JPH0741507U - Faraday mirror - Google Patents

Abstract

(57) [Summary] [Purpose] In the conventional Faraday mirror, the fiber and lens are divided, and since the optical fiber is pre-polished and the outgoing light beam is emitted obliquely to the fiber axis direction, X , Y plane adjustment and Z direction adjustment, rotational alignment around the fiber core axis, and angle adjustment of the fiber so that the radiation angle is perpendicular to the mirror. It is necessary to adjust the total of 6 axes, and it is not easy to adjust the joint, and there is a problem that the number of parts increases, which is solved. [Construction] In a Faraday mirror in which a 45 ° Faraday rotator 5 and a mirror 6 are arranged, and a permanent magnet 9 for magnetizing the Faraday rotator is externally inserted, the end of the optical fiber 1 is equivalent to the core of the optical fiber. A Faraday mirror in which a fiber 2 having the same outer diameter having a uniform refractive index and a converging fiber terminal having a spherical portion 3 formed at its tip are opposed to introduce and emit light.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical component for compensating for polarization fluctuation in an optical fiber system.

[0002]

[Prior art]

 Polarization fluctuations that occur in single-mode optical fibers cause problems in optical communications and optical fiber measurement systems. For example, in an optical system that uses a polarization mode, thermal changes and mechanical fluctuations change the birefringence state of the optical fiber, which changes the polarization state of the propagating light beam and causes optical system noise. For this reason, polarization-maintaining fibers are used, but they have the drawback of being expensive and difficult to use, and there is the problem that the polarization modes are distorted and become elliptically polarized if the polarization directions are aligned and fixed, or if they become longer. there were. In general, the instability of the light intensity due to the change in the polarization state of the light beam during fiber propagation is caused by the reversal of the light beam whose polarization state is shifted by 90 ° in the opposite direction. A Faraday mirror composed of a 45 ° rotating Faraday rotator and a reflecting mirror has been proposed.

[0003]

[Problems to be solved by the device]

 As the simplest structure, if the Faraday rotator and mirror are connected to the optical fiber via a lens, the optical level will be stabilized by compensating for polarization distortion due to birefringence. Fig. 2 is a schematic diagram of such a Faraday mirror structure. The light beam emitted from the optical fiber is rotated by 45 ° in the polarization state when passing through the Faraday rotator by the lens and then reflected by the reflecting mirror. Then, the same path is returned to the optical fiber again, so that the polarization state turns by 90 °.

Therefore, the influence of birefringence fluctuation occurring during the propagation of the optical fiber is compensated because the polarization states of the reciprocating rays are diagonalized to each other, and the fluctuation of the polarization state does not seem to change. Therefore, it is extremely effective when applied to a measurement relationship that uses the coherence of light (matching of phase and frequency). In this case, the condition is that the birefringence change of the optical fiber is so gentle that it can be regarded as an infinite length with respect to the round-trip time of the light beam, and the regressed light beam propagates in the same birefringent state in the optical fiber. It is satisfied under the conditions.

That is, in the configuration of FIG. 2, the coupling loss of light rays returning from the mirror is small. Limit near-end reflections such as fiber end faces as much as possible. Easy to assemble. Is mentioned. In the currently used configuration, the lens and the fiber are separated, and since the optical fiber is pre-polished and the outgoing light beam is emitted obliquely to the fiber axis direction, coupling adjustment is not easy. In other words, in order to adjust the planar state of X and Y and the Z direction, and to adjust the rotational position with the fiber core axis as the center of rotation, and to adjust the angle of the fiber so that the ray emission angle is perpendicular to the mirror, the biaxial Including the tilt angle adjustment, the total 6 axes had to be adjusted. As described above, in the conventional Faraday mirror, since the fiber 1 and the lens 11 are divided, it is difficult to adjust, and there is a problem that the number of parts increases.

[0006]

[Means for Solving the Problems]

 The present invention is a Faraday mirror in which a 45 ° Faraday rotator and a mirror are arranged, and a permanent magnet for magnetizing the Faraday rotator is externally inserted. A fiber with the same outer diameter and a focusing fiber terminal with a spherical portion formed at the tip of the fiber are made to face each other to introduce and emit the incoming and outgoing light.The spherical lens portion and the fiber are integrated, and the tip is Since it has a spherical shape and the number of parts is small, coupling adjustment can be reduced and near-end reflection can be suppressed to 60 dB or more. The mirror is made of a dielectric multilayer vapor deposition film or a metal film of gold or aluminum.

