JP2007192927A - 2-dimensional photonic crystal waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epoch-making two-dimensional photonic crystal waveguide that can reduce diffractive effect and that can suppress spread of an optical beam out in the air. <P>SOLUTION: Either the arrangement of rods or the shape of the rods themselves, or both the arrangement and the shape, are varied near the output end of a photonic crystal waveguide. Then, the output end of the waveguide is designed to have a structure in which, for example, an opening is expanded or equivalently expanded, in the two-dimensional photonic crystal waveguide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to control of output light from a photonic crystal waveguide.

  Photonic crystals are artificial crystals in which materials with significantly different refractive indexes (semiconductors, dielectrics, etc.) are regularly arranged with the same period as the wavelength of light (electromagnetic waves). To do.

  In particular, in a crystal in which a wavelength band called a photonic band gap (PBG) appears, PBG corresponds to a semiconductor forbidden band, and light does not travel in any direction in this region.

  When an impurity that breaks regularity is introduced into the photonic crystal, light can propagate in the photonic crystal, like the impurity level in the semiconductor. This is a so-called photonic crystal waveguide (PBG waveguide), which is expected to be applied to an optical integrated circuit and the like because it has a strong optical confinement and can make a waveguide with a very small radius and an acute angle.

  By the way, in the conventional photonic crystal waveguide, for example, a photonic in which a cylindrical hole (that is, an air rod, hereinafter simply referred to as a rod) is formed so as to be arranged in a regular triangle in a dielectric material such as a semiconductor. It is configured so that light can be concentrated and guided in this part of the crystal by removing one row of cylindrical parts. The output end of this photonic crystal waveguide is arranged by the rod arrangement on the end face. There are types such as “Stright1” illustrated in FIG. 1A and “Stright2” illustrated in FIG.

  However, conventionally, when light is extracted from a photonic crystal waveguide and input to an optical fiber or a photodiode, the light is once radiated into uniform air, so that it is greatly expanded by diffraction, and an optical fiber, a photodiode, etc. There was a problem that the coupling efficiency with the remarkably decreased. Actually, the output end of the photonic crystal waveguide is usually a rod arrangement as shown in FIG. 1A or FIG. 1B, but the beam radiation pattern from the output end is as shown in FIG. In the type of FIG. 1 (a), it is emitted as a wide beam over a range of about 56 degrees, and in the type of FIG. 1 (b), it is emitted as a wide beam over a range of about 35 degrees. )

  In order to solve the above-mentioned problems, the present invention configures the output end of the photonic crystal waveguide by changing the shape and arrangement of the rod in the vicinity of the output end. To provide an epoch-making two-dimensional photonic crystal waveguide capable of reducing the influence of diffraction and suppressing the spread of the light beam emitted into the air by, for example, increasing the output end opening equivalently. Is an issue.

  The gist of the present invention will be described with reference to the accompanying drawings.

  Two-dimensional photonic crystal characterized in that the output end of this photonic crystal waveguide is configured by changing the arrangement of rods near the output end of the photonic crystal waveguide, or the shape of the rod itself, or both This relates to a waveguide.

  In addition, the arrangement of the rods near the output end of the photonic crystal waveguide, or the shape of the rod itself, or both, was changed to widen the opening at the output end of the photonic crystal waveguide. The present invention relates to a characteristic two-dimensional photonic crystal waveguide.

  In addition, the arrangement of the output end of the photonic crystal waveguide is equivalently widened by changing the arrangement of the rods near the output end of the photonic crystal waveguide, the shape of the rod itself, or both. The present invention relates to a two-dimensional photonic crystal waveguide.

  4. The two-dimensional photonic crystal waveguide according to claim 1, wherein at least the shape of the rod itself in the vicinity of the output end of the photonic crystal waveguide is deformed into a wedge shape. 5. Is.

  Since the present invention changes the arrangement of the rods near the output end of the photonic crystal waveguide or the shape of the rod itself, or both, as described above, the output end of this photonic crystal waveguide is configured. For example, when the opening of the output end is increased by changing the arrangement of the rods near the output end, or the shape of the rod itself, or both, the opening of the end face is, for example, compared to the width of the waveguide. Since it is several times larger, the influence of diffraction can be reduced accordingly, and thus the spread of the output light beam from the output end can be suppressed.

  In addition, for example, by using a wedge-shaped rod, the diameter of the light beam can be increased smoothly, which changes the impedance of the electromagnetic field from the impedance of the waveguide to the impedance of the external air through the impedance of the output end opening. This is equivalent to smooth and efficient conversion.

  Next, for example, when the arrangement of the rods near the output end, or the shape of the rod itself, or both are changed to make the opening of the output end equivalent (for example, multiple wedge-shaped rods, tapered) In this case, the light efficiently leaks out of the waveguide in a tapered shape and greatly spreads to reach the output end. This is equivalent to the fact that the opening when light is emitted to the outside is equivalently enlarged, and the opening is made equivalently large as in the case where the opening at the output end is actually enlarged as described above. Accordingly, the influence of diffraction can be reduced correspondingly, and thus the spread of output light can be suppressed.

