JPH05210131A - Nonlinear optical material and optical functional element - Google Patents

Abstract

PURPOSE:To obtain a large nonlinear optical constant and short cut-off wavelength by using a specified tetrazolium salt deriv. as a medium for a nonlinear optical element. CONSTITUTION:This nonlinear optical material consists of a tetrazolium salt compd. expressed by formula. In the formula, at least one of R1, R2 and R3 is an aromatic ring, hetero ring, or org. group having a conjugated system, and others are hydrogen atoms, halogen atoms, nitro groups, amino groups, cyano groups or org. residues. Further, these may be same, different, or substd. X is an inorg. ion such as halogen ion, hypochlorous acid ion, and tosyl acid ion. In this case, the medium used is in a crystalline or noncrystaline state in a form of block, plate, fiber, powder or thin film. Other materials of different kinds or different structures may be used or mixed with this compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear optical element using an organic material excellent in nonlinear optical effect such as optical mixing, optical parametric oscillation, optical harmonic generation, Pockels effect, Kerr effect, etc. The present invention relates to optical elements such as optical wavelength conversion elements, optical modulators, optical switches, and optical memories.

[0002]

2. Description of the Related Art Non-linear optical elements have been attracting attention as wavelength conversion elements utilizing second-order and third-order optical harmonic generation, optical mixing, or optical parametric oscillation. In addition, it is attracting attention as a basic element of an optical computer expected to be realized in the future, such as an optical bistable element as an optical switch.

Conventionally, inorganic materials such as lithium niobate (LiNbO ₃ ) and gallium arsenide (GaAs) have been studied in detail as nonlinear optical materials. However, in recent years, organic nonlinear optical materials with much higher nonlinear optical performance (10 to 100 times) than those materials and very high optical response speed, which is important for optical bistable devices, have been studied. Became.

These organic nonlinear optical materials include urea,
2-Methyl-4-nitroaniline (name MNA)
55-500960), N- (4-nitrophenyl) -L
-Prolinol (abbreviation NPP) (Japanese Patent Laid-Open No. 59-21665) has been proposed. In particular, it is known that MNA and NPP have a second-order nonlinear optical effect that is 100 times or more that of inorganic materials.

[0005]

The above-mentioned conventional organic nonlinear optical material has a very large nonlinear optical constant, but on the other hand, it is difficult to obtain a large single crystal, the stability of the crystal is poor, and light transmittance is exhibited. There is a problem in that the cutoff wavelength is long, that is, the light absorption is in the visible range. In particular, the problem that the cutoff wavelength is long is considered to be a problem to be improved in practical use such as application to an optical second harmonic generation (SHG) wavelength conversion element. The same applies not only to the SHG wavelength conversion element, but also to a wide range of optical processing in the visible range. MN
In A, the cutoff wavelength is 480 nm, and in NPP, it is about 490 nm. Therefore, the near-infrared semiconductor laser currently used (oscillation wavelength of about 80
It is considered that the material of the SHG wavelength conversion element of 0 to 900 nm) is not preferable. Furthermore, most of the organic nonlinear optical materials known today as materials for SHG wavelength conversion elements for red semiconductor lasers (oscillation wavelengths of about 600 to 800 nm), which have recently been put into practical use, should be used for their long cutoff wavelengths. I can't.

When developing such an organic nonlinear optical material having excellent transparency, the molecular design policy is to improve nonlinearity per molecule and transparency, and at the same time control the molecular orientation in the crystalline state. It becomes important.

Of these, the second-order nonlinear polarizability β per molecule is given by the equation (1) according to the two-level model in which only the ground state and the excited state having the largest contribution are considered. (Reference: See, for example, Masahiro Umegaki, "Organic Nonlinear Optical Materials," published by Bunshin (1990).)

[0008]

[Equation 1]

Where e is the elementary charge, h is Planck's constant, Δr _e is the difference between the permanent dipole moments of the ground and excited states, r _ge is the transition moment from the ground state to the excited state, and ω _eg is the ground state. And the frequency difference between excited states, and ω is the frequency of incident light. To increase this β, Δr
_It is necessary to increase _e and r _eg and decrease ω _eg . For that reason, a molecule in which the electron distribution in the molecule in the ground state and the excited state largely changes is preferable. That is, the larger the intramolecular charge mobility, the greater the non-linearity per molecule. However, the longest absorption spectrum showing the transparency of a molecule has a peak at ω _eg and its relaxation intensity is shown in an amount depending on r _eg. Therefore, even if ω _eg is made small and r _eg is made large, the absorption edge becomes long. And the transparency of the compound decreases. In other words, there is a trade-off relationship between non-linearity per molecule and transparency, and there is a limit to improving the characteristics only by designing the molecular structure.

