JPH11142789A - Optical non-reciprocal circuit device and optical switch using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unnecessitate the optical adjustment of an optical element and to provide an inexpensive optical isolator by providing an optical waveguide and a lens element on both sides so as to interpose the optical element in which an azimuth rotator is arranged before/after plural specific Faraday rotators. SOLUTION: Faraday rotators 3, 4 made of magnetic garnet arranged in the direction intersecting the propagating direction of light have a characteristic in which a polarizing surfaces are rotated in the mutually reverse directions and with the same magnitude to the light transmitted through in the same direction by means of applied magnetic field in the same direction. The azimuth rotators 5, 6 made of a rotatory material are arranged either before and after or before or after the respective Faraday rotators 3, 4 in the propagating direction of light. Moreover, the optical waveguide and the lens elements 1, 2 are provided on both sides of the azimuth rotators 5, 6. External magnetic field is impressed to the Faraday rotators 5, 6 by a magnet 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator and an optical non-reciprocal circuit device such as an optical circulator mainly used for organizing optical signals in the optical communication field and an optical switch using the same. The present invention relates to an optical isolator as an optical passive component, an optical circulator used for organizing optical signals, and an optical switch such as a 1: 2 optical switch and a 2: 2 optical switch.

[0002]

2. Description of the Related Art In an optical communication system, use of an optical fiber amplifier for directly amplifying an optical signal as it is without replacing the optical signal with an electric signal has been studied in recent years.
In this case, an Er-doped optical fiber having a specific length is provided in the amplifier, and the amplified signal light and pumping light are transmitted therethrough to obtain amplified light. For this optical fiber amplifier, it is essential to use an optical isolator that transmits only the transmitted light in the forward direction with low loss and blocks the return light in the reverse direction.

[0003] Optical isolators include a polarization-dependent type that transmits only a specific polarization component of the transmitted light in the forward direction, and a polarization-independent type that transmits all components of the transmitted light. Although both optical isolators are used in an optical communication system, the polarization-dependent type is often used in the vicinity of an optical communication laser, and the polarization-independent type is often used in the middle of an optical fiber through which signal light passes.

Among them, a polarization-independent optical isolator having a relatively complicated structure is of a type using a birefringent parallel flat plate (see Japanese Patent Application Laid-Open No. 54-159245) and a tapered birefringent plate. Type (Sho 61
Some structures have been proposed.

FIG. 6 is a diagram proposed recently by Shintaku et al. (C-3-9, 1997 IEICE General Conference).
8, page 283, polarization independent optical isolator with new structure,
FIG. 3 is a diagram illustrating an example of a polarization independent optical isolator. As shown in FIG. 6, the optical isolator according to the related art has one Faraday rotator 59, two half-wave plates 57 and 58, and two lens mechanisms 54 and 55, and optical devices at both ends. Fibers 52 and 53 are arranged. In this prior art optical isolator, the light
The two types of separated light contain the same amount of the same polarization component, respectively, and in the case of forward transmitted light from the optical fiber 52, the optical fiber 53 shown in FIG.
Combined again at the end face. In this case, the two separated lights to be combined have the same polarization plane and the same phase, and are in a mutually reinforcing relationship, so that transmitted light having the same light intensity as the incident light can be obtained.

Conversely, the light incident from the optical fiber 53 is split into two paths, which have the same polarization plane after passing through the optical element of each path and have a 180 ° phase shift relationship with each other. No light is transmitted through the optical fiber without being coupled to the optical fiber. From the above, it can be seen that this optical device functions as an optical isolator.

The light transmitted through the Faraday rotator 59 and the half-wave plates 57 and 58 between the two lenses 54 and 55 is most preferably parallel light.

On the other hand, in an optical communication system, as the use of an optical fiber amplifier becomes active, the demand for an optical circulator, which is an optical component used in the optical fiber amplifier, is increasing.

At present, the conventional method of once converting an electric signal into an electric signal is being replaced by a method using an optical fiber amplifier, and if this method is advanced, it is considered that the realization of wavelength multiplexing communication capable of large-capacity optical communication will be easier. ing. It is considered that a wavelength multiplexing communication system requires a large amount of a structure combining a narrow band optical filter and an optical circulator, and the optical circulator is expected to be used for an optical device that is in great demand in the future optical communication system. It is considered one.

Incidentally, there are two types of optical circulators, a polarization dependent type and a polarization independent type. Among them, in the polarization-independent type, in which the transmitted light is attenuated in the optical circulator, no loss occurs except for the inevitable attenuation due to reflection, scattering, loss, and the like when passing through the optical element.

FIG. 7 is a sectional view of a main part showing a polarization independent optical circulator according to the prior art. In FIG. 7, for example, the incident light from the port I ′ is split by the 3 dB coupler 62 into two lights, one having the same phase as the incident light and the other having a 90 ° phase delay with respect to the incident light. The two divided light beams have the same intensity, and are each halved with respect to the incident light. 3dB
The lights split by the coupler 62 are separated by different optical elements (1/1 /
Through the two-wavelength plate 68 and the Faraday rotator 71, and the Faraday rotator 70 and the half-wavelength plate 69), and
Coupled by the dB optical coupler 63. At this time, light having a phase difference of 180 ° is incident on one of the ports of the 3 dB optical coupler 63, and light having the same phase is incident on the other port. Therefore, light does not transmit to one side and light having the same intensity as the original incident light transmits to the other side.

