JP4227558B2 - Inline type optical component and method for manufacturing the same - Google Patents

Description

  The present invention relates to an in-line type optical component used for an optical communication device and an optical sensor system.

  Along with the miniaturization of optical components and the integration of optical modules, in-line optical components of a type in which a minute optical element is mounted in a ferrule and made into one component have been proposed. As shown in FIG. 6, a single optical fiber 2 having a lens function is inserted and fixed in the through-hole of the ferrule 1, and a groove portion that divides the optical fiber 2 is formed in an intermediate portion, and functions such as an optical isolator are formed there. By mounting the optical element 3 having, the light source and the connector can be connected in the same manner as the ferrule alone. For the connection between the optical element 3 and the optical fiber 2 installed in the ferrule 1, an optical fiber having a lens function in which a core expansion fiber, a large-diameter single mode fiber, and a indexed index fiber are connected is used ( Patent Documents 1 and 2).

In recent years, a collimator using a mode field expansion and a low diffraction angle function of a photonic crystal fiber having a regular air hole in the cladding has been studied (Non-patent Document 1). An optical fiber having such a lens function is mounted and fixed in the groove portion of the ferrule intermediate portion, and the optical element 3 is mounted in the intermediate portion, thereby realizing a small in-line type optical component having a function by the optical element 3 mounted in the ferrule 1 is doing.
JP 2002-71963 A JP 2002-14253 A 2003 IEICE Electronics Society Conference C-3-40

  In the case of Patent Document 1, a Faraday rotator (refractive index: 2 to 2.3) having a high refractive index is used as an optical element, for example, and propagating light is transmitted through the optical fiber 2 (refractive index is about 1.5). When incident on a Faraday rotator inclined at a certain angle, the incident angle and the refraction angle are different due to the difference in refractive index with the optical fiber 2. As a result, the diffraction loss due to incidence and displacement on the other fiber increases. However, when a fiber having a single lens function is inserted into the ferrule 1 and a close-contact optical element is installed between them as in the prior art, it is difficult to correct the optical axis deviation Δ.

  That is, in order to correct the optical axis deviation Δ, when the optical axis deviation Δ is corrected using a member having a smaller refractive index (refractive index of about 1.3), the thickness of the member must be taken. The groove width L1 increases with the thickness, and the diffraction loss between fibers having a lens function increases.

  As described above, the problems to be solved in order to realize an in-line type optical component having a low loss and a high return loss in which an optical element is built in the middle part of the ferrule 1 are summarized as follows.

  (1) In order to prevent end face reflection, a groove is obliquely arranged in the middle of the ferrule 1 and the optical element 3 is obliquely installed at a maximum of about 8 degrees, so that the optical axis shift Δ due to the refractive index difference between the optical fiber 2 and the optical element 3 Occurs.

  (2) In order to correct the optical axis deviation Δ, a member having a refractive index different from that of the optical element 3 and the optical fiber 2 is added as an optical element separately. L1 must be taken longer and the loss increases.

  Unless the above is solved, it is difficult to realize an in-line type optical component in which the optical element 3 is mounted in the middle part of the ferrule 1 having a high return loss and low coupling between fibers.

In order to solve the above problems, the present invention provides a ferrule having a through hole in the center and having an inclined groove for dividing the through hole, an optical fiber inserted and fixed in both of the divided through holes, and the inclined An in-line type optical component is composed of two optical elements closely attached to the inclined end face so as to cover each end face of the optical fiber exposed in the groove, and the two optical elements include a Faraday rotator, an absorption type polarizer, It consists of a single unit or a combination of a group consisting of a birefringent crystal typified by a rutile crystal, a filter element, and an AR coat plate that prevents end-face reflection. Nearly the same, the thickness of the space portion is t0, the thickness of the one optical element is t2, the inclination angle of the inclined groove with respect to the plane perpendicular to the axis of the optical fiber is θ1, and the incident angle θ1 is the front of the optical fiber. T2 = [cos θ2 · sin (θ0−) where θ2 is the refraction angle when incident on one optical element, and θ0 is the refraction angle when incident on the space from the other optical element at the incident angle θ1. θ1)] / [cos θ0 · sin (θ1−θ2)] · t0 is satisfied .

