JP2003273454A - Two-dimensional photonic crystal face emitting laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a two-dimensional photonic crystal face emitting laser wherein light emission efficiency is improved by a relatively easy method. <P>SOLUTION: There is provided a two-dimensional photonic crystal face emitting laser which includes a photonic crystal period structure 21 where there are laminated on a substrate 11 a lower clad layer 12, an active layer 13 for emitting light by doping a carrier, and an upper clad layer 14, and a refractive index period is arranged on the lower clad layer 12 two dimensionally, and which face emits light from the upper surface of the upper clad layer 14 by resonating in the structure 21. Refractive indexes of the lower clad layer 12 and the photonic crystal period structure 21 are different from each other, and an occupation rate that is a rate occupied by a low refractive index material in a crystal lattice is large for both of secondary diffraction efficiency and primary diffraction efficiency. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-dimensional photonic crystal surface emitting laser, and more particularly to a photonic crystal periodic structure in which a refractive index period is two-dimensionally arranged in or near an active layer emitting light by carrier injection. The present invention relates to a two-dimensional photonic crystal surface emitting laser which has a body and resonates with a photonic crystal to perform surface emission.

[0002]

2. Description of the Related Art Conventionally, various surface emitting lasers which emit laser light in a vertical direction from a substrate surface have been developed and studied. A surface-emitting laser can integrate (array) a large number of elements on the same substrate and emit coherent light from each element in parallel. Therefore, in the field of parallel optical pickup, parallel optical transmission, and optical parallel information processing. Applications are expected.

As a surface emitting laser of this type, a two-dimensional photonic crystal surface emitting laser utilizing a photonic crystal is disclosed in Japanese Patent Laid-Open No. 2000-332351. A photonic crystal is a crystal having a refractive index period that is about the same as or smaller than the wavelength of light. In a dielectric multidimensional periodic structure, the same principle as that in which a band gap occurs in the electronic state in a semiconductor crystal As a result, a wavelength band (photonic band gap) that suppresses the waveguiding of light is generated, and light can be confined in two dimensions or three dimensions.

The two-dimensional photonic crystal surface emitting laser described in the above publication is provided with a photonic crystal periodic structure having a two-dimensionally arranged refractive index period in the vicinity of an active layer which emits light by carrier injection. The crystal resonates and emits surface light.

[0005]

By the way, in order to increase the emission efficiency of the above-mentioned two-dimensional photonic crystal surface emitting laser, the photonic crystal effect which is the second-order diffraction efficiency and / or
Alternatively, it is necessary to improve the surface emission efficiency, which is the first-order diffraction efficiency. It is considered that the crystal lattice shape and the material and shape of the periodic structure material are taken into consideration as factors that define the first-order and second-order diffraction efficiencies. However, it is extremely difficult to determine the optimal structure because these multiple elements are intricately related.

Therefore, an object of the present invention is to provide a two-dimensional photonic crystal surface emitting laser which can increase the light emitting efficiency by a relatively easy method.

[0007]

In order to achieve the above objects, the two-dimensional photonic crystal surface emitting laser according to the present invention has an active layer which emits light by carrier injection sandwiched between clad layers, and the clad layers or the clad layers. In a two-dimensional photonic crystal surface emitting laser including a photonic crystal periodic structure in which an active layer has a two-dimensional refractive index period, the cladding layer and the photonic crystal periodic structure have different refractive indices. The occupancy, which is the ratio of the low refractive index material in the crystal lattice, is large in both the second-order diffraction efficiency and the first-order diffraction efficiency.

In the two-dimensional photonic crystal surface emitting laser according to the present invention, the light leaked from the active layer is second-order diffracted (resonated) by the periodic structure of the photonic crystal and amplified, and is clad by the first-order diffraction. Emits surface light from the upper surface of.

The cladding layer and the photonic crystal periodic structure are materials having different refractive indexes. Therefore, the present inventor paid attention to the occupancy, which is the ratio of the low refractive index material in the crystal lattice, and found that the occupancy defined the second-order diffraction efficiency and the first-order diffraction efficiency. An increase in luminous efficiency was obtained by setting a high occupation rate for both efficiency and first-order diffraction efficiency.

