JP3003819B2 - Nonlinear optical element and optical signal processing device - Google Patents

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 and an optical signal processing device 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. As a method of reading the refractive index change, for example, a method of amplifying a small refractive index change using a Fabry-Perrot resonator has been proposed, but in this method, slight instability of the light source is sensitive to resonance stability. As a result, the entire system is extremely delicate, and the high dimensional quality accuracy required for stable operation thereof is an obstacle in terms of cost and mass production. In addition, extremely high energy must be injected in order to increase the change in the refractive index, and there are problems such as heat resistance of the material, a thermal effect, and a technical barrier for putting information at high injection energy.

As a method for improving this, there has been proposed a method of detecting an elliptical polarization of a weak probe light with extremely high sensitivity. In this method, a strong excitation light induces optical anisotropy in a substance to cause a change in polarization in a linearly polarized signal light. In this method, it is necessary to make the excitation light circularly polarized in order to utilize the optically induced optical anisotropy, or to incline the polarization direction of the excitation light from the polarization direction of the signal light. There were restrictions on the method.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and to use a third-order nonlinear optical material which exhibits large third-order nonlinearity and has no thermal or optical damage caused by a laser. An 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 a rate change. The present invention comprises a nonlinear optical element comprising a chiral compound having a third-order nonlinearity,
Non-linear optical element having as input signals linearly polarized light having the same orientation as the input signal, and a change in rotation angle of the plane of polarization of linearly polarized light and / or a change in ellipticalization of linearly polarized light as an output signal,
The polarization rotation at the time of linear response when linearly polarized light enters the nonlinear optical element is (2m−1) × 90 ° (m is an integer), or the polarization rotation at the time of nonlinear response is (2m−1) × 90 °.
(M is an integer),
The present invention also relates to an optical signal processing device including a laser light source, a polarization element having the same orientation, and the nonlinear optical element.

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. Therefore, various optical signal processings can be performed by detecting this chiral nonlinear effect as a change in the rotation angle of the plane of polarization.

However, since the chiral compound also has a linear optical rotation, the reference polarization angle is deviated, and it is necessary to adjust the orientation of the analyzer and the like in accordance therewith. For this reason, the analyzer can be provided with an orientation adjustment function,
It is necessary to prepare analyzers of various directions, and there has been a problem that modularization and integration are difficult. In order to solve this problem, the nonlinear optical element according to the present invention has a polarization rotation of (2 m-
1) × 90 ° (m is an integer), or the polarization rotation during nonlinear response is (2m−1) × 90 ° (m is an integer). Thereby, all the polarizers and analyzers can be directed in the same direction, which facilitates modularization and integration of elements. The polarization rotation of the nonlinear optical element is set to (2m-
1) As a method of setting the angle to 90 ° (m is an integer), the length of the element and the concentration of the chiral compound in the element may be adjusted so as to have a desired rotation angle.

The non-linear optical element of the present invention utilizes the chiral non-linear effect, so that if the above-mentioned elliptic polarization analysis technique is used, even if it is linearly polarized light in the same direction as the signal, it is not necessary to devise polarization as excitation light. Since the same measurement can be performed, more complicated optical signal processing is possible. Further, the excitation light and the signal light are converted into one linearly polarized light, and the signal waveform can be controlled by self-rotation based on the light intensity. Further, by using a high repetition pulse light source, higher sensitivity and accuracy can be secured in combination with a high-frequency polarization modulation element.

In the present invention, by combining a nonlinear optical element having a nonlinear optical element made of a chiral compound having a third-order nonlinearity with a laser light source and a polarizing element, an optical signal capable of performing various optical signal processing is provided. A processing device is configured. This optical signal processing device can easily perform signal processing such as signal conversion, optical operation, and waveform control without using special processing such as shifting circular polarization or polarization angle to polarized light by using the nonlinear optical element. It can be suitably used as an optical information element for optical communication, optical information processing and the like. Although the present invention has been described according to the change in the real component of the change in the refractive index of the chiral nonlinear optical material, the same effect can be obtained for the imaginary component of the change in the refractive index only by changing the optical rotation into an elliptical polarization. Needless to say,

[0011]

The present invention will be specifically described below with reference to examples. Embodiment 1 FIG. 1 shows an optical car shutter device using polarization rotation. Numerals 11 and 12 are incident optical fibers. Reference light, which is a weak laser light, enters from 11 and is converted by the collimator 13 into parallel light. In addition, a signal light, which is a strong laser light, enters from 12 and is converted by the collimator 14 into parallel light. The reference light is converted into vertical linearly polarized light by the polarizer 15, and is incident on the nonlinear optical element 17 by the lens 16. At this time, since the reference light is weak, the nonlinear optical effect due to the reference light itself can be ignored.

