JPH11167131A - Light modulator - Google Patents

Abstract

(57) Abstract: A novel optical modulator capable of separating and erasing control light mixed in modulated light when an optical signal is modulated at high speed as it is. SOLUTION: Three light pulses of linearly polarized signal light, control light, and compensation light are incident from a signal light input terminal 1, a control light input terminal 2, and a compensation light input terminal 3, respectively. Each light pulse is introduced into the signal light polarizer 4, the control light polarizer 5, and the compensation light polarizer 5, respectively. The signal light and the control light are coaxially combined by the coupler 8, and then the tertiary nonlinear optical medium. 10 is introduced. When passing through the coupler 8, the polarization relationship between the signal light and the control light is -45 degrees for the signal light and 0 degrees for the control light. Nonlinear optical medium 10
The signal light undergoes phase modulation by the control light, and induces a modulated light having a component orthogonal (+45 degrees) to the polarization direction (−45 degrees) of the signal light at the time of incidence. These output lights are output from the coupler 9.
Then, the control light and the compensating light are combined with the compensating light that has passed through the compensating light polarizer 6, and the control light and the compensating light cancel out and cancel out the photoelectric field. The polarizer 7 transmits only the modulated light and outputs the modulated light to the modulated light output terminal 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical modulator, and more particularly, to an optical modulator having an optical waveguide structure that makes effective use of third-order nonlinear optical performance.

[0002]

2. Description of the Related Art With the rapid development of the multimedia society, there is an ever-increasing demand for high-capacity, high-speed optical communication for exchanging more information at high speed. To increase the amount of signal per unit time, optical signal transmission of shorter optical pulses is required.Currently, silica glass optical fiber is mainly used, and the wavelength of 1.3 μm or 1.55 μm where the optical transmission loss is minimized
μm light is used as the signal. The optical transmission loss at this wavelength is
The transmission loss is about 0.5 dB / km, but if the wavelength is slightly different, the transmission loss immediately exceeds 1 dB / km. Therefore, a laser having a good monochromaticity according to the characteristics of the optical fiber is used as a light source used for optical communication. By changing the intensity of the laser light using an optical modulator according to an electric signal serving as information, and generating an optical pulse train,
Forming an optical signal.

[0003] Even in such optical communication using optical pulses, when an optical pulse is transmitted over several hundred kilometers, an optical signal is attenuated, and a repeater for amplifying the optical pulse is used on the way. Currently used repeaters use a photodetector to temporarily convert an optical signal arriving at the repeater into an electrical signal, perform electrical demodulation such as amplification, reproduction, and retiming. Is transmitted to the next receiving base. However, it is said that optical modulation via electrical processing in a repeater is limited to several tens of Gbit / sec, and a technology for modulating an optical signal as it is for high-speed optical communication beyond that is required.

[0004] Light modulation by light uses four-wave mixing, optical bistability, and the like, which are one of the third-order nonlinear optical effects of a substance. Usually, when light is irradiated on a substance, polarization is induced in the substance in proportion to the magnitude of the photoelectric field. The nonlinear optical effect refers to the general effect of the polarization of a substance induced when light is incident on the substance, which is nonlinearly proportional to the incident photoelectric field. . Are proportional to the second, third,. . Is called the nonlinear optical effect (P.
N. Butcher, D. Cotter, The Elements of Nonlin
ear Optics ”; Cambridge Modern Optics Study 9, Cambridge University Press, 1990).

[0005] The polarization P due to the third-order nonlinear optical effect is expressed by Equation 1 when the substance has central symmetry.

[0006]

(Equation 1)

Here, t indicates time, ω indicates an angular frequency of light, e ₀ indicates a dielectric constant in a vacuum, and E _ω (t) indicates an incident photoelectric field.

Further, ¹ ( ¹ ) indicates the linear susceptibility of a substance,
It is related to the linear refractive index n _{0 of the} substance by Expression 2.

[0009]

(Equation 2)

Here, Re indicates that the real part of χ ( ¹ ) is taken.

Further, χ ( ³ ) indicates the third-order nonlinear susceptibility of the substance, and is related to the third-order nonlinear refractive index n _{2 of the} substance by Expression 3.

[0012]

(Equation 3)

[0013] From these, the refractive index n (ω) of a substance is expressed as in Equation 4 from the linear refractive index n ₀ and the nonlinear refractive index n ₂ .

[0014]

(Equation 4)

Here, I indicates the intensity of the control light for changing the optical constant of the substance.

From equation (4), the refractive index of the substance appears to be a constant value n ₀ when the light intensity is low, regardless of the intensity of the incident light. It changes according to.

Since the physical properties such as the refractive index, the absorptivity, the polarization, and the phase of the substance change due to the modulation of the substance constant by the light as described above, the light modulation that changes the direction and the intensity of the light passing or reflected by the substance is performed. Will be possible. Since the light modulation is caused by the photoelectric field of the incident light, the polarization of the substance occurs at the speed of the light, and the physical properties can be rapidly changed.

