WO2002021192A1

WO2002021192A1 - Polarized light multiplexer

Info

Publication number: WO2002021192A1
Application number: PCT/JP2001/007577
Authority: WO
Inventors: Yoshihiro Konno
Original assignee: Namiki Seimitsu Houseki Kabushiki Kaisha
Priority date: 2000-09-04
Filing date: 2001-08-31
Publication date: 2002-03-14
Also published as: JP2002072141A

Abstract

A polarized light multiplexer comprises an outgoing-side fiber assembly part inserted and fixed in a two-core ferrule having a structure where two polarization retaining fibers having two polarization retaining planes perpendicular to each other and parallel with the axial direction, parallel flat plates made of one uniaxial double-refraction crystal having such an optical path that two light beams from the two polarization retaining fibers are multiplexed into one beam, a lens for multiplexing the light beams outgoing from the parallel flat plates, another lens arranged at the front end of the optical fiber on the incoming side, and one optical fiber on the incoming side. These components are arranged in the order of the two-outgoing-side polarization retaining fibers, one parallel flat plate of the uniaxial double-refraction crystal, one or two lenses, and one incoming side optical fiber.

Description

Description Polarization synthesizer Technical field

The present invention relates to a polarization combiner for optical fiber amplification mainly used for optical communication and optical measurement, and a polarization separator. Background art

With the recent development of optical communication technology, so-called optical fiber amplifiers, which amplify optical signals with light, have attracted attention and are being used. This optical fiber amplifier has many advantages, such as high gain, low noise, and suitability for wavelength multiplexing, and plays an important role in current optical communication technology.

For example, in wavelength division multiplexing optical communication, several hundred channels of signal light with different wavelengths can be put in one optical fiber, but as the number of channels increases, the pumping light power required for optical amplification also increases. The need comes out. As one method of increasing the power of the pumping light, there is known a method of increasing the output light power of the semiconductor laser for pumping.

In the waveguide structure of the pumping semiconductor laser having a high output light power, the active layer has a more flat structure, so that the spot shape of the light beam emitted from the semiconductor laser also becomes flat. In order to efficiently couple such a flat spot-shaped light beam to the optical fiber, a special polishing technique is used to process the tip of the optical fiber 102 into a semi-cylindrical shape as shown in Fig. 3. However, a coupling technology for increasing the optical coupling efficiency with a flat light beam from the semiconductor laser 101 for excitation has already been developed.

Furthermore, in order to increase the power of the pumping light, there is a method in which light emitted from such an optical output semiconductor laser is optically coupled to an optical fiber with high efficiency to combine the light. There are two methods of this synthesis, "polarization synthesis" and "wavelength synthesis". The present invention has conducted research on the former "polarization synthesis". “Polarization synthesis” is a method of combining lights having two orthogonal polarization planes. The configuration shown in FIG. 2 is an example of a schematic configuration of a conventional polarization synthesizer. In FIG. 2, reference numerals 201a and 201b denote polarization maintaining fibers, and the two polarization maintaining fibers 201a and 201b have polarization planes of light (F1, F2) passing therethrough which are orthogonal to each other. Retention fibers 201a and 201b pass through separate lenses 202a and 202b, respectively, and enter polarization beam splitter 203 as shown.

The polarization beam splitter 203 has a multi-stage structure in which a multilayer film is formed on the surface to which the triangular prism is bonded, and is adhered and fixed with an optical organic adhesive. Inside the polarization beam splitter 203, the light (P The wave: F1) is transmitted in the straight direction, and the light (S wave: F2) on the other side of the polarization maintaining fiber 201b has the function of being reflected by the multilayer film surface. Show.

In this manner, the light (P wave: F1) on the polarization maintaining fiber 201a side and the light (S wave: F2) on the polarization maintaining fiber 201b side are synthesized in the polarization beam splitter 203, pass through the lens 202c, and pass through the optical fiber. Light (F3) is propagated to 204.

However, in the above-described conventional configuration, the polarization beam splitter 203 itself has a multi-stage structure in which a large number of triangular prisms are adhered to each other. There was a structural problem that the light resistance and reliability over time against heat and the like were low. In other words, the adhesive for fixing the triangular prisms is an organic adhesive, so there was a particular problem in reliability.

