WO2006073194A1

WO2006073194A1 - Optical waveguide, optical device and optical communication device

Info

Publication number: WO2006073194A1
Application number: PCT/JP2006/300111
Authority: WO
Inventors: Akiko Gomiyou; Jun Ushida; Hirohito Yamada; Tou Thu
Original assignee: Nec Corporation
Priority date: 2005-01-06
Filing date: 2006-01-06
Publication date: 2006-07-13
Also published as: JPWO2006073194A1

Abstract

An optical waveguide and an optical device consisting of photonic crystal which enable the use of two optical waveguide modes perpendicular to the advancing direction of light to thereby enhance a degree of freedom of designing. Light is propagated in an optical waveguide consisting of photonic crystal using a refractive index guide mode that is an optical waveguide mode at a minimum frequency in dispersion relation with photonic crystal. Or, light is propagated using a line defect waveguide mode as the first optical waveguide mode out of two optical waveguide modes perpendicular to the advancing direction of light and using the above refractive index guide mode as the second optical waveguide mode. Alternatively, light is propagated using a refractive index guide mode that is an optical waveguide mode at a minimum frequency in dispersion relation with the photonic crystal as respectively two optical waveguide modes perpendicular to the advancing direction of light.

Description

Specification

Optical waveguide, optical device, and optical communication apparatus

Technical field

The present invention relates to an optical waveguide made of a photonic crystal obtained by arranging two or more kinds of substances having different refractive indexes in a one-dimensional, two-dimensional, or three-dimensional period, an optical device including the same, and an optical communication Relates to the device.

Background art

[0002] Photonic crystals in which two or more types of materials with different refractive indices are arranged in a multidimensional period in the order of the wavelength of light (usually 0.3 to 0.7 m) have strong light confinement due to the photonic band gap. It is expected to be effective, and it is expected to be applied to various optical devices and micro optical circuits using this. It is also known that an optical waveguide is formed inside a photonic crystal by providing a linear defect in the photonic crystal (see, for example, Non-Patent Document 1).

[0003] Non-Patent Document 1: J. D. Joannopoulos, P. R. Villeneuve, and S. Fan Photonic Crystal: pu tting a new twist on light, Nature 386 卷 143 pages 1997

Non-Patent Document 2: Proceedings of the 51st Joint Conference on Applied Physics, Kitagawa et al., 3rd pp. 1169, Lecture No. 31a-M-3

Non-Patent Document 3: Physical 'Review' Letters (2001), Notomi et al., No. 87, No. 25, 25 pages 3902 to 253905

Disclosure of the invention

Problems to be solved by the invention

[0004] An electromagnetic wave (light) in an optical waveguide made of a photonic crystal includes an optical waveguide mode that can be guided (light propagates) and a slab mode that cannot be guided (no light propagates). Or there is a radiation mode.

[0005] An optical waveguide obtained by providing a linear defect in the above-described photonic crystal (hereinafter referred to as a linear defect optical waveguide) is sandwiched between two slab mode bands obtained by providing a linear defect. Line-defect waveguide mode formed in the photonic band gap It is common to use it.

[0006] Therefore, in an optical waveguide made of a conventional photonic crystal, one of the two optical waveguide modes orthogonal to the light traveling direction has an electric field vector that forms a photonic band gap. There was a problem that the degree of freedom in designing an optical waveguide and an optical device using the optical waveguide was low because the polarized light could not be transmitted.

[0007] For example, Non-Patent Document 2 proposes a photonic crystal structure that realizes polarization independence in the photonic band gap. However, for optical waveguides made of photonic crystals, a configuration capable of guiding both of the two optical waveguide modes orthogonal to the light traveling direction has been realized.

[0008] The present invention has been made in view of a serious problem, and it is possible to use two optical waveguide modes orthogonal to the traveling direction of light to improve the degree of design freedom. It is an object of the present invention to provide an optical waveguide and an optical device.