However, once the polarization is induced in a substance,
The incident light remains for a certain time after passing, and the time depends on the polarization mechanism of the substance. For example, in semiconductors such as GaAs and InSb, photoexcitation produces excitons separated into electrons and holes,
It takes several nanoseconds (10 to ⁹
Seconds) or more. This is because the atoms constituting the semiconductor are regularly linked by covalent bonds, so that the separated electrons and holes walk across a plurality of atoms, and the distance between the two is increased.

On the other hand, in organic molecules such as polydiacetylene and metal phthalocyanine and quartz glass, even when a molecule is brought into an excited state by photoexcitation, there is no band structure derived from a covalent bond or the like with an adjacent molecule. There is no separation between the excited state and the holes, and it takes less than several picoseconds (10 to ¹² seconds) to deactivate the excited state and return to the original state. Therefore, if the third-order nonlinear optical effect of organic molecules or quartz glass is used, an optical switch having a high-speed response of several picoseconds or less can be realized.

However, three of these materials having high-speed response are
Next nonlinear optical susceptibility is about 10 ~ ¹⁴ ~10 ~ ¹² esu, and requires a very large control light intensity in order to realize an optical switch. For example, in the literature (T. Morioka and M. Saruwata
ri, IEEE J. Select. AreasCommun. Volume 6, 1186, 19
According to 1988), in an optical Kerr effect type optical modulator in which the polarization state of a substance is changed by control light, two different nonlinear refractive indices, n and n, in a direction parallel and perpendicular to the control light are introduced into the substance by the control light. ₂ raised to the XX power and n ₂ raised to the XY power are respectively induced. The difference Δn (t) between the refractive indices in both directions at time t
Is expressed by Expression 5 using the nonlinear refractive index and the intensity Ip (t) of the control light.

[0021]

(Equation 5)

The phase difference Δφ (t) of the light when the light having the wavelength λ travels by the length L in the optical waveguide made of the substance having such a refractive index difference is given by the following equation (6).

[0023]

(Equation 6)

In this optical switch, since the polarization plane is rotated by the control light, the minimum required control light amount to be driven as the optical switch is Δφ (t) = π. Since Δn (t) is a material constant, when the material to be used and the wavelength of light are determined, the length L of the optical waveguide of the optical switch and the required driving light amount Ip (t) are in inverse proportion.

For example, when a single mode silica fiber having a nonlinear refractive index of about 10 to ¹⁶ cm ² / W is used, the nonlinear response speed is as fast as several tens of femtoseconds or less, and the signal from the 1.9 GHz optical signal train is used. Extraction is easily realized. However, when the fiber length is 20m, the control light amount is 30W, and when the fiber length is 150m, it is 3.
It is reported that 4W was needed.

3 showing high-speed response of several pico to sub-pico second
As the next nonlinear optical material, there is an organic compound having a molecular skeleton composed of a π-electron conjugated system. For example, molecules such as p-nitroaniline, 3-methyl-4-nitroaniline, urea, chalcone, stilbene, tolan, benzylidene, porphyrin, phthalocyanine, polyacetylene, polydiacetylene, and polythiophene are known (HS Nalwa, S. et al.
Miyata, Nonlinearoptics of organic molecules
and polymers ”, CRC Press, 1997).

[0027]

[0007] Organic nonlinear optical materials and glasses can switch optical pulses with a much shorter time width at a higher repetition rate than the current several Gbps optical communication. Indispensable material for. However, the third-order nonlinear optical effect generally requires a very strong laser beam, and a light intensity of several hundred W / cm ² or more to drive an optical switch.

After the strong drive light is incident on the optical switch simultaneously with the transmitted signal light, it is necessary to separate modulated signal light and unmodulated signal light from the drive light. According to the confirmation of the switching phenomenon by the third-order nonlinear optical effect,
By making the signal light and the control light incident on the switching medium at different incident angles, the signal light and the drive light can be spatially separated. However, this method has problems such as mixing of scattered light of driving light on the surface of the switching medium, and disturbance of switching characteristics due to light pulses not simultaneously reaching the medium at the same time.

Further, since a switching effect is generated only in a portion where two optical paths overlap, a switching medium having a sufficient length cannot be used. Therefore, an optical Kerr switch has been proposed in which the signal light and the control light are on the same optical path and an optical fiber such as quartz is used as a longer switching medium. However, since the signal light and the control light have a 45-degree polarization relationship, the two cannot be completely separated by the polarizer, and the control light is always superimposed as noise. A method of changing the wavelengths of the signal light and the control light has also been proposed, but the more the control light deviates from the wavelength, the smaller the nonlinear optical effect and the lower the switching characteristics.
Due to the chromatic dispersion in the fiber, the propagation speeds of the signal light and the control light were different, and the two could not be effectively overlapped.

As described above, since there is no effective method of processing the control light after switching using an organic nonlinear optical material having a high-speed response as a medium, an optical switch applicable to practical optical communication has been realized. Had made it difficult.

An object of the present invention is to provide a waveguide type optical modulator which overcomes the problems of the prior art, reduces noise due to control light, and can be used for large-capacity high-speed optical communication. Another object of the present invention is to provide an organic nonlinear optical medium having a high-speed response by a third-order nonlinear optical effect and a method for manufacturing the same.

