DE3426138A1 - OPTICAL DISPOSAL - Google Patents

Description

Optical one-way line

The invention relates to an optical one-way line that in particular is provided with an element which itself has a magneto-optical effect and fulfills the function of a polarizer, so that it is no longer necessary to provide an external polarizer.

An optical one-way line is known to be an element with two connections, which has the irreversible property that it only transmits light in one direction while it does the Prevents light transmission in the opposite direction. Such an optical one-way line represents the transmitter of an optical communication system to avoid interference from the light reflected from the receiver of the system.

In the case of an optical oscillator, especially when a semiconductor laser is used as the light source, the Vibration adversely affected when the laser beam is reflected back from the outside in the oscillation range, what leads to a distortion of the oscillation waveform of the semiconductor laser and a lack of stability of the wavelength and the output signal level, as well as the Noise level increased. To avoid this, an optical communication system with an optical one-way line between the semiconductor laser and the light guide or the fiber optic cable has been proposed.

A typical conventional one-way optical line makes use of the Faraday effect and is shown in the diagram in FIGS.

provided way with a first polarizer 1, a Faraday rotating element 2 and a second polarizer 3, which are arranged along the optical axis X.

When a laser beam L1 is directed from the semiconductor laser 4 to an optical fiber line 5, as shown in Fig. 1A where the direction of this laser beam is referred to as the forward direction in the following, the laser beam becomes L1 polarized to linearly polarized light L2 when it passes through the first polarizer 1. The linearly polarized Light L2 is then rotated by the Faraday rotating element 2 under the influence of an external magnetic field H to to become linearly polarized light L3, its plane of polarization by, for example, 45 ° in the clockwise direction is rotated viewed in the forward direction. The linearly polarized light L3 then passes through the second polarizer 3, the plane of which is arranged so that it runs at 45 ° to the optical axis, so that the light L3 without any polarization passes into the optical fiber line 5.

Reflected light L4, for example light emitted by the End face of the optical fiber 5 is reflected and comes back in the direction of the semiconductor laser 4, but can directly pass through the second polarizer 3, but when passing through the Faraday rotating element 2 in its The plane of polarization rotated by 45 ° in the counterclockwise direction. The linearly polarized light L5, which from Faraday rotary element 2, thus has a plane of polarization which is rotated by 90 ° with respect to that of the linearly polarized light L2 going in the forward direction. Of the The first polarizer 1 consequently prevents linearly polarized light L5 from reaching the semiconductor laser 4. This arrangement therefore works effectively as a one-way optical line.

With this one-way optical cable, however, it is necessary

To provide polarizers on both sides of the Faraday rotating element so that the size of the entire one-way line increases.

A one-way optical line for an optical communications system, using a semiconductor laser is required to have a very high performance. The one at such a Polarizers related to optical one-way line usually consist of a prism made of natural calcite, which is associated with high costs. The cost of a one-way optical line, the two associated with high cost Calcite crystals used are therefore much higher than those of the semiconductor laser. This prevents the use of optical communication systems in various industrial fields.

The invention is thus intended to provide an optical one-way line be created in which elements made of a magneto-optical material themselves have an optical one-way function, so that it is no longer necessary to provide external polarizers and thus a reduction not only in size and the weight but also the cost of the one-way optical line is achieved.

The invention is intended in particular to create an optical one-way line which thereby has a good one-way function shows that elements are made of a magneto-optical material are combined with an isotropic transparent element having an index of refraction substantially equal to that of the magneto-optical material is.

For this purpose, the invention proposes the plane polarization function of a magneto-optical material, so that an element made of this material can also be used as a polarizer is working. The optical one-way line according to the invention

namely is with an element of a magneto-optical Provided material, both ends of which are cut at an angle complementary to Brewster's angle, so that inclined end polarization surfaces result.

