JP3507659B2 - Optical function element - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical functional element which can be used as an optical delay element, a wavelength conversion element, an optical switch, an optical modulation element, an optical amplifier, an optical memory, a dispersion compensator, a soliton generating element, or the like.

[0002]

2. Description of the Related Art In optical communication and optical circuits, improvements in various optical functional elements are desired. For example, in optical communication, an optical switch equipped with an optical delay element is required to set a communication path. This is because an optical switch cannot process multiple optical signals at the same time, so by delaying some of the multiple optical signals, multiple optical signals can be sequentially introduced into the optical switch. This is because the order of the optical signals is changed and processed. Conventionally, an optical fiber having a length corresponding to a desired delay time, which is provided separately from an optical fiber as a signal line, is used as an optical delay element, and an optical switch is used to introduce and take out an optical signal to be delayed. I have to. However, the length of the optical fiber used as the optical delay element is several tens of meters, and a large space is required to install this.

In the wavelength conversion element (second harmonic generation, SHG) utilizing the second-order nonlinear optical effect, phase matching between the fundamental wave and the second harmonic (SH wave) is realized in terms of wavelength conversion efficiency. Is important. However, since the refractive index of the substance depends on the wavelength of light, it is difficult to achieve phase matching. Conventionally, as a method for realizing phase matching, an angle tuning method utilizing birefringence of a single crystal, a Cherenkov radiation method, a quasi phase matching method, etc. are known. Considering conversion efficiency, the single crystal system is advantageous. However, it is difficult to produce large crystals. Further, although the angle tuning is realized in the bulk, it is difficult to realize the angle tuning in the waveguide because the crystal orientation cannot be finely adjusted three-dimensionally.
In the Cherenkov radiation method, the angle condition of the fundamental wave with the SH wave is strict, and substantially low conversion efficiency can be obtained. The quasi phase matching method is difficult to manufacture because the element structure becomes complicated. Further, the quasi phase matching is an offset added to the shifted phase, and is not exactly phase matching.

Due to these problems, it is difficult to put the wavelength conversion element into practical use, although it is expected to have a wide range of uses such as a light source for an optical disk. In particular, an organic nonlinear optical material is advantageous in that it has a very large nonlinear susceptibility as compared with an inorganic material, but it has not been put into practical use because of a problem in a device manufacturing process. Further, when a polymer second-order nonlinear material or a material in which an organic nonlinear optical material is dispersed in a polymer is used, alignment treatment by poling is required, and a measure against orientation relaxation is also required.

In an element such as an optical switch that utilizes third-order nonlinear optical characteristics, it is known that the longer the phase relaxation time, the higher the nonlinear susceptibility. Therefore, the nonlinear susceptibility is large in the resonance region of absorption and small in the non-resonance region. However, since the signal light is absorbed in the resonance region, the intensity of the switched light is reduced, and the heat generated by the absorption causes material destruction. In this respect, a third-order nonlinear optical element that operates in the resonance region is not practically desirable. Therefore, an element that operates in the non-resonance region is desired, but it has not been put to practical use because the nonlinear susceptibility is small as described above.

Known optical modulation methods are electro-optical modulation (EO modulation) using the Pockels effect, absorption modulation in which absorption is changed by applying an electric field, and direct modulation in which the injection current of a semiconductor laser is controlled. ing. Direct modulation does not require a special modulator and requires a small number of total parts, but has the drawbacks that high-speed modulation is difficult and the half-width of wavelength is wide. Therefore, research and development of a high-speed external modulator using a material such as GaAlAs or LiNb ₃ has been advanced, but sufficient performance has not been obtained. Therefore, there is a demand for a modulator that is easy to manufacture, can perform high-speed modulation, and has a high on-off ratio.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical functional element capable of delaying an optical signal in a small installation space, and a function of various optical functional materials by utilizing optical signal delay and refractive index control. An object of the present invention is to provide an optical functional element capable of effectively exhibiting the above.

[0008]

[0009]

The optical functional device of the present invention comprises:
The diffraction grating forming the photonic band and the metal film, the optical functional film, and the metal film sequentially formed on the surface of the diffraction grating
The optical functional film has a second-order nonlinear optical material, a third-order nonlinear
Optical material, light emitting material, light amplifying material and electro-optical material?
It is characterized by containing an optical functional material selected from the group consisting of:

Other optical functional elements of the present invention are paired with each other.
Facing each other, forming a photonic band
Two diffraction gratings each having a metal film formed on the surface or
Diffraction grating with a metal film formed on the surface and flat metal body
Between the two diffraction gratings or the diffraction grating and the flat
And a light functional film sandwiched between a transparent metal body and the optical device.
The functional film is a second-order nonlinear optical material, a third-order nonlinear optical material, light emission.
Material, optical amplification material and electro-optic material
It is characterized by including an optical functional material selected.
It

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. First, the photonic band will be described.
Here, it is easy to understand the photonic band by analogy with the semiconductor band. As a result of the Bragg reflection of the electron wave by the atoms arranged periodically in the semiconductor crystal, a dispersion relation between the energy E and the wave number k, that is, a band is generated. The generation of this band is partly due to the fact that the wavelength of the electron wave is approximately the same as the lattice constant of the semiconductor crystal. As can be easily analogized, such a phenomenon can occur not only in electron waves but also in any waves. The photonic band is a band in the wavelength range of light.

The photonic band is formed by periodically arranging two or more kinds of substances having different refractive indexes, and a medium forming the photonic band is called a photonic crystal. Light is Bragg-reflected by a medium having a periodicity of refractive index, and forms a band like an electron wave. Under certain conditions, a region where light cannot exist is observed, such as the energy gap of a semiconductor. This is called a photonic bandgap. A unique transmission spectrum, absorption spectrum, and reflection spectrum are observed in the photonic crystal. These spectra change with the arrangement of the constituent material of the photonic crystal and the change of the refractive index of the constituent material.

The optical functional element of the present invention has a structure in which materials having different refractive indexes (or dielectric constants) are periodically arranged so as to form a photonic band.
The wavelength of the light corresponding to the band edge is set near the wavelength of the light to be transmitted.