[0032]

SUMMARY OF THE INVENTION The present invention, which achieves the above object, uses a third-order nonlinear optical effect to change the direction and intensity of an optical signal as it is. The signal light and the control light input in the step are superimposed on the same optical axis and incident on a third-order nonlinear optical medium, and modulated from the signal light by the third-order nonlinear optical effect of the medium driven by the presence of the control light. While inducing the light, the output light from the medium has the same polarization plane as the control light, and the compensation light having a phase shift of 180 degrees is combined to cancel the control light, so that the modulated light can be output. It is characterized by having comprised in.

More specifically, a light source for inputting signal light, control light and compensation light with the polarization plane of the linearly polarized light pulse being controlled, and a first light source for multiplexing the signal light and the control light.
A third-order nonlinear optical medium that receives output light from the first mixer, controls the phase state of the signal light with the control light, and enables the induction of modulated light; and A second mixer for multiplexing the output light and the compensation light, and a polarizer for passing the output light from the second mixer, and the polarization planes of the polarizer and the signal light are controlled by the control unit. When there is no light and the compensating light, there is an orthogonal relationship, and the polarization planes of the signal light and the control light are 4 in a state where they are multiplexed by the first mixer.
When the signal light is not incident, the polarization planes of the control light and the compensation light have the same polarization plane when multiplexed by the second mixer, and the phases are shifted by 180 degrees. And the third-order nonlinear optical medium enters and exits via an optical waveguide.

A first distributor having two distribution destinations is inserted between the second mixer and the polarizer, and one distribution destination of the first distributor is the polarizer. And the other distribution destinations are guided to the second polarizer, and the polarization planes of the first and second polarizers are orthogonal to each other.

In addition, a first distributor having at least two distribution destinations is inserted between the second mixer and the polarizer, and one distribution destination of the first distributor is the polarized light. Being led by a child and having a luminometer at the other destination,
A phase compensating element capable of controlling the phase electrically or thermally or mechanically so that the light quantity by the light meter is minimized in a state where the signal light is not incident; And between the two.

[0036] The control light and the compensation light are generated via a second distributor for distributing light pulses from the same light source.

The optical modulator according to the present invention is characterized in that a single mode optical fiber for inputting and outputting to the third-order nonlinear optical medium is directly connected to form an integral structure. in this case,
At least two or more single mode optical fibers are directly connected, and a pair of optical fibers for input and output are connected so as to coincide with the same central symmetry axis. The whole of the medium or its connection part is sealed with resin.

The optical modulator of the present invention is characterized in that the third-order nonlinear optical medium contains an organic compound such as metal phthalocyanine having a third-order nonlinear optical susceptibility of 10 to ¹² esu or more.

According to the present invention, it is possible to form a degenerate optical modulator which cannot be realized conventionally because control light is mixed into modulated light. In addition, with the element configuration in which the third-order nonlinear optical medium is integrated with the optical waveguide, the modulation element can be more easily driven with a small amount of control light. The novel optical modulator of the present invention can realize high-speed and high-repetition-rate information extraction of terabit-class high-capacity optical communication.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail below with reference to the optical circuit configuration of an optical modulator, the configuration and manufacturing method of a waveguide type tertiary nonlinear optical medium, and specific combinations of each optical element and phase control means. The configuration of the optical modulator will be described.

[Embodiment 1] The optical modulator of the present invention superimposes a signal light pulse transmitted from a distant place on another control light pulse coaxially and introduces the signal light pulse into a third-order nonlinear optical medium, thereby introducing the control light. The optical element realizes the function of modulating the signal light by the third-order nonlinear optical effect, extracting the modulated light, and simultaneously canceling the control light with the compensation light.

FIG. 1 shows an example of a basic optical circuit of an optical modulator. In this basic optical circuit, three light pulses of linearly polarized signal light, control light, and compensation light are incident from a signal light input terminal 1, a control light input terminal 2, and a compensation light input terminal 3, respectively. Each optical pulse is a signal light polarizer 4, a control light polarizer 5,
Introduced to the compensating light polarizer 5, each polarizer is adjusted to transmit only light having a specific polarization relationship. The signal light and the control light are coaxially combined by the coupler 8 and then introduced into the third-order nonlinear optical medium 10.

After passing through the coupler 8, the polarization relationship between the signal light and the control light is -45 degrees for the signal light and 0 degrees for the control light.
The polarization relation of the incident light on the nonlinear optical medium 10 depends on the optical anisotropy of the medium used. However, in general, if the control light is introduced with a polarization relation coinciding with one of the optical principal axes of the medium, adjustment after modulation is easy. Become. In the case where the polarization relation is introduced so as to generate an extra polarization component, another optical element for finally detecting the modulated light with higher sensitivity may be required.

