JPS6155623A - Optical isolator and light source provided with isolator - Google Patents

Abstract

PURPOSE:To obtain a highly reliable, cheap and small-sized optical isolator by arranging two fiber type polarizers to make principal axes to 45 deg., and providing a device that makes light beam parallel light between the two polarizers and squeeze it into fibers and a devide that gives Faraday rotation to the parallel light. CONSTITUTION:Fiber type polarizers 6-a, 6-b made by winding 10m of stress-giving type birefringent optical fibers 6-a, 6-b are arranged to make their principal axes to 45 deg.. Light emitted from the fiber type polarizer 6-a is made to parallel light by a lens 2-a, and the plane of polarization is rotated by 45 deg. by a Raraday element provided with a magnet and squeezed into the fiber polarizer 6-b by a lens 2-b. On the other hand, reflected light from the fiber polarizer 6-b passes through the lens 2-b and the plane of polarization is rotated by 45 deg. by the element 4, and intercepted by the fiber polarizer 6-a. Thus, a highly reliable, cheap and small-sized optical isolator is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a small and low-cost optical isolator and a one-dimensional isolator light source.

[Prior art] The conventional optical isolake constructed between optical fibers is
As shown in the figure. The light emitted from the optical fiber 1-a is transmitted through the lens 2-
a makes it a parallel beam. The planes of polarization of the polarizer 3-a and the analyzer 3-b form an angle of 45 degrees with each other.
[Contains a Faraday element consisting of G. The straight-wave light that has passed through the polarizer 3-a is rotated, for example, by 45 degrees clockwise by the 7 Rady elements 4, passes through the analyzer 3-b, and is coupled to the optical fiber 1-b via the lens 2-b. Ru. On the other hand, when the reflected light from the optical fiber 1-b passes through the analyzer 3-b and enters the Faraday element 4, it rotates counterclockwise by 4
It rotates by 5 degrees, and the reflected light is cut off by the polarizer 3-a. 5 in the figure is a magnet.

The above is the configuration of a commonly used optical isolator.
Calcite is used for the bulk polarizers of the polarizer 3-a and analyzer 3-b.

The same applies to the isolator forming the isolator-equipped light source.

[Problems to be Solved by the Invention] Conventionally, the calcite used in the bulk polarizer of the polarizer 3-8 #3 and the analyzer 3-b is a natural stone, so it cannot be crystal grown and is extremely expensive. Therefore, the optical isolator itself becomes expensive. Furthermore, since the number of component parts is large, reliability is also a problem.

[Means for Solving the Problems] The optical isolator of the first invention is an elliptical core optical fiber or a stressed tower birefringent optical fiber.
+ mode has a cutoff wavelength λc(
Under the condition that λc<λ) is 1.4<λ/λc<1.7, one mode out of the two modes existing in the optical fiber undergoes bending loss. Two fiber-shaped polarizers constructed by bending are arranged so that their main axes are at an angle of 45 degrees,
It is characterized by having means for once collimating the light beam between the two fiber-type polarizers and converging it into a fiber again, and means for imparting Faraday rotation to the parallel light.

The isolator-equipped light source of the second invention provides a T
E01 mode has a cutoff wavelength λc for the usage wavelength λ
Under the condition that (λc × λ) is 1.4<λ/λc<1.7, one mode out of the two modes existing in the optical fiber undergoes bending loss. A fiber-shaped polarizer constructed by bending a fiber and a semiconductor laser are arranged such that the main axis of the polarizer and the light-emitting wave plane of the semiconductor laser form an angle of 45 degrees to each other, and the fiber-shaped polarizer and the semiconductor laser It is characterized by having means for once collimating the light beam and converging it into a fiber between the two, and means for imparting Faraday rotation to the parallel light.

[Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 to 7.