Also, as an assembly procedure of the conventional configuration, the polarization maintaining fiber 201a and the lens 202a, the polarization maintaining fiber 201b and the lens 202b, and the optical fiber 20 and the lens 202c, which are respectively integrated, are assembled one by one first. However, it is general to adjust the position through a polarizing beam splitter 203 having a structure in which the four triangular prisms are bonded to each other and assemble the light. To adjust the beam axis Spent a lot of trouble and time on each adjustment part during the assembly work. At the same time, it is structurally necessary to incline the polarizing beam splitter ₂₀₃ in order to prevent the reflected light from the end face of the polarizing beam splitter 203 from returning to the optical fiber on the emission side. For this reason, it was technically more difficult to adjust two light beams three-dimensionally to make one light beam, and there was also a structural problem that highly efficient optical coupling was extremely difficult to obtain.

Also, with respect to the miniaturization of the entire device configuration, there was a problem that the number of components, particularly the prism components constituting the polarizing beam splitter, was large, and it was difficult to save space with the polarizing beam splitter alone.

The present invention solves the above-described problems, and provides a polarization combining structure that can improve light resistance and high reliability, increase optical coupling efficiency, facilitate assembly, and further reduce the size compared to a conventional polarization combining device. The purpose is to: Disclosure of the invention

In order to achieve the above object, the present invention provides, as a polarization combiner, a two-core filter having a structure in which two polarization maintaining fibers whose polarization maintaining surfaces are orthogonal to each other can be arranged in parallel in an axial direction. The outgoing fiber assembly inserted and fixed inside, and one uniaxial birefringent crystal parallel plate with an optical path length such that two light beams from both polarization maintaining fibers are combined into one. A lens for beam-combining a light beam emitted from the uniaxial birefringent crystal parallel plate, and one optical fiber on the incident side. From the light output side, in order from the output side, two output side polarization maintaining fibers held in a two-core filter, one uniaxial birefringent crystal parallel plate, one or two lenses, one input side Single-mode optical fiber The components are arranged and arranged.

The structure of this polarization synthesizer is described in more detail as shown in FIG. First, light (F1, F2) from the left side of the figure passes through each polarization maintaining fiber 301a and the polarization maintaining fiber 301b, and passes through a two-core ferrule (not shown) having a parallel arrangement structure. With the polarization maintaining surfaces of The optical path system is housed and configured as an integrated assembly. One end of the optical fibers of the polarization maintaining fibers 301a and 301b is obliquely polished and is provided with an antireflection film in order to improve the return loss performance.

Polarization synthesis for the light beam whose two polarization maintaining surfaces are orthogonal to each other is performed by the following parallel plate 302 made of uniaxial birefringent crystal. The uniaxial birefringent crystal parallel flat plate 302 is disposed between the two polarization maintaining fibers and a lens 303a to be described later, and emits two orthogonally polarized light beams emitted from the polarization maintaining fibers 301a and 301b. (F1, F2) passes through the optical path system of the uniaxial birefringent crystal parallel flat plate 302, and is polarized and combined into one light beam.

After that, the light (F3) is propagated through the two lenses 303a and 303b to the single mode optical fiber 304. At this time, the structure shown in Fig. 1 uses two lenses 303a and 303b for highly efficient optical coupling. Here, either one of the lenses can be optically coupled. It satisfies enough. The new structure without using the conventional triangular prism enables a structure without an adhesive on the optical path, eliminating the risk of light deterioration of the adhesive and improving the reliability over time.

Next, the structural ease of assembly will be described. The polarization maintaining fibers 301a and 301b are housed in a two-core ferrule with their respective polarization maintaining surfaces perpendicular to each other.Since the two axes of the fiber are structurally integrated with the ferrule, they are made of uniaxial birefringent crystal. As a method of aligning the optical axis of the parallel plate 302 with the polarization maintaining surface of the polarization maintaining fiber 301a '301b, the optical beam is monitored by an imager and made of a uniaxial birefringent crystal so that the two light beams become one. Either fine-tuning the parallel plate 302 or aligning the polarization axis of either polarization maintaining fiber (301a or 301b) with the optical axis of the uniaxial birefringent crystal parallel plate 302 by marking. be able to.