In the nonlinear optical medium 10, the signal light undergoes phase modulation by the control light, and the polarization direction of the signal light at the time of incidence (−).
(45 degrees) and light of a component orthogonal to (+45 degrees) is induced.
Assuming that the orthogonal components are modulated light, the light passing through the nonlinear optical medium 10 is three kinds of light, control light, signal light, and modulated light.
These lights are combined with the compensating light that has passed through the compensating light polarizer 6 by the coupler 9, and are introduced into the modulated light polarizer 7.

The control light and the compensation light that have reached the coupler 9 are adjusted in advance so that they have the same polarization direction, are shifted by 180 degrees, and overlap at the same time. Accordingly, the control light and the compensation light cancel each other out of the optical electric field and are erased by the multiplexing of the coupler 9. Thereafter, the modulated light polarizer 7 transmits only the light in the polarization direction of the modulated light, and finally only the modulated light is output to the modulated light output terminal 11.

The elements subsequent to the input end are coupled by a polarization-maintaining single-mode optical fiber by an optical waveguide 12 capable of maintaining the polarization state of an optical pulse. Here, as a reference of the polarization state, the polarization plane of the control light is configured to coincide with the main axis of the optical fiber.

FIG. 2 shows the polarization relationship and the phase relationship between the signal light, the control light, the compensation light, and the modulated light in the optical circuit of FIG.
The synchronous position of the signal light and the control light is the entrance of the nonlinear optical medium 10, and the synchronous position of the compensation light and the control light is the exit of the coupler 9.

FIG. 3 shows a modification of the basic optical circuit shown in FIG. 1. An optical circuit for extracting both modulated signal light (modulated light) and unmodulated signal light (non-modulated light) is shown in FIG. Is shown. A demultiplexer 13 is inserted between the coupler 9 and the modulated light polarizer 7 to split the modulated light and the non-modulated light into one-to-one, one of which is the modulated light polarizer 7 and the other is the unmodulated light polarizer 14. It is led to. The polarizer 14 is adjusted so as to transmit only unmodulated light (polarization relationship orthogonal to the polarizer 7), and the unmodulated light output terminal 1
Take out from 5. This unmodulated light can be directly introduced as signal light into the second similar light modulator and another light pulse signal can be extracted, so that such a combination facilitates acquisition of all necessary light pulses. As a result, assembling of the optical transmitter / receiver integrated with the optical modulator becomes easy.

FIG. 4 shows another modification of the basic optical circuit of FIG. 1, which shows an optical circuit which derives control light and compensation light from one optical pulse and controls the phase relationship after optical modulation. In FIG. 1, three input terminals of signal light, control light, and compensation light are used.
In this optical circuit, only two input terminals of the signal light and the control light are used.

The control light that has passed through the control light polarizer 5 is split one-to-one by a splitter 16 inserted before being multiplexed by the coupler 8, and one of the splitters is guided to the coupler 8. The other split light is guided to the non-linear optical medium 17 having the same configuration as the medium 10, and passes therethrough to reach the phase modulation element 18.

Examples of the phase modulation element 18 include an electro-optic modulation element such as lithium niobate single crystal and an organic secondary nonlinear optical material such as 2-methyl-4-nitroaniline dispersed in polymethyl methacrylate, a quartz thin film and a polyimide thin film. For example, a planar optical waveguide type thermo-optic modulator having an electric heater made of a material such as described above can be used.

The control light branched to the side not multiplexed with the signal light has its phase changed by the phase modulation element 18 and is output as compensation light similar to the basic optical circuit of FIG.
The control light and the compensating light are multiplexed by the coupler 9 with the control light passing through 0, and the phase of the control light and the compensation light is canceled.

In order to efficiently cancel the control light, the phase is adjusted before introducing the signal light. That is, only the control light is introduced into the optical modulator, the light quantity of the light split by the demultiplexer 13 is measured by the light meter 20, and the phase modulation element control circuit 19 is operated so that the light quantity is minimized. The phase of the phase modulation element 18 is adjusted to an optimum cancellation state.

FIG. 5 shows still another modification of the basic optical circuit. An optical modulator (FIG. 3) for outputting both modulated light and non-modulated light and an optical modulator for generating compensation light by branching from control light. 5 shows an optical circuit that combines the functions of the device (FIG. 4). Here, a one-to-three branch type is used for the demultiplexer 13, and three branch destinations are connected to the modulated light output terminal 11, the non-modulated light output terminal 15, and the light meter 20, respectively. When signal light and control light are incident on the optical modulator from the outside, only modulated light and unmodulated light are output, and control light having a higher intensity than signal light can be efficiently separated from output light. .

[Embodiment 2] Next, a description will be given of the configuration of an element with a waveguide of a third-order nonlinear optical medium used in the optical modulator of the present invention, and a manufacturing procedure thereof.

FIG. 6 shows an element configuration of a waveguide type third-order nonlinear optical medium used in the optical modulator of the present invention. Non-linear optical medium is a thin film (0.1-10μm thick) formed by evaporation
To form a nonlinear optical medium with a waveguide in which a quartz optical fiber is directly connected to the medium to enable input and output of light. FIGS. 1A to 1C show element configurations with different connection methods, which are selected as appropriate depending on the ease of forming a thin film on a material.

