JPH05100257A - Nonlinear optical device - Google Patents

Abstract

PURPOSE:To provide optical switching operation with lower power by using secondary nonlinear optical effect twice. CONSTITUTION:This nonlinear optical device consists of a multiplexer 1 which functions to multiplex light beams of angular frequencies omega1 and omega2, a 1st medium 2 and a 2nd medium 3 with the secondary nonlinear optical effect, and an optical filter 4 which absorbs or reflects light of angular frequency omega3 and transmits light of angular frequency omega3 and the light of angular frequency omega1 in relation omega3=omega1+omega2. In this case, the light beams of angular frequencies omega1 and omega2 which are multiplexed by the multiplexer 1 are made incident on the 1st medium 2, projection light from the medium 2 is made incident on the optical filter 4, and projection light from the optical filter 4 is made incident on the 2nd medium 3. Further, control light, difference frequency light, and sum frequency light projected from the 2nd medium 3 are made incident on an optical filter 5, which intercepts the control light and sum frequency light and transmits and projects only the difference frequency light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear optical device such as an optical switch and an optical modulator used in the fields of optical transmission, optical information processing and the like, and more particularly to a nonlinear optical device capable of realizing high speed operation. Is.

[0002]

2. Description of the Related Art In the field of nonlinear optical devices such as high-speed optical switches and optical modulators used in the fields of optical transmission, optical information processing, etc., absorption and refraction caused by changes in carrier density in a semiconductor due to current flow. A method utilizing a change in the refractive index or a method utilizing a change in the refractive index due to the electro-optical effect of the crystal by applying an electric field has been studied. Further, as a non-linear optical device that operates by light without applying a current or an electric field, a device that utilizes a refractive index change due to a third-order non-linear optical effect has been studied.

[0003]

However, in the above-mentioned optical switch, optical modulator, etc., which are operated by applying a current or an electric field, there is a limit in the operating speed due to the carrier moving speed or the stray capacitance, and even in the case of high speed. The limit is about 50 GHz. Further, in an optical switch, an optical modulator, etc., which is based on the third-order nonlinear optical effect, an extremely high-speed operation can be expected, but since the third-order nonlinear optical constant is generally extremely small, it cannot be operated in a low power light and is practically used. Has not reached the target element. For example, 3
The car shutter using carbon disulfide as the following non-linear material has a structure as shown in FIG. That is, the gate light 71 causes anisotropy in the refractive index in the carbon disulfide 72. Then, the polarization of the signal light 74, which has been transmitted through the carbon disulfide 72 with the same linear polarization as that at the time of incidence until then and blocked by the analyzer 73, has an anisotropic refractive index generated in the carbon disulfide by the gate light. It rotates due to its nature, passes through the analyzer 7, and exits.
The output intensity of the signal light is controlled by OFF and the intensity. However, in the case of such a non-linear optical device, since the third-order non-linear optical effect is extremely small,
A gate light of 100 W or more is required as an operating power, and none of them can be practically used. The problem to be solved by the present invention is to provide a non-linear optical device such as an optical switch and an optical modulator driven at high speed and low power.

[0004]

In order to solve the above-mentioned problems, a nonlinear optical device according to the present invention includes a multiplexer having a function of multiplexing lights having angular frequencies ω ₁ and ω ₂ , and a second-order nonlinear optical device. The first medium and the second medium having an effect, and the angular frequency ω
An optical filter that absorbs or reflects the light of ₂ and transmits the light of the angular frequency ω _{3 and} the light of the angular frequency ω ₁ in the relationship of ω ₃ = ω ₁ + ω ₂ , and combines them by the multiplexer. The light having the angular frequencies ω ₁ and ω ₂ is made incident on the first medium, the light emitted from the first medium is made incident on the optical filter, and the light emitted from the optical filter is made the second medium. It is designed to be incident on.

