JP3031390B2 - Nonlinear optical 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 device such as an optical switch and an optical modulator used in the fields of optical transmission and optical information processing, and more particularly to a nonlinear optical device capable of realizing a high-speed operation. It is.

[0002]

2. Description of the Related Art In the field of non-linear 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 a change in carrier density in a semiconductor due to electric current. A device utilizing a change in the refractive index or a device utilizing a change in the refractive index due to the electro-optic effect of the crystal by applying an electric field has been studied. Further, as a nonlinear optical device which operates by light without applying a current or an electric field, a device utilizing a refractive index change due to a third-order nonlinear optical effect is being studied.

[0003]

However, in the above-mentioned optical switches and optical modulators which operate by applying a current or an electric field, the operating speed is limited by the carrier moving speed or the stray capacitance, respectively. The limit is about 50 GHz. In an optical switch, an optical modulator, and the like based on the third-order nonlinear optical effect, extremely high-speed operation can be expected. However, since the third-order nonlinear optical constant is generally extremely small, operation with low power light cannot be performed, so that practical use is not possible. It has not reached the target element. For example, 3
A car shutter using carbon disulfide as a material having the following nonlinearity has a structure as shown in FIG. That is, the gate light 71 causes anisotropy of the refractive index in the carbon disulfide 72. Then, the polarization of the signal light 74 that has been transmitted through the carbon disulfide 72 and blocked by the analyzer 73 with the same linearly polarized light as that at the time of incidence is changed into an anisotropic refractive index generated in the carbon disulfide by the gate light. It rotates due to the nature, emits through the analyzer 7, and turns on the gate light.
The emission intensity of the signal light is controlled by the OFF and the intensity. However, in the case of such a nonlinear optical device, since the third-order nonlinear optical effect is extremely small,
A gate light of 100 W or more was required as an operating power, and none of them could be used practically. It is an object of the present invention to provide a non-linear optical device such as an optical switch or an optical modulator which is driven at high speed and with low power.

[0004]

In order to solve the above-mentioned problems, a nonlinear optical device according to the present invention comprises: a multiplexer for multiplexing and outputting lights having two different angular frequencies ω1 and ω2;
Light having angular frequencies ω1, ω2 and ω3 =
2 for emitting light of angular frequency ω3 having a relationship of ω1 + ω2
A first medium having the following nonlinear optical effect, said first medium
First which transmits the light of the light and the angular frequency ω1 of the cutoff vital angular frequency ω3 light of angular frequency ω2 based on light emitted from the quality
An optical filter, based on light emitted from the first optical filter;
The relationship between the light of angular frequencies ω1, ω3 and ω2 = ω3-ω1
Second-order nonlinear optical effect that emits light at a certain angular frequency ω2
Based on a second medium having
At the angular frequencies ω1 and ω3 and at the angular frequency ω2
A second optical filter that transmits light .

The present invention also provides two different angular frequencies ω
1, a multiplexer for multiplexing and emitting light of ω2, and
Of the angular frequencies ω1, ω2 and ω3 = ω1
A first medium having a second-order nonlinear optical effect for emitting light having an angular frequency ω3 having a relationship of + ω2, and a first medium
Angular frequency ω1 based on light emitted al, and reflects light ω2
Combines light with angular frequency ω3 and light with angular frequency ω1 from outside
And a multiplexer / demultiplexer that emits light based on the light emitted from the multiplexer / demultiplexer.
The relationship between the light of angular frequencies ω1, ω3 and ω2 = ω3-ω1
Second-order nonlinear optical effect that emits light at a certain angular frequency ω2
Based on a second medium having
At the angular frequencies ω1 and ω3 and at the angular frequency ω2
It also discloses a means including an optical filter that transmits light .

[0006]

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

[0007]

【Example】

(Embodiment 1) 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 multiplexed by the multiplexer 1.
The light is incident on the medium 2 having the first secondary nonlinear optical effect. The medium 2 having the first-order nonlinear optical effect has a phase matching condition for generating a 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 adjusted so as to satisfy control light, signal light, and sum frequency light, respectively, which satisfy the propagation constant when the medium 2 having the first-order nonlinear optical effect propagates. In such a state, sum frequency light (angular frequency ω ₃ ) is generated in the medium 2 having the first-order nonlinear optical effect according to the intensity of the control light and the signal light. The control light, signal light, and sum frequency light emitted from the medium 2 having the first second-order nonlinear optical effect enter the optical filter 4, where the signal light is cut off, and the control light and the sum frequency light transmit. The light enters the medium 3 having the second secondary nonlinear optical effect.

