JP2007041388A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module facilitating polarization combination and achieving reduced size, simplified structure, and reduction of costs, by devising selection of a filter material and an arrangement of optical components constituting a module. <P>SOLUTION: The optical module 100 includes a dielectric multilayer filter 130 having a polarization plane-dependent transmittance characteristic, a first laser light source 110 set to the polarization plane having high transmittance of the dielectric multilayer filter, and a second laser light source 120 set to the polarization plane having high reflectance of the dielectric multilayer filter. The light of the first laser light source transmitted through the dielectric multilayer filter and the light of the second laser light source reflected by the dielectric multilayer filter are polarization combined. The dielectric multilayer filter is used as a filter used for polarization combination and the arrangement of the optical components is devised. Thus, the polarization combination is facilitated and the reduced size, the simplified structure, and the reduction of costs are achieved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical module, and relates to a configuration of a polarization combining optical module used for a pumping light source for an optical fiber amplifier or an optical fiber sensor. The optical module of the present invention is characterized by the selection of constituent filter materials and the configuration of the optical element, and achieves miniaturization and cost reduction in the polarization combining optical module.

  Conventionally, optical fiber amplifiers have been developed mainly for long-distance and large-capacity transmission systems as a method for reinforcing optical attenuation during transmission of optical fibers. Recently, however, the demand for high-speed communication has increased to the field of short-distance network systems including subscriber systems, and the practical application of optical fiber communication in this field is progressing. This short-distance network system requires a large number of optical amplifiers, and as a result, there is an increasing demand for downsizing and cost reduction of component parts. The optical module of the present invention has been devised to satisfy such a demand for an optical amplifier, and is a polarization combining optical module device that can be reduced in size and price.

  Furthermore, the optical module of the present invention is also applied to an OTDR device that detects a failure point of an optical fiber and a sensor that detects a change in transmission characteristics of the fiber using the optical fiber itself as a sensing element. In these devices, the polarization combining module is an important component, and the high performance, small size, and low cost polarization combining module is also an important technology. The polarization combining optical module of the present invention thus provides an excellent device for reducing the size and cost of optical amplifiers, OTDR devices, and optical fiber sensors.

  Here, the polarization combining optical module is a device that inserts into a fiber the optical energy obtained by inserting two laser lights whose polarization planes are orthogonal to each other into a single mode optical fiber. Conventionally, the following method is known as such an apparatus.

  The first method is to use a polarizing filter. In other words, a polarization filter is installed so that two orthogonal laser beams are made into parallel beams, and the two laser beams are transmitted to one polarization plane and reflected to the other polarization plane. It is a method of wave synthesis. A second method is to use a fiber coupler in which a polarization maintaining fiber is welded. FIG. 6 shows a conventional example of polarization combining using a fiber coupler.

  This fiber coupler fuses two polarization-maintaining fibers as shown in the figure. Orthogonally polarized light is inserted into ports 1 and 2 of the polarization-maintaining fiber. By adjusting the approach distance and length of both cores, the Y-polarized light travels straight and the X-polarized light moves to port 4. As a result, light energy inserted from two fibers can be added to one fiber.

"High-performance polarization beam combiner and polarization maintaining coupler" (Ouchi, Ohashi, Tanaka, Fujikura Technical Report (2003) No. 104, P1)

  However, the above two conventional methods have the following drawbacks. In other words, the price of the polarizing filter is high in the former example, so there is a limit to reducing the cost of an optical module using this as a constituent material. In addition, the latter method using a fiber coupler requires high processing accuracy, and the mounting space for fiber routing becomes large, which makes it difficult to reduce the size and cost.

  The present invention has been devised in view of the above-mentioned problems of the conventional method using a polarizing filter and the polarization combining optical module using a fiber coupler, and the object of the present invention is to select the filter material and the module. By devising the arrangement of the optical elements that make up, it is possible to easily synthesize polarization, and to realize a small size, easy structure, and low cost. The optical module of the present invention can be applied to a light source for optical amplification that requires high output operation and an optical fiber sensor that requires high sensitivity operation.