Moreover, it is preferable that the vicinity of the end face exposed to the inclined groove of each optical fiber has a lens function . Further, it is preferable that the one optical element is an element in which an absorption polarizer and a Faraday rotator are in close contact with each other, and the other optical element is an absorption polarizer.

The one optical element is preferably a Faraday rotator, and the other optical element is preferably a band-pass filter element.

It is also preferable that the one optical element is a Faraday rotator, and the other optical element is an absorptive polarizing plate.

  Further, the tip of the optical fiber on the one end face of the ferrule is processed into a tip ball.

  From the above, the following excellent effects can be realized by using the inline-type optical component according to the present invention.

  End face reflection can be prevented by forming a groove in the ferrule middle portion at an angle θ1 and placing the optical element in close contact with the inclined surface.

  An optical axis shift occurs between two optical elements installed at an inclination. However, by providing a space between the optical elements, the optical axis shift can be corrected by the air layer having the thickness, and there is no optical axis shift. An optical system can be realized.

  The refractive index of the air layer in the space is 1, which is greatly different from the refractive indexes of the two optical elements and the optical fiber, and the optical axis deviation can be corrected at a short distance by a large refraction angle. Further, the groove interval can be reduced, and a low-loss optical system can be realized between the fibers.

  As described above, an in-line optical component having a low loss and a high return loss in which an optical element is mounted in a ferrule can be realized.

  Hereinafter, embodiments of the in-line type optical component of the present invention will be described.

  FIG. 1 is an example of an in-line type optical component of the present invention. The ferrule 1 to be used has an outer diameter of 1.25 mm or 2.5 mm, and a through-hole having an inner diameter of about 125 μm is processed inside, and the outer diameter and inner diameter are both precisely processed. . Examples of the material include ceramic materials such as zirconia and alumina, and metal materials such as glass and stainless steel.

  A single optical fiber 2 having a lens function is inserted into the ferrule 1, and is fixedly mounted with an adhesive at a position where the lens region is in the middle of the ferrule 1, and then the optical fiber 2 is divided. The inclined groove 1a is formed in the step. The inclined groove 1a is inclined at an angle θ1 with respect to a plane perpendicular to the optical axis of the ferrule 1 and has a width L1, and the optical fiber 2 has a lens function in the vicinity of the end face of the inclined groove 1a.

Two optical elements 3 , 4 are installed on the end face of the inclined groove 1 a and are in close contact with the end face of each optical fiber 2 by the translucent adhesive 5. The optical elements 3 and 4 include a Faraday rotator, an absorption polarizer, a birefringent crystal represented by a rutile crystal, a filter element, an AR coat plate for preventing end face reflection, and the like. , Used as one optical element.

For example, when an optical polarizer that uses an absorption polarizer and a Faraday rotator in close contact as the optical element 3 and an absorption polarizer as the optical element 4 , it is used as an optical isolator that removes reflected light reflected back to the semiconductor laser. Can do. In that case, since the garnet film (refractive index: 2.1 to 2.3) used as the Faraday rotator has a higher refractive index than the absorption polarizer (refractive index: 1.5), the optical elements 3 and 4 are used. Is tilted at an angle θ1, then an optical axis shift of Δ occurs. In order to suppress this, a space portion having a width L2 is provided between the optical elements 3 and 4 , and the optical axis deviation Δ previously generated due to the difference in refractive index from the space portion is canceled. Such an inline-type component can be mounted directly in the semiconductor laser module by processing the tip of the fiber on one side and making it directly connectable to the semiconductor laser (see FIG. 4 (e)). By taking out the optical fiber as it is from one end, it can be used as an output fiber for the semiconductor laser module. Further, by attaching a band pass filter function to the side surface of the space of the absorption polarizer of the optical elements 3 and 4 , unnecessary light other than the return light from the emitted light of the semiconductor laser can be removed.

