JPS58176616A - Fiber type isolator - Google Patents

Abstract

PURPOSE:To obtain an optical isolator which eliminates the need for an external magnetic field by using a fiber type polarizer and a single polarized-wave optical fiber as a polarizer and a lambda/4 element respectively. CONSTITUTION:The clad of the fiber type polarizer 4-1 including cores 4-3 and 4-5 is etched asymmetrically and a metal 4-4 is vapor-deposited thereupon. The component of an electric field vector perpendicular to the metallic surface has large loss, so the fiber type polarizer operates as a 45 deg. polarizer in a figure. Light of 45 deg. linear polarization entering a single polarized-wave optical fiber 4-2 through the fiber type polarizer is converted into circular polarized light in propagating therein by specific distance. Light reflected by the end surface of the single polarized-wave optical fiber 4-2 and the surface of another optical element is opposite in the rotation direction of the circular polarized light in a direction +z and reconverted into linear polarized light perpendicular to the incident light in passing through the lambda/4 plate again.

Description

Detailed Description of the Invention This invention relates to an optical isolator for preventing operational instability of light sources such as semiconductor lasers due to reflected light from Honjitsu W14 Co., Ltd. In particular, this invention relates to an optical isolator that does not require an external magnetic field and is small and economical. be.

Optical isolation is an important optical component in order to prevent unstable operation of light sources such as semiconductor lasers due to reflected light from other optical elements such as optical fibers and connectors, and to perform highly reliable communications. Conventionally, as an optical isolator, the first
1! ! A bulk type isolator and a second
An isolator using a fiber-shaped magneto-optical material as shown in the figure and an isolator using a magnetic thin film as shown in Fig. 3 are known (with regard to Fig. 1, Iwamura et al.
rYaFeso□, Compact near-infrared isolator using crystals,” IEICE Technical Report OQE 78-59, P, 9,
1978, regarding Figure 2, Kikuchi et al., “Prototype of optical fiber type Faraday rotator element and its characteristics” Tohoku University Dentsu Reading Group Record VO1, 49, no. 2, P. 56, 1
980, with regard to Figure 8, Miyazaki et al., TE-7M mode conversion characteristics in a waveguide optical isolator with a single-substituted YIG thin film on a GGG substrate, IEICE National University, No. 827.
, P, 4-21°1981).

In Figures 1, 2 and 3, l is an optical fiber or laser, 2 is a lens, 8 is a polarizer, 4 is a magneto-optical material, 5 is an analyzer, H is a magnetic field, and 6 is a metal dielectric multilayer. film,
7 is a fiber type Faraday rotation element, 8 is a rutile pribum, 9 is a mode selection element, 10 is a non-reciprocal mode conversion element, and 11 is a reciprocal one-mode conversion element.

These conventional isolators had the following drawbacks.

(+) All use the Faraday effect in magneto-optical materials, so they require a permanent magnet or solenoid electromagnet to apply the magnetic field.

(1) Since the bulk type requires a lens system, the optical circuit is complicated and the system lacks stability.

(Ill) Optical isolators using 7-eyeper magnetic materials have small Perdet constants, so they require large external magnetic fields or long fibers. For example, when FR-5 glass is used as the core, the relationship between (magnetic field) and X (length) is H-t=1.08X10 (Oe・aw) (1
) is given by -For example, when j=10am, H-
An external magnetic field of 1.08 Woe is required.

Kan: Thin film isolators have a large insertion loss due to scattering due to imperfections in the film, and it is difficult to completely remove reflected light due to the generation of non-polarized light components due to scattering.

The object of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology by using a fiber polarizer and a single polarization optical fiber as a polarizer and a λ/4 element, respectively, thereby providing a compact and high performance device that does not require an external magnetic field. Our goal is to provide high-performance optical isolators. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 4 is a diagram showing an embodiment of the present invention, and 4-1 is a fiber-type polarizer (Hosaka et al., "Method for manufacturing a fiber-type polarizer").
4-2 is a single polarization optical fiber (?, Ho5aka etal ” Low -
1oss single polarizat soil
n fibers with, asyxn%-1
ngence', Ii:1ectron, L
ett, .