Further, according to the present invention, a multiplexer having a function of multiplexing lights of angular frequencies ω ₁ and ω ₂ , a first medium and a second medium having a quadratic nonlinear optical effect, Frequency ω ₁ ,
It reflects omega ₂ of the light, and made demultiplexer for transmitting the angular frequency omega ₃ of light in a relation of _{ω 3 = ω 1 + ω 2} , the angular frequency omega ₁ were combined by the multiplexer, omega ₂ light is made incident on the first medium, light emitted from the first medium and light having an angular frequency ω ₁ from the outside are made incident on the multiplexer / demultiplexer, and emitted from the first medium. It also discloses means for combining light of the angular frequency ω ₃ of the emitted light and light of the angular frequency ω ₁ from the outside so as to be incident on the second medium.

[0006]

In general, the second-order nonlinear optical effect accompanied by wavelength conversion has a higher efficiency than the third-order nonlinear optical effect and responds at the same high speed. In the present invention, by using two media having a second-order nonlinear optical effect, the sum frequency of the signal light (angular frequency ω ₂ ) and the control light (angular frequency ω ₁ ) due to the second-order nonlinear effect can be generated. The wavelength is converted into light having a different wavelength (angular frequency ω ₃ ), and the wavelength-converted light is converted into the original signal light wavelength by generating a difference frequency due to the second-order nonlinear optical effect. Since the intensity of the emitted light of the wavelength of the signal light is controlled by the intensity of the control light, it becomes possible to operate as a high-speed and efficient optical switch or as an optical modulator.

[0007]

First Embodiment FIG. 1 is a diagram schematically showing the concept of the configuration of the first embodiment of the present invention. Signal light (angular frequency ω ₂ )
And the control light (angular frequency ω ₁ ) are combined by the multiplexer 1,
It is incident on the medium 2 having the first second-order nonlinear optical effect. The medium 2 having the first second-order nonlinear optical effect is a phase matching condition for generating the sum frequency of the signal light and the control light, that is, k ₃ −k ₁ −k ₂ ≈ 0 (1) (where k ₁ , k ₂ and k ₃ are respectively adjusted to satisfy the conditions (propagation constants when propagating through the medium 2 having the first-order second-order nonlinear optical effect of control light, signal light, and sum frequency light). In such a state, the sum frequency light (angular frequency ω ₃ ) is generated in the medium 2 having the first second-order nonlinear optical effect according to the intensities of the control light and the signal light. The control light, the signal light, and the sum frequency light emitted from the medium 2 having the first second-order nonlinear optical effect enter the optical filter 4, the signal light is blocked, and the control light and the sum frequency light are transmitted. The light enters the medium 3 having the second quadratic nonlinear optical effect.

The medium 3 having the second quadratic nonlinear optical effect has a phase matching condition for generating a difference frequency between the control light and the sum frequency light, that is, k ₃ -k ₁ -k ₂ ≈0 (2 ) (Where k ₁ , k ₂ , and k ₃ are propagation constants when propagating in the medium 3 having the second-order second-order nonlinear optical effect of control light, signal light, and sum frequency light) Has been adjusted. In such a state, the difference frequency light (angular frequency ω ₂ ) is generated in the medium 3 having the second quadratic nonlinear optical effect according to the intensities of the control light and the sum frequency light. Control light emitted from the medium 3 having the second quadratic nonlinear optical effect,
The difference frequency light and the sum frequency light enter the optical filter 5, the control light and the sum frequency light are blocked, and only the difference frequency light is transmitted and emitted. Here, the emitted difference frequency light has the same frequency as the signal light, and its intensity depends on the intensity of the incident signal light and control light. Therefore, when the part of the present invention is considered as one black box 6, the transmission intensity of the signal light (angular frequency ω ₂ ) is controlled by the control light (angular frequency ω ₁ ) as shown in FIG. The structure of the terminal element allows high-speed switching and optical modulation because of the high-speed response of the second-order nonlinear optical effect.