The occupancy rate is preferably 5 to 45%. In particular, when the photonic crystal periodic structure made of a high refractive index material is arranged in the clad layer made of a low refractive index material, the occupation rate is preferably 5 to 45%. Further, when the photonic crystal periodic structure made of a low refractive index material is arranged in the clad layer made of a high refractive index material, the occupation ratio is preferably 5 to 20%.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a two-dimensional photonic crystal surface emitting laser according to the present invention will be described below with reference to the accompanying drawings.

(Basic Structure and Resonance Function, See FIGS. 1 and 2) In a two-dimensional photonic crystal surface emitting laser array according to the present invention, a plurality of the two-dimensional photonic crystal surface emitting lasers shown in FIG. 1 are provided on the same substrate. The elements are arranged side by side.

In this two-dimensional photonic crystal surface emitting laser 10, a lower clad layer 12, an active layer 13, and an upper clad layer 14 are laminated on a substrate 11, and the lower clad layer 12 is provided in the vicinity of the active layer 13. The two-dimensional photonic crystal 20 is built in.

The substrate 11 is made of, for example, an n-type InP semiconductor material. The lower clad layer 12 and the upper clad layer 14 are, for example, n-type and p-type InP semiconductor layers, respectively, and have a lower refractive index than the active layer 13. The two-dimensional photonic crystal 20 is composed of holes (photonic crystal periodic structure 21) formed in the lower cladding layer 12,
The lower cladding layer 12 is composed of a square lattice or a triangular lattice in which media having different refractive indexes are arranged in a two-dimensional period.
The pores may be filled with SiN or the like. The active layer 13 is
For example, it has a multiple quantum well structure using an InGaAs / InGaAsP-based semiconductor material, and emits light when carriers are injected.

Lower clad layer 12 and upper clad layer 1
4 forms a double heterojunction with the active layer 13 sandwiched between them, thereby confining the carriers and concentrating the carriers contributing to light emission in the active layer 13.

A lower electrode 16 and an upper electrode 17 made of gold or the like are formed on the bottom surface of the substrate 11 and the upper surface of the upper cladding layer 14. The active layer 13 emits light by applying a voltage between the electrodes 16 and 17, and the light leaked from the active layer 13 enters the two-dimensional photonic crystal 20. Light whose wavelength matches the lattice spacing of the two-dimensional photonic crystal 20 is
It is resonated and amplified by the two-dimensional photonic crystal 20. Thereby, the upper surface of the upper clad layer 14 (the electrode 17
The coherent light is surface-emitted from the light emitting region 18) located around the area.

The resonance action of the two-dimensional photonic crystal 20 having a square lattice as shown in FIG. 2 will be described. The lattice shape is not limited to the square lattice, and may be a triangular lattice or the like.

The two-dimensional photonic crystal 20 is composed of a square lattice formed in the first medium 12 in the same period in two directions orthogonal to the second medium 21 such as holes. Square lattice is Γ
It has a representative direction of −X direction and Γ−M direction. Γ
When the distance between the second media 21 adjacent in the −X direction is a,
A basic lattice E, which is a square with one side of a, using the second medium 21 as a lattice point, is formed.

When the light L whose wavelength λ matches the lattice spacing a of the basic lattice E travels in the Γ-X direction, the light L is second-order diffracted at the lattice point. Of these, 0 ° with respect to the traveling direction of the light L,
Only the light diffracted in the directions of ± 90 ° and 180 ° satisfies the Bragg condition. Further, since there are lattice points also in the traveling direction of the light diffracted in the directions of 0 °, ± 90 °, and 180 °, the diffracted light is again 0 °, ± 90 °, 1 with respect to the traveling direction.
Diffract in the 80 ° direction.

When the light L repeats the second-order diffraction once or a plurality of times, the diffracted light returns to the original lattice point and a resonance action occurs. In addition, the light that is first-order diffracted in the direction perpendicular to the paper also satisfies the Bragg condition. Therefore, the light amplified by resonance is emitted through the upper clad layer 14 and has a surface emitting function. Further, since this phenomenon occurs at all the lattice points, coherent laser oscillation is possible in the entire plane.

In the following description, the in-plane second-order diffraction efficiency of the two-dimensional photonic crystal is also called the photonic crystal effect, and the first-order diffraction efficiency in the vertical direction is also called the surface emission efficiency.