Light incident from the port I 'in FIG. 7 as forward light (from left to right on the paper) as transmitted light (point F)
First, the 3 dB optical coupler 62 on the left side of FIG.
(Point G). In this case, the transmitted light separated into the lower path in the figure has a phase delayed by 90 ° from the transmitted light that has proceeded straight. Next, the phase of the transmitted light separated into the upper path in FIG. 7 is changed by the half-wave plate 68. In this prior art, a half-wave plate 68 is used.
Has a direction of -22.5 ° when viewed from the forward direction, and the phase changes accordingly. Next, the light passes through the magnetic garnet, which is the Faraday rotator 71,
Since the direction of the magnetic field applied to the magnetic garnet is defined as the light transmission direction in the forward direction, each phase is shifted rightward by 45 ° (4
Turn 5 ° (delayed) (point H).

Thereafter, the transmitted light separated into the lower path in the figure passes through the magnetic garnet, which is the Faraday rotator 70, and the direction of the magnetic field applied to the magnetic garnet is changed to the forward light transmission direction. Therefore, each phase rotates rightward by 45 ° (lagged by 45 °). 1/2 wave plate 69
Changes the phase. In this conventional technique, the direction of the optical axis of the half-wave plate 69 is + 22.5 ° when viewed from the forward direction, and the phase changes accordingly (point H). Finally, the separated lights of the upper and lower paths independently enter the 3 dB optical coupler 63 on the right side of the figure. At the time of transmission, each separated light further separates the light having a phase difference of 190 ° into the path on the other side, and the transmitted light obtained by combining them is emitted from the ports II ′ and IV ′ in FIG. .
Here, the two separated lights that have reached the port IV 'cancel each other out because they are lights having phases opposite to each other, and nothing is actually emitted. On the other hand, the two separated lights that have reached the port II 'are lights having the same phase as each other, so that they are combined and become light emitted from the optical circulator. Except for the unavoidable attenuation inside the optical circulator, the intensity of this outgoing light is the same as the light incident on port I '. However, the incident light to port I 'and the port
The phase with the light emitted from IV 'is not equal. The phases of the two are inverted, for example, if the incident light is right-handed circularly polarized light, the outgoing light is left-handed circularly polarized light.

Similarly, transmitted light from port II 'in FIG. 7 is transmitted from port III', transmitted light from port III 'is transmitted from port IV', and transmitted light from port IV 'is transmitted from port I'. Outgoing, the intensity of each outgoing light is equal to the intensity of each incoming light, except for the unavoidable attenuation inside the optical circulator. The same is true for the phase of each of the incident light and the outgoing light being inverted.

In such a four-terminal optical circulator, if the means for applying a magnetic field to the magnetic garnet has a structure in which the direction of application of the magnetic field is variable, the switch becomes a 2: 2 optical switch.

In order to make the direction of application of the magnetic field variable, for example, a yoke-like structure made of a magnetic material having a small hysteresis, such as a semi-hard magnetic material, is placed on the upper surface of a magnetic garnet, and a coil is wound around a part of the yoke. It is good to flow. Reversing the direction of the current also reverses the direction of the magnetic field applied to the magnetic garnet. If the strength of the magnetic field is large enough to magnetically saturate the magnetic garnet, the device operates as an optical switch.

In a general optical circulator configuration, the port through which transmitted light is emitted can be changed by changing the direction of application of a magnetic field applied to the Faraday rotator.
The configuration of the optical switch can be easily taken.

The portion of the magnetic field applying means of the optical circulator according to the prior art shown in FIG. 7 is a device such as an electromagnet, which can change the direction of the applied magnetic field, from a device having a fixed magnetic field, such as a permanent magnet. If the direction of application of the magnetic field is reversed, the path of the transmitted light from port I 'to port II'
'→ Port IV' can be changed. in this way,
It is possible to realize an optical switch by using the device configuration other than the magnetic field applying means of the optical circulator almost as it is.

[0019]

In the above-mentioned optical isolator according to the prior art, it is difficult to manufacture an optical isolator having excellent optical characteristics because it is difficult to perform precise alignment during assembly. The reason will be described below.

In an optical isolator according to the prior art, since a half-wave plate is used, optical axis adjustment is indispensable.
It is difficult to automate the production of optical isolators and to increase the precision. The half-wave plate has an optical axis called a slow axis.
The polarization plane of the light transmitted through the half-wave plate is 2α−θ, where θ is the angle of the polarization plane before transmission through the half-wave plate, and α is the angle of the slow axis.

