JP4183640B2 - Two-dimensional photonic crystal device - Google Patents

Description

  The present invention relates to a two-dimensional photonic crystal device, and more particularly to a two-dimensional photonic crystal device used in a technical field such as wavelength division multiplexing (WDM).

  Over the past few years, the technological field of wavelength division multiplex communication has made remarkable progress. The advancement and development of this technology is mainly due to efforts to meet the demand for higher communication speeds of network users on the Internet. Since the cost of the components of WDM technology is high, an attempt to construct an Internet network by optical communication using this WDM technology increases the cost of forming the entire optical communication network, but the optical communication circuit It is becoming a major technology that should be adopted in network construction. Today, optical engineering is treated as a medium for the transmission of information in communication networks. Optical engineering in the next-generation communication circuit network is expected as a technology that bears part or all of the switching operation and control operation in optical communication. The new optical engineering technology will open the way for users to lower the cost and improve the performance of WDM components.

By the way, the WDM technology is based on various conventional technologies. The conventional technologies that are the basis include technologies such as Fabry Perot filters, thin film interference filters, Mach-Zehnder filters, birefringent filters, fiber grating Bragg reflection filters, and waveguide diffraction gratings. On the other hand, in an optical integrated circuit, in order to bend a waveguide with low loss, it is necessary to bend gently over a long distance exceeding several hundreds of μm, which leads to an increase in the size of the optical integrated circuit. .
In order to obtain a WDM device having a smaller size and a larger number of channels than a conventional device, the object can be achieved by employing a photonic crystal. The photonic crystal refers to an artificial crystal in which two types of transparent media having greatly different refractive indexes are regularly arranged alternately with a period of about the light wavelength. Photonic crystals have the ability to bend and direct light and be handled on a submillimeter scale to form a complex device composed of a single structure that performs multiple optical functions and is dense. .

The photonic crystal is roughly classified into a one-dimensional photonic crystal in which a medium having a refractive index n _{1 and} a medium having a refractive index n ₂ are alternately arranged one-dimensionally, and a medium having a refractive index n _{1 and} a medium having a refractive index n ₂ . There are a two-dimensional photonic crystal constituted by alternately arranging two-dimensional periodic media, and a three-dimensional photonic crystal comprising a medium having a refractive index n _{1 and} a medium having a refractive index n ₂ alternately arranged in a three-dimensional cycle. . In such a photonic crystal, for example, a medium having a refractive index n ₁ on the high refractive index side is composed of silicon, gallium arsenide, indium phosphorus, or other semiconductor, and a medium having a refractive index n ₂ on the low refractive index side is air. And glass.
As described above, the photonic crystal has a periodic structure in which its constituent elements are arranged with a period of the order of a half wavelength of light. For example, when the low-refractive index medium is air and the high-refractive index medium is a dielectric, the constituent elements of the two-dimensional periodic structure photonic crystal are dielectric pillars arranged in the air, The holes can be arranged in the same manner. An important feature of photonic crystals is the existence of a photonic band gap. In the photonic band gap, light within a certain frequency range is prohibited from propagating. However, the photonic crystal can be used for light control in the sense that by introducing crystal defects inside the photonic crystal, the photonic crystal can be used as a light conducting waveguide. In general, a waveguide in a photonic crystal is formed by breaking components of a periodic structure into a linear shape.

  Patent Document 1 discloses a technique in which crystal defects are formed along a waveguide as a main conventional technique that operates as an Add-Drop filter. As shown in FIG. 24, the Add-Drop filter shown in Patent Document 1 has cylindrical holes 16 arranged in a triangular lattice pattern in a slab 11 made of a material having a higher refractive index than air. It has a two-dimensional photonic crystal structure in which a refractive index distribution is formed, and a linear defect 12 is formed in a periodic array of photonic crystals to form a waveguide, and the periodicity of the photonic crystal is adjacent to this waveguide. The point defect 14 that disturbs the arrangement is provided by changing the diameter of one cylindrical hole 16, and includes a plurality of wavelengths (λ1, λ2,..., Λi,...) That are incident on the waveguide and propagate. Of the light 13 in the wavelength band, light 15 having a specific wavelength (λi) is captured by the point defect 14 and emitted in a direction orthogonal to the surface of the slab 11.

  Further, in Non-Patent Document 1, as shown in FIG. 25A, point defects C1 and C2 made of columns having a different diameter and a different refractive index from the periodic structure column 71 in the periodic structure of the two-dimensional photonic crystal. , C3, and C4, and the periodic structure pillar 71 is linearly removed from one end 72 of the two-dimensional photonic crystal structure to form a waveguide 73, and the waveguide 73 is sequentially branched to provide point defects C1, Four waveguides 73 are provided in the vicinity of C2, C3, and C4 and branched in a state where two pillars 71 having a periodic structure exist before and after the point defects C1, C2, C3, and C4, respectively. The structure provided up to the other end 74 of the crystal is shown, and broadband light incident on the waveguide 73 from the one end 72 side is shown in FIG. 25B by point defects C1, C2, C3, and C4 operating as resonators. Select as shown It has become what is umbrella.

