JP3206949B2 - Polarization-independent optical isolator array - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-independent optical isolator array which is not affected by the polarization plane of an optical fiber. It concerns the device.

[0002]

2. Description of the Related Art As a polarization-independent optical isolator used for bidirectional optical communication, optical measurement, and the like, there is an optical circulator shown in FIG. 2, two polarization beam splitters 15, 16 and two total reflection mirrors. Consists of 17, 18, Faraday rotator 19, and optical rotator 20.
It has four ports of 1, 12, 13, and 14, and the incident light from the 11 port is emitted to the 12 port, and the incident light from the 12 port is emitted to the 13 port, and therefore does not return to the 11 port. Similarly, when light enters from port 14, light is emitted to port 11, and when light enters from port 13, light is emitted to port 14, and this relationship is not related to the polarization plane of light.

If this is used as a bidirectional polarization-independent optical isolator, it will be used as 11 → 12 and 13 → 14 ports. The output port rotates by 90 °, which complicates the connection of the optical fiber in a large connection system. Moreover, a high-performance dielectric multilayer film such as a polarizing beam splitter or a total reflection mirror is required, and the entire system becomes expensive. In terms of performance, since it includes an integral Faraday rotator and optical rotator, if there is a temperature change or a wavelength change, the elliptic component returns as it is, which causes deterioration of the extinction characteristic.

In addition, there are drawbacks in that only a pair of lines can be formed, the positions of the light beam ports cannot be separated to form a parallel structure, and the size of the device cannot be reduced because a polarizing beam splitter or the like is used.

[0005]

SUMMARY OF THE INVENTION The present invention has been developed from the prior application of Japanese Patent Application No. 2-220555 filed by the present applicant. The most significant feature is to synchronize the optical isolator function with the fiber array. (1) A light collecting function is provided at the tip of the fiber array. Of course, when the spherical lens array and the gradient index rod lens array are produced using the conventional technology, the effect of the present invention can be obtained, but the beam becomes thick and the size of the optical system becomes large. (2) Form a composite polarizing plate in accordance with the dimensional cycle of the lens array. However, the boundary is 100-200 μm from the top
This is necessary, and the width of the polarizing plate and the thickness of the birefringent crystal plate are restricted.

(3) The direction of the crystal optical axis of the birefringent crystal plate and the arraying direction of the composite polarizing plate, that is, the polarization plane of the polarizing plate with respect to ordinary light and extraordinary light are formed so as to match. (4) When performing bidirectional optical communication with two fibers, when forming a fiber array from an even number of n fibers, the composite polarizing plate is an array of (n + 1) pieces of polarizer pieces whose polarization directions are orthogonal to each other. Place in a shape. (5) When the polarizer pieces are arranged in an array, they can be formed on the same plane without any gaps, resulting in a small device. (6) Due to the structure, the Faraday rotator is elongated in a strip shape, and there is a restriction that the magnetic field intensity distribution of the permanent magnet for saturation magnetization must be sufficient.

When these are embodied, for example, when four polarization-independent optical isolators are arrayed, the structure becomes as shown in FIG. 1, and the first birefringent crystal in which the crystal optical axis is inclined with respect to the light axis. A plate BP1, a first Faraday rotator FR1 for rotating the plane of polarization by 45 °, a polarizing plate PR combining a plurality of orthogonal polarization absorbing polarizers, a second Faraday rotator FR2 for rotating the plane of polarization by 45 °, and Ri same thickness der the first birefringent crystal plate and the light traveling direction, the said first double refraction crystal plate
A second birefringent crystal plate BP2 arranged in accordance with the direction of the same crystal optical axis, the polarization directions of the plurality of polarizing plates are orthogonal to each other, and the plurality of It is sufficient to mount only one optical isolator on a fiber array formed from the above fibers.

In this case, two-way optical communication can be applied to two pairs of lines. In the optical isolator array of the present invention, adjacent optical ports have light transmission and light blocking mechanisms opposite to each other. For example, in FIG. 1, the Faraday rotators FR1,
When the FR2 is configured to be saturated in the same direction, the port P1
, The port P2 and the port P5 to the port P6 show a forward direction (transmission direction) function, and for the adjacent fiber, the port P4 to the port P3 and the port P8 to the port P7 operate as the forward direction.

To explain the operation of the present invention, P1-P
2. The behavior of the light beam between P3 and P4 is taken up. For example, P
When the polarization-combined light as shown in FIG. 3 is propagated to P1 and P3, the direction of the crystal optical axis of BP1 is adjusted so that the extraordinary light is split upward by the BP1 to become ordinary light and extraordinary light. In some cases, the rotation directions of FR1 and FR2 are rotated clockwise by 45 °, and the polarizing plate (PR1, PR2,
The transmission linear polarization directions of PR3, PR4, and PR5) are calculated based on the polarization direction of the extraordinary light in PR1 (0 °).
3 and PR5 are arranged at (+ 45 °), and PR2 and PR4 are arranged at (−45 °). BP2 is aligned with the same crystal optical axis as BP1.

