JPH01289922A - Nonlinear optical device - Google Patents

Abstract

PURPOSE:To obtain a nonlinear optical device having high dependency of wavelength, high response speed, requiring remarkably small intensity of inputted light necessary for operation, by using a specified poly(2,5-thienylene vinylene) (abbreviated to PTV) as optical medium having a nonlinear refractive index. CONSTITUTION:In the title nonlinear optical device, a PTV expressed by the formula I is used as a nonlinear optical medium. Since the PTV can be synthesized by a process via a soluble polymer intermediate, it has superior formability and handleability, as well as chemical stability. The PTV has an extremely large tertiary nonlinear effect, resulting a large value of nonlinear refractive index due to its large tertiary effect. Accordingly, if a nonlinear optical device such as an optical bistable element, optical switch, phase shift conjugate wave oscillator, etc., is constituted by using the material as nonlinear optical medium, a practically usable nonlinear optical device having high performance, usable in a wide wavelength range, having fast response characteristic, requiring small intensity of inputted light for operation, is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to nonlinear optical devices such as optical switches, optical memories, or optical signal processing devices that will be used in the future in optical information processing and optical communication systems. It is.

[Conventional technology and issues]

Nonlinear optical effect is when light enters a material,
The electric polarization P of a substance is expressed by the general formula P-χ [20χ E
While it can be written as 2+χ E3(-...(II),
This refers to the effect produced by the second and subsequent terms (
χ(i) is the first-order electric susceptibility, and E is the electric field intensity of light. ). In particular, the second harmonic generation (SHG) by the second term and the third harmonic generation (THG) by the third term are well known as wavelength conversion effects, but the third term also It is important as it provides a change in optical constant depending on the intensity, such as a nonlinear refractive index effect or a nonlinear absorption effect. For example, the nonlinear refractive index effect is one in which the refractive index n of a substance changes in proportion to the input q4 light intensity, and is written as n=n, +n21 (no is a constant and 2 is the nonlinear refractive index coefficient). ).When a medium exhibiting this effect is combined with other optical elements such as optical resonators, polarizers, or reflectors, optical information processing such as optical bistable elements, optical switches, or phase conjugate wave generators can be realized. It is possible to realize important devices that will be used in the future in optical communication systems.

As a conventional example of a nonlinear optical device using a medium exhibiting such a nonlinear refractive index effect, an example of an optical bistable element will be shown below with reference to FIG.

Reference numeral 1 in FIG. 5 is an optical material having a nonlinear refractive index (nonlinear refractive index medium), and 2a and 2b are nonlinear refractive index media 1.
It is a dielectric vapor-deposited mirror with a reflectance of about 90% coated on both sides. In this configuration, the resonance condition is satisfied by avoiding a slight change in the wavelength of the input light, and the output light Pt is as shown in Fig. 1(c) and (d) for the paraj light intensity Pi. Bride Physics Letter (Appl, Phys, Let
't, )voJ3! i, 451 (1976)). Each of these supports limiter operation and bistable operation, and can be applied to input optical pulse waveform shaping, optical switches, optical signal memory, optical logic operation, etc. in optical communication systems and optical information processing systems. It is something.

By the way, in this type of nonlinear optical device, three important values are the usable input light wavelength, input light intensity, and response time that can follow changes in the intensity of the optical signal. For example, nonlinear optical medium 1 in FIG.
In an example using a superlattice crystal made by alternately growing GaAs and GaAJAS semiconductor thin films, the refractive index changes as the light intensity increases as excitons are excited within the crystal as light is absorbed. Since the operating principle is to show dependence (absorption nonlinear effect), the above general formula (II
The coefficient of the third term of
Although it is excellent in terms of culm and small size, the usable input light wavelength is limited to an extremely narrow range near the exciton absorption spectrum, and the response time is critical to the exciton absorption spectrum. The problem was that it could not be used for high-speed optical signal processing of 3×10' sec J.

In another conventional example, a glass cell filled with carbon disulfide (C82), which is a nonlinear optical liquid, is used as a nonlinear optical medium, and an external mirror is used instead of the dielectric vapor-deposited mirrors 2a and 2b. The operating principle is that the refractive index shows light intensity dependence due to the rotational arrangement of molecules in response to the optical electric field (molecular rotational nonlinear effect), so the input light wavelength that can be used covers a wide range from visible to near-infrared regions. Although it is excellent in this respect, the third-order nonlinear efficiency is not so high, the input light intensity required for operation is as large as about 108 W/cd, and the response time is determined by the rotational relaxation time of the molecules, which is 10- 11. .

