JPH0822036A - Optical modulating method - Google Patents

Abstract

PURPOSE:To make it possible to apply large modulation to signal light with weak control light and to lessen the loss of the signal light by adopting different wavelengths for the wavelengths of the signal light and the control light. CONSTITUTION:The signal light A of specified intensity is made incident from an input port 3 and the control light B of variable intensity from an input port 4. The exit light from an output port 5 is delivered as output and its intensity is measured. An Ar<+> laser (wavelength 488nm) and He-Ne laser (wavelength 633nm) are prepd. The output light intensity decreases with an increase in the control light intensity in the case of lambdaA=lambdaB=488nm in a relation between the control light intensity and the output light intensity. The output light intensity when the control light intensity is zero is large and the loss of the signal light is lessened in the case of lambdaA=633nm and lambdaB=488nm. Namely, the two contradicting conditions of the generation of switching by the weak control light and the small loss of the signal light are simultaneously satisfied by adopting lambdaAnot equal to lambdaB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch using a non-linear optical material, an optical modulation method for a non-linear optical element used in an optical memory, an arithmetic processing unit for optical signals and the like.

[0002]

2. Description of the Related Art A non-linear optical phenomenon in which a refractive index and an absorption coefficient change depending on the intensity of light has been attracting attention. Non-linear optical materials having such non-linear optical characteristics have been conventionally known, and many studies on non-linear optical elements such as optical switches and optical logic operation elements using the same have been made. For example, consider a case where the signal light A (wavelength λ _A ) and the control light B (wavelength λ _B ) which are information media are incident on the nonlinear optical material and the control light modulates the signal light. However, there are cases where one ray has both the roles of A and B (in this case, obviously λ _A = λ _B ), and when A and B are different rays (in this case, further λ _A = λ _B ). _There are cases of _B and cases of λ _A ≠ λ _B ). In this case, the characteristics of the non-linear optical element are significantly affected by the properties of the non-linear optical material and the wavelengths of the signal light and the control light incident on the non-linear optical material.

As characteristics required for the above-mentioned nonlinear optical element, it is required that a weak control light B can apply a large modulation to the signal light A and a loss with respect to the signal light A is small. As a non-linear optical material capable of imparting such characteristics, as to how the refractive index of the signal light A of the wavelength λ _A changes relative to the intensity of the control light B of the wavelength λ _B , It is necessary that the ratio (change amount of refractive index of signal light A) / (change amount of intensity of control light B) (hereinafter referred to as χ (λ _A , λ _B )), which is an index, is large. On the other hand, it is necessary that the absorption coefficient of the signal light A (hereinafter referred to as α (λ _A )) is small.

Since the requirements for nonlinear optical materials are usually contradictory conditions, χ (λ _A , λ _B ) and α (λ _A )
_A large value of χ (λ _A , λ _B ) / α (λ _A ) is a criterion for determining the quality of the nonlinear optical material.

As conventional non-linear optical elements, (a) various kinds of polymer materials, non-linear optical materials such as silica glass and chalcogenide glass are used, and the wavelengths λ _A and λ _B of signal light and control light are λ _A = λ _B or λ _A ≠ λ _B
(Japanese Patent Laid-Open No. 2-195329, etc.). In a nonlinear optical element made of these nonlinear optical materials, α (
Although λ _A ) is small, it is disadvantageous in that χ (λ _A , λ _B ) is small. (B) Further, a non-linear optical material composed of semiconductor fine particle-dispersed glass / metal fine particle-dispersed glass in which fine particles of semiconductor or metal are dispersed in a glass matrix is used with λ _A = λ _B (JP-A-1-201626). JP-A-4-33
8735). In this nonlinear optical element, χ
Although (λ _A , λ _B ) is large, it is disadvantageous in that α (λ _A ) is large. As described above, there is no combination of the nonlinear optical material and the wavelengths of the signal light and the control light that simultaneously satisfy the above conditions.

The present inventors have conducted intensive studies to solve the above-mentioned problems of the prior art, that is, to develop a light control method that simultaneously satisfies the above conditions. As a result, using a fine metal particle dispersion, selecting an appropriate combination of the metal and the matrix material, and setting the wavelength λ _A of the incident light and the wavelength λ _{B of the} emitted light to different values, α (λ _A ) is Small, and χ (λ _A , λ _B ) is large, resulting in χ (λ
The inventors have found that _A , λ _B ) / α (λ _A ) may be large, and have completed the present invention. The present invention is capable of adding large modulation to signal light with weak control light, and
An object of the present invention is to provide an optical modulation method for a non-linear optical element that can reduce loss for signal light.

