JP2614301B2 - Nonlinear optical device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical device such as an optical switch, an optical memory, or an optical signal processing device used in optical data / information processing or an optical communication system. .

[Conventional technology]

The nonlinear optical device is an effect that occurs because the electric polarization P in a substance has higher-order terms of E ² and E ^{3 in} addition to a term proportional to the electric field E of light as described below.

P = χ ⁽¹⁾ E + χ ⁽²⁾ E ² + χ ⁽³⁾ E ³ + ··· (1) In particular, the third term is the third harmonic generation (of frequency ω) well known as a third-order nonlinear effect. (A phenomenon of emitting light of 3ω with respect to the incident light) and a change in the refractive index depending on the intensity of light represented by the following equation.

n = n ₀ + n ₂ I (2) n ₂ is the third-order nonlinear susceptibility χ ^{(3) in the} equation (1). Here, n ₀ is a normal refractive index, and c is the speed of light.

When an optical medium having this effect is combined with another optical element such as an optical resonator, a polarizing mirror, or a reflecting mirror, optical information processing such as an optical bistable element, an optical control optical switch, or a phase conjugate wave generating device can be performed. Important devices used in optical communication systems can be constructed.

Hereinafter, an optical control optical switch using an optical Kerr shutter, which is known as a representative example of a nonlinear optical device using a nonlinear refractive index, will be described.

As shown in FIG. 1, the optical Kerr shutter is to gate input light with gate pulse light and obtain output light corresponding to the time waveform of the gate pulse.

In FIG. 1, reference numeral 1 denotes a nonlinear refractive index medium having a length.
A CS ₂ (carbon disulfide) liquid is sealed in a 1-mm glass cell. Reference numerals 2a and 2b denote direct-light polarizers consisting of two polarizers arranged so that their polarization axes are orthogonal to each other. is there. In this configuration, only while the gate pulse light Pg is incident, the linearly polarized light of the input light Pi that has passed through the polarizer 2a changes to elliptically polarized light due to the change in the refractive index of the non-linear refractive index medium 1, so that the light The portion can pass through the orthogonal polarizer 2b, and the output light Pt is obtained. That is, the input light Pi is optically switched by the pulse of the gate pulse light Pg.

The instantaneous transmittance T of the input light Pi becomes maximum when the polarization direction of the gate pulse light Pg and the polarization direction of the input light Pi are inclined by 45 °.

In this case, T = sin ² (Δφ / 2) (4) It is represented by Where L is the medium length, λ is the input light wavelength, Iin
Is the intensity of the gate pulse light Pg, and n ₂ is the nonlinear refractive index.
(4) When Δφ is sufficiently small in formula, because the _{^{Tαn 2 2 L 2 Iin 2 (}} 6), T is proportional to the square of n _2.

[Problems to be solved by the invention]

However, in the present inventors have been additional test the optical Kerr shutter CS ₂ shown in FIG. 1 is, λ = 0.83μm, L = 1mm , I
When in = 300 MW / cm ² , an instantaneous transmittance T = 0.8% was obtained. From this result, it is (4) of the calculation of the nonlinear refractive index n ₂ with ^{_{(5), n 2 = 7.7 × 10 -14}} cm 2 / W (7). When the nonlinear susceptibility χ ⁽³⁾ is calculated from this n ₂ value, 非 線形⁽³⁾ = 3.6 × 10 ⁻¹² esu is calculated.

The response speed of the CS ₂ optical Kerr shutter has been confirmed to exhibit a high speed response of the order of 1 picosecond and are therefore extensively used in the measurement system such as instant photography and fast spectroscopy.
However, there is a drawback that the nonlinear efficiency is not always large, as determined by the equation (7), and therefore an extremely large gate light intensity is required.

As is clear from the above, the performance of the nonlinear optical device is almost determined by the characteristics of the nonlinear optical material used as the optical medium. That is, the nonlinear effect is large,
There is an aspiration for the development of a material having a small input light intensity required for the operation, and active material development research is currently being conducted.