The nonlinear optical element 17 is formed, for example, by doping a polymer with a nonlinear optical material made of a chiral compound, and has a doping concentration and an optical path such that the polarization plane rotates 90 ° when only the reference light is incident. The length is set. Therefore, when the signal light is not incident, the reference light whose polarization plane is rotated by 90 ° and is in the horizontal direction becomes parallel light by the lens 18 and the analyzer 20 whose azimuth is in the vertical direction.
Is shut off by

On the other hand, the signal light is converted into vertical linearly polarized light by the polarizer 15, and the nonlinear optical element 1 is formed by the lens 16.
7, the signal light is strong light, so that the nonlinear optical element 17 causes a nonlinear optical effect. As a result, the polarization plane of the reference light rotates from the horizontal direction, so that a vertical component is generated, which passes through the analyzer 20. The transmitted reference light is collimated by an output optical fiber 22 by a collimator 21.
Emitted to Unnecessary signal light that has passed through the nonlinear optical element 17 passes through the lens 18 and then enters the beam stop 1.
Blocked by 9

As described above, according to the present invention, a polarizer,
An optical Kerr shutter can be realized in the same direction without attaching a direction adjusting mechanism to the analyzer. Further, in the above optical Kerr shutter device, by setting the doping concentration and the optical path length so that the polarization plane rotates 90 ° when the reference light and the signal light enter, the nonlinear optical element 17 is referred to when there is no signal light. It is also possible to emit light and block reference light when signal light is incident.

Embodiment 2 FIG. 2 shows a waveform processing apparatus using an optical waveguide utilizing self-polarization rotation. Reference numeral 31 denotes a waveguide substrate made of, for example, SiO ₂ glass. The waveguide 32 is made of a polymer having a higher refractive index than the substrate 31. Reference numerals 33 and 35 denote polarizers and analyzers, which apply a vertical electric field to the liquid crystalline polymer in a molten state, and then cool and orient the liquid crystal polymer in the vertical direction to transmit a vertical electric field component. 34 is a nonlinear optical element of the present invention. Nonlinear optical element 34
Is formed by doping a polymer with a nonlinear optical material made of a chiral compound, for example, and adjusting the doping concentration and the optical path length so that the polarization plane of the weak signal light incident along the optical waveguide rotates by 90 °. You have set. Therefore, the incident weak signal light has its polarization plane rotated by 90 ° to be in the horizontal direction, and is blocked by the analyzer 35. The signal light emitted from the laser 36 having undergone the sine curve intensity modulation is incident on the end of the waveguide 32 by the lens 37 and propagates in the waveguide. The light enters the element 34. At this time, the signal light causes nonlinear polarization rotation in proportion to the intensity of the incident light due to the nonlinear optical effect. As a result, the polarization plane of the signal light rotates, so that a vertical component is generated, which passes through the analyzer 35. Since the intensity at this time is proportional to the cube of the incident light intensity,
When a sine curve is incident, the sine curve is emitted after receiving the intensity change of the cube of the sine curve, and light close to a square wave can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an optical car shutter device.

FIG. 2 is a schematic diagram of a waveform processing device using an optical waveguide.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-201632 (JP, A) JP-A-1-182283 (JP, A) Proceedings of the Optoelectronic Materials Symposium for Next-Generation Industrial Technology Vol. 2 pp. 173-183 (October 1991) Hidetoshi Ashidaka, "Study on Nonlinear Optoelectronic Materials for Organic Low-Molecule Systems" Autumn 1991 (The Heisei 19th year) The 52nd Annual Meeting of the Japan Society of Applied Physics 3rd volume p. 1126 Y. Yokozawa et. al. , “11p-T-7 Chiral nonlinear optical effect” (October 9, 1991) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/00-1/01 G02F 1/35 -3/02 JICST file (JOIS) CA (STN)

Claims (3)

(57) [Claims] 1. A Ri name comprises a nonlinear optical element comprising a chiral compound having a third-order nonlinear properties, one or more of the same orientation
Is the input signal and the rotation angle of the plane of polarization of the linearly polarized light
And / or the change in linear polarization ellipticity as the output signal.
A non-linear optical element you polarization rotation during linear response when the incident linearly polarized light into non-linear optical element (2M-
1) A nonlinear optical element having a size of 90 ° ( m is an integer). Wherein Ri name comprises a nonlinear optical element comprising a chiral compound having a third-order nonlinear properties, one or more of the same orientation
Is the input signal and the rotation angle of the plane of polarization of the linearly polarized light
And / or the change in linear polarization ellipticity as the output signal.
A non-linear optical element you polarization rotation during non-linear response when the incident linearly polarized light into non-linear optical element (2m
-1) A non-linear optical element having a size of 90 ° ( m is an integer). 3. An optical signal processing device comprising: a laser light source; all the polarization elements having the same orientation; and the nonlinear optical element according to claim 1 or 2.