JPH11218627A - Photonic crystal waveguide and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize characteristics of the photonic crystal waveguide and to reduce the manufacturing cost. SOLUTION: The photonic crystal waveguide is provided with a photonic crystal 14 structure which has a slab optical waveguide 3 on the top surface of a substrate 2 and also has refractive index variation areas 13 with a different refractive index from that of the core layer of the slab optical waveguide 3 arranged in a lattice array shape at part of the slab optical waveguide 3. In this case, the refractive index variation areas 13 are formed of the same material as the material constituting the core layer of the slab optical waveguide 3. The refractive index variation areas 13 are arranged in the lattice array shape on both the sides of an optical waveguide area 6 where light is propagated. The refractive index of the core layers of the refractive index variation areas 13 is larger than that of the core layer of an area off the refractive index variation areas 13 and the relative index difference is about 10<-4> to 10<-2> . A unit lattice is in regular triangle array.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photonic crystal waveguide and a method of manufacturing the same, for example, in the field of an optical communication system, an optical switching system, or an optical measurement system, transmitting an optical wavelength (wavelength transmission of propagating light) or an optical measuring system. The present invention relates to a technology effective when applied to an optical filter, an optical multiplexer / demultiplexer, an optical dispersion compensating device, and the like for blocking (wavelength limitation of propagating light).

[0002]

2. Description of the Related Art A photonic crystal waveguide is known as one of optical filters used in an optical communication system or the like.

[0003] For photonic crystal waveguides, JD
Joannopoulos et al., “Photonic Crystals” Princeton Univ.
ersity Press, 1995.pp94-pp104.

FIGS. 10 and 11 are views showing a conventional photonic crystal waveguide. Photonic crystal waveguide 1
Is composed of a substrate 2 and a slab optical waveguide 3 provided on the surface of the substrate 2, and a plurality of air holes 9 in a grid array on both sides of an optical waveguide region 6 through which light of the slab optical waveguide 3 propagates. Is provided. The refractive index of a portion of the air hole 9 corresponding to the core layer of the slab optical waveguide 3 is different due to air, and forms a refractive index change region 13.

[0005] The slab optical waveguide 3 comprises a lower cladding layer 1.
The air holes 9 extend from the upper upper cladding layer 12 to the lower lower cladding layer 10 to form a cylindrical space. Air enters the air holes 9 and has a different refractive index from the core layer 11 of the slab optical waveguide 3.

The lattice arrangement of the air holes 9 satisfies the Bragg condition and constitutes a photonic crystal that reflects and propagates only light having a predetermined wavelength.

The optical waveguide region 6 of the photonic crystal waveguide 1
When the input optical fiber 4 is connected to one end of the optical fiber and the output optical fiber 5 is connected to the other end, the input light 7 entering the optical waveguide region 6 from the input optical fiber 4 has a wavelength satisfying the Bragg condition. Only light is output from the output optical fiber 5 as output light 8.

As shown in FIG. 12, after the slab optical waveguide 3 is formed on the substrate 2, the air holes 9 are formed by, for example, electron beam (EB) lithography and reactive ion etching (RIE). Is done. The diameter of the air hole 9 is 0.1 to 0.24 μm, the depth is 0.6 to 0.8 μm, and the pitch is 0.18 to 0.36 μ.
m. The upper end of the air hole 9 is open.

[0009]

In the production of a conventional photonic crystal waveguide, a slab optical waveguide 3 is produced on the surface of a substrate 2 by the following method.

(1) A thin film serving as a lower clad layer 10, a core layer 11, and an upper clad layer 12 constituting the slab optical waveguide 3 is formed by a vapor phase epitaxy (MO-CVD) method or a liquid phase epitaxy (LPE) method. Prepare sequentially.

(2) Slab optical waveguide 3 made of quartz glass or the like
Is produced by sintering the glass produced on the substrate 2 in an electric furnace to make it transparent.

In these methods, the temperature of the substrate 2 is
The temperature is about 500 to 700 ° C. in the MO-CVD method and the LPE method, and about 1300 ° C. in the sintering by the electric furnace, which is a high temperature.

[0013] Such high temperature processes are difficult to control.

On the other hand, the air holes 9 are formed by reactive ion etching (RIE). However, since the diameter of the air holes 9 is as small as submicron, it is difficult to process them well into a cylindrical shape. For example, the diameter of the air hole 9 is different between the upper portion and the bottom portion, and it is difficult to produce the air hole 9 with high reproducibility so as to satisfy a predetermined Bragg condition.

Further, since there are many steps of forming a thin film, forming holes, and processing steps, it is difficult to reduce the manufacturing cost of the photonic crystal waveguide.

As described above, according to the conventional manufacturing method,
Process control is difficult, and as a result, it has not been easy to stably realize a photonic crystal waveguide with good reproducibility.

An object of the present invention is to provide a photonic crystal waveguide having good transmission and wavelength limiting characteristics of propagating light, and a method of manufacturing the same.

Another object of the present invention is to provide a method of transmitting wavelength of propagating light.
It is an object of the present invention to provide a method for manufacturing a photonic crystal waveguide having good wavelength limiting characteristics with good reproducibility and at low cost.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0020]

The following is a brief description of an outline of typical inventions disclosed in the present application.

