below the allowable range. The effective refractive index difference described later was 0.0165 in this surface emitting laser element.
[0051]
Based on this result, the inventors of the present invention made the condition that the diameter of the current injection region 19a of the surface emitting laser element according to the first embodiment is 3.5 μm or more. This is because the suppression of the increase in the threshold current is poorly correlated with the emission wavelength of the surface emitting laser element, and even when the threshold current is suppressed to an allowable range in the 850 nm band surface emitting laser element, even in the case of 1300 nm. It is because it is thought that it can suppress in an allowable range similarly. However, the present inventors consider that it is more preferable to increase the diameter of the current injection region 19a in accordance with the ratio of the emission wavelengths, and the optimum value of the diameter of the current injection region 19a is set to 3.5 μm (1300 / 850) multiplied by 5.3.
[0052]
Next, the optimum value of the film thickness of the selective oxidation region 19b necessary for realizing the single transverse mode oscillation under the condition regarding the diameter of the current injection region 19a will be examined. This is because the transverse mode oscillation affects not only the diameter of the current injection region 19a but also the effective refractive index difference in the refractive index waveguide. In the following, first, the effective refractive index difference is briefly described, and after the optimum value of the effective refractive index difference is derived, the film thickness condition of the selective oxidation region 19b necessary for realizing the optimum value is derived.
[0053]
As described above, the surface-emitting laser element according to the first embodiment is provided with the refractive index waveguide because the selective oxidation region 19b exists. For example, as shown in FIG. 3, the refractive index waveguide type waveguide includes a first region 21 that is a stacking direction region including a current injection region 19a and a second region 22 and 23 that includes a selective oxidation region 19b. This is a structure in which the first region 21 functions as a waveguide due to an effective refractive index difference which is a difference in equivalent refractive index. The structure of the refractive index waveguide type waveguide is explained by the refractive index distribution of the surface emitting laser element. Specifically, the optical confinement in the horizontal direction is evaluated by equivalently replacing it with a planar waveguide having an equivalent refractive index of the first region 21 and the second region 22 and 23. The structure and transverse modes can be analyzed.
[0054]
For example, in the surface emitting laser element according to the first embodiment, the refractive index of the selective oxidation region 19b is smaller 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 through the first region 21 and emitted to the outside. The The structure of the refractive index waveguide type waveguide corresponds to an effective refractive index difference which is a difference value between the equivalent refractive index of the first region 21 and the equivalent refractive index of the second regions 22 and 23. The mode of light guiding varies.
[0055]
Diameter Φ of current injection region 19a capable of realizing single transverse mode oscillation _c And the effective refractive index difference Δn using the emission wavelength λ,
Φ _c ∝λ / (Δn) ^1/2 (1)
It is known that Therefore, the horizontal width and film thickness of the selective oxidation region 19b in the surface emitting laser element according to the first embodiment are determined using the measurement result obtained for the 850 nm band surface emitting laser element and the equation (1). can do.
[0056]
First, in order to suppress an increase in 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 as follows from the measurement result and the expression (1):
Φ _c (Λ = 1.3μm) / Φ _c (Λ = 0.85μm) = {1.3 / (Δn) ^1/2 } / {0.85 / (0.0165) ^1/2 } (2)
Is required. Where Φ _c Since (λ = 0.85 μm) = 3.5 μm, if the value of the right side of the formula (2) is 1 or more, the diameter of the current injection region 19a in the surface emitting laser element according to the first embodiment is 3. 5 μm or more. When the equation (2) is calculated with respect to Δn, in order to satisfy the above condition, Δn ≦ 0.038 may be satisfied with respect to the effective refractive index difference Δn. 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 expression (1), when the effective refractive index difference Δn is 0.0165 as in the measurement result of the 850 nm band surface emitting laser element, the diameter of the current injection region 19a is 1.5 times corresponding to the wavelength ratio. This is more preferable.