In addition to the arrangement of the magneto-optical element with polarization function, according to the invention is also an isotropic transparent element between the two magneto-optical elements with inclined end polarization surfaces arranged, wherein the transparent element has an index of refraction equal to that of the magneto-optical Elements is. In this case, however, the Brewster's angles at the two end faces of each element are made of magneto-optic Material not the same, although both end faces are cut at angles complementary to the local one Brewster angles are, since each element is transparent at one end with air and at the other end with the isotropic Element is in contact.

The invention creates an optical one-way line which has at least one magneto-optical element at an angle has extending end surfaces cut at angles complementary to Brewster's angle, the tapered end surfaces being arranged relative to one another so that their orientations are the same when they are rotated 45 ° or 225 ° in the direction of Faraday rotation around the optical 'axis, and the magneto-optical Element has such a length of the light path that an external magnetic field causes a 45 ° rotation of the plane of polarization can cause.

In a further embodiment of the invention are two magneto-optical elements arranged in series with an isotropic transparent element in between, the transparent element has a refractive index that is essentially

lichen is the same as that of the magneto-optical elements.

Particularly preferred exemplary embodiments of the invention are described in more detail below with reference to the accompanying drawings. Show it:

Fig.1A and 1B schematically the known structure of a

conventional one-way optical cable,

2A and 2B an embodiment of the optical one-way line according to the invention,

3 shows a modification of that shown in FIGS

2B shown optical one-way line,

Fig.4 another embodiment of the he

optical one-way line according to the invention, and

Fig.5 shows a modification of the Darge in Fig.4

presented embodiment of the optical one-way line according to the invention.

In FIGS. 2A and 2B, an exemplary embodiment of the one-way line according to the invention is shown schematically, FIG. 2A shows an example in which the light goes in the forward direction, i.e. from the semiconductor laser to the optical fiber line, while Figure 2B shows the example where the light goes in the reverse direction. In the case of the one shown in FIGS. 2A and 2B Embodiment of the invention consists of an optical one-way line element 10 made of a material that has a has magneto-optical effect, for example from a yttrium-iron-garnet single crystal. An axial face of this Element is complementary to Brewster's angle tf at an angle which depends on the index of refraction of the material, i.e.

cut 4, to provide a first inclined surface A - at an angle of 90 °. The other axial face is also cut at an angle complementary to Brewster's angle 4 to provide a second inclined surface B. The first inclined surface A and the second inclined surface B are related to one another in such a way that their surface orientations would match if the surfaces were rotated 45 ° relative to one another in the direction of Faraday rotation about the optical axis. The element has such a light path length LP that an external magnetic field H can cause a rotation of 45 ° of the plane of polarization of the incoming light about the optical axis. The two inclined end faces A and B must be well polished, but do not have to be provided with anti-reflective coatings, as is the case with a conventional one-way optical cable.

Such a one-way optical line operates in the following manner. In the embodiment shown in FIGS. 2A and 2B, the optical one-way line element 10 is arranged such that its first inclined surface A faces the semiconductor laser 4. As shown in Fig. 2A, the light L10 emitted from the semiconductor laser 4 is incident on the first inclined surface A of the one-way optical guide element 10 at the Brewster's angle 4. In this case, the component of the laser beam which is polarized in the plane of incidence, this plane containing the direction of propagation of the incident beam and the line perpendicular to inclined surface A, refracted at an angle complementary to Brewster's angle, while most of the component polarized perpendicular to the plane of incidence is reflected back. The end face A, which is cut at an angle complementary to Brewster's angle 4 , therefore acts as a polarizer, so that only the light component which is polarized in the plane of incidence can reach the optical through-guide element 10. The plane of polarization of the

Λ-

first inclined surface A of refracted light entering the one-way optical guide element 10 is determined by the external magnetic field A, for example, clockwise around the optical axis X rotated. Since the distance between the entry point on the first inclined surface A and the second inclined surface B is predetermined so that a rotation of 45 ° of the plane of polarization of the incident light is possible this will be the exit point at the second inclined Light reaching surface B becomes linearly polarized light with a plane of polarization surrounding the direction of propagation rotated 45 ° clockwise. As described above, the second inclined surface B is under one Cut angles complementary to Brewster's angle and their orientation by 45 ° in the direction of the Faraday rotation rotated about the optical axis with respect to the orientation of the first inclined surface A. That the exit point at the The light reaching the second inclined surface B thus goes directly to the optical glass fiber line 5.