Means for solving the problem

[0009] The optical waveguide according to the first invention of the present application is an optical waveguide comprising a photonic crystal obtained by arranging two or more kinds of substances having different refractive indexes in a one-dimensional, two-dimensional or three-dimensional period. In the dispersion relation of crystals, light is propagated using a refractive index guide mode which is an optical waveguide mode with the lowest frequency. (See Figure 1 and Figure 3)

[0010] The optical waveguide according to the second invention of the present application is such that light travels in an optical waveguide made of a photonic crystal obtained by arranging two or more kinds of substances having different refractive indexes in a one-dimensional, two-dimensional or three-dimensional cycle. Of the two optical waveguide modes orthogonal to the direction,

A line defect waveguide mode is used for the first optical waveguide mode,

The second optical waveguide mode is characterized in that light is propagated by using a refractive index guide mode which is an optical waveguide mode having the lowest frequency in the dispersion relationship of the photonic crystal. (See Figure 9 and Figure 11)

[0011] An optical waveguide according to the third invention of the present application is an optical waveguide made of a photonic crystal obtained by arranging two or more kinds of substances having different refractive indexes in a one-dimensional, two-dimensional or three-dimensional period. Light is propagated in two optical waveguide modes orthogonal to the traveling direction of light using a refractive index guide mode which is an optical waveguide mode of the lowest frequency in the dispersion relationship of the photonic crystal. (See Figure 10)

[0012] In the optical waveguide according to the present invention, in the dispersion relationship of the photonic crystal, the refractive index guide mode, which is the optical waveguide mode with the lowest frequency, is used for light propagation, so that the optical waveguide has a direction substantially perpendicular to the light traveling direction. Two optical waveguide modes with electric field vectors can propagate.

The invention's effect

[0013] According to the present invention, two optical waveguide modes each having an electric field vector in a direction substantially perpendicular to the traveling direction of light can be used in an optical waveguide made of a photonic crystal. Therefore, the degree of freedom in designing the optical waveguide and various optical devices using the optical waveguide is improved. Brief Description of Drawings

FIG. 1 is a perspective view showing a configuration example of a line defect optical waveguide provided in a photonic crystal.

FIG. 2 is a perspective view showing an example of an electric field vector of light propagating in the line defect optical waveguide shown in FIG.

FIG. 3 is a graph showing the dispersion relationship of the optical waveguide mode shown in FIG.

4 is a graph showing the light transmission characteristics of the optical waveguide mode shown in FIG.

FIG. 5 is a perspective view showing a second example of an electric field vector of light propagating in the line defect optical waveguide shown in FIG. 1.

6 is a graph showing the dispersion relationship of the optical waveguide mode shown in FIG.

7 is a graph showing the light transmission characteristics of the optical waveguide mode shown in FIG.

FIG. 8 is a perspective view showing another configuration example of a photonic crystal in which a line defect optical waveguide is formed.

FIG. 9 is a perspective view showing another configuration example of a photonic crystal in which a line defect optical waveguide is formed.

FIG. 10 is a perspective view showing another configuration example of a photonic crystal in which a line defect optical waveguide is formed. FIG. 11 is a perspective view showing another configuration example of a photonic crystal in which a line defect optical waveguide is formed.

FIG. 12 is a graph showing light transmission characteristics when TE-like mode light propagates in a line-defect waveguide mode in a line-defect optical waveguide formed in a photonic crystal.

FIG. 13 is a graph showing light transmission characteristics when TM-like mode light propagates in a line defect optical waveguide formed in a photonic crystal by a refractive index guide mode.

FIG. 14 is a graph showing light transmission characteristics including a wavelength band corresponding to a mode gap when TM-like mode light propagates through a refractive index guide mode in a line defect optical waveguide formed in a photonic crystal.

[15] Line defect light formed in photonic crystal with a structure in which SiO is embedded in the hole

2

6 is a graph showing light transmission characteristics including a wavelength band corresponding to a mode gap when TM-like mode light propagates in a waveguide by a refractive index guide mode.

圆 16] In a line-defect optical waveguide formed in a triangular lattice hole-type photonic crystal, how the mode gap frequency changes when the ratio of the lattice constant to the hole radius (rZa) is changed as a parameter. It is a graph to show.

圆 17] Changes in the gap width of the mode gap when the ratio of the lattice constant to the hole radius (rZa) is changed as a parameter in a line-defect optical waveguide formed in a triangular lattice hole-type photonic crystal It is a graph which shows.

FIG. 18 is a plan view showing a configuration example of an optical device including the optical waveguide of the present invention. FIG. 19 is a perspective view showing a configuration example of an optical switch including the optical waveguide of the present invention. FIG. 20 is a plan view showing a configuration example of an optical multiplexing / demultiplexing device including the optical waveguide of the present invention.