[0057]
Here, it is possible to derive the film thickness of the selective oxidation region 19b necessary to realize the above effective refractive index difference by performing calculation known to those skilled in the art in consideration of the position of the selective oxidation region 19b in the stacking direction. Is possible. 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 set to 32 nm in order to reduce the effective refractive index difference Δn to 0.038 or less. What is necessary is as follows. Further, when the effective refractive index difference is 0.0165, the film thickness of the selective oxidation region 19b is 13 nm. Therefore, in order to realize single transverse mode oscillation in the surface emitting laser element according to the first embodiment, the film thickness of the selective oxidation region 19b needs to be 32 nm or less, more preferably 13 nm or less.
[0058]
Next, the minimum value of the film thickness of the selective oxidation region 19b will be examined. As already described, the selective oxidation region 19b is formed by once laminating the AlAs layer and then selectively oxidizing it by introducing oxygen atoms in a water vapor atmosphere. Here, when the selective oxidation region 19b is formed, if the thickness of the AlAs layer is too thin, it is difficult to introduce oxygen atoms and it is difficult to form the selective oxidation region 19b. The film thickness of the selective oxidation region 19b which is the minimum necessary for introducing oxygen atoms is 6 nm, and it is possible to easily perform selective oxidation by having a film thickness of 10 nm or more.
[0059]
From the above discussion, the range of the film thickness d of the selective oxidation region 19b necessary for realizing the single transverse oscillation mode while keeping the threshold current low is as follows:
6 nm ≦ d ≦ 32 nm (3)
It becomes. Further, a more preferable range of the film thickness d that allows rapid selective oxidation and can increase the diameter of the current injection region 19a is as follows.
10 nm ≦ d ≦ 13 nm (4)
It becomes. Since it is more preferable that the selective oxidation region 19b has a film thickness satisfying the expression (4), in the first embodiment, the film thickness of the selective oxidation region 19b is 13 nm and the diameter of the current injection region 19a is 5.3 μm. Yes.
[0060]
The inventors of the present application actually manufactured a surface emitting laser element that satisfies the above conditions and examined its characteristics. Specifically, an n-type GaAs buffer layer is stacked by 0.1 μm on an (100) plane substrate of n-type GaAs, and an n-type Al _0.9 Ga _0.1 A lower reflective layer was formed by laminating 34.5 mirror layers made of As and GaAs. The active layer includes a triple quantum well layer, and the optical length of the optical resonator including the active layer is 2λ. In addition, p-type Al _0.9 Ga _0.1 An upper reflective layer was formed by laminating 25 mirror layers made of As and GaAs. These semiconductor layers are grown by gas source MBE (Molecular Beam Epitaxy) method, MBE method, MOCVD (Metalorganic Chemical Vapor Deposition) method, carbon (C) as p-type impurity, silicon (Si) as n-type impurity Doped. The AlAs layer is an Al layer that forms the mirror layer of the lowermost layer (that is, the first period) of the upper reflective layer. _0.9 Ga _0.1 It arrange | positioned at the upper end part of As layer, and the film thickness was 12 nm. And the outer diameter of the horizontal cross section of the part formed in mesa shape was 40 micrometers, and the selective oxidation area | region was formed by hold | maintaining in 420 degreeC water vapor atmosphere for 20 minutes after mesa formation. The diameter of the current injection region formed by the unoxidized AlAs layer was set to 5.2 μm.
[0061]
When the oscillation characteristics of the surface-emitting laser element manufactured in this manner were examined, the threshold current value was 0.5 mA, the slope efficiency was 0.25 W / A, and continuous oscillation was possible at 100 ° C. or higher. Further, when the injection current value is 10 mA or less, single transverse mode oscillation is possible. When an optical signal directly modulated at 10 Gbit / s is incident on the transmission optical fiber, the transmittable distance is 15 km or more, and 15 km A good eye pattern of the optical signal after transmission was obtained.