There was a problem that it could not be used for optical signal processing faster than 10" sec.

As is clear from the above, the performance of a nonlinear optical device is determined mostly by the characteristics of the nonlinear optical material1.
Therefore, the development of materials with a wide usable wavelength range, high third-order nonlinear efficiency, low manual light intensity required for operation, and short response time is eagerly awaited, and active research is being conducted toward this end. is the current situation.

Among materials that exhibit third-order nonlinear effects, benzene rings and
Organic nonlinear optical materials with π-electron conjugation such as double or triple bonds have recently attracted particular attention. For example, polydiacetylene bis-(paratoluenesulfonate) (abbreviation P
T S ) and (well, the constant of cubic effect χ(3) χ(3
)-1×1O-100Su (converted to a nonlinear refractive index coefficient, it becomes n2-2×1O-12(W/cd)-'), which is two orders of magnitude larger than the C82 liquid in "-". . Furthermore, since the mechanism of this nonlinear effect is not due to absorption or interaction with molecules or crystal lattices, but is derived purely from electronic polarization, it is possible to follow changes in the intensity of the optical signal. Response time is 1O-1
It has excellent characteristics such that it is extremely fast at 4 seconds, and the usable input optical wavelength ranges over a wide range from around 0.65 μm to 2.0 μ71L or more.

However, since polydialerene such as PTS is generally used as an IC which is a crystalline polymer, when it is used as a medium for an optical device, it is necessary that the entire medium be a single crystal. If there is an amorphous part in a part of the medium, or if the entire medium is in a polycrystalline state and is an aggregate of minute single crystals, the scattering loss of the incident light will immediately increase. Therefore, in manufacturing optical devices using polydiacetylene, techniques such as growing large crystals or thin film crystallization depending on the purpose are essential, and even if these crystals are obtained, It is necessary to establish techniques for cutting the crystal, polishing the surface, and grinding.These peripheral technologies related to polydiacetylene have not yet been solved.Therefore, nonlinear techniques using polydiacetylene have not yet been solved. No optical device has yet been put into practical use.

The present invention has been made in view of the above circumstances, and solves the problems in nonlinear optical devices using nonlinear refractive index, such as conventional optical bistable elements, optical switches, phase conjugate wave generators, etc. The objective of this technology is to eliminate the disadvantages of conventional optical systems, such as wavelength limitations, slow response, high operating input light intensity, and the inability to easily obtain the desired optical medium. It is an object of the present invention to provide a high-performance nonlinear optical device that has high-speed response and low operating input light intensity and can be used in practice.

[Means to solve the problem]

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention consists of the following structure. That is, the present invention includes an optical medium having a nonlinear refractive index, an optical resonator, a polarizer,
Alternatively, in a nonlinear optical device composed of optical elements such as an anti-9A mirror, the nonlinear optical medium is used as °C1 by the following formula (
It is characterized by using poly-(2,!D-dienylenevinylene) represented by I>.

The poly-(2,5-chenylene vinylene) (abbreviation P
T V ) is already known as a conductive polymer material with an amorphous structure. The synthesis method is also well known, and as described later, it can be synthesized via a soluble polymer intermediate, so it has excellent moldability, is easy to handle, and is chemically stable. The present inventors found that this third-order nonlinear effect of PTV has an extremely large value.
I was able to make it clear for the first time. We also confirmed that the nonlinear refractive index coefficient is large due to its large third-order effect, and used this material as a nonlinear optical medium to construct nonlinear optical devices such as optical bistable elements, optical switches, and phase conjugate wave generators. The most important point of the present invention is that they can be put to practical use.

FIGS. 4(a) and 4(b) show measurement data from an experiment conducted to evaluate the efficiency of the third-order effect of PTV. The third-order effect of organic materials is generally evaluated by measuring the intensity of third harmonic light (D-HG light). FIG. 4(a) shows a PTV film with a uniform thickness (thickness in this case is 0.05 mm).
17 μm), a laser pulse beam with a wavelength of about 2.0 μm was input, and while the sample was rotated around an axis perpendicular to the direction of incidence of the laser beam, the output 1rHG light intensity was measured. . This pattern is called a maker fringe, and it is measured using the same observation system using a material whose efficiency is already known (quartz glass was used here).
The efficiency of the third-order effect can be measured by comparing the peak intensity of

Lett, ) voJ 23. No, 11. 5
95 (1987)).