FIG. 21 is a perspective view showing a configuration example of an optical communication device including the optical waveguide of the present invention. Explanation of symbols

1, 12, 22, 321, 322, 42 photonic crystal

2-wire defect optical waveguide

3, 5, 7, 10 Photonic crystal region

4, 6, 8, 11 line defect area 131, 132, 231 to 234, 331 to 334

141, 142 interface §

241 、 242 Spot size change

25 Micro heater

341, 342 3dB coupler

41 SOI substrate

43 channel waveguide

44 Optical fiber

BEST MODE FOR CARRYING OUT THE INVENTION

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

(Optical waveguide)

First, the optical waveguide according to the first embodiment of the present invention will be described. First, the refractive index guide mode used in the optical waveguide of this embodiment will be described. This refractive index guide mode is an optical waveguide mode in which light is guided by a refractive index difference formed by providing a linear defect in a photonic crystal.

FIG. 1 is a perspective view showing a configuration example of a line defect optical waveguide provided in a photonic crystal, and FIG. 2 shows an example of an electric field vector of light propagating in the line defect optical waveguide shown in FIG. FIG.

The optical waveguide shown in FIG. 1 includes, as a photonic crystal 1, a slab layer having a large number of vacancies 10 and also having a silicon (Si) force, and a line in which no vacancies 10 are formed. In this configuration, a defect region is provided. Note that the refractive index of the linear defect region is set to a value larger than the average refractive index of the photonic crystal. This linear defect region becomes a line defect optical waveguide 2, and light travels in the direction of the arrow (Ei) in FIG.

Here, the direction of the electric field vector of the light traveling in the line defect optical waveguide 2 is parallel to the slab surface of the photonic crystal 1 as shown in FIG. 2, for example. The direction perpendicular to the direction (Ex vector in Fig. 2). Hereinafter, when the electric field vector of light propagating in the photonic crystal 1 is in the direction of the Ex vector shown in FIG. 2, the optical waveguide mode is called a TE-like mode. FIG. 3 is a graph showing the dispersion relationship of the optical waveguide mode shown in FIG. As shown in FIG. 3, in the line defect optical waveguide 2 shown in FIG. 1, in the vicinity of the standard frequency k = 0 and k ≠ 0, the frequency side lower than the lower end frequency of the continuous slab mode band. The TE-like mode light propagates by the refractive index guide mode, which is an optical waveguide mode at the lowest frequency. The reason why TE-like mode light propagates in the line defect optical waveguide 2 provided in the photonic crystal 1 by the refractive index guide mode is as follows.

[0021] For example, Non-Patent Document 3 has already revealed that a refractive index guide mode based on the structure of a line-defect optical waveguide exists at the lowest frequency of the slab mode band. This refractive index guide mode is formed by a refractive index difference in a direction orthogonal to the light traveling direction of the line defect optical waveguide 2.

[0022] The refractive index guide mode based on the structure of the line defect optical waveguide overlaps the frequency band force S slab mode band as shown in the graph of FIG. For this reason, it has been conventionally considered that the refractive index guide mode cannot be used as an optical waveguide mode with a large propagation loss of light (TE-like mode).

However, this refractive index guide mode has a dispersion relationship close to that of a simple thin-line optical waveguide using the material constituting the photonic crystal 1. Therefore, even if the refractive index guide mode frequency band is close to or within the slab mode, light propagates while feeling a weak refractive index difference on the plane orthogonal to the light traveling direction.

FIG. 4 is a graph showing the results of calculating the light transmission characteristics of the line defect waveguide 2 shown in FIG. 1 using the FDTD (Finite Difference Time Domain) method.

[0025] The frequency band with a flat light transmission characteristic shown in FIG. 4 (a) is a line defect waveguide mode region, and the frequency band with a flat light transmission characteristic shown in FIG. 4 (b) is a refractive index guide mode. It is an area.

As shown in FIG. 4 (b), the refractive index guide mode is similar to the line defect waveguide mode (FIG. 4 (a)) formed in the well-known photonic band gap. Light can be propagated with little propagation loss. In other words, the refractive index guide mode can propagate light in a lower frequency band than the line defect waveguide mode. In particular, in the region where the standard wavenumber k is close to the edge of the Brillian zone, the difference between the wave number in the slab mode band becomes large, and the light propagates only in the refractive index guide mode because the coupling between the two modes is weak. This refractive index guide mode is desirably used as an optical waveguide mode when the standard wavenumber k is in the range of 0.25 or more and 0.5 or less in the dispersion relationship of the photonic crystal. The reason is explained below.