Among materials having a third-order nonlinear optical effect, an organic nonlinear optical material having a π-electron conjugated system such as an aromatic ring or a double or triple bond has recently received particular attention. For example, poly (2,4
-Hexadiyne-1,6-diol bis (p-toluenesulfonate) (abbreviated as PTS) has a third-order nonlinear susceptibility χ ⁽³⁾
値⁽³⁾ = 1 × 10 ^-10 esu (nonlinear refractive index n ₂
When converted to ^{CS2, it} has a large value of n ₂ = 2 × 10 ⁻¹² cm ² / W (a value that is two orders of magnitude larger than CS ₂ ). Furthermore, since the mechanism of this nonlinear optical effect is not based on absorption or interaction with molecules or crystals, but is derived from pure intramolecular π-electron polarization, the response time that can follow the intensity change of the optical signal Is very fast, about 10 ^-14 sec.

However, the polydiacetylene-based material represented by the PTS generally becomes insoluble and infusible and has poor workability. Therefore, it has been very difficult to obtain an optical medium having a desired shape, surface smoothness, and the like. In fact, a nonlinear optical device using PTS as an optical medium has not yet been realized.

On the other hand, low-molecular-weight crystalline materials such as benzene derivatives, pyridine derivatives, styrene derivatives, butadiene derivatives, stilbene derivatives, tolan derivatives, azobenzene derivatives, and benzylidene aniline derivatives, or stilbazolium salts are examples of organic nonlinear optical materials having a third-order effect having an aromatic ring. ,
Low molecular ionic crystalline materials such as pyridinium salts, azulhenium salts, quinolium salts and the like have been reported. However, in these molecular crystal materials or ionic crystal materials, it is easier to grow large crystals than the above-mentioned polyacetylene-based materials, and those having excellent optical quality can be obtained. Is still scarce. For this reason, it is still difficult to obtain an optical medium having a desired shape, surface smoothness, and the like.

Attempts have also been made to obtain an optical medium using a solution in which the above-mentioned molecular crystal material or ionic crystal material is dissolved in an organic solvent, and the nonlinear harmonics of the solution material are generated by third harmonic generation (THG). Constants have been evaluated and reported. Table 1 shows the results of measurement of the χ ⁽³⁾ value of the molecular crystalline material or the ionic crystalline material solution by THG measurement, which was recently supplemented by the present inventors.

As is clear from Table 1, the value of χ ⁽³⁾ obtained in a solution having a concentration of about 5 wt% is at most χ ⁽³⁾ = 1 × 10 ⁻¹³ esu, and the value of CS ₂ described above (前述^{( 3)} = 3.6 × 10 ^-12 es
Compared with u), it was considerably small, and was not a sufficient value to realize a nonlinear optical device.

The present invention has been made in view of the above problem, and has as its object to provide a nonlinear refractive index medium having a large nonlinearity, and as a result, to provide a nonlinear optical device that operates with low light intensity.

[Means for solving the problem]

In the present invention, in a nonlinear optical device including an optical medium having a nonlinear refractive index and an optical element such as a polarizer, an optical resonator, or a reflecting mirror, a molecular crystalline material is used as the optical medium having a nonlinear refractive index. Alternatively, the solution is to use a solution medium in which the ionic crystal material is dissolved in a single organic solvent or a mixed solvent.

As already described in the conventional example, the solution of the molecular crystalline material or the ionic crystalline material does not show a sufficiently large χ ⁽³⁾ value as long as it is observed by THG measurement. However, when this is used as a nonlinear refractive index medium of a nonlinear optical device, it shows extremely high efficiency, and it is possible to realize an efficiency that is more than 10 times higher than the value conventionally evaluated by THG by appropriately selecting a solvent. The present invention has been clarified for the first time.

