JPH01244423A - Farady rotator with tapered one face - Google Patents

Abstract

PURPOSE:To obtain a required rotational angle without requiring and end face working of high dimensional accuracy by forming one surface of a Farady rotator oblique to the other surface. CONSTITUTION:An optical isolator 10 is constituted in such a way that a hollow cylindrical permanent magnet 15 is held by flanges 13 and 14 respectively provided with projecting parts 11 and 12 and a double-refractive prism 16 is fixed onto the projecting part 11, and then, a Farady rotator 17 and another double- refractive prism 18 are provided on the projecting part 12. The surface 2 of the Farady rotator 17 crossing the optical axis is inclined against the other surface 3 and the optical axes of the prisms 16 and 18 are inclined at 45 deg. from each other. When the setting position of the optical axis 1 is changed, the Farady rotational angle theta can be changed. Therefore, even if the optical axis of the optical isolator is parallel-displaced after the optical axis is set by rotating one of the discoid flanges 13 and 14 against the other, the angular relations between the optical axis of the optical isolator 10 and optical axes of the prisms 16 and 18 can be maintained and the rotational angle is appropriately set.

Description

[Detailed description of the invention] For the purpose of eliminating the need for end face processing with high dimensional accuracy regarding Faraday rotators used for rotating the plane of polarization of light in optical devices such as optical isolators, the present invention aims to eliminate the need for end face processing with high dimensional accuracy. It is constructed by forming one intersecting surface obliquely to the other surface.

INDUSTRIAL APPLICATION FIELD The present invention relates to a Faraday rotator used for rotating the polarization plane of light in an optical device such as an optical isolator.

In the field of optical communication or optical transmission, in addition to transmitting devices, receiving devices, and optical transmission lines, various optical devices such as optical isolators and optical switches are used. The Faraday rotator, which is used in these optical devices to rotate the polarization plane of propagating light by a required angle toward the propagation direction, has been conventionally used because its shape directly affects the rotation angle, etc. It was required to be processed with high dimensional accuracy.

BACKGROUND OF THE INVENTION FIG. 4 is a diagram showing an example of a conventional optical isolator constructed using a Faraday rotator. In this example, 45
Tapered birefringent prisms 1, 42, 43 are arranged on both sides of the Farade rotor 41, and the birefringent prisms 42.
Polarization separation is performed by utilizing the fact that when light passes through 43, the refraction angles of ordinary light and extraordinary light are different. That is, when the output light from the optical fiber 44, which has been made into a parallel beam by the lens 45, is incident on the birefringent prism 42 in the forward direction (from left to right in FIG. It separates into extraordinary light, is refracted in a different direction, and enters a 45° Farade single rotator 41. 45° Hualade single rotor 4
1, the ordinary light and extraordinary light whose polarization planes have been rotated by 45° are incident on the birefringent prism 43. Birefringent prism 4
Since the optical axis of No. 3 is rotated by 45° around the optical axis direction with respect to the optical axis of the birefringent prism 42,
Ordinary light and extraordinary light are ordinary light inside the birefringent prism 43,
Each corresponds to an abnormal light. Therefore, the ordinary light and the extraordinary light that have passed through the birefringent prism 43 are emitted in parallel to each other. These parallel rays of ordinary light and extraordinary light are transmitted through the lens 46.
The light can then be focused onto the optical fiber 47.

On the other hand, the light rays in the opposite direction (from right to left in Figure 4) enter the birefringent prism 43, are separated into ordinary light and extraordinary light, are refracted in different directions, and enter the 45° Farade single rotator 41. death,
The plane of polarization is rotated by 45 degrees and the light is emitted. Polarization plane is 4
The ordinary light of the birefringent prism 43 rotated by 5 degrees becomes polarized light rotated by 90 degrees with respect to the optical axis of the birefringent prism 42, and therefore is refracted as extraordinary light in the birefringent prism 42. The extraordinary light of the birefringent prism 43 whose plane of polarization has been rotated by 45 degrees is transmitted to the birefringent prism 42 in the same way.
undergoes refraction as ordinary light. That is, since the ordinary light and extraordinary light are converted into extraordinary light and ordinary light, respectively, by the 45° Faraday rotator 41, the direction after passing through the birefringent prism 42 is different from that of the incident light. Therefore, in a lens arrangement with low loss in the forward direction, light in the reverse direction does not enter the optical fiber 44.

In order to provide the Faraday rotator with optical rotation as described above, an appropriate magnetic field is applied in the optical axis direction of the Faraday rotator. Therefore, the length of the Faraday rotator in the optical axis direction is β,
When the applied magnetic field in the optical axis direction is H, the angle of optical rotation θ is expressed as θ - F · β · H (F is a material-specific constant called the Verdet constant), so β and H should be set appropriately. The required angle of optical rotation can be obtained. Here, since it is technically difficult to stabilize the applied magnetic field H at a constant value with high precision, usually H is the saturation magnetic field and the length β of the Faraday rotator in the optical axis direction is set to the design value. The end faces were machined to match accurately.

FIG. 5 is a diagram for explaining a general means for applying a magnetic field to a Faraday rotator. End surface 51a.

Parallel polished Faraday rotators 51 b are arranged at predetermined intervals inside a cylindrical permanent magnet 52 . According to this configuration, since the saturation magnetic field is applied near the optical axis 53 of the Faraday rotator 51, the required angle of optical rotation can be obtained by adjusting only the distance (β) between the end surfaces 51a and 51b. .

Problems to be Solved by the Invention In the optical isolator shown in FIG. 4, the optical rotation angle of the Faraday rotator and the inclination angle between the optical axes of the birefringent prism are set to 45°.