In the optical isolator according to the prior art, the light path is divided into two, and each path uses one or more half-wave plates.
If the angle of the low axis is different, the light passing through the two paths will not have an accurate phase difference, increasing insertion loss, deteriorating isolation characteristics, and leaking light to ports where light should not pass. Occurs. In order to avoid this, high-precision optical axis adjustment is required, and an optical isolator that does not require optical axis adjustment has been sought for cost reduction and integration of the optical isolator.

On the other hand, in the optical circulator according to the prior art, for the same reason as the optical isolator according to the prior art, the use of a half-wave plate requires adjustment of the optical axis.
It is difficult to automate the production of optical circulators and increase the precision. Therefore, as with the optical isolators according to the prior art, high-precision optical axis adjustment is required, and optical circulators that do not require optical axis adjustment have been sought for cost reduction and integration of optical circulators. .

Accordingly, one technical object of the present invention is to provide a non-reciprocal optical circuit such as a polarization independent optical isolator and a polarization independent optical circulator that does not use a polarization splitting element and does not require optical axis adjustment of an optical element. It is to provide a device.

Another technical object of the present invention is to provide a polarization-independent optical switch using the optical non-reciprocal circuit device.

[0025]

According to the present invention, the polarization planes are arranged in a direction intersecting the traveling direction of light, and the planes of polarization rotate in opposite directions with respect to light transmitted in the same direction. At least two Faraday rotators having characteristics, and at least one optical rotation arranged before, after, before or after each of the two Faraday rotators with respect to the traveling direction of the light A first type of optical element having an optical rotator made of a material having a property, an optical waveguide provided on both sides of the first type of optical element, a lens element having a lens function, and a Faraday rotator. An optical nonreciprocal circuit device characterized by having an external magnetic field applying means for applying an external magnetic field is obtained.

According to the present invention, in the optical nonreciprocal circuit device, the magnetic field applying means is installed in parallel,
It has a structure in which a pair of the first type optical elements comprising the Faraday rotator and the optical rotator are provided in the vicinity of the magnetic field applying means, each pair being magnetized in opposite directions to each other. Optical non-reciprocal circuit device is obtained.

According to the present invention, in the optical non-reciprocal circuit device, the Faraday rotator rotates the planes of polarization in opposite directions by an applied magnetic field in one direction by the external magnetic field applying means. Thus, an optical non-reciprocal circuit device is obtained.

According to the present invention, in any one of the optical non-reciprocal circuit devices, each set of the first type optical element including the Faraday rotator and the optical rotator is independently driven in a light traveling direction. An optical non-reciprocal circuit device characterized by being inclined with respect to.

Further, according to the present invention, there is provided an optical isolator using any one of the optical non-reciprocal circuit devices, wherein the optical waveguide has an optical coupler, whereby the optical path is reduced to two. Light that is split and transmitted through one path is transmitted through one set of the first type optical elements, and light transmitted through the other path is transmitted through another set of the first type optical elements. As a result, an optical isolator characterized by providing a light path is provided.

According to the present invention, there is provided an optical isolator using any one of the optical non-reciprocal circuit devices, wherein the optical waveguide and the lens element have a lens function instead of the optical waveguide and the lens element. An optical isolator characterized by using a second type of optical element that integrates

Further, according to the present invention, there is provided an optical circulator using any one of the optical non-reciprocal circuit devices, wherein the optical waveguide has a 3 dB optical coupler, whereby the optical path is reduced to two. A light path is provided so that light that is split and transmits through one path transmits through the one optical rotator, and light that transmits through the other path transmits through the other optical rotator. An optical circulator characterized by the following is obtained.

Further, according to the present invention, in the optical circulator, a second type of optical element in which an optical waveguide and a lens element having a lens function are integrated in place of the optical waveguide and the lens element having a lens function. An optical circulator characterized by using an element is obtained.

According to the present invention, the optical circulator is characterized in that the optical circulator is constituted by an optical waveguide having a PLC structure as an optical element in which the optical waveguide and the lens element having a lens function are integrated. An optical circulator is obtained.

According to the present invention, there is provided an optical switch characterized by using any one of the above optical non-reciprocal circuit devices.

According to the present invention, there is provided an optical switch characterized by using any one of the above-described optical circulators.

Further, according to the present invention, in any of the above optical switches, a function of switching the output port by reversing the magnetic field is provided by having a mechanism for reversing the direction of the magnetic field as the magnetic field applying means. An optical switch characterized as above is obtained.

[0037]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1A is a plan view showing a main part of an optical isolator as a non-reciprocal circuit device according to a first embodiment of the present invention, and FIG. Figure,
FIG. 1C is a perspective view. In FIG. 1C, the magnetic field applying means is removed.

Referring to FIG. 1 (a), Faraday rotators 3 and 4 made of magnetic garnets which rotate the polarization plane in the same direction in the opposite directions by the applied magnetic field in the same direction.
Is used. The first type of optical element is a Faraday rotator 3 and a rotator 5, and a Faraday rotator 4 and a rotator 6
It consists of each set. In addition, TEC fibers 1 and 2 are used as a second type of optical element in which the optical waveguide structure and the lens function are integrated.

In the first embodiment, the structure is simplified by using one magnet 7 used as the magnetic field applying means, which is suitable for miniaturization.

