JPH04131833A - Nonlinear optical elements and optical signal processing devices - Google Patents

Abstract

PURPOSE:To apply various signal processing methods to read variation in refractive index by using a cubic nonlinear optical material which has neither thermal nor optical damage due to a laser by providing a nonlinear optical element made of a chiral compound having cubic nonlinearity. CONSTITUTION:The nonlinear optical element 16 made of the chiral compound which has the cubic nonlinearity is provided. Linear polarized light emitted by the laser 11 is split by a beam splitter 13 and light which is transmitted through it has its intensity modulated by a light intensity modulator 15 to become exciting light 21, which is made incident on the nonlinear optical element 16. Signal light 22 which is reflected and changes its optical path by a mirror 14, on the other hand, is made incident on the nonlinear optical element 16 and guided out as light 23 whose polarizing direction is rotated through the operation of the element according to the signal intensity of the exciting light 21. Consequently, signal processes such as signal conversion, optical arithmetic, optical amplification, etc., are easily performed without any special process such as the circular polarization of polarized light and deviation of the angle of polarization.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a nonlinear optical element and an optical signal processing device used in fields such as optoelectronics, optical information processing, and optical communication.

(Prior art and its problems) Nonlinear optical materials are materials that exhibit nonlinear response of second order or higher under the strong electric field of laser light, and are important materials in optical signal processing such as frequency conversion, oscillation, and switching. .

In particular, tertiary nonlinear optical materials are attracting attention as key materials for next-generation optical communication and information processing, which fully utilize the excellent characteristics of light, such as high speed and parallelism.

Among these nonlinear optical materials, organic nonlinear optical materials are particularly important because they have faster response times and larger nonlinear optical constants than conventional inorganic nonlinear optical materials.

Although the mechanism by which third-order nonlinear optical effects occur has not yet been elucidated, it is known that, for example, materials with large delocalized π-electron systems exhibit third-order nonlinear characteristics.

Aromatic compounds in which aromatic rings are connected in a linear chain are known as having a delocalized π-electron system.

However, such aromatic compounds become thermally unstable when the number of aromatic rings increases, and the absorption wavelength of light shifts to the longer wavelength side. Ta.

On the other hand, nonlinear optical elements using third-order nonlinear optical materials are
It attempts to utilize the fact that the refractive index changes in response to light irradiation.

As a method of reading this refractive index change, for example, Fa
A method has been proposed to amplify minute changes in refractive index using a Bry-Perrot resonator, but in this method, slight instability of the light source sensitively affects resonance stability.
The entire system is extremely delicate, and a high degree of dimensional quality accuracy is required to ensure stable operation, which can lead to high costs and
This is an obstacle to mass production. Additionally, there are issues such as material heat resistance, thermal walls, thermal effects, and technical barriers to attaching information to high implant energies, which necessitate implanting extremely high energies to increase the refractive index change. Ta.

As a method to improve this, a method has been proposed in which detection is performed with extremely high sensitivity by measuring the ellipsoidal polarization of weak probe light.

In this method, optical anisotropy is induced in a substance using strong excitation light to cause a polarization change in linearly polarized signal light.

This method requires measures such as making the excitation light circularly polarized or tilting the polarization direction of the excitation light from the polarization direction of the signal light in order to utilize photo-induced optical anisotropy, so signal processing is required. There were limitations to the method.

(Technical Means for Solving the Problems) The object of the present invention is to solve the above-mentioned problems by using a third-order nonlinear optical material that exhibits large third-order nonlinearity and is free from thermal and optical damage caused by laser. Another object of the present invention is to provide a nonlinear optical element and an optical signal processing device to which various signal processing methods can be applied to read changes in refractive index.

The present invention relates to a nonlinear optical element including a nonlinear optical element made of a chiral compound having third-order nonlinearity, a laser light source, a nonlinear optical element including a nonlinear optical element made of a chiral compound having third-order nonlinearity, and a photodetector. The present invention relates to an optical signal processing device comprised of a device.

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 suitable, 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 consisting of a co-condensed ring of henzene and a heterocycle such as thiophene, furan, pyridine, virol, etc.

Furthermore, the carbohelicene or heterohelicene may have various substituents attached to its aromatic ring or heterocycle.

Such carbohelicenes and peterohelicenes include, for example, Top, Curr, Chen+, 125 (Ster
eochemistry), 63-130 (19
84).

