JP2988574B2 - Wavelength selection method for optical signal processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal processing apparatus used in fields such as optoelectronics, optical information processing, and optical communication.

[0002]

2. Description of the Related Art A nonlinear optical material is a material that exhibits a second-order or higher nonlinear response under a strong electric field of laser light, and is an important material in optical signal processing such as frequency conversion, oscillation, and switching. is there. In particular, tertiary nonlinear optical materials are attracting attention as key materials in next-generation optical communication and information processing that fully exhibit the excellent characteristics of light, such as high speed and parallelism. The non-linear optical element using the third-order non-linear optical material attempts to utilize the fact that the refractive index changes with light irradiation. The present inventors have found that a chiral compound having third-order nonlinearity has a property of rotating a plane of polarization depending on the intensity of light with respect to linearly polarized light, and have proposed an optical signal processing device using this. This effect is significantly increased in the resonance region of the compound. However, chiral compounds have circular dichroism in the resonance region, so even if the detection light is incident as linearly polarized light, it becomes elliptically polarized, which becomes afterglow noise and detects polarization rotation due to the nonlinear effect with high sensitivity. There is a problem that the large effect of the resonance region cannot be used.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to obtain a large third-order nonlinear effect in the resonance region of a chiral compound having a third-order nonlinearity.
An object of the present invention is to provide an optical signal processing device to which a signal processing method having a high OFF ratio can be applied.

The present invention relates to an optical signal processing apparatus comprising a nonlinear optical element having a polarizing element and a nonlinear optical element made of a chiral compound having a third-order nonlinearity. Wavelength selection of an optical signal processing device characterized by selecting a wavelength at which the sign of the polarization dichroism curve is inverted, or a wavelength within the window of the circular dichroism curve of the nonlinear optical element as the wavelength of the detection light. About the method.

The chiral compound in the present invention preferably has a large delocalized π-electron system and a large optical rotation. As such a chiral compound, a chiral compound having a condensed aromatic ring is preferable, and examples thereof include optically active helicenes. Optically active helicenes include carbohelicene and heterohelicene. Carbohelicene is a compound having a helical structure in which 5 or more, preferably 6 to 20 aromatic rings are connected. Further, heterohelicene is a compound comprising a co-condensed ring of benzene and a hetero ring such as thiophene, furan, pyridine, pyrrole and the like. Further, carbohelicene or heterohelicene may have an aromatic ring or a heterocyclic ring with various substituents.

Such carbohelicene and heterohelicene are described, for example, in Top. Curr. Chem. 125 (Stereochemistr.
y), 63-130 (1984). The method for synthesizing carbohelicene and heterohelicene is not particularly limited. For example, it is synthesized by Wittig reaction or Siegrist reaction
It can be obtained by photocyclization of 1,2-diarylethylenes, bis (arylvinyl) arenes and the like. Since the helicenes have a large delocalized π-electron system, they exhibit a large third-order nonlinearity and are free from thermal and optical damage caused by a laser, and are therefore excellent as third-order nonlinear optical materials.

The nonlinear optical element of the present invention comprises a nonlinear optical element made of a chiral compound having a third-order nonlinearity. The form of the nonlinear optical element made of a chiral compound having third-order nonlinearity may be, for example, doping a solution, crystal, thin film, or resin of the chiral compound.
The chiral compound having the third-order nonlinearity in the present invention,
It has the property of rotating the plane of polarization of linearly polarized light depending on the light intensity. This effect is significantly increased in the resonance region of the compound, but since the chiral compound has circular dichroism in the resonance region, even if the detection light is incident as linearly polarized light, it becomes elliptically polarized. As a result, the polarization rotation due to the nonlinear effect could not be detected with high sensitivity.