On the other hand, as shown in FIG. 26, Non-Patent Document 2 also includes two linear waveguides 81 and 82 in a two-dimensional photonic crystal structure, and is sandwiched between the two waveguides 81 and 82. It is shown that a point defect 84 made of a column having a diameter and a refractive index different from that of the periodic structure column 83 is provided in the periodic structure column 83, and this point defect 84 is operated as a resonator. Of the multi-wavelength light propagating through the waveguide 81, only light of a specific wavelength is selected and propagated to the waveguide 82.
JP 2001-272555 A C. Jin, S. Han, X. Meng, B. Cheng, and D. Zhang, “Demultiplexer using directly resonant-tunneling between point defects and waveguides in a photonic crystal” J. Appl. Phys., 2002, Vol. 91 , No.7, P.4771-4773 S.Fan, PRVilleneuve, JDJoannopoulos, and HAHaus “Channel drop filters in photonic crystals” Opt.Express, 1998, Vol.3, No.1, P.4-11

As described above, conventionally, a waveguide is formed by a linear defect in the photonic crystal structure, and a point defect that functions as a resonator is formed in the periodic structure of the photonic crystal adjacent to the waveguide. Thus, a two-dimensional photonic crystal device that functions as a wavelength selection filter has been realized.
However, in the configuration shown in Patent Document 1, for example, when the wavelength of propagating light is 1.55 μm, the thickness of the wall of the slab 11 between the cylindrical hole 16 that forms the periodic structure and the cylindrical hole that forms the point defect 14. The thickness is about 0.06 μm, and since it is extremely thin, it has been difficult to manufacture. Further, in the configurations shown in Non-Patent Documents 1 and 2, a column having a different refractive index must be formed as a point defect among the columns constituting the periodic structure of the two-dimensional photonic crystal, and the refractive index is changed. Is not easy in manufacturing, and in particular, in the case of forming four point defects and having four channels as in the configuration of Non-Patent Document 2 shown in FIG. 25A, two media constituting a photonic crystal In addition to these, four more media having different refractive indexes are required, which makes it extremely difficult to manufacture.
An object of the present invention is to provide a two-dimensional photonic crystal device that is easy to manufacture and can be used as an excellent wavelength selective filter.

According to the present invention, in the two-dimensional photonic crystal device, the columns made of the second medium having the second refractive index different from the first refractive index are embedded in the first refractive index in the first medium layer in the rows and columns at the same interval. A two-dimensional photonic crystal, a linear waveguide formed by crystal defects in the photonic crystal, and a resonance column provided on the linear waveguide and made of the second medium. The resonance column includes a main column arranged at the center in the width direction of the linear waveguide, a set of sub-columns arranged on the light incident side with respect to the main column, and a light beam with respect to the main column. It consists of a set of sub-pillars arranged on the exit side. The set of sub-pillars arranged on the light emission side is composed of two sub-pillars, and the two sub-pillars have their centers aligned with the center in the width direction of the linear waveguide, and the linear guides are arranged. They are arranged in the width direction of the waveguide.

  According to the two-dimensional photonic crystal device according to the present invention, the resonance column is formed of the same medium as the column constituting the periodic structure of the two-dimensional photonic crystal, and thus is manufactured using only two types of media having different refractive indexes. Therefore, it can be manufactured very easily.

  Embodiments of the present invention will be described with reference to the drawings.

First, the basic structure of the two-dimensional photonic crystal device of Example 1 will be described with reference to FIG. In this example, in the two-dimensional photonic crystal device, a SiO ₂ oxide film 61 is formed on a substrate 6 made of silicon, and a silicon thin film formed on the SiO ₂ oxide film 61 is patterned using a lithography technique and an etching technique. Formed by.
The pillars 62 formed by patterning the silicon thin film are arranged in rows and columns at the same interval in a columnar shape, that is, in a square lattice, and in the air (refractive index 1.0). A two-dimensional photonic crystal is constituted by the periodic structure of the pillars 62 made of silicon (refractive index 3.4). This two-dimensional photonic crystal has crystal defects in which one column 62 is removed, that is, one column 62 is not formed, and a resonator is provided in a linear waveguide 5 formed by the crystal defect. 51 is formed.

In this example, the resonator 51 is configured by providing five resonance columns made of silicon on the linear waveguide 5. The five resonance columns having a columnar shape are the main column 21 and the main column 21. Are composed of two sub-columns 23 positioned on the light incident side of the waveguide 5 and two sub-columns 22 positioned on the light output side of the waveguide 5 with respect to the main column 21. ing.
Each of the two sub pillars 22 and 23 is arranged in a direction orthogonal to the extending direction of the waveguide 5, that is, in the width direction of the waveguide 5, and the center of the two sub pillars 22 and the two sub pillars are arranged. The center of 23 coincides with the center of the waveguide 5 in the width direction. The main column 21 is located at the center of the waveguide 5 in the width direction. An arrow 31 in FIG. 1 indicates the direction of light propagating through the waveguide 5. The main pillar 21 and the sub pillars 22 and 23 constituting the resonator 51 are formed together with the pillar 62. FIG. 1A is a diagram schematically showing the height of the pillar 62, the main pillar 21, and the auxiliary pillars 22 and 23 in a greatly compressed state.