FIG. 1 is a schematic diagram of an embodiment of the optical isolator of the present invention. In the figure, the same parts as those in FIG. 8 are given the same reference numerals, and the reference numeral "rJ2" is omitted. 6-a in the figure
, 6-b is a stressed tower-shaped birefringent optical fiber. Figure 2 shows the stress-applied birefringence optical fiber.
is the core, and 8 is the stress-applying part, which is a glass whose coefficient of thermal expansion is at least one order of magnitude larger than that of the cladding 9. In the case of silica-based glass, impurity dopants such as boron, germanium, and alumina are contained in the silica glass in an amount of several tens of percent. It is. Due to this large coefficient of thermal expansion, tensile stress remains in the core 7, and birefringence is induced in the core 7 due to the photoelastic effect of the glass. If the propagation constants of light polarized in the X-axis direction and the y-axis direction are βX and βy, respectively, then the mode low refractive index β is β = (βX - βV)/k ・・・・・・・・・・・・・・・
... is given by (1). Just (), k=2a/
λ and λ are the wavelengths of the light used, and a is the core radius. Here, if β>1×10−, linear polarization is sufficiently maintained.

Now, the cutoff wavelength λ for a single mode optical fiber is
c is 1.4<λ/λc<1.7・・・・・・・・・・・・
...If we use (2), the normalized propagation constant ny (=βy/k) of light polarized in the y-axis direction will be smaller than the normalized propagation constant nx (=βx/k) in the X-axis direction, Clad 9
The refractive index is close to that of As a result, light polarized in the y-axis direction experiences greater bending loss than light polarized in the °X-axis direction.

Figure 3 shows the relative refractive index difference Δ=0.28% between the core and cladding.
, core tM2a = 5.4t, tm, fiber outer diameter 2
b = 150 μm, ratio r/a-3 of inner radius r of stress applying part to core radius a, boron 15IIIO% of stress applying part, T
Birefringent light beam with cutoff wavelength λc-0, 86 μm of E-1 mode and mode birefringence β=4.1XIO'? -(The optical fiber is wound around a drum with a radius of 15 CT11.The loss spectral characteristics of the two modes 11 and 7 are shown.Compared to the X-axis polarized light, the loss increase wavelength on the long wavelength 5 side of the y-axis side wave light is on the shorter and longer side.

In this way, the movement of the polarizer is obtained by the difference in bending loss between the X and y polarized waves.

In Figure 1, these fiber polarizers are 10 m long with a radius of 5 C.
It is wound around the drum of TI+ and arranged so that the X-axis is 45 degrees to each other. This birefringent optical fiber, that is, a fiber polarizer has an extinction ratio of 1 wavelength as shown in Figure 4.
．． 41 dB was obtained at 3 μm+. On the other hand, the xll loss of transmitted light was less than 0.1 dB. The function of the optical isolator is exactly the same as the configuration using the bulk type polarizer shown in FIG. However, since fiber polarizers are short, they are two orders of magnitude cheaper in price than bulk polarizers. Further, alignment is also simpler than in the case of FIG. 8. Optical isolation is 32d at wavelength 1.3μm
There was a B. Insertion loss including fiber connection loss is 1.8dB
Met. Note that when the )1 Iba Katazono Kyuko 6-b was fusion-spliced with a normal single mode optical fiber, the connection loss between the fibers was 0.5 dB. This means that the outer diameters of the fiber polarizer and single mode optical fiber are each 150 μm1.
This is due to the difference in the outer diameter of 125 μm, and if the outer diameter is the same, it is possible to lower it by 0.1 dBg. Since no calcite polarizer is used, fiber 6-a and lens 2-
a, Faraday element 4, lens 2-a1 fiber 6-b
There is no deterioration of the element even when heat is applied to it, and it can be fixed with solder.

FIG. 5 shows a case where the Floday element 10 made of YIG is made into a ball lens in order to further reduce the number of parts, and the lenses 2-a and 2-b are omitted from the configuration shown in FIG. 4. The focal length of the spherical lens is Q, 7 mm at a wavelength of 1.3 μm, and both surfaces of the spherical lens are treated with anti-reflection coatings.

The characteristics of the optical isolator are optical isolation 33d3,
The insertion loss was 2.26 [3]. Optical fiber (3-a
, 6-b and] 1 La Day Nanko have two connections, so
Reliability with earthquake resistance and temperature resistance has been improved.