The wave number k of the light with which the optical functional element having such a structure is irradiated depends on the period and the refractive index of the two materials. This is expressed by the following equation when a simple one-dimensional structure is considered.

[0015]

[Equation 1]

Where n ₁ and n ₂ are the refractive indices of the first and second materials, a and b are the thicknesses of the first and second materials, d is the period and d = a + b, and ω is the angle. Frequency, c is the speed of light in a vacuum (JP Dowl
ing and C. M. Bowden, J .; Mod.
Opt. 41 (1994) 345).

Based on the above equation, n ₁ = 1 and n ₂ = 1.
7, a = b = 2.35 × 10 ⁻⁷ m, d = 4.7 × 10 ⁻⁷
FIG. 1 shows the relationship between the frequency ν and the wave number k when m.
The group velocity (the velocity at which the wave packet energy of pulsed light advances) is the derivative of the angular frequency ω (k), that is, dω (k) /
Since it is dk, the relationship between the wavelength and the speed of light is as shown in FIG. In FIGS. 1 and 2, the region where no curve exists is the photonic bandgap, and light in this wavelength range is reflected without being transmitted.

Qualitatively explaining this phenomenon is as follows. Since the relationship between k and ω in vacuum is proportional, the k-ω relationship in k space (referred to as phase space) is a straight line. However, if a regular periodicity of the refractive index is given to this space, the k-ω relationship is folded back at a certain value of k to form a zigzag shape. At this time, at the turning point (the end of the first Brilliant zone), there is a region in which the value of k does not exist for ω, and this becomes the band gap. For this reason,
In particular, considering one-dimensional periodicity, the minimum or maximum energy value in the branch of the band is taken at the point where k is 0 or the minimum and the point where k is the maximum. A decrease in group velocity is generally seen at this band edge.

The frequency dependence of the refractive index of the band before being folded back is considered to be the same as the frequency dependence of the ordinary refractive index. However, the refractive index of the folded band changes between 0 and 1 with respect to the change of the light frequency. That is, if the band can be controlled, the refractive index can be controlled between 0 and 1. This is the refractive index peculiar to the photonic band.

When an optical functional element is manufactured by using a metal such as aluminum, aluminum exhibits a refractive index dispersion and has a complex band structure because it has a complex portion in the refractive index. A = 2.35 for aluminum and air
× 10 ^-8 m, b = 4.465 × 10 ^-7 m, d = 4.7 ×
Regarding the optical functional element periodically arranged as 10 ⁻⁷ m,
The relationship between the frequency ν and the wave number k is shown in FIG. As shown in FIG. 3, no clear bandgap is formed in this case. However, even in this case, the group velocity decreases at the point where k is the minimum and the point where it is the maximum.

The present invention, as described above, uses a photonic
The group velocity dω (k) / dk decreases near the band edge and becomes 0
It was made paying attention to approaching. The optical functional element of the present invention utilizes the above phenomenon to produce a photonic
By setting the wavelength of the light corresponding to the band edge in the vicinity of the wavelength of the light to be transmitted, the effect of delaying the optical pulse is shown. This element can be used not only as an optical delay element in optical communication but also in the case of performing optical mixing by matching the group velocities of a plurality of optical pulses. Moreover, the space for installing the optical functional element of the present invention can be smaller than that of the conventional optical delay element composed of an optical fiber.

In order to form a photonic band structure in which materials having different refractive indexes (or dielectric constants) are periodically arranged, it is considered that two kinds of materials are arranged in a face-centered cubic structure or a body-centered cubic structure. To be Conventionally, as a typical example of a photonic crystal, a photonic crystal (E. Yablono) in a microwave region in which a regular hole is formed in a dielectric with a drill is used.
vitch, T .; J. Gmitter and K.M.
M. Leung, Phys. Rev. Lett. , 6
7, 2295 (1991)) and a photonic crystal in the infrared region (K. Inoue, M. Wada, K. Sakoda, manufactured by processing a bundle of glass fibers.
A. Yamanaka, M .; Hayashi, and
J. W. Haus, Jpn. J. Appl. Phy
s. , 33, L1463 (1994)). However, it is difficult to realize a three-dimensional array with a cycle of about the wavelength of visible light. Therefore, in order to form a photonic band structure, it is realistic to arrange two kinds of materials one-dimensionally.

As a material capable of forming a photonic band structure with a one-dimensional array, a dielectric multilayer film applied to a bandpass filter can be considered. This dielectric multilayer film bandpass filter is an application of an antireflection film and a dielectric multilayer film mirror. The antireflection film cancels the light reflected from the substrate by reflecting the light whose phase is shifted by π with respect to the light reflected from the substrate. The dielectric multilayer mirror has the opposite principle. The dielectric multilayer film bandpass filter reflects light of a specific wavelength by these applications. However, if the periodicity of the refractive index is broken in the spatial region of the wave packet, the photonic band is not formed, so that the optical path length of at least about 100 μm is required. Further, it is necessary that the phases match even at distant portions in the wave packet. Considering these points, it is difficult to form a photonic band structure with a dielectric multilayer film.

In the present invention, for example, materials having different refractive indexes (resist and air in this example) are periodically arranged by exposing and developing a resist to form a line pattern having a predetermined width at a predetermined pitch. The optical functional element having a structure can be easily manufactured. In particular, the method of irradiating laser light from two directions and directly exposing the resist using the interference light can form a pattern having excellent long periodicity. In this case, the resist pattern may be used as it is as a waveguide, or another material having a different refractive index may be embedded in the gap between the resist patterns and used as a waveguide.

In the present invention, a structure in which materials having different refractive indexes are periodically arranged in the core of the optical fiber by the method of irradiating the core of the optical fiber with an excimer laser beam having an oscillation wavelength of 248 nm or 193 nm to irradiate the core of the optical fiber through a phase mask. May be formed. This method is effective in suppressing the zero-order light (KO Hil).
1, OPTRONICS, 14 (1995) 135).

In the present invention, after forming a mask on the medium, an electric field is applied to implant Ti ⁺ , K ^+, etc. ions, or a solution is brought into contact to apply an electric field to implant ions. It is also possible to form a structure in which materials having different dielectric constants are periodically arranged.