The optical fiber line 5 is usually made of quartz glass with an extremely fine structure, so that it is difficult to apply an anti-reflective coating on the glass fiber end faces to be provided. It can therefore be assumed that approximately 4% of the incident light passes through the End face of the optical fiber line are reflected. The light L12 reflected from the end face of the glass fiber optic line 5 travels back to the semiconductor laser 4, as shown in Fig. 2B. This reflected light falls on the second inclined surface B of the optical One-way line element 10 and is broken through this area into the optical one-way line element 10. The light will polarized in the optical one-way line element 10 so that its Plane of polarization in a counterclockwise direction around the optical axis through the outer magnetic Field H is rotated by 45 °. The linearly polarized light

that the first oblique surface reaches A and its plane of polarization is rotated by 45 °, is opposite the incident laser beam of Fig. 2A in its plane of polarization turned by 90 degrees. This light is therefore reflected by the first inclined surface A so that it becomes a reflected one Light beam L13 becomes. As a result, it is reflected from the end face of the optical fiber line 5 and light traveling in the reverse direction is almost completely prevented from returning to the semiconductor laser 4, since it passes through the first inclined surface A of the one-way optical guide element 10 is reflected. It is thus possible to create an optical To obtain one-way line element made of a magneto-optical material that has this special structure.

The small dots and small arrows in Figs. 2A and 2B schematically show the directions of polarization. The small In particular, points represent the polarization in a direction perpendicular to the plane of incidence. The little arrows perpendicular to the optical axis show a polarization in the plane of incidence, while the small arrows are oblique to optical axis show a polarization at an angle to the plane of incidence.

The Faraday rotation angle (° / cm) in a magneto-optic material is a function of the wavelength of light. Since, according to the invention, the end faces of the optical one-way line element run obliquely, it is possible to get a rotation of the plane of polarization by 45 ° even then, when the wavelength of light changes by changing the entry point of the optical axis. I.e. that a one-way optical guide element of a given shape designed for a given wavelength of light can be used as a one-way optical line for light of various wavelengths. According to the invention it is thus possible to use a one-way optical broadband

tion to create with a smaller number of components.

In the embodiment described, the second was inclined surface of the optical element at 45 ° relative to the first inclined surface in the direction of the Faraday rotation around the optical axis oriented. However, this is not strictly necessary, a relative orientation of 225 ° in The direction of the Faraday rotation is also possible, as shown in FIG. One modified in this way optical one-way line operates in essentially the same manner as the embodiment shown in FIGS. 2A and 2B. In FIG. 3, the same reference symbols are therefore used for the same components and parts as in FIGS. 2A and 2B, it is possible to dispense with the detailed description of these components and parts.

The currently available semiconductor lasers can produce linearly polarized light with a very high degree of polarization it is known that returning light polarizes perpendicular to the emitted linearly polarized light does not adversely affect a semiconductor laser very much. The polarizer on the entry side of the optical One-way line therefore does not need to have a very high extinction ratio. It follows that an arrangement at which a laser beam falls on an inclined surface of a magneto-optical material and is polarized by this, can deliver good results without their function being impaired in any way.

4 shows a further embodiment of the invention. In this embodiment, two elements 20a and 20b are provided, each of which is similar to the magneto-optical Element 10 in the embodiment shown in FIGS. 2A and 2B example'ist, with between the two elements 20a and 20b an isotropic transparent element 24 is provided.

Ά-

In the embodiment shown in Figure 4 are the The ends of the first magneto-optical element 20 are provided with inclined surfaces A and B. One of the inclined end surfaces A is usually in contact with air, while the other inclined end face B with the transparent element 24 or is more precisely in contact with a transparent adhesive. In this embodiment, the for Brewster's angle complementary angles at end face A different from that at end face B.

