Optical Module, Alignment System and Optical Monitoring Method

Provided is an optical module that accurately observes the overall intensity of visible light having a relatively short wavelength and propagating through an optical fiber, and is suitable for downsizing an optical device. An optical module provided in an optical fiber connected to an optical component capable of inputting or outputting light. The optical module includes: a case body that forms a closed space C in which a part of the optical fiber is accommodated; a fiber fixing portion that fixes the optical fiber to predetermined position and shape inside the case body; and a photodiode that is attached inside the case body at a position capable of receiving radiation light radiated from the optical fiber fixed to the fiber fixing portion.

TECHNICAL FIELD

The present invention relates to an optical module using an optical fiber, an alignment system of the optical module, and an optical measurement method of an optical fiber.

BACKGROUND ART

Small optical modules including a plurality of optical components combined have been developed. Such an optical module is disclosed in, for example, Non Patent Literature 1, and the 3D measurement system disclosed in Non Patent Literature 1 is configured by connecting a laser light source and a planar light wave circuit (hereinafter, referred to as “PLC”) via an optical fiber. The 3D measurement system disclosed in Non Patent Literature 1 is described such that a laser beam emitted from a laser light source is divided into two equal light beams by a 3 dB fiber coupler, and the divided light beams interfere with each other to project a fringe pattern on an object. In addition, Non Patent Literature 2 discloses development of a small RGB fiber coupler with a small amount of loss for each color. Such an optical module can achieve a small optical device in which the number of alignment steps is small and the optical axis is hardly shifted due to vibration as compared with an optical system including a bulk component.

In addition, in order to continuously and stably operate the 3D measurement system as described above, it is necessary to monitor the intensity of light propagating through the PLC of the optical module and the optical fiber, and perform maintenance such as axial alignment (alignment) or replacement of the optical fiber as necessary. Known maintenance of the optical system using an optical module is performed by calculating the overall light intensity propagating through the optical fiber using the intensity of the light divided by the fiber coupler as described above.

CITATION LIST

Non Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, it is known that a commercially available fiber coupler cannot obtain sufficient reliability for visible light having a relatively short wavelength. Such a feature is considered to be caused by the fact that the optical fiber of the fiber coupler causes fluctuation in transmittance and refractive index called photodarkening with respect to light having a particularly short wavelength among visible light. Such a tendency is remarkable for visible light having a wavelength of 500 nm or less and a light intensity of about several tens of mW, and when visible light having a short wavelength is input to the fiber coupler, the branching ratio to the optical fiber varies over time.

In order to avoid the above point, it is conceivable to use a bulk component such as a beam splitter instead of the fiber coupler. However, when the beam splitter is used, the size of the optical device including the optical module is increased, and application of the optical device is considered to be limited. In addition, the beam splitter causes a connection loss of light when the light is recombined to the optical fiber at the subsequent stage of the beam splitter. The connection loss is an error in calculating the overall light intensity propagating through the optical fiber from the light split by the beam splitter.

The present invention has been made in view of the above points, and relates to: an observation module, which is an optical module that accurately observes the overall intensity of visible light having a relatively short wavelength and propagating through an optical fiber, and is suitable for downsizing an optical device; an alignment system; and an optical measurement method.

Solution to Problem

An optical module according to an aspect of the present invention is an optical module provided in an optical fiber connected to an optical component capable of inputting or outputting light, the optical module including: a case body that forms a closed space in which a part of the optical fiber is accommodated; a fiber fixing portion that fixes the optical fiber to predetermined position and shape inside the case body; and a light receiving element that is attached inside the case body at a position capable of receiving radiation light radiated from the optical fiber fixed to the fiber fixing portion.

An alignment system according to an aspect of the present invention is an alignment system that aligns an optical fiber connected to an optical component capable of inputting or outputting light, the alignment system including: an optical module including a case body that forms a closed space in which a part of the optical fiber is accommodated, a fiber fixing portion that fixes the optical fiber to predetermined position and shape inside the case body, and a light receiving element that is attached inside the case body at a position capable of receiving radiation light radiated from the optical fiber fixed to the fiber fixing portion; a light source that causes light to be incident on at least a portion accommodated inside the case body of the optical fiber from one end portion of the optical fiber; and an alignment mechanism that adjusts a position of at least one of the light source and the end portion on the basis of the radiation light received by the light receiving element.

