JP2012119635A - Photonic crystal surface emission laser array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photonic crystal surface emission laser array in which laser light emitted from one photonic crystal surface emission laser and arriving at the other photonic crystal surface emission laser arranged in the proximity to the one photonic crystal surface emission laser is reduced.SOLUTION: The photonic crystal in a photonic crystal surface emission laser is a photonic crystal of tetragonal lattice or hexagonal lattice. For the angle θ, the photonic crystal of tetragonal lattice satisfies formula (1), and the photonic crystal of hexagonal lattice satisfies formula (2). 0°≤θ≤22.5° formula (1), 0°≤θ≤15° formula (2).

Description

  The present invention relates to a surface emitting laser array using a photonic crystal.

  In recent years, many examples of applying photonic crystals to semiconductor lasers have been reported. Patent Document 1 discloses a surface emitting laser light source in which an active layer containing a light emitting material is provided and a two-dimensional photonic crystal is formed in the vicinity of the active layer. This is a kind of distributed feedback (DFB) laser and has a resonance mode in the in-plane direction of the substrate.

  As shown in FIG. 11, in the photonic crystal surface emitting laser, a semiconductor layer 1110 is formed on a substrate 1000, and an active layer 1120 and a two-dimensional photonic crystal 1130 are provided on the semiconductor layer 1110. . In the two-dimensional photonic crystal 1130, cylindrical holes are periodically provided in the semiconductor layer 1110, and the refractive index distribution has a two-dimensional periodicity. Due to this periodicity, light having a specific wavelength among the light generated in the active layer 1120 resonates in the in-plane direction of the substrate as indicated by reference numeral 1140, forms a standing wave, and oscillates. Further, the light is extracted in the direction perpendicular to the surface as indicated by reference numeral 1150 by the first-order diffraction and operates as a surface emitting laser.

JP 2000-332351 A

  By the way, considering that the photonic crystal surface emitting laser is used as an exposure light source for electrophotography, for example, it is desirable from the viewpoint of speeding up to arrange the lasers in a two-dimensional direction.

  However, when a plurality of photonic crystal surface emitting lasers are arranged, laser light emitted from one laser element into the substrate surface may reach the inside of the other laser element and affect its operation. For example, overheating of the element, photoexcitation of the active part, interference with the resonance mode of the photonic crystal.

  Therefore, in order to put the photonic crystal surface emitting laser array into practical use, it is necessary to reduce the crosstalk between adjacent lasers as described above.

  Accordingly, the present invention provides a photonic crystal surface emitting laser array that reduces the laser light reaching the inside of the other photonic crystal surface emitting laser from one photonic crystal surface emitting laser disposed at a close position. For the purpose.

The photonic crystal surface emitting laser array according to the present invention is a photonic crystal surface emitting laser in which a plurality of photonic crystal surface emitting lasers having an active layer and a photonic crystal having a resonance mode in the in-plane direction of the substrate are arranged. The photonic crystal in the photonic crystal surface emitting laser is a photonic crystal having a tetragonal lattice or a hexagonal lattice, and is closest to the photonic crystal surface emitting laser and the photonic crystal surface emitting laser. Among the angles formed by the straight line connecting the other photonic crystal laser and the bisector of the angle divided by the straight line parallel to the lattice vector of the photonic crystal, the square lattice The photonic crystal satisfies the formula (1), and the hexagonal lattice photonic crystal satisfies the formula (2). Photonic crystal surface-emitting laser array.
0 ° ≦ θ ≦ 22.5 ° Formula (1)
0 ° ≦ θ ≦ 15 ° Formula (2)

  ADVANTAGE OF THE INVENTION According to this invention, the photonic crystal surface emitting laser array which reduces the laser beam which reaches | attains the inside of a photonic crystal from the photonic crystal surface emitting laser arrange | positioned in the close position can be provided.

It is a figure which shows the structure of Embodiment 1 which concerns on this invention. It is a figure which shows the structure of a comparative example. It is a figure which shows the structure of Embodiment 1 which concerns on this invention. It is a figure used in order to explain Embodiment 1 concerning the present invention. It is a figure which shows the structure of Embodiment 2 which concerns on this invention. It is a figure which shows the structure of Embodiment 3 which concerns on this invention. It is a figure used in order to explain Embodiment 3 concerning the present invention. It is a figure used in order to explain Embodiment 3 concerning the present invention. It is a figure used in order to explain Embodiment 3 concerning the present invention. It is a figure which shows the structure of other embodiment which concerns on this invention. It is a figure used in order to explain a photonic crystal surface emitting laser.

(Embodiment 1)
1A and 1B are plan views showing the configuration of the first embodiment of the present invention. FIG. 1B shows a photonic crystal laser array. This laser array is configured by arranging a plurality of photonic crystal lasers 10 using a square lattice photonic crystal shown in FIG. As described with reference to FIG. 11, the photonic crystal laser 10 is a photonic crystal surface emitting laser having an active layer and a photonic crystal having a resonance mode in the in-plane direction of the substrate.