A second magneto-optical element 20b may have a shape which is identical to that of the first element 20a. The inclined end faces of the second magneto-optical element 20b are labeled C and D, respectively. The first magneto-optical Element 20a and the second magneto-optical element 20b are arranged in a row so that their inclined faces B and C run parallel to and face one another with their optical axes substantially in are aligned with each other in a line. The two inclined end faces of the isotropic transparent element 24 run parallel to each other and are cut at an angle complementary to Brewster's angle so that they are tight fit on the inclined surfaces B and C of the corresponding magneto-optical elements. The direction of the magnetic field, acting on the first magneto-optical element 20a is opposite to the direction of the magnetic field, the acts on the second magneto-optical element 20b. This can easily be done by a suitable choice of the arrangement of the magnets be achieved. It can, for example, magnetic fields Ha and Hb are placed on both magneto-optic elements by placing a south pole near the transparent element 24 while north poles are provided on both sides of the south poie. It goes without saying that it is possible is to apply these magnetic fields in that solenoid coils, not shown, around each magneto-optical element 2oa,

3426133

20b are arranged around and these coils are supplied with electric currents in different directions.

The three elements mentioned are connected to one another by a transparent adhesive. The two axial ends of the integrated optical one-way line 20 must be well polished, but not ver with an anti-reflective coating see how it would be with a conventional one-way line Case is.

When a yttrium iron garnet single crystal as a magneto-optical Material is used, its refractive index is about 2.2. In this case, therefore, titanium oxide with a Refractive index of 2.25, strontium titanate with a refractive index of 2.21 or a mixture of Tl-Cl and Tl-Br with a refractive index 2.19 as isotropic transparent Material are used.

The operation of the one-way magneto-optic line 20 will now be described. In the arrangement shown in FIG. 4, the inclined end face A of the first magneto-optical element 20a of the one-way optical line 20 is arranged so that it faces the semiconductor laser 4. As shown in FIG 4 is emitted on the inclined surface A of the first maqneto-o pti see element 20a of the optical one-way line 20 at the Brewster angle 4. In the same way as in the embodiment according to FIGS. 2A and 2B, only the component of the light which is polarized in the plane of incidence, in the optical one-way line 20 go. The plane of polarization of the light refracted by the inclined surface A and introduced into the one-way optical line 20 is then rotated, for example, in a clockwise direction about the optical axis X by the external magnetic field Ha. That the exit point at the

Mt-

Light reaching inclined surface B is linearly polarized light whose plane of polarization is rotated by 45 ° about its direction of propagation. The inclined surface B extends at an angle complementary to the Brewster angle with respect to the optical axis X ₁ and the orientation of the surface B is rotated by 45 ° in relation to that of the inclined surface A in the direction of the Faraday rotation. Furthermore, since the isotropic transparent member 24 which is in contact with the inclined surface B of the first magneto-optical element 20 has a refractive index substantially equal to that of the element 20a, the exit point at the second inclined surface B can be reached Light go directly into the transparent element 24.

The light then travels straight through the transparent element 24 and enters the second magneto-optical element 20b. When the light enters the second magneto-optic element 20b, all components become with undesirable polarization switched off by the polarization effect. While the light passes through the second magneto-optical element 20b, its plane of polarization becomes in one direction rotated counterclockwise about the optical axis X by the external magnetic field Hb, which in one direction acts, which is opposite to the direction in which the magnetic field Ha is located on the first magneto-optical element. Because the distance between the point of incidence on the oblique Surface C and the exit point on the inclined surface D of the second magneto-optical element is so large that one Rotation of the plane of polarization of the incident light by 45 ° occurs, is the light that the exit point at reaches the inclined surface D, linearly polarized light with a plane of polarization that is opposite in one direction is rotated clockwise about the direction of propagation of the light by 45 °. The inclined surface D runs under one Angle complementary to Brewster's angle with respect to the

"'' **" 3426133

y ■

Άζ-

optical axis X, its orientation with respect to the inclined surface C in the direction of the Faraday rotation Is rotated 45 °. The light that the exit point at the reaches inclined surface D, passes through this surface and directly reaches the optical glass fiber line 5.