In the present invention, a diffraction grating or a block copolymer having a regular phase separation structure may be used as a medium having a structure in which materials having different refractive indexes are periodically arranged.

In the present invention, the period of two kinds of materials having different refractive indexes (thickness of one set of two kinds of materials) is preferably 10 μm or less, and should be determined in consideration of the wavelength of light to be used. Is preferred. For example, the wavelength used for optical communication is 1.5
Considering 5 μm, the period interval is set to about half of this used wavelength. In the present invention, the photonic
Setting the wavelength of the light corresponding to the band edge near the wavelength of the light to be transmitted means that photonic
This means that the wavelength of light to be transmitted falls within at least ± 15% of the band edge wavelength.

In the present invention, when a plurality of optical signals are introduced into a waveguide type or optical fiber type optical functional element forming a photonic band structure, the optical functional element is used to extract any optical signal. It is possible to use a method of extracting the evanescent wave oozing out with a scanning near-field microscope.

In the optical functional device of the present invention, if the periodicity of the arrangement of the two kinds of materials is disturbed, the photonic band will not be established and the optical delay will be eliminated. Examples of such means include an ultrasonic generator or a temperature controller. Ultrasonic generators or temperature controllers move the lattice points of the two materials and are an excellent means of breaking the photonic bands. When ultrasonic waves are used, it is sufficient to select a frequency at which one or more, for example, several, wavelengths of ultrasonic waves stand in the spatial region of the optical pulse to be delayed. It should be noted that when two standing waves of ultrasonic waves are erected by using two ultrasonic oscillators or ultrasonic resonators, the one-dimensional photonic band structure can be formed by this alone.

The optical functional element (optical delay element) of the present invention can also be applied as a memory. That is, if the optical signal is injected in a state where the ultrasonic wave is applied to the optical delay element and then the irradiation of the ultrasonic wave is stopped, the optical signal slowly progresses, which serves as a temporary memory. At this time, if light in a wavelength range that does not pass through the optical delay element is injected while irradiating the ultrasonic wave when the ultrasonic wave is stopped, the optical signal is stopped in the optical delay device while the ultrasonic wave is stopped.
To extract this optical signal, irradiate ultrasonic waves again,
Alternatively, a method of extracting an evanescent wave can be used.

In the optical delay element of the present invention, when the frequency (wavelength) broadens due to the dispersion effect, the dispersion may be corrected by a grating pair or a prism pair.
It is effective to combine two optical delay elements that correct dispersion.

Next, another optical functional element of the present invention will be described. As described above, in the photonic band structure, the group velocity of transmitted light becomes slow near the band edge. Therefore, if the photonic band structure and the optical functional material can be combined, the interaction between the light having the slower group velocity and the electron of the optical functional material becomes stronger, so that the function of the optical functional material can be exerted. Be advantageous However, in the photonic band structure such as the conventionally known dielectric multilayer film, it is difficult to form an element by combining it with an optical functional material. On the other hand, the present invention provides an optical functional element capable of effectively exhibiting the function of the optical functional material by using a diffraction grating having a space capable of forming a photonic band and holding the optical functional material. .

In the present invention, as the optical functional material, it is possible to use a material having various functions such as a secondary or tertiary nonlinear optical material, a light emitting material, a light amplifying material and an electro-optical material. These optical functional materials may be used by being dispersed in a polymer.

If a diffraction grating is used, the photonic band structure can be easily controlled by controlling the number of grating grooves per mm. Examples of the diffraction grating used in the present invention include a holographic diffraction grating manufactured by using light interference and having a precise groove interval. The holographic diffraction grating is formed by coating a resist on a substrate, dividing a laser beam into two light beams, irradiating the resist from two directions to expose the interference fringes, and then developing the fringes according to the intensity distribution of the interference fringes. And a grating groove having a sinusoidal cross section.

In the optical functional device of the present invention, it is sufficient if the interval of the periods, that is, the interval of the gratings is 10 μm or less. Therefore, it is sufficient that the number of grating grooves per 1 mm of the diffraction grating is 100 or more. Here, the lattice spacing is preferably about half the wavelength of the light to be used. For example, a holographic diffraction grating having 3600 grating grooves per 1 mm is commercially available, and if this is used, the grating spacing is twice as large as about 556 nm, so that a photonic band in the visible region can be formed. . Note that the band edge does not need to have the lowest energy (that is, the longest wavelength), and may have the highest energy. In this case, the number of grid grooves per mm may be small.

In the present invention, optical functional devices having various structures can be produced by appropriately disposing the diffraction grating and the optical functional material. For example, the optical functional material may be simply spin-coated on the surface of the diffraction grating to form the optical functional film along the grating groove. Deposit a metal film on the surface of the diffraction grating,
An optical functional film may be spin-coated thereon and a metal film may be further vapor-deposited thereon. Forming metal films on the surfaces of the two diffraction gratings and arranging them so as to face each other,
An optical functional film may be sandwiched between these. Also,
One diffraction grating having a metal film formed on its surface and a flat metal body may be arranged to face each other, and the optical functional film may be sandwiched between the diffraction grating and the flat metal body. With any of these structures, a photonic band can be formed, and an optical functional material can be easily arranged. In particular, the element formed with the metal film has a good diffraction efficiency and can easily form the photonic band.

In the present invention, in the element in which two diffraction gratings are opposed to each other, the relative positional relationship between peaks is not particularly limited. This element exhibits polarization anisotropy. In such an element, the photonic band structure can be changed by changing the metal film or the material by changing the refractive index between the one diffraction grating and the other diffraction grating.

In an element in which two diffraction gratings face each other, the distance between the diffraction gratings is preferably within 1/50 of the optical path length (element length), specifically within 5 mm. In the case where the two diffraction gratings opposed to each other are considered as the optical delay element in this way, ON / OFF of the optical delay can be controlled by changing the distance between the two diffraction gratings. That is, the optical signal introduced into the device can be held for the delay time, and the optical memory can be turned on / off. In addition, the wavelength density of the group velocity of light can be controlled to some extent by controlling the grating density of the diffraction grating. For example, the anomalous dispersion can be realized by slowing the speed of light having a longer wavelength than that of light having a shorter wavelength.