(1) A slab optical waveguide is provided on the surface of a substrate, and a refractive index change region having a refractive index different from that of a core layer of the slab optical waveguide is formed in a part of the slab optical waveguide in a lattice array. A photonic crystal waveguide provided with a photonic crystal structure disposed in
The refractive index change region is made of the same material as the material constituting the core layer of the slab optical waveguide, and is made of a material which has been subjected to a refractive index change process by a light-induced effect. Refractive index change regions are arranged in a lattice array on both sides of an optical waveguide region through which light propagates. The unit grids of the grid row are arranged in a regular polygonal array, for example, in a triangular array. The refractive index of the core layer in the refractive index change region is larger than the refractive index of the core layer in a region outside the refractive index change region, and the relative refractive index difference is 1
Is 0 to ⁴ -10 to ² about. The slab optical waveguide is composed of a glass optical waveguide or an organic optical waveguide.

Such a photonic crystal waveguide is manufactured by the following method.

After a slab optical waveguide comprising a lower cladding layer, a core layer, and an upper cladding layer is formed on a substrate, any one of an electron beam, synchrotron orbital radiation (SOR) light, ultraviolet light and near infrared light is applied to the upper cladding layer. The core layer is selectively irradiated through the layer to cause a change in the refractive index due to a light-induced effect to produce the refractive index change region.

(2) A photonic crystal waveguide having the structure of the means (1), wherein the core layer is sandwiched between a lower cladding layer and an upper cladding layer, and both layers are formed of organic thin films. Is a slab optical waveguide configuration.

Such a photonic crystal waveguide is obtained by forming a slab optical waveguide made of an organic optical waveguide on the surface of a substrate in the manufacturing method of the means (1) to form a photonic crystal waveguide. It is manufactured by peeling the organic optical waveguide from the substrate.

(3) In the configuration of the means (1) or (2), the refractive index changing regions are arranged in a grid array along one end of the slab optical waveguide. An optical waveguide region in which light propagates in parallel, perpendicularly or obliquely to a refractive index change region in a lattice arrangement provided on one end side of the slab optical waveguide is set.

(4) In the configuration of the means (1) to (3), the grating rows formed by the refractive index changing regions are a plurality of grating rows having different grating pitches.

According to the means (1), (a) the refractive index change region of the photonic crystal waveguide is made of the same material as the material constituting the core layer of the slab optical waveguide, and the refractive index change region is caused by the light-induced effect. It is made of a treated material.
For this reason, the size of each part in the depth direction of the refractive index change region is constant, and the size does not change up and down as in the case of the conventional air hole, so that the Bragg condition is satisfied well, and the propagation light Wavelength limitation or wavelength transmission can be performed with high accuracy. Therefore, for example,
It can be used as a demultiplexing element.

(B) Since the refractive index change region has a regular triangular lattice arrangement and satisfies a sufficient Bragg condition, a highly accurate wavelength limitation or wavelength transmission of propagating light is guaranteed.

(C) In the manufacture of a photonic crystal waveguide, the refractive index change regions arranged in an array are
One of SOR light, ultraviolet light and near infrared light,
Since the core layer is selectively irradiated through the upper cladding layer of the slab optical waveguide to cause a change in the refractive index due to the light-induced effect, the refraction is uniform with high precision and uniform depth in the depth direction. A rate change region can be manufactured.

(D) In the manufacture of the photonic crystal waveguide, the refractive index changing regions arranged in an array form one of an electron beam, SOR light, ultraviolet light, and near-infrared light with the upper cladding of the slab optical waveguide. It is manufactured by selectively irradiating the core layer through the layer to produce a change in the refractive index due to the light-induced effect, and does not require any mechanical processing such as etching as in the past, making it extremely easy to manufacture and reducing manufacturing costs Can be achieved.

(E) When manufacturing a photonic crystal using a glass optical waveguide, a special processing technique is not required, so that it is possible to significantly reduce the cost, increase the reliability, and realize mass production.

(F) When the slab optical waveguide is composed of an organic optical waveguide, the organic optical waveguide is a low-temperature process, so that the optical waveguide can be easily manufactured and the manufacturing cost can be reduced.

According to the means (2), the organic slab optical waveguide is peeled off from the substrate, so that the polarization-independent core layer of the photonic crystal waveguide that guides the light can be achieved.

According to the above-mentioned means (3), the refractive index changing regions are arranged in a lattice array along one end of the slab optical waveguide, and the refractive index changing regions are arranged in a grid array by the refractive index changing regions. Since an optical waveguide region in which light propagates in parallel or perpendicularly or obliquely is set,
The degree of freedom in designing an optical waveguide is increased. That is, if light enters the grid array perpendicularly, the output light is reflected by the grid array and emitted. Also, if light enters the grid row obliquely, the output light is reflected by the grid row and emitted at a predetermined angle. Therefore, if the angle is selected, the light propagation direction can be bent at a right angle. In the case of bending in these light propagation directions, the bending loss is also reduced.