As it was mentioned earlier, this will be about 4% of the incident Light is reflected back through the end face of the optical fiber optic cable. The reflected light travels in that direction back to the semiconductor laser 4 and strikes the inclined surface D of the second magneto-optical element 20b of the optical One-way line. The light is then refracted by the inclined surface D and enters the one-way optical line 20 a. As the reflected light beam passes through the second magneto-optical element 20b, it becomes through influences the external magnetic field Hb so that its plane of polarization is rotated 45 ° clockwise about the optical axis X during the time during which the light beam reaches the inclined surface C of the second magneto-optical element 20b. The reflected light that the Reached inclined surface C is linearly polarized light with a plane of polarization that is 90 ° compared to that of the in the forward direction passing light is rotated so that this light is reflected by the inclined surface C.

That from the end face of the optical fiber line 5 light reflected and returning to the optical one-way line 20 is thus through the inclined surface C of the second magneto-optical element 20b is reflected again and can therefore not reach the semiconductor laser. Although a small one Part of the returning light is not reflected by the inclined surface C and into the first magneto-optical element 20a can pass through the transparent element 24, this light is polarized again and through the inclined surface A of the first magneto-optical element re-

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inflected. It is therefore possible to have a one-way optical line using two magneto-optical elements a certain structure in a combination with a transparent one Item to receive.

In the embodiment shown in Figure 4 were Orientations of the inclined surfaces B and D about the optical axis in the direction of Faraday rotation relative to the Orientations of the corresponding inclined surfaces A and C reversed. However, this arrangement is not exclusively required the rotation of the orientations can also amount to 225 ° in the direction of the Faraday rotation around the optical axis, as shown in Fig.5. The operation of this modification of the one-way optical line is substantial identical to that of the optical one-way line shown in FIG. In Figure 5, the same reference numerals are used for the same components or parts as in Figure 4, related, a description of these components and parts in detail is superfluous.

As described above, it is with the present invention optical one-way line not necessary to use expensive outer polarizers, so that the one-way line according to the invention can be manufactured at a low cost. Furthermore, the structure is simplified, resulting in a reduction the size and weight allowed. It should be noted that the inclined end faces of the magneto-optical elements also not with an anti-reflective coating must be provided.

Claims (5)

Dr. F. Zumsiein ββή: -ϊ Dr. E. zÄQsrrjrann? A? R 1? R Dipl.-Ing. F. Klingseisen * - D * r. F. Zumstein jun. PATENT LAWYERS APPROVED REPRESENTATIVES AT THE EUROPEAN PATENT OFFICE REPRESENTATIVES BEFORE THE EUROPEAN PATENT OFFICE 3 / Li Ref. 361-SF NIPPON TELEGRAPH AND TELEPHONE PUBLIC CORPORATION Tokyo, Japan FUJI ELECTROCHEMICAL CO., LTD., Tokyo 1. Optical one-way line,
marked by at least one magneto-optical element that is inclined Has end faces at a Brewster angle complementary angles are cut, wherein the inclined end faces are arranged relative to one another are that their orientations coincide when they are in the direction of Faraday rotation by 45 ° or 225 ° are rotated about the optical axis, and wherein the magneto-optical element such a length of the light path has that an external magnetic field can cause a rotation of 45 ° of the plane of polarization. 2. Disposable line according to claim 1, characterized in that two magneto-optical elements in a row with an intermediate union isotropic transparent element are connected, wherein the isotropic transparent element has a refractive index which is substantially the same as that of the magneto-optical elements. 3. One-way line according to claim 2, characterized in that the transparent element by a transparent adhesive with the magneto-optical Elements is connected. 4. Disposable line according to claim 1, characterized in that the magneto-optical element consists of a yttrium-iron-garnet single crystal. 5. One-way line according to claim 2, characterized in that the first magneto-optical element of the two magneto-optical elements is so arranged is that it faces a semiconductor laser, with a laser beam from the semiconductor laser on the inclined The end face of the first magneto-optical element falls.