The molecular crystalline material referred to herein is 4-nitroaniline (p-NA), 4- (N, N-diethylamino) nitrobenzene (p-DEANB), 2-methyl-4-nitroaniline (MNA), Nitrophenylprolinol (NPP), 4
Nitroaniline and its derivatives such as -cyclooctylaminonitrobenzene (COANB); nitropyridine derivatives such as 4-cyclooctylaminonitropyridine (COANP) and 4-adamantaneaminonitropyridine (AANP); 4-methoxy-4'-nitro Stilben (MN
S), 4-bromo-4'-nitrostilbene (BNS), 4
Para-aminonitrostilbene derivatives such as-(N, N-dimethylamino) -4'-nitrostilbene (DMANS) and 4- (N, N-dipropylamino) -4'-nitrostilbene (DPANS); , N-dimethylamino) -4'-
Nitroazobenzene derivatives such as nitroazobenzene (DMANAB) and 4- (N, N-diethylamino) -4'-nitroazobenzene (DEANAB), 4- (N, N-dimethylamino) benzylidene-4'-nitroaniline (DMANBA) ,
Para-aminobenzylidenenitroaniline derivatives such as 4- (N, N-diethylamino) benzylidene-4'-nitroaniline (DEANBA), 4-nitrobenzylidene-4 '
-(N, N-dimethylamino) aniline (NDMABA), 4-
Nitrobenzylidene-4 '-(N, N-diethylamino)
Paranitrobenzylideneaminoaniline derivatives such as aniline (NDEABA), nitrotran derivatives such as 4-methoxy-4'-nitrotran (MNT) and 4-bromo-4'-nitrotran (BNT), 4- (N, N-dimethylamino) )
Paraaminonitrostyrene derivatives such as -β-nitrostyrene (DMANST), paraaminonitrobutadiene derivatives such as 1- (paradimethylamino) phenyl-4-nitrobutadiene (DMAPNB), 5-nitroindole (5NI
N) or a benzoheterocyclic derivative such as chloronitrobenzoxadial (NBD-C1), and the ionic crystalline material is a 4′-diethylamino-N-methyl-4-stilbazolium methsulfonate salt (DESM), It refers to a dialkylaminostilbazolium derivative such as iodine salt of 4'-diethylamino-N-methyl-4-stilbazolium (DESI), a pyridinium derivative, an azurenium derivative, and a quinolium derivative.

 Hereinafter, the present invention will be described in detail with reference to examples.

〔Example〕

(Example 1) As a molecular crystalline material, 1- (paradimethylamino)
An example of an optical Kerr shutter device using phenyl-4-nitrobutadiene (hereinafter, referred to as DMAPNB) will be described below.

The crystal material was synthesized as follows. First, p- (N, N
-Dimethylamino) cinnamaldehyde To a solution of 117 g (0.67 mol) in nitromethane (500 ml) was added ammonium acetate (17 g). Thereafter, the reaction solution was cooled in a dry ice-acetone bath until crystallization was completed,
The precipitated solid was separated by filtration and dried in vacuum. Recrystallization was performed twice using ethanol as a solvent to obtain red crystals. This crystal powder
A solution dissolved in DMF (dimethylformamide) was sealed in a glass cell and used as a nonlinear refractive index medium, and the other configuration was exactly the same as that in FIG.

FIG. 2 shows the instantaneous transmittance characteristics of the optical switch according to the present embodiment when DMAPNB is dissolved in DMF as a function of the DMAPNB concentration. As can be seen from FIG. 2, the obtained transmittance increased in proportion to the square of the concentration. At a concentration of 22% by weight or more, a characteristic exceeding that of the conventional material CS ₂ was obtained. Concentration 30wt
In%, the transmittance efficiency of even 2 times that of CS ₂ was confirmed. The n ₂ value at a concentration of 30 wt% is (4), (5)
From the formula, n ₂ = 1.1 × 10 ⁻¹³ cm ² / W (χ ⁽³⁾ = 4.5 × 10 ⁻¹² es
u) was asked.

The obtained value of the chi ⁽³⁾ (concentration 30 wt%) when compared to THGχ ⁽³⁾ values in the DMF solution of DMAPNB cited Table 1 (concentration 5wt%), g = 4.5 × 10 -12 / 6.0 × 10 ^-14 = 75, and when converted to concentration, g = 12.5 is obtained. That is, by using the solution material of the present example as the nonlinear refractive index medium, an enhancement effect larger by one digit or more than the conventionally reported value was recognized. The mechanism of this enhancement effect is
It is thought to be due to the molecular orientation effect, but details are not clear. The molecular orientation effect is a phenomenon in which nonlinear molecules try to align in the direction of the electric field of light in a solution, resulting in optical anisotropy and increasing the apparent nonlinear refractive index.