Further, by using a Faraday rotator in the optical element 3, the band-pass filter element to the optical element 4, can be used as an in-line type Faraday rotation mirror. Such a component is used as a measurement component such as a Michelson interferometer to suppress interference between outgoing light and reflected return light.

  The shape of the ferrule 1 end is PC or APC polished on both sides so that the connector can be connected. Alternatively, the optical fiber 2 having a certain length from both ends or one end may be stretched as it is to have a pigtail configuration. Alternatively, the configuration may be such that one end of the optical fiber 2 is slightly extended from the end of the ferrule 1 and the end surface of the optical fiber 2 has a lens function so that it can be directly coupled to the semiconductor laser.

FIG. 2 is an enlarged detailed view of the inclined groove 1a of FIG. 1, in which optical elements 3 and 4 having thicknesses t1 and t2 having a slit width L1 are tilted by θ1 each with respect to the direction perpendicular to the optical axis. It is installed at the end of the optical fiber 2. The end of the optical fiber 2 and the optical elements 3 and 4 are bonded and fixed by a translucent adhesive 5. When the refractive index of the core of the optical fiber 2 is n1, the refractive index of the optical element 3 is n2, and the refractive index of the optical element 4 is substantially matched with the refractive index n1 of the fiber core . Further, the end faces on the space side of the optical elements 3 and 4 are AR-coated with a dielectric multilayer film to prevent Fresnel reflection. Light propagated through the core of optical fiber 2 having a lens function, enter the optical element 3 at an incident angle .theta.1, in refraction angle θ2 by the optical element 4, propagating in the optical element 3 having a thickness of t2. At that time, Δ = {t2 × sin (θ1−θ2)} / cos θ2 in the vertical direction from the optical axis due to the refraction angle θ2.
An optical axis deviation Δ expressed by

Thereafter, the light beam is incident at an incident angle θ 1 , propagates at a refractive angle θ 0 , and enters the optical element 4 at an incident angle θ 0 .

Here, the refractive index n0 of the space portion is
n0 <n1, n2
In order to eliminate the optical axis deviation Δ,
Δ = {t0 × sin (θ0−θ1)} / cos θ0
Should just hold. Thereby, the optical axis deviation Δ can be canceled.

In addition, since the refractive index of air in the space is small at n0 = 1, usually θ0> θ1, θ2
It becomes. The air layer thickness t0 of the space part is given by s0 as the optical path length of the space part.
t0 = s0 × cos θ0
It becomes. Therefore, if θ0 is large, the space interval t0 necessary for canceling the optical axis deviation Δ can be shortened.

The propagating light incident on the optical element 4 propagates at a refraction angle θ1, that is, propagates in a state parallel to the optical axis like the incident light.

FIG. 3 is a configuration example of the optical fiber 2 having a lens function inserted into the ferrule 1. (A) is a thing at the time of using the core expansion fiber 6 for the optical fiber which has a lens function. The core expansion fiber 6 diffuses Ge in the core by fixing the optical fiber 2 from which the protective coating has been removed straightly and heating it to 1500-1700 ° C. for about 10 to 30 minutes using a microburner that can be locally heated. The core can be expanded to 20-40 microns. Further, when the dopant is diffused, the core enlargement and the decrease in the relative refractive index difference occur at the same time. Therefore, the value is proportional to the normalized frequency. R × D ^1/2
However, r: Fiber core diameter D: The relative refractive index difference is constant, and the single mode condition is maintained.

When the core expansion fiber 6 is used, the numerical aperture of the fiber is {NA = (n1 ² −n2 ² )}
Becomes smaller and closer to parallel light. When the core diameter is expanded so that the mode field diameter of propagating light is expanded to about 40 microns, an interval (air) of about 1 mm can be obtained with a coupling loss of 1 dB. When propagating through a medium having a higher refractive index than air, that is,
n2> n0 = 1
In this case, the value of NA becomes smaller and more intervals can be taken.