[0028] As described above, the refractive index guide mode light propagating in the line defect optical waveguide 2 provided in the photonic crystal 1 is present in the vicinity of the frequency band slab mode or in the slab mode. However, it propagates while feeling a weak difference in refractive index on a plane orthogonal to the traveling direction of light. This refractive index guide mode often exists in the slab mode in the region where the standard wavenumber k is less than 0.25. In addition, in the region where the normalized wave number k is less than 0.25, the light confinement effect by the refractive index guide mode is weak, so the propagation loss of guided light becomes very large, and it propagates only by traveling a distance of about several meters. The light intensity drops from 1/100 to less than 1/1000. On the other hand, when the normalized wavenumber k is 0.25 or more, the optical confinement effect by the refractive index guide mode becomes strong, and the refractive index guide mode exists on the low frequency side away from the slab mode. Therefore, the property as a refractive index guide mode appears strongly, and light can be propagated with lower loss. In this case, the inventors of the present application have confirmed by simulation or the like that there is almost no propagation loss in the propagating light even after traveling through the optical waveguide more than several hundreds of meters. Note that the value of the standard wave number k is equivalent to the case where all wave numbers are considered, considering the values from 0 to 0.5 in the first Brillian zone. Therefore, it is desirable that the standard wavenumber k of the refractive index guide mode is 0.25 or more and 0.5 or less.

Next, another optical waveguide mode propagating in the line defect optical waveguide shown in FIG. 1 will be described. The electric field vector of the light propagating through the line-defect optical waveguide provided in the photonic crystal is perpendicular to the slab surface of the photonic crystal as shown in Fig. 5, which is only in the TE-like mode direction shown in Fig. 2. There is also a direction (Ex vector in Fig. 5) that is orthogonal to the traveling direction of light. At this time, in the line-defect optical waveguide provided in the photonic crystal 1, as shown in FIG. 6, it is further away from the lower end frequency of the continuous slab mode band, and is formed based on the structure of the line-defect optical waveguide. It is possible to propagate light by the refractive index guide mode. Hereinafter, when the electric field vector of light propagating in the line-defect optical waveguide 2 is in the direction of the Ex solid shown in FIG. 5, the optical waveguide mode is called a TM-like mode. The reason why TM-like mode light can be propagated in the refractive index guide mode is that the TE-like mode light described above is used. This is the same as the reason for propagation.

As shown in FIG. 6, the TM-like mode light propagating in the refractive index guide mode also has a frequency band overlapping with the slab mode band as in the case of the TE-like mode light. For this reason, in the refractive index guide mode, it has been conventionally considered that TM-like mode light cannot be used as an optical wave mode because of its large propagation loss.

[0031] However, as shown in the calculation result of the light transmission characteristic obtained by the FDTD method shown in Fig. 7, it can be used as an optical waveguide mode with little propagation loss of the TM-like mode.

[0032] As described above, the well-known line-defect waveguide mode has an electric field vector in which a photonic band gap is formed between two optical waveguide modes orthogonal to the light traveling direction. Only one polarized light (TE-like mode) can be propagated, and TM-like mode light cannot be propagated. According to the optical waveguide using the refractive index guide mode, which is a feature of the present invention, not only the TE-like mode but also the TM-like mode light can be propagated, so the optical waveguide and the optical device using the optical waveguide are designed. The degree of freedom when doing so is improved.

[0033] When propagating TM-like mode light, as in the above-described TE-like mode, the refractive index guide mode is an optical waveguide in which the normalized wavenumber k is in the range of 0.25 to 0.5. It is desirable to use it as a mode.

Next, a specific example of an optical waveguide that propagates the light in the TE-like mode and the TM-like mode will be described.

[0035] As described above, in the line defect optical waveguide 2 provided in the photonic crystal, TE-like mode light can be propagated by using a well-known line defect waveguide mode. . Furthermore, in the optical waveguide of the present invention, light in the TE-like mode and the TM-like mode can be propagated by using the refractive index guide mode.

[0036] At that time, the structure of the photonic crystal 1, the lattice constant of the photonic crystal 1, the photonic crystal

The band structure of photonic crystal 1 is optimized using the refractive index difference, periodicity (ratio of high refractive index material and low refractive index material, periodic structure) and slab layer thickness as parameters. By setting, it is possible to propagate the TE-like mode and TM-like mode light into the line defect optical waveguide 2 while maintaining the same light intensity. Like mode and TM-like mode light can be propagated in the same frequency band.

[0037] Specifically, Si / SiO

2 Use a ZSi substrate (SOI substrate) and set the thickness of the top Si layer to 0.25.

The SiO layer is formed with a thickness of about 1 μm. In addition, the substrate has a plurality of holes.