[0062]
(Modification)
Next, the structure of the surface emitting laser element according to the modification of the first embodiment will be described. FIG. 4 is a cross-sectional view showing the structure of a surface emitting laser element according to a modification. In the first embodiment, the mirror layer in which the selective oxidation region 19b is disposed is the first-period mirror layer, but may be disposed in the second-period mirror layer. Since the distance from the center of the active layer 4 to the lower end is 580 nm, the mirror layer of the second period is included in the numerical range of 370 nm to 680 nm defined for the position in the stacking direction, ensuring reliability and threshold current. This is because suppression is possible.
[0063]
Since the mirror layer in which the selective oxidation region 19b is arranged is in the second period, the film thickness of the selective oxidation region 19b changes in order to maintain the diameter of the current injection region 19a and maintain the effective refractive index difference. This is because the equivalent refractive indexes of the second regions 22 and 23 also change 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 selective oxidation is possible is as follows:
6nm ≦ d ≦ 46nm (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 as follows:
10 nm ≦ d ≦ 20 nm (6)
It becomes.
[0064]
(Embodiment 2)
Next, a surface emitting laser element according to the second embodiment will be described. As shown in FIG. 5, the surface emitting laser element according to the second embodiment has an emission wavelength of 1300 nm, and the optical length of the optical resonator formed by the lower cladding layer, the active layer, and the upper cladding layer is output. It has a structure equal to the wavelength of incident light. Specifically, the surface emitting laser element according to the second embodiment 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 cladding layer 26, the active layer 4, the upper cladding layer 27, and the upper reflective layer 6 are sequentially stacked on the mesa-shaped region. In addition, this mesa shape is formed so that a horizontal cross-sectional shape may be circular. Further, a contact layer 7 is laminated on the upper reflective layer 6, and a p-side electrode 8 having a ring shape having a current injection region in the center is disposed on the contact layer 7, and n on the lower surface of the substrate 1. Side electrodes 9 are arranged. Inside the upper clad layer 27, the current confinement layer 30 is disposed by a selective oxidation region 29b disposed adjacent to the current injection region 29a disposed in the vicinity of the center of the mesa and having a circular shape in the horizontal section. Yes. In the second embodiment, the parts denoted by the same or similar reference numerals as those in the first embodiment have the same or similar structures and perform the same or similar functions unless otherwise specified. To do.
[0065]
In the second embodiment, the optical length of the λ resonator 28 formed by the lower cladding layer 26, the active layer 4 and the upper cladding layer 27 is equal to the wavelength of the emitted light. Therefore, the position of selective oxidation region 29b in the stacking direction and the optimum value of the film thickness are different from those in the first embodiment. Hereinafter, optimization of the selective oxidation region 29b of the surface emitting laser element having an emission wavelength of 1300 nm and having the λ resonator 28 will be described.
[0066]
First, optimization of the position of the selective oxidation region 29b in the stacking direction will be described. In the first embodiment, the inventors of the present application and the like lead that the selective oxidation region 29b is preferably disposed in a mirror layer whose end surface on the active layer side is in a range of 370 nm to 680 nm from the center of the active layer 4. ing. In the second embodiment, it is necessary to determine an appropriate mirror layer in consideration of the difference in the optical length of the λ resonator 28, and the mirror layer in the second period is selected as a mirror layer suitable for this. ing. 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 satisfies the above conditions. In the second period mirror layer, the selective oxidation region 29b is preferably disposed on the far side of the low refractive index layer from the active layer, as in the first embodiment. Thereby, the position of the selective oxidation region 29b in the stacking direction is determined to the position shown in FIG.
[0067]
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 an increase in threshold current and realizing a single transverse mode oscillation. What is the optical length of the optical resonator? It is determined independently. Therefore, the same discussion as in the first embodiment is established, and from the measurement result of the 850 nm band surface emitting laser element, the diameter of the current injection region 29a needs to be 3.5 μm or more, and considering the wavelength ratio, More preferably, it is 5.3 μm.