The medium 3 having the second-order 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 0 (2 (Where k ₁ , k ₂ , and k ₃ are the propagation constants when the control light, the signal light, and the sum frequency light propagate through the medium 3 having the second-order nonlinear optical effect). Has been adjusted. In such a state, the difference frequency light (angular frequency ω ₂ ) is generated in the medium 3 having the second second-order nonlinear optical effect according to the intensity of the control light and the sum frequency light. Control light emitted from the medium 3 having the second secondary 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 cut off, 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 portion 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. Since the terminal element has a structure and the response of the second-order nonlinear optical effect is fast, high-speed switching and light modulation are possible.

FIG. 2 is a diagram showing a more specific structure of the first embodiment, wherein 21 is a multiplexer, 22 and 23 are lithium niobate single crystal optical fibers, respectively, and 24 and 25 are optical filters, respectively. , 26, 27, 28 and 29 are lenses. In the present 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 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 of the single crystal optical fiber 22 is 3 cm, and that of the single crystal optical fiber 23 is 20 cm. Light having a wavelength of 0.86 μm (angular frequency 2.2 × 10 ¹⁵ (S ⁻¹ )) as control light and 1.32 μm (angular frequency 1.4 ×) as signal light.
10 ¹⁵ (S ⁻¹ )) light, and the wavelength of the sum frequency light is 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 a 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. Reference numeral 23 denotes a phase matching condition adjusted by temperature so that a difference frequency light having a wavelength of 1.32 μm is generated from light having a wavelength of 0.86 μm and light having a wavelength of 0.52 μm.

A continuous light of 1 mW is incident as a signal light, and a peak power of 100 mW and a repetition of 20 GH are used as control light.
When the pulse light of z was input, a signal light modulated by the waveform of the control light was obtained as shown in FIG. In this case, the ratio between the signal light output when control light is input and the signal light output when no control light is input, that is, the extinction ratio is 30 dB or more, indicating that this embodiment can be applied not only to modulation but also to a switch. ing. The waveform of the signal light sufficiently follows the control light, indicating that this embodiment has a high-speed response. The response speed limit is not clear yet,
It is considered that a response of GHz or more 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. 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 a second embodiment of the present invention. The signal light (angular frequency ω ₂ ) and the first control light (angular frequency ω ₁ ) are
1 and is incident on a medium 42 having a first-order nonlinear optical effect. The medium 42 having the first-order second-order nonlinear optical effect is adjusted to a state that satisfies the phase matching condition for generating the sum frequency of the signal light and the control light, that is, the condition of the above equation (1). In such a state, sum frequency light (angular frequency ω ₃ ) is generated in the medium 42 having the first secondary nonlinear optical effect according to the intensity of the control light and the signal light. The first control light, signal light, and sum frequency light emitted from the medium 42 having the first secondary nonlinear optical effect enter the multiplexer / demultiplexer 44, where the signal light and the first control light are reflected. , The sum frequency light is multiplexed with the second control light and transmitted, and the second 2
The light enters the medium 43 having the following nonlinear optical effect.

The medium 43 having the second-order nonlinear optical effect satisfies the phase matching condition for generating a difference frequency between the second control light and the sum frequency light, that is, the condition of the above equation (2). The condition has been adjusted. In such a state, the difference frequency light (angular frequency ω ₂ ) is generated in the medium 43 having the second secondary non-linear optical effect according to the intensity of the second control light and the sum frequency light. Medium 43 having a second secondary non-linear optical effect
The second control light, the difference frequency light, and the sum frequency light emitted from the optical filter 45 enter the optical filter 45, the control light and the sum frequency light are cut off, 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 the intensity thereof depends on the intensity of the incident signal light and the first control light and the second control light. Accordingly, when the portion of the present invention is considered as one black box 46, as shown in FIG. 4B, the transmission intensity of the signal light (angular frequency ω ₂ ) is made equal to that of the first control light (angular frequency ω ₁ ). It has a structure of an element controlled by a second control light (angular frequency ω ₁ ), and as a logic element, an AND of the first and second control lights
It is also an element. Since the response of the second-order nonlinear optical effect is fast, high-speed switching and light modulation are possible.