FIG. 6A shows an element structure in which a non-linear optical thin film 25 is formed on a substrate 26, an incident optical fiber 22 is connected from the thin film side with a photo-curable resin 24, and an outgoing optical fiber is connected from the substrate side. 28 are connected by a photocurable resin 27. Incoming optical fiber core 23 and outgoing optical fiber core 29
Are arranged symmetrically about the central symmetry axis 21.

FIG. 7 shows the procedure for fabricating the element configuration shown in FIG. Then, a substrate 26 for forming a thin film is prepared. The substrate is transparent to the wavelength of the light to be used. When using a single mode fiber, the thickness may be 3 mm or less and the parallelism may be 5 minutes or less. Desirable. The substrate is pre-cleaned to remove surface contaminants.

In the embodiment, borosilicate glass is used for the substrate,
The one having a thickness of 1 mm, a parallelism of 5 seconds, and a surface accuracy of λ / 10 was used (manufactured by Sigma Koki). The substrate was cleaned by ultrasonic cleaning in acetone for one hour. Silicon, gallium arsenide, or the like can be used for the substrate.

Then, a non-linear optical thin film 25 is formed on a substrate by vacuum evaporation. In the embodiment, a molecular beam deposition apparatus (OMBE-620 manufactured by Nidec Anelva) was used, and a base pressure of 1 × 10 to ¹⁰ To
At rr, a substrate temperature of 23 ° C., a thin film having a thickness of 0.1 to 1 μm was formed.

Then, the single mode quartz optical fiber 22 is connected to the thin film 25. In this embodiment, a polarization-maintaining optical fiber (manufactured by Sumitomo Electric, PM-130, core diameter 9μ) is used as the optical fiber.
m, a cladding diameter of 125 μm), which was cut vertically using an ultrasonic vibration type optical fiber cutting machine (Ericsson, EFC-11, PMF), and stains on the end face were removed with acetone. The fiber and the substrate are fixed to a special holder and a micro stage with a thick electric element (manufactured by Melles Griot, Nanotrack System, 17NTT01, etc.), 1.3 μm semiconductor laser light is introduced from the other end of the fiber, and the transmittance is measured. While finely adjusting the position of the microstage, the optical fiber was held perpendicular to the substrate, and then the fiber and the thin film were gradually brought into contact.

Then, a photocurable resin 24 (GS-001, manufactured by Nippon Electric Glass) was dropped on the contact portion between the fiber 22 and the thin film 25, and cured with an ultraviolet lamp. Then, a similar optical fiber 28 is prepared on the substrate side, semiconductor laser light is incident from the other end of the optical fiber 22, and the transmitted light is finely adjusted while tracing the fiber 28.
The optical fibers 28 were rotated so that 3, 29 were symmetrically arranged around the central symmetry axis 21 and the polarization planes of both fibers coincided. Thereafter, the optical fiber 28 was slowly brought into contact with the substrate.

In the above, the photocurable resin 27 was dropped on the contact portion between the optical fiber 28 and the substrate 26, and was cured with an ultraviolet lamp. Thereafter, the entire element may be sealed with another ultraviolet curable resin.

FIG. 6B shows a device configuration in which a nonlinear optical thin film 25 is formed on a substrate 26 and the incident optical fiber 2 is formed from the thin film side.
3 is connected, an etching part 30 is provided on the substrate, and the output optical fiber 28 is connected near the thin film 25.

FIG. 8 shows the procedure for fabricating the device configuration of FIG.
Is shown. Are the same as those in FIG. However, a single crystal of potassium chloride (Horiba Seisakusho, thickness 3)
mm, (001) surface polishing, surface precision λ, parallelism 1 minute), and heated at 300 ° C. for 6 hours under ultra-high vacuum before thin film deposition to remove surface contaminants.

Then, the substrate fabricated up to this point is reversed, and the substrate surface is turned to the vertical upper surface (however, the orientation with respect to the vertical axis is not shown in the drawing to clearly show the connection relationship).
Pure water is placed on the substrate surface just above the incident optical fiber 22.
Immediately after dripping and allowing to stand for about 5 minutes, dry nitrogen was sprayed to remove water, and the same operation was repeated five times in a hole formed by dissolving the substrate, thereby forming a substrate etching portion 30.

In the above, the outgoing optical fiber 28 was arranged in the substrate etching section 30 in the same manner as in FIG.

In the element configuration shown in FIG. 6C, a nonlinear optical thin film 25 is formed directly on an incident optical fiber 23, and an output optical fiber 28 is integrally connected. FIG. 9 shows a procedure for creating an element configuration.

Then, the incident light optical fiber 22 is prepared.
Then, the optical fiber 22 is mounted on a dedicated fiber holder 31 for vapor deposition. The holder 31 is made of stainless steel, and is formed so that a hole corresponding to the clad diameter of the optical fiber is vertically formed, and can be partially held down with a screw from the side.

Then, the optical fiber 22 is attached to the vacuum deposition apparatus together with the holder, and the nonlinear optical thin film 25 is deposited.
Then, the optical fiber 22 is taken out from the holder. At this time, if the fiber 22 is taken out so as to be pushed out, peeling of the fiber end from the thin film 25 hardly occurs.