FIG. 3 shows a solution at the same molar concentration (1.5 mol /) using nitrobenzene, chlorobenzene, benzene, acetone and chloroform in addition to DMF in order to find the best organic solvent in this example. 5 shows the results of an experiment using, and plots the obtained value of n ₂ as the dielectric constant of the solvent. As can be seen from FIG. 3, as the solvent, the higher the dielectric constant, the better, and the aromatic solvent is superior to the non-aromatic solvent. In other words, the highest efficiency characteristics were obtained when DMAPNB was dissolved to the maximum concentration using nitrobenzene, which is an aromatic high dielectric constant material.
The value of n ₂ at this time was 1.5 × 10 ⁻¹³ cm ² / W, and
Is twice that of the S _2. As the transmittance, 2 ² = 4 compared to CS ₂
Twice the efficiency was confirmed.

As described above, in the present invention, it has been found that the efficiency varies greatly depending on the type of the solvent even when the solution has the same concentration, and the result that an organic solvent having a higher dielectric constant than chloroform was obtained as the solvent was obtained. . Such optimal solvents include, in addition to the above solvents, N-methylacetamide, N-methylformamide, formamide,
Acetamide, dimethylformamide, N, N-dimethylacetamide, acetonitrile, nitromethane, acrylonitrile, methanol, diethylene glycol, benzonitrile, ethanol, acetaldehyde, propanol, benzoaldehyde, benzyl alcohol, 1,3-
Examples thereof include those having a higher dielectric constant than chloroform, such as propanediol and pyridine.

(Example 2) As a molecular crystalline material, 4-nitroaniline (p-N
A), 4- (N, N-diethylamino) nitrobenzene (p
-DEANB), 2-methyl-4-nitroaniline (MNA),
4-nitrophenylprolinol (NPP), 4-cyclooctylaminonitrobenzene (COANB), 4-cyclooctylaminonitropyridine (COANP), 4-adamantaneaminonitropyridine (AANP), 4-methoxy-
4'-nitrostilbene (MNS), 4-bromo-4'-
Nitrostilbene (BNS), 4- (N, N-dimethylamino) -4'-nitrostilbene (DMANS), 4- (N, N-
Dipropylamino) -4'-nitrostilbene (DPAN
S), 4- (N, N-dimethylamino) -4'-nitroazobenzene (DMANAB), 4- (N, N-diethylamino)-
4'-nitroazobenzene (DEANAB), 4- (N, N-dimethylamino) benzylidene-4'-nitroaniline (DMANBA), 4- (N, N-diethylamino) benzylidene-4'-nitroaniline (DEANBA), 4-nitrobenzylidene-4 '-(N, N-dimethylamino) aniline (N
DMABA), 4-nitrobenzylidene-4 '-(N, N-diethylamino) aniline (NDEABA), 4-methoxy-4'
-Nitrotolan (MNT), 4-bromo-4'-nitrotolan (BNT), 4- (N, N-dimethylamino) -β-nitrostyrene (DMANST), 5-nitroindole (5NIN)
And chloronitrobenzoxadial (NBD-C1) 22
For each compound, a solution of crystal powder dissolved in DMF was sealed in a glass cell and used as a nonlinear refractive index medium,
With respect to other configurations, the instantaneous transmittance characteristics of the optical switch were obtained by the same method as that of the first embodiment. From these results, it is found that n _{2 of} each nonlinear refractive index medium (concentration is 25 wt%)
The value was determined. The results are shown in Table 2.

As shown in Table 2, a value in excess of CS ₂ in any case are obtained. Also, for these compounds,
Examination of the most excellent organic solvent revealed that, as in Example 1, the higher the dielectric constant of the solvent, the better, and that an aromatic-based solvent gave better results than a non-aromatic-based solvent.

(Example 3) As an ionic crystal material, 4'-diethylamino-N
Dialkylaminostilbazolium derivatives such as -methyl-4-stilbazolium methsulfonate salt (DESM) and 4'-diethylamino-N-methyl-4-stilbazolium iodine salt (DESI); pyridinium derivatives; azurenium derivatives; quinolium derivatives With respect to the five types of compounds, a solution obtained by dissolving crystal powder in formamide was sealed in a glass cell and used as a nonlinear refractive index medium. The other configurations were exactly the same as in Example 1, and the instantaneous transmittance of the optical switch was used. The characteristics were determined. The pyridinium derivative, azurenium derivative and quinolium derivative are compounds represented by the structural formulas shown in Table 3, respectively.