FIG. 5 is a diagram showing the actual configuration of the second embodiment, in which 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. The filters 56, 57, 58 and 59 are lenses. In this embodiment, a lithium niobate single crystal optical fiber 52 is used as a medium having a first-order nonlinear optical effect, and a lithium niobate single crystal optical fiber 53 is used as a medium having a second-order nonlinear optical effect. I'm using Both lithium niobate single crystal optical fibers have a fiber outer diameter of 80 μm,
The core diameter is 5 μm and the fiber length is a 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. The phase matching condition of the single crystal fiber 52 is adjusted by temperature so as to generate a 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 temperature so that a difference frequency light having a wavelength of 1.32 μm is generated from light having a wavelength of 0.86 μm and light having a wavelength of 0.52 μm.

When a continuous light of 1 mW is input as signal light and a pulse light having a peak power of 100 mW and a repetition of 20 GHz is input as the first and second control lights, as shown in FIG. The characteristic that the output signal light is obtained when the light is input simultaneously is obtained. In this case, the ratio between the signal light output when the first and second control lights are simultaneously input and the signal light output when at least one of the control lights is absent, that is, the extinction ratio is 30 dB or more. This indicates that the present invention can be applied not only to modulation but also to 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 yet clear, 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 called a high-speed optical switch or modulator having the function of an element.

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

[0016]

As described in detail above, the present invention provides
By using two media having a second-order nonlinear optical effect that is more efficient than the third-order nonlinear optical effect, light-light modulation and light-light similar to an element using the third-order nonlinear effect can be achieved. Switching operation is realized with lower power. As a result, low power optical operation and high speed operation
An optical switch, an optical modulator, and an optical logic element having two features can be realized.

[Brief description of the 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 a 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 using a third-order nonlinear optical effect.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 multiplexer 2 medium having first secondary nonlinear optical effect 3 medium having second secondary 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 Combiner 42 Medium having first secondary nonlinear optical effect 43 Medium having second secondary nonlinear optical effect 44 multiplexer / demultiplexer 45 optical filter 51 multiplexer 52 lithium niobate single crystal optical fiber 53 lithium niobate single crystal optical fiber 54 multiplexer / demultiplexer 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)

(57) [Claims] 1. A light source having two different angular frequencies ω1 and ω2
A multiplexer that combines and emits light, and a light that is output from the multiplexer.
The relationship between the light of angular frequencies ω1, ω2 and ω3 = ω1 + ω2
A first medium that emits light of a certain angular frequency ω3 and has a second-order nonlinear optical effect, and light emitted from the first medium
A first optical filter that blocks light of angular frequency ω2 and transmits light of angular frequency ω3 and light of angular frequency ω1 ;
Angular frequencies ω1, ω3 based on light emitted from one optical filter
Of light and the angular frequency ω2 in the relationship of ω2 = ω3-ω1
Second medium having a second-order nonlinear optical effect for emitting light
And angular frequencies ω1, ω based on the light emitted from the second medium.
3 that blocks the light of 3 and transmits the light of the angular frequency ω2.
A nonlinear optical device, comprising: an optical filter . 2. Light of two different angular frequencies ω1, ω2 is
A multiplexer that combines and emits light, and a light that is output from the multiplexer.
The relationship between the light of angular frequencies ω1, ω2 and ω3 = ω1 + ω2
A first medium that emits light of a certain angular frequency ω3 and has a second-order nonlinear optical effect, and light emitted from the first medium
The angular frequency .omega.1, the reflecting light ω2 and angular frequency ω3
Combination of light and external light with angular frequency ω1
And an angular frequency ω1, based on light emitted from the multiplexer / demultiplexer.
Light of ω3 and angular frequency ω in a relation of ω2 = ω3-ω1
Second light having a second-order nonlinear optical effect that emits a second light
Angular frequency ω based on the medium and the light emitted from the second medium
1. Block light at ω3 and transmit light at angular frequency ω2
A nonlinear optical device, comprising: an optical filter . 3. A single crystal optical fiber in which at least one of the first medium and the second medium is a fiber made of an optical crystal having a second-order nonlinear optical effect. The nonlinear optical device according to claim 1 or 2.