  Embodiments of the present invention that are considered suitable (how to carry out the invention) will be briefly described with reference to the drawings, illustrating the operation of the present invention.

  The output end of the photonic crystal waveguide is configured by changing the arrangement of the rods near the output end of the photonic crystal waveguide and / or the shape of the rod itself.

  For example, as shown in FIG. 4, the output port of the output end of this photonic crystal waveguide is enlarged. Specifically, the rod (air rod) is removed in the vicinity of the output end in a tapered shape, and the opening is gradually enlarged. (To be more specific, for example, as shown in FIG. 4, three wedge-shaped rods are arranged in the vertical direction with the length changed parallel to the waveguide.)

  As a result, the light reaching the conversion portion from the waveguide spreads smoothly along the wedge-shaped rod and reaches the output end face.

  Accordingly, the influence of diffraction is reduced, and therefore the spread of the output light beam can be kept small.

  Further, for example, as illustrated in FIGS. 6A and 6B, the output port of the output end of the photonic crystal waveguide is equivalently enlarged (specifically, for example, illustrated in FIG. 6). In this way, multiple wedges (12 in FIG. 6A, 10 in FIG. 6B) are arranged vertically so that the tip of the wedge-shaped rod faces the waveguide, and light is guided near the output end. It is designed to spread vertically from the waveguide.

  In this way, for example, by configuring so that the guided light efficiently leaks out of the waveguide and reaches the output end, the light efficiently leaks out of the waveguide in a tapered shape. , Will spread greatly and reach the output end. In other words, this corresponds to the fact that the opening when light is emitted to the outside is equivalently large, and thus an equivalently large opening is realized, and the influence of diffraction can be reduced accordingly. The spread of the output light beam can be kept small.

  For example, in order to efficiently leak light out of the waveguide, the wedge-shaped rod is used as described above. However, in this case, it is not necessary to change the size of each rod, and the same rod may be used. The goal can be achieved sufficiently. In this way, the radiation pattern from the output end face becomes, for example, as shown in FIGS. 7A and 7B, and the spread of the output light beam is suppressed to about 16 to 12 degrees.

  As described above, for example, the configuration in which the opening at the output end is widened and the case in which the opening at the output end is equivalently widened, for example, are caused by the following differences in how the light beam spreads: It seems like.

  For example, when the opening at the output end is widened, there is no rod in the taper-shaped portion, and the light distribution is caused by interference between the reflected light from the output end and the incident light as shown in FIG. It is confused. On the other hand, for example, when the opening at the output end is equivalently widened, the wedge-shaped rod is also present in the portion where the light leaks in a tapered shape as shown in FIGS. The reflected light and the incident light are distributed on average without strong interference. This difference in the light distribution causes a difference in the spread of the output light beam, and the beam spread is considered to be narrower in the above-described configuration in which, for example, the opening at the output end having a more uniform distribution is equivalently widened.

  A first embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 4, in the vicinity of the output end of the triangular lattice air rod two-dimensional photonic crystal waveguide, a plurality of ordinary circular air rods are removed, and the surrounding rods are deformed into wedge-shaped rods.

  As a means for changing the shape of the rod, the droplet type rod shown in FIG. 3B is overlapped with the normal circular rod shown in FIG. 3A to be transformed into a wedge-shaped rod as shown in FIG.

  At this time, the length of the wedge-shaped rod is changed, and three wedge rods are arranged parallel to the waveguide and symmetrically in the vertical direction. The length of the wedge rod is chosen to increase with distance from the waveguide. In this manner, the portion without the rod is tapered toward the output end, and the opening at the output end is enlarged. The direction of taper spread is preferably a parabola rather than a straight line.

  In this way, the light that has entered the conversion section from the waveguide spreads along the taper, so that the beam diameter is large when it reaches the output end. Accordingly, the beam is emitted to the outside with a large beam diameter, and the spread of the output light beam is suppressed accordingly.

  Actually, when simulating the radiation pattern, the half width of the beam divergence angle is suppressed to about 21 degrees as shown in FIG. 5, and is less than half of the beam divergence angle from the normal output end shown in FIG. Become.

  In addition, it is desirable that the waveguide spread in a parabolic manner as in the case of a flashlight reflector. However, it is not possible to use a wedge-shaped rod but to achieve this spread only with a circular rod. It is difficult to adjust the position finely. However, if the length is adjusted using a wedge-shaped rod as in this embodiment, a parabolic spread can be easily realized.

  Further, the spread of the output light beam can be controlled by adjusting parameters such as the number and length of wedge-shaped rods used. That is, if the size of the wedge-shaped rod, the radius of the wedge tip, and the direction of the wedge are adjusted, the way in which the waveguide spreads can be controlled, so that the spread of the output light beam can be controlled. In this example, the number of wedge-shaped rods is three at the top and the bottom, but if it is desired to further control the spread of the output beam, the number of the wedge-shaped rods may be increased or decreased as necessary to adjust their length.