Next, the optical functional element using the diffraction grating and various optical functional materials will be individually described. In the present invention, a wavelength conversion element can be manufactured by using a second-order nonlinear optical material. The fact that the traveling speed of light in the nonlinear optical material that constitutes this wavelength conversion element becomes slower is equivalent to the longer the phase relaxation time. Therefore, even in the non-resonant region, the time for one excited dipole moment to oscillate becomes long. Therefore, the second-order nonlinear susceptibility also increases, and the wavelength conversion efficiency also increases. Moreover, since there is no absorption in the non-resonant region, it is convenient as a device material. Also, without changing the original characteristics of the second-order nonlinear optical material,
Since the refractive index can be controlled, the light velocities of the fundamental wave and the second harmonic can be matched and phase-matched. Particularly, in a wavelength conversion element having a structure in which a metal film is provided on both sides of a thin film of a nonlinear optical material, an electric field can be applied using the metal film as an electrode, and poling can be easily performed. If the permanent dipole moment of the organic molecule in the polymer is oriented in the direction of the electric field by poling and then the electric field is continuously applied, the orientation can be maintained and the orientation relaxation can be prevented.

A calculation example showing that phase matching can be realized in the wavelength conversion element having the above structure will be described. Specifically, the calculation result of the wavelength dependence of the refractive index in the wavelength conversion element using the holographic diffraction grating having 1800 grating grooves per 1 mm and the second-order nonlinear optical material having the refractive index of about 1.8. Is shown in FIG. Here, polarized light in which the direction of the electric field vector is perpendicular to the grating groove is used.
The broken line in the figure indicates the refractive index for light having a wavelength twice the value on the horizontal axis. In this figure, the phase velocities match at the points where the solid lines and the broken lines intersect, and phase matching can be realized.

Further, if anomalous dispersion is realized in an optical functional element using two diffraction gratings and a third-order nonlinear optical material, it can be used as a soliton generating element. In the present invention, an optical switch can be manufactured by using third-order nonlinear optics. Also in this case, slowing the traveling speed of the optical signal is equivalent to lengthening the phase relaxation time,
The non-linear susceptibility increases. Generally, when the phase relaxation time is long and the nonlinear susceptibility is large like the resonance region, the switching speed and the reaction speed become slow. On the other hand, in the optical switch of the present invention, since the speed of light increases when an optical signal is emitted, there is a great advantage that the bit rate of signal processing does not decrease even if the nonlinear susceptibility increases.

In the present invention, an optical functional element that exhibits a photonic bandgap and uses a light emitting material as an optical functional material, even if the emission wavelength band of the light emitting material is wide,
Light emission can be controlled by wavelength selection. Therefore, it is possible to form not only a bandpass filter but also a light emitting element capable of concentrating energy at a specific wavelength.

In the present invention, a light modulator can be manufactured by using a material having a Pockels effect (first-order electro-optical effect) or Kerr effect (second-order electro-optical effect), or a material such as liquid crystal whose orientation is changed. In this case, a metal film coated on the surface of the diffraction grating is used as an electrode in order to increase the diffraction efficiency. An electric field can be applied to a material having the Pockels effect or Kerr effect by the metal film to change the refractive index and change the photonic band. Then, modulation is performed by controlling the electric field so that the wavelength of the light to be transmitted is within and outside the range of the photonic band gap. That is, if the wavelength of the light to be transmitted is within the range of the photonic band gap, the light cannot enter the element, and if it is out of the range, the light can enter the element. Also, after light enters the device, photonic
When the bandgap is formed, the light stops inside the device.

FIG. 5 shows a change in transmittance when the refractive index is changed from 1.6 to 1.7 by 0.1 in an optical modulator using a material exhibiting the Pockels effect. From this figure, it can be seen that, for example, light with a wavelength of about 625 nm can be turned on and off. In this modulation method, as long as the polarization direction of the transmitted light is determined, there is no need for two polarizing plates as in a general EO modulator.

When the group velocity is slowed by using the photonic band device and the light is modulated in that state, the modulated light emitted from these devices returns to the original light velocity, and the modulation velocity becomes higher. . That is, it is possible to perform light modulation at a higher speed than the performance of the material to be modulated. This method can also be applied to conventional modulation elements.

Further, in the light modulation element using the material exhibiting the Kerr effect, the photonic band can be controlled by turning on / off the light irradiation instead of the electric field. In such an element, it is not necessary to coat the surface of the diffraction grating with a metal film.

In the present invention, even when another material such as a light amplifying material is applied as the optical functional material, the speed of light becomes slow, and the interaction between light and electron becomes strong.
An optical functional element such as an efficient optical amplifier can be formed.

The optical functional element of the present invention can be applied to an element for correcting the deformation of the signal pulse of the optical fiber in optical communication, that is, a so-called dispersion compensator. Further, since the optical functional element of the present invention can achieve negative group velocity dispersion, it can be used also as a soliton generating element by using a non-linear optical material together.

The optical functional element of the present invention is a kind of optical waveguide, and the function can be further enhanced by defining the distance between two diffraction gratings so that the waveguide mode of the light used becomes a single mode. it can. In the optical functional device of the present invention, two surfaces parallel to the light guiding direction are covered with a dielectric multilayer film or a metal film to prevent the guided light from being emitted in a direction other than the guiding direction due to light scattering. It is effective for increasing the height and is also advantageous for coupling with optical fibers.

In the present invention, a block copolymer having a regular phase separation structure can be used as a medium having a structure in which materials having different refractive indexes are periodically arranged. It is known that certain block copolymers form ordered phase-separated structures, and that they are regularly arranged (EL Thomas, DB Alwa.
rd, D.I. J. Kinning, and D.M. C. Ma
rtin, Macromolecules 19, 21
97 (1986); Hasegawa, H .; Tan
aka, K .; Yamasaki, and T.S. Hash
imoto, Macromolecules 20, 1
651 (1987)). When these copolymers are dissolved in a solvent such as toluene and a thin film is formed by a casting method or a spin coating method, a microphase-separated structure is exhibited by a self-forming force. Micro phase separation structure is sea island structure, lamella structure,
It is called a cylinder structure or bicontinuous structure. In such a thin film of the block copolymer, two kinds of phases having different refractive indexes are regularly arranged, so that it can be a photonic crystal. Such a photonic crystal is easy to manufacture and the manufacturing cost can be reduced.