An optical measurement method according to an aspect of the present invention is an optical measurement method used for observing light propagating through an optical fiber connected to an optical component capable of inputting or outputting light, the optical measurement method including: a step of receiving radiation light radiated from an optical fiber fixed to predetermined position and shape inside a case body forming a closed space; and a step of determining intensity of the light propagating through the optical fiber on the basis of intensity of the radiation light that has been received.

Advantageous Effects of Invention

According to the aspects described above, it is possible to provide: an optical module that accurately observes the overall intensity of visible light having a relatively short wavelength and propagating through an optical fiber, and is suitable for downsizing an optical device; an alignment system; and an optical measurement method.

DESCRIPTION OF EMBODIMENTS

Overview

Prior to describing an embodiment of the present invention, an overview of the present invention will be described below.

FIG.1is a schematic diagram for explaining an experiment showing the basis of the present invention. The configuration illustrated inFIG.1includes an optical module1including a closed space C having a photodiode (indicated as “PD” in the drawing)33therein, optical fibers21,22inserted into the closed space C, and a control unit3that inputs a radiation signal Ss indicating received light intensity of light received by the photodiode33and a propagation signal St indicating received light intensity of light received by the photodiode34.

The optical fiber21and the optical fiber22are connected in the closed space C. In the experiment, the optical fibers21and22were thermally fused and connected by arc discharge. A fused portion of the optical fibers21and22is illustrated inFIG.1as a fused portion M. Light is incident from a light source (not illustrated) toward the optical fiber22from the optical fiber21among the optical fibers21,22that have been fused to each other. In the experiment, a laser device was used as a light source, and laser light was incident on the optical fibers21,22. The laser light incident on the optical fiber21is referred to as incident light Lin, and the laser light emitted from the optical fiber22is referred to as emission light Lout. The wavelength of the laser light is 405 nm, and the propagation light intensity propagating through the optical fibers21,22is approximately 12 dbm to 18 dbm. Both the optical fibers21and22used in the experiment are non-doped core fibers.

It is known that laser light passing through an optical fiber leaks to the outside at a connection portion or a bent portion of the optical fiber. Hereinafter, of the laser light, light radiated to the outside of the optical fibers21,22is referred to as “radiation light”, and light that has passed through the optical fibers21,22without being scattered and is emitted from an end portion of the optical fiber22is referred to as “propagation light”. In this experiment, the emission light Lout corresponds to the propagation light.

The photodiode33is provided at a position capable of receiving the radiation light Ls with respect to the optical fibers21,22, and receives the radiation light Ls. The intensity of the received radiation light Ls is converted into a radiation signal Ss and output from the photodiode33. The photodiode34is provided at a position capable of receiving the propagation light emitted from the optical fiber22, and receives the propagation light. The intensity of the received propagation light is converted into a propagation signal St and output from the photodiode34.

In this experiment, a heat shrinkable tube25is provided on the surface of the fused portion M as a scattering member having a larger scattering coefficient than a scattering coefficient of the surfaces of the optical fibers21,22. The heat shrinkable tube25is transparent to laser light, but has a larger scattering coefficient than larger scattering coefficients of the optical fibers21,22due to its material, surface roughness, and the shape of surface irregularities. Although the fused portion M is located inside the heat shrinkable tube25, the heat shrinkable tube25is indicated by a broken line inFIG.1, and the fused portion M is clearly shown inFIG.1. The radiation light Ls radiated from the optical fibers21,22is scattered on the surface of the heat shrinkable tube25and is easily received by the photodiode33.

The control unit3receives the radiation signal Ss and the propagation signal St. Then, the control unit3compares the radiation signal Ss with the propagation signal St input at the timing coincident with the input timing of the radiation signal Ss.

FIGS.2A and2Bare graphs for explaining a comparison result between the radiation signal Ss and the propagation signal St with the same input timing to the control unit3. InFIG.2(a), the horizontal axis represents the propagation light intensity, and the vertical axis represents the radiation light intensity. The propagation light intensity is a value determined by the signal intensity (dbm) of the propagation signal St, and the radiation light intensity is a value determined by the signal intensity (dbm) of the radiation signal Ss. InFIG.2(b), the horizontal axis represents time (hour), and the vertical axis represents a difference (db) between the propagation light intensity and the radiation light intensity.