  In order to solve the above-mentioned problems, the first feature of the present invention is to use a dielectric multilayer filter that is widely used and can be manufactured at a low cost without using an expensive polarizing filter. The second feature is that the optical coupling method using a spatial parallel beam using a collimator lens is employed without using a fiber coupler that requires a highly accurate alignment and mounting space for the module configuration. In the present invention, when light is incident on the dielectric multilayer filter from an oblique direction, the filter exhibits polarization plane dependency on the transmittance and the reflectance. It is characterized by realizing synthesis.

  As described above, according to the present invention, a dielectric multilayer filter is used as a filter used for polarization synthesis, and the arrangement of optical elements is devised to enable easy polarization synthesis. In addition, low cost can be realized. Furthermore, by selecting the same filter material and devising the arrangement of the optical elements, the optical module can be used as a sensor for detecting an abnormality in the output fiber.

  Hereinafter, preferred embodiments of an optical module according to the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 shows a polarization combining type high power laser module for fiber excitation of an optical fiber amplifier. This is an optical module for performing optical amplification operation with an erbium-doped fiber by adding the optical outputs of two lasers and optically pumping the erbium-doped optical fiber.

  As shown in FIG. 1, the polarization combining module 100 according to the present embodiment includes a first laser light source 110, a second laser light source 120, a filter 130, a collimator 140, and an output fiber 150. It is configured. In the example shown in FIG. 1, the first laser light source 110, the second laser light source 120, the dielectric multilayer filter 130, and the collimator 140 are attached to the side wall of the package 160, and the output fiber 150 protrudes outside the package 160. It is the composition made to do.

(First laser light source 110, second laser light source 120)
The first laser light source 110 and the second laser light source 120 are collimator lens-integrated light emitting optical elements that convert light emitted from the LD chip into parallel light by a collimator lens and emit parallel light. As shown in FIG. 1, the first laser light source 110 and the second laser light source 120 are arranged on adjacent side walls of the package 160, and each emit light to the dielectric multilayer filter 130. Incident angles from the first laser light source 110 and the second laser light source 120 to the dielectric multilayer filter 130 are each set to about 45 °.

  The polarization plane of the first laser light source 110 is set to P polarization in this embodiment. In addition, the polarization plane of the second laser light source 120 is set to S polarization in this embodiment.

(Dielectric multilayer filter 130)
The dielectric multilayer filter 130 is a short wavelength transmission filter in this embodiment. As shown in FIG. 1, the dielectric multilayer filter 130 is disposed so that the incident angle is about 45 ° with respect to the first laser light source 110 and the second laser light source 120.

  The transmittance and reflectance of the dielectric multilayer filter 130 exhibit polarization dependency. The reflectance and transmittance of the dielectric multilayer filter 130 are independent of polarization in the case of normal incidence. However, by changing the incident angle, the transmittance wavelength characteristic changes greatly depending on the polarization.

FIG. 2 is an explanatory diagram showing transmittance wavelength characteristics when the incident angle is changed.
The wavelength dependence of transmission loss is shown for incident angles of 18 degrees and 45 degrees. When the incident angle is 45 degrees, a wavelength capable of distinguishing transmission or reflection can be secured at 50 nm or more. In the example shown in FIG. 2, the dielectric multilayer filter 130 becomes almost completely transmitted at a wavelength of a symbol A (about 1510 nm) to a symbol B (about 1560 nm) in the graph if it is incident with P polarization, and S polarization In this case, the dielectric multilayer filter 130 can be almost completely reflected. Therefore, even when light having the same wavelength (for example, 1550 nm) is emitted from the first laser light source 110 and the second laser light source 120, the dielectric multilayer filter 130 is almost completely obtained if it is incident with P polarization. When the light is transmitted and incident with S-polarized light, the dielectric multilayer filter 130 can be almost completely reflected.