[0068]
Finally, optimization of the film thickness of the selective oxidation region 29b will be described. From the viewpoint of realizing single transverse mode oscillation, there is a relationship of the formula (1) between the effective refractive index difference between the first region 21 and the second regions 22 and 23 and the diameter of the current injection region 29a shown in FIG. Is satisfied, 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 requires that the effective refractive index difference is 0.038 or less, and the diameter of the current injection region 29a is 5 In order to oscillate a single transverse mode in the case of .3 μm, the effective refractive index difference is 0.0165.
[0069]
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 for a surface emitting laser element having a λ resonator (KDChoquette et al. al., Proceedings of SPIE Vertical-Cavity Surface-Emitting Lasers, vol. 3003, pp.194-200, 1997.). In FIG. 6, curve l ₁ Indicates a case where a selective oxide layer is disposed in the first period, and hereinafter, curve l ₂ , L _Three , L _Four , L _Five These show the cases where the selective oxidation regions are arranged in the second period, the third period, the fourth period, and the fifth period, respectively. The horizontal axis of the graph indicates the film thickness of the selective oxidation region, and the vertical axis of the graph indicates the effective refractive index difference.
[0070]
In the surface emitting laser element according to the second embodiment, the selective oxidation region 29b is arranged in the mirror layer of the second period, and therefore, the curve l in the graph of FIG. ₂ Refer to 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. It can also be seen that the film thickness is 13 nm in order for the effective refractive index difference to be 0.0165.
[0071]
As for the minimum value of the film thickness, the same argument as in the first embodiment is established. As a result, the film thickness d of the selective oxidation region 29b necessary for realizing the single transverse oscillation mode while suppressing the threshold current low. The range of
6 nm ≦ d ≦ 32 nm (7)
Thus, a more preferable range of the film thickness d that allows rapid selective oxidation and can increase the diameter of the current injection region 29a is as follows:
10 nm ≦ d ≦ 13 nm (8)
It becomes. As described above, in the surface emitting laser element according to the second embodiment, the structure of the selective oxidation region 29b is optimized.
[0072]
(Modification)
Next, a surface emitting laser element according to a modification of the second embodiment will be described. FIG. 7 is a cross-sectional view showing the structure of a surface emitting laser element according to a modification, which is different from the second embodiment in that the selective oxidation region 29b is arranged in the third-period mirror layer.
[0073]
As already described, also in the second embodiment, the selective oxidation region 29b can be arranged 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. When the output wavelength is 1300 nm and the optical length of the optical resonator is equal to the wavelength of the output light, the lower end of the third-period mirror layer is separated from the center of the active layer 4 by 596 nm, and is included in the above range. I understand that. Therefore, it is possible to adopt a structure in which the selective oxidation region 29b-1 is arranged in the third period mirror layer.
[0074]
The conditions of the diameter of the current injection region 29a-1 and the effective refractive index difference can be considered in the same manner as in the surface emitting laser element according to the second embodiment. As a 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 needs to be 0.038 or less, preferably 0.0165. .
[0075]
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 modification, the selective oxidation region 29b-1 is arranged in the mirror layer of the third period, and therefore, in the drawing, the curve l _Three Need to refer to. Curve l _Three According to the above, in order for the effective refractive index difference to be 0.038 or less, the film thickness must be 46 nm or less, and for the effective refractive index difference to be 0.0165, the required film thickness is 20 nm. This completes the optimization of the structure of the selective oxidation region 29b-1 according to the modification.
[0076]
In addition, although the surface emitting laser element concerning this invention was demonstrated using Embodiment 1, 2 and these modifications, it is also possible to employ | adopt structures other than the said description. For example, in the first and second embodiments and the modifications thereof, the emission wavelength of the surface emitting laser element is 1300 nm. 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 element having a long wavelength of 850 nm or longer. This will be described below.