In this example, as described above, in the two-dimensional photonic crystal, the first medium layer having the first refractive index is constituted by air, and the second medium having the second refractive index different from the first refractive index is made of silicon. The column 62 is embedded in air.
In the two-dimensional photonic crystal, a photonic band gap is formed, and light propagation is prohibited for in-plane light in a predetermined wavelength range. On the other hand, in the linear waveguide 5, the wavelength range in which light can propagate is relatively large, and light having a wavelength within the photonic band gap propagates. By arranging the resonator 51 in this waveguide 5, Only light of a specific wavelength resonates and passes through the resonator 51. Therefore, this two-dimensional photonic crystal device functions as a wavelength selection filter. The main column 21 functions to selectively transmit light of a specific wavelength, and the sub columns 22 and 23 function to control the sharpness of the peak of the transmitted light, that is, to increase the Q factor. This will be described in the following specific configuration.

Next, a specific configuration of the two-dimensional photonic crystal device will be described. FIG. 2 shows a configuration of a two-dimensional photonic crystal device for WDM that can be used to separate and transmit multi-wavelength light into light of different wavelengths in the field of wavelength division multiplex communication (WDM). In the periodic structure of pillars 62 made of silicon arranged in a square lattice, five waveguides 5 ₀ , 5 ₁ , 5 ₂ , 5 ₃ , and 5 ₄ are each removed by one column 62. Is formed.
The periodic structure of the pillars 62 forms a photonic band gap with respect to light in the wavelength range of 1.15 to 1.80 μm, the diameter d of the pillars 62 is 0.2 μm, and the lattice interval a is 0. It is 5 μm. The height of the column 62 is determined according to the spot diameter of the incident light, and is about 10 μm, for example.

Waveguide 5 ₀ in a portion where the multi-wavelength optical incident, located in the longitudinal center of the two-dimensional photonic crystal device plane shape a rectangular shape, from one long side 41 of the rectangle other long side 42 The column 62 is formed by removing 12 columns in a row. Waveguide ₅ 3, _{5 4} are formed on the waveguide _{5 0} perpendicular direction so as to reach from the inner end of the waveguide _{5 0} in a rectangular two short sides 43 and 44, waveguide ₅ 1, _{5 2} It is formed in the waveguide 5 ₀ perpendicular direction to reach the respective two short sides 43, 44 from the middle of the waveguide 5 _0. Incidentally, the waveguide 5 _1, 5 ₂ posts 62 located 5 times the position of the lattice spacing a from the outermost pillar 62 along the long side 41 is constructed by removing one column, waveguide 5 _3, 5 ₄ Is constructed by removing one column of columns 62 located at a position five times the lattice interval a from the next column 62 after the position where one column is removed.

Waveguide _{5 1,} 5 _2, 5 3, ₅ respectively ₄ resonator _{51 1,} 51 _2, 51 3, 51 ₄ are formed different from each other these resonators _{51 1,} 51 _2, 51 3, 51 ₄ Only light of a specific wavelength is transmitted, and light of the specific wavelength is emitted from each of the waveguides 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ . Therefore, in this example, these waveguides 5 ₁ , 5 ₂ , 5 ₃ and 5 ₄ constitute four channels (output channels) ₁ , ₂ , ₃ and ₄ .
Resonator ₅₁ 1 for each channel _1-4, 51 _2, 51 3, 51 ₄ of the configuration and the transmission characteristics of light obtained by simulation using the software "Full Wave" is the name of Rsoft Inc. company. This software is created based on the Finite Difference Time Domain method (FDTD).
Here, by determining the diameter of the main column 21 of each resonator 51 ₁ , 51 ₂ , 51 ₃ , 51 ₄ first and optimizing the configuration and position of the sub-columns 22, 23, the transmittance is high and the peak is increased. Steep and high Q factor transmitted light can be obtained.

Figure 3A~D, is shown by omitting the columns 62 located resonator ₅₁ 1 of each channel 1-4 is obtained by _simulation, 51 _2, 51 3, 51 ₄ of the arrangement on both sides, 4 Shows the relationship between the wavelength and the transmittance of the light of each of the channels 1 to ₄ selectively transmitted by the resonators 51 ₁ , 51 ₂ , 51 ₃ , and 51. In FIG. 4, 1, 2, 3, and 4 attached to the waveform indicate channel numbers.
First, the configuration of each resonator 51 ₁ , 51 ₂ , 51 ₃ , 51 ₄ will be described. 3A to 3D, the light incident side is shown as the left side of the paper as indicated by the arrow 31. The diameter of the main column 21 in resonator 51 ₁ 0.24 .mu.m, the resonator 51 ₂ 0.28 .mu.m, the resonator 51 ₃ 0.30 .mu.m, was 0.34μm in the resonator 51 _4. These main column 21 is located at the 5 times the distance of the lattice spacing a from the widthwise center of the waveguide 5 ₀ As shown in FIG.

Fukuhashira 22 and 23 similar to the resonator 5 shown in resonator ₅₁ 1, 51 ₂ in Fig. 1, arranged two by two across the main column 21, thus these resonators ₅₁ 1, 51 ₂ is present a total of 5 having a pillar to the waveguide ₅ 1, _{5 2.} On the other hand, the resonators ₅₁ 3, 51 ₄ and the other one for the main column 21 side of the two sub pillars 23, adds Fukuhashira 24, thus these resonators ₅₁ 3, 51 ₄ is six pillars In the waveguides 5 ₃ and 5 ₄ .
The diameters of the sub pillars 22, 23 and 24 are all 0.1 μm, and the distance between the two sub pillars 22 and the distance between the two sub pillars 23 are both 0.2 μm. Further, the distance between the two sub pillars 23 and the main pillar 21 is 0.7 μm, and the distance between the main pillar 21 and the two sub pillars 22 is 0.9 μm. The sub pillar 24 is located on a line passing through the center of the main pillar 21 in the light incident direction, and the distance between the sub pillar 24 and the main pillar 21 is 0.55 μm.