[0007]

The optical modulation method of the present invention comprises:
This is a method in which a signal light and a control light that modulates the signal light are incident on a nonlinear optical material made of a transparent dielectric material in which fine metal particles are dispersed, and a high-intensity signal light is emitted from the nonlinear optical material. The wavelengths of the signal light and the control light are different from each other.

[0008]

[Operation and effect] When the signal light A is input as an input to a non-linear optical element such as an optical switch, an output light is obtained. In this case, when the control light B is irradiated onto the nonlinear optical material at the same time as the signal light A, the refractive index and the absorption coefficient of the nonlinear optical material change. Along with this, the element characteristics with respect to the signal light A change, and the emission position / direction of the output light, the intensity, the polarization state, and the like change as compared with the case without the signal light B. in this case,
Since the signal light A and the control light B have different wavelengths, χ (
Even though λ _A and λ _B ) are large, α (λ _A ) can be made small. That is, the weak control light B can apply a large modulation to the signal light A, and the loss for the signal light A can be reduced.

[0009]

【Example】

(Invented Invention) The non-linear optical material used in this embodiment is composed of a transparent dielectric material and fine metal particles dispersed in a matrix of the transparent dielectric material. The transparent dielectric may be transparent to light having wavelengths λ _A and λ _B , which are the wavelengths of the signal light and the control light, and examples thereof include silica glass, alumina (Al ₂ O ₃ ), titania (TiO ₂ ), and the like. Various metal oxides, various polymers such as PMMA, and the like. Further, it is desirable that the metal has a small real part of the refractive index with respect to the light having the wavelength of λ _B , and is selected from tin, gold, platinum, silver and the like. Further, the diameter of the metal fine particles varies depending on the kind of the metal, but is preferably 2 to 20 nm, and if it is larger than 20 nm, the loss of light is large.
If the thickness is smaller than nm, the property of the metal is different from that of the bulk, and it becomes difficult to select the material forming the fine particles and the wavelength of light.

The non-linear optical element is composed of a multilayer film containing the non-linear optical material, a waveguide and an optical fiber.

As the method for producing the non-linear optical material, there are a melt deposition method, a sol-gel method, a multi-source sputtering method, an ion implantation method and the like, and there is no particular limitation.

Further, the wavelengths λ _A and λ of the signal light A and the control light B
_B is not particularly limited, but the effect becomes large when λ _B is set so as to satisfy the following conditions and. (i) Let λ _{A be} the wavelength (λ _df ) corresponding to the transition energy from the d band of the metal to the Fermi level. (ii) Let λ _{B be} the surface plasma resonance wavelength of the fine particle dispersion (λ _p , which is determined by the combination of the metal and the matrix). Further, it is desirable that λ _A and λ _B are separated by at least 50 nm or more. When the distance is closer than 50 nm, α (λ _A ) becomes large due to the influence of surface plasma resonance, which is not preferable. In particular, the wavelength λ of the signal light A and the control light B
Table 1 shows examples of combinations of _A and λ _B, and specific materials and wavelengths (light sources used).

[0013]

[Table 1]

The process in which the refractive index of the signal light A is changed by the irradiation of the control light B is as follows: (a) absorption of the control light B → (b) increase in electron temperature in metal → (c) near Fermi level in metal Change of electron occupancy number → (d) change of optical transition probability from metal d band (occupied state) to unoccupied state near Fermi level → (e) change of refractive index of signal light A .

When the wavelengths λ _A and λ _B of the signal light A and the control light B are set so as to satisfy the above conditions and as in this example, the efficiency of each process is increased for the following reasons. Therefore, a large value of χ (λ _A , λ _B ) can be obtained. By setting λ _B to the condition of (ii) (λ _B = λ _p ), the efficiency of the process of (a) → (b) is increased. The method of selecting λ _A is related to the efficiency of the process of (d) → (e). If λ _A is λ _B like λ _{B, that} is, λ _A = λ _p (that is, λ _A = λ _{B in the} prior art), (d) →
Although the efficiency of the process of (e) is large, under this condition α
(λ _A ) becomes large. Let λ _{A be} the condition of (i) (λ
_{If A} = λ _d ), the efficiency of the process of (d) → (e) can be kept as high as that of λ _A = λ _p , and α (λ _A ) can be significantly reduced. Therefore, the loss of the signal light A can be reduced. Therefore, a large χ (λ _A , λ _B ) / α
(λ _A ) values are obtained.