On the other hand, the nonlinear constant of the crystal state depends on the orientation state and density of the molecules in the unit cell of the crystal. When a centrosymmetric orientation state is adopted, the crystal cannot exhibit non-linearity no matter how large the non-linearity per molecule is, and it is necessary to form a crystal structure in any other orientation state. However, it is not currently possible to theoretically predict the crystal structure in advance, and it is necessary to actually synthesize a new compound and measure the non-linearity with a single crystal. For this reason, there is a demand for a design guideline for a molecule that tends to have a crystal structure that can surely utilize the non-linearity per molecule even in a crystalline state.

Furthermore, when an organic nonlinear compound is used in an actual optical functional device, the ease of producing a single crystal thereof is indispensable from the viewpoint of device design and mass production. Since many organic nonlinear optical materials form molecular crystals that are bonded by weak Van der Waals forces, the single crystal production is more controlled than the single crystal production of inorganic semiconductors such as Si and GeAs. However, many organic compounds are weak in chemical and thermal stability and often deteriorate with long-term crystal growth. .. Moreover, since the grown crystal is a molecular crystal, its mechanical and mechanical strength is extremely weak, and it is difficult to cut and polish it as an optical element.

An object of the present invention is to provide a nonlinear optical element using a stable organic nonlinear optical material having a large nonlinear optical constant and a short cutoff wavelength.

[0013]

The gist of the present invention for solving the above problems is as follows.

General formula (1)

[0015]

[Chemical 3]

(In the formula, at least one of R ₁ , R ₂ and R ₃ represents an aromatic ring, a hetero ring, or an organic group having a conjugated system, and the others are hydrogen atom, halogen atom, nitro group, amino group, A cyano group or an organic residue, which may be different from each other or substituted, and X represents an inorganic or organic anion such as a halogen ion, a hypochlorite ion, or a tosylate ion. The non-linear optical material is characterized by being composed of a tetrazolium salt compound represented by.

General formula (2)

[0018]

[Chemical 4]

(In the formula, R ₁ ′, R ₂ ′ and R ₃ ′ represent a hydrogen atom, a halogen atom, a nitro group, an amino group, a cyano group, or an organic residue, and if they are different from each other, they are substituted. X is a halogen ion,
Inorganic and organic anions such as hypochlorite ion and tosylate ion are shown. It is desirable that the nonlinear optical material is composed of a tetrazolium salt compound having a para-substituted phenyl group represented by the formula (1).

The non-linear optical material of the present invention, in a crystalline or non-crystalline state as a simple substance, is in the form of a lump, a plate, a fiber, a powder,
It can be formed into a thin film and used. Further, in this shape, different materials or other materials having different structures according to the present invention can coexist or be mixed. In particular, specific application examples of these include optical waveguides, optical cables, optical integrated circuits, and display devices.

When the nonlinear optical material of the present invention is used in a crystalline state, a known method can be used for forming the crystal.
For example, there are the Bridgman method, the temperature drop method, the solvent evaporation method, the solvent composition change method, and the like.

Further, other materials which can coexist and coexist are inorganic substances such as glass, quartz, diamond, silicon dioxide, mica, marble, calcite, single crystal silicon, amorphous silicon, GaP, CdS. , KDP, K
TP, lithium niobate, charisma, Rochelle salt, copper sulfate, calcium fluoride, graphite, tin dioxide, barium titanate, red blood salt, ceramics, ceramics, bentonite, cement, etc. and metals or alloys can be used. .. Examples of organic substances include polycarbonate, polysulfone, polyarylate, polyester,
Polyamide, polyimide, polysiloxane, polyethylene terephthalate, polyvinyl acetate, polyethylene, polypropylene, acrylic resin, polybutadiene, polyvinyl chloride, polyvinylidene chloride, petroleum resin, melamine resin, epoxy resin, phenol resin, isoprene rubber,
Ethylene-propylene rubber, norbornene resin, cyanoacrylate resin, styrene resin and copolymers of these resins, or cellulose, starch, chitin, agar, silk thread, cotton thread, nylon thread, albumin, globulin and other proteins, wood, bone meal However, examples of low-molecular organic substances include condensed aromatic compounds such as naphthalene and anthracene, dyes, pigments, urea, tartaric acid, and optically active amino acids.

The non-linear optical material may be adhered, fused, electrodeposited, vapor deposited, pressure bonded, sputtered, MBE method, dyeed, melt-molded, kneaded, press-molded, coated from a solution or the like depending on its use or purpose. Can be formed by various methods.

