JPH02176621A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain stable characteristics without varying the main characteristics of a laser oscillation source greatly in the case of fine wavelength variation by shifting the wavelengths of 1st and 2nd birefringent diffraction grating type polarizers where the maximum extinction ratios are obtained from the using wavelength of the optical isolator in mutually opposite directions. CONSTITUTION:This optical isolator is provided with a polarizer 1, a Faraday rotator 2, an analyzer 3, and a magnet 4 and the using wavelength of the optical isolator is denoted as lambda. When the birefringent diffraction grating type polarizers are manufactured, the 1st and 2nd birefringent diffraction grating type polarizers are designed in the mutually opposite directions so that the wavelengths at which the maximum extinction ratios are obtained are lambda+DELTAlambda1 and lambda-DELTA1; and one polarizer is used as a polarizer and the other is used as the analyzer. Here, the AR coating of the 1st and 2nd birefringent diffraction grating type polarizers is carried out at the using wavelength of the optical isolator. Consequently, the stable isolation characteristics are obtained without varying the maximum extinction ratios greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator using a birefringent diffraction grating that has reduced wavelength dependence within a certain range.

[Prior Art and Problems to be Solved by the Invention] Generally, a birefringent grating polarizer has a wavelength λ set at the time of manufacture. If it is used at a wavelength λ that deviates from the wavelength λ, the extinction ratio will be greatly degraded.

FIG. 1 is a diagram showing the wavelength characteristics of a conventional birefringent grating type polarizer. As shown in this figure, the deviation of the normalized wavelength shown on the vertical axis causes a large change in the degree of deflection separation shown on the horizontal axis.

This is because the manufacturing design changes slightly depending on the wavelength used.

The separation distance d of the extraordinary light is expressed by equation (1) where A is the period and λ is the wavelength of the light.

d-fiλ/Δ...(1) Also, extraordinary ray: k (na 1)T,+Δn*Tb-
π (diffraction)...(2) Ordinary ray: k (na 1) Ta + ΔnOTb
-π (straight ahead)...(3) T4: Dielectric film thickness, T,: Proton exchange film thickness, n,;
Refractive index of the galvanic film, Δn: Increase in refractive index of the proton exchange layer for extraordinary light, Δno: Increase in refractive index of the proton exchange layer for ordinary light, k is the number of periods.

As shown by equations (2) and (3), in the proton exchange region of the refractive diffraction grating, the refractive index increases for a set wavelength, and conversely decreases for extraordinary light.

Therefore, the proton exchange layer and dielectric film thickness must be controlled and manufactured according to the wavelength used. Further, the period of the proton exchange region and the non-proton exchange region is proportional to the wavelength used.

This birefringent grating type polarizer is used as an optical isolator.
Use one sheet. Therefore, deterioration of the extinction ratio due to a slight deviation in the wavelength used poses a major problem in managing the characteristics of the optical isolator.

Therefore, the technical problem of the present invention is to use a birefringence grating type polarizer with a larger set wavelength than the wavelength used by the optical isolator and a birefringent grating type polarizer with a smaller set wavelength as a polarizer analyzer. It is an object of the present invention to provide an optical isolator that can be used in an isolator to reduce deviations in extinction ratio due to subtle wavelength changes.

[Means for Solving the Problems] According to the present invention, there is provided a polarizer that converts incident light into first plane-polarized light, and a polarizer that rotates the first plane-polarized light by a first predetermined angle to produce second plane-polarized light. An optical isolator comprising: a Faraday rotator that has a polarization plane tilted at a second predetermined angle with respect to the polarizer, and an analyzer that transmits and emits the second plane-polarized light; The analyzer includes a first birefringent grating polarizer and a second birefringent grating polarizer, and the wavelength at which the maximum extinction ratio of the first and second birefringent grating polarizers is obtained is , an optical isolator is obtained which is characterized in that the wavelengths used in the optical isolator are shifted in opposite directions.

[Example] Next, examples will be specifically described.

FIG. 1 is a side view showing the configuration of an optical isolator according to an embodiment of the present invention.

In this figure, the optical isolator directs the incident light to the first
a polarizer 1 that converts the first plane-polarized light into plane-polarized light; a Faraday rotator 2 that rotates the first plane-polarized light by 45 degrees and converts it into the second plane-polarized light;
An analyzer 3 having a plane of polarization inclined at 45 degrees with respect to the polarizer 1 and transmitting and emitting second plane polarized light, and an analyzer 3 disposed near the Faraday rotator 2 to apply a magnetic field to the Faraday rotator 2. It has a magnet 4.

The polarizer 1 and the analyzer 3 are each made of a birefringent diffraction grating type polarizer.

Let λ be the wavelength used by this optical isolator. When producing a birefringent diffraction grating type polarizer, it is designed so that the wavelength at which the maximum extinction ratio is obtained is λ + Δλ1, λ - Δλ1,
Two types of first and second birefringence grating type polarizers are produced, and one of the first and second birefringence grating type polarizers is used as a polarizer and the other as an analyzer. However, the AR coating applied to the first and second birefringent grating type polarizers is applied at the wavelength used by the optical isolator. Optical isolators with such a configuration do not significantly change the maximum extinction ratio compared to conventional ones.
Shows stable isolation characteristics.

An optical isolator according to an example of the present invention was manufactured as follows.

The birefringence grating type polarizer has a proton exchange layer thickness of approximately 5 μm.
The dielectric film thickness was set to 420 nm, and the set wavelength was changed by changing the period.

The respective periods were 830 μm and 860 μm.

An optical isolator was fabricated using these two birefringence grating type polarizers as a polarizer and an analyzer, and using TbB11G as a Faraday rotator.

When we measured the isolation characteristics of this optical isolator, we found that it was 30 ± 3 in the wavelength range of 1.30 to 1.32 μm.
dB was obtained.

[Effects of the Invention] From the above results, it was found that the optical isolator using the birefringent grating polarizer using the present invention significantly changes its main characteristics in response to minute changes in the wavelength of the laser oscillation source. It can be seen that it has stable characteristics without any problems.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an optical isolator according to an embodiment of the present invention, and FIG. 2 is a diagram showing wavelength characteristics of a birefringence grating type polarizer. In the figure, 1 is a polarizer, 2 is a Faraday rotator, 3 is an analyzer,
4 is a magnet, 5 is incident light, 6 is outgoing light, and 7 and 8 are returning lights.

Claims (1)

[Scope of Claims] 1. A polarizer that converts incident light into first plane-polarized light; and a Faraday rotator that rotates the first plane-polarized light by a first predetermined angle to turn it into second plane-polarized light; In the optical isolator, the optical isolator includes the polarizer and an analyzer having a polarization plane inclined at a second predetermined angle and transmitting and emitting the second plane-polarized light, wherein the polarizer and the analyzer It consists of a refractive grating type polarizer and a second birefringent grating type polarizer, and the wavelength at which the maximum extinction ratio of the first and second birefringent grating type polarizers is obtained is the wavelength used by the optical isolator. An optical isolator characterized by being shifted in opposite directions relative to each other.