  A second embodiment of the present invention will be described with reference to the drawings.

  As shown in FIGS. 6A and 6B, a normal circular air rod is deformed into a wedge-shaped rod in the vicinity of the output end of the triangularly arranged air rod two-dimensional photonic crystal waveguide. At this time, 10 or 12 wedge-shaped rods are arranged on the upper and lower sides of the waveguide in a tapered shape so that the tip ends perpendicular to the waveguide. In this case, all the wedge-shaped rods may have the same shape, and it is not necessary to adjust the length or the like one by one.

  In this way, the light that has entered the conversion section from the waveguide leaks out little by little at the wedge-shaped rod portion, and reaches the output end with a large spread. This corresponds to the fact that the opening at the output end is equivalently increased, and the spread of the output light beam is suppressed accordingly.

  The spread of the output light beam can be controlled by adjusting parameters such as the number and length of wedge rods used.

  The difference between the second embodiment and the first embodiment is whether or not there is a rod in the converter near the output end. When simulating the state of the light distribution in the converter near the output end, the distribution of Example 1 is as shown in FIG. 8, and the distribution of Example 2 is as shown in FIGS. It has become.

  In FIG. 8, there is no rod in the tapered conversion part, and the incident wave and the reflected wave from the end face interfere strongly, and the light distribution is disturbed. On the other hand, in FIGS. 9 and 10, since the wedge-shaped rod is also present in the conversion unit, the incident wave and the reflected wave do not interfere greatly, and the light distribution is not so disturbed. Therefore, the spread of the output light beam is suppressed more than in the first embodiment.

  The present invention is not limited to the first and second embodiments, and the specific configuration of each component can be designed as appropriate.

It is explanatory drawing which shows the output end of the conventional linear photonic crystal waveguide. It is explanatory drawing which shows the directivity of the output light from the conventional linear photonic crystal waveguide. It is explanatory drawing which shows the formation method of the wedge-shaped rod of the photonic crystal waveguide which concerns on Example 1, Comprising: (a) shows a normal circular rod, (b) is a droplet-shaped rod and its parameter. (C) is a figure which shows a wedge-shaped rod. In the vicinity of the output end of the photonic crystal waveguide according to Example 1, the upper and lower three rows of rods of the waveguide are removed in a tapered shape (baseball home base shape), and the surrounding rods that are inclined are changed to wedge-shaped rods. FIG. 8 is an explanatory diagram showing a configuration in which the length is increased as the distance from the waveguide increases, and the ratio of changing the length of the rod is such that the tip of the wedge-shaped rod becomes a parabolic shape. It is explanatory drawing which shows the directivity of the output light from the output end of the two-dimensional photonic crystal waveguide which concerns on Example 1, Comprising: It has shown that the breadth of an output beam is restrained to about 21 degree | times. In the vicinity of the output end of the two-dimensional photonic crystal waveguide according to the second embodiment, the upper and lower rows of rods in the waveguide are removed, and the upper and lower rows are changed from a circular rod to a wedge-shaped rod within a triangular range. It is explanatory drawing, Comprising: All the wedge-shaped rods are the same, The structure of FIG. 6 (a) from which arrangement | positioning of the rod in an end surface differs, and the structure of FIG.6 (b) are shown. It is explanatory drawing which shows the directivity of the output light from the output terminal of Example 2, Comprising: Radiation angle dependence of the light output from each output terminal of Fig.6 (a) and FIG.6 (b), ie, output FIG. 7 (a) shows the directivity of the output end of the type of FIG. 6 (a), and the beam divergence is suppressed to about 16 degrees. FIG. 7B shows the directivity of the output end of the type shown in FIG. 6B, and shows that the beam divergence is suppressed to about 12 degrees. It is explanatory drawing which shows light distribution (The shape of a waveguide is also shown overlapping) of the output end vicinity of Example 1. FIG. FIG. 7 is an explanatory diagram showing light distribution (the shape of a waveguide is also shown superimposed) in the vicinity of the output end of the type of FIG. FIG. 7 is an explanatory diagram showing the light distribution in the vicinity of the output end of the type of FIG.

Claims (4)

  Two-dimensional photonic crystal characterized in that the output end of this photonic crystal waveguide is configured by changing the arrangement of rods near the output end of the photonic crystal waveguide, or the shape of the rod itself, or both Waveguide.   The feature is that the opening of the output end of the photonic crystal waveguide is widened by changing the arrangement of the rods near the output end of the photonic crystal waveguide or the shape of the rod itself, or both. 2D photonic crystal waveguide.   The structure of the output end of the photonic crystal waveguide is equivalently widened by changing the arrangement of the rods near the output end of the photonic crystal waveguide, the shape of the rod itself, or both. A two-dimensional photonic crystal waveguide characterized by   The two-dimensional photonic crystal waveguide according to any one of claims 1 to 3, wherein at least the shape of the rod itself in the vicinity of the output end of the photonic crystal waveguide is deformed into a wedge shape.