The resonator _{51 1,} 51 _2, 51 3, 51 ₄ of each channel 1-4 is configured as described above, each of the waveguides _{5 0} when incident light in a wavelength range of 1.15~1.80μm light selective transmission by the channel 1-4 is as shown in FIG. 4, the light of the channel 1 wavelength 1.306μm is selected transmitted by the resonator 51 _1, the channel 2, 3 and 4 wavelengths 1.390μm , 1.452 μm and 1.587 μm are selectively transmitted, and as shown in FIG. 4, these four wavelengths of light have extremely steep peaks. Note that FIG. 4 shows the relationship between the wavelength and the transmittance obtained individually for each of the channels 1, 2, 3, and 4 overwritten.
Table 1 shows the light transmittance of these four wavelength in each channel 1-4 when caused to enter the four wavelengths of light from each waveguide 5 ₀ summarized in Table.

Figure 5A~D have the meanings indicated 1.306μm, 1.390μm, the electric field distribution at a moment when made incident respectively light of the four wavelengths from the waveguide _{5 0} of 1.452μm and 1.587μm, + Indicates a positive electric field, and − indicates a negative electric field. As can be seen from Figure 5A, the light of wavelength 1.306μm can not propagate channels 2, 3, 4, and resonance occurs only the resonator 51 ₁ channel 1 propagates channel 1. Similarly, the light of wavelength 1.390μm propagates the channel 2 resonates only the resonator 51 ₂ of the channel 2 as shown in Figure 5B, the channel so that light of a wavelength 1.452μm is shown in FIG. 5C 3 only resonates in the resonator 51 ₃ propagates through the channel 3, the light of wavelength 1.587μm is resonated in the resonator 51 ₄ channels 4 only propagate channel 4 as shown in FIG. 5D.
Therefore, according to this two-dimensional photonic crystal device, the incident wavelength multiplexed light can be separated and selected into four different wavelengths of light and transmitted.

FIG. 6 shows the relationship between the diameter d ₁ of the main column 21 and the wavelength of transmitted light. It can be seen that the wavelength that is selectively transmitted increases as the diameter d ₁ is increased.
Here, the role of the main column 21 and the sub-columns 22 and 23, which are elements of the resonator 51, will be described based on a simulation result in which one channel is used.
First, as shown in FIG. 7A, and as having a waveguide 5 ₁ 2-dimensional photonic crystal device constituting the waveguide 5 ₀ and channel 1, formed by arranging only the main column 21 to the waveguide 5 ₁ The resonator 51a is simulated. Here, the diameter of the main column 21 is 0.28 μm. From the waveguide 5 ₀ in Figure 7A is shown the electric field distribution when light is incident, Figure 7B is a waveguide 5 ₀ when applying a light having a wavelength range of 1.15~1.80μm The wavelength-transmission characteristic of the light selectively transmitted by the resonator 51a is shown. The transmittance peak is 1.4 μm wavelength, and light having a wavelength of 1.4 μm is selected, but broadband light of 1.15 to 1.65 μm is transmitted, that is, the selectively transmitted light has a peak. Is not steep and the spread is large, so the Q factor is not good.

The presence of the main column 21 changes the local limitation of the electric field or electric field interval, and leads to selection of the light wavelength. The negative electric field and the positive electric field always exist partially on both sides of the main pillar 21 in the waveguide extension direction. Therefore, it can be analogized that the role of the main pillar 21 is to select the transmission wavelength.
FIGS. 8A to 8C show electric field distributions of light having wavelengths of 1.2 μm, 1.4 μm, and 1.6 μm, respectively, in the resonator 51a of FIG. 7A in which only the main column 21 is arranged, and are shown in FIG. 8A. In the case of the wavelength of 1.2 μm and the case of the wavelength of 1.6 μm shown in FIG. 8C, it can be seen that the electric field distribution is asymmetric with respect to the resonator 51a, that is, with the main column 21 as the center. This asymmetry results in low transmittance at these wavelengths. On the other hand, at a wavelength of 1.4 μm shown in FIG. 8B, an electric field distribution is generated symmetrically with respect to the main column 21, and the transmittance is increased by this symmetrical electric field distribution.

As described above, the transmission wavelength of the main column 21 is selected. However, the Q factor of the transmission wavelength is not high, and the Q factor is configured by forming an optical cavity that confines an electric field before and after the main column 21 in the light transmission direction. Can be increased. Such a cavity is constituted by the presence of the sub-columns 22, 23 and 24.
Figure 9A is a two-dimensional photonic resonator 51 ₂ arranged in the channel 2 of the crystal device shown in Figure 2 shows the electric field distribution of light of wavelength 1.390μm is permselective. The resonator 51 ₂ As is surrounded by a dotted line, looks 4 mirror C. Two sub column 22 defines an emission side mirror range of the resonator 51 ₂ light, two sub pillars 23 defines a mirror range of the light incident side. Further, 5 pillars 62 of the periodic structure of the photonic crystal located respectively on both sides in the width direction of the waveguide 5 ₂ defines the mirror range of the resonator 51 ₂ in the width direction on both sides of the waveguide 5 _2. It can be said that the four-sided mirror C is constituted by _two optical cavities C ₁ and C ₂ indicated by bold lines, and positive and negative electric fields are confined in these optical cavities C ₁ and C ₂ as shown in FIG. 9A. . High-level electric field confinement occurs when the spatial arrangement of the electric field coincides with the resonance wavelength, and the peak becomes sharp. The electric field is locally limited to the vicinity of the main column 21 and the sub-columns 22 and 23. Resonator 51 ₂ reflects light of non-resonant wavelength, 1 two optical cavities C _1, C ₂ confinement only light of resonance wavelength, thus a high Q-factor of about 300, according to the resonator 51 ₂ .Light having a wavelength of 390 μm is selectively transmitted. 9B is a wavelength when the light is incident in the wavelength range 1.15~1.80μm to the resonator 51 ₂ - shows the transmission characteristics.