  FIG. 3 is an explanatory diagram showing a case where wavelengths of light having different wavelengths are synthesized using a short wavelength transmission type edge filter as the dielectric multilayer filter 130. In this case, the first laser light source 110 can be used as transmitted light by setting the polarization plane of the first laser light source 110 to P polarization and setting the wavelength to λ2 or less. In addition, the second laser light source 120 can be used as reflected light by setting the polarization plane of the second laser light source 120 to S polarization and setting the wavelength to λ1 or more. In this way, wavelength synthesis can be realized efficiently.

(Collimator 140, output fiber 150)
The collimator 140 is an optical element that converts incident light into convergent light (or converted into parallel light) with a lens. In the present embodiment, the light synthesized by the dielectric multilayer filter 130 is incident on the collimator 140, converted into convergent light by the lens at the tip of the collimator, and incident on the end face of the output fiber 150. The output fiber 150 is an outgoing optical fiber that transmits light incident from the collimator 140 to the outside. An optical element in which the collimator 140 and the output fiber 150 are integrated may be referred to as a collimator.

(Effects of the first embodiment)
As described above, according to the present embodiment, the dielectric multilayer filter 130 is used as a filter used for polarization synthesis, and the arrangement of optical elements such as the first laser light source 110 and the second laser light source 120 is devised. Therefore, it is possible to easily combine polarization, and to realize a small size, easy structure, and low cost.

(Second Embodiment)
In the present embodiment, a case where a long wavelength transmission edge filter is used as the dielectric multilayer filter 130 will be described.

  In this embodiment, the polarization plane of the first laser light source 110 is set to S polarization. In addition, the polarization plane of the second laser light source 120 is set to P polarization in this embodiment.

  FIG. 4 is an explanatory diagram showing a case where wavelengths of light having different wavelengths are synthesized using a long wavelength transmission type edge filter as the dielectric multilayer filter 130. In this case, the first laser light source 110 can be used as transmitted light by setting the polarization plane of the first laser light source 110 to S polarization and setting the wavelength to λ1 or more. Moreover, the second laser light source 120 can be used as reflected light by setting the polarization plane of the second laser light source 120 to P polarization and setting the wavelength to λ2 or less. In this way, wavelength synthesis can be realized efficiently.

(Effect of 2nd Embodiment)
As described above, according to the present embodiment, as in the first embodiment, the dielectric multilayer filter 130 is used as a filter used for polarization synthesis, and the first laser light source 110 and the second laser light source 120 are used. By devising the arrangement of the optical elements, etc., it is possible to easily synthesize the polarization, and to realize a small size, a simple structure, and a low cost.

(Third embodiment)
The above has described the case where the polarization combining optical module of the present invention is used as a high-output pumping light source for an optical amplifier. Next, an apparatus using the polarization combining optical module of the present invention as a fiber sensor is shown in FIG. That is, the apparatus according to the third embodiment is characterized in that a light receiving element 320 is provided instead of the second laser light source 120 of the optical module 100 (FIG. 1) according to the first embodiment.

  The laser light source 310 is substantially the same as the first laser light source 110 according to the first embodiment. The dielectric multilayer filter 330, the collimator 340, and the package 360 are substantially the same as the dielectric multilayer filter 130, the collimator 140, and the package 160 according to the first embodiment.

  350a is a reflector present in the fiber. The reflector is a physical change caused by a change in propagation loss of the fiber caused by fiber breakage, strain, temperature difference and the like. In this figure, the dielectric filter 330 operates as a polarization branching function. The dielectric filter 330 selectively receives the light returning from the collimator 340 and the function of transmitting the light from the laser light source. 320 has a function to be introduced. The polarization filter of this figure has the same optical characteristics as the polarization synthesis module of FIG. 1, except that the polarization separation operation is performed by changing the traveling direction of light. In other words, the light emitted from the laser light source 310 can be detected by the light receiving element 320 after being reflected and returned from the obstacle point 350. Normally, the return light is independent of polarization, so that part of the return light is reflected by the dielectric filter 330 and enters the light receiving element 320.