From these results, the n ₂ value of each nonlinear refractive index medium was determined. The results are shown in Table 4 (concentrations are entered in Table 4).

As shown in Table 4, in each case, CS ₂
Was obtained. Examination of the most excellent organic solvents for these compounds revealed that the higher the dielectric constant of the solvent, the more excellent the results.

Fourth Embodiment FIG. 4 shows a non-linear optical device according to another embodiment of the present invention. In this embodiment, the DMAPNB solution described in the first embodiment is used as the non-linear refractive index medium 1, and this solution medium and the dielectric multilayer mirrors 3a and 3b which reflect about 90% of the input light and pass the rest. Were opposed to each other to form an optical resonator. In order to operate this device, the resonance condition of the resonator may be adjusted by slightly changing the wavelength of the input light or by slightly changing the resonator length (mirror interval). In the case of this embodiment, since the light of 1.064 μm from the Nd ³⁺ -YAG laser was used, the adjustment depended on the method of changing the cavity length. Between the input light intensity Pi and the output light intensity Pt, there were a limiter operation characteristic and a bistable operation characteristic as shown in FIG. 5 and FIG.

The minimum input light intensity (Pi min) necessary for the operation is analytically calculated as Pi min = (Kλ) / (n ₂ L) (where λ is the light wavelength, L is the optical medium length, and K (Ｋ0.00)
1) is given by a coefficient determined by the reflectance of the mirror and the adjustment of the cavity length. In this embodiment, λ = 1.064 μm, L = 1 mm, and n
Since ₂ is from Example ^{_{1 n 2 = 1.1 × 10 -13}} cm 2 / W, Pi m
in = 1.1 × 10 ⁷ W / cm ² was obtained.

When a semiconductor laser with an effective output of 100 mW (pulse oscillation) and an oscillation wavelength of 0.83 μm is used as the light source, when the beam diameter is narrowed down to 1 μm, the light intensity is calculated as 1.3 × 10 ⁷ W / cm ^2, and the nonlinear optics at this wavelength is calculated. Greater than the Pi min value of the device. In fact, this nonlinear optical device was operable even when a semiconductor laser was used as a light source.

Response time t of the material or molecular crystal material or an ionic crystal material solution, like the conventional material CS ² liquid 10
It is estimated to be about ^-12 sec. However, the reaction time of the device is determined by the larger of the medium response time t and the photon lifetime tp in the resonator. Tp = −1op / (c 1n R) (where 1op is the optical power of the resonator) Tp calculated from the length, c is the speed of light, and R is the reflectance of the mirror) is obtained as 6 × 10 ^-11 sec.
Since> t, this tp value is the response time of the device. In this example, it was confirmed that the response time was shorter than 10 ⁻¹⁰ sec.

Embodiment 5 FIG. 7 is a diagram for explaining an embodiment of a phase conjugate generator. In the figure, 4a and 4b are transflective mirrors, 5 is a total reflection mirror, and 1 is the DMAPNB solution described in the first embodiment. This configuration is an optical configuration called degenerate four-wave mixing, and when three light waves A1, A2 (in the opposite direction to A1) and Ap (oblique incidence) enter a medium having a nonlinear refractive index, Ap A fourth lightwave (Ac) is generated in which only the spatial phase term is conjugate. This phase conjugate wave is attracting attention as an effective means for image correction in image information processing technology and real-time holography. Also in this example, the high-speed response and low operation input light intensity of the device were confirmed.