When the polarization states of the light beams P1 → P2, P3 → P4 are traced, the fiber lens arrays FA, BP1, FR1,
The polarization states of the light beams that have passed through PR, FR2, and BP2 are shown in FIG. 3 to FIG. 3, respectively. In P1 → P2, P4 → P3, the light beams are combined regardless of the polarization, and propagate to the opposite ports. For P1, P3 → P4, both ordinary light and extraordinary light are cut off by the polarizing plate, almost quenched, and the minute (40 dB or more) elliptical component generated during propagation also deviates from the ray propagation axis, and finally, 50 dB or more quenching Give the state. Also, it can be seen that P2 and P4 of the polarizer array contribute bidirectionally, and that an array of optical isolators can be realized as a whole. Similarly, when the number of ports is increased, an optical isolator mechanism of the opposite direction is obtained.

[0011]

EXAMPLE An optical isolator array of the components shown in Table 1 was prepared.

[Table 1]

In the case of this configuration, the distance between the spherical lenses ゛ is about 8.5 mm, but the effective optical path length is about 4.3 mm. Therefore, the design of the spherical lens is approximately 2.2 mm from the lens surface to the beam waste.
It is sufficient to take the optical coupling of However, since the lens is fixed on a ceramic having a V-groove structure, if coordinates are taken as shown in FIG. 1, there is a drawback that fine adjustment cannot be performed with respect to the inclination with respect to the Y-axis direction or the tilt in the tilt direction. It is important to manufacture such that the dimensional accuracy of the lens and the light emitted from the lens do not warp from the Z-axis direction.

Each of the optical components must be provided with an antireflection film. It is also an important factor that the optical component is tilted by about 2 to 12 ° with respect to the light beam in order to suppress the return loss. In the present embodiment, the two Faraday rotators are magnetized in the same direction. However, it is also possible to design the magnetization directions to be opposite to each other in consideration of temperature change and wavelength broadening.

Table 2 shows the optical characteristics.

[Table 2]

The design wavelength was 1.55 μm. The extinction characteristic can achieve a numerical value of 50 dB or more, and it has been confirmed that the extinction characteristic is sufficiently used for practical use. In addition, the forward insertion loss between the four ports by the fiber array was -1.9 ± 0.6 dB, and a slight fluctuation width was recognized. However, this is not an inherent technical difficulty, but by improving the precision of the fiber array at the end of the ball lens, improving the dimensional accuracy of the V-groove jig for fixing the fiber array, and improving the optical coupling efficiency between the lenses. Can be solved.

A polarizer array is manufactured by cutting a polarizing glass plate provided with an antireflection film in advance with a precision cutter, polishing the cut surface, finishing the squareness and smoothness with the flat plate surface, and forming an optical adhesive. Fixed with. However, the polarizer pieces adjacent to each other were formed so that the polarization was shifted by 90 °.
If the two polarizing glasses are adjusted so as to be in a completely quenched state, temporarily fixed, and then cut and polished as they are, the polarizing glass can be manufactured while maintaining the polarization state of 90 °. In addition to bonding, the polarizer array may be bonded to a metal piece after glass fusing and metallizing. Further, it is also possible to adopt a structure in which two adjacent surfaces are optically adhered to each other without being joined, and the other two sides are fixed by bonding or the like.

[0017]

The present invention provides a polarization-independent optical isolator array for parallel optical communication using a multi-core optical fiber array as well as for bidirectional optical communication using a two-core optical fiber line. It is most suitable as an in-line optical isolator for optical fiber, and the optical isolator that was conventionally mounted for each optical fiber can be replaced by one optical isolator for each fiber array. , Which is promoted to consumer equipment and contributes to stabilization of information communication.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical fiber array of the present invention.

FIG. 2 is a schematic diagram of a conventional optical circulator.

FIG. 3 shows P1-P in the optical fiber array of the present invention.
FIG. 2 is a polarization state diagram of light rays P3 and P4.

[Explanation of symbols]

 BP Birefringent crystal plate FR Faraday rotator PR Orthogonal polarization absorbing polarizer FA Fiber lens array P port

Claims (3)

(57) [Claims] 1. A combination of a first birefringent crystal plate having a crystal optical axis inclined with respect to a ray axis, a first Faraday rotator rotating a polarization plane by 45 °, and a plurality of orthogonal polarization absorption polarizers. polarizing plate, a second Faraday rotator for rotating the polarization plane 45 °, and the first birefringent crystal plate and the same thickness der in light traveling direction is, the same crystal optical axis and the first birefringent crystal plate Direction
Consisting of a second birefringent crystal plate arranged according to the
A polarization independent optical isolator array, wherein the polarization directions of the plurality of polarizing plates are orthogonal to each other, and the polarizing plates are arranged without a gap. 2. A combination of a first birefringent crystal plate in which the crystal optical axis is inclined with respect to the ray axis, a first Faraday rotator rotating the plane of polarization by 45 °, and a plurality of orthogonally polarized light absorbing polarizers. polarizing plate, a second Faraday rotator for rotating the polarization plane 45 °, and the first birefringent crystal plate and the same thickness der in light traveling direction is, the same crystal optical axis and the first birefringent crystal plate Direction
Consisting of a second birefringent crystal plate arranged according to the
When the number of the polarizing plates is n, (n + 1)
A polarization-independent optical isolator array, wherein the polarization directions of adjacent polarizers are orthogonal to each other and are arranged on the same plane without any gap. 3. A polarization-independent optical isolator array according to claim 1 or 2, wherein a pair of fiber arrays having a light-collecting function at the tip end are optically coupled to each other with respect to a forward light beam. Optical device fixed at a position that blocks light in the opposite direction.