In this case, the incident optical fiber 22 with a thin film and the optical fiber for outgoing light 28 are fixed to the microstage, and the centrally symmetric axis 21 and the plane of polarization are arranged so as to make gentle contact. Then, both fibers are made of photo-curable resin 24.
Connected with.

As described above, in each of the element configurations (a), (b) and (c), an optical waveguide for introducing signal light and control light into the third-order nonlinear optical medium is integrally formed. This allows
The required amount of control light can be greatly reduced as compared with the conventional spatial light modulation, and the polarization plane can be prevented from being disturbed due to scattering during transmission or on the medium surface. In addition, since the precise propagation state of the light pulse can be maintained by the direct coupling between the optical waveguide and the nonlinear optical medium, it is not necessary to constantly adjust the phase state of the control light and the compensation light. Also, the use of the waveguide-integrated element facilitates the assembly and miniaturization of the optical modulator and the optical transceiver using the same.

FIG. 10 shows the structural formula of the organic tertiary nonlinear optical material used in this example. The nonlinear optical material of this example is a metal phthalocyanine derivative (M-Pc) having four different central metals M, namely, titanyloxyphthalocyanine (M = TiO), tin dichloride phthalocyanine (M = SnCl ₂ ), and lead phthalocyanine. (M = Pb) and aluminum chlorophthalocyanine (M = AlCl) were used. Titanyloxyphthalocyanine was synthesized independently, and other materials used were commercially available (manufactured by Aldrich).

These tertiary nonlinear optical media made of a metal phthalocyanine organic compound have a high-speed response of several picoseconds or less and a large nonlinear optical reception rate of 10 to ¹² esu or more.

In addition, as a medium having a light modulation effect applicable to the light modulator of the present invention, 2-methyl-4-nitroaniline (H2N-C6H3 (-CH3)
-NO2) and 4-methyl-4'-tolan (H3C-C6H4-C≡C-C6H
Organic compounds such as 4-CN), polydiacetylene, and polyacetylene. In particular, in order to effectively induce light modulation, it is preferable that the third-order nonlinear optical constant be 10 to ¹² esu or more at the wavelength of light to be modulated in the state of a single or multiple layers of the constituent material layers. Further, it can be used together with another material having a different structure.

[Embodiment 3] FIG. 11 shows a device configuration of a waveguide type optical modulator according to an embodiment. In this embodiment, based on the optical circuit shown in FIG. 4, a system for splitting the control light from the control light source 32 to generate compensation light via the nonlinear optical medium 53, and combining the signal light from the signal light source 34 with the control light. It is composed of a system for modulating the wave via the nonlinear optical medium 54, a computer 58 for controlling the phase for canceling the phase, and the like. A dotted line connecting the respective elements indicates an optical fiber waveguide. The signal light source 34 is provided for test adjustment.

The correspondence between the optical circuit of FIG. 4 and the present embodiment is as follows. The polarizer 35 is used as the signal light polarizer 4, the polarizer 36 is used as the control light polarizer 5, the selective reflection mirror 44 is used as the coupler 8, and the coupler is used. 9, a non-linear optical medium with optical waveguides 54 and 53, non-linear optical media 10 and 17; a partial reflection mirror 47 for the optical demultiplexer 16; a selective reflection mirror 45 for the demultiplexer 13; The Babinet Soleil phase plate 60 corresponds to the photon 37, the phase modulation element 18, and the computer 58 corresponds to the phase modulation element control circuit 19.

The control light source is a titanium sapphire laser 32
(Cohernt, MIRA 900F, wavelength 790 nm, repetition frequency 76 MHz, pulse time width 90 fsec, average output 500 mW), and using this as seed light, a regenerative amplifier 33 (BMi, Alpha
-1000S, a wavelength of 790 nm, a repetition frequency of 1 kHz, a pulse time width of 120 fsec, and an average pulse energy of 800 μJ) were used as the control light.

The control light passes through the polarizer 36, is reflected by the total reflection mirror 41, passes through the variable filter 59, a part of the light is separated by the partial reflection mirror 46, and its intensity is measured by the photodetector 55. To the computer 58. Most of the control light passes through the partial reflection mirror 46 and the partial reflection mirror 47
, And the transmitted light becomes the actual control light, and the reflected light is used to generate compensation light.

As a signal light source, a semiconductor laser 34 (manufactured by Sumitomo Electric Industries, SL-13A2, wavelength 1.3 μm, continuous start, average output 6 mW)
Was used. The signal light passes through the polarizer 35, is totally reflected by the total reflection mirrors 39 and 40, and when passing through the selective reflection mirror 44, is superimposed on the same optical path as the control light selectively reflected here.