Electric field distribution and the wavelength when the relative resonator 51 ₂ described above have deleted the two sub pillars 22 - transmission characteristics Fig 10 (1) A, shown in B. The field distribution and the wavelength of deleting the two sub pillars 23 with respect to the resonator 51 ₂ - transmission characteristics Fig 10 (2) A, shown in B. Furthermore, the electric field distribution and the wavelength in the case where is located a single sub-pillars 23 remaining waveguide width direction center with respect to the resonator 51 ₂ Remove secondary column 23 only one - the transmission characteristics 10 ( 3) Shown in A and B. 10 (1) B and FIG. 10 (2) B have a wide peak width and transmit broadband light, and FIG. 10 (3) B shows a fairly steep peak.

Figure 11 (1) A is similar to the configuration shown in FIG. 7A, has a waveguide _{5 1} constituting the waveguide _{5 0} and channel 1, the main column 21 to the waveguide _{5 1} and of the two sub-pillars 22 , which shows a two-dimensional photonic crystal device the resonator 51 ₅ made more and 23 formed by arranged, where the diameter of the main column 21 is set to 0.32 [mu] m. Such size Satoshi diameter of the main column 21, the light selective transmission by the channel 1 when the light is incident in the wavelength range 1.15~1.80μm from the waveguide _{5 0} 11 (1) to B now shown, light of wavelength 1.530μm is selected transmitted by the resonator 51 _5. It shows the electric field distribution when light is incident of the wavelength 1.530μm from the waveguide _{5 0} in FIG. 11 (1) A.

On the other hand, FIG. 11 (2) A whereas FIG 11 (1) A, only the changed width of the waveguide _{5 1,} showed the electric field distribution of light of wavelength 1.530μm when made into narrower than 1 [mu] m 0.8 [mu] m FIG. 11 (2) B shows the wavelength-transmission characteristics of light in the configuration shown in FIG. 11 (2) A. These views 11 (2) A, when B is a width of the waveguide _{5 1} to 0.8 [mu] m, light in the wavelength range of 1.15~1.80μm indicates that it is not possible to propagate in the waveguide _{5 1} ing.
In contrast, FIG. 11 (3) A is wider width of the waveguide _{5 1,} which shows the electric field distribution of light of wavelength 1.530μm in the case of the 1.2 [mu] m, FIG. 11 (3) B Fig. 11 shows the wavelength-transmission characteristics of light in the configuration shown in Fig. 11 (3) A. These views 11 (3) A, although the optical waveguide 5 ₁ if you increase the width of the waveguide 5 ₁ than B propagates, the width of the peak of the light selective transmission by the resonator 51 _5b is widened, It turns out that Q factor worsens.

11 (1) A to (3) A, the distance between the two sub-columns 23 and the main column 21 and the distance between the main column 21 and the two sub-columns 22 are 0.7 μm and 0.9 μm, respectively. That is, the dimensions of the optical cavities C ₁ and C ₂ (see FIG. 9A) are the same in the waveguide extension direction, but the dimensions of the optical cavities C ₁ and C ₂ are different because the dimensions in the waveguide width direction are different. has become a thing, it shows that the volume of the optical cavity C _1, C ₂ is outside the preferred volume not act effectively as an optical cavity C _1, C _2. That is, the volumes of the optical cavities C ₁ and C ₂ play an important role in increasing the selective transmission of light and the Q factor of the transmitted light, and making the peak steep.

Next, an example resonator 51 ₂ disposed in the channel 2 in FIG. 2, the relationship between the positional relationship between the transmission characteristics of the waveguide extending direction of the main column 21 and Fukuhashira 22 and 23 constituting the resonator 51 ₂ Description To do.
FIG. 12B shows the change in transmittance when the positions of the sub-columns 22 and 23 are fixed as shown in FIG. 12A and only the position of the main column 21 is changed in the waveguide extension direction. position of the pillar 21 is the maximum transmittance is obtained in the initial position of L _{1 =} 0 .mu.m, decrease in transmittance even when changing the position of the main column 21 is gradual, 0 L ₁ from -0.1Myuemu. A transmittance higher than 25% can be obtained within the range of 4 μm. Therefore, in order to obtain a high transmittance, the position of the main pillar 21 between the sub pillar 22 and the sub pillar 23 in the waveguide extension direction is not particularly required to be high. This is a major feature of the present invention.