Vol.1? ', no, 15, P, 1580.
1981), 4-8 and 4-5 are cores.

Further, 4-4 is a metal deposited after asymmetrically etching the cladding, and 4-6 is a stress applying portion for applying a non-axisymmetric stress to the core. In the 774 bar type polarizer, the component whose electric field vector is parallel to the metal surface hardly suffers from absorption loss, but the component whose electric field vector is perpendicular to the metal surface suffers a large loss. For example, when Mut is used as the metal, an extinction ratio of 41 (iB) and an insertion loss of 1 dB (λ = 1.15 μll1) are obtained when the length of the polarizer is 4. The electric field with the smallest loss The angle between the direction of the vector, that is, the direction parallel to the metal surface, and the principal axis of the single polarization fiber (direction of principal stress; X-axis and y-axis in FIG. 4) is 46°.

At this time, the linearly polarized light that comes out of the laser and passes through the fiber polarizer enters the single polarization fiber at an angle of 45° with the X axis (black arrow in Figure 4), so that ■ ■ Ex and] The cy acid component is excited with equal amplitude.

That is, if the two coordinates of this point are 2=-1, then it is expressed as follows. Now, the length of the single polarization optical fiber is t=cW1+
/riπ/(β8−βy) If it is determined to satisfy (a), the following relationship holds true for 2-0.

In other words, as shown in FIG. 5, the emitted light becomes circularly polarized light, and it can be seen that it functions as a single polarization optical fiber 2/4 element. At this time, the light reflected by the end face of the single polarization optical fiber,
Alternatively, when the light is reflected by another optical element and enters the single polarization optical fiber, the rotation direction of the circularly polarized light is reversed when viewed from the +2 direction. This phenomenon is well known as an anti-reflection device for cathode ray tubes such as radar, and is shown schematically in Figure 6 (W, M).

5hurcliff, ' C1rcular pol
arizer impraves viewing”+
Electronlcs Design' + Ap
ril 1 +1956).

In FIG. 6, 12 is white light, 18 is a polarizer, 14 is a quarter plate, 15d reflection 1i1 (for example, a cathode ray tube surface), 1
6 is right-handed circularly polarized light, 17 is an incident wave, 18 is a reflected wave, 19
is left-handed circularly polarized light. Note that a circularly polarizing plate is constituted by the polarizer 18 and the 274 plate, and there is no reflected light at the eye position shown at the lower left end in FIG.

As can be seen from Figure 186, the circularly polarized light whose rotation direction has been reversed passes through the quarter plate again and becomes linearly polarized light making an angle of 906 with the incident linearly polarized light. That is, as shown by the white arrow in FIG. 4, the reflected wave becomes linearly polarized light perpendicular to the incident wave. Here, since the electric field vector of this reflected wave is perpendicular to the metal surface, it suffers a large loss due to the fiber polarizer, and the reflected wave becomes zero at the point of 2=-2°.

FIG. 7 is a diagram of an embodiment in which a metal-loaded optical waveguide is used as a polarizer instead of a fiber polarizer.

In Fig. 7, 7-2 is a single polarization optical fiber, 7-5
is the core, 7-6 is the stress applying part, ? -7 is a high refractive index optical waveguide, 7-8 is a low refractive index medium, and 7-9 is a substrate. -No is metal.

The light propagates while being confined in the high refractive index optical waveguide 7-7,
An electric field having a vector in the direction of 4s degrees with respect to the principal axis of the single polarized optical fiber buff 2 is incident (black arrow). The reflected light reflected by the end face of the single polarization optical fiber 2 or other optical element has a vector perpendicular to the incident electric field at the point 2=-1 (white arrow), as described above. At this time, the reflected wave is subjected to large FI and loss due to the metal, so the reflected wave returning to the light source side becomes /It almost zero.