There are no particular restrictions on the method of synthesizing carbohelicene and heterohelicene, but examples include Wittig reaction and S
1+ 2-diar synthesized by iegrist reaction
ylethylenes, bis(arylvin
yl) arenes and the like by photocyclization.

These helicenes have large delocalized π-electron systems, exhibit large third-order nonlinearity, and are not thermally or optically damaged by lasers, making them excellent as third-order nonlinear optical materials.

The nonlinear optical element of the present invention includes a nonlinear optical element made of a chiral compound having cubic nonlinearity.

The form of the nonlinear optical element made of a chiral compound having third-order nonlinearity may be, for example, a solution, crystal, thin film, or doped resin of the chiral compound.

The chiral compound having third-order nonlinearity in the present invention is
It has the property of rotating the plane of polarization depending on the intensity of linearly polarized light. By utilizing this chiral nonlinear effect, various optical signal processing becomes possible.

The principle of rotation of the plane of polarization with respect to linearly polarized light will be explained below.

FIG. 1 shows the CD spectrum of (+)-hexahelicene, which is a chiral compound having third-order nonlinearity, and FIG. 2 shows the ORD spectrum.

In the CD spectrum, a positive peak is seen around 330 nm, strong absorption of left-handed circularly polarized light (L), and 2
A negative peak is seen near 4 Onm, and right-handed circularly polarized light (R
) has strong absorption. Furthermore, in the ORD spectrum, the signs are reversed near these wavelengths.

From this, if a chiral compound is expressed in an extremely simplified model, it is considered to have different energy units for L-polarized light and R-polarized light, as shown in FIG.

In this case, the absorption spectrum and refractive index dispersion are shown in Figure 4 (a
), (b) (solid line), a frequency shift occurs between the L polarized light and the R polarized light. The refractive index for L polarized light is n,
,, If the refractive index for R-polarized light is n8, the optical rotation is caused by (nL - nR) as shown in Figure 4 (C) (solid line), and the polarization rotation angle is given by 2 for the sample length and λ for the wavelength. πl/λ (nL - nR).

Next, when a nonlinear refractive index change is caused by strong linearly polarized excitation, linearly polarized light is considered to be a combination of left and right circularly polarized light, so it acts on both nLsnl, and the refractive index changes as shown in Figure 4 (b). (dotted line).

Letting this nonlinear refractive index change be Δnl and Δnu, the polarization rotation angle due to the nonlinear effect is zll/λ((nL−n
,) ((nt+Δnt) (nu+Δn-)))=πl
/λ(Δn, -Δn1I). That is, it is considered that polarization rotation occurs according to the difference in nonlinear refractive index changes for L-polarized light and R-polarized light. Furthermore, this effect is expected to increase as the optical rotation increases.

Therefore, when a chiral compound having cubic nonlinearity is irradiated with linearly polarized light, changing the intensity of the light can be detected as a change in the rotation angle of the plane of polarization.

By utilizing this characteristic, if you use the elliptical polarization analysis method described above, you can perform similar measurements using linearly polarized light in the same direction as the signal, without having to make any special efforts to polarize the excitation light, allowing you to analyze more complex optical signals. processing becomes possible.

Furthermore, the excitation light and the signal light are made into one linearly polarized light beam, and the signal waveform can be controlled by self-rotation depending on the intensity of the light.

Furthermore, by using a high repetition pulse light source, higher sensitivity and accuracy can be ensured in combination with a high frequency polarization modulation element.

In the present invention, by combining a nonlinear optical element comprising a nonlinear optical element made of a chiral compound having third-order nonlinearity with a laser light source and a photodetector,
An optical signal processing device capable of various types of optical signal processing is constructed.

By using the nonlinear optical element, this optical signal processing device can perform signal processing such as signal conversion, optical calculation, and optical amplification without performing special processing such as circularly polarizing polarized light or shifting the polarization angle. It can be easily performed and used as an optical information device.
It can be suitably used for optical communication, optical information processing, etc.

Although the present invention has been explained according to the change in the real component of the refractive index change of a chiral nonlinear optical material, the same effect can be obtained for the imaginary component of the refractive index change simply by changing the optical rotation to elliptical polarization. Needless to say, it will happen.

(Example) EXAMPLES The present invention will be specifically described below with reference to Examples.

Embodiment 1 FIG. 5 shows an optical signal processing device that converts the intensity of signal light into a polarization angle.