In the case of a 1.3 μm wavelength optical isolator,
For a magnetic field in the same direction parallel to the light transmission direction, the (TbBi) ₃ Fe ₅ O ₁₂ crystal and the (GdBi) ₃ (FeGaAl) ₅ O ₁₂ crystal of the pair of Faraday rotators 3 and 4 rotate in the polarization direction. Are opposite to each other, and the thickness required to rotate 45 ° is about 370 μm in both cases. As the optical rotators 5, 6, right and left quartz optical rotators each having a length of 12 mm and having a polarization plane reversely rotated were used as the Faraday rotators 3, 4 in the light transmission direction.

FIG. 1B is a side view of FIG. 1A, in which the Faraday rotators 3 and 4 as optical elements and the optical rotators 5 and 6 are tilted with respect to the light incident direction. As a result, a very high effect can be obtained in preventing reflected return light on the element surface, leading to an improvement in characteristics.

FIG. 1 (c) shows a Faraday rotator 3, 4, and an optical rotator 5, 6 which are optical elements of FIG. 1 (a) embedded in a groove 9 formed on a glass substrate 8 to form an optical waveguide. Similarly, a modified example is shown in which a V-shaped groove 9 formed on a glass substrate 8 is embedded. This structure is very effective when using an optical waveguide having a TEC structure, and can improve the manufacturing accuracy and simplify the manufacturing. By using an optical waveguide having a TEC structure, the number of parts can be reduced, thereby reducing the size.
High accuracy can be realized.

In addition to the TEC fiber used in this embodiment, examples of the second type of optical element include an optical waveguide with a spherical head and an optical waveguide having a PLC structure.
Similar effects can be obtained by using these optical elements instead of the optical waveguide having the TEC structure shown in FIG.

The characteristics of the optical isolator according to the first embodiment of the present invention as described above have an insertion loss of about 1.0 dB and an isolation of about 40 dB.

Next, the operation of the optical isolator according to the first embodiment of the present invention will be described.

Referring to FIG. 1A, the Faraday rotator 3 is set so that the plane of polarization is rotated clockwise by 45 °. Similarly, the Faraday rotator 4 is set to rotate the plane of polarization by 45 ° in a direction opposite to that of the Faraday rotator 3. The optical rotators 5 and 6 are made of an optical rotation crystal, and the optical rotator 5 is set to rotate the polarization plane by 45 ° counterclockwise with respect to the light incident from the left side in the figure.
The optical rotator 6 is set so as to rotate the plane of polarization by 45 ° clockwise with respect to light incident from the left side in the figure.

The light incident on the optical elements 3 and 4 from the optical waveguide 1 is substantially at the center of the diameter of the optical elements 3 and 4.
Divided by Thereafter, the light incident on the magnetic garnet 3 rotates the plane of polarization by 45 ° clockwise, and then rotates 45 ° counterclockwise by the rotator 5. The light incident on the magnetic garnet 4 rotates the polarization plane 45 ° counterclockwise by the magnetic garnet 4 and 45 ° clockwise by the rotator 6.

Therefore, since the light transmitted through the upper stage and the light transmitted through the lower stage in the drawing have the same polarization plane and the same phase,
And is transmitted through.

On the contrary, the light incident from the optical waveguide 2 is shown in FIG.
In the upper path in (a), the rotator 5 rotates clockwise by 45 °,
The Faraday rotator 3 rotates the plane of polarization by 45 ° clockwise. In the lower path in the figure, the rotator 6 rotates 45
(4) The magnetic garnet rotates the plane of polarization 45 ° counterclockwise. Therefore, although the light transmitted through the upper stage and the light transmitted through the lower stage in the figure have the same polarization plane, their phases are opposite to each other and are not coupled to the optical waveguide. From the above, it can be seen that the optical isolator operates.

Here, in the first embodiment of the present invention, since the optical rotation phenomenon does not depend on the polarization state of the incident light, the optical element of this optical isolator has a Faraday rotator and an optical rotation in the traveling direction of light. It does not matter which of the children comes first, and the condition is that the element satisfy the following relationship.

The optical rotator is a reciprocal element and the Faraday rotator is a non-reciprocal element. To operate as an optical isolator, light incident from one side is split into two paths,
After passing through an optical rotator and a Faraday rotator consisting of one or more optical rotation crystals, they have the same polarization plane and the same phase as each other, and light incident from the opposite direction passes through the optical rotation crystal and the Faraday rotator and then has the same polarization plane. Need to have opposite phases to each other. Based on the conditions, the rotation angle of the polarization plane required for the optical rotator and the Faraday rotator is obtained. The rotation angle of the polarization plane is θ.

The required condition is that the phases of the lights transmitted through the two paths in the forward direction are equal.

[0054]

(Equation 1) Similarly, the phase of light transmitted through two paths in opposite directions is ± π +
The condition is that there is a difference of 2nπ. Here, n represents an integer.

[0055]

(Equation 2) The optical rotator is a reciprocal element, and the Faraday rotator is a non-reciprocal element. From this relationship, the following equation (3) is derived from equation (1) and equation (2).