  As described above, according to the present embodiment, the light receiving element 320 can detect an abnormality occurring in the output fiber 350a or a change in the intensity of the return light caused by a physical change. It is also possible to detect the distance from the light source to the obstacle point from the time when the pulsed light emitted from the laser light source 310 reaches the light receiving element. As described above, by using the optical module of the present invention, it becomes possible to detect a physical state of a specific point of the fiber like a point search of a fiber laid like an OTDR device or a fiber sensor for measurement.

(Effect of the third embodiment)
As described above, the polarization combining optical module using the dielectric multilayer filter is excellent in miniaturization and cost reduction, and is an excellent method as an optical module for an OTDR device or an optical fiber sensor that requires these features. It is.

  The preferred embodiments of the optical module according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be obvious to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  The present invention can be used for an optical module, and in particular, can be used for an optical module that detects an abnormality of an optical fiber by using a pumping light source for a high-power optical amplifier and a return light from the optical fiber.

It is explanatory drawing which shows the structure of the optical module concerning 1st Embodiment. It is explanatory drawing which shows the transmittance | permeability wavelength characteristic when changing the incident angle of a filter. It is explanatory drawing which shows the case where wavelength synthesis | combination is used for the light of a different wavelength using a short wavelength transmission type edge filter. It is explanatory drawing which shows the case where wavelength synthesis | combination is used for the light of a different wavelength using a long wavelength transmission type edge filter. It is explanatory drawing which shows the structure of the optical module concerning 3rd Embodiment. It is explanatory drawing which shows the prior art example of the polarization | polarized-light combination by a fiber coupler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Polarization synthesis module 110 1st laser light source 120 2nd laser light source 130 Dielectric multilayer filter 140 Collimator 150 Output fiber 160 Package 300 Optical module 310 Laser light source 320 Light receiving element 330 Dielectric multilayer filter 340 Collimator 350 Output fiber 360 packages

Claims (9)

A dielectric multilayer filter having transmittance characteristics depending on the polarization plane;
A first laser light source set on a polarization plane having a high transmittance of the dielectric multilayer filter;
A second laser light source set on a polarization plane with high reflectivity of the dielectric multilayer filter;
An optical fiber from which light is emitted from the first and second laser light sources through the dielectric multilayer filter;
Including
An optical module, wherein the light of the first laser light source transmitted through the dielectric multilayer filter and the light of the second laser light source reflected by the dielectric multilayer filter are combined by polarization. The dielectric multilayer filter is a short wavelength transmission filter,
The polarization plane of the first laser light source is set to P polarization,
The optical module according to claim 1, wherein a polarization plane of the second laser light source is set to S polarization.   The optical module according to claim 2, wherein the wavelength of the first laser light source is equal to or less than the wavelength of the second laser light source. The dielectric multilayer filter is a long wavelength transmission filter,
The polarization plane of the first laser light source is set to S polarization,
The optical module according to claim 1, wherein a polarization plane of the second laser light source is set to P polarization.   The optical module according to claim 4, wherein the wavelength of the first laser light source is equal to or greater than the wavelength of the second laser light source. A dielectric multilayer filter having transmittance characteristics depending on the polarization plane;
A laser light source set on a polarization plane with high transmittance of the dielectric multilayer filter;
An optical fiber from which light is emitted from the laser light source via the dielectric multilayer filter;
A light receiving element that receives the return light from the optical fiber through the dielectric multilayer filter;
An optical module comprising: The dielectric multilayer filter is a short wavelength transmission filter,
The optical module according to claim 6, wherein a polarization plane of the laser light source is set to P polarization. The dielectric multilayer filter is a long wavelength transmission filter,
The optical module according to claim 6, wherein a polarization plane of the laser light source is set to S polarization.   9. The optical module according to claim 6, wherein the return light is generated due to an abnormality of the optical fiber.

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