JPS6153707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wavelength conversion element using the third-order nonlinear effect of an optical fiber.

(Prior Art) Conventionally, it has been known that when light with high energy density is incident on an optical fiber, a portion of the incident energy is converted into light of a different wavelength due to the nonlinear effect of the optical fiber material. ing. An optical wavelength conversion device shown in FIG. 7 is known as an optical wavelength conversion device that utilizes the principle of optical wavelength conversion for such a third-order nonlinear effect. To explain the figure, numeral 1 is a laser light source, 2 is an optical fiber as an optical wavelength conversion element,
3 and 4 are objective lenses, and 5 is a demultiplexer. As the laser light source 1, one having a Q-switch function is usually used because it is necessary to increase the power incident on the optical fiber 2 in order to obtain a strong nonlinear effect. In addition, the length of the optical fiber 2 is from several meters to several tens of meters.
It is.

In the above device, a part of the laser beam of wavelength λp emitted from the laser light source 1 is caused by the third-order nonlinear effect inside the optical fiber 2, causing the incident light (λ
p) into light of different wavelengths (λs, λ _A ), and the demultiplexer 5 separates the wavelengths λp, λs, λ _A
(However, λ _A < λp < λs). Therefore, according to the apparatus shown in FIG. 1, the light of wavelength λp emitted by the laser light source 1 can be converted into light of wavelength λs and _λA .

By the way, the optical wavelength conversion by the apparatus shown in FIG. 2 is performed under the following conditions, so that the wavelengths λs,
λ _A is determined.

1/λ _A -1/λp=1/λp-1/λs=Δ
...(1) Note that Δ is the normalized frequency shift amount. At this time, if the phase constants in the optical fiber of light waves with wavelengths λp, λs, and _λA are Kp, Ks, and K _A , the phase matching condition Ks+K _A −2Kp=0 (2) holds. This phase matching condition can be separated into a term Δk (Δ) due to the refractive index dispersion of the optical fiber material and a term f (Δ) due to the structure of the optical fiber, etc., Δk (Δ) + f (Δ) = 0 ... (3 ) becomes. Therefore, based on the relationships of equations (1) to (3) above, the incident light (λp) is converted into converted light having wavelengths λs and _λA .

(Problems to be Solved by the Invention) Therefore, the conventional wavelength conversion device shown in FIG. Frequency shift amount (Δ) caused by
The fixed wavelength λ is uniquely determined, and the fixed wavelength λ
It was possible to obtain only light of s, λ _A. For this reason, conventionally, the only way to convert the converted lights λs and _λA while keeping the wavelength λp of the incident light constant is to use fibers with different fiber parameters such as relative refractive index difference and core shape. Ta. Therefore, it is very inconvenient to use it as a wavelength tunable light source.

An object of the present invention is to provide an optical wavelength conversion element that can continuously vary the wavelength of converted light.

(Means for Solving the Problems) The present invention is characterized by having an optical fiber inserted between a light source and a light receiving means, and converting the wavelength of incident light from the light source by a nonlinear effect of the optical fiber. In the optical wavelength conversion device, the optical fiber is a birefringent optical fiber, and the optical wavelength conversion device is provided with temperature control means for controlling the temperature of the optical fiber.

(Function) By controlling the fiber parameters of the birefringent optical fiber using the temperature control means, the wavelength of the converted light can be arbitrarily controlled.

(Example) FIG. 1 is a principle diagram of an optical wavelength conversion device to which the optical wavelength conversion element of the present invention is applied. In this figure, the same components as in FIG. 2 are given the same reference numerals and their explanations will be omitted. Optical wavelength conversion element 10 shown in this figure
consists of a birefringent optical fiber 11 and a temperature control means, such as a heating device 12, for controlling the temperature of the birefringent fiber light 11. Birefringent fiber 1
1, due to birefringence caused by residual stress inside the fiber 11, the light incident on the fiber 11 is divided into two polarization planes whose polarization planes are orthogonal to each other.
It has the property of propagating by solving the degeneracy of HE ₁₁ mode. In this case, the short axis and long axis of the fiber are set in the X and Y directions, respectively. The heating device 12 applies heat to the birefringent fiber, and is designed to be temperature controllable. Note that reference numeral 13 is an analyzer placed on the optical path between the objective lens 4 and the demultiplexer 5.