As illustrated inFIG.2(a), the radiation light intensity and the propagation light intensity are in a direct proportional relationship, and both exhibit preferable linearity. As illustrated inFIG.2(b), the difference between the radiation light intensity and the propagation light intensity is substantially constant over 1000 hours or more (42 days or more). Such experimental results show that there is a strong correlation between the propagation light and the radiation light, and the correlation is stable over a long period of time. The present inventors have conceived of obtaining a relationship between a propagation light intensity and a radiation light intensity in advance for one optical system, and observing the intensity of the propagation light on the basis of the intensity of the radiation light of the optical fiber. Observation of propagation light using radiation light can reduce an error of an observation value as compared with observation using light split using a fiber coupler, regardless of photodarkening that occurs when visible light having a relatively short wavelength is incident on an optical fiber. In addition, since the optical module1can be downsized as compared with a bulk component such as a beam splitter, it is also suitable for downsizing an optical device.

Next, a first embodiment and a second embodiment of the present invention will be described. The drawings of the first embodiment and the second embodiment described later are intended to describe the technical idea, configuration, function, effect, and the like of the present invention, and do not limit the specific configuration of the embodiment. The drawings of the first embodiment and the second embodiment are schematic views, and the aspect ratio and the thickness are not necessarily accurately indicated. In the first embodiment and the second embodiment, the same members among the illustrated members are denoted by the same reference numerals. Configurations denoted by the same reference numerals may be partially omitted in the following description.

First Embodiment

FIG.3is a perspective view illustrating an appearance of the optical module1of the first embodiment.FIG.4is a schematic cross-sectional view of the optical module1illustrated inFIG.3taken along the z-x plane of the coordinate system illustrated inFIG.3.FIG.4is a longitudinal sectional view of the optical module1cut at a position bisecting the length of the optical module1in the y direction. In the first embodiment, the vertical direction is determined along the z-axis of the coordinate system, and a side having a relatively large z coordinate is defined as an upper side and a side having a small z coordinate is defined as a lower side.

The optical module1is a module provided on an optical fiber connected to an optical component capable of inputting or outputting light. Here, the optical component refers to a component to which light can be input or output, and may be a component having an optical waveguide or a light source that outputs light. The shape of the optical component having the optical waveguide is not limited, and may be, for example, an optical fiber, a sheet-like or a plate-like PLC. In addition to the optical waveguide, the optical component may incorporate a structure for branching and coupling the optical waveguide, or an electrical element, or may be a component of a bulk optical system such as a lens or a prism.

As illustrated inFIGS.3and4, the optical module1includes: a case body10that forms a closed space C in which a part of optical fibers21,22is accommodated; a fiber fixing portion120(121,122) that fixes the optical fiber to predetermined position and shape inside the case body10; and a photodiode33that is a light receiving element attached inside the case body10at a position capable of receiving radiation light radiated from the optical fiber fixed to the fiber fixing portion120. The optical fibers21,22may be non-doped core fibers or may be optical fibers into which rare earth is injected.

Also in the first embodiment, the optical fibers21and22are connected to each other by fusion. In the first embodiment, the photodiode33observes radiation light radiated from the fused portion M of the optical fibers21,22. However, fusion is a widely used method for connecting optical fibers, and a connection loss in the fused portion M is small. In the first embodiment, light leaking from the fused portion M is efficiently received, and the intensity of light propagating through the optical fiber is monitored with a simple configuration and low loss as compared with the case of using a fiber coupler or a beam splitter. AlthoughFIG.4illustrates the configuration in which the photodiode33receives the radiation light Ls from above the fused portion M, the photodiode33is not limited to being provided above the fused portion M, and may be provided at any position as long as the position can receive the radiation light Ls having sufficient intensity for observation.