FIG. 2 is a diagram showing a more specific construction of the first embodiment, in which 21 is a multiplexer, 22 and 23 are lithium niobate single crystal optical fibers, and 24 and 25 are optical filters. , 26, 27, 28 and 29 are lenses, respectively. In this embodiment, a lithium niobate single crystal optical fiber 22 is used as a medium having a first secondary nonlinear optical effect, and a lithium niobate single crystal optical fiber 23 is used as a medium having a second secondary nonlinear optical effect. I'm using it. Each of the lithium niobate single crystal optical fibers has an outer diameter of 80 μm and a core diameter of 5 μm, and forms a waveguide structure by internal diffusion of magnesium (Mg). The fiber length is 3 cm for the single crystal optical fiber 22 and 20 cm for the single crystal optical fiber 23. Control light having a wavelength of 0.86 μm (angular frequency 2.2 × 10 ¹⁵ (S ⁻¹ )) and signal light having a wavelength of 1.32 μm (angular frequency 1.4 ×)
10 ¹⁵ (S ^-1 )), and the sum frequency light has a wavelength of 0.5
2 μm (angular frequency 3.6 × 10 ¹⁵ (S ⁻¹ )). The phase matching condition of the single crystal optical fiber 22 is adjusted by temperature so as to generate the sum frequency light of the wavelength 0.52 μm from the light of the wavelength 0.86 μm and the light of the wavelength 1.32 μm. In No. 23, the phase matching condition is adjusted by the temperature so as to generate the difference frequency light having the wavelength of 1.32 μm from the light having the wavelength of 0.86 μm and the light having the wavelength of 0.52 μm.

Continuous light of 1 mW is made to enter as signal light, peak power is 100 mW as control light, and 20 GH is repeated.
When pulsed z light was input, signal light modulated by the waveform of the control light was obtained as shown in FIG. In this case, the ratio of the signal light output when the control light enters and the signal light output when the control light does not exist, that is, the extinction ratio, is 30 dB or more, which shows that the present embodiment can be applied not only as a modulation but also as a switch. ing. The waveform of the signal light sufficiently follows the control light, indicating that this embodiment has a high-speed response. The limit of response speed is not clear yet, but 100
It is considered that a response of GHz or higher is possible. In addition, the peak power of the output signal light is 2 mW, and the input signal light is amplified by the parametric amplification effect in the single crystal optical fiber 23, and this embodiment can be said to be a high-speed optical switch or modulator having an amplification effect. ..

(Embodiment 2) FIG. 4 is a diagram schematically showing the concept of the configuration of the second embodiment of the present invention. The signal light (angular frequency ω ₂ ) and the first control light (angular frequency ω ₁ ) are combined by the multiplexer 4
They are multiplexed by 1 and are incident on the medium 42 having the first secondary nonlinear optical effect. The medium 42 having the first quadratic nonlinear optical effect is adjusted to satisfy the phase matching condition for generating the sum frequency of the signal light and the control light, that is, the condition of the above-mentioned formula (1). In such a state, the sum frequency light (angular frequency ω ₃ ) is generated in the medium 42 having the first second-order nonlinear optical effect according to the intensities of the control light and the signal light. The first control light, the signal light, and the sum frequency light emitted from the medium 42 having the first second-order nonlinear optical effect enter the multiplexer / demultiplexer 44, and the signal light and the first control light are reflected. , The sum frequency light is multiplexed with the second control light and transmitted,
The light enters the medium 43 having the following nonlinear optical effect.