According to the means (4), the chirping characteristic can be realized by forming a plurality of grid rows having different grid pitches.

[0037]

Embodiments of the present invention will be described below in detail with reference to the drawings. In all the drawings for describing the embodiments, components having the same function are denoted by the same reference numerals, and a repeated description thereof will be omitted.

(Embodiment 1) FIGS. 1 to 4 are views related to a photonic crystal waveguide and a method of manufacturing the same according to an embodiment (Embodiment 1) of the present invention.

The photonic crystal waveguide 1 of the first embodiment
1 has a structure in which a glass optical waveguide is formed as a slab optical waveguide 3 on a substrate (silicon substrate) 2 made of silicon, as shown in FIGS.

The slab optical waveguide 3 is, as shown in FIG.
Lower cladding layer 1 sequentially formed on silicon substrate 2
0, a core layer 11, and an upper cladding layer 12, all of which are SiO ₂ films (quartz glass,
(Glass such as fluoride glass).

The core layer 11 contains, for example, GeO ₂ to increase the refractive index.

In order to increase the difference in the refractive index, hydrogen (H ₂ ) is applied after the upper clad layer 12 is formed.

The thickness of each layer constituting the slab optical waveguide 3 is, for example, as follows. Lower cladding layer 10
The thickness of the upper cladding layer 12 is about 15 μm, and the thickness of the core layer is several μm. The relative refractive index difference between the core and the clad is about 0.3 to 1%.

As shown in FIG. 2, a region having a predetermined width along the center line is an optical waveguide region 6, and a refractive index change region 13 is provided along both sides of the optical waveguide region 6 in a lattice arrangement. ing. The width of the optical waveguide region 6 is preferably several μm to several tens μm in consideration of connection with an optical fiber.

In the figure, the refractive index change regions 13 are provided in three rows, respectively, and are equilateral triangular grids (triangles) between adjacent rows.
lattice). Therefore, although the unit lattice is formed by the two-row arrangement, the three-row arrangement prevents light from leaking between the refractive index changing regions 13 and enhances the light confinement effect. Further, some grating patterns require an array of more rows to enhance the light confinement effect.

The pitch of the regular triangular lattice is, for example, 0.5 μm, and the diameter of the refractive index changing region 13 is 0.45 μm.
It is.

The refractive index of the core layer in the refractive index changing region 13 is larger than the refractive index of the core layer out of the refractive index changing region 13, for example, the relative refractive index difference is about 10 to ⁴ .

The crystal in which the refractive index changing regions 13 are arranged in a lattice on the slab optical waveguide 3 is called a photonic crystal (two-dimensional photonic crystal) 14.

The photonic crystal 14 is made of, for example, an ultraviolet (UV) light generated by an external high-output laser such as an excimer laser.
The slab optical waveguide 3 is formed by selectively irradiating light or near-infrared light to the surface of the slab optical waveguide 3 to cause a change in the refractive index due to a light-induced effect in the core layer of the slab optical waveguide 3.

At this time, the minute refractive index change regions 13 whose refractive index has changed in a columnar shape with a radius r are regularly aligned to form, for example, an equilateral triangular lattice.

A crystal is a periodic arrangement of atoms or molecules, and a crystal lattice is formed when a small basic structure of atoms or molecules is spatially repeated. Thus, the crystal imparts a periodic potential to the electrons propagating therein, and the crystal structure governs conductivity. In particular, since a lattice can introduce a gap into the energy band structure of a crystal, electrons having a certain energy are prohibited from propagating in a certain direction by Bragg-like diffraction from atoms.

The optical analog is a photonic crystal, and its periodic potential is given by a macroscopic lattice of an optical semiconductor medium or a dielectric medium instead of atoms. Therefore, the photonic crystal has a band gap determined by the lattice structure and lattice constant, that is, a reflection wavelength region by Bragg diffraction.

The refractive index of quartz glass is 1.
46, which is 1.53 for a fluorinated polyimide described later.
As the refractive index change is large good, practical refractive index increase that can be achieved with these materials is in the range of 10 to ^{4 10-2.}

In a photonic crystal, it is generally desirable that the refractive index difference between a columnar region and a region other than the columnar region is large. It is advantageous to reduce the number of grids to obtain

However, on the other hand, there is a disadvantage that the pitch and the inner diameter of the grid become small and the processing becomes difficult.

On the other hand, as in the present invention, the refractive index difference is 0.01
When the number is smaller, the same effect can be expected in principle if the number of lattices is increased.

This situation will be described mathematically in more detail. For simplicity, taking as an example a one-dimensional Bragg waveguide grating in which the gratings are equally spaced along a straight waveguide, the optical power reflectivity at the Bragg wavelength λ _B is R = tanh ² (κ
L) and is determined by the product of the mode coupling coefficient κ and the grating length L.

As described above, when a grating is formed by changing the refractive index, since the coupling coefficient is generally small, it is necessary to increase the length L of the grating portion and arrange many gratings in order to obtain a high reflectance. It turns out that it becomes.