(Example 1) An ion implantation apparatus was used to prepare a non-linear optical material composed of glass in which fine metal particles were dispersed,
The optical modulation method of the present invention was applied to this nonlinear optical material, and its effect was investigated. Ion implantation of Sn ⁺ ions into a 2 cm square quartz glass substrate (implantation condition: ion acceleration voltage is 1.5
Mev, injection amount is 4 × 10 ¹⁷ ions / cm ² )
Then, a Sn fine particle dispersion layer was formed on the substrate. The thickness of this layer was 0.6 μm. The wavelengths λ _A and λ _B of the signal light and the control light which are incident on the Sn fine particle dispersion layer are (a) λ
_A = λ _B = 488 nm, (b) λ _A = 633 nm, λ _B
= 488 nm, (c) λ _A = λ _B = 633 nm, and the relative values of χ (λ _A , λ _B ) were calculated from the transmittance by four-wave mixing for each of the results, and the results shown in Table 2 were obtained. Met.

When comparing the case (b) in which the signal light and the control light have different wavelengths with the case (a) in the prior art, χ (
It was revealed that λ _A and λ _B ) were comparable to each other and α (λ _A ) was much smaller, resulting in an improved χ (λ _A , λ _B ) / α (λ _A ) value. In the case of (c), α (λ _A ) is small but χ (λ _A , λ _B ) is small, which is not suitable for practical use.

[0018]

[Table 2]

(Embodiment 2) In this embodiment, a high frequency sputter deposition apparatus is used to prepare a non-linear optical material composed of glass in which fine metal particles are dispersed, and the optical modulation method of the present invention is applied to this non-linear optical material. I investigated the effect. Four 5 mm square Au chips were placed on a 4-inch diameter titania target, sputter vapor deposition was performed, and titania and Au multi-source sputtering was performed to form an Au fine particle dispersion thin film on a glass substrate. The thickness of this film was 2.5 μm. The sputtering conditions were as follows: sputtering gas: argon gas containing 5% oxygen, gas pressure: 5 × 10 ⁻³ Torr, substrate temperature: 150
C., input power: 400 W, film formation time: 60 minutes. The wavelengths λ _A and λ _B of the signal light and the control light incident on the Au fine particle dispersion thin film are (a) λ _A = λ _B = 633 nm,
(B) λ _A = 730 nm, λ _B = 633 nm, (c) λ
_A = λ _B = 730 nm was set in three ways, and the relative values of χ (λ _A , λ _B ) and α (λ _A ) were measured for each, and the results shown in Table 3 were obtained. The case where the wavelengths of the light and the control light are different (b) is the most desirable result.

[0020]

[Table 3]

Example 3 A waveguide type optical switch as shown in FIG. 1 was produced using the Sn fine particle dispersion layer which is the nonlinear optical material used in Example 1. The optical modulation method of the present invention was applied to this optical switch, and its effect was investigated. FIG.
As shown in (1), a mask 10 having windows in the shapes of the waveguides 1 and 2 was produced on a quartz glass substrate 11 having a width of 20 mm and a length of 25 mm by using a photolithography technique. Next, Sn ⁺ ions are implanted (the substrate temperature is 800 ° C., the accelerating voltage is 1.5 MeV, and the implantation amount is 1 × 10 ¹⁸ ions / cm ² ) in the hatched portion of FIG. Diffused inside the substrate, width 4μm, thickness 1.8
A non-linear waveguide 1 (waveguide made of a non-linear material) having a thickness of 5 μm and a length of 5 mm was formed. Then, as shown in FIG. 1 (3), He ⁺ ions are implanted into a portion other than the hatched portion (substrate temperature is room temperature, accelerating voltage is 400 KeV, implantation amount is 3 × 10 ¹⁵ io).
ns / cm ² ) and width 4 μm, thickness 1.8 μm,
5 mm long linear waveguide 2 (waveguide made of linear material)
Was formed. The distance between the nonlinear waveguide 1 and the linear waveguide 2 is 3 μm. Finally, the mask was removed by chemical etching as shown in FIG.