[0077]
First, regarding the position of the selective oxidation region in the mirror layer, it is preferable that the selective oxidation region is disposed in the vicinity of the interface far from the active layer of the low refractive index layer regardless of the emission wavelength. And in which mirror layer to arrange, the determinant is performed from the viewpoint of suppressing the increase of the threshold current and ensuring the reliability, and these viewpoints are poorly correlated with the emission wavelength. Further, the diameter of the current injection region is also derived from the measurement result regarding the 850 nm band surface emitting laser element, 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 making the necessary effective refractive index difference may be derived by a known method. Therefore, the structure of the selective oxidation region can be optimized using the method described in Embodiment 1 or 2 for a long wavelength surface emitting laser element of 850 nm or more. For the same reason, the structure of the selective oxidation region can be optimized also for the surface emitting laser elements having optical resonators having 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. In consideration of the film thickness of the low refractive index layer constituting the layer, the upper limit of the distance from the center of the active layer is preferably 780 nm.
[0078]
In addition to 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.
[0079]
In addition, AlAs is used as a semiconductor material for forming the selective oxidation region and the current injection region. _x Ga _1-x Even when As (0.97 ≦ x <1) is used, selective oxidation is possible, and a current injection region can be formed.
[0080]
For the mirror layer constituting the upper reflective layer and the lower reflective layer, the low refractive index layer is made of Al. _x Ga _1-x As (0.5 ≦ x ≦ 1), the high refractive index layer is made of Al _x Ga _1-x Even when configured with As (0 ≦ x ≦ 0.2), it is possible to reflect the light having the emission wavelength and to function as a mirror layer. In addition, the low refractive index layer and the high refractive index layer may have a structure in which a composition gradient layer that relaxes the refractive index difference between the low refractive index layer and the high refractive index layer is disposed in the vicinity of the boundary surface between them.
[0081]
In addition to the GaAs substrate, the surface emitting laser element according to the present invention can also be realized by using a substrate such as an InP substrate or a GaInAs substrate.
[0082]
In addition, the active layer may be constituted by a single quantum well layer, not a structure comprising a triple quantum well layer and a barrier layer separating them, or a structure having other number of quantum well layers It is also good. The quantum well layer can be formed of a GaInAs-based or GaAsSb-based semiconductor material. Furthermore, it is good also as a quantum dot formed with (Ga) InAs etc. instead of a quantum well layer. Alternatively, a surface emitting laser element having a double hetero structure may be simply used.
[0083]
In addition, the conductivity type of the semiconductor material forming the surface emitting laser element can be reversed. For example, the substrate, the lower clad layer, and the lower reflective layer may be formed of a p-type semiconductor, and the upper reflective layer and the upper clad layer may be formed of an n-type semiconductor.
[0084]
Further, the current confinement layer composed of the selective oxidation region and the current injection region is preferably disposed in the p-type reflective layer, but the same argument is established even if it is disposed in the n-type reflective layer, and the same effect is obtained. It is possible to demonstrate.
[0085]
(Embodiment 3)
Next, an optical transceiver according to the third embodiment will be described. FIG. 8 is a block diagram of the structure of the optical transceiver according to the third embodiment. The optical transceiver according to the third 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 electrical signal to the transceiver 31, and a transceiver. 31 has a signal separation circuit 33 that separates an electrical signal obtained from the received optical signal.
[0086]
The optical transmitter 34 is for converting the electrical signal input from the signal multiplexing circuit 32 into an optical signal and transmitting it. Specifically, the optical transmission unit 34 includes a surface emitting laser element 36 that emits an optical signal, a control circuit 37 that controls the surface emitting laser element 36 based on the input electric signal, and a surface emitting laser element 36. And an output optical system 38 for outputting the emitted optical signal to the outside.
[0087]
The surface emitting laser element according to the first or second embodiment is used for the surface emitting laser element 36 included in the optical transmitter 34. Therefore, the surface-emitting laser element 36 has a low threshold current, high reliability, and can perform single transverse mode oscillation.