Further, the fact that the transmittance can be set to a desired value by selecting the position of the main pillar 21 indicates that the optical attenuation function can be provided, that is, the output with respect to the intensity of the input light. It shows that the light intensity ratio can be set to a desired value. This is capable of realizing both the wavelength selection filter function and the optical attenuation function at the same time, which is a major feature of the present invention.
FIG. 13B shows the change in transmittance when the positions of the main pillar 21 and the sub pillar 22 are fixed as shown in FIG. 13A and the positions of the two sub pillars 23 are changed in the waveguide extension direction. The maximum transmittance is obtained at the initial position of L ₂ = 0 μm at the positions of the _two sub-columns 23, and the position accuracy of the sub-columns 23 is higher than that of the main column 21 described above. It is what is required.

FIG. 14B shows the change in transmittance when the positions of the main pillar 21 and the sub pillar 23 are fixed as shown in FIG. 14A and the positions of the two sub pillars 22 are changed in the waveguide extending direction. As for the position of the two sub-columns 22, the maximum transmittance is obtained at the initial position of L ₃ = 0 μm, and the position accuracy of the sub-column 22 is required to be high as in the case of the sub-column 23. It has become.
FIG. 15B shows the change in transmittance when the positions of the sub-columns 22 and 23 are simultaneously changed in the waveguide extending direction with respect to the main column 21 as shown in FIG. 15A. The positions 23 are moved closer to each other or moved away from each other. From FIG. 15B, the maximum transmittance is obtained at the initial position of L ₄ = 0 μm, and a high transmittance is obtained even at L ₄ = 0.4 μm. However, when L ₄ = 0.4 μm, the transmission wavelength is wide. As a result, the Q factor was poor.

Then, in addition to the two sub pillars 23 on the incident side of light in the resonator 51 ₄ resonators 51 ₃ and the channel 4 of the channel 3, as shown in Figure 3C and D, provided the other one sub-pillar 24 This point will be described based on the simulation result in channel 4.
As shown in Table 1, the transmittance of light having a wavelength of 1.587 μm in channel 4 is 29%. If the sub pillar 24 is removed here, the transmittance is reduced to 4%. On the other hand, in the channels 1 and 2, as shown in Table 1, a high transmittance of 63% or 70% is obtained without providing such a sub pillar 24.

This is despite initially in channels 1 branches into Fukuhashira 24 from the waveguide 5 ₀ which light is incident is not required, then it branched provided Fukuhashira 24 in channels 3 and 4 are It is presumed that the provision of the auxiliary pillars 24 is important for increasing the number of channels and maintaining a high light transmittance.
According to the above-described example, the five or six resonance columns such as the main column 21 and the sub columns 22, 23, and 24 that constitute the resonator 51 are the columns 62 that constitute the periodic structure of the two-dimensional photonic crystal. And a configuration in which a point defect (column) for resonance is provided by a medium having a refractive index different from that of the column forming the periodic structure, as in the configuration described in Non-Patent Documents 1 and 2. In contrast, since the device can be manufactured using only two media constituting the photonic crystal, the manufacturing becomes extremely easy.

  Further, in the configuration described in Patent Document 1, the wall between the point defect 14 made of a cylindrical hole and the cylindrical hole 16 having a periodic structure becomes, for example, about 0.06 μm when the wavelength of propagating light is 1.55 μm. However, in this example, the gap between adjacent pillars is at least 0.1 μm, that is, the thickness of the air layer is at least 0.1 μm. It can be easily manufactured. Further, the center wavelength of the selectively transmitted light is basically determined by the diameter of the main column 21. In this example, there is a large space around the main column 21, and the diameter of the main column 21 is selected in a wide range. Therefore, as a result, it is possible to select wavelengths of a plurality of channels such as four channels for light in a wide wavelength range.

In addition, although the incident light 13 is incident in the in-plane direction of the slab 11 from the waveguide end face in the configuration described in Patent Document 1, the light 15 captured and selected by the point defect 14 is emitted in a direction perpendicular to the slab surface. Therefore, for example, it is difficult to arrange a device that receives the emitted light, and it is difficult to handle in this respect. However, in this example, since light is incident and emitted in the same plane, this point is easy to handle. It has become a thing .

In the second embodiment, in the portion constituting the resonator, the width of the linear waveguide is locally narrowed so that a high Q factor can be obtained, the performance of the resonator is improved, and more excellent wavelength selection characteristics. The basic structure of the two-dimensional photonic crystal device of Example 2 is shown in FIG. Note that portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
In this example, the positions of the pillars 62 of the periodic structure located on both sides in the width direction of the waveguide 5 are shifted in the portion constituting the resonator 51 of the waveguide 5, so that the width of the waveguide 5 is changed with respect to the center line. It is narrowed symmetrically. As shown in FIG. 16 with dots, the columns 62 for shifting the position are five columns 62 each defining both sides of the resonator 51 in the waveguide width direction. The positions of the columns 62 are sequentially shifted, and the width of the waveguide 5 is narrowest at the center of the resonator 51 where the main column 21 is located, and symmetrically from this position toward the light incident side and the light emitting side. It has been spread.

The resonator 51 is configured by forming the main column 21 and the two sub-columns 22 and 23 in the waveguide 5 having such a narrow width. By adopting such a configuration, the resonator 51 is formed. A high Q factor can be obtained.
FIG. 17 shows a specific configuration of a two-dimensional photonic crystal device having such a resonator structure, as in the device shown in FIG. FIG. 2 shows a configuration of a two-dimensional photonic crystal device for WDM that can be separated and selected into two different lights, and the same reference numerals are given to portions corresponding to those in FIG. 2, and detailed description thereof is omitted. .