[0056]

(Equation 3) Since it is not very practical to prepare a crystal having a thickness such that the absolute value of the angle of rotation of the polarization plane exceeds π, n = 0 is considered for simplicity. In that case, the following equation 4 is obtained.

[0057]

(Equation 4) From the above equation 4, it is clear that two Faraday rotators are required. If the absolute values of θ _F1 and θ _F2 are equal, the following equation (5) is appropriate.

[0058]

(Equation 5) Substituting Equation 3 into Equation 1 or Equation 2 results in
It turns out that the following equation (6) is appropriate.

[0059]

(Equation 6)

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
FIG. 5 is a plan sectional view showing an optical isolator as an optical non-reciprocal circuit device according to the embodiment. As shown in FIG. 2, magnetic garnets having the same composition are used as the Faraday rotators 16 and 17, and two magnets 20 and 20 'are used as magnets used as magnetic field applying means. The directions of the magnetic fields applied to the Faraday rotators 16 and 17 are opposite to each other. The first type of optical element includes a combination of a Faraday rotator 16 and a rotator 18 and a combination of a Faraday rotator 17 and a rotator 19, respectively. In the second embodiment, the optical multiplexer / demultiplexer 10,
11, the light is split into two at the same intensity, and then incident on the Faraday rotator 16 and the optical rotator 18 as the first type optical element and the Faraday rotator 17 and the optical rotator 19 as the first type optical element. It is appropriate to do so.

In the optical isolator for 1.3 μm, the Faraday rotators 16 and 17 have a thickness of 370 μm (TbB).
i) Using two ₃ Fe ₅ O ₁₂ crystal plates and one 12 mm right and left crystal rotator as the rotators 18 and 19, each having an insertion loss of 0.8 dB and an isolation characteristic of 40 d.
The result of B was obtained. In the first embodiment, the center of the light passes through the boundary of the optical element, causing insertion loss. However, this can be solved almost completely.

(Third Embodiment) FIGS. 3A and 3B show an optical circulator as an optical nonreciprocal circuit device according to a third embodiment of the present invention.
FIG. 3A is a diagram showing the configuration of the optical element and the optical waveguide when viewed from above, and FIG. 3B is a diagram showing the light in a configuration in which the optical element portion is placed obliquely with respect to the optical path of the transmitted light. FIG. 4 is a view of the circulator viewed from the lateral direction, in which the configuration of FIG. 3A is realized on a glass substrate.

The optical circulator shown in FIGS. 3A and 3B is called a four-terminal optical circulator. As the substrate material, glass or Si is suitable in addition to glass. Here, the optical waveguides 23, 24, 25, and 26 having the TEC structure are used as the second type optical element.
If an optical waveguide having a TEC structure is used here, the number of components of the optical circulator can be reduced, and high precision and low loss can be realized.

The optical circulator according to the third embodiment is an optical circulator for a wavelength of 1.3 μm. The optical rotators 29 and 30 used are 12 mm thick right and left quartz optical rotators, and a Faraday rotator. The magnetic garnet used as 27, 28 has a thickness of 370 μm (TbB
i) ₃ Fe ₅ O ₁₂ crystal. In order to combine them, it is appropriate to bond each set of the optical rotator and the Faraday rotator, which are the first type of optical element, with an adhesive or to join them with solder or the like.

The optical circulator manufactured as described above achieves an insertion loss of 0.8 dB and an isolation characteristic of 40 dB at each input / output port.

Next, the operation of the four-terminal optical circulator according to the third embodiment of the present invention will be described with reference to FIG. The polarization plane and phase of the transmitted light when the transmitted light from each of the boats I to IV is incident will be described with reference to FIG. The light (point A) incident as transmitted light from the port I in FIG. 3 in the forward direction (from left to right on the paper) is first split into two by the 3 dB optical coupler 21 (point B). In this case, the transmitted light separated into the lower path in the figure has a phase delayed by 90 ° from the transmitted light that has proceeded straight. next,
The transmitted light separated into the upper path in the figure passes through the Faraday rotator 27 made of magnetic garnet, and the direction of the magnetic field applied to the Faraday rotator 27 is defined as the forward light transmission direction. The polarization plane of 45 ° (45
゜ They turn (delay) (point C). Next, the polarization plane is changed by the optical rotator 29.

In the third embodiment, the rotator 29
The angle of rotation of the light is −45 ° when the light travels in the forward direction, and the polarization plane changes accordingly (point D).

Next, the transmitted light split into the lower path in the figure passes through the Faraday rotator 28 made of magnetic garnet, and the direction of the magnetic field applied to the lower Faraday rotator 28 is changed to the forward light. Since the transmission direction is determined, each polarization plane rotates rightward by −45 ° (lagged by −45 °). Next, the phase is changed by the optical rotator 30.

In the third embodiment, the angle of rotation of the lower optical rotator 30 is 45 ° in the forward direction of light, and in the third embodiment, the angle of rotation of the optical rotator is Is 45 °, and the phase changes accordingly (point E).