A signal light A having a constant intensity is inputted from the input port 3,
The intensity-variable control light B was input from the input port 4 and the output light from the output port 5 was output, and the intensity was measured.
Ar ⁺ laser (wavelength 488 nm) and He are used as the light source.
A -Ne laser (wavelength 633 nm) was prepared.

FIG. 2 shows the relationship between the control light intensity and the output light intensity. 2A shows the case where λ _A = λ _B = 488 nm (conventional technology), and shows that the output light intensity decreases as the control light intensity increases. (B) is λ _A = 633n
This is the case where m and λ _B = 488 nm. It can be seen that the output light intensity when the control light intensity is zero is larger than that in the case of (a), that is, the loss of the signal light is small. The control light intensity at which the output light intensity becomes zero (that is, the control light intensity required for switching) is only slightly higher than that in the case of (a). That is, by setting λ _A ≠ λ _B , two normally contradictory conditions that switching occurs with weak control light and a loss of signal light is small can be satisfied at the same time. (C) is λ _A = λ _B = 633
This is the case of nm. Although the loss of the signal light is slightly smaller than that in the case of (b), the control light intensity required for switching is considerably larger than that in the case of (b), which is not practical. In the case of (b), the control light is separated from the output light from the output port 6 through a sharp cut filter (not shown), and the intensity is measured. As a result, the change as shown in (d) of FIG. showed that. That is, FIG. 1 (4)
It was confirmed that the signal light from the input port 3 in (1) is emitted from the output port 5 when the control light intensity is zero, but the output is switched to the port 6 side as the control light intensity increases. When λ _A ≠ λ _B as described above, there is also an advantage that the signal light (or output light) and the control light can be easily separated by using a sharp cut filter, a dichroic mirror, or the like.

Example 4 An optical Kerr shutter type optical switch as shown in FIG. 3 was produced using the Au fine particle dispersion thin film which is the nonlinear optical material used in Example 2. The optical modulation method of the present invention was applied to this optical switch, and its effect was investigated. The optical car shutter type optical switch is for gating signal light with control light to obtain output light corresponding to the intensity of the control light.

This switch is a thin film material 7 on a glass substrate.
Is sandwiched between two orthogonal polarizing plates 8 and 9. The linearly polarized signal light (constant intensity) was vertically incident on the thin film material 7 through the polarizing plate 8, and the intensity of the transmitted light was measured after passing through the polarizing plate 9. As the control light (variable intensity), linearly polarized light whose polarization direction forms an angle of 45 degrees with the main axis of the polarizing plate 8 is used, and after passing through the thin film material 7, the thin film material 7 can be separated from the transmitted light of the signal light. Incident from a direction slightly inclined from the vertical. As a light source, a He-Ne laser (wavelength 633 nm) and a semiconductor laser (wavelength 73)
0 nm) was prepared, and measurement was performed for three combinations of λ _A and λ _{B in} the same manner as in Example 3.

FIG. 4 shows the relationship between the control light intensity and the output light intensity.
( _A ) is λ _A = λ _B = 633 nm, (b) is λ _A = 73
0 nm, λ _B = 633 nm, (c) is λ _A = λ _B = 73
This is the case of 0 nm. In both cases, the output light intensity increased as the control light intensity increased, but as in Example 3, in the case of (b), switching occurred with weak control light and the loss of signal light was small.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a waveguide type optical switch.

FIG. 2 is a diagram showing operating characteristics of a waveguide type optical switch.

FIG. 3 is a schematic view of a car shutter type optical switch shown in a fourth embodiment.

FIG. 4 is a diagram showing operating characteristics of a car shutter type optical switch.

[Explanation of symbols]

 1 Nonlinear Waveguide 2 Linear Waveguide 3 Signal Light Input Port 4 Control Light Input Port 5 Output Optical Port I 6 Output Optical Port II 7 Thin Film Nonlinear Optical Material 8 Polarizing Plate I 9 Polarizing Plate II 10 Mask 11 Substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Noda 41, Yokomichi, Nagakute-cho, Nagakute-cho, Aichi-gun, Aichi-1 Toyota Central Research Institute Co., Ltd.

Claims (1)

[Claims] 1. A signal light and a control light for modulating the signal light are made incident on a nonlinear optical material made of a transparent dielectric material in which fine metal particles are dispersed, and a high-intensity signal light is emitted from the nonlinear optical material. A light modulation method, wherein the signal light and the control light have different wavelengths.