On the other hand, an input optical fiber 4 is connected to one end of the optical waveguide region 6 of the photonic crystal waveguide 1,
The output optical fiber 5 is connected to the other end. The input optical fiber 4 and the output optical fiber 5 are composed of a single mode fiber, a dispersion shift fiber, a polarization maintaining fiber, or the like. For example, a single mode fiber is used in this embodiment.

FIG. 1 schematically shows a usage form of the photonic crystal waveguide 1, but as an actual product,
The photonic crystal waveguide 1 is arranged in a container (package), and the input optical fiber 4 and the output optical fiber 5 are supported in an optical cable state or the like by an optical fiber guide or the like provided in the container. In addition, the photonic crystal waveguide 1 may be formed on a silicon substrate, a glass substrate, or a part of a compound semiconductor substrate constituting the OEIC.

In such a photonic crystal waveguide 1, when light (input light 7) from the input optical fiber 4 is input to one end of the optical waveguide region 6 where no crystal lattice exists.
When the input light 7 spreads in the slab space, it is reflected or transmitted by the photonic crystal where the refractive index change region 13 exists. At this time, only light having a wavelength that satisfies the so-called Bragg condition is reflected by the crystal, and light having other wavelengths is transmitted through the crystal. At this time, the reflected light causes optical multi-beam interference. As a result, light having a wavelength that satisfies the Bragg condition is confined in a portion of the slab optical waveguide 3 where there is no grating, and is allowed to propagate through the optical waveguide region 6.

This multi-beam interference has the effect of limiting the passing wavelength. The propagating light waves strengthen when the pitch a of the grating is an integral multiple of the wavelength, and weaken when the pitch a is an integral multiple of the (1 + １) wavelength. With such a configuration, it is possible to easily realize an optical filter having wavelength characteristics as compared with the related art.

Next, a method for manufacturing such a photonic crystal waveguide 1 will be described. As shown in FIG.
A lower cladding layer 10, a core layer 11, and an upper cladding layer 12 are formed of quartz (SiO ₂ ) glass on a silicon substrate 2 by a flame hydrolysis method or an ion exchange method so that light is not confined in a two-dimensional direction. A slab-structured glass optical waveguide 3a (slab optical waveguide 3) is manufactured. The substrate 2 may be a quartz glass substrate or another glass substrate.

In order to increase the refractive index, impurities such as germanium (GeO ₂ ) and phosphorus (P) are added to the core layer 11 in advance in the process of forming the core. In the first embodiment, for example, GeO ₂ is added. After forming the glass optical waveguide 3a, a hydrogen (H ₂ ) pressurizing treatment may be performed.

The thickness of the lower cladding layer 10 is about 15 μm.
m, the thickness of the core layer 11 is several μm, and the thickness of the upper cladding layer 12 is about 15 μm. The relative refractive index difference between the core and the clad is about 0.3 to 1%.

Next, an ultraviolet pulse light (ultraviolet light) 20 generated by a Kr-F excimer laser having an oscillation wavelength of 248 nm, an Ar-F laser having a wavelength of 193 nm, or a YAG laser (using the second or fourth harmonic) is used. As shown in FIG. 4, the slab optical waveguide 3 is
Irradiation is performed from above the surface to the portion where the refractive index change region 13 is formed.

The irradiation object may be any one of an electron beam, SOR light, ultraviolet light, and near infrared light.

The two-dimensional glass phase mask 21 used here has a circular or square hole 22 having a depth of 1/2 wavelength (π in phase) formed by quartz, for example, by photolithography and reactive ion etching. The glass plates 23 are formed and arranged in a two-dimensional direction. The pitch of the holes 22 of the glass phase mask 21 is about 1 μm.

As a result, the -1st-order and 1st-order diffracted lights interfere with each other, and an interference fringe of 0.5 μm pitch having a sinusoidal intensity distribution having a half period of the unevenness period of the phase mask surface is generated. Generated in the core layer 11. As a result, the refractive index changes due to the light-induced effect, and the refractive index of the core becomes 10 to ⁴
A two-dimensional lattice having a pitch 0.5 μm increased in order is formed in the core layer 11.

On the other hand, when near-infrared ultrashort pulse laser light having an oscillation wavelength of about 810 nm is irradiated, a larger increase in the refractive index on the order of 10 to ² can be caused in the core. In this case, the number of lattices can be reduced for the above-described reason, and as a result, there is an advantage that the crystal size can be reduced by about two orders of magnitude.

In this case, there is a great advantage that almost all kinds of glass such as fused silica glass, synthetic quartz glass, fluoride glass, and chalcogenite glass can be used without being limited to GeO ₂ -added quartz glass.

The energy for causing a change in the refractive index by irradiation with ultraviolet light is about 0.5 to 1 W in terms of average optical power. Since the refractive index change reflects the sinusoidal light intensity distribution of the interference fringes, it does not become cylindrical, but if the core layer thickness is about several μm, this effect can be almost ignored.

Even if ultraviolet light 20 is irradiated from outside after the formation of the glass optical waveguide 3a, the refractive index does not change due to the light-induced effect because GeO ₂ is not added to the upper cladding layer 12.

When the glass to which GeO ₂ is not added is irradiated with near-infrared light, the upper clad layer also undergoes a change in the refractive index due to the light-induced effect. However, since light propagates through the core, there is no effect.