After forming a product using the non-linear optical material of the present invention, a treatment for improving the appearance and characteristics and extending the life may be performed. Examples of such a post-treatment include thermal annealing radiation irradiation, electron beam irradiation, light irradiation, radio wave irradiation, magnetic force line irradiation, and ultrasonic wave irradiation, but are not particularly limited.

The nonlinear optical material of the present invention is Nd in a powder state.
-By irradiating YAG laser light (wavelength 1.06 μm), it is possible to generate green light (wavelength 0.53 μm) which is the second harmonic of light.

Further, the single crystal nonlinear optical material can generate a coherent optical second harmonic by injecting an Nd-YAG laser beam from a specific crystal plane, and such a crystal can be used as a laser beam. It is possible to generate a coherent optical second harmonic with high conversion efficiency by holding it in the resonator.

By filling the non-linear optical material in the space to be the core surrounded by the cladding layer to form a single crystal,
It is possible to generate an optical second harmonic even with a small incident light intensity. In this case, when a GaAlAs semiconductor laser (wavelength 0.88 to 0.75 μm) is used as a light source, a short wavelength solid-state laser that oscillates blue light (wavelength 0.44 to 0.37 μm) can be formed. The cladding and core can be formed in either fiber or waveguide configurations.

The non-linear optical material of the present invention is used in devices utilizing various non-linear optical effects, particularly non-linear optics characterized by even-order non-linear susceptibility including second-order non-linearity. Further, by using the organic nonlinear optical element of the present invention, the resonator type light 2 having high laser light resistance can be obtained.
It is possible to realize a second harmonic generation element and a compact and high power density Cherenkov type optical second harmonic generation element.

A specific application is a nonlinear optical element using an organic material excellent in nonlinear optical effect such as light mixing, optical parametric oscillation, generation of optical harmonics, Pockels effect, Kerr effect, etc., in particular, an optical wavelength conversion element. , Optical modulators, optical switches, optical memories, optical mixers, optical phase separators, optical phase conjugate mirrors, optical waveguides, optical functional elements such as optical logic circuits.

[0030]

According to the present invention, as in a nonlinear optical element using a conventional organic nonlinear optical material, a crystal having a cutoff wavelength in the visible region or an inversion symmetry due to a large dipole moment in a molecule. The problem that the tendency to form is strong is solved. In addition, since the medium is composed of a compound containing a structure having a tetrazolium salt skeleton at the molecular center, substituents that cause optical nonlinear polarization can be bonded at high density, and the tetrazolium group can be substituted by multiple optical nonlinear polarizations. The non-linear susceptibility per molecule can be increased to give the groups a common electron donating or donating property. Furthermore, since this medium is composed of a compound containing a structure having a tetrazolium salt skeleton, which is a 5-membered heterocyclic ring, at the center of the molecule, crystallization is specifically carried out at the skeleton portion,
In addition, since a crystal is formed by ionic coupling, it has a non-centrosymmetric crystal structure, which is indispensable for optical second harmonic generation, which is one of the organic nonlinear optics. A non-linear optical element made of a high medium can be provided. Further, by using a non-linear optical element made of a medium having such characteristics, a resonator-type optical second harmonic generation element requiring particularly high laser light resistance and a compact and high power density Cerenkov-type optical second harmonic generation element A wave generating element can be realized.

[0031]

EXAMPLES Examples of the organic nonlinear optical element according to the present invention will be described below.

Example 1 First, a structural formula (3) which is one of the compound tetrazolium salt derivatives represented by the above structural formula (1).

[0033]

[Chemical 5]

The results of confirming the optical second harmonic generation (SHG) and the transparency of the 2,3-bis (p-nitrophenyl) -5-phenyltetrazolium chloride represented by are explained below.

Commercially available 2,3-bis (p-nitrophenyl) -5-phenyltetrazolium chloride (manufactured by Tokyo Kasei) was dissolved in 98% ethanol at 70 ° C to give a saturated solution, and the temperature was changed from 70 ° C to -10 ° C. The mixture was gradually cooled at a rate of −0.23 ° C./hour for about 2 weeks to obtain a plurality of colorless and transparent single crystals of 10 × 5 × 5 mm to several hundreds of μm square.

Next, among these single crystals, relatively small single crystals having a size of 1 mm square or less are collected, crushed in an agate bowl, and sieved to collect powder having a particle size of 100 μm to 300 μm, and then pelletized. Compacted. This pellet was attached to a non-fluorescent slide glass, and a Q-switched Nd-YAG laser beam (Kantaray Co., DCR-
When irradiated with a wavelength of 1.06 μm, a peak power of 0.1 MW, and a repetition frequency of 10 Hz, a green second harmonic wave was observed. The intensity was 16.7 times as high as when the urea laser was irradiated with the same laser beam.