  FIG. 3B shows an embodiment in which a refractive index distribution type multimode (GI) fiber is used as a lens. The GI fiber 7 has a substantially square refractive index distribution. This is formed by fusion splicing between fibers. Since the propagating light propagates in a sine wave shape, if it is cut at the peak of the sine wave, it is emitted as almost parallel light. Two GI fibers 7 having the lens function are prepared, and each of them is fusion-bonded to the end of the optical fiber 2. Then, the GI fibers 7 are connected to each other by a connection fiber 8. As the connection fiber 8, a large-diameter single mode fiber, a photonic crystal fiber, or the like is used. The inclined groove width L1 may be cut in the connecting fiber 8 to constitute a coupling system. The emitted light from the GI fiber 7 acts as a waveguide for collimator light in the connection fiber. If it cut | disconnects with the inclination groove | channel with the width | variety L1 in the connection fiber 8, it can be used as a coupling system.

  FIG. 4 is a diagram showing a manufacturing process of the in-line type optical component of the present invention. First, as shown in FIG. 4A, an optical fiber having a lens function at the center is prepared by cleaning the surface of the optical fiber with the protective coating removed. Next, as shown in FIG. 4B, a ferrule 1 longer than the length of the lens region is prepared, and an optical fiber 2 having a lens function is inserted into the inner hole of the ferrule 1 so that the lens region is at its center position. Then, fix with a thermosetting adhesive or solder material.

Next, as shown in FIG. 4C, a depth of about 70% of the diameter of the ferrule 1 is formed at the center of the ferrule 1 by a dicing machine at an angle θ1 and a width L1 with respect to the vertical direction of the ferrule optical axis. Then, the inclined grooves are formed by machining. Next, as shown in FIG. 4D, the optical elements 3 and 4 are fixed in close contact with both side surfaces of the formed inclined groove with a translucent adhesive 5 or the like.

  Finally, as shown in FIG. 4 (e), the end face of one ferrule is polished, and the fiber on the other face is extended by about 1 to 2 mm from the end of the ferrule, and the tip is processed. As the processing shape of the tip, there are conical shape, wedge shape, and cylindrical shape having a spherical tip.

  Note that the end surface of the ferrule 1 may be polished at both ends depending on the use conditions, or may be configured in such a manner that the fiber can be extended from one side or both sides and fused or connected to another optical fiber end. In short, it can be configured in any way depending on how it is used.

  FIG. 5 is a graph showing the characteristics of the core expansion fiber 6 used as a fiber having a lens function as the connection fiber 8 of the present invention. This shows the relationship between the inter-groove distance L1 and the diffraction loss when the mode field diameter is expanded to 35 μm and 40 μm. (Filled with refractive index matching agent between grooves) When a core expansion fiber with a mode field diameter of 35 to 40 μm is used, even when the groove interval is about 1 mm, the connection can be made with a loss of about 0.2 to 0.4 dB. it can. (B) shows the relationship between the inclination angle θ1 of the groove and the return loss. It can be seen that a high return loss of 40 to 50 dB or more can be obtained as the return loss when the inclination angle θ1 is about 3 °. .

  Hereinafter, specific examples of the present invention will be described.

A plurality of quartz single-mode optical fibers cut to about 1 m with a mode field diameter of about 10 μm were prepared, and a core expansion fiber was manufactured. By heating for about 20 to 30 minutes at about 1500 to 1700 ° C. using a microburner apparatus using oxygen and propane gas, a core expansion fiber having a mode field diameter of about 35 to 40 μm and a core expansion region of about 12 mm is obtained. It was. The portion was used as a connection optical fiber 8 and inserted into a zirconia ferrule having a diameter of 1.25 mm and a length of 15 mm, and fixedly mounted with a thermosetting epoxy adhesive. Thereafter, an inclined groove having an angle θ1 = 3 °, L1 = 780 μm, and a depth of 700 μm was formed in a middle portion of the ferrule 1 by a dicing machine. The optical element 3 on both sides of the groove is a Faraday rotator (refractive index n2 = 2.2) having a thickness t2 = 350 μm, and the optical element 4 is an absorptive polarizing plate (refractive index n1 = 1) having a thickness t1 = 200 μm. .5) was installed. The bonding surface with each fiber was bonded with a light-transmitting adhesive 5 having an end-surface antireflection film and matching the refractive index. The thickness of the layer of translucent adhesive 5 is about 5 μm. An AR coat was formed on the side surface of the space part of the Faraday rotator and the side surface of the space part of the absorption polarizer. Thereby, the width t0 of the space portion is 220 μm.