Either method without through the intermediate lens, since it is polarization maintaining fiber 301a ^'3 01b and the adjustment of the polarization plane only uniaxial birefringent crystal made parallel plate 302, the polarization rotation adjustment and high efficiency optical coupling It is not necessary to perform such beam axis adjustment at the same time. Therefore, the assembly process can be separated, resulting in easier assembly work Can be. Therefore, the productivity in the assembly process can be improved. For high-efficiency optical coupling, only two polarization maintaining fibers 301a and 301b and a uniaxial birefringent η η-fold crystal parallel plate 302 are used to make two light beams into one.

ο λ e

Therefore, after the uniaxial birefringent crystal parallel plate 302, the light passing through the two lenses 303a '303b and the optical fiber 304 can be treated as one light beam. Since one end of each of these optical fibers is obliquely polished to improve the return loss performance, it is not necessary to structurally incline the side of the uniaxial birefringent crystal parallel plate 302. Therefore, the two light beams emitted from the two polarization maintaining fibers 301a '301b and passing through the uniaxial birefringent crystal parallel plate 302 become one light beam so that the uniaxial birefringent crystal parallel plate is used. By setting the thickness (optical path length) of 302, the two light beams are always one, and high efficiency optical coupling can be obtained easily.

The equation representing the relationship between the distance between the two light beams on the orthogonal polarization planes and the thickness for obtaining the optical path length of the uniaxial birefringent crystal parallel plate 302 for combining the two light beams into one is: The contents are shown as the explanatory words of the following Equation 1 and symbols. Formula 1

nn-no

d = t ■

λ ne ² -no ²

ηη =

ne ² 'cos ² af + no ² -sin ²

d Distance between two optical beams

Thickness of uniaxial birefringent crystal parallel plate

Ordinary refractive index of uniaxial birefringent crystal

Extraordinary light refractive index of uniaxial birefringent crystal

Angle formed between the plane of incidence of the uniaxial birefringent crystal parallel plate and the crystal optical axis Further, in another embodiment of the present invention, one light beam from a single mode optical fiber is divided into two light beams through a lens. Two cores in which one uniaxial birefringent crystal parallel plate having an optical path length to be separated as a polarization maintaining light beam and two polarization maintaining fibers whose polarization maintaining surfaces are orthogonal to each other are arranged in parallel in the axial direction. The entrance-side fiber assembly, which is inserted and fixed in the ferrule, faces The arrangement order is one optical fiber on the entrance side, one or two lenses, one parallel plate made of uniaxial birefringent crystal, and two polarization maintaining fibers on the entrance side fixed to a ferrule. By arranging and configuring the components in such a manner as described above, it can be used also as a polarization separator in which an optical path advancing system has the completely opposite operation effect to the polarization synthesizer.

For example, if the traveling direction of the incoming and outgoing light (F1, F2, F3) in FIG. 1 is reversed, the light naturally returns from F3 to F1, F2 from the configuration shown in FIG. Mechanism. Applications of this polarization separator include a polarization mode dispersion (PMD) (Polarization Mode Dispersion) monitor in the transmission line and coherent optical communication.

Incidentally, the uniaxial birefringent crystal, rutile (Ti0 _2), ortho yttrium Vanadium (YV0 _4), can be considered parallel plates of Karusai bets (calcite) selected from the plate. However, Karusai bets in three (calcite) is because of the deliquescence, preferably rutile (Ti0 _2), ortho yttrium Vanadium (YV0 ₄₎ are suitable. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram showing a configuration of a polarization synthesizer according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a conventional polarization synthesizer.

FIG. 3 is a schematic perspective view showing an example of a mode in which a light beam from a semiconductor laser for excitation is efficiently coupled to an optical fiber.

FIG. 4 is an example of a two-core ferrule used in the embodiment of the present invention, in which (a) is a cross-sectional view, and (b) is a view schematically showing a hole see through from the front. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the polarization synthesizer according to the present invention will be specifically described with reference to the drawings.