Finally, the separated lights of the upper and lower paths independently enter the 3 dB optical coupler 22 on the right side of the figure. At the time of transmission, each separated light has a phase difference of -90 on the path of the other party.
The light of ゜ is further separated, and the transmitted light obtained by combining them is emitted from port II and port IV in the figure. Here, the two separated lights reaching the port IV cancel each other out because they are lights having phases opposite to each other, and nothing is actually emitted.

On the other hand, the two separated lights reaching the port II are lights which have the same phase with each other and are combined to become light emitted from the optical circulator. Except for the unavoidable attenuation inside the optical circulator, the intensity of this outgoing light is the same as the light incident on port I. However, the phases of the light incident on the port I and the light emitted from the port IV are not equal. The phases of the two are inverted, for example, if the incident light is right-handed circularly polarized light, the outgoing light is left-handed circularly polarized light.

Similarly, the transmitted light entering from port II in the figure exits from port III, the transmitted light entering from port III exits from port IV, and the transmitted light entering from port IV exits from port I, respectively. The intensity of the emitted light is equal to the intensity of each incident light, except for the unavoidable attenuation inside the optical circulator. The same is true for the case where the phases of the incident light and the outgoing light are reversed.

Since the optical rotatory phenomenon does not depend on the polarization state of the incident light, the optical element portion of this optical circulator has a problem as to which of the Faraday rotator and the optical rotatory crystal plate comes first in the light traveling direction. Instead, the condition is that the elements satisfy the following relationship.

Here, it is assumed that the rotation angle of the polarization plane is θ. For the sake of simplicity, both the Faraday rotator and the optical rotator in the figure have the suffix 1 at the top and the suffix 2 at the bottom, and the suffix F for the Faraday rotator. The required condition is that the phases of the light transmitted through the two paths in the forward direction are equal. That is, it is shown in the following equation (7).

[0075]

(Equation 7) Similarly, the phase of light transmitted through two paths in opposite directions is ± π +
The condition is that there is a difference of 2nπ. Here, n represents an integer.

[0076]

(Equation 8) The optical rotation crystal plate is a reciprocal element, and the Faraday rotator is a non-reciprocal element. From this relationship, the following Expression 9 is established from Expression 7 and Expression 8.

[0077]

(Equation 9) It is not very practical to prepare a crystal having a thickness such that the absolute value of the angle of rotation of the polarization plane exceeds π, so n = 0 is considered for simplicity. In that case, the following equation 10 is established.

[0078]

(Equation 10) This proves that two Faraday rotators are required. When the absolute values of θ _F1 and θ _F2 are made equal, it is appropriate to make the following equation (11).

[0079]

[Equation 11] In addition, when Equation 9 is substituted into Equation 7 or Equation 8, it becomes clear that Equation 12 is appropriate as a result.

[0080]

(Equation 12) In such a four-terminal optical circulator, if the magnetic field applying means to the Faraday rotator made of a magnetic garnet has a structure in which the direction of the applied magnetic field is variable, it becomes a 2: 2 optical switch.

To make the direction of application of the magnetic field variable, for example, a yoke-like structure made of a magnetic material having a small hysteresis such as a semi-hard magnetic material is placed on the upper surface of a Faraday rotator made of a magnetic garnet and a part thereof. What is necessary is just to wind a coil and to apply an electric current. Reversing the direction of the current also reverses the direction of the magnetic field applied to the Faraday rotator. If the strength of the magnetic field is large enough to magnetically saturate the magnetic garnet of the Faraday rotator, the device operates as an optical switch.

The specific operation is as follows. The magnetic field applying means of the optical circulator shown in FIG. 3 is changed to the above-mentioned magnetic circuit or a coil for generating a magnetic field having a strength at which the rotation angle of the polarization plane of the Faraday rotator is 45 °. Then, when the direction of the magnetic field is reversed, the operation is not port I to port II but from port I to port IV.

(Fourth Embodiment) FIGS. 4A and 4B are a plan view and a side view showing an optical circulator as an optical non-reciprocal circuit device according to a fourth embodiment of the present invention. 4 (a) and 4 (b), a Faraday rotator 35, 36 for rotating the polarization plane of light in the opposite direction under a magnetic field in the same direction is used. An optical circulator using an optical waveguide 34 having a PLC structure having a function of a 3 dB coupler, in addition to one having a single magnet. As the first type of optical element, a combination with the Faraday rotator 35 and the optical rotator 37 and a combination with the Faraday rotator 36 and the optical rotator 38 are used.

In the case of an optical circulator for a wavelength of 1.3 μm, the (TbBi) ₃ Fe ₅ O _{12 of the} Faraday rotators 35 and 36 is applied to a magnetic field in the same direction parallel to the light transmission direction.
The crystal and the (GdBi) ₃ (FeGaAl) ₅ O ₁₂ crystal
The rotation directions of the polarized light are opposite to each other, and the thickness required for 45 ° rotation is approximately 370 μm in the case of the embodiment.
m. Each of the optical rotators 37 and 38 has a length 1 in which the polarization plane is reversely rotated with respect to the Faraday rotators 35 and 36 in the light transmission direction.
One 2 mm right and left crystal rotator was used.