On the other hand, the unit cell size differs from that of the prior art due to the difference in the refractive index. Since the refractive index of the medium without air holes and the refractive index of the air holes are different from those of the present invention, the size of the grating is larger in the case of the present invention than in the prior art.

That is, as described above, in the case of the present invention, since the difference in the refractive index is small, the mode coupling coefficient becomes small,
In order to obtain a high reflectance, it is necessary to increase the grating size and increase the number of gratings. For example, 100 × 100 to 10000 × 10000 gratings may be provided on both sides of a region (optical waveguide region 6) which is not a columnar region through which light propagates. In this case, the area occupied by the grating increases from about 1 × 1 mm ² to 100 × 100 mm ² , but the substrate size (diameter) is 1 to 6 inches (25.4 mm φ to
152.4 mmφ), there is no practical problem at all.

As is apparent from the above results, a photonic crystal waveguide having a filter characteristic can be realized by a very simple manufacturing process as compared with the prior art.

According to the first embodiment, the following effects can be obtained.

(1) The refractive index changing region 13 of the photonic crystal waveguide 1 is a slab optical waveguide 3 (glass optical waveguide 3).
It is made of the same material as the material constituting the core layer 11 of a), and has been subjected to a refractive index change treatment by a light-induced effect. For this reason, the size of each portion in the depth direction of the refractive index change region 13 is constant, and the size does not change up and down as in the case of the conventional air hole, so that the Bragg condition is satisfied well, and the propagation light The wavelength limitation or wavelength transmission can be performed with high accuracy. Therefore, for example, it can be used as a high-performance multiplexing / demultiplexing element.

(2) Since the refractive index changing region 13 has a regular triangular lattice arrangement and satisfies a sufficient Bragg condition, a highly accurate wavelength limitation or wavelength transmission of propagating light is guaranteed.

(3) In the manufacture of the photonic crystal waveguide 1, the refractive index changing regions 13 arranged in an array form any one of an electron beam, SOR light, ultraviolet light, and near-infrared light with the slab optical waveguide 3. Since the core layer 11 is selectively irradiated to the core layer 11 through the upper cladding layer 12 to produce a refractive index change due to a light-induced effect, the dimensions of each part in the depth direction are uniform with high precision. The area can be manufactured.

(4) In manufacturing the photonic crystal waveguide 1, the refractive index changing regions 13 arranged in an array
Is to selectively irradiate an electron beam, SOR light, ultraviolet light or near-infrared light to the core layer 11 through the upper cladding layer 12 of the slab optical waveguide 3 to cause a change in the refractive index due to a light-induced effect. Since it is manufactured and does not require any mechanical processing such as etching as in the related art, it is extremely easy to manufacture and a reduction in manufacturing cost can be achieved.

(5) When manufacturing a photonic crystal using the glass optical waveguide 3a, a special processing technique is not required, so that it is possible to significantly reduce the cost, increase the reliability, and realize mass production.

(Embodiment 2) FIGS. 5 and 6 relate to a photonic crystal waveguide according to another embodiment (Embodiment 2) of the present invention.

The second embodiment is an example of the photonic crystal waveguide 1 using the organic optical waveguide 3b as the slab optical waveguide 3.

That is, the second embodiment differs from the first embodiment in that an organic optical waveguide 3b is formed as a slab optical waveguide 3 having a photonic crystal 14 using a polymer material such as fluorinated polyimide. At this point, electron beams, ultraviolet rays or SOR light are further applied from outside to the organic optical waveguide 3.
b, thereby changing the refractive index of the core to form the refractive index changing regions 13 in a lattice array.

In particular, the change in the refractive index due to SOR light irradiation is 10 to ² which is two orders of magnitude larger than that of a glass waveguide. The other parts and operations are basically the same as those in the first embodiment, and thus the description is omitted.

However, both ends of the optical waveguide region 6 of the photonic crystal waveguide 1, that is, the input / output of the slab optical waveguide 3
Although not shown, the output end face is coated with a non-reflective coating to prevent reflection. As an example of the anti-reflection coating film, two target layers of anti-reflection coating are applied by using Si ₃ N ₄ / SiO ₂ as a target material and irradiating them with an ion beam to scatter toward the end face of the optical waveguide. The reflectivity obtained by this method is about -30 dB or less.

As another means for preventing reflection, the incident / exit end face may be polished obliquely. The angle of the oblique polishing is at least 8 degrees with respect to a direction perpendicular to the light propagation direction. Instead of this diagonal polishing, dicing may be used to cut diagonally. In these cases, a high reflectance of −50 to −60 dB is obtained.

The photonic crystal waveguide 1 of the second embodiment
A method of manufacturing the device will be described.

In the second embodiment, after the slab optical waveguide 3 composed of the organic optical waveguide 3b is formed on the silicon substrate 2, the SOR (synchrot) is selectively applied to the organic optical waveguide 3b.
ron orbital radiation) Irradiation of light to change the refractive index 1
3 are formed in a lattice array to form a photonic crystal 14.