  In FIG. 1, the x direction and the y direction indicate the directions of lattice vectors in a square lattice photonic crystal. In FIG. 1B, the photonic crystal of the photonic crystal laser 10 is inclined at an angle of 45 ° with respect to the adjacent photonic crystal.

  FIGS. 1C and 1D are diagrams for explaining the effect of the embodiment shown in FIG. As shown in FIG. 1C, the photonic crystal laser 10 is arranged with the square lattice tilted obliquely, and a beam having the same frequency as the resonant frequency of the square lattice photonic crystal is irradiated from the direction indicated by the arrow. . FIG. 1D shows the simulation result of FIG. From this result, it is understood that the beam irradiated to the photonic crystal is reflected at the boundary of the photonic crystal and does not reach the inside.

  In the photonic crystal laser array shown in FIG. 1B, since all the lasers have the same arrangement relationship, the simulation result in FIG. 1D is valid for all elements.

  Therefore, in the configuration shown in FIG. 1B, the laser light from the proximity laser is reflected at the interface of the photonic crystal in any element, and the laser light reaching the inside of the photonic crystal can be reduced. It is.

  FIG. 2A shows a photonic crystal laser array of a comparative example. This laser array is configured by arranging the same laser as the photonic crystal laser 10 shown in FIG.

  In this comparative example, as shown in FIG. 2B, the photonic crystal laser 10 is arranged in a state where the square lattice photonic crystal is not inclined obliquely. As in FIG. 1, a beam having the same frequency as the resonant frequency of the square lattice photonic crystal is irradiated from the direction indicated by the arrow.

  FIG. 2C shows the simulation result. From this result, it can be seen that the beam irradiated to the photonic crystal reaches the inside of the element without being reflected on the surface of the photonic crystal.

  From the above study, it is understood that an array in which crosstalk between adjacent lasers is suppressed can be provided by rotating a photonic crystal laser.

  Next, this will be described in a more general manner with reference to FIGS.

  FIG. 3 shows how a beam incident from various angles behaves for a square lattice photonic crystal. In the figure, the X axis and the Y axis indicate straight lines parallel to the lattice vector of the photonic crystal, and the broken line 30 indicates a bisector of an angle divided by these straight lines.

  A white arrow indicates a pointing vector of the incident beam. A solid line arrow indicates a pointing vector component (transmitted beam) in a direction in which it is easily transmitted, and a broken line arrow indicates a pointing vector component (reflected beam) in a direction in which it is easily reflected.

  The comparative example shown in FIG. 2B corresponds to θ = 45 ° in FIG. That is, it is an example in which the light enters from a direction parallel to the lattice vector.

  Here, the angle θ is an angle formed between the optical axis of incident light and a bisector (broken line 30) of an angle divided by a straight line (X axis, Y axis) parallel to the lattice vector of the photonic crystal. Is the smallest angle (minimum angle). The optical axis of incident light refers to the first photonic crystal surface emitting laser on which light is incident and the second photonic crystal surface emitting laser closest to the first photonic crystal surface emitting laser. It is a straight line that connects.

  A straight line parallel to the lattice vector is equally divided into four in all directions, and the equally divided angles are each 360 ° / 4. The lattice vector is a vector that connects the closest lattice points among the translation vectors that connect the lattice points of the photonic crystal.

  Referring to FIG. 3, when θ = 45 °, most of the incident beam (outlined) from the outside is a component of the transmitted beam (solid line).

  On the other hand, when θ = 0 °, most of the incident beam (outlined) is a component of the reflected beam (broken line).

  When θ = 22.5 °, the incident beam (outlined) is not only a component of the transmitted beam (solid line) but also a component of the reflected beam (broken line).

  Thus, due to the symmetry of the structure, the photonic crystal with a square lattice reflects strongly in the direction opposite to the incident direction of the beam (reflecting direction) and the direction that hardly reflects the incident beam from the outside (non-reflecting direction). ) Can be found.

  In a square lattice photonic crystal, there are four such reflection directions and non-reflection directions. When the incident beam from the outside is parallel to the non-reflecting direction, the incident beam is hardly reflected and enters the photonic crystal.

  FIG. 4 shows the relationship between the angle θ and the beam intensity (non-reflective component 41, reflective component 42). When θ = 45 °, all of the incident beam becomes a non-reflective component. However, as θ decreases, the non-reflective component decreases, and conversely the reflective component increases. When 0 ° ≦ θ ≦ 22.5 °, the reflection component 42 is equal to or exceeds the non-reflection component 41. In FIG. 3, the range of θ that satisfies this condition is indicated by a double-line arc.

  In general, the intensity of light propagating by being emitted in the direction parallel to the substrate from the laser constituting the two-dimensional array decreases as the propagation distance increases due to absorption of the material constituting the array or the spread of the beam. That is, crosstalk is greatest between the nearest elements. Therefore, in order to form a two-dimensional array of lasers having a square lattice photonic crystal, the closest elements may be rotated with respect to each other within a range where 0 ° ≦ θ ≦ 22.5 ° is satisfied.