In the photonic crystal using the block copolymer, the refractive index can be controlled by changing the side chains of the two kinds of polymers. It is also possible to selectively impregnate one polymer chain with a complex such as an osmium complex to control the refractive index. If a photosensitive polymer is used as the polymer forming the copolymer, the waveguide can be formed after the photonic crystal is formed. If a waveguide can be formed, it can be used as a dispersion compensator in the optical communication field.

When a substance that disturbs the periodic change of the refractive index is mixed as an impurity in the photonic crystal using the block copolymer as described above, light in a specific wavelength range is generated in the photonic band gap. A transparent region can be formed. Such a region corresponds to the impurity level in the semiconductor. In this case, if a laser dye is introduced into the side chain of the block copolymer, or one of the polymer chains is mixed with a laser dye having a high specific affinity, the oscillation wavelength range of the laser dye is adjusted to the impurity level. , A photonic crystal laser can be manufactured. Such a photonic crystal laser cannot emit light in the band gap wavelength range other than the impurity level,
Oscillation loss is reduced. Conversely, a photonic crystal using a block copolymer can also be used as a three-dimensional resonator.

A non-linear optical material may be introduced into the side chain of the block copolymer, or a polymer having a non-linear optical effect may be used. In this case, the nonlinear effect can be enhanced under the condition that the strength of the optical oscillator is increased by the impurities or the group velocity is slowed down. Further, by controlling the phase velocity, it is possible to realize the phase matching in the second harmonic generation. An element using a material exhibiting third-order nonlinear optical characteristics can be applied as an optical switch.

The optical functional element of the present invention can be applied to various applications in optical circuits and optical systems which are expected to develop in the future, and can be a basic element corresponding to a resistance element or a capacitor element in an electronic circuit or an electronic system. .

[0056]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 In this example, the resist was exposed to an electron beam and developed to manufacture the optical functional element shown in FIG. Thickness 100
A resist 2 (manufactured by Shipley Co.,
The product name SAL601) was spin-coated to a thickness of about 1.5 μm. The resist 2 on the glass substrate 1 was exposed to an electron beam so that a pattern having a width of 0.25 μm was formed at intervals of 0.25 μm, and then developed. This resist 2
Is further patterned so that the length of the resist in the vertical direction is 300 μm, and the length along the width of the resist is 7 cm.
The waveguide type optical functional element of was formed. As shown in FIG.
This waveguide-type optical functional element has a structure in which a resist 2 having a thickness of 0.25 μm and air having a thickness of 0.25 μm are arranged at a cycle of d = 0.5 μm.

A Ti: sapphire laser beam with a pulse width of 100 femtoseconds was made incident from one end of this waveguide type optical functional element through a prism (not shown), and the transmitted light was measured at the other end (in the figure, it was made incident. Light and transmitted light are indicated by arrows respectively). At this time, when the transmitted light was measured while changing the wavelength of the incident light, the vibration frequency was 370 THz (wavelength 810 n
It was found that there is a wavelength region where transmitted light is not observed on the higher energy (shorter wavelength) side than m). Further, the transmission time of light having a frequency of 333 THz (wavelength 900 nm) is 35
0 psec (350 × 10 ^-12 sec), frequency 36
The transmission time of light of 9.5 THz (wavelength 812 nm) is 2.
It was 3 nsec (2.3 × 10 ⁻⁹ sec). As described above, it was confirmed that the light having the wavelength of 812 nm causes a delay.

Example 2 In this example, the optical functional device shown in FIG. 7 was manufactured. First, in the same manner as in Example 1, after forming a waveguide having an optical path length of 7 cm, gold having a thickness of about 1 nm and a thickness of about 1 were formed by a sputtering method.
SiO ₂ of 0 nm was alternately deposited and buried in the groove portion between the resists 2. As shown in FIG. 7, this waveguide type optical functional device has a resist 2 having a thickness of 0.25 μm and a thickness of 0.
It has a structure in which a 25 μm gold / glass multilayer film 3 is arranged in a cycle of d = 0.5 μm.

Similar to the first embodiment, a prism (not shown)
Through this, Ti: sapphire laser light was made incident with a pulse width of 100 femtoseconds from one end of this waveguide type optical functional device, and the transmitted light was measured at the other end. In this case, 1.04μ
It was found that there is a wavelength region where transmitted light is not observed on the longer wavelength side than m. Further, the transmission time of light having a wavelength of 1.03 μm is 5.2 nsec (5.2 × 10 ⁻⁹ sec), and the transmission time of light having a wavelength of 0.98 μm is 370 psec (37
It was 0 × 10 ⁻¹² sec). Thus, the wavelength 1.
It was confirmed that the light of 03 μm caused a delay.

Example 3 In this example, the optical functional device shown in FIG. 8 was manufactured. As shown in FIG. 8, a 2 m long single mode fiber having a core 11 having a diameter of 8 μm and a clad 12 having a diameter of 200 μm was prepared. When light with a wavelength of 1534 nm was introduced into this fiber, the transmission time was 10 nsec.

Next, by a phase mask photolithography method, excimer laser light having a repetition rate of 50 pulses / sec, a power of 300 mJ / cm ² / pulse and a wavelength of 248 nm is irradiated for 400 minutes, and the length of the core 11 of this fiber is increased by the interference light. 5mm is exposed and 5mm
Two materials having different refractive indexes between the two formed a structure in which they were periodically arranged. Such structures were formed at intervals of 1 mm, and about 330 optical functional elements were produced in a fiber having a length of 2 m. This fiber has a wavelength of 1534 nm
When the above light was introduced, the transmission time was 220 nsec, and it was confirmed that a delay had occurred.