[0088]
The optical receiver 35 is for converting an optical signal received from the outside into an electrical signal and outputting it to the signal separation circuit 33. Specifically, the optical receiver 35 includes a photoelectric conversion element 39 for receiving an optical signal and converting it into an electrical signal, an input optical system 40 for guiding the optical signal to the photoelectric conversion element 39, and a photoelectric conversion element. And an amplifier circuit 41 that amplifies the electrical signal output from the terminal 39. The photoelectric conversion element 39 outputs an electric signal based on the intensity of the received optical signal. As the photoelectric conversion element 39, a photo resistor or the like can be used in addition to a photodiode.
[0089]
The signal multiplexing circuit 32 is for multiplexing a plurality of electric signals input from the outside into one electric signal. One electrical signal obtained by multiplexing is output to the optical transmitter 34 constituting the transceiver 31.
[0090]
The signal separation circuit 33 is for separating the electrical signal obtained from the optical receiver 35 constituting the transceiver 31 into a plurality of electrical signals. Since the optical signal received by the optical receiver 35 originally includes a plurality of signals, the 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.
[0091]
The operation of the optical transceiver according to the third embodiment will be described. The optical transceiver according to the third embodiment is for transmitting and receiving a plurality of electrical signals. First, the transmission operation will be described.
[0092]
First, a plurality of electrical signals input from the outside are converted into a single electrical signal by the signal multiplexing circuit 32. The single electric signal is input from the signal multiplexing circuit 32 to the control circuit 37, and the control circuit 37 controls the current injected into the surface emitting laser element 36 based on the electric signal. Specifically, the control circuit 37 emits an optical signal having a waveform corresponding to the electrical signal waveform from the surface emitting laser element 36. Since the surface emitting laser element 36 includes the surface emitting laser element according to the first or second embodiment, direct light modulation can be performed 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.
[0093]
Next, the reception 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 is amplified by the amplifier circuit 41. Thereafter, the amplified electrical signal is input to the signal separation circuit 33 and separated into a plurality of electrical signals. This completes the reception operation.
[0094]
The optical transceiver according to the third embodiment includes the surface emitting laser element according to the first or second embodiment. Therefore, in the third embodiment, the threshold current of the surface emitting laser element 36 has a low value and has high reliability. Further, it can be directly modulated at 10 Gbit / s, and an optical signal having a large amount of information can be output. Furthermore, when the optical signal to be output is transmitted through an optical fiber, the transmittable distance is 15 km or more, and long distance transmission is possible.
[0095]
(Embodiment 4)
Next, an optical communication system according to the fourth embodiment will be described. FIG. 9 is a schematic diagram illustrating the structure of the optical communication system according to the fourth embodiment. The optical communication system according to the fourth embodiment uses the surface emitting laser element according to the first or second embodiment as a signal light source. Specifically, the surface emitting laser element 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 emitting laser element connected to the control circuit 43. 44, a transmission optical fiber 46, and an optical system 45 for optically coupling the surface emitting laser element 44 and one end of the transmission optical fiber 46 to each other. In addition, a photoelectric conversion element 48 optically coupled to the other end of the transmission optical fiber 46 via an optical system 47, an amplification circuit 49 connected to the photoelectric conversion element 48, and a signal separation circuit 50 connected to the amplification circuit 49. And have.
[0096]
A single electrical signal obtained by the signal multiplexing circuit 42 is input to the control circuit 43, and the control circuit 43 controls the current injected into the surface emitting laser element 44 based on this electrical signal. As a result, the optical signal output from the surface emitting laser element 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.
[0097]
The optical signal transmitted through the transmission optical fiber 46 is emitted from the other end of the transmission optical fiber 46 and enters the photoelectric conversion element 48 via the optical system 47. The photoelectric conversion element 48 outputs an electrical signal based on the received optical signal, and is amplified by the amplifier circuit 49 and then input to the signal separation circuit 50.