Next, a part of this powder was dissolved in ethanol to form a solution having a concentration of 1.0 × 10 ^-5 mol / l, and a wavelength of 200 was obtained using a spectroscope (Hitachi 340 type self-recording spectrophotometer). The absorption spectrum was measured in the range of ˜850 nm. As a result, λ _max = 332 nm, cutoff wavelength 3
It was found to be 55 nm.

Example 2 Next, another tetrazolium salt compound, 2,3-diphenyl-5- (p-methoxyphenyl) tetrazolium chloride and 2,3-diphenyl chloride.
5- (p-chlorophenyl) tetrazolium chloride 2,
3-bis (p-ethylphenyl) -5-phenyltetrazolium, 2,3-bis (p-methoxyphenyl) chloride
Table 1 summarizes the results of testing the non-linear optical characteristics in the powder state for -5- (p-cyano) phenyltetrazolium in the same procedure as in Example 1 above. It can be seen that the non-linearity is inferior to the tetrazolium salt shown in Example 1, but the transparency is improved.

[0039]

[Table 1]

Example 3 Next, using the tetrazolium salt compound and 2,3-bis (p-nitrophenyl) -5-phenyltetrazolium chloride shown in Example 1, light 2 was added.
The results of fabricating a Cherenkov type device, which is one of the next harmonic generation devices, are shown. Put 3 grams of 2,3-bis (p-nitrophenyl) -5-phenyltetrazolium chloride in a glass ampoule, and set up a glass hollow capillary with an inner diameter of 2 μm, an outer diameter of 1 mm, a length of 10 cm and a refractive index of 1.70. The glass ampoule was sealed under a high vacuum of 10 ⁻⁴ Torr. This glass ampoule was heated to 250 ° C. to melt 2,3-bis (p-nitrophenyl) -5-phenyltetrazolium chloride and encapsulated in a hollow capillary by a capillary phenomenon. After this glass ampoule was left to cool to room temperature, the vacuum was broken and the capillary inside was taken out. This is moved in a micro heater with a heating section length of 1 cm, moving speed 0.5 cm / h
Then, remelting and recrystallization were performed from one end of the capillary, and a single crystal with a maximum size of 6 cm was produced inside the capillary. A single crystal portion of this capillary was cut into a length of 2 to 3 mm to obtain an SHG element. This element was held in the Cherenkov type device evaluation system shown in FIG. 2, and the oscillation wavelength was 940 nm and the output was 40 m.
When the laser diode light of W was introduced into the inside of the single crystal from one end thereof, a blue ring of an optical harmonic having a wavelength of 470 nm was observed from the other end thereof.

[0041]

According to the present invention, it is possible to obtain an organic nonlinear optical element using a material having a short cutoff wavelength and a large nonlinear optical constant.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical system for confirming generation of an optical second harmonic used in an example of the present invention.

FIG. 2 is an explanatory diagram of a Cherenkov type device which is one of the optical second harmonic generation devices used in the examples of the present invention.

[Explanation of symbols]

1 ... Q-switch Nd-YAG laser, 2 ... Substrate, 3 ...
Sample, 4 ... Damper, 5 ... Lens, 6 ... Infrared cut filter, 7 ... Monochromator, 8 ... Photomultiplier tube, 9 ... Pen recorder, 10 ... Incident light, 11 ... Reflected light, 12 ... Scattered light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Kawabata 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Institute, Ltd.Hitachi Research Laboratory (72) Masato Isogai 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Nitate Works Co., Ltd. Hitachi Research Laboratory (72) Inventor Atsushi Tsunoda 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. A general formula (1): (In the formula, at least one of R ₁ , R ₂ and R ₃ is an aromatic ring,
Represents a heterocyclic ring or an organic group having a conjugated system, other represents a hydrogen atom, a halogen atom, a nitro group, an amino group, a cyano group, or an organic residue, and these may be different from each other or may be substituted. Good. X represents an inorganic or organic anion such as a halogen ion, a hypochlorite ion, or a tosylate ion. ) A non-linear optical material comprising a tetrazolium salt compound represented by the formula (1). 2. A general formula (2): (In the formula, R ₁ ′, R ₂ ′ and R ₃ ′ represent a hydrogen atom, a halogen atom, a nitro group, an amino group, a cyano group, or an organic residue, and these are different from each other and are substituted. In addition, X is a tetrazolium salt compound represented by an inorganic or organic anion such as a halogen ion, a hypochlorite ion, or a tosylate ion.), A non-linear optical material. 3. An optical functional element using the nonlinear optical material according to claim 1 or 2.