11 is a laser as a light source; 12 is a polarizer for linearly polarizing light; 13 is a beam splitter for splitting laser light; 114 is a mirror; 15 is a light intensity modulator; and 16 is a nonlinear optical element of the present invention.

The light emitted from the laser 11 is converted into linearly polarized light by the polarizer 12 . Note that if the emitted light from the laser 11 is sufficiently linearly polarized, the polarizer 12 may be omitted. The linearly polarized light is split into two beams by a beam splitter 13. The light transmitted through the beam splitter 13 becomes excitation light 21 whose intensity is modulated by the light intensity modulator 15, and enters the nonlinear optical element 16.

On the other hand, it is reflected by the beam splitter 13 and is reflected by the mirror 14.
The signal light 22 whose optical path has been changed at is incident on the nonlinear optical element 16. At this time, it is desirable that the intensity of the signal light 22 is sufficiently weaker than that of the excitation light.

The signal light 22 is converted into excitation light 2 by the action of the nonlinear optical element 160.
According to the signal strength of 1, the light 23 with a rotated polarization direction can be extracted.

Embodiment 2 FIG. 6 shows an optical signal processing device that performs logical product calculation processing.

The signal light A31, the signal light B32, and the reference light 33 are all linearly polarized light having the same polarization direction, and the signal light A and the signal light B change digitally.

40 is a nonlinear optical element, and 41 is an analyzer, which is set in a direction to extinguish the reference light 33 in the absence of signal light A and signal light B.

The output light 34 is light that has passed through the analyzer 41, and can be considered to be approximately O when the signal light A and the signal light B are 0. Output light 34
The intensity of I. . 1. If the intensity of signal light A is IA, the intensity of signal light B is 6, and the intensity of reference light is 1, then 1oot "stn" (IA + Im) ・I
F, and near the extinction angle it becomes Iout'' (In + I++) 2.IF.

Therefore, the output light when both A and B are ON is four times as much as when only one is ON.

In this way, when ■4 and I□ are both 1, I is extremely large.
. , is obtained, and by setting an appropriate threshold value, logical product operation becomes possible.

Furthermore, it is also possible to further clarify the digital signal by combining it with a waveform control device that utilizes the self-rotation effect shown in FIG.

Example 3 FIG. 7 shows an optical signal processing device that controls waveforms.

51 is a laser light source, and 52 is a polarizer for converting the laser light into linearly polarized light, which is not necessary if the laser light source 51 is sufficiently linearly polarized.

53 is a nonlinear optical element, and 54 is an analyzer that is set so that the incident light 61 is quenched when it is sufficiently weak.

The light emitted from the laser 51 becomes linearly polarized incident light 61 by the polarizer 52 and enters the nonlinear optical element 53 . The light transmitted through this undergoes polarization rotation proportional to the intensity I in of the incident light. Therefore, the intensity I of the output light 63 detected after passing through the analyzer 54. ut is I Out cc I in ・5in2θ (however, θ
is the polarization rotation angle and is proportional to the light intensity. ) Near the extinction angle, I oat ocr, .fin""Ii++, and a minute change can be detected as a large change, making it possible to control the waveform.

For example, if a signal of a sine wave 5in2ωt (ω (ω0.ω0: angular frequency of light)) is input, the output light becomes a signal proportional to 5in6ωt and shows an extremely steep rise.

Further, by combining the present invention with the arithmetic processing device of the second embodiment, digital computation can be made even clearer.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the CD spectrum and ORD spectrum of (+)-hexahelicene, respectively, and Figure 3 is a diagram showing the mechanics of a simplified model of a chiral compound for R-polarized light and R-polarized light. Figure 4 shows the absorption spectrum, refractive index dispersion, optical rotation, and nonlinear polarization rotation of chiral compounds for left-right circularly polarized light, and Figure 5 shows the intensity of signal light as a function of polarization angle. FIG. 6 is a schematic diagram of an optical signal processing device that performs logical product calculation processing, and FIG. 7 is a schematic diagram of an optical signal processing device that controls waveforms. It is a diagram. Patent Applicant: Ube Industries, Ltd. Figure λ (nm) Figure Figure Input (nm) Figure Figure Figure Figure

Claims (2)

[Claims] (1) A nonlinear optical element comprising a nonlinear optical element made of a chiral compound having third-order nonlinearity. (2) An optical signal processing device comprising a laser light source, a nonlinear optical element including a nonlinear optical element made of a chiral compound having third-order nonlinearity, and a photodetector.