  Note that the polarization direction of the laser light emitted from the square lattice photonic crystal in the direction perpendicular to the substrate is rotated with respect to the traveling direction of the light, and even if the laser is rotated as in this embodiment, the polarization direction Will not be affected. Therefore, the present invention does not disturb the uniformity of the laser array, which is required by the copying machine or printer.

(Embodiment 2)
In FIG. 1, an example in which a plurality of square lattice photonic crystals are arranged in a square lattice shape has been described, but in this embodiment, an example in which a plurality of square lattice photonic crystals are arranged in a triangular lattice shape will be described.

  FIG. 5A shows square lattice photonic crystals 10 arranged in an array with an apex angle of 60 °. FIG. 5B shows an example in which the apex angle is 90 ° and the array is arranged.

  Here, in the example of FIG. 5A, θ = 15 °, and in the example of FIG. 5B, θ = 0 ° and θ = 22.5 °. Therefore, since the condition of 0 ° ≦ θ ≦ 22.5 ° is satisfied, the reflection component exceeds the non-reflection component.

(Embodiment 3)
FIG. 6A shows an example in which hexagonal lattice photonic crystals 80 are arranged in a square lattice pattern. FIG. 6B shows a single element of the hexagonal lattice photonic crystal 80. Here, the hexagonal lattice photonic crystal 80 has straight lines parallel to the lattice vector directions of the X1 direction, the X2 direction, and the X3 direction.

  As shown in FIG. 7A, the beam is incident in the X1 direction. FIG. 7B shows the simulation result of FIG. This result shows that most of the incident beam is a transmitted beam. 7A and 7B, the beam is incident from the X1 direction, but the same result is obtained even when the beam is incident from the X2 direction or the X3 direction.

  On the other hand, FIG. 7C shows an example in which hexagonal lattice photonic crystals 80 are arranged at θ = 0 °. In this case, as shown in FIG. 7D, the incident beam becomes a reflected beam.

  Referring to FIG. 8, when θ = 30 °, most of the incident beam (outlined) from the outside is a component of the transmitted beam (solid line).

  On the other hand, when θ = 0 °, most of the incident beam (outlined) is a component of the reflected beam (broken line).

  When θ = 15 °, the incident beam (outlined) is not only the component of the transmitted beam (solid line) but also the component of the reflected beam (broken line).

  In this way, the hexagonal lattice photonic crystal, due to the symmetry of its structure, strongly reflects the direction opposite to the incident direction of the beam (reflective direction), and hardly reflects the incident beam from the outside (non-reflective direction). ) Can be found.

  In a hexagonal lattice photonic crystal, there are six such reflection directions and non-reflection directions. When the incident beam from the outside is parallel to the non-reflecting direction, the incident beam is hardly reflected and enters the photonic crystal.

  FIG. 9 shows the relationship between the angle θ and the beam intensity (non-reflection component 41, reflection component 42). At θ = 30 °, all of the incident beam becomes a non-reflective component. However, as θ decreases, the non-reflective component decreases, and conversely the reflective component increases. When 0 ° ≦ θ ≦ 15 °, the reflection component is equal to or exceeds the non-reflection component. In FIG. 8, the range of θ that satisfies this condition is indicated by a double-line arc.

(Other embodiments)
FIG. 10A shows an example in which a plurality of square lattice photonic crystals 10 are arranged in a triangular lattice pattern to form an array. FIG. 10B shows an example in which a plurality of square lattice photonic crystals 10 are arranged in a square lattice pattern. In this way, the array may be configured by arranging more photonic crystal surface emitting lasers.

  The photonic crystal surface emitting laser array described in the above embodiment can also be used as an exposure light source for electrophotography and a light source for other uses.

  Note that a lattice such as a tetragonal lattice or a hexagonal lattice has only to have a substantially lattice shape, and the lattice shape may be deformed due to a manufacturing error or the like.

10 Photonic crystal laser (square lattice photonic crystal)
41 Non-reflective component 42 Reflective component 80 Photonic crystal laser (hexagonal lattice photonic crystal)

Claims (3)

A photonic crystal surface emitting laser array in which a plurality of photonic crystal surface emitting lasers having an active layer and a photonic crystal having a resonance mode in the in-plane direction of the substrate are arranged,
The photonic crystal in the photonic crystal surface emitting laser is a photonic crystal having a square lattice or a hexagonal lattice,
Two lines divided by a straight line connecting the photonic crystal surface emitting laser and another photonic crystal laser closest to the photonic crystal surface emitting laser and a straight line parallel to the lattice vector of the photonic crystal. The square lattice photonic crystal satisfies the formula (1) and the hexagonal lattice photonic crystal satisfies the formula (2) with respect to the smallest angle θ among the angles formed with the equipartition lines. Photonic crystal surface emitting laser array.
0 ° ≦ θ ≦ 22.5 ° Formula (1)
0 ° ≦ θ ≦ 15 ° Formula (2)   2. The photonic crystal surface emitting laser array according to claim 1, wherein the plurality of photonic crystal surface emitting lasers are arranged in a square lattice pattern to form an array.   2. The photonic crystal surface-emitting laser array according to claim 1, wherein the plurality of photonic crystal surface-emitting lasers are arranged in a triangular lattice pattern to form an array.

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