The control light and the signal light are collected by the lens 51,
The output light guided to the nonlinear optical medium with optical waveguide 54 and taken out from the other end is returned to the parallel light by the lens 52.
At this time, the polarizer 36 is adjusted so that the polarization plane of the control light and the main axis of the optical fiber are parallel to each other, and the polarizer is adjusted so that the polarization plane of the signal light becomes −45 degrees with respect to the polarization plane of the control light. 35
Has been adjusted. The polarization plane of the signal light passing through the non-linear optical medium 54 is rotated by the Kerr effect of the control light, and is divided into modulated light and unmodulated light. The effect increases as the amount of control light increases and as the control light passes through a longer waveguide.

A part of the control light reflected by the partial reflection mirror 46 passes through the lens 49 equivalent to the lens 51, the medium 54, and the lens 52, the nonlinear optical medium 53 with an optical waveguide, and the lens 50, respectively. The light is bent by the total reflection mirror 43 and guided to the Babinet Soleil phase plate 60.

With this configuration, control light, modulated light, and non-modulated light are sent out from the nonlinear optical medium with optical waveguide 54, and compensation light is sent out from the nonlinear optical medium 53 with optical waveguide. , The control light and the compensation light are cancelled. After that, the modulated light and the unmodulated light pass through the selective reflection mirror 45 and are reflected by the total reflection mirror 4.
The light is guided to the modulated light analyzer 37 whose polarization plane is made to match the modulated light by being bent by 2, and the transmitted modulated light is emitted. Also,
The light amount of the modulated light is measured by the light detector 56 and sent to the computer 58. The computer 58 observes the modulated light from the photodetector 56, the control light from the photodetector 57, and the like in synchronization with the timing when the value measured by the photodetector 55 exceeds the threshold.

In the adjustment for preventing the signal light from being incident,
Since the control light and the compensation light are reflected by the selective reflection mirror 45, the control light is taken out through the modulated light analyzer 38 whose polarization plane is made to match the control light, and the light amount is measured by the photodetector 57. When the measured value is input, the computer 58 adjusts the phase difference amount of the Babinet Soleil phase plate 60 so that the amount of light is minimized.

FIG. 12 shows the evaluation results of the characteristics of optical modulators manufactured using four types of nonlinear optical materials with different element configurations. TiO, SnC for the central metal M of the nonlinear optical material
Six kinds of elements shown in FIGS. 6A to 6C were manufactured using l ₂ , Pb, and AlCl, and an optical modulator of Example 3 was formed. With this optical modulator, the minimum control light amount (referred to as characteristic control light amount) required to detect the modulated light was measured.

The results for each material show that titanyloxyphthalocyanine (M = TiO) and tin dichloride phthalocyanine (M = SnC
l ₂ ) requires control light of about tens to 100 MW / cm ² , lead phthalocyanine (M = Pb) needs control light of about several hundred MW / cm ² , and aluminum chlorophthalocyanine (M = AlCl) needs control light of about several thousand MW / cm ² (However, in the configuration (a) using AlCl, it was impossible to detect even if the maximum control light amount in the experiment was incident).

According to the results for each element configuration, the type (c) requires the least amount of control light, and increases in the order of (b) and (a) below. In addition, when the compensation light was blocked by an obstacle in these measurements, a large amount of control light was mixed into the detector of the modulated light, making measurement impossible.

As described above, according to the optical modulator of this embodiment, it is recognized that light modulation by the third-order nonlinear optical effect can be performed with a small amount of control light, and the modulated control light can be canceled by the compensation light. Was.

In this verification, laser beams having different wavelengths were used for the signal light and the control light. However, it is generally known that the modulation characteristics of the optical Kerr effect can be further improved by using light having the same wavelength. However, the present invention is not limited to the specific wavelength used in this embodiment.

Further, by filling a medium exhibiting an optical modulation effect into a space surrounded by the cladding layer and serving as a core, an optical amplification effect can be effectively obtained even with a smaller incident light intensity. In particular, wavelengths from 1.3 μm to 1.5 μm
As an optical parametric amplifier for signal light pulses in the optical communication band, a GaAlAs semiconductor laser having a wavelength of 0.65 to 0.8 μm, a titanium-doped sapphire solid-state laser, or the like is used.
It can be used for pump light pulses. Alternatively, these lasers can be formed as an integrated device incorporating an optical waveguide or an optical fiber.

[0091]

According to the present invention, it is possible to provide a novel optical modulator capable of effectively obtaining modulated light by canceling out control light in an optical circuit. The third-order nonlinear optical susceptibility is 10 to ¹² e.
A high-speed and high-sensitivity optical modulator applicable to terabit-class optical communication is realized by using a medium of an organic compound layer such as metal phthalocyanine of su or higher, or by adopting an element configuration in which a waveguide is integrated with the medium. realizable.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a basic optical circuit of an optical modulator according to the present invention.

FIG. 2 is a table showing a polarization relationship and a phase relationship of input and output light in the optical circuit of FIG. 1;

FIG. 3 is a configuration diagram showing another example of a basic optical circuit of the optical modulator according to the present invention.

FIG. 4 is a configuration diagram in which a compensating light generation circuit is added based on the optical circuit of FIG. 1;

FIG. 5 is a configuration diagram in which the functions of the optical circuits of FIGS. 3 and 4 are integrated.