In the present invention, the wavelength of the detection light is a wavelength at which the sign of the circular dichroism curve of the nonlinear optical element is inverted, or is within the window of the circular dichroism curve of the nonlinear optical element. By setting the wavelength, a large third-order nonlinear effect in the resonance region can be obtained. That is, as shown in FIG. 1, when the wavelength of the detection light is the wavelength 11 at which the sign of the circular dichroism curve is inverted or the wavelength 12 is within the window of the circular dichroism curve, Since the specific ellipticity can be regarded as practically zero, even if linearly polarized light is incident, almost no ellipticity occurs. Therefore, the detection light that has entered as linearly polarized light is emitted from the non-linear optical element without being substantially elliptical, so that afterglow noise due to elliptical polarization is not generated. For this reason, a large nonlinear effect in the resonance region can be used with a good ON / OFF ratio. In the present invention, the wavelength at which the sign of the circular dichroism curve is inverted does not need to strictly satisfy the above conditions, and is practically within a range in which the effect of afterglow noise due to the ellipticalization of linearly polarized light can be ignored. I just need. The wavelength within the window of the circular dichroism curve is defined as an absolute value of the ellipticity of 0.
Means a wavelength in a region where the minimum value is close to.

[0009]

The present invention will be specifically described below with reference to examples. Embodiment 1 FIG. 2 shows an optical switching device according to the present invention. 2
Reference numeral 1 denotes a non-linear optical element comprising a non-linear optical element made of a chiral compound having a third-order non-linearity. Specifically, a (+)-thiaheptahelicene 0.05% THF is used.
The solution was placed in a quartz cell having an optical path length of 2 mm. 2
Reference numeral 7 denotes a laser light source. Reference numeral 23 denotes strong control light emitted from the laser light source, the intensity of which can be changed by the controller 28, and becomes linearly polarized light by the polarizer 26 and enters the nonlinear optical element 21. Reference numeral 22 denotes a weak detection light separated from the laser light source.
3 and enters the nonlinear optical element 21 as linearly polarized light having the same direction as that of the light. When there is no control light 23, the direction of the analyzer 25 is arranged so as to block the detection light. When the control light 23 is incident, the detection light is rotated by the nonlinear effect due to the non-linear effect, and a vertical component is generated and transmitted through the analyzer 25.

FIG. 3 shows the relationship between the intensity of the control light and the signal intensity when the wavelength of the laser light source is set to the wavelength of 444.5 nm according to the present invention, that is, 11 in FIG. Table 1 shows the signal intensity and the magnitude of the afterglow noise when OFF when the relative intensity of the control light is 1, based on the value of the afterglow noise at 444.5 nm. At a wavelength of 490 nm, which is not related to the present invention, in the non-resonant region, that is, at a wavelength of 14 in FIG. 1, no signal was detected weakly. Wavelength 435 not related to the present invention in the resonance region
nm, ie, the afterglow noise is large at the wavelength of 13 in FIG.
The signal could not be determined. On the other hand, a signal is detected at a wavelength of 444.5 nm according to the present invention, and ON at this time is detected.
The / OFF ratio was about 30.

[0011]

[Table 1]

As described above, according to the present invention, a light capable of extracting a large third-order nonlinear effect in the resonance region of a chiral compound having a third-order nonlinearity and applying a signal processing method having a high ON / OFF ratio and a high S / N ratio. A signal processing device can be provided. In this embodiment, the control light and the detection light have the same wavelength, but it goes without saying that the same effect can be obtained even if the wavelength of the control light is different. Further, the effect is the same even if the control light and the detection light are integrated and controlled by one light beam.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circular dichroism curve of thiaheptahelicene.

FIG. 2 is a schematic diagram of an optical switching device according to one embodiment of the present invention.

FIG. 3 is a diagram showing switching characteristics in the device of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Nonlinear optical element 22 Detection light 23 Control light 24 Polarizer 25 Analyzer 26 Polarizer 27 Laser light source 28 Controller

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Claims (2)

(57) [Claims] 1. A optical signal processing device in which is constructed from the nonlinear optical element comprising comprise a nonlinear optical element comprising a chiral compound having a polarization component and third-order nonlinear properties, circular polarization second nonlinear optical element as the wavelength of the detection light A wavelength selection method for an optical signal processing device , wherein a wavelength at which the sign of a chromaticity curve is inverted is selected . 2. The optical signal processing device in which is constructed from the nonlinear optical element comprising comprise a nonlinear optical element comprising a chiral compound having a polarization component and third-order nonlinear properties, circular polarization second nonlinear optical element as the wavelength of the detection light A wavelength selecting method for an optical signal processing device , wherein a wavelength within a window of a chromaticity curve is selected .