Figure 4(b) shows the obtained results as the third-order electrical susceptibility χ(3)
This is the result obtained by subtracting the incident light wavelength by °C. The value of χ(3) is around 3 x 10" esu, and when compared with the above-mentioned PTS, it was confirmed that the value is about 173. From this measured value, the nonlinear refractive index is r)z =5x 10 (W/C#ri -' It is expressed as before and after.

In addition, the PTV absorption spectra 1 to 1 were measured using a spectrophotometer using a PL-V film with a thickness of about 20 μm.

As a result, it was found that the non-absorption wavelength range was as wide as 0.75-2.2 μnL. However, this material has a wider usable wavelength range than the above-mentioned p-r s. Although the third-order effect efficiency of PTV in the wavelength range 075μ7rL to 18μm has not yet been measured, considering that the mechanism of the nonlinear effect is due to pure electronic polarization like PTS, even in these wavelength ranges,
It is easily inferred that χ(3) or n2 of PTV has a value almost equivalent to the value in FIG. 4(b).

Furthermore, from similar considerations, the response time of this material is estimated to be about 10-'' sec, similar to PTS, and is sufficiently high-speed.

Hereinafter, the features of the nonlinear optical device using poly(2°5-thenylene vinylene) according to the present invention will be explained in detail using Examples.

[Example 1] FIG. 1(a) is a diagram illustrating an example of the nonlinear optical device of the present invention, in which the nonlinear refractive index medium 1 used in the present invention C is one manufactured by the method described to the queen. ■It is a film, and in the device of the present invention, it deflects about 90% of the input light,
This is an external optical resonator in which dielectric multilayer mirrors 3a and 3b, which transmit the remaining light, are arranged to face each other.

The method for producing the 1) TV film described above will be described.

First, 2.5-chenylenebis(dimethylsulfonium) dichloride was treated with an alkaline aqueous solution at 0°C, then 0.3 mol of tetramethylammonium hydroxide was added in a methanol-water mixture solution, and the mixture was heated at -30°C. The mixture was stirred at the bottom and polymerized. The obtained yellow precipitate was collected and dissolved in dichloromethane, and then coated on a quartz glass plate by spin coating and air-dried.

Finally, this is heated at 200 to 250°C for 5 hours under a vacuum of 10-2 Torr to produce a PET with excellent optical quality.
'TV film was obtained. The reaction scheme during the final heat treatment process is shown in FIG. 1(b). In this way, a film-like optical medium with a size of about 1010 x 10 x 1 is obtained at a ratio of 1:1.

To operate the device shown in FIG. 1(a), as in the conventional example shown in FIG. Just adjust it. In the case of this example, Nd"-YAG
Since 1064μ skin light from the laser was used, tuning relied on varying the cavity length. A limiter operation J3 and a bistable operation as shown in FIG. 1 (cHd) were obtained between the input light bullet hole Pi and the output light intensity Pt.

・The minimum manual light intensity (Pl) required for 1n operation is analytically determined as pHmfn = (Kλ)/(n2J) (where λ is the wavelength of light, J is the length of the optical medium, and K(・-〇, 001) is It is given by the coefficient determined by the chain reflectance and the resonator length adjustment.
In this example, λ=1°O1n 64μm, , 1''41 ttvn, so pi
=2×106W/ctj.

Effective output 300 mW (pulse oscillation), oscillation wavelength 0.
When using an 83μIrL semiconductor laser as a light source, if the beam diameter is narrowed down to 3μmrL, the light intensity is 4.2×1
The value of Pi of the in nonlinear optical device at this wavelength is sufficiently large.

In fact, this nonlinear optical device was also able to operate when a semiconductor laser was used as the light beam.

The response time τ of this material < p − r v ) is i o −
” I have already mentioned that it is estimated to be around sec.

However, the reaction time of VR placement is this medium response time τ
It is determined by the larger value of tp and intra-cavity photon lifetime tp, but from tp = -Jalt/ (C left R) (where JOp is the optical length of the resonator, C is the speed of light, and 1 is the reflectance of the mirror). Calculated tp is 6×10-11s
ec is obtained, and the value of tp>r is the response time of the device. In this example, the response time is 10
” It was confirmed that it was shorter than “see”.