Hereinafter, the configuration and light transmission characteristics of the resonators 51 ₆ , 51 ₇ , 51 ₈ , and 51 ₉ of the channels 1 to 4 obtained by simulation will be described.
First, it will be described with reference to FIGS. 18 to 21 the construction of the resonator _{51 6,} 51 _7, 51 8, 51 _9. The diameter of the main column 21 in this example the resonator 51 ₆ 0.276μm, the resonator 51 ₇ 0.280μm, the resonator 51 ₈ 0.284μm, there is a 0.288μm in resonator 51 _9. Each of the two sub-columns 22 and 23 has a diameter of 0.1 μm, and the interval between the two sub-columns 22 and the interval between the two sub-columns 23 are both 0.2 μm. Further, the distance between the two sub pillars 23 and the main pillar 21 is 0.7 μm, and the distance between the main pillar 21 and the two sub pillars 22 is 0.9 μm. In this example, the resonators 51 ₈ and 51 ₉ of the channels 3 and ₄ are also arranged in the waveguides 5 ₃ and 5 ₄ with five columns including the main column 21 and the two sub-columns 22 and 23 respectively. It has become a thing.

Each of the five pillars 62 positioned on both sides of the waveguide width direction and shifted in position (in this example, the pillars are 62 ₁ , 62 ₂ , 62 ₃ , 62 ₄ , 62 ₅ in order from the light incident side). position of) is that in column 62 ₁ 0.05 .mu.m, the pillars 62 ₂ 0.1 [mu] m, the pillars 62 ₃ 0.15 [mu] m, the pillars 62 ₄ 0.1 [mu] m, the pillars 62 ₅ 0.05 .mu.m, respectively the waveguide width direction toward the center, it is offset in any of the resonator _{51 6,} 51 _7, 51 8, 51 _9.
Figure 22 is permselective by each channel 1-4 when the resonator _{51 6,} 51 _7, 51 8, 51 ₉ of each channel 1 to 4 is incident light from the structure described above, the waveguide _{5 0} The relationship between the wavelength of transmitted light and the transmittance is obtained separately and overwritten, and in this example, light of four wavelengths can be selectively transmitted within a narrow wavelength range of 1.35 μm to 1.42 μm. These four wavelengths of light have extremely steep peaks and a Q factor between 400 and 600 is obtained.

Figure 23 is shows the electric field distribution when the light of resonance wavelength is incident on the resonator 51 ₇ disposed in the channel 2 as an example, the electric field is almost entirely in the resonator 51 _7, i.e. the optical cavity It can be seen that the light confinement performance is improved.
The diameter of the main column 21 is set to 0 from the diameter of the main column 21 of each of the channels 1 to 4 shown in FIGS. 18 to 21 and the wavelength-transmission characteristics of the transmitted light of each of the channels 1 to 4 shown in FIG. It was found that when the wavelength was changed by 4 nm, the selected wavelength was changed by 1 nm.
The two-dimensional photonic crystal device as described above has a shape and dimension that can be formed by using a lithography technique and an etching technique, and is formed by using techniques such as electron beam lithography and inductively coupled plasma etching, for example. .

2 and 17, the number of channels is 4 in both devices, but the number of channels can be more than 4 or less than 4.
Further, in the above description, a two-dimensional photonic crystal is configured by periodically arranging columns made of silicon in the air, and a column structure using a resonance column made of silicon is used. For example, even when a hole structure is employed in which holes are periodically formed in a dielectric such as silicon and a resonance hole is formed, the same result as described above can be obtained.
The two media to be used are silicon and air in the above description, but are not limited to these media. For example, a dielectric material such as indium phosphide or gallium arsenide may be used instead of silicon.