Example 4 In this example, the optical functional device shown in FIG. 9 was produced. 1 mm
A holographic diffraction grating 21 having 1250 grating grooves was prepared. This holographic diffraction grating 2
Silver 22 was vapor-deposited on No. 1 to a thickness of 200 nm. On top of this, nonlinear optical materials such as 2-methyl-4-nitroaniline (MNA) and polymethylmethacrylate (PM
(MA) THF solution is spin-coated and then the solvent is evaporated to form a 4 μm thick optical functional film (MNA-doped PMMA film).
23 was formed. The refractive index of this optical functional film 23 is unknown. Silver 24 was vapor-deposited to a thickness of 200 nm on the optical function film 23. Then, at 120 ° C., the two layers of silver 22, 2
After applying an electric field of 0.3 MV / cm to the optical functional film 23 for 30 minutes using 4 as an electrode to perform poling,
It returned to room temperature. After that, in order to prevent orientation relaxation, an electric field of 50 kV / cm was continuously applied to the optical functional film 23.

From one end of the optical functional film 23 of this optical functional element, polarized light whose electric field vector direction is perpendicular to the grating groove was introduced, and the intensity of the second harmonic wave emitted from the other end was measured. At this time, the wavelength of the incident light was changed within the range of 0.9 to 1.1 μm. FIG. 10 shows the relationship between the wavelength of incident light and the intensity of the second harmonic. It can be seen from FIG. 10 that phase matching is achieved when the wavelength of the incident light (fundamental wave) is 1 μm.

Example 5 In this example, the optical functional device shown in FIG. 11 was manufactured. 1m
Two holographic diffraction gratings 21 having 1800 groove grooves per m and having aluminum 22 deposited on the surface were prepared. In addition, 2-methyl-4-nitroaniline (MN
A solution was prepared by dissolving A) and polymethylmethacrylate (PMMA) in THF at a weight ratio of 1: 0.55. After spin coating the solution on one of the holographic diffraction gratings, the solvent was evaporated to form an optical functional film (MNA-doped PMMA film) 23 having a thickness of 5 μm.
The other holographic diffraction grating 21 was provided on the optical function film 23 so as to face it. Next, at 80 ° C,
A two-layer aluminum 22 was used as an electrode, a direct current voltage of 30 V was applied to the optical functional film 23 from the power supply 25 for 30 hours to perform poling, and then the temperature was returned to room temperature.

The refractive index of MNA / PMMA in this device is unknown. 800n using wavelength tunable laser
A laser beam in the wavelength range of m to 2 μm was used as a fundamental wave and was incident from one end of the optical functional film 23 of this optical functional element. This incident laser light is polarized light whose electric field vector is perpendicular to the grating grooves. Thus, the intensity of the second harmonic wave emitted from the other end of the optical function film 23 was measured. FIG. 12 shows the relationship between the wavelength and the intensity of the second harmonic. From FIG. 12, the wavelength 980
The SHG intensity is high at the wavelength of nm, and the fundamental wave (wavelength 1.
It can be seen that the phase is matched with that of 96 μm).

Example 6 In this example, the optical functional device shown in FIG. 13 was manufactured. Number of lattice grooves 360, with silver coating (not shown)
Two 0 / mm holographic diffraction gratings were prepared. On one holographic diffraction grating 31, a THF solution of rhodamine 110 and PMMA was spin-coated, and then the solvent was evaporated to form an optical functional film 33 having a thickness of 3 μm.
Was formed. The other holographic diffraction grating 31 is provided on this, and the optical function film 33 is formed by the two diffraction gratings 31 and 31.
Sandwiched. A cylindrical lens 34 is provided above the optical function film 33.

For comparison, a flat quartz glass substrate was used instead of the diffraction grating to fabricate an element having the same structure as described above. CW Argon Ion Laser (not shown)
From the cylindrical lens 34 through the wavelength 514.5
A laser beam of nm with a power of 1 W was introduced in the direction along the lattice groove. In this state, a pulse laser beam (time width: about 1 psec) having a wavelength of 580 nm is repeated from the dye laser excited by the second harmonic of the mode-locked YAG laser.
The light was introduced from one end of the optical functional film 33 so as to be orthogonal to the grating groove at MHz and a peak power of about 100 W, and the light emitted from the other end of the optical functional film 33 was measured. At this time, the peak power of the emitted light was 30 kW, and the amplification effect of the optical functional element was confirmed.

On the other hand, in the device using the flat quartz glass substrate, the peak power of the emitted light was 700 W, and the amplification effect was small. Example 7 In the same manner as in Example 6, an optical functional film made of polydihexylsilane having a thickness of 2 μm was sandwiched between two holographic diffraction gratings each having 3600 grooves / mm of silver-coated grating grooves. A light function element was manufactured. This optical functional device is a prototype of an optical switch that utilizes the third-order nonlinear optical effect of polydihexylsilane.

For comparison, a flat quartz glass substrate was used instead of the diffraction grating to fabricate an element having the same structure as the above. Based on the degenerate four-wave mixing method, the above two elements have a wavelength of 565 nm and a power density of 2 × 10 ^6.
Using three laser lights having a width of about 100 femtoseconds and W / cm ² , the ratio of the power of the signal light to be incident on the optical functional film and emitted from the optical functional film was measured. As a result,
The signal light power of the element using the diffraction grating was about 1600 times that of the element using the flat quartz glass substrate. Converting this to a third-order nonlinear susceptibility, the element using the diffraction grating corresponds to about 40 times the element using the flat quartz glass substrate.

Example 8 A silver coating was applied on the holographic diffraction grating having 3600 grooves / mm to form a PMMA film having a thickness of 3 μm.

For comparison, a silver coating was applied on a quartz glass substrate to form a PMMA film having a thickness of 3 μm. Mode-locked Y for the above two elements
A laser beam of 580 nm was made incident on the PMMA film from the dye laser excited by the second harmonic of the AG laser so as to be orthogonal to the lattice groove, and the transmitted light was measured. As a result, the transmission time when compared with the same optical path length was about 10 times in the element using the diffraction grating as compared with the element using the flat quartz glass substrate.