[Embodiment 2] FIG. 2 is a diagram illustrating an embodiment of the optically controlled optical switch. In the figure, numerals 4a and 4b+ indicate an orthogonal polarizer system consisting of two polarizers arranged such that their polarization axes are orthogonal to each other, and 1 is the medium crystal obtained in Example 1. . In this configuration, the linearly polarized light that passes through the orthogonal polarizer 4a only while the gate pulse Pal is incident undergoes rotation of the polarization angle due to the change in the refractive index of the nonlinear refractive index medium 1, and the linearly polarized light passes through the orthogonal polarizer 4b. Passing through. That is, the incident light is optically switched by the gate light.

In this device as well, the values of usable wavelength range, response time, and operating input light intensity (gate pulse light) are important, and it is clear from Example 1 that the usable wavelength range and response time are extremely excellent1. There is no need to explain it further.

The required gate pulse light intensity (Pπ/2) is analytically given by 1]rc/2−λ/(2・n2J), and in this example, λ−1,064μ77L, J
= 1 cocoon, so P, 72 = 1 x 109W/
It asked for cm. In reality, even at gate pulse light intensity lower than this, the transmittance T is T= 5i112((1]i/P,/2) Xπ/2
), it was found that operation is possible even with semiconductor laser light with a narrowed beam diameter.

(Example 3) FIG. 3 is a diagram illustrating an example of a phase conjugate wave generator. In the figure, 5a and 5b are semi-transparent mirrors, 6 is a total reflection mirror,
1 is the optical medium obtained in Example 1. This configuration is an optical arrangement called degenerate four-wave mixing, and when three light waves, AI, A2 (in the opposite direction to AI), and △p (inclined!)l) enter a medium with a nonlinear refractive index, A fourth light wave (AC") is generated in which only the spatial phase term is conjugate to At). This phase conjugate wave is useful for image correction in image information processing technology, real-time holography, etc. (For applications, see O1otus E, March issue, p.
73 (1982)).

In this example as well, the high-speed response of the device and the low operating input light intensity were confirmed.

〔Effect of the invention〕

According to the present invention, nonlinear optical devices such as optical bistable elements, optical switches, or phase conjugate wave generators, which will be important in the fields of optical information processing or optical communications, can be used with extremely high response speed and a large nonlinear refractive index. Poly(2,5
-Thienylene (vinylene) film is used as a nonlinear refractive index medium, so compared to conventional nonlinear optical liquids or semiconductor superlattice crystals, there is a difference in wavelength dependence, response speed, and operation required. The input light intensity can be significantly improved, and an existing semiconductor laser can be moved as a light source, which has practical value.

[Brief explanation of the drawing]

1(a) to (d) show a first embodiment of the present invention, in which (a) is a block diagram of an optical bistable element, and (b) is a nonlinear optical medium poly(2,5- (C) (d) shows the operating characteristics, (C) shows the limiter action, (d) shows the bistable action, and the arrow in the figure shows the reaction scheme when synthesizing chenylene (vinylene). The paths showing the characteristics of 1]t when Pi increases and decreases are shown. FIG. 2 shows a second embodiment of the present invention, and is a configuration diagram of a light-controlled optical switch. FIG. 3 shows a third embodiment of the present invention, and is a block diagram of a phase conjugate wave generator. FIG. 4(a) shows the THG intensity pattern of poly(2,5=thienylenevinylene) used in the present invention, and FIG. 4(b) shows the THG intensity pattern of poly(2,5-thienylene vinylene) used in the present invention. FIG. 2 is a diagram showing the spectrum of the χ(3) value of (vinylene). FIG. 5 is a block diagram showing an example of a conventional nonlinear optical device (optical bistable device). 1...Nonlinear refractive index medium, 2a, 2b...Dielectric vapor deposited mirror (reflectance approximately 9
0%), 3a, 3b... (external) dielectric multilayer deposited film mirror, Pi... input light, Pt... output light, 4a, 4b... ...Polarizer (constituting an orthogonal polarizer system), PO...Gate pulse light, 5a, 5b...Semi-transmitting mirror, 6...Total reflection mirror . Applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] An optical medium having a nonlinear refractive index, an optical resonator, a polarizer,
Alternatively, in a nonlinear optical device composed of an optical element such as a reflecting mirror, the following formula (I) is used as an optical medium having a nonlinear refractive index.
A nonlinear optical device characterized by using poly(2,5-thennylenevinylene) represented by: ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I)