A is a perspective view schematically showing a basic configuration of the first embodiment of the present invention, and B is a plan view of A. FIG. The top view which shows the specific structure of 1st Example of this invention. A is a partially enlarged plan view showing a main configuration of a resonator 51 ₁ channel 1 in FIG. 2, B is a partially enlarged plan view showing a main configuration of a resonator 51 _{and second} channel 2 in FIG. 2, C is 2 partially enlarged plan view showing a main configuration of a resonator 51 ₃ channel 3 in, D is partially enlarged plan view showing a main configuration of a resonator 51 ₄ channels 4 in FIG. The figure which shows the wavelength-transmission characteristic of the transmitted light each selectively permeate | transmitted by the channels 1-4 of the device of FIG. A is a plan view showing an electric field distribution when light having a wavelength of 1.306 μm is incident on the device of FIG. 2, and B is a plane showing an electric field distribution when light having a wavelength of 1.390 μm is incident on the device of FIG. Fig. C is a plan view showing the electric field distribution when light having a wavelength of 1.452 µm is incident on the device of Fig. 2, and D is the electric field distribution when light having a wavelength of 1.587 µm is incident on the device of Fig. 2. FIG. The figure which shows the relationship between the diameter of the main pillar 21 of a resonator, and the wavelength of transmitted light. A is a plan view showing a one-channel two-dimensional photonic crystal device and a field distribution of the one-channel two-dimensional photonic crystal device provided with a resonator in which only the main column 21 is arranged in the waveguide, and B is a wavelength-transmittance of transmitted light of the device shown in A. The figure which shows a characteristic. A is a partially enlarged plan view showing an electric field distribution in the vicinity of the main column when light having a wavelength of 1.2 μm is incident on the device shown in FIG. 7A, and B is a light having a wavelength of 1.4 μm applied to the device shown in FIG. 7A. FIG. 7C is a partially enlarged plan view showing the electric field distribution in the vicinity of the main column when it is incident, and C is a partial enlarged plane showing the electric field distribution in the vicinity of the main column when light having a wavelength of 1.6 μm is incident on the device shown in FIG. 7A. Figure. A is a partially enlarged plan view showing the electric field distribution of the resonator 51 ₂ channels 2 of the device shown in Figure 2, B is the wavelength of the cavity of the A - showing transmission characteristics. (1) A is a partially enlarged plan view showing an electric field distribution of a resonator in which two sub-columns 22 are deleted from the resonator of FIG. 9A, and (1) B is (1) wavelength-transmission characteristics of the resonator of A. (2) A is a partially enlarged plan view showing the electric field distribution of the resonator in which the two sub-columns 23 are deleted from the resonator of FIG. 9A, (2) B is (2) the wavelength of the resonator of A— (3) A is a partially enlarged plane showing an electric field distribution of a resonator in which one sub-column 23 is deleted from the resonator of FIG. 9A and the remaining one is arranged at the center in the width direction of the waveguide. FIG. 3B is a diagram showing the wavelength-transmission characteristics of the resonator of FIG. (1) A is a plan view showing a one-channel two-dimensional photonic crystal device provided with a resonator in which a main column 21 and two sub-columns 22 and 23 are arranged in a waveguide, and an electric field distribution thereof. (1) B is (1) the wavelength of the resonator a - showing transmission characteristics, (2) a is 0 to 1μm only the width of the waveguide 5 ₁ resonator is provided in the device (1) a FIG. 8 is a plan view showing the configuration narrowed to 8 μm and its electric field distribution, (2) B is a diagram showing the wavelength-transmission characteristics of (2) A resonator, and (3) A is (1) the resonator of the device of A. plan view showing a configuration and an electric field distribution and spread to 1.2μm from 1μm only waveguide 5 _first width provided is, (3) B is (3) the wavelength of the resonator a - shows the transmission characteristic Figure . A is a diagram showing a direction of changing the position of the main column 21 in the resonator 51 ₂ shown in FIG. 3B, B is a diagram showing a change in transmittance in the case of changing the position of the main pole 21 as shown in A . A is a view showing FIG, B is a variation of the transmittance in the case of changing the position of Fukuhashira 23 as shown in A indicating the direction of changing the position of the sub-pillar 23 in the resonator 51 ₂ in FIG. 12A. A is a view showing FIG, B is a variation of the transmittance in the case of changing the position of Fukuhashira 22 as shown in A indicating the direction of changing the position of the sub-pillar 22 in the resonator 51 ₂ in FIG. 12A. A is a diagram showing a direction of changing the position of the sub-pillar 22, 23 at the same time in the resonator 51 ₂ in FIG. 12A, B is the change in transmittance in the case of changing the position of Fukuhashira 22 and 23 as shown in A FIG. A is a perspective view schematically showing a basic configuration of a second embodiment of the present invention, and B is a plan view of A. FIG. The top view which shows the specific structure of the 2nd Example of this invention. Partially enlarged plan view showing a configuration of a resonator 51 ₆ Channel 1 in Figure 17. Partially enlarged plan view showing a configuration of a resonator 51 ₇ channel 2 in FIG. 17. Partially enlarged plan view showing a configuration of a resonator 51 ₈ channel 3 in FIG. 17. Partially enlarged plan view showing a configuration of a resonator 51 ₉ of the channel 4 in Fig. 17. The figure which shows the wavelength-transmission characteristic of the transmitted light each selectively permeate | transmitted by the channels 1-4 of the device of FIG. Partially enlarged plan view showing the electric field distribution of the resonator 51 ₇ channels 2 of the device shown in Figure 17. The perspective view which shows the 1st prior art example of a two-dimensional photonic crystal device. A is a plan view showing a second conventional example of a two-dimensional photonic crystal device, and B is a diagram showing frequency characteristics of incident light and selected transmitted light of the device of A. FIG. The top view which shows the 3rd prior art example of a two-dimensional photonic crystal device.

Claims (2)

A two-dimensional photonic crystal in which columns made of a second medium having a second refractive index different from the first refractive index are embedded in rows and columns at the same interval in a first medium layer having a first refractive index;
A linear waveguide composed of the crystal defects in the photonic crystal;
A resonance column provided on the linear waveguide and made of the second medium ;
The upper Symbol resonance pillar main pillars arranged in the width direction center of the line waveguide, a set of Fukuhashira arranged on the light incident side with respect to the main post, the light for the main column Na more and set of arranged Fukuhashira the exit side is,
Set of Fukuhashira disposed on the exit side of the upper Symbol light consists of two Fukuhashira, they two Fukuhashira their centers are coincident in the widthwise center of the line waveguide and the linear A two-dimensional photonic crystal device characterized by being arranged in the width direction of a waveguide. In the two-dimensional photonic crystal device according to claim 1 Symbol placement,
2. A two-dimensional photonic crystal device, wherein the width of the linear waveguide is narrowed symmetrically with respect to the center line of the linear waveguide at a portion where the resonance column is located.

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