The medium 43 having the second quadratic nonlinear optical effect satisfies the phase matching condition for generating the difference frequency between the second control light and the sum frequency light, that is, the condition of the above-mentioned formula (2). It is adjusted to the state. In such a state, the difference frequency light (angular frequency ω ₂ ) is generated in the medium 43 having the second quadratic non-shaped optical effect according to the intensities of the second control light and the sum frequency light. Medium 43 with second quadratic non-formal optical effect
The second control light, the difference frequency light, and the sum frequency light emitted from the laser light are incident on the optical filter 45, the control light and the sum frequency light are blocked, and only the difference frequency light is transmitted and emitted. Here, the emitted difference frequency light has the same frequency as the signal light, and its intensity depends on the intensity of the incident signal light and the intensity of the first control light and the second control light. Therefore, when the part of the present invention is considered as one black box 46, the transmission intensity of the signal light (angular frequency ω ₂ ) is regarded as the first control light (angular frequency ω ₁ ) as shown in FIG. 4B. It has a structure of an element controlled by the second control light (angular frequency ω ₁ ), and when it is viewed as a logic element, an AND of the first and second control lights is taken.
It is also an element. Since the response of the second-order nonlinear optical effect is fast, high-speed switching and optical modulation are possible.

FIG. 5 is a diagram showing an actual configuration of the second embodiment, wherein 51 is a multiplexer, 52 and 53 are lithium niobate single crystal optical fibers, 54 is a multiplexer / demultiplexer, and 55 is an optical fiber. Filters 56, 57, 58 and 59 are lenses. In this embodiment, a lithium niobate single crystal optical fiber 52 is used as the medium having the first secondary nonlinear optical effect, and a lithium niobate single crystal optical fiber 53 is used as the medium having the second secondary nonlinear optical effect. I'm using it. All lithium niobate single crystal optical fibers have an outer diameter of 80 μm,
The core diameter is 5 μm, and the fiber length is the single crystal optical fiber 5.
2 is 3 cm, and the single crystal optical fiber 53 is 20 cm.
Light having a wavelength of 0.86 μm as the first and second control lights,
Light having a wavelength of 1.32 μm is used as a signal, and the wavelength of the sum frequency light is 0.52 μm. Further, the single crystal fiber 52 has a phase matching condition adjusted by temperature so as to generate sum frequency light having a wavelength of 0.52 μm from light having a wavelength of 0.86 μm and light having a wavelength of 1.32 μm. 53
The phase matching condition is adjusted by the temperature so as to generate the difference frequency light having the wavelength of 1.32 μm from the light having the wavelength of 0.86 μm and the light having the wavelength of 0.52 μm.

When continuous light of 1 mW was incident as the signal light and pulsed light of 20 mHz was repeatedly input as the first and second control lights with a peak power of 100 mW, the first and second control lights were obtained as shown in FIG. The characteristic that the output signal light is obtained when the light is simultaneously input is obtained. In this case, the ratio of the signal light output when the first and second control lights enter at the same time and the signal light output when at least one of the control lights does not exist, that is, the extinction ratio is 30 dB or more. It is shown that it can be applied not only as a modulation but also as a switch. The waveform of the signal light sufficiently follows the control light, indicating that this embodiment has a high-speed response. Although the limit of the response speed is not clear yet, it is considered that a response of 100 GHz or more is possible as in the first embodiment. in addition,
The peak power of the output signal light is 3 mW, and the input signal light is amplified by the parametric amplification effect in the single crystal optical fiber 53. In this embodiment, the amplification effect and AND
It can be said to be a high-speed optical switch or modulator having the function of an element.

In the above two embodiments, the single crystal fiber of lithium niobate was used as the medium having the second-order nonlinear optical effect. However, the single crystal optical fiber structure enables a high light intensity density and a long interaction length. Therefore, the efficiency of wavelength conversion is high, and the control light can be reduced in power. From this, it can be said that the single crystal optical fiber structure is suitable for the present invention. Lithium niobate and potassium niobate are 2
The following non-linear optical effect is relatively large, and it is a typical crystal that can be easily formed into a single crystal optical fiber.
For example, dielectric materials such as KTP (KTiOPO ₄ ), β-BaB ₂ O ₄ , DAN (2- (N, N-dimethylamino) -5-nitroacetanilide), ANNP (2-adamantylamino-5-nitropyridine) It is needless to say that such an organic material can be similarly applied to the present invention as long as it has a second-order nonlinear optical effect and can be formed into a single crystal fiber structure. Although the operating power is higher than that of the single crystal optical fiber structure, the present invention can be similarly applied to the present invention as long as it is a medium having a secondary nonlinear optical effect such as a substrate waveguide structure and a bulk structure.