2

By forming a triangular lattice, a triangular lattice hole-type photonic crystal is formed. This lattice constant is about 0.3, and the hole diameter r is about rZa = 0.3. Furthermore, the line defect optical waveguide 2 is formed by providing a linear defect that does not form a hole in the light traveling direction. Then, the length of the line defect optical waveguide 2 is set to about 600 m with 20 m force. With such a structure, it is possible to propagate light in the TE-like mode and the TM-like mode to the optical waveguide made of the photonic crystal 1 that has been considered difficult.

[0038] In the above description, TE-like mode is an example in which light in the TE-like mode and TM-like mode propagates in the same frequency band in the line defect optical waveguide 2 provided in the photonic crystal 1. It is also possible to propagate mode and TM-like mode light in different frequency bands.

Next, another configuration example of the photonic crystal in which the line defect optical waveguide of this embodiment is formed will be described.

[0040] The optical waveguide shown in FIG. 8 shows the configuration of an optical waveguide made of a general photonic crystal including the optical waveguide shown in FIG. Each of the photonic crystal regions 3 is formed. In such a configuration, the light traveling direction is the + y direction. Further, the optical waveguide shown in FIG. 8 has a configuration in which the refractive index distribution in the X direction in FIG. Furthermore, when looking at the slab structure of the photonic crystal region 3 and its refractive index distribution in the vertical direction (z-axis direction), the refractive index increases on the slab surface of the photonic crystal region 3.

[0041] As shown in FIG. 8, by providing a structure in which the average refractive index of the line defect region 4 is increased in both the X-axis and z-axis directions, light having an electric field vector substantially parallel to the X direction (TE (Like mode) and light with an electric field vector almost parallel to the z direction (TM—like mode) can be propagated by the refractive index guide mode.

On the other hand, in the optical waveguide shown in FIG. 9, the width and height of the line defect region 6 are appropriately determined, and the line defect region 6 Compared to 6, the slab layer of the photonic crystal region 5 is formed thinner. Even in such a configuration, similarly to the optical waveguide shown in FIG. 8, light having an electric field vector substantially parallel to the X direction and light having an electric field vector substantially parallel to the z direction can be propagated in the refractive index guide mode, respectively. . More specifically, when a line defect optical waveguide is formed using the triangular lattice hole photonic crystal, for example, the lattice constant is 0.38 μm, the hole diameter is 0.16 μm, the line defect region is The width of the slab is about 0.25 m and the slab layer thickness of the photonic crystal region is about 0.05 m.

In addition, the optical waveguide shown in FIG. 10 has a configuration using a square lattice rod type having a plurality of square lattice rods in the photonic crystal region 7 formed on both sides of the line defect region 8. Have. Even with such a configuration, light having an electric field vector substantially parallel to the X direction and light having an electric field vector substantially parallel to the z direction can be propagated in the refractive index guide mode, similarly to the optical waveguide shown in FIG.

Furthermore, the optical waveguide shown in FIG. 11 has a configuration using a three-dimensional photonic crystal structure in which a plurality of rod-shaped substances are laminated in the photonic crystal region 10 with a predetermined gap. The line defect region 11 is formed by providing a material having a refractive index higher than that of the photonic crystal region 10 at a position surrounded by the photonic crystal region 10. Even with such a configuration, similarly to the optical waveguide shown in FIG. 8, two lights having an electric field vector in a direction substantially orthogonal to the light traveling direction can be propagated in the respective refractive index guide modes.

Next, the verification result of the optical waveguide shown in the first embodiment will be described.

In the following, the results of measuring the light transmission characteristics of an optical waveguide using a sample in which a line defect optical waveguide is formed on a triangular lattice hole type photonic crystal are shown. The sample used for the measurement has a so-called air bridge structure in which Si is used as the slab layer of the photonic crystal and a large number of vacancies are provided on both sides of the linear defect. SiO in each hole

Even with a structure in which an insulating film having two strengths is embedded, the same effects as described below can be obtained.

[0047] First, TE-like mode light whose wavelength band is around 1550 nm and whose electric field vector direction is parallel to the slab surface of the photonic crystal is propagated in the sample by the line defect waveguide mode. . The light transmission characteristics of the line defect optical waveguide at this time are as shown in FIG. In Fig. 12, the transmitted light level is about 20 dB overall. The coupling loss between the recessed optical waveguide and the optical fiber for entering light into the line-defect optical waveguide is about 10 dB, and the optical fiber that receives light emitted from the line-defect optical waveguide and the line-defect optical waveguide The coupling loss is about -10dB. Therefore, there is almost no propagation loss of the line defect optical waveguide itself formed in the photonic crystal.

