JPS6021023A - Optical isolator element - Google Patents

Abstract

PURPOSE:To reduce a device in size and weight without arranging a polarizer at the outside of the device by providing the device with an optical isolator function only by an element consisting of a magneto-optical material. CONSTITUTION:The isolator element 10 consists of a material showing a magneto-optic effect and its one end surface has the 1st inclined surface 12 cut with the complementary angle of a Brewster's angle depending upon the refractive index of the material from the axial direction. The other end surface also has the 2nd inclined surface 13 cut with the complementary angle of the Brewster's angle from the axial direction. The inclined surfaces 12 and 13 coincide with each other with respect to their surface bearings when rotated around the optical axis relatively by 45 deg. in the direction of Faraday's rotation. The element 10 has the optical path LP allowing the polarized surface of the incident light to rotate by 45 deg. around the optical axis by the action of an external magnetic field H. Thus, the optical isolator element 10 reflecting the returned light reflected by the optical fiber 5 by the 1st inclined surface 12 of the optical isolator to prevent the reflected light from returning to a semiconductor laser 4 can be constituted.

Description

[Detailed description of the invention]

The present invention 1; L. Concerning the improvement of the optical isolator, in more detail, the element exhibiting a strong optical effect has the function of a polarizer itself, thereby eliminating the need to place a polarizer externally. The present invention relates to an optical isolator element that has been devised so that it can be used easily. As is well known, an optical isolator is a two-terminal element that is irreversible in that it transmits light only in one direction and does not transmit light in the opposite direction. This device is used when the device receives interference from reflected light from the receiver (g side).Especially when a semiconductor Rayleigh"-4 is used as an optical oscillator, its oscillation When laser light that returns from the outside enters the area, the oscillation state is disturbed, and as a result, the oscillation waveform of the semiconductor laser is distorted, the wavelength and output become unstable, and noise increases. Therefore, in an optical communication system using a semiconductor laser, an optical isolator is installed between the semiconductor laser and the optical fiber. As shown in Figures A and B, first polarizers 1 are sequentially arranged along the optical axis X,
It is a combination of a Faraday rotator 2 and a second polarizer 3. Now, if we consider the case where the light from the semiconductor laser 4 goes toward the optical fiber 5 (this is called the forward direction), as shown in FIG. A, the light L1 from the semiconductor laser 4 passes through the first polarizer 1. This results in linearly polarized light 1-2, which is then transferred to the Faraday rotation element 2 and subjected to the action of an external magnetic field I. :@ Linear light 12 is linearly polarized light [3] whose polarization plane is rotated, for example, 45 degrees clockwise toward the traveling direction, and the linearly polarized light L3 is rotated 45 degrees about the optical axis so that it passes through L3 as it is. The light passes through the second polarizer 3 arranged in the same direction and enters the optical fiber 5. On the other hand, in the case of the opposite direction as shown in FIG. The linearly polarized light L5 passes through the Faraday rotator 2 as it is, but is rotated 45 degrees counterclockwise this time by the Faraday rotator 2, so the obtained linearly polarized light L5 becomes the linearly polarized light L2 that is generated at the time of input q' described above. When compared