Although not shown, a solution of fluorinated polyamic acid, which is a precursor of fluorinated polyimide, is spin-coated on the silicon substrate 2 and heated at 380 ° C. in an oven to form the lower cladding layer 10 (FIG. 6).

Next, a solution of a fluorinated polyamic acid was spin-coated on the lower cladding layer 10 and then
The core layer 11 is formed by heating at 80 ° C. (see FIG. 6).

Next, an upper cladding layer 12 having the same refractive index as that of the lower cladding layer 10 is formed on the core layer 11 by the same method as described above, to produce an organic optical waveguide (polymer optical waveguide) 3b. At this time, the thickness of each layer is almost the same as that of the glass optical waveguide 3a of the first embodiment.

As a result, an organic optical waveguide 3b having a refractive index of 1.53 is obtained.

The method of forming such a slab optical waveguide 3 is a low-temperature process which is lower in temperature than the high-temperature process of semiconductor crystal growth. The slab optical waveguide can be easily manufactured by a low-temperature process, and the manufacturing cost can be reduced.

Further, this method has an excellent feature that the organic optical waveguide 3b can be easily formed by spin coating, which is not found in other materials.

Next, a thin film such as silicon nitride which transmits X-rays is disposed on the organic optical waveguide 3b, and an X-ray absorber having a thickness of about 1 μm made of a heavy metal such as tantalum, tungsten or gold is placed thereon. the SOR light UHF length of about 0.7nm through the X-ray mask is provided a structure, dose 10 ²
The organic optical waveguide 3b is irradiated from the outside on the order of (Amps / sec).

Unlike the case of a glass phase mask, the SOR light transmitted through the X-ray mask having holes in a lattice shape is applied to the core layer 11 as spot light having a columnar intensity distribution. Is done. As a result, a grating having a large refractive index on the order of 10 to ² is formed in the core layer 11.

Here, the hole diameter of the X-ray mask is 0.25 μm.
m and the pitch are 0.5 μm.

In this case, since the wavelength is extremely small as compared with the irradiation of ultraviolet light, there is an excellent feature that fine processing is possible and the grating can be easily written on the core with high accuracy.

In the second embodiment, the effects of the first embodiment are similarly exhibited.

(Embodiment 3) FIG. 7 is a plan view of a photonic crystal waveguide according to another embodiment (Embodiment 3) of the present invention.

In the third embodiment, as shown in FIG. 7, the unit lattice formed by the refractive index changing region 13 is a regular hexagonal lattice (hexa lattice).
gonal lattice).

A regular hexagonal grating is extremely effective because it has the same band gap, that is, the Bragg reflection wavelength, for TE polarized light and TM polarized light.

In the present invention, a regular polygonal lattice other than the aforementioned regular triangular lattice or regular hexagonal lattice may be used as the unit lattice. That is, a unit cell is a square cell, a regular octagon cell,
A grid array such as a regular dodecagon grid may be used. In addition, at least two rows of the refractive index changing regions 13 are required to form a grid (grating row).

(Embodiment 4) FIG. 8 is a schematic plan view schematically showing a photonic crystal waveguide according to another embodiment (Embodiment 4) of the present invention.

This embodiment is an example in which the refractive index changing region 13 provided along one side of the optical waveguide region 6 of the photonic crystal waveguide 1 has a plurality of lattice columns, and a plurality of lattice columns G1, This is an example in which grating intervals (pitch) a of G2 and G3 are different from each other. This is an example in which a so-called chirping characteristic in which a pass band is widened is realized.

Although not particularly limited, the lattice rows G1, G
If 2, G3 of the pitch was _{a 1, a 2, a 3} , a 1> a
_2> is an example that has become a _3.

Chirping means that the wavelength band is widened when the pitch of the grating is continuously changed at a certain ratio. The chirping of the lattice pitch is performed step by step.
A case of a regular triangular lattice in which lattices are arranged so that the lattice pitch is unequal depending on the location will be described.

For example, if the lattice pitch a is a ₁ , a ₂ , a ₃
G ₁ , G ₂ , G _3.
In each of the grating regions, the Bragg reflection wavelength λ _B becomes slightly smaller, such as λ _B1 , λ _B2 , λ _B3 . In this case, since the pitch microscopically changes in a stepwise manner, a lattice mismatch occurs between adjacent lattice regions. Since this value is extremely small between adjacent grid regions, there is no problem in macroscopically assuming that it is the same as continuously changing.

In this case, the Bragg reflection wavelength shifts little by little, so that the band gap is equivalently widened.
That is, there is an advantage that a so-called chirping characteristic in which the reflection band is widened can be realized. This effect can be applied to compensation for chromatic dispersion generated in an optical fiber. Here, an example is shown in which the pitch of the grating monotonically decreases, but it goes without saying that the same effect occurs when the pitch monotonically increases.

In the fourth embodiment, the photonic crystal 14 is provided only on one side of the optical waveguide region 6. In other words, the refractive index changing region 1 extends along one end of the slab optical waveguide 3.
3 are arranged in a lattice arrangement, and an optical waveguide region 6 in which light propagates parallel to, perpendicular to, or oblique to the array of the refractive index changing regions 13 is set.