In the optical fibers21,22, the heat shrinkable tube25covers at least a radiation portion from which radiation light is radiated, and functions as a scattering member having a scattering coefficient of light larger than a scattering coefficient of the radiation portion. In the example illustrated inFIG.4, the heat shrinkable tube25covers a portion including the fused portion M to protect the fused portion. The radiation portion of the radiation light is the surface of the fused portion M, and the scattering coefficient of the heat shrinkable tube25is larger than a scattering coefficient of the surface of the fused portion due to the composition and surface roughness of the material and the shape of irregularities of the surface. By providing the heat shrinkable tube25, the degree of scattering of the radiation light of the optical fibers21,22increases, and the light is easily received by the photodiode33. According to such a configuration, the signal intensity of the radiation signal Ss output from the photodiode33can be increased, and the measurement accuracy of the radiation light can be increased.

The case body10includes an upper case portion11and a lower case portion12, and is configured such that the upper case portion11and the lower case portion12overlap and are screwed by a screw111. Packing portions112a,112bof rubber members, for example, are provided in the lower case portion12with the optical fibers21,22interposed therebetween, and cutout portions113a,113bhaving semicircular cross sections are formed in the packing portions112a,112b,respectively, in order to pass the optical fibers21,22. The upper case portion11has a base portion11bhaving a small length (hereinafter, referred to as “height”) in the z-axis direction and a convex portion11ahaving a height higher than that of the base portion11b,and the base portion11bcomes into contact with the packing portion112a.The material of the case body10is preferably a material that does not transmit light from the outside, and for example, metal or an opaque resin is preferable. When the case body10is made of metal, the degree of scattering of light in the closed space C can be increased, and the light intensity of radiation light received by the photodiode33can be increased.

FIG.5is a schematic top view of the optical module1illustrated inFIGS.3and4as viewed from above. InFIG.5, the upper case portion11is illustrated outside the lower case portion12by an imaginary line of a two-dot chain line in order to avoid overlapping with the lower case portion12.FIGS.6(a),6(b), and6(c)are cross-sectional views illustrating cross-sections of the lower case portion12taken along cross-sectional lines VIa, VIb, and VIc inFIG.5, respectively.FIG.6(a)is a view of a cross section along a cross-sectional line VIa as viewed in a direction of an arrow,FIG.6(b)is a view of a cross section along a cross-sectional line VIb as viewed in a direction of an arrow, andFIG.6(c)is a view of a cross section along a cross-sectional line VIc as viewed in a direction of an arrow.FIG.6(d)is a diagram illustrating a positional relationship between the cross section illustrated inFIG.6(c)and the optical fiber21and the photodiode33.

As illustrated inFIGS.5,6(a), and6(b), the fiber fixing portion120formed on the upper surface12aof the lower case portion12includes a fused portion fixing portion121having a shape along the heat shrinkable tube25that covers the fused portion M of the optical fibers21,22, and a non-fused portion fixing portion122having a shape along a portion of the optical fibers21,22that is not covered with the heat shrinkable tube25. Both the fused portion fixing portion121and the non-fused portion fixing portion122are groove-shaped recesses formed on the upper surface12a,the heat shrinkable tube25is fitted to the fused portion fixing portion121, and the optical fibers21,22are fitted to the non-fused portion fixing portion122. The non-fused portion fixing portion122illustrated inFIG.6(a)has the shortest length (width) in the y-axis direction illustrated inFIG.3in the fiber fixing portion120, and the fused portion fixing portion121illustrated inFIG.6(b)has a width larger than those of the optical fibers21,22by the thickness of the heat shrinkable tube25. The lengths (depths) in the −z-axis direction with respect to the upper surface12aof the fused portion fixing portion121and the non-fused portion fixing portion122are constant. The fused portion fixing portion121and the non-fused portion fixing portion122fix the optical fibers21,22in a state of being connected to each other in a certain position and shape.