Example 9 Two holographic diffraction gratings each having 2900 grooves / mm were prepared by vapor-depositing aluminum to a thickness of 50 nm. A THF solution of polymethylphenylsilane was spin-coated on one holographic diffraction grating, and the solvent was evaporated to form a polymethylphenylsilane thin film having a thickness of 0.6 μm. On this, the other holographic diffraction grating was placed so as to face it, and an optical functional element was produced. In this element, aluminum on both sides of the polymethylphenylsilane thin film also serves as electrodes, and the polymethylphenylsilane functions as a light emitting material.

For comparison, a flat quartz glass substrate was used instead of the diffraction grating to fabricate an element having the same structure as described above. First, light of various wavelengths was made incident from one end of the polymethylphenylsilane thin film, and the transmitted light emitted from the other end was measured. As a result, light of all wavelengths was transmitted through the device using the flat quartz glass substrate. On the other hand, the element using the diffraction grating did not transmit light in the wavelength range of 450 to 600 nm.

Next, when a voltage of 11 V was applied between the aluminum electrodes at −240 ° C., light emission was confirmed from the interface. At this time, in the device using the flat quartz glass substrate, a broad emission peak at 460 to 620 nm due to impurities was observed in addition to a sharp emission peak near 350 nm. On the other hand, in the device using the diffraction grating, only the emission peak at 350 nm was observed on the shorter wavelength side than 600 nm. Regarding the amount of light emission at the emission peak of 350 nm, the element using the diffraction grating
The size was about four times larger than that of an element using a flat quartz glass substrate.

Example 10 Two holographic diffraction gratings having 1800 grooves / mm of grating grooves and aluminum vapor-deposited on the surface were prepared.
In addition, methyl (2,4-dinitrophenyl) amino-2
-Propanoate (MAP) in dioxane 1 x 10 ^-4
A solution dissolved at a concentration of mol / L was prepared. A MAP solution was spin-coated on one of the diffraction gratings, and the solvent was evaporated to form an optical functional film having a thickness of 10 μm. The other holographic diffraction grating was provided on the optical functional film so as to face it. The optical path length of this device was 1 cm.

A wavelength of 5 from a CW dye laser was applied to this device.
A 30 nm laser beam was incident, a driving voltage with a pulse width of 1 μsec and an electric field of 1 kV / mm was applied from the aluminum film on the diffraction grating, and the transmitted light intensity was measured. as a result,
As shown in FIG. 14, the transmitted light was detected and modulated by the application of the drive voltage.

Example 11 In this example, an optical functional element (optical modulator) shown in FIG. 15 was manufactured. Holographic diffraction grating 4 having 1800 grooves / mm of grating grooves and aluminum 42 vapor-deposited on the surface.
Two pieces of 1 were prepared. In addition, 2-methyl-4-nitroaniline (MNA): poly (methyl methacrylate) = 1:
A solution was prepared by dissolving 0.55 (weight ratio) in the TFT. This solution was spin-coated on one diffraction grating and the solvent was evaporated to form an optical functional film 43 with a thickness of 5 μm.
The other holographic diffraction grating 41 was arranged on the optical functional film 43 so as to face it. The optical path length of this device is 3
It was 0 μm. This device was heated to 80 ° C., and a direct current voltage of 80 V was applied from the direct current power source 44 through the two-layer aluminum 42 for 30 hours to perform poling. Also, 2
A drive circuit 45 for applying an AC voltage to the optical functional film 43 made of MNA / PMMA to change the refractive index of the optical functional film 43 is connected to the aluminum layer 42.
Two holographic diffraction gratings 51 each having a grating groove of 1920 lines / mm and having aluminum 52 vapor-deposited on the surface were provided in the subsequent stage of this light modulation element so as to face each other. These holographic diffraction gratings 51 act as an optical delay element that delays the group velocity of light after the light exits the light modulation element.

Laser light having a wavelength of 530 nm from a CW dye laser was made incident on the optical modulator and the optical delay element. The incident light is polarized light whose electric field vector is perpendicular to the grating grooves. In the optical modulator and the optical delay element, the group velocity of light is about 1/8 of the velocity of light in vacuum. Drive circuit 45
To 300 peak voltage through 2 layers of aluminum 42
By applying an AC voltage of V and a frequency of 240 MHz, the refractive index of the optical functional film 43 was changed to perform AM modulation.
As a result of extracting the signal from the optical delay element section in the latter stage, the frequency of the output light was 1.7 GHz. Thus, it can be seen that after the group velocity of light is delayed within the element, the group velocity of light is increased when leaving the element.

Example 12 Styrene and isoprene represented by the following chemical formulas were used as the monomers constituting the block copolymer.

[0080]

[Chemical 1]

Styrene and isoprene were successively subjected to living anionic polymerization in tetrahydrofuran using sec-butyllithium as an initiator. as a result,
Polystyrene chain with molecular weight 34 × 10 ⁴ and molecular weight 18 × 1
A block copolymer consisting of 0 ⁴ polyisoprene chains was obtained. The obtained block copolymer was dissolved in a solvent and cast on a substrate to form a thin film. When observed with an electron microscope, this thin film had a diamond structure with a lattice constant of about 200 nm. This thin film is referred to as a copolymer film A.

On the other hand, a molecular weight of 47 was obtained by sequential living anionic polymerization in the same manner as above except that the monomer ratio was changed.
A block copolymer consisting of 10,000 polystyrene chains and a polyisoprene chain having a molecular weight of 110,000 was synthesized. Similar to the above,
The obtained block copolymer was dissolved in a solvent and cast on a substrate to form a thin film. When observed with an electron microscope, this thin film has a face-centered cubic (F
CC) structure. This thin film is referred to as a copolymer film B.

The transmission spectra of copolymer films A and B were measured. The transmission spectrum of copolymer film A is shown in FIG. As shown in this figure, it can be seen that the copolymer film A does not transmit light in the wavelength region near about 400 nm and a photonic band gap is formed.
On the other hand, although not shown, the photonic film
No band gap was formed. These results are
This is consistent with the finding that a photonic bandgap is unlikely to appear in the FCC structure and is likely to appear in a diamond structure having low symmetry.

Example 13 By sequential living anionic polymerization as in Example 12,
A block copolymer of a laser dye monomer represented by the following chemical formula and isoprene was synthesized.