〔The invention's effect〕

As described above, the non-linear optical device of the present invention has a third-order non-linear effect larger than ever. In addition, using a solvent having a high dielectric constant and an aromatic ring, such as nitrobenzene, as the solvent has the effect of obtaining a large nonlinear refractive index, and is an optical control optical switch or optical bistable element that can operate at low light intensity. And a phase conjugate wave generator.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the configuration of a nonlinear optical device and an optical switch. FIG. 2 is a graph showing the instantaneous transmittance in the first embodiment of the present invention. FIG. 4 is a graph showing nonlinear refractive index n ₂ characteristics for various solvents in the first embodiment of the present invention. FIG. 4 is a schematic configuration diagram showing another example of the nonlinear optical device of the present invention. 6 and 7 are graphs showing the operating characteristics of the device shown in FIG. 4, FIG. 5 is a graph showing a limiter operation, FIG. 6 is a graph showing an optical bistable operation, FIG. 7 is a schematic configuration diagram showing a phase conjugate wave generator as another example of the nonlinear optical device of the present invention. 1 ... Non-linear refractive index medium, 2a, 2b ... Polarizer, 3a, 3b ... Dielectric multilayer evaporation mirror, 4a, 4b ... Semi-transmitting mirror, 5 ... Total reflecting mirror, Pi ... Input light, Pt …… Output light, Pg …… Gate pulse light.

Claims (5)

(57) [Claims] 1. A nonlinear optical device comprising an optical medium having a nonlinear refractive index and an optical element such as a polarizer, an optical resonator, or a reflecting mirror, wherein a molecular crystal is used as the optical medium having a nonlinear refractive index. A nonlinear optical device using a solution medium in which a material or an ionic crystal material is dissolved in a single organic solvent or a mixed solvent. 2. The molecular crystalline material includes 4-nitroaniline (p-NA), 4- (N, N-diethylamino) nitrobenzene (p-DEANB), 2-methyl-4-nitroaniline (MNA), 4-nitrophenylprolinol (NP
P), 4-cyclooctylaminonitrobenzene (COAN
Nitroaniline and its derivatives such as B), nitropyridine derivatives such as 4-cyclooctylaminonitropyridine (COANP) and 4-adamantaneaminonitropyridine (AANP), 4-methoxy-4'-nitrostilbene (MNS), -Bromo-4'-nitrostilbene (BN
S), 4- (N, N-dimethylamino) -4'-nitrostilbene (DMANS), 4- (N, N-dipropylamino)-
Para-aminonitrostilbene derivatives such as 4'-nitrostilbene (DPANS), 4- (N, N-dimethylamino)
-4'-nitroazobenzene (DMANAB), 4- (N, N-
Diethylamino) -4'-nitroazobenzene (DEANA
Nitroazobenzene derivatives such as B), 4- (N, N-dimethylamino) benzylidene-4′-nitroaniline (DM
ANBA), 4- (N, N-diethylamino) benzylidene-
Para-aminobenzylidene nitroaniline derivatives such as 4'-nitroaniline (DEANBA), 4-nitrobenzylidene-4 '-(N, N-dimethylamino) aniline (NDMAB)
A), p-nitrobenzylideneaminoaniline derivatives such as 4-nitrobenzylidene-4 '-(N, N-diethylamino) aniline (NDEABA), 4-methoxy-4'-nitrotran (MNT), 4-bromo-4'- Nitrotran (B
NT) and the like; para-aminonitrostyrene derivatives such as 4- (N, N-dimethylamino) -β-nitrostyrene (DMANST); 1- (para-dimethylamino) phenyl-4-nitrobutadiene (DMAPNB) Paraaminonitrobutadiene derivatives, 5-nitroindole (5NIN) and chloronitrobenzoxadials (NB
2. The nonlinear optical device according to claim 1, wherein a benzo heterocyclic derivative such as D-C1) is used. 3. The ionic crystalline material according to claim 1, wherein the methosulfonate salt of 4'-diethylamino-N-methyl-4-stilbazolium (DESM), 4'-diethylamino-N-
2. The nonlinear optical device according to claim 1, wherein a dialkylaminostilbazolium derivative such as an iodine salt of methyl-4-stilbazolium (DESI), a pyridinium derivative, an azurenium derivative, or a quinolium derivative is used. 4. The nonlinear optical device according to claim 1, wherein an organic solvent having a higher dielectric constant than chloroform or a mixed solvent thereof is used as said organic solvent. 5. The nonlinear optical device according to claim 1, wherein the organic solvent is an organic solvent having a higher dielectric constant than chloroform and having an aromatic ring, or a mixed solvent thereof. .