[0016]

As described in detail above, the present invention is
By using the second-order nonlinear optical effect that is more efficient than the third-order nonlinear optical effect twice, the same optical-optical modulation and optical-optical switching operation as that of the device using the third-order nonlinear effect can be achieved. It is realized with lower power. as a result,
It is possible to realize an optical switch, an optical modulator, and an optical logic element having two features of low power optical operation and high speed operation.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the concept of the configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration of the first embodiment of the present invention.

FIG. 3 is a characteristic diagram of the first embodiment of the present invention.

FIG. 4 is a schematic diagram showing the concept of the configuration of the second embodiment of the present invention.

FIG. 5 is a diagram showing a specific configuration of a second embodiment of the present invention.

FIG. 6 is a characteristic diagram of the second embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a conventional car shutter based on a third-order nonlinear optical effect.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multiplexer 2 Medium which has 1st 2nd-order nonlinear optical effect 3 Medium which has 2nd 2nd-order nonlinear optical effect 4 Optical filter 5 Optical filter 21 Multiplexer 22 Lithium niobate single crystal optical fiber 23 Niobium Lithium oxide single crystal optical fiber 24 Optical filter 25 Optical filter 26 Lens 27 Lens 28 Lens 29 Lens 41 Multiplexer 42 Medium having first second-order nonlinear optical effect 43 Medium having second second-order nonlinear optical effect 44 Combiner / splitter 45 Optical filter 51 Combiner 52 Lithium niobate single crystal optical fiber 53 Lithium niobate single crystal optical fiber 54 Combiner / splitter 55 Optical filter 56 Lens 57 Lens 58 Lens 59 Lens 71 Gate light 72 Disulfide Carbon 73 Analyzer 74 Signal light 75 Multiplexer

Claims (3)

[Claims] 1. A multiplexer having a function of multiplexing lights having _two different angular frequencies ω ₁ and ω ₂ , a first medium and a second medium having a second-order nonlinear optical effect, and an angular frequency omega ₂ of the light absorption or reflection, and made of a light filter which transmits and ω ₃ = ω ₁ + ω the angular frequency omega ₃ light and the angular frequency omega ₁ of the light on the _second relationship, if by the multiplexer Waves with angular frequencies ω ₁ and ω ₂ are made incident on the first medium, light emitted from the first medium is made incident on the optical filter, and light emitted from the optical filter is made the second light. A non-linear optical device characterized by being incident on a medium. 2. A multiplexer having _two lights having different angular frequencies ω ₁ and ω ₂ , a first medium and a second medium having a second-order nonlinear optical effect, and angular frequencies ω ₁ and ω ₂ Reflects the light of
And a light having an angular frequency ω ₃ having a relationship of ω ₃ = ω ₁ + ω ₂ is transmitted, and the light having the angular frequencies ω ₁ and ω ₂ combined by the multiplexer is added to the first light. The light emitted from the first medium and the light having an angular frequency ω ₁ from the outside are incident on the multiplexer / demultiplexer, and the angular frequency ω _{3 of the} light emitted from the first medium is input. A non-linear optical device, characterized in that the light of (1) and the light of angular frequency ω1 from the outside are combined and made incident on the second medium. 3. A single crystal optical fiber in which at least one of the first medium and the second medium is a fiber-shaped optical crystal having a second-order nonlinear optical effect. The nonlinear optical device according to claim 1 or 2.