[li; i The light surface is rotated by 90 degrees, so the first optical element 1 prevents the light from passing l
It is stopped and does not return to the semiconductor laser 4. Thus, by using the above configuration, it is possible to effectively function as an optical isolator. However, in the 114-component optical isolator as described above, it is necessary to arrange polarizers before and after the Faraday rotation element, which has the disadvantage that the optical isolator becomes large. In particular, optical isolators used in optical communication systems using semiconductor lasers are required to have extremely high performance, and the polarizers incorporated therein are generally made into a prism shape using natural calcite crystals. For this reason, it is extremely expensive, for example, several hundred thousand yen per piece, so an optical isolator that requires two polarizers is even more expensive than a semiconductor laser. This was a huge problem in the wide development of optical communication systems in various fields. The present invention was developed in view of the actual state of the prior art as described above, and its zero purpose is to provide an optical isolator function only with an element made of magneto-optic material, and there is no need to install any polarizer outside the element. It is an object of the present invention to provide an optical isolator element that can reduce the size and weight of the device, and can also significantly reduce the cost. The present invention, which was devised to achieve the above object, skillfully applies the surface function of the II magneto-optic material, and is devised so that the element made of the magneto-optic material itself also functions as a polarizer. , has inclined surfaces cut at complementary angles to the Bricoster angle on both end faces, and is configured so that a single-width light effect is produced on the inclined surfaces.The present invention will be described in detail with reference to the drawings below. Figure 2 is an explanatory diagram schematically showing an embodiment of the present invention, where A shows the case where the light travels in the forward direction (from the semiconductor laser side to the optical fiber side), and B shows the case where the light travels in the forward direction (from the semiconductor laser side to the optical fiber side). Each case is shown in the following direction. As shown in the figure, the optical isolator element 10 according to the present invention is made of a material exhibiting a magneto-optic effect (for example, yttrium-iron-garnet single crystal).
One end face is a first inclined face 12 cut at an angle complementary to the fricoster angle φ (i.e. 90 degrees - φ) which depends on the refractive index of the material 1 with respect to the axial direction. The end face is also a second inclined surface 13 that is aligned in the axial direction and is L7J II7 so that it is a complementary angle to Brewster's angle φ, but ii
The first inclined surface 12 and the second inclined surface 13 in i+ are in a relationship such that their plane orientations match when rotated by one rotation of 45 inches relative to the optical axis, and the action of the external magnetic field 1-1 This element has an optical path length LP that can rotate the plane of polarization of the light input by /'15 degrees with respect to the optical axis. Both end faces must be polished neatly, but unlike conventional ones, there is no special need. In principle, a coating of 7+i J is not necessary. The operation of an optical isolator element with such a configuration is as follows. In the case of FIG.
The inclined surface 12 of the semiconductor laser 4 is arranged so as to face the semiconductor laser 4 . First, as shown in FIG.
The first II! i is incident on the 12 planes at Brewster's angle φ]. At this time, in the incident plane 04 (the plane that includes the propagation direction of the JJ ray and the normal line of 1 and 12 set at the point of incidence) 'C (all the components of the Q ray are the remainder of Brewster's angle φ). Most of the polarized light component will be reflected. In other words, the end face 12 cut at the complementary angle of Brewster's angle φ
serves as a polarizer, and only the components polarized within the plane of incidence are introduced into the optical isolator cable 10. The light diffracted by the first angle 12 and introduced into the optical isolator 3HT-10 is caused by the external magnetic field 1-1 171-. It rotates towards the horn. At that time, as mentioned above, the angle from the first slope 120 to the second slope 13 is set to a length that rotates the polarization plane of the incident light by 45 degrees. , second inclined surface 1
The light that has reached the point of use in 3 is 11) with respect to its traveling direction.
It becomes linearly polarized light with one plane of polarization rotated 45 degrees in the diagonal direction. As described above, the second inclined surface 13 is set at a complementary angle to the Brewster angle, and has a surface orientation obtained by rotating the surface orientation of the first inclined surface 12 by 45° in the Farad rotation direction with respect to the optical axis. Therefore, the light that has reached the output point of the second inclined surface 13 passes through as it is and reaches the optical fiber 5. Since the optical fiber 5 is usually made of quartz glass and is extremely thin, it is impossible to apply a 1M coating on its surface.
It is said that about 10% of the light is reflected at the end facets. For this reason,
The light L12 reflected at the end face of the optical fiber 5 travels backward toward the semiconductor laser 4, as shown in FIG. 13, and is refracted and enters the inside of the optical isolator element 10. Then, inside the optical isolator element 10, under the action of the external magnetic field 1-1, its sunny surface is now opposite to the optical axis. The linearly polarized light whose polarization plane has rotated 45 times and reached the first inclined plane 12 is
When compared with the case in FIG. 2A, the rotation is exactly 90 degrees, and therefore the reflected light L1
It becomes 3. Thus, the optical fiber, fiber 5'c, and second return light are directed to the first +ln slope 1 of the optical isolator element 10.
Since it is reflected by the laser beam 2, it hardly returns to the semiconductor laser 4.In this way, an optical isolator element can be constructed using a magneto-optical structure with a specific structure such as the first one. In Figure 2, the black circles and the small arrows schematically indicate the direction one sector ahead, and the black circles indicate the l'lla waves perpendicular to the incident plane, and the ones perpendicular to the optical axis. The small arrow (, 1, 1) indicates one flat wave in the q4 plane, and the tilted small arrow indicates the polarization tilted from the input QJ plane.By the way, the Faraday cycle 111I in magneto-optical monthly interest
The 7th angle (°, -'C11) is a function of the wavelength of light, and in this light, the end face of the fiisolator element is 1lr.
Since the optical axis is shifted by 1 line, even if the wavelength of the light changes, the plane of polarization can be changed to 4.
It can be rotated 5 degrees. This means that an optical isolator element with a certain shape can be applied to an optical isolator of a different wavelength (σ), which is extremely effective in that it can be made broadband and the number of parts can be reduced by four. 1 The above embodiment is an optical isolator Toyo glue']2
The plane orientation of the inclined plane is L IY of the first inclined plane
This is an example of a structure in which X"l is rotated in the direction of Faraday rotation by 1345 degrees relative to the optical axis, as shown in Figure 3.
It is also possible to have a structure rotated in the 7-love-rotation direction (relatively 225 degrees). The operation as an optical isolator in that case (as it is the same as in the case of Fig. 2, the corresponding parts are marked with the same number as -rq, and the description thereof is omitted.J8゜By the way, recent semiconductor lasers ,
It outputs linearly polarized light with a fairly high luminosity, and this linear direction,
It is said that returning light with a polarization perpendicular to the light does not have much of an effect on semiconductor lasers. Therefore, the polarizer on the side facing the light in the optical isolator does not have a very good extinction ratio. Taking these points into consideration, the configuration in which the laser beam is polarized on the inclined surface of the magneto-optic material provides an extremely good lli flux without deteriorating the performance. Since the present invention is an optical isolator element that has been constructed according to J.
It can be manufactured at a very low cost, and its structure is extremely suitable for downsizing and eaves in the cylinder.Furthermore, since the end face of the magneto-optical side is an inclined surface, no anti-reflection coating is required, making it easy to manufacture. It has many excellent effects such as:

[Brief explanation of drawings]

1A and 1B are explanatory diagrams of conventional technique 4 (j), FIG. 2A is an explanatory diagram showing one embodiment of the optical isolator element according to the present invention, and FIG. It is an explanatory diagram. 1... First polarizer, 2... Faraday rotation element,
3... Second polarizer, 4... Semiconductor laser, 5...
... Optical fiber, 10 ... Optical isolator element, 1
2...first llr+slope, 13...second slope.

Claims (1)

[Claims] 1. Both end surfaces (sloped surfaces cut to the complementary angle of the Noriko-Sku angle, but the inner slope is 45 mm relative to the optical axis)
1 madness b L <l; L 225 degrees Faraday rotation direction is rotated and the plane orientation coincides with Ij, and the action of an external magnetic field J: has an optical path length that rotates the polarization plane by 45 degrees Uo 1rj Ij2 consisting of magneto-optical VJ material
Doriru optical isolator element.