[0098]
The signal separation circuit 50 separates the input electric signal into individual electric signals before being multiplexed by the signal multiplexing circuit 42 and restores information. In this way, the optical communication system according to the fourth embodiment transmits information.
[0099]
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 a signal light source on the transmission side. Therefore, it is possible to use a signal light source having a low threshold and high reliability. In addition, since single transverse mode oscillation is possible, an optical signal can be reliably transmitted without distorting the signal waveform during transmission. Specifically, it is possible to transmit an optical signal directly modulated at 10 Gbit / s even if the fiber length of the transmission optical fiber 46 is 15 km or more.
[0100]
In addition, since the surface emitting laser element 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 a wavelength with low loss in the transmission optical fiber 46. . Moreover, it has the advantage that the existing optical communication system can be utilized in these wavelength bands. For example, the emission wavelength may be 980 nm, and an EDFA (Erbium Doped Fiber Amplifier) may be disposed on the transmission optical fiber 46. In this case, since the intensity of the optical signal can be amplified by the EDFA, the transmission distance can be further extended. Similarly, a TDFA, a Raman amplifier, or the like may be used.
[0101]
【The invention's effect】
As explained above, This According to the invention, since the structure of the selective oxidation region is optimized, the threshold current is suppressed to a low value, high reliability, single transverse mode oscillation is possible, and direct modulation can be performed at 10 Gbit / s. There is an effect that a surface emitting laser element capable of long-distance transmission can be provided.
[0102]
Also, This According to the present invention, the configuration using the surface emitting laser with the optimized structure of the selective oxidation region is provided, so that 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. There is an effect that can be done.
[Brief description of the drawings]
1 is a cross-sectional view showing a structure of a surface emitting laser element according to a first embodiment;
FIGS. 2A to 2C are cross-sectional views showing the structure of an 850 nm band surface emitting laser element used for measurement. FIGS.
FIG. 3 is a schematic diagram for explaining an effective refractive index difference.
4 is a cross-sectional view showing a structure of a surface emitting laser element according to a modification of the first embodiment. FIG.
FIG. 5 is a cross-sectional view showing the structure of a surface emitting laser element 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 disposed.
7 is a cross-sectional view showing a structure of a surface emitting laser element according to a modification of the second embodiment. FIG.
FIG. 8 is a block diagram showing a structure of an optical transceiver according to a third embodiment.
FIG. 9 is a block diagram showing a structure of an optical communication system according to a fourth embodiment.
FIG. 10 is a cross-sectional view showing the structure of a conventional surface emitting laser element.
[Explanation of symbols]
1 Substrate
2 Lower reflective layer
3, 26 Lower cladding layer
4 Active layer
5, 27 Upper cladding 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-13d barrier layer
14a-14d quantum well layer
15 2λ resonator
19a, 29a, 29a-1 Current injection region
19b, 29b, 29b-1 selective oxidation region
20, 30 Current confinement 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 element
37, 43 Control circuit
38 Output optical system
39, 48 photoelectric conversion element
40 Input optics
41, 49 Amplifier circuit
45, 47 Optical system
46 Optical fiber for transmission

Claims (12)

It has 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 formed of GaAs, and has a wavelength of 1260 nm or more and 1360 nm or less in a direction perpendicular to the substrate A surface emitting laser element that oscillates a laser beam having
The upper reflective layer and the lower reflective layer have a low refractive index layer having an optical length of ¼ of the oscillation wavelength and containing Al _x Ga _1-x As (0.5 ≦ x ≦ 1) and 1 of the oscillation wavelength. A plurality of mirror layers having a two-layer structure of a high refractive index layer having an optical length of / 4 and containing Al _x Ga _1-x As (0 ≦ x ≦ 0.2),
Inside the lower reflective layer or the upper reflective layer, a region separated from the center of the active layer by a distance of 370 nm or more and 780 nm or less in the stacking direction, and in the low refractive index layer in any mirror layer A selective oxidation region formed by selective oxidation of Al _x Ga _1-x As (0.97 ≦ x ≦ 1), which is disposed in the vicinity of the position where the electric field intensity distribution of