In order to reliably fix the heat shrinkable tube25to the fused portion fixing portion121, for example, an adhesive may be placed in advance on the bottom surface of the fused portion fixing portion121, and the optical fibers21,22covered with the heat shrinkable tube25may be placed on the adhesive with the fused portion fixing portion121. For example, the wall surface along the length direction of the fused portion fixing portion121, which is a recessed portion, may be inclined so as to approach upward from the bottom surface. As described above, the heat shrinkable tube25fitted in the fused portion fixing portion121is less likely to come off upward, and the reliability of measurement of the radiation light of the optical fibers21,22can be enhanced. The non-fused portion fixing portion122is formed to have a width approximately equal to the diameter of the optical fibers21,22in order to prevent the upper surfaces12aof the optical fibers21,22from being flexed or bent. The optical fibers21,22are sandwiched between the packing portions112aand112bunder the base portion11b.For example, the packing portions112a,112b,which are rubber members, generate a relatively large frictional force between each other, and the reliability of fixing the optical fibers21,22can be further enhanced. With the above configuration, the optical fibers21,22are fixed without being bent inside the case body10.

The lower case portion12includes an element fixing portion123further above the fused portion fixing portion121formed on the upper surface12a.The element fixing portion123is a recess along the shape of the photodiode33. As illustrated inFIG.6(d), the photodiode33is partially fitted and fixed to the element fixing portion123at the time of receiving radiation light. According to such a configuration, since both the photodiode33and the heat shrinkable tube25can be fixed at the time of receiving radiation light, radiation light emitted from a certain portion of the optical fibers21,22can be always received at a certain position. In addition, since the photodiode33can be brought close to the optical fibers21,22and the heat shrinkable tube25, the intensity of radiation light received by the photodiode33can be further increased.

Optical Measurement Method

The optical measurement method performed using the optical module1of the first embodiment described above is an optical measurement method used to observe light propagating through the optical fibers21,22connected to an optical component. The optical measurement method according to the first embodiment includes: a step of receiving radiation light radiated from optical fibers21,22fixed to predetermined position and shape inside a case body10forming a closed space C; and a step of deciding intensity of the light propagating through the optical fibers21,22on the basis of intensity of the radiation light Ls that has been received. In such an optical measurement method, since the propagated light is observed using the radiation light reflecting the propagation light, even when visible light having a relatively short wavelength is observed, the optical measurement method is not affected by the photodarkening, and a highly reliable observation result can be obtained.

Alignment System

Next, an alignment system using the optical module1described above will be described.

FIG.7is a schematic diagram for explaining an alignment system100. The alignment system100is an alignment system that aligns the optical fibers21,22connected to the optical component. The alignment system100includes the optical module1described above, a light source5that allows light to enter at least a portion of the optical fiber21accommodated inside the case body from one end portion (hereinafter, also referred to as an “incident end portion”)27of the optical fiber21, and an alignment mechanism8that adjusts the position of at least one of the light source5and the incident end portion27on the basis of the radiation light received by the photodiode33. The light source5is, for example, a laser light source, and a condenser lens6is provided between the light source5and the incident end portion27. The laser light Lo emitted from the light source5is condensed by the condenser lens6and enters the incident end portion27. The incident end portion27is formed by, for example, end-capping the end portion of the optical fiber21facing the light source5.

The alignment system100illustrated inFIG.7adjusts an optical axis of a device including, for example, the light source5, the condenser lens6, the optical module1, and an optical component (not illustrated) connected to the optical fiber22extending from the optical module1. As such a device, for example, a measurement device that three-dimensionally measures an object can be considered.

The alignment system100includes a control unit3connected to the optical module1, the alignment mechanism8, and the light source. The control unit3controls a fixing position of the light source5and a fixing position of the incident end portion27. The fixing position of the light source5can be changed by, for example, attaching the light source5to a drive shaft (not illustrated) and causing the control unit3to output a control signal Sc1to the drive shaft to drive the drive shaft. The fixing position of the incident end portion27can be changed, for example, by the control unit3outputting a control signal Sc2to the alignment mechanism8and driving a fixing table (not illustrated) to which the incident end portion27is fixed. At this time, the control unit3inputs the radiation signal Ss from the optical module1, and specifies the positions of the light source5and the incident end portion27where the light intensity indicated by the radiation signal Ss is the strongest. Then, the control unit3outputs the control signal Sc1so as to fix the light source5at the specified position and the control signal Sc2to the alignment mechanism8so as to fix the incident end portion27.