(Photonic crystal effect in the first embodiment, see FIGS. 3 and 4) FIG. 3 shows a case where the columnar photonic crystal periodic structures 21 are arranged in a square lattice as the first embodiment of the present invention. Indicates. FIG. 3A shows an example 1a in which a periodic structure 21 made of a low refractive index material is arranged in a medium (lower clad layer 12) made of a high refractive index material, and FIG. 3B shows a low refractive index material. The 1b example in which the periodic structure 21 made of a high refractive index material is arranged in the medium (lower clad layer 12) made of is shown.

In the present invention, the occupancy, which is the ratio of the low refractive index material in the crystal basic lattice E, is a problem. In FIGS. 3A and 3B, the shaded portion in the crystal lattice E is the region occupied by the low refractive index material. Since the periodic structure 21 is circular in plan view, the occupation ratio can be assumed to be in the range of 0 to 80% in the example 1a (see FIG. 3A), and the occupancy rate can be assumed in the example 1b (see FIG. 3B. )reference)
Then, a range of 20 to 100% can be assumed.

In the above Examples 1a and 1b, the photonic crystal effect (second-order diffraction efficiency) on the occupation ratio is shown in FIGS. 4 (A) and 4 (B). FIG. 4A corresponds to the example 1a, and it is understood that a sufficient photonic crystal effect is exhibited at an occupancy rate of about 5 to about 20%. FIG. 4B shows the first
It can be seen that, corresponding to the example b, a sufficient photonic crystal effect is exhibited at an occupancy rate of about 45% or less.

(Photonic Crystal Effect in Second Embodiment; See FIGS. 5 and 6) FIG. 5 shows a second embodiment of the present invention in which square columnar photonic crystal periodic structures 21 are arranged in a square lattice. Indicates. FIG. 5A shows a second example in which the periodic structure 21 made of the low refractive index material is arranged in the medium (the lower clad layer 12) made of the high refractive index material,
FIG. 5B shows a second example in which the periodic structure 21 made of the high refractive index material is arranged in the medium (the lower clad layer 12) made of the low refractive index material.

In FIGS. 5A and 5B, the crystal lattice E
The shaded portion is the region occupied by the low refractive index material. Since the periodic structure 21 has a quadrangular shape in plan view, the occupation rate is assumed to be in the range of 0 to 100% in both the 2a example (see FIG. 5A) and the 2b example (see FIG. 5B). be able to.

In the examples 2a and 2b described above, the photonic crystal effect (second-order diffraction efficiency) on the occupation ratio is shown in FIGS. 6 (A) and 6 (B). FIG. 6A corresponds to the example 2a, and it can be seen that a sufficient photonic crystal effect is exhibited at an occupancy rate of about 5 to about 20%. FIG. 6B corresponds to the second example, and it can be seen that a sufficient photonic crystal effect is exhibited at an occupancy rate of about 5 to about 45%.

(Surface Emission Efficiency, See FIG. 7) Next, the surface emission efficiency (first-order diffraction efficiency) relating to the occupation ratio will be described.
The surface emission efficiency is irrespective of the shape of the photonic crystal periodic structure 21 and the medium in which the magnitude of the refractive index is set, that is, the first embodiment (1a example, 1b example),
Any of the second embodiments (the 2a example and the 2b example) has the efficiency shown in FIG. 7. As is clear from FIG. 7, sufficient surface emission efficiency is exhibited at an occupancy rate of about 5 to 45%.

(Summary of Luminous Efficiency) As is apparent from the graphs of FIGS. 4, 6 and 7, the two-dimensional photonic crystal surface emitting laser has a photonic crystal effect in the in-plane direction of the crystal (2nd time). Resonance is strengthened by (folding efficiency),
In addition, light is emitted in the direction perpendicular to the crystal plane based on the surface emission efficiency (first-order diffraction efficiency). Therefore, in order to increase the light emission efficiency of the surface emitting laser, the photonic crystal effect and the surface light emitting efficiency may be large.

Regarding the improvement of the luminous efficiency, it is easier and more reliable in design to change the occupancy of the low refractive index material in the crystal lattice than to change the crystal lattice shape and the material and shape of the periodic structure. Will be done. Therefore, Table 1 below shows preferable combination examples 1 and 2 that can improve the luminous efficiency.

[0031]

[Table 1]

The combination example 1 shown in Table 1 is the case where the periodic structure made of the high refractive index material is arranged in the clad layer made of the low refractive index material (Examples 1b and 2b), and the occupation ratio is Should be set to 5 to 45%. Also, combination example 2
Is a case where a periodic structure made of a low refractive index material is arranged in a clad layer made of a high refractive index material (example 1a, 2a
In the example), the occupation rate may be set to 5 to 20%.