[0048] Next, the direction of the electric field vector of the incident light is rotated by 90 degrees, and TM-like mode light orthogonal to the slab surface of the photonic crystal is incident on the sample. The light transmission characteristics of the line defect optical waveguide at this time are as shown in FIG.

[0049] As shown in Fig. 13, even if the direction of the electric field vector of the incident light is rotated by 90 degrees and light in the TM-like mode is propagated in the refractive index guide mode, transmission of light having a wavelength band near 1550 nm is possible. The characteristics are similar to the graph shown in Fig. 12. In this way, a line defect optical waveguide formed by providing a line defect in a photonic crystal has the same transmission characteristics for two lights having an electric field vector in a direction substantially orthogonal to the light traveling direction. Have

Next, the mode gap of the refractive index guide mode of the line defect optical waveguide shown in FIG. 1 will be described.

[0051] The light of the refractive index guide mode is folded (reflected) at the edge of the Brilliant zone in the wave number space of the refractive index guide mode shown in Figs. That is, a mode gap is formed at the end of the Brillian zone because a periodic structure with a refractive index in the traveling direction of light exists. The mode gap when the optical waveguide mode is the TE-like mode is as shown in FIG. 3, and the mode gap when the optical waveguide mode is the TM-like mode is as shown in FIG.

[0052] When light is propagated in the line defect optical waveguide formed in the photonic crystal by the refractive index guide mode, as described above, the normalized wave number k is 0.25 or more in the dispersion relationship of the photonic crystal. In the range of 5 or less, light propagates with little loss. On the other hand, in the frequency band of the mode gap, light does not propagate through the line defect optical waveguide.

FIG. 14 shows the result of calculation by the FDTD method for the light transmission characteristics when light having an electric field vector orthogonal to the slab surface is incident in the line defect optical waveguide.

As shown in FIG. 14, there is a region where the light transmittance is significantly reduced in the wavelength band corresponding to the mode gap of the TM-like mode. [0055] Next, light transmission is performed using a sample having a structure in which SiO is embedded in the holes of the photonic crystal.

2

Figure 15 shows the results of measuring the over-characteristics.

[0056] As shown in FIG. 15, the existence of a mode gap in which the light transmission rapidly decreases at a wavelength width of about 10 nm is observed in the vicinity of the wavelength of 1600 nm.

[0057] In order to control the frequency and gap width of the mode gap, it is necessary to control the difference in refractive index of the materials constituting the photonic crystal, the lattice constant of the photonic crystal, and the periodicity.

[0058] Fig. 16 shows the ratio of the lattice constant (a) to the hole radius (r) (rZa) in a triangular lattice hole type photonic crystal as an example of controlling the mode gap frequency and gap width. This shows how the mode gap frequency changes when) is changed as a parameter. Figure 17 shows how the gap width (Δλ) changes when (r Za) is changed as a parameter. Figures 16 and 17 both show the results calculated by the FDTD method. Band-1 in Fig. 16 is the lower frequency (low frequency side) of the mode gap (see Fig. 3) at the standard frequency k = 0.5, and band-2 in Fig. 16 is the standard frequency. This is the upper frequency (high frequency side) of the mode gap at a wave number of k = 0.5. Figure 17 shows the change in the gap width (Δλ) with respect to the change in the ratio (rZa) of the lattice constant (a) to the hole radius (r) when light in the 1550nm band is propagated.

[0059] The frequency and gap width of the mode gap can be controlled by changing the ratio (rZa) of the lattice constant (a) to the hole radius (r) so that the graph forces in Figs. 16 and 17 are also divided. . It can also be seen that a practically effective wavelength width of 1 nm or more and lOnm or less can be obtained as the gap width.

[0060] In order to reduce the insertion loss of light into the line defect optical waveguide composed of the photonic crystal shown in FIG. 1 in FIG. 18, a well-known channel optical waveguide is provided at the light input / output portion for the line defect optical waveguide. The configuration is shown.

[0061] The optical waveguide shown in FIG. 18 is an SOI wafer having a SiZSiO ZSi structure on the substrate (Si layer

2

A photonic crystal on the Si layer, with a thickness of about 0 · 25; z m and a SiO layer thickness of about 1 m)

2

It is the structure provided with the structure.