[0085]

[Chemical 2]

After the obtained block copolymer was dissolved in a solvent, crosslinked modified polyisoprene spheres having a diameter of about 100 nm which were insoluble in the solvent were mixed. This solution was cast on a substrate to form a thin film. This thin film is referred to as a copolymer film C. Polyisoprene spheres become impurities that disturb the periodic change in the refractive index in the phase-separated block copolymer. The transmission spectrum of copolymer film C is shown in FIG. As shown in this figure, a wavelength region that penetrates the thin film appears at the center of the photonic bandgap.

A wavelength of 337 nm from a nitrogen laser, a repetition rate of 10 Hz, and a time width of 10 nsec were applied to the copolymer film C.
Was irradiated with the laser beam, and the average power was gradually increased to measure the output energy. FIG. 18 shows the relationship between the input energy and the output energy at this time. As shown in this figure, when the input energy exceeds the threshold value, the output energy increases in proportion to the input energy. From this, it can be seen that laser oscillation is occurring.

[0088]

As described above in detail, according to the present invention, an optical functional element capable of delaying an optical signal in a small installation space, and various optical functional materials utilizing optical signal delay and refractive index control. It is possible to provide an optical functional device capable of effectively exhibiting the above function.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the frequency of light passing through a photonic band structure and the wave number of a wave packet.

FIG. 2 is a diagram showing a relationship between a wavelength of light transmitted through a photonic band structure and a speed of light.

FIG. 3 is a diagram showing the relationship between the frequency of light transmitted through a photonic band structure containing metal and the wave number of a wave packet.

FIG. 4 is a diagram showing a relationship between a wavelength of a fundamental wave and a second harmonic and a refractive index.

FIG. 5 is a diagram showing a relationship between wavelength and transmittance with a change in the refractive index of the light modulation element.

FIG. 6 is a perspective view of an optical delay element in Example 1 of the present invention.

FIG. 7 is a perspective view of an optical delay element in Example 2 of the present invention.

FIG. 8 is a perspective view of an optical delay element in Example 3 of the present invention.

FIG. 9 is a sectional view of a wavelength conversion element according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing the relationship between the wavelength of incident light and the intensity of the second harmonic measured by the wavelength conversion element in Example 4 of the present invention.

FIG. 11 is a sectional view of a light wavelength conversion element according to a fifth embodiment of the present invention.

FIG. 12 is a diagram showing the relationship between the wavelength and intensity of the second harmonic measured by the wavelength conversion element according to the fifth embodiment of the present invention.

FIG. 13 is a perspective view of an optical amplifier according to a sixth embodiment of the present invention.

FIG. 14 is a diagram showing a modulation signal obtained by an optical modulation element according to Example 10 of the present invention.

FIG. 15 is a sectional view of an optical modulator according to an eleventh embodiment of the present invention.

FIG. 16 is a transmission spectrum of the copolymer film A of Example 12 of the invention.

FIG. 17 is a transmission spectrum of the copolymer film C of Example 13 of the present invention.

FIG. 18 is a diagram showing a relationship between input energy and output energy of the copolymer film C of Example 13 of the present invention.

[Explanation of symbols]

1 ... Glass substrate 2 ... Resist 3 ... Gold / glass multilayer film 11 ... Core 12 ... Clad 21 ... Holographic diffraction grating 22 ... Silver 23 ... Optical functional film 24 ... Silver 25 ... DC power supply 31 ... Holographic diffraction grating 33 ... Optical functional film 34 ... Cylindrical lens 41 ... Holographic diffraction grating 42 ... Aluminum 43 ... Optical functional film 44 ... DC power supply 45 ... Drive circuit 51 ... Holographic diffraction grating 52 ... Aluminum

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01S 3/10 H01S 3/10 Z 3/16 3/16 (56) Reference JP-A-7-159609 (JP, A) Kaihei 4-241486 (JP, A) J. P. Dowling, C.I. M. Bowden, ANOMALOUS IN DEX OF REFRACTION IN PHOTONIC BANDGA P MATERIALS, Journal of Modern Optics, 1994, vol. 41, no. 2, pp. 345-351 Kazuaki Sakoda, Kazuo Otaka, Nonlinear Optical Process in Photonic Crystals, "Quantum Phase Electronics" 1995 Research Results Report (Proceedings of Training Results Report Meeting), Japan, February 1, 1996 , Pp. 95-100 Kenneth O.M. Hill, Bragg Grating Fiber Devices, OPTRONICS, 1995, pp. 135-141 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/00-1/125 G02F 1/29- 7/00

Claims (5)

(57) [Claims] 1. A diffraction grating that forms a photonic band, and a metal film, an optical functional film, and a metal film that are sequentially formed on the surface of the diffraction grating , wherein the optical functional film is a second-order nonlinear optical material.
Materials, third-order nonlinear optical materials, light-emitting materials, optical amplification materials and
Including an optical functional material selected from the group consisting of electro-optical materials
Optical functional device according to claim no possible. 2. A photonic device arranged facing each other.
Two diffraction gratings each having a metal film formed on the surface or a pair of a diffraction grating having a metal film formed on the surface and a flat metal body forming a band, and between or between the two diffraction gratings And an optical functional film sandwiched between a flat metal body, and the optical functional film is a second-order nonlinear optical material or a third-order nonlinear optical material.
Non-linear optical materials, light emitting materials, light amplification materials and electro-optics
An optical functional element comprising an optical functional material selected from the group consisting of materials . 3. The optical functional film is a second-order nonlinear optical material,
Non-linear optical materials, luminescent materials, optical amplification materials and electro-optics
3. A polymer in which an optical functional material selected from the group consisting of scientific materials is dispersed.
The optical functional device described in 1. 4. Two diffraction gratings, which are arranged to face each other and each have a metal film formed on the surface thereof to form a photonic band, and an electro-optical material sandwiched between these diffraction gratings. A drive circuit connected to the metal film and applying a voltage for changing the refractive index of the electro-optical material. Of 5. The method of claim 4, wherein, downstream of the optical functional device functions as an optical modulation element, are arranged opposite to each other, respectively a metal film formed on the surface thereof, two of forming a photonic band An optical function element further comprising an optical delay element having the diffraction grating of 1.