  Next, the fibers at both ends of the ferrule were cut and each end face was polished by a polishing machine.

As a result, an in-line type optical component having an optical isolator function of the configuration shown in FIG. 1 having an insertion loss of 0.6 dB and a return loss of about 50 dB at a wavelength of 1550 nm was obtained. By mounting it in the sleeve, it is possible to realize an in-line type optical component that is connected by a connector. If the Faraday rotator used for the optical element is a spontaneously magnetized garnet, no magnet is required. If not, a samarium cobalt magnet is used for applying a saturation magnetic field to the optical elements 3 and 4 in the inclined grooves . Install using the surrounding space. Alternatively, the optical element 3 may be composed of a composite element type (element thickness meter: 550 μm) in which an absorption polarizer and a Faraday rotator are closely bonded with an adhesive or the like. In the embodiment, when a birefringent crystal such as a rutile crystal is used as the polarizer of the optical elements 3 and 4 , it can function as an inline isolator.

The Example of the in-line type optical component of this invention is shown, (a) is a top view, (b) is the sectional view on the AA line of (a). It is the figure which showed the B section detail of FIG. The lens area | region of the fiber which has a lens function fixed to a ferrule intermediate part is shown, (a) is a figure at the time of using a core expansion fiber, (b) is a figure at the time of using a GI fiber. . (A)-(e) is a figure for demonstrating the manufacturing method of the in-line type optical component of this invention. (A) (b) is the figure which showed the characteristic of the core expansion fiber used by this invention. It is a figure which shows the conventional in-line type optical component.

Explanation of symbols

1. Ferrule 2. 2. Optical fiber Optical element 1
4). Optical element 2
5. Translucent adhesive 6. 6. Core expansion fiber GI fiber8. 8. Connection fiber Tip ball fiber 10. AR coat surface

Claims (6)

A ferrule having a through hole in the center and provided with an inclined groove that divides the through hole, an optical fiber that is inserted and fixed in both of the divided through holes, and an end face of each optical fiber exposed to the inclined groove is covered. Two optical elements that are in close contact with the inclined end surface, and are spaced apart from each other so as to have a space portion therebetween ,
The two optical elements consist of a Faraday rotator, an absorption polarizer, a birefringent crystal typified by a rutile crystal, a filter element, or a single unit or a combination of an AR coating plate that prevents end face reflection,
The other optical element has a refractive index substantially equal to the refractive index of the core of the optical fiber,
The thickness of the space portion is t0, the thickness of the one optical element is t2, the inclination angle of the inclined groove with respect to a plane perpendicular to the axis of the optical fiber is θ1, and the incident angle θ1 is from the optical fiber to the one optical element. When the refraction angle when incident is θ2 and the refraction angle when incident from the other optical element at the incident angle θ1 is θ0,
t2 = [cos θ2 · sin (θ0−θ1)] /
[Cos θ0 · sin (θ1-θ2)] · t0
An in-line optical component characterized by satisfying 2. The inline optical component according to claim 1, wherein the vicinity of the end face exposed to the inclined groove of each optical fiber has a lens function. The one optical element is an element and absorptive polarizer and the Faraday rotator are in close contact, the other optical element in-line type light according to claim 1, wherein it is absorptive polarizer parts. The one optical element is a Faraday rotator, the other optical element in-line type optical component according to claim 1, wherein it is a band-pass filter element. The one optical element is a Faraday rotator, the other optical element in-line type optical component according to claim 1, wherein it is absorptive polarizer. 6. The in-line optical component according to claim 1, wherein a tip of an optical fiber on one end face of the ferrule is processed into a tip.

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