[0062] The photonic crystal 12 uses a triangular lattice hole type in which a plurality of holes are arranged in a triangular lattice shape, the lattice constant a is about 0, the hole diameter r¾: Za = 0.3, In the direction of travel A line-defect optical waveguide is formed by not providing holes.

[0063] Further, thin wire optical waveguides 131 and 132 made of Si are connected to the light input / output side of the line defect optical waveguide. Furthermore, trapezoidal interface portions 141 and 142 having a length of about 0.3 / zm are provided between the thin-line optical waveguides 131 and 132 and the line-defect optical waveguide in order to reduce the coupling loss of light.

[0064] The holes provided in the substrate are formed, for example, by forming a resist having an opening in a hole forming region by an electron beam exposure method and removing the Si layer by dry etching using the resist as a mask. . After that, SiO is embedded in the pores with a thickness of about.

2

[0065] In such a configuration, a tip single-mode optical fiber is connected to the end faces of the thin-line optical waveguides 131 and 132, and light in the TE-like mode and TM-like mode with a wavelength of 1550 nm is guided through the refractive index. When propagating according to the mode, the same results as in FIGS. 12 to 15 are obtained as the light transmission characteristics.

[0066] As described above, when the optical waveguide using the refractive index guide mode, which is a feature of the present invention, is used, the same transmission characteristics can be obtained for light in the TE-like mode and the TM-like mode, respectively. Therefore, the degree of freedom in designing an optical device including this optical waveguide is improved.

[0067] For the material of the photonic crystal 12, a material having a refractive index of about 3 or more, such as GaAs, InP, a compound thereof (eg, GalnAsP) or an A1 compound, is selected instead of Si. It is also possible to do this. In that case, to set the light transmission wavelength to the 1550nm band, adjust the lattice constant and the hole diameter, respectively.

[0068] (Optical switch)

Next, a second embodiment in which the optical waveguide using the refractive index guide mode of the first embodiment of the present invention is applied to an optical switch will be described.

As shown in FIG. 19, the optical switch includes two line-defect optical waveguides provided in the photonic crystal 22 and a thin-line optical waveguide connected to the input / output side of the two line-defect waveguides. With ~ 34. Spot size converters 241 and 242 for converting the spot size of light are connected to the tips of the thin optical waveguides 231 to 234 connected to the input and output sides of the line defect waveguide, respectively.

[0070] The thin-line optical waveguides 231 and 232 connected to the input side of the line defect waveguide have different spot sizes. The thin-line optical waveguides 233 and 234 branched at the input end near the converter 241 and connected to the output side of the line defect waveguide are joined immediately before the spot size converter 242. A micro heater 25 is provided in the vicinity of one of the line defect optical waveguides.

In such a configuration, the light incident through the spot size converter 241 is branched in two directions by the thin-line optical waveguides 231 and 232 and is input to the line-defect optical waveguide made of a photonic crystal, respectively.

On the other hand, the light output from the two line defect optical waveguides is combined by the thin line optical waveguides 233 and 234 and output through the spot size change 242. At this time, the temperature of the photonic crystal is changed by heating one of the line-defect optical waveguides with the microheater 25, and the effective refractive index of the line-defect optical waveguide is changed. This change in refractive index makes it possible to change the phase difference of the output light from the two line-defect optical waveguide forces from 0 to π. When the phase difference force between the two lights, the output light of the line defect optical waveguide has the same light intensity as the input light, and when the phase difference is π, the output light of the line defect optical waveguide has a light intensity of zero.

[0073] Thus, an optical switch can be realized by forming two line-defect optical waveguides in a photonic crystal. In this embodiment, it is a matter of course that the above-described refractive index guide mode is used as the optical waveguide mode in the line defect optical waveguide! /.

[0074] According to the present embodiment, it is possible to switch light in the TE-like mode and the TM-like mode by using the optical waveguide using the refractive index guide mode, which is a feature of the present invention. Therefore, the degree of freedom in designing the optical switch is improved.

[0075] (Optical multiplexing / demultiplexing device)

Next, a third embodiment in which the optical waveguide using the refractive index guide mode of the first embodiment of the present invention is applied to an optical multiplexing / demultiplexing device will be described.

As shown in FIG. 20, the optical multiplexing / demultiplexing device includes two photonic crystals 321 and 322 arranged in parallel and forming a line defect optical waveguide, and an input / output side of the line defect waveguide, respectively. And thin wire optical waveguides 331 to 334 to be connected. The thin optical waveguides 331 to 334 connected to the input / output side of the line defect waveguide respectively form a directional coupler by being partly arranged on the input side and the output side.