A current injection region having a diameter of 3.5 μm or more disposed between the selective oxidation regions;
The difference value between the effective refractive index of the stacking direction region including the current injection region and the effective refractive index of the stacking direction region including the selective oxidation region is determined by the diameter of the current injection region and the following formula: and it is 0.038 or less, further wherein selectively oxidized region has a thickness that is calculated from the relationship between the position in the stacking direction of the difference value and the selected oxide region, wherein the laser beam is single transverse mode oscillation A surface-emitting laser element characterized by:
Φ _c (λ) /3.5= {λ / (Δn) ^1/2 } / {0.85 / (0.0165) ^1/2 }
Here, Φ _c (λ) is the diameter of the current injection region when the wavelength of the laser light oscillated by the surface emitting laser element is λ [μm], and Δn is the difference value. The optical resonator formed by the lower cladding layer, the active layer, and the upper cladding layer has an optical length that is twice the wavelength of the laser beam,
2. The surface emitting laser element according to claim 1, wherein the selective oxidation region is arranged in a mirror layer laminated in a first period from the active layer side in the upper or lower reflection layer. . The optical resonator formed by the lower cladding layer, the active layer, and the upper cladding layer has an optical length equal to the wavelength of the laser beam,
2. The surface emitting laser element according to claim 1, wherein the selective oxidation region is disposed in a mirror layer stacked in a second period from the active layer side in the upper or lower reflection layer. .   4. The surface emitting laser element according to claim 2, wherein the selective oxidation region has a thickness of 6 nm or more and 32 nm or less.   4. The surface emitting laser element according to claim 2, wherein the selective oxidation region has a thickness of 10 nm or more and 13 nm or less. The optical resonator formed by the lower cladding layer, the active layer, and the upper cladding layer has an optical length that is twice the wavelength of the laser beam,
2. The surface emitting laser element according to claim 1, wherein the selective oxidation region is disposed in a mirror layer stacked in a second period from the active layer side in the upper or lower reflection layer. . The optical resonator formed by the lower cladding layer, the active layer, and the upper cladding layer has an optical length equal to the wavelength of the laser beam,
2. The surface emitting laser element according to claim 1, wherein the selective oxidation region is disposed in a mirror layer stacked in a third period from the active layer side in the upper or lower reflection layer. .   8. The surface emitting laser element according to claim 6, wherein the selective oxidation region has a film thickness of 6 nm or more and 46 nm or less.   8. The surface emitting laser element according to claim 6, wherein the selective oxidation region has a thickness of 10 nm or more and 20 nm or less. An optical transmitter comprising: the surface emitting laser element according to claim 1; and a control circuit that controls a current value injected into the surface emitting laser element based on an input electric signal;
An optical receiver having a photoelectric conversion element that receives an optical signal incident from the outside and converts it into an electrical signal;
A transceiver comprising: The surface-emitting laser element according to any one of claims 1 to 9,
A signal multiplexing circuit for multiplexing a plurality of electrical 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 that receives an optical signal incident from the outside and converts it into an electrical signal;
A signal separation circuit for separating an electrical signal output from the photoelectric conversion element into a plurality of electrical signals;
An optical transceiver characterized by comprising: The surface-emitting laser element according to any one of claims 1 to 9,
A control circuit for controlling the surface emitting laser element;
An optical fiber for transmission that transmits an optical signal emitted from the surface emitting laser element from one end and transmits the optical signal;
A photoelectric conversion element that receives the optical signal incident from the other end of the transmission optical fiber and converts the optical signal into an electrical signal;
An optical communication system comprising:

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