As described above, the alignment system100is not limited to the configuration in which the positions of both the light source5and the incident end portion27are adjusted, and one may be fixed and the other may be adjusted. The control unit3may be a dedicated device that performs the above control, or may cause a general-purpose computer to execute the above control program. The control unit3includes a known central processing unit (CPU), a memory device, an interface used for input and output of information, and the like in order to control the light source5and the alignment mechanism8and further decide the intensity of the radiation signal Ss.

The alignment system100described above can compensate for the axial deviation caused by expansion and contraction of the member due to the fluctuation in the environmental temperature and vibration, and can stabilize the ratio (optical coupling rate) of the laser light emitted from the light source5taken into the optical fiber21over a long period of time. Since the alignment system100can make the optical coupling rate constant even in the case of using visible light having a relatively short wavelength, the optical fiber21can be easily replaced without fixing the light source5and the optical fiber21with an adhesive. It is known that an end surface of an optical fiber is deteriorated particularly by use for visible light having a short wavelength. Therefore, the alignment system of the first embodiment in which the optical fiber21is easily replaced is particularly suitable for alignment of a device using visible light having a short wavelength.

Second Embodiment

FIG.8is a diagram for explaining an overview of a second embodiment of the present invention. In an optical module9of the second embodiment, at least a part of an optical fiber28is inserted into a case body90in a bent state, and incident light Lin is incident from one end portion extending to the outside of the case body90and emission light Lout is emitted from the other end portion. Then, radiation light Ls radiated from the bent portion of the optical fiber28is received by a photodiode33. Such a configuration can increase the light intensity of the radiation light Ls and increase the measurement accuracy of the radiation light Ls. That is, it is known that the amount of light leaking (lost) from the core changes when the optical fiber is bent, and the amount of loss increases as the bending radius increases. In the second embodiment, the radiation light Ls is observed by bending the optical fiber28to such an extent that the amount of light leaking from the core of the optical fiber28increases and the amount of loss does not become a problem.

FIG.9is a diagram for explaining a configuration for achieving the above configuration, and is a schematic top view of the optical module9as viewed from above. The case body90of the optical module9is configured by combining an upper case portion91and a lower case portion92. InFIG.9, the upper case portion91is illustrated outside the lower case portion92by an imaginary line of a two-dot chain line in order to avoid overlapping with the lower case portion92.

The lower case portion92includes a fiber fixing portion281on an upper surface92a.The fiber fixing portion281includes a groove for fixing the optical fiber28in a bent state. The groove width of the fiber fixing portion281is designed to be about the same length as the diameter of the optical fiber28in order to prevent the optical fiber28from being flexed or detached. The optical fiber28is fitted into the groove of the fiber fixing portion281and is fixed in a state of curving along the shape of the fiber fixing portion281. At this time, the optical fiber28may be fitted into the fiber fixing portion281and temporarily fixed, and the optical fiber28may be reliably fixed with a thermosetting resin or the like after confirming that the photodiode33can receive radiation light having sufficient light intensity.

It is known that the optical loss of the optical fiber28changes depending on the degree of bending of the optical fiber, that is, the bending radius. In the second embodiment, the optical fiber28is bent and fixed within a range in which the optical loss is larger than in a state without bending, propagation of light is not hindered, and mechanical damage does not occur. As such a range, for example, it is conceivable to determine the range on the basis of the short term bend radius described in the specification table of the optical fiber. At this time, it is conceivable to set the bending radius of the optical fiber28to 2 cm or less. The fiber fixing portion281is formed on the upper surface92aas a groove having a curve matching the bending radius set in this manner.

As described above, in the second embodiment, the amount of radiation light leaking from the optical fiber28can be increased by bending, and the measurement accuracy of the radiation light can be enhanced. In the second embodiment, the fiber fixing portion281is formed on the upper surface92aof the lower case portion92to fix the optical fiber at a constant bending radius. Therefore, the light amount and the radiation position of the radiation light radiated from the optical fiber are fixed, and the radiation light can be stably received by the photodiode33. Also in the second embodiment, as similar to the first embodiment, a recess into which a part of the photodiode33is fitted may be provided together with the fiber fixing portion281, and the photodiode33may also be fixed. As a result, the second embodiment can further stabilize the state of radiation and reception of radiation light.

REFERENCE SIGNS LIST