Therefore, the light (input light) can be propagated in parallel to the grating row, and the light extraction direction can be variously changed by selecting the light incident direction.

That is, if light enters the grid array perpendicularly, the output light is reflected by the grid array and emitted. Also, if light enters the grid row obliquely, the output light is reflected by the grid row and emitted at a predetermined angle. Therefore, if the angle is selected, the light propagation direction can be bent at a right angle. In the case of bending in these light propagation directions, the bending loss is also reduced.

According to the fourth embodiment, the degree of freedom in designing an optical waveguide is increased. Further, by applying this configuration to an optical waveguide that branches or merges with a silicon substrate or the like, the degree of design freedom is further increased.

The plurality of grating rows having different pitches may be provided on both sides of the optical waveguide region 6, respectively. Further, it may be provided in a partial length region of the optical waveguide region 6.

(Embodiment 5) FIG. 9 is a perspective view showing a cross section of a part of a photonic crystal waveguide according to another embodiment (Embodiment 5) of the present invention.

The Photonic Crystal Waveguide 1 of the Fifth Embodiment
Is constituted only by the organic optical waveguide 3b.

That is, the photonic crystal waveguide 1 is
In the photonic crystal waveguide 1 of the second embodiment,
The organic optical waveguide 3b (slab optical waveguide 3) formed on the silicon substrate 2 is converted into a silicon substrate 2 using an acid solution or the like.
And is supported by a support member in use.

When the slab optical waveguide 3 is separated from the substrate 2 as described above, the stress distortion caused by the difference in the coefficient of thermal expansion from the substrate 2 is released, so that the polarization dependence of the refractive index due to birefringence does not occur. Therefore, it is necessary to mount the photonic crystal waveguide 1 of the fifth embodiment in a support mode in which no mechanical stress or thermal stress is generated in a state where the photonic crystal waveguide 1 is mounted on the support member.

Photonic Crystal Waveguide 1 of Embodiment 5
According to this, polarization independence can be achieved.

Although the invention made by the inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention. Needless to say.

For example, the present invention can be applied to a case where a slab optical waveguide is formed by a compound semiconductor on a compound semiconductor substrate and refractive index change regions are arranged in a lattice.

For example, GaAlAs is formed on a GaAs substrate.
In the case of the photonic crystal waveguide having the slab optical waveguide 3 formed by the method described above, the photonic crystal waveguide can be used in a short wavelength band of 0.7 to 0.9 μm, and an InGaAsP compound semiconductor or a silicon substrate or a quartz glass substrate is formed on an InP substrate. 1.3 to 1.5 μm in the case of a photonic crystal waveguide on which a slab optical waveguide 3 is formed using quartz glass or a polymer material.
Can be used in the long wavelength band.

In the above description, the case where the invention made by the present inventor is mainly applied to the manufacturing technique of the optical demultiplexing element, which is the application field of the background, has been described.
The present invention is not limited to this, and can be applied to, for example, a multiplexing element manufacturing technique.

The present invention can be applied to at least an element having an optical waveguide, a module, and the like.

[0128]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

(1) The refractive index changing region of the photonic crystal waveguide is made of the same material as the material forming the core layer of the slab optical waveguide, and is made of a material which has been subjected to a refractive index changing process by a light-induced effect. I have. For this reason, since the size of each part in the depth direction of the refractive index change region becomes constant including the size in the depth direction, the Bragg condition is satisfied well, and the wavelength limitation or wavelength transmission of the propagating light is reduced. It can be performed with high accuracy. Therefore, for example,
It can be used as a demultiplexing element.

(2) When the unit cell is a regular hexagonal lattice, T
The band gap becomes the same for the E-polarized light and the TM-polarized light, so that the wavelength limitation or wavelength transmission of the propagating light can be performed with high accuracy.

(3) In the manufacture of a photonic crystal waveguide, the refractive index changing regions arranged in an array form
One of SOR light, ultraviolet light and near infrared light,
By irradiating the core layer through the upper cladding layer of the slab optical waveguide and selectively producing a change in the refractive index due to the light-induced effect in the core layer, the dimensions of each part in the depth direction with high precision dimensions are reduced. A uniform refractive index change region can be manufactured. Further, since no mechanical processing such as etching is required for producing the refractive index change region, the production is extremely easy and the production cost can be reduced.

(4) When manufacturing a photonic crystal using a glass optical waveguide, a special processing technique is not required, so that it is possible to significantly reduce the cost, increase the reliability, and realize mass production.

(5) When the slab optical waveguide is composed of an organic optical waveguide, the organic optical waveguide is a low-temperature process, so that the optical waveguide can be easily manufactured and the manufacturing cost can be reduced.

(6) In a photonic crystal waveguide having a structure in which an organic slab optical waveguide is peeled off from a substrate, polarization independence can be achieved.

(7) Chirp characteristics can be realized by changing the lattice pitch of a plurality of lattice rows of the photonic crystal provided on one or both sides of the optical waveguide region.

(8) In a photonic crystal waveguide having a structure in which a lattice array is provided along one end of a slab optical waveguide, light is propagated by allowing light to enter parallel, perpendicular, or oblique to the lattice array. The direction can be changed. In this case, there is also an effect that bending loss of light is small.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a photonic crystal waveguide according to an embodiment (Embodiment 1) of the present invention.