[0077] The distance between the cores of the thin optical waveguides 331 to 334 is about 0.2 m, and the length of the coupling site is 2 Set to about 5 μm. In this case, the complete coupling length is about 5 μm, and 3 dB couplers 341 and 342 are formed as directional couplers. The light input from port 1 of the thin optical waveguide 331 is branched in two directions by the 3 dB force bra 341. At this time, at the wavelength corresponding to the band gap of the refractive index guide mode formed by the line defect optical waveguide, the branched light is reflected by the line defect optical waveguide, and further passes through the 3 dB force bra 341 to be multiplexed. The output light is output as drop light from port 2 of the thin optical waveguide 332.

Other wavelength light passes through the output-side 3 dB force bra 342 and is combined and output from the port 4 of the thin-line optical waveguide 334. In addition, it is possible to output light combined from port 4 by inputting light having the same wavelength as that of port 2 from port 3 of the thin optical waveguide 333.

According to the present embodiment, TE-like mode light and TM-like mode light can be multiplexed / demultiplexed by using an optical waveguide using the refractive index guide mode, which is a feature of the present invention. The degree of freedom in designing an optical multiplexing / demultiplexing device is improved.

[0080] (Optical communication device)

Next, a fourth embodiment in which the optical waveguide using the refractive index guide mode of the first embodiment of the present invention is applied to an optical communication device will be described.

As shown in FIG. 21, in the optical communication device of this embodiment, the photonic crystal 42 and the channel waveguide 43 are formed on the SOI substrate 41, and the line defect optical waveguide formed in the photonic crystal 42 is formed. In this configuration, an optical fiber 44 is connected to the waveguide via a channel waveguide 43.

In general, in the optical fiber 44, light propagates while the direction of the electric field vector rotates.

Therefore, the direction of the electric field vector of the light incident on the line defect optical waveguide is indefinite. In other words, the direction of the electric field vector of the light incident on the line-defect optical waveguide can be any direction (Ex) shown in (1), (2), and (3) of FIG.

[0083] By using the optical waveguide utilizing the refractive index guide mode of the embodiment of the present invention, a light beam having a line defect is generated without causing any propagation loss regardless of the direction of the electric field vector. Can propagate light. In FIG. 21, only the configuration of the light input side of the line defect optical waveguide formed in the photonic crystal 42 is shown, but this configuration is also possible in the configuration in which one optical fiber is connected to the output side of the line defect optical waveguide. The electric field of light supplied to the fiber The direction of the vector can be set freely.

Industrial applicability

As described above, the optical waveguide made of the photonic crystal of the present invention is suitable for application to various optical devices including the optical waveguide.

Claims

The scope of the claims

[1] In an optical waveguide made of a photonic crystal obtained by arranging two or more kinds of materials having different refractive indexes with a one-dimensional, two-dimensional or three-dimensional period,

An optical waveguide characterized in that light is propagated using a refractive index guide mode which is an optical waveguide mode having a lowest frequency in the dispersion relationship of the photonic crystal.

[2] In an optical waveguide made of a photonic crystal obtained by arranging two or more kinds of substances having different refractive indexes in a one-dimensional, two-dimensional or three-dimensional period,

Of the two optical waveguide modes that are orthogonal to the light traveling direction,

A line defect waveguide mode is used for the first optical waveguide mode,

An optical waveguide characterized in that light is propagated to the second optical waveguide mode by using a refractive index guide mode which is an optical waveguide mode having the lowest frequency in the dispersion relationship of the photonic crystal.

[3] In an optical waveguide made of a photonic crystal obtained by arranging two or more kinds of materials having different refractive indexes with a one-dimensional, two-dimensional or three-dimensional period,

It is characterized by propagating light by using a refractive index guide mode, which is an optical waveguide mode of the lowest frequency, in two dispersion modes of the photonic crystal in two optical waveguide modes orthogonal to the light traveling direction. Optical waveguide.

[4] The refractive index guide mode is:

4. The optical waveguide according to claim 1, wherein in the dispersion relationship of the photonic crystal, the standard wavenumber k is in a range of 0.25 or more and 0.5 or less.

5. The optical waveguide according to any one of claims 1 to 4, wherein the optical waveguide has periodicity in a light traveling direction.

6. An optical device comprising an optical waveguide comprising the photonic crystal according to any one of claims 1 to 4.

7. An optical communication device comprising an optical waveguide made of the photonic crystal according to any one of claims 1 to 4.