The optical wavelength conversion element 10 described above converts a part of the light of wavelength λp emitted from the laser light source 1 into light of λs _{and λA} , and in this case, the temperature given to the fiber 11 is adjusted by the heating device 12. By this, the wavelengths λs and λ _A of the converted light can be continuously changed.

Next, the principle of the wavelength conversion action of the optical wavelength conversion element 10 will be explained. Now the wavelength λp of the incident light is 1.3μ
If it is set to less than m, Δk(Δ) of equation (3) mentioned above
is positive, so one example of satisfying the phase matching condition of equation (2) is to set the polarization plane of the incident light in the Y direction and the polarization plane of the converted light in the X direction. When λp>1.3 μm, Δk (Δ) is negative, but if the combination of the polarization planes of the incident light and the converted light is considered, it can be implemented in the same way as when Δk (Δ) is positive.

Under the above conditions, f(Δ) in equation (3) is calculated by using birefringence Bg due to the structure of the optical fiber and birefringence Bs due to the residual stress of the optical fiber, f(Δ)=-4π(Bs+Bg) /λp ……(4) can be written.

For example, considering an elliptical core fiber, the stress birefringence Bs of the elliptical core fiber is Bs = Bs ₀ H (V) ... (5) Bs ₀ = -0.5n (p ₁₁ - p ₁₂ ) (α ₀ - α ₁ ) qΔT ... (6) Here, Bs ₀ is the stress birefringence in the core, and H
(V) is a quantity related to the spread of the mode field distribution and stress distribution, n is the refractive index of the core p ₁₁ and p ₁₂ are the Pockels constants, α ₁ and α ₁ are the linear expansion coefficients of Sio and GeO ₂ , respectively, and q is the molar concentration of GeO ₂ and ΔT is the difference between room temperature and solidification temperature. Therefore, when heat is applied to this elliptical fiber, the stress birefringence Bs ₀ changes as ΔT changes. Therefore, the amount of frequency shift (Δ) of the converted light caused by four-photon mixing
is given in Figure 3. Generally, the stress birefringence Bs of a birefringent fiber changes depending on the temperature, and Bs=f(n, p ₁₁ , p ₁₂ , α ₀ , α ₁ , q)ΔT
...It can be expressed as (7). On the other hand, the relationship between Δk(Δ) and Δ is
When the pump light is 1.064 μm, it becomes as shown in Figure 4. FIG. 5 shows the relationship between the total birefringence and the heating temperature T of an elliptic clad fiber, and shows a large change in birefringence with temperature changes. Therefore, according to the phase matching condition of equation (3), the relationship between the superheating temperature T and the frequency shift amount Δ of the converted light is as shown in FIG. Therefore, from FIG. 6, if the temperature applied to the fiber is known, the frequency of the generated converted light can be found. From this figure, by changing the temperature by about 700°C, the wavelength of the converted light can be converted over a wide frequency range of about 2000 cm ^-1 .

(Effects of the Invention) As described above, if a birefringent fiber is used as an optical wavelength conversion element, the stress of the optical fiber can be changed by changing the heating temperature of the optical fiber, and the birefringent fiber can be It has the advantage that the wavelength of the converted light obtained through this process can be made continuously variable.

Furthermore, by selecting and preparing structural parameters such as the relative refractive index difference of the birefringent fiber and dopant materials, it is possible to convert wavelengths over a wider range of wavelengths, which has the advantage of being usable as a wavelength-tunable light source.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of an optical wavelength conversion device constructed using the optical wavelength conversion element of the present invention, FIG. 2 is a principle diagram of an optical wavelength conversion device using a conventional optical fiber, and FIG.
The figure shows the relationship between the heating temperature T and the normalized frequency shift amount in the elliptical fiber, and Figure 4 shows the pump light 1.084
Δk(Δ
), Figure 5 shows the relationship between heating temperature and birefringence in an elliptic clad fiber, and Figure 6 shows the relationship between birefringence and
The figure has been modified to show the relationship between the frequency shift amount Δ and the heating temperature. 1: Pump light source, 2: Optical fiber, 3, 4:
Objective lens, 5: prism, 10: birefringent fiber, 12: heating device, 13: analyzer.

Claims (1)

[Claims] 1. An optical wavelength conversion device that has an optical fiber inserted between a light source and a light receiving means, and converts the wavelength of incident light from the light source by the nonlinear effect of the optical fiber, wherein the optical fiber is a birefringent optical fiber. An optical wavelength conversion device comprising: a temperature control means for controlling the temperature of the optical fiber.