(Other Embodiments) The two-dimensional photonic crystal surface emitting laser according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention.

In particular, the materials for the semiconductor layer, the photonic crystal, the electrodes, the structure for aligning the polarization of light, the lattice shape, etc. are arbitrary. Further, in the above embodiment, an example in which the photonic crystal periodic structure is provided in the lower clad layer has been shown.
It may be provided in the vicinity of the active layer in the upper cladding layer.

Alternatively, as shown in FIG. 8, the photonic crystal periodic structure 21 may be formed in the active layer 13.

Further, as shown in FIG. 9, the photonic crystal periodic structure 21 may be formed so as to penetrate from the clad layer 14 to the active layer 13 and the clad layer 12.

Further, as shown in FIG. 10, the photonic crystal periodic structure 21 is formed from the cladding layer 12 to the active layer 13,
You may form so that it may penetrate even to the clad layer 14.

Further, as shown in FIGS. 11, 12 and 13, the photonic crystal periodic structure 21 is formed on the cladding layer 14.
You may form in the inside and the clad layer 12.

Furthermore, in each of the above embodiments, an example in which two types of media are used has been shown, but even if there are three or more types of media, the luminous efficiency can be improved based on the occupancy rate.

[Brief description of drawings]

FIG. 1 is a perspective view showing the basic configuration of a two-dimensional photonic crystal surface emitting laser according to the present invention.

FIG. 2 is an explanatory view showing a resonance action of the surface emitting laser.

3A and 3B are explanatory views showing a photonic crystal periodic structure according to the first embodiment, FIG. 3A is an example 1a, and FIG. 3B is an example 1b.
Here is an example:

FIG. 4 is a graph showing a photonic crystal effect on the occupation ratio in the first embodiment, (A) is a first example,
(B) shows a 1b example.

5A and 5B are explanatory views showing a photonic crystal periodic structure according to a second embodiment, FIG. 5A is a second example, and FIG.
Here is an example:

FIG. 6 is a graph showing the photonic crystal effect on the occupancy in the second embodiment, (A) is a second example,
(B) shows a 2b example.

FIG. 7 is a graph showing surface emission efficiency with respect to occupancy in the first and second embodiments.

FIG. 8 is a perspective view showing another embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention.

FIG. 9 is a perspective view showing still another embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention.

FIG. 10 is a perspective view showing still another embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention.

FIG. 11 is a perspective view showing still another embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention.

FIG. 12 is a perspective view showing still another embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention.

FIG. 13 is a perspective view showing still another embodiment of a two-dimensional photonic crystal surface emitting laser according to the present invention.

[Explanation of symbols]

10. Two-dimensional photonic crystal surface emitting laser 11 ... Substrate 12 ... Lower clad layer (first medium) 13 ... Active layer 14 ... Upper clad layer 16 ... Lower electrode 17 ... Upper electrode 20 ... Two-dimensional photonic crystal 21 ... Photonic crystal periodic structure (second medium)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yokoyama Hikaru             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. (72) Inventor Kojiro Sekine             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. F-term (reference) 5F073 AA63 AA74 AA75 AA89 AB17                       CA12

Claims (4)

[Claims] 1. An active layer that emits light by carrier injection is sandwiched between clad layers, and the clad layer or the active layer is provided with 2
In a two-dimensional photonic crystal surface emitting laser including a photonic crystal periodic structure having a three-dimensional refractive index period, the cladding layer and the photonic crystal periodic structure have different refractive indices, A two-dimensional photonic crystal surface-emitting laser, characterized in that the occupancy, which is the ratio occupied by the low refractive index material, is large in both the second-order diffraction efficiency and the first-order diffraction efficiency. 2. The two-dimensional photonic crystal surface emitting laser according to claim 1, wherein the occupation ratio is 5 to 45%. 3. When the photonic crystal periodic structure made of a high refractive index material is arranged in a cladding layer made of a low refractive index material, the occupancy rate is 5 to 45%. Item 2. A two-dimensional photonic crystal surface emitting laser according to item 1. 4. When the photonic crystal periodic structure made of a low refractive index material is arranged in a clad layer made of a high refractive index material, the occupancy rate is 5 to 20%. Item 2. A two-dimensional photonic crystal surface emitting laser according to item 1.