FIG. 2 is a perspective view showing a part of a cross section of the photonic crystal waveguide of the first embodiment.

FIG. 3 is a perspective view, partly in section, showing a state in which a slab optical waveguide is formed on a semiconductor substrate in manufacturing the photonic crystal waveguide of the first embodiment.

FIG. 4 shows a method for forming a photonic crystal waveguide according to the first embodiment in which a slab optical waveguide formed on the surface of a semiconductor substrate has a refractive index change region different from a refractive index of a core arranged in a lattice. It is a typical sectional view.

FIG. 5 is a configuration diagram schematically showing a photonic crystal waveguide according to another embodiment (Embodiment 2) of the present invention.

FIG. 6 is a perspective view showing a part of a cross section of the photonic crystal waveguide of the second embodiment.

FIG. 7 is a configuration diagram schematically showing a photonic crystal waveguide according to another embodiment (Embodiment 3) of the present invention.

FIG. 8 is a partial configuration diagram schematically illustrating a photonic crystal waveguide according to another embodiment (Embodiment 4) of the present invention.

FIG. 9 is a perspective view, partially in section, schematically showing a photonic crystal waveguide according to another embodiment (Embodiment 5) of the present invention.

FIG. 10 is a configuration diagram schematically showing a conventional photonic crystal waveguide.

FIG. 11 is a perspective view, partially in section, showing a conventional photonic crystal waveguide.

FIG. 12 is a perspective view showing a semiconductor substrate used for manufacturing a conventional photonic crystal waveguide.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photonic crystal waveguide, 2 ... Substrate, 3 ... Slab optical waveguide, 3a ... Glass optical waveguide, 3b ... Organic optical waveguide,
4 input optical fiber, 5 output optical fiber, 6 optical waveguide region, 7 input light, 8 output light, 9 air hole, 10
... Lower cladding layer, 11 core layer, 12 upper cladding layer, 13 refractive index change region, 14 photonic crystal,
20 ... ultraviolet light (ultraviolet pulse light), 21 ... glass phase mask, 22 ... hole, 23 ... quartz glass plate.

Claims (11)

[Claims] 1. A substrate having a dielectric slab optical waveguide on a surface of a substrate and refractive index changing regions having a refractive index different from that of a core layer of the slab optical waveguide are arranged in a part of the slab optical waveguide in a lattice array. A photonic crystal waveguide provided with a photonic crystal structure, wherein the refractive index change region is made of the same material as a material constituting a core layer of the slab optical waveguide, and a refractive index change process by a light-induced effect is performed. A photonic crystal waveguide characterized by being made of a coated material. 2. A slab optical waveguide in which a core layer is sandwiched between a lower clad layer and an upper clad layer, and both layers are formed of an organic thin film, and a part of the slab optical waveguide is formed as a part of the slab optical waveguide. The photoreceptor, wherein the refractive index changing regions having a refractive index different from the refractive index are arranged in a lattice array, and the core layer of the refractive index changing region is formed by a refractive index changing process by a photo-induced effect. Nick crystal waveguide. 3. The photonic crystal waveguide according to claim 1, wherein the refractive index change regions are arranged in a lattice array on both sides of the optical waveguide region through which light propagates. 4. The photonic crystal waveguide according to claim 1, wherein the refractive index change regions are arranged in a lattice array along one end of the slab optical waveguide. 5. An optical waveguide region in which light propagates parallel, perpendicularly or obliquely to a refractive index change region in a lattice arrangement provided at one end of the slab optical waveguide. Item 5. A photonic crystal waveguide according to item 4. 6. The photonic crystal waveguide according to claim 1, wherein the lattice rows formed by the refractive index change regions are a plurality of lattice rows having different lattice pitches. Wave path. 7. The photonic crystal waveguide according to claim 1, wherein the unit lattices of the lattice row are arranged in a regular polygonal arrangement. 8. The refractive index of the core layer of the refractive index change region is larger than the refractive index of the core layer in a region deviated from the refractive index change region, at which the relative refractive index difference of 10 ~ ⁴ -10 ~ ² about The photonic crystal waveguide according to claim 1, wherein: 9. The photonic crystal waveguide according to claim 1, wherein the slab optical waveguide is formed of a glass optical waveguide or an organic optical waveguide. Wave path. 10. The method for manufacturing a photonic crystal waveguide according to claim 1, wherein a slab optical waveguide including a lower clad layer, a core layer, and an upper clad layer is formed on the substrate. The core layer is selectively irradiated with any one of an electron beam, SOR light, ultraviolet light, and near-infrared light through the upper cladding layer to cause a change in refractive index due to a photo-induced effect, thereby producing the refractive index change region. A method for manufacturing a photonic crystal waveguide. 11. The method according to claim 10, wherein
3. The method for manufacturing a photonic crystal waveguide according to claim 2, wherein the organic optical waveguide including the lower cladding layer, the core layer, and the upper cladding layer is separated from the substrate to manufacture the photonic crystal waveguide according to claim 2. .