The optical waveguide having the PLC structure is an element which shows the same optical behavior as the 1: 2 3 dB optical coupler 33 as can be seen from FIG. PLC with 3dB optical coupler 33
Replacing with an optical waveguide having a structure has the advantage that the outer shape of the optical device can be reduced in size.

The operation of the circulator according to the fourth embodiment is the same as that of the third embodiment in which the port IV is terminated, and the adjustment is simplified because the configuration is simplified. The characteristics can be improved and the cost can be reduced.

As for the characteristics of the optical circulator according to the fourth embodiment of the present invention, the insertion loss is 0.9 dB at each port and the isolation characteristic is 40 dB at 1.3 μm. Although the bulk configuration is shown in this example, it is also effective for application to an optical waveguide.

(Fifth Embodiment) FIG. 5 shows a fifth embodiment of the present invention.
It is a perspective view which shows the optical switch by embodiment. The optical switch shown in FIG. 5 is called a 2: 2 optical switch, and shows a case where a yoke-shaped semi-hard magnetic material 40 is used as a magnetic field applying means. Here, if termination processing is performed on the port IV of the 2: 2 optical circulator, it is easy to make 1: 2
It becomes an optical circulator. The configuration of the configuration of the optical element and the optical waveguide of the 2: 2 optical switch in FIG. 5 is the same as the configuration in FIG. 3 showing the third embodiment, so that the drawing is omitted.

The yoke-shaped semi-hard magnetic material 40 shown in FIG. 5, which is a means for applying a magnetic field to the optical element, is a magnetic material having a small hysteresis. By flowing a current, a magnetic field along the shape of the yoke can be formed. If the intensity of this magnetic field is large enough for the magnetic saturation of the magnetic garnet of the Faraday rotator, the phase of the transmitted light inside it can be rotated by 45 °.

When the direction of the current to the coil 41 is changed, the direction of the magnetic saturation is also reversed, and the direction of the 45 ° rotation of the phase of the transmitted light is also reversed. As a result, an operation of switching the output end of the light transmitted through the optical switch becomes possible.

Since the configuration of the optical element is the same as that of the optical circulator described in the third embodiment, the characteristics of the 1.3 μm optical switch have an insertion loss of 0.9 dB and an isolation of 40 dB. In this optical switch, the magnetic field applying means can be composed of only a coil. However, since current supply is always required, the temperature rise of the optical switch becomes a problem.

Here, FIG. 3 shows an example in which an optical waveguide having a TEC structure is used as a means for guiding transmitted light inside the optical device. This optical waveguide is not limited to an optical waveguide having a TEC structure. An optical waveguide with a spherical lens, a combination of an aspherical lens and an optical fiber, or another optical waveguide structure may be used as long as it can guide the transmitted light with low loss. However, a waveguide structure cannot be provided in a region of an optical element that transmits an optical rotator made of an optical rotation crystal plate and a Faraday rotator made of a magnetic garnet, and the coupling loss between these optical elements and the waveguide structure is suppressed. Therefore, the transmitted light must be parallel light or light equivalent thereto, and therefore, at this coupling point, it is necessary to provide some kind of lens structure on the optical waveguide side.

In each of the optical circulators and optical switches according to the embodiments shown in FIGS. 3 to 5, the optical path lengths of the two upper and lower optical waveguide structures in each figure are two 3 dB.
In the region between the optical couplers, it is required to be equal or to be a multiple of the wavelength of the transmitted light. Since the phase of the transmitted light changes with its progress, if this relationship is not satisfied, the optical device of this embodiment will not function as an optical circulator or an optical switch.

When the transmitted light enters and exits the optical element surface perpendicularly, the reflected light on the optical element surface returns to the original waveguide and returns to the original waveguide, and the function as an optical device is obtained. May be inhibited. In order to prevent this, it is effective to install each optical element at an angle.
An optical device using a Faraday rotator or an optical rotation crystal plate often has a tilt angle of 4 ° to 8 °. In the case of the above-mentioned optical device, the optical element may be installed to be tilted either vertically or horizontally as shown in FIG.

[0095]

As described above, according to the present invention, an optical isolator that does not require optical axis adjustment of an optical element can be manufactured, and the cost of the optical isolator can be reduced.

Further, according to the present invention, in an optical circulator and an optical switch used as constituent devices in an optical communication system, cost reduction, miniaturization and integration can be achieved.

[Brief description of the drawings]

FIG. 1A is a plan view showing an optical isolator as an optical non-reciprocal circuit device according to a first embodiment of the present invention. (B) is a side view of the optical isolator of (a).
(C) is a perspective view of the optical isolator of (a).

FIG. 2 is a plan view showing an optical isolator as an optical non-reciprocal circuit device according to a second embodiment of the present invention.

FIG. 3A is a plan view showing an optical circulator as an optical nonreciprocal circuit device according to a third embodiment of the present invention. (B) is a side view of the optical circulator of (a).