) does not match almost completely, the performance of removing reflected feedback light will deteriorate. In this case, the tolerance of the optical rotation angle of the Faraday rotator is usually 1% or less. Therefore,
For example, the thickness of a Faraday rotator made of YIG is 2 m.
m, it becomes necessary to set the thickness on the order of microns, and there is a problem in that the processing cost of the material increases. On the other hand, in recent years, Faraday rotators are sometimes formed using GGG epitaxial crystals that have a large Verdet constant and can be made thinner. Dimensional accuracy of the layers is required.

The present invention was created in view of the above circumstances, and an object of the present invention is to eliminate the need for end face processing with high dimensional accuracy in a Faraday rotator.

Means to solve problems FIG. 1 is a diagram showing the principle of the present invention.

This single-sided tapered Faraday rotator is constructed such that one surface 2 intersecting the optical axis 1 is formed obliquely with respect to the other surface 3.

In Fig. 1, the angle formed by one surface 2 and the other surface 3 is φ, the distance between the shortest side surface of this Faraday rotator and the optical axis 1 is a, and the distance of this shortest side surface is φ. Assuming that the length is b, the distance between the points where the optical axis 1 intersects one surface 2 and the other surface 3, that is, the effective length β that this Faraday rotator contributes to Faraday rotation is (i= a−t anφ+b Therefore, Faraday rotation angle (optical rotation angle) θ
is θ −F (a−tan φ−+−b) ・
H is given. Here, F is a Verdet constant, and H is a magnetic field in one direction of the optical axis. In this way, by changing a, that is, by changing the set position of the optical axis 1, the Faraday rotation angle θ can be changed, and therefore, b
Even if it is not set with high dimensional accuracy, the Faraday rotation angle θ can be made to completely match the required angle. As a result, in an optical isolator, for example, constructed using this Faraday rotator, it is possible to prevent an increase in reflected feedback light, and it is possible to provide a high-performance optical device.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a sectional view of the main parts of an optical isolator constructed using the Faraday rotator of the present invention. This optical isolator 10 has a hollow cylindrical permanent magnet 15 sandwiched between flanges 13.14 each having a protrusion 11.12, and a birefringent prism 16 is arranged and fixed on the protrusion 11.
A Faraday rotator 17 and a birefringent prism 18 are arranged and fixed on the protrusion 12. The target value of the optical rotation angle of the Faraday rotator 17 is set to 45°, and therefore the optical axes of the birefringent prisms 16 and 18 are 45° with respect to each other.
It is set at a 5° tilt. To set this axis, one of the disc-shaped flanges 13 and 14 may be rotated relative to the other.

If the optical axes of the birefringent prisms 16 and 18 are set in this way, even if the optical axes of this optical isolator are moved in parallel, the angular relationship between the optical axes will be maintained. The angle of optical rotation of the Faraday rotator 17 can be adjusted to the optimum value by changing the optical rotation angle of the Faraday rotator 17 under the same action of the polar prism.

FIG. 3 shows an LD constructed using an optical isolator 10.
(Semiconductor laser) module is a cross-sectional view. This LD
The module includes an LD assembly 21 and an optical isolator 1.
0 and the fiber assembly 22 are integrally assembled in this order. The LD assembly 21 is constructed by attaching an LD component 24 having an LD chip 23 to a lens holder 26 into which a ball lens 25 is press-fitted. 27 and 28 are electrode terminals for driving. The fiber assembly 22 is configured by inserting and defining a ferrule 30 into which an optical fiber 29 is inserted and fixed into a lens holder 32 into which a focusing rod lens 31 is inserted and fixed. L
When creating the D assembly 21, the LD chip 23
Focus and alignment are adjusted so that the light emitted from the lens 25 becomes a predetermined beam shape and its propagation direction is a predetermined direction. In addition, when creating the fiber assembly 22, the focus is adjusted so that the light beam propagating from the LD assembly 21 is focused by the focusing Rondo lens 31 and enters the input end face of the optical fiber 29 with high efficiency. There is. Therefore, the LD assembly 21 and the fiber assembly 22
When adjusting the alignment of the module by sliding it with respect to the optical isolator 10, the optical axis of the light beam passing through the Faraday rotator 17 can be freely moved in parallel. In this way, in the present invention, the Faraday rotator 27
Even if the dimensional accuracy of the optical axis is low, the Faraday rotation angle can be set appropriately by moving the optical axis in parallel.
It becomes possible to provide high-quality optical devices.

The above explanation is about the case where the Faraday rotator of the present invention is applied to an optical isolator configured using a birefringent prism. Applicable to various optical devices, such as isolators, optical switches that use electromagnets to apply a magnetic field in any direction to a Faraday rotator, and optical modulators that change the magnetic field applied to a Faraday rotator depending on the signal. It is.

Effects of the Invention As detailed above, according to the present invention, it is possible to obtain a required rotation angle without requiring end face processing with high dimensional accuracy. As a result, it becomes possible to provide high-quality optical devices at low prices.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a sectional view of the main part of an optical isolake constructed by applying the single-sided tapered Faraday rotator of the present invention, and Fig. 3 is a diagram of the optical isolake of Fig. 2. L configured using
The cross-sectional view of the D module, FIGS. 4 and 5, are explanatory diagrams of the prior art. DESCRIPTION OF SYMBOLS 1... Optical axis, 2... One surface of Faraday rotator, 3... Other surface of Faraday rotator, 10... Optical isolake, 17... Faraday rotator. N

Claims (1)

[Claims] A single-sided tapered Faraday rotator, characterized in that one surface (2) that intersects with the optical axis (1) is formed obliquely with respect to the other surface (3).