As is clear from the above explanation, the 7-eyeper type isolator of the present invention does not require an external magnetic field and is a small reflected wave prevention element with low insertion loss and high extinction ratio. It has advantages.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a bulk type isolator, Fig. 2 is a block diagram of an isolator using a fiber type magnetic material, Fig. 8 is a block diagram of an isolator using a magnetic thin film, and Fig. 4 is a summary of the present invention. Example diagrams, Figure 5 is a diagram showing the state of polarization at the output end of a single polarization optical fiber, and Figure 6 is a diagram showing the state of polarization at the output end of a single polarization optical fiber.
FIG. 7, which is a schematic diagram of a conventional technique in which a plate is used to remove reflected waves, is another embodiment of the present invention. 4-1...Fiber type polarizer, 4-2.7-2...
Single polarization optical fiber, 4-8...core, 4-4...
Metal, 4-5.7-5 River core, 4-6.7-6... Stress applying part, 7-F... High refractive index optical waveguide, 7-8...
-Low refractive index medium, 7-9...substrate, 7-10...metal. Patent Applicant: Nippon Telegraph and Telephone Public Corporation Procedural Amendment (Method) August 3, 1980 1, Indication of Case 1982 Patent Application No. 60490 2, Name of Invention Fiber Type Isolator 3, Person Making Amendment Case Relationship between patent applicant (+22) Figure 5 of the Nippon Telegraph and Telephone Public Corporation drawings is corrected as shown in the attached corrected drawing. Figure 5 (a) (b) Procedural Amendment August 3, 1981 1. Indication of the case 1982 Patent Application No. 60490 2. Name of the invention Fiber type isolator 3. Person making the amendment Related Patent Applicant (422) Nippon Telegraph and Telephone Public Corporation (1) The scope of claims on page 1, line 8 to page 2, line 8 of the specification is amended as follows. ``2. Claim L: A single polarized optical fiber in which stress applying parts having a thermal expansion coefficient different from those of the core and cladding are arranged on both sides of the core, and the cladding part on one side of the core is asymmetrically etched. The propagation constants of the two orthogonal fundamental modes of the single-polarized optical fiber are β and β9, m is an integer of y, and the length l of the single-polarized optical fiber is t-+m-1-34)+c
/1βkneeβy1, and the angle between the direction of the electric field vector in which the absorption loss caused by the metal in the fiber polarizer is the smallest and the principal axis of the single polarization optical fiber is 45 degrees. A fiber isolator characterized in that a fiber polarizer and a single polarization optical fiber are connected. i A high refractive index optical waveguide is sandwiched between two media with a lower refractive index, and on one side of the taX low refractive index medium, a metal-loaded optical waveguide with metal vapor-deposited and a single polarization optical fiber are sandwiched. , m is a positive integer, and the length l of the single polarization optical fiber is j-(II+%)π/1β ny βy1
1. A fiber isolator which satisfies the following conditions and is connected such that the angle between the metal surface of the metal-loaded optical waveguide and the principal axis of the single polarized light 7-eyeper is 45 degrees. (2) Add the following phrase between "ima" and "single polarization optical fiber" on page 6, line 15 of the specification. "If m is a positive integer," (8) "It will be the opposite." and "this phenomenon" on page 7, line 7.
In between, add the following sentence: [That is, if the turtle is an even number, the result will be as shown in FIG. 5(a), and if m is an odd number, the result will be as shown in FIG. 5 Φ). ”

Claims (1)

[Claims] L A single-polarized optical fiber in which stress-applying parts having a thermal expansion coefficient different from that of the core and cladding are arranged on both sides of the core, and a cladding part on one side of the core is asymmetrically etched to form a metal. The propagation constants of the two orthogonal fundamental modes of the single polarization optical fiber are β and βa, m is an integer, and the length t of the single polarization optical fiber is t=(m+2)π/1βnyβy1, and the electric field vector direction in which the absorption loss caused by the metal in the fiber polarizer is the smallest and the main axis of the single polarization optical fiber A fiber type isolator characterized in that a 7-eyeper type polarizer and a single polarization optical fiber are connected at λ so that the angle is 45 degrees. t A high refractive index optical waveguide is sandwiched between two low refractive index media, and one side of the low refractive index medium has a metal-loaded optical waveguide with a metal vapor deposited on it and a single polarization optical fiber. and the length t of the single-polarized light 7 eyer satisfies the condition t=(Il+1/2)π/l/x-βy1, and the metal surface of the metal-loaded optical waveguide and the single-polarized optical fiber A fiber type isolator characterized in that it is connected so that the angle formed with the main axis is 45 degrees.