FIG. 6 is a schematic diagram of an embodiment of a light source with an isolator according to the present invention. In the figure, 1'1 is a semiconductor laser, 12.13
is a lens, 14 is a fiber-shaped width photon, and 15 is a single mode optical fiber. The semiconductor laser 11 is made of InGa
Emitted by As P-LD (thin wavelength is 1.3 μm. Semiconductor ray If11 normally emits in TE0 mode, and its extinction ratio is about 25 dB. Therefore, instability of the emission amplitude due to reflected light is prevented. 30 dB is sufficient for optical isolation.If the X-axis of the fiber polarizer 14 is set at 45 degrees with respect to the TE and mode polarization plane, the influence of reflected light on the semiconductor laser 11 can be reduced.

Fiber type polarizer 14 and single mode light)? The time 15 is connected via a fusion splice or a connector.

In FIG. 7, the lenses 12 and 13 in FIG. 6 are omitted, and the YIG Fraday element 10 is provided with a lens function.The number of parts is reduced, making assembly easier, and improving reliability. do.

J3, if the optical isolation is still insufficient and 30d3 or more is required, it can be obtained by connecting the optical isolators shown in FIGS. 1 and 5 in multiple stages. In this case as well, since the optical isolator is equipped with an optical fiber, it is easy to connect it by fusion splicing or connectors while aligning the main axes of the fiber polarizers.

:L. In this embodiment, the wavelength of 1.3 μn1 was described, but the same optical isolator can be realized for the old wavelength by changing the material parameters of the Floday element.

"Effects of the Invention" As explained above, the optical isolator and the light source with isolator of the present invention use fiber-shaped fan photons instead of bulk shoulder photons, so (1) the reliability as @photons is improved. , (2) Since it is now possible to heat the optical shift isolator when assembling it, it is now possible to solder it in place. (3) By significantly reducing the price of polarizers, it has become possible to make the optical isolator more affordable. (4) ) In order to reduce the number of parts, it is easier to assemble the optical isolator, making it possible to make it more compact. The advantage is that you only need to connect to

[Brief Description of the Drawings] Fig. 1 is a schematic configuration diagram showing one embodiment of the optical isolator of the present invention, Fig. 2 is a cross-sectional view of a stress-applied birefringent optical fiber of 1 m, and Fig. 3 is a birefringent optical fiber. Loss spectral characteristic diagram of ＼,
Fig. 4 is a diagram of extinction ratio and insertion loss characteristics of a fiber polarizer (birefringent optical fiber), and Fig. 5 is a schematic configuration diagram showing another embodiment of the optical isolator of the present invention. Fig. 6 7 are schematic configuration diagrams showing different embodiments of the light source with an isolator of the present invention, and FIG. 8 is a schematic configuration diagram of a conventional optical isolator.

Claims (4)

[Claims] (1) In an elliptical core optical fiber or a stressed birefringent optical fiber, the TE_0_1 mode uses wavelength λ
Set the cutoff wavelength λc (λc<λ) to 1.4<λ
/λc<1.7, one mode out of the two modes existing in the optical fiber undergoes bending loss. Fiber-type polarizers are arranged so that their main axes are at an angle of 45 degrees to each other, and a means is provided between the two fiber-type polarizers to once convert the light beam into parallel light and narrow it into the fiber again, and a means to give Faraday rotation to the parallel light. An optical isolator comprising: (2) Claim 1, characterized in that the means for once converting the light beam into parallel light and converging it into a fiber again, and the means for imparting Faraday rotation to the parallel light, are constituted by a Faraday element having a lens action. The optical isolator described. (3) In an elliptical core optical fiber or a stressed birefringent optical fiber, the TE_0_1 mode has a cutoff wavelength λc (λc<λ) of 1.4<λ
/λc<1.7, a fiber shape constructed by applying bending to the fiber by utilizing the fact that one mode out of the two modes existing in the optical fiber undergoes bending loss. A polarizer and a semiconductor laser are arranged so that the main axis of the polarizer and the emission polarization plane of the semiconductor laser make an angle of 45 degrees to each other, and the light beam is once made parallel between the fiber polarizer and the semiconductor laser, and then parallelized again. 1. A light source with an isolator, comprising means for concentrating into a fiber and means for imparting Faraday rotation to parallel light. (4) A means for once converting the light beam into parallel light and converging it into the fiber again, and a means for imparting Faraday rotation to the parallel light,
4. The light source with an isolator according to claim 3, characterized in that it is constituted by a Farade element having a lens function.