The 45 ° Faraday rotator is preferably attached at an angle of 1 to 15 ° with respect to the optical axis in order to avoid multiple reflection between garnet films and reflected light on the film surface. If is small, it works even if it is not angled. As a method of adjusting the Faraday mirror according to the present invention, a quartz rod 2 is fused to a fiber cleave cut portion 1 as shown in FIG. 1, and the tip of the quartz rod 2 is melted and formed into a spherical shape 3 larger than the fiber diameter. Fixed to the stainless steel fiber holder 4 and integrated with the combination part of the Faraday rotator 5 and the mirror 6, the mirror part is clamped, and the tail end A of the spherical stainless steel fiber holder 4 is moved to the strongest position of the reflected light. After the adjustment, fix it at that position by YAG fusion bonding or the like.

[0008]

[Action]

 When the element thickness is such that the polarization state rotates through 45 ° when it passes through the Faraday rotator, and when it returns after being reflected by the mirror, it reverts to 90 ° polarization rotation, and the polarization state always overlaps with the diagonal component, that is, in the opposite direction. The birefringence of 2 occurs at the same time, and as a result, a stable polarization state is maintained with respect to the time axis.

[0009]

【Example】

 In the configuration of FIG. 1, the diameter of the quartz ball lens was processed to about 1.2 mm. The spatial propagation distance to this beam waist is about 2.7 mm, and a mirror was installed at that position. The mirror used a dielectric multi-layer vapor deposition film that gives a reflectance of 98% or more in the wavelength range λ = 1.31 μm. In order to make the Faraday rotator 5 compact, a Bi-substituted rare earth iron garnet film with a thickness of about 300 μm manufactured by the LPE method is adopted, and light is propagated to avoid multiple reflection between garnet films and reflected light on the film surface. It is fixed to a Faraday rotator holder 7 which is angled at 4 ° to the direction.

The fiber holder metal member 4 having the spherical portion B formed at the tip is provided with the optical fiber 1 in the center through hole and the ferrule holding member 8, and a single refraction equivalent to the core portion of the optical fiber at the tip. Fiber 2 having the same outer diameter and a converging fiber integrated end having a spherical portion 3 formed at the tip thereof are inserted, and the spherical portion is projected, while a 45 ° Faraday rotator 5 and a mirror 6 are arranged facing each other. Then, the permanent magnet 9 for magnetizing the Faraday rotator was sealed with a cap 10 having been inserted.

The tail end portion A of the spherical stainless fiber holder 4 is moved to adjust the angle to the position where the mirror reflection is maximum. The coupling efficiency of the obtained collimator fiber is less than 0.2 dB, which is extremely stable. In addition, it was found that the entire system including the Faraday rotator had a loss of 0.5 dB or less, and sufficient coupling could be easily formed. In addition, the near-end reflection (return loss) of the collimator fiber used in this example alone was 62 dB, and it was found that the effect of the Faraday mirror was hardly reduced and was suppressed. If the film is formed accurately, the loss can be further reduced.

[0012]

[Effect of device]

 When the focused sphere fiber end of the present invention is used, the lens fiber is integrated, there is no concern about optical axis misalignment for a long time, a compact design is possible, optical axis alignment becomes easy, and all are fixed to a stainless steel holder, making it compact. In addition, YAG can be fixed, so the reliability is extremely high.

[Brief description of drawings]

FIG. 1 is a sectional view of a Faraday mirror device incorporating the present invention.

FIG. 2 is a schematic view of a conventional Faraday mirror.

[Explanation of symbols]

 1 Optical fiber 2 Quartz rod fiber 3 Focusing lens sphere 4 Stainless fiber holder 5 Faraday rotator 6 Mirror 7 Faraday rotator holder 8 Ferrule holding member 9 Ring-shaped permanent magnet 10 Cap 11 Lens A Stainless fiber holder tail end B Stainless fiber Holder spherical part

Claims (2)

[Scope of utility model registration request] 1. A Faraday mirror in which a 45 ° Faraday rotator and a mirror are arranged, and a permanent magnet for magnetizing the Faraday rotator is externally inserted, and the end of the optical fiber is equivalent to the core of the optical fiber and is a single unit. A Faraday mirror, characterized in that a fiber having the same outer diameter having a refractive index and a focusing fiber terminal having a spherical portion formed at its tip are opposed to introduce and emit light. 2. A 45 ° Faraday rotator with respect to the optical axis
The Faraday mirror according to claim 1, wherein the Faraday mirror is mounted at an angle of -15 °.