FIG. 4A is a plan view showing an optical circulator as an optical nonreciprocal circuit device according to a fourth embodiment of the present invention. (B) is a side view of the optical circulator of (a).

FIG. 5 is a perspective view showing an optical switch according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing an optical isolator according to the related art.

FIG. 7 is a diagram showing an optical circulator according to the related art.

[Explanation of symbols]

 1, 2 Optical waveguide (having TEC structure) 3, 4 Faraday rotator 5, 6 Rotator 7 Magnet 8 Substrate 9 V-shaped groove 10, 11 Optical multiplexer / demultiplexer 12, 13, 14, 15 Optical waveguide (TEC structure) ) 16,17 Faraday rotator 18,19 Rotator 20,20 'Magnet 21,22 3dB optical coupler 23,24,25,26 Optical waveguide (TEC structure) 27,28 Faraday rotator 29,30 Rotator 31,32 Magnet 33 3 dB optical coupler 34 Optical waveguide (PLC structure) 35, 36 Faraday rotator 39 Magnetic field applying means 40 Semi-hard magnetic material 41 Coil 42 Substrate 52, 53 Optical fiber 54, 55 Lens 57, 58 1/2 wavelength plate 59 Faraday Rotor 60 Magnet 62, 63 3 dB optical coupler 64, 65 Lens 68, 69 1/2 Elongated plate 70, 71 Faraday rotator 72 Magnet

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takuya Kawamura 6-7-1, Koriyama, Taishiro-ku, Sendai, Miyagi Prefecture Tokin Co., Ltd. (72) Inventor Kenichi Shiraki 6-7-1, Koriyama, Tashiro-ku, Sendai, Miyagi Prefecture No. Tokinnai Co., Ltd. (72) Inventor Toshihiro Shinke 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Co., Ltd. Inside Nippon Telegraph and Telephone Corporation (72) Akiyuki Tate Inventor Nippon Telegraph and Telephone Corporation

Claims (12)

[Claims] 1. At least two Faraday rotators disposed in a direction intersecting with a traveling direction of light and having a characteristic that polarization planes rotate in opposite directions to light transmitted in the same direction. An optical rotator made of at least one optically rotatory substance disposed in front of or behind or before or behind each of the Faraday rotators with respect to the traveling direction of the light. First of each set
Type optical element, an optical waveguide and a lens element having a lens function provided on both sides so as to sandwich each set of the first type optical element, and an external magnetic field for applying an external magnetic field to the Faraday rotator An optical non-reciprocal circuit device comprising an application unit. 2. The optical non-reciprocal circuit device according to claim 1, wherein said magnetic field applying means comprises a pair arranged in parallel and magnetized in opposite directions to each other, and said Faraday rotation is provided near said magnetic field applying means. An optical non-reciprocal circuit device having a structure in which one set of a first type optical element composed of a polarizer and the optical rotator is provided. 3. The optical non-reciprocal circuit device according to claim 1, wherein the Faraday rotator rotates polarization planes in opposite directions by a magnetic field applied in one direction by the external magnetic field applying means. An optical non-reciprocal circuit device comprising: 4. The optical non-reciprocal circuit device according to claim 1, wherein each set of the first type optical element comprising the Faraday rotator and the optical rotator is independently light-controlled. An optical non-reciprocal circuit device, wherein the optical non-reciprocal circuit device is inclined with respect to the traveling direction of the light. 5. An optical isolator using the optical non-reciprocal circuit device according to claim 1, wherein the optical waveguide has an optical splitter, whereby an optical path is provided. Is divided into two, and light transmitted through one path transmits through one set of first-type optical elements, and light transmitted through the other path transmits through another set of first-type optical elements. An optical isolator characterized in that a light path is provided so as to perform the above operation. 6. An optical isolator using the optical non-reciprocal circuit device according to claim 1, wherein the optical waveguide and the lens element are replaced with the optical waveguide and the lens function. An optical isolator characterized by using a second type of optical element in which a lens element is integrated. 7. An optical circulator using the optical non-reciprocal circuit device according to claim 1.
The optical waveguide has a 3 dB optical coupler, whereby a light path is divided into two, and light transmitted through one path is transmitted through the one optical rotator, and light transmitted through the other path is divided by the optical path. An optical circulator, wherein a light path is provided so as to transmit the other optical rotator. 8. An optical circulator according to claim 7, wherein said optical waveguide and a lens element having a lens function are integrated with each other, instead of said optical waveguide and said lens element having a lens function. An optical circulator characterized by using: 9. The optical circulator according to claim 8, wherein the optical waveguide is formed of an optical waveguide having a PLC structure as a second type of optical element in which the optical waveguide and the lens element having a lens function are integrated. Optical circulator. 10. An optical switch using the optical non-reciprocal circuit device according to claim 1. Description: 11. An optical switch using the optical circulator according to any one of claims 7 to 9. 12. The optical switch according to claim 10, wherein the magnetic field applying means has a function of reversing the direction of the magnetic field, thereby having a function of switching an output port by reversing the magnetic field. Light switch.