Note that the present invention is not limited to this embodiment, and the component structure is an example. FIG. 1 is a diagram showing a schematic structure of a polarization synthesizer of the present invention. In the hole of the 2-core ferrule 401 (see Fig. 4), which has a structure in which the cladding outer diameters of two polarization maintaining fibers 301a and 301b having a cladding outer diameter of 0.125mm and 301b can be circumscribed and arranged in parallel. Then, the polarization maintaining surfaces are housed in a perpendicular combination, fixed with a glass adhesive, polished diagonally on the tip of the firer to improve the return loss performance, and coated with an anti-reflection film on the processed end surface. The outgoing side firer assembly was used.

Next, a laser beam for adjustment is passed through two polarization maintaining fibers 301a and 301b, and a parallel plate 302 made of rutile uniaxial birefringent crystal with a thickness of 1.26 mm is attached. The parallel plate 302 made of uniaxial birefringent crystal is rotated and adjusted so that two light beams passing through the parallel plate 302 made of uniaxial birefringent crystal become one beam. The holding case and the holding case made of a uniaxial birefringent crystal parallel plate were fused and fixed by YAG laser welding.

After that, two lenses 303a-303b and an optical fiber 304 are added as the side receiving the light adjusted to one light beam, and the beam axis is adjusted to achieve more efficient optical coupling. The bodies were fused and fixed by YAG laser welding to complete the polarization synthesizer body.

When the insertion loss of the obtained polarization synthesizer was measured, an insertion loss value of 0.3 dB was obtained, which was higher than that of the conventional structure. As described above, the terms and expressions used in the present specification are used merely for explanation, and do not limit the content of the present invention in any way. Even if limited terms and expressions are used, there is no intention to exclude equivalents or some of the embodiments of the present invention described above. Obviously, various modifications may be made within the scope of the claimed invention. Industrial applicability As described above, according to the polarization synthesizer and the polarization separator according to the present invention, a parallel plate made of a small uniaxial birefringent crystal can be used without using a polarization beam splitter that frequently uses a conventional organic adhesive. By using for polarization synthesis, light resistance and reliability are improved.

In addition, one end of each optical fiber of the polarization maintaining fiber is obliquely polished to improve the return loss performance, and the end face is coated with an antireflection film. You don't have to. In addition, while being structurally simple, work such as optical axis adjustment and assembly can be easily performed, and high optical coupling efficiency can be easily obtained.

Also, in order to reduce the size of the entire device configuration, each component, in particular, a plurality of prism components constituting the polarizing beam splitter is eliminated, and only one uniaxial birefringent crystal parallel plate is required. A space-saving polarization combiner and polarization separator can be obtained.

Claims

Range of request

1. An emitting fiber assembly component in which two polarization maintaining fibers whose polarization maintaining surfaces are orthogonal to each other are inserted and fixed in a two-core ferrule that has a structure that can be arranged in parallel and parallel to the axial direction. And the light emitted from one uniaxial birefringent crystal parallel flat plate having an optical path length such that two outgoing light beams from It consists of a lens that couples the beam and one single-mode optical fiber on the incident side, and the order of each component is two emission-side polarization maintaining fibers and one uniaxial birefringent crystal. A polarization synthesizer characterized by being arranged so as to be a parallel plate, one or two lenses, and one input single-mode optical fiber.

A single uniaxial birefringent crystal parallel plate with an optical path length that separates and emits the light beam emitted from one single-mode optical fiber through a lens as two polarization-maintaining light beams. An incident-side fiber assembly component, which is inserted and fixed in a two-core funirule, in which two polarization maintaining fibers whose polarization maintaining surfaces are orthogonal to each other are arranged in parallel and parallel in the axial direction, are combined in opposition, and the arrangement order of the components Are arranged to be one optical fiber on the incident side, one or two lenses, one parallel plate made of uniaxial birefringent crystal, and two polarization maintaining fibers on the incident side fixed to a ferrule. A polarized light separator, comprising:

3. The uniaxial birefringent crystal, the scope of the claims, characterized in that it consists of rutile (Ti0 _2), ortho yttrium Vanadium (YV0 _4), Karusai bets (calcite) selected from a plate-like parallel flat plate 3. The polarization synthesizer or polarization separator according to paragraph 1 or 2.