FIG. 6 is a configuration diagram of a third-order nonlinear optical medium element used in the optical modulator of the present invention.

FIG. 7 is an explanatory view showing the procedure for manufacturing the element of FIG.

FIG. 8 is an explanatory view showing a procedure for manufacturing the element of FIG. 6 (b).

FIG. 9 is an explanatory view showing a procedure for manufacturing the element in FIG. 6 (c).

FIG. 10 is a diagram showing a structural formula of an organic nonlinear optical material used in an example of the optical modulator of the present invention.

FIG. 11 is a configuration diagram showing an example of a device configuration of an optical modulator according to the present invention.

FIG. 12 is a table showing test characteristics of the optical modulator according to the embodiment.

[Description of Signs] 1 ... Signal light input end, 2 ... Control light input end, 3 ... Compensation light input end, 4 ... Signal light polarizer, 5 ... Control light polarizer, 6 ... Compensation light polarizer, 7 ... Modulation Optical polarizer, 8, 9 coupler, 10 nonlinear optical medium, 11 modulated light output end, 12 optical waveguide,
13: demultiplexer, 14: unmodulated light polarizer, 15: unmodulated light output terminal, 16: demultiplexer, 17: nonlinear optical medium, 18 ...
Phase modulation element, 19: phase modulation element control circuit, 20: light meter, 21: central symmetry axis, 22: incident optical fiber, 23
... incident optical fiber core, 24 ... photocurable resin, 25 ... nonlinear optical thin film, 26 ... substrate, 27 ... photocurable resin, 28
... Outgoing optical fiber, 29 ... Outgoing optical fiber core, 30 ...
Substrate etching part, 32 ... titanium sapphire laser, 3
3 Regeneration amplifier, 34 Semiconductor laser, 35, 36 Polarizer, 37, 38 Analyzer, 39-43 Total reflection mirror, 44, 45 Selection reflection mirror, 46-48 Partial reflection mirror, 49- 52: lens, 53, 54: nonlinear optical medium with optical waveguide 55-57: photodetector, 58: computer, 59: variable filter, 60: Babinet Soleil phase plate.

Claims (8)

[Claims] 1. An optical modulator for changing the direction and intensity of an optical signal as it is by using a third-order nonlinear optical effect, wherein the signal light and the control light, which are input as linearly polarized light pulses, are coaxial. Superimposed on top and incident on the third-order nonlinear optical medium,
Modulated light is induced from the signal light by the third-order nonlinear optical effect of the medium driven by the presence of the control light, and the output light from the medium has the same polarization plane as the control light and a phase of 180. An optical modulator characterized in that it is configured to combine the compensating light shifted by a degree to cancel the control light and output the modulated light. 2. An optical modulator that uses a third-order nonlinear optical effect to change the direction and intensity of an optical signal while keeping the signal light, wherein the signal light is controlled while the polarization plane of the linearly polarized light pulse is controlled. A light source for injecting light and compensation light, a first mixer for multiplexing the signal light and the control light, and an output light from the first mixer for incidence and control of the phase state of the signal light A third-order nonlinear optical medium capable of inducing modulated light by controlling with light, a second mixer for multiplexing output light from the medium and the compensation light, and output light from the second mixer And the polarization planes of the signal light and the control light are orthogonal to each other in the absence of the control light and the compensation light, and the polarization planes of the signal light and the control light are the first. 45 degrees shifted in the state of being multiplexed by the mixer, and the state where the signal light is not incident The polarization planes of the control light and the compensation light have the same polarization plane in a state where they are multiplexed by the second mixer, are out of phase by 180 degrees, and are transmitted through an optical waveguide to the third-order nonlinear optical medium. An optical modulator characterized in that it is configured to enter and exit. 3. The distributor according to claim 2, wherein a first distributor having two distribution destinations is inserted between the second mixer and the polarizer, and one distributor of the first distributor is provided. The tip is guided to the polarizer, and the other distribution destination is the second
Wherein the polarization planes of the first and second polarizers are orthogonal to each other. 4. The first distributor according to claim 2, wherein a first distributor having at least two distribution destinations is inserted between the second mixer and the polarizer.
One of the distributors is guided to the polarizer, and the other
A phase compensating element having a light meter at two distribution destinations and capable of controlling the phase so that the light amount by the light meter is minimized when the signal light is not incident; An optical modulator provided between the optical modulator and the optical mixer. 5. The optical modulator according to claim 2, wherein the control light and the compensation light are generated through a second distributor that distributes light pulses from the same light source. vessel. 6. The optical modulator according to claim 1, wherein a single-mode optical fiber for inputting / outputting the third-order nonlinear optical medium is directly connected to and integrated with the third-order nonlinear optical medium. 7. The optical communication system according to claim 6, wherein at least two or more single mode optical fibers are directly connected, and a pair of input and output optical fibers are connected so as to coincide with the same central symmetry axis. An optical modulator characterized by the above-mentioned. 8. The optical modulation method according to claim 1, wherein the third-order nonlinear optical medium contains an organic compound having a third-order nonlinear optical susceptibility of 10 to ¹² esu or more. vessel.