JPH085864A - Formation of spherical end fiber lens - Google Patents

Abstract

PURPOSE:To easily form a spherical end fiber lens having a prescribed focal length with high accuracy. CONSTITUTION:An optical fiber fusing device 2 which balls up the front end of an optical fiber 10 by electric discharge heating, a light source device 1 and a photodetector 3 which introduces the light from the light source 1 to the other end of the optical fiber 10 and determines the focal length by keeping the light radiated from the ball up end of the optical fiber 10 and detecting the radiation light are provided. The signal from the photodetector 3 is fed back and the discharge power, discharge time, etc., of the optical fiber fusing device 2 are adjusted, by which the prescribed focal length is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a spherical fiber lens in which light emitted from an optical fiber has a predetermined focal length.

[0002]

2. Description of the Related Art Conventionally, grinding has been used as a method of processing the tip of an optical fiber into a lens shape. There is also a method in which the front end portion of the optical fiber is heated and melted to form a front spherical fiber lens. A method has been proposed in which the state of ball-up during melting and heating is image-processed, and the image is monitored, and heating is stopped when the amount of pull-in matches a preset pull-in amount.
However, this method has a very strict relationship between the position of the light leaking from the end of the core when melted, the positional relationship between the tip of the front ball and the radius of curvature of the front ball, and moreover, the point where the light leaks from the end of the core. When it cannot be regarded as a light source, it is difficult to obtain a predetermined focal length. That is, even if the outer shape of the front sphere is the same, there is variation in the relationship between the position where light leaks as the point light source at the core end portion and the radius of curvature. Therefore, when trying to obtain a fiber lens having a fixed focal length, variations tend to occur, which is a problem.

[0003]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention In order to make almost parallel rays and to form a front-end fiber lens having a predetermined focal length, the radius of curvature of the front-end ball and the discharge power and the discharge time for melting. It is intended to provide a method for producing a front spherical fiber lens which has good reproducibility and is easy to control by adjusting a predetermined focal length.

[0004]

As a method of melting the tip of the optical fiber 10 by the optical fiber melting device 2 to form the front spherical fiber lens 20, for example, when the focal length is infinite, that is, when parallel rays are obtained. It is known that the distance L between the core end of the optical fiber that can be regarded as a point light source and the tip of the tip sphere should be about three times the average radius of curvature R of the tip sphere. In such a case, the photodetector 3 for detecting the focal length
An optical sensor is provided behind the optical slit having a predetermined opening area, or the optical fiber 11 for detecting light serving as an optical slit having a predetermined opening area detects that the light beam is substantially parallel and feedback is performed. Discharge power
And control the discharge time. Further, when the front spherical fiber lens 20 having a large radius of curvature is produced, a feeding mechanism may be provided in the clamp of the optical fiber melting device 2 for fixing the fiber to be melted and heated for control.

Further, during discharge heating in the optical fiber melting device 2, light having wavelengths in various regions is radiated, so that the light introduced into the optical fiber 10 is current-modulated by a chopper or a laser diode. By introducing the signal light modulated by the above, and using the bandpass filter having the wavelength of the signal light, the signal light component can be accurately and accurately detected from the ambient light by the photodetector 3.

For example, when an LED is used to generate a signal light by a current modulation signal, an electric modulation signal from an oscillator is used as a reference signal, or the signal light is divided into two, one of which is a fiber for processing a sphere and the other is a reference light. It is also possible to separate the signal light from the ambient light with a large SN ratio by performing synchronous detection like a lock-in amplifier. Of course, at this time, if a bandpass filter for the signal light is used, SN will be further improved.
The ratio can be increased. When the wavelength of the signal light is 1.3 μm, 1.3 μm introduced from the optical fiber for photodetection 11 is used.
An interference filter that passes m light may be provided in the photodetector 3 as a bandpass filter.

When the optical fiber 11 for detecting light having a focal length for the light emitted from the ball-up end during melting is used, one optical fiber 11 and two or more optical fibers 11 parallel to each other at a constant interval from the optical axis are used. By installing it, information on the light intensity distribution can be obtained, and a more accurate front spherical fiber lens 20 having a predetermined focal length can be obtained.

[0008]

When the present inventors make a calculation formula based on Snell's law to calculate the spherical fiber lens 20,
When the light is emitted into the air (refractive index n2 is about 1.0), the distance L between the core end portion A and the center portion C of the optical axis at the tip of the tip ball.
However, a theory and a method of making parallel rays can be obtained by forming the tip so that it has a radius of curvature R of about 3 times the average radius R near the center of the optical axis (Japanese Patent Application No. 6-1222).
No. 11).

In order to produce the front-end fiber lens 20, the optical fiber melting device 2 is used to melt and heat the tip of the fiber for ball-up. At this time, what is important is the relationship between the average radius of curvature R of the front ball and the distance L from the center of the optical axis at the tip of the front ball to the end of the core.

In the present invention, for example, in order to obtain a parallel light beam, light is introduced from the other end of the front spherical fiber and is emitted from the ball-up end, and from the position where the front sphere is formed on the optical axis. While the light intensity is monitored by the optical fiber 11 for light detection of the photodetector 3 having the focal length arranged at a sufficiently distant place, the ball is raised. The light intensity gradually increases as the distance L from the tip of the tip ball to the end of the core becomes shorter, and the distance L from the tip of the tip to the end of the core becomes almost three times the average radius of curvature R of the tip. By the way, it becomes maximum, and at that time, if the discharge power and discharge time of the optical fiber melting device 2 are stopped, almost parallel rays can be obtained.

Further, it is preferable that different optical fibers are fusion-spliced to the core end portion of the optical fiber, and a predetermined distance from that position is cut by a fiber cutter to form a sphere. In this way, the radius of curvature of the tip sphere can be made the same size by keeping the distance from the end of the core cut by the fiber cutter constant, and it is possible to suppress the variation of the radius of curvature of the tip sphere. is there.

[0012]

Examples of the invention

[0013]

Embodiment 1 FIG. 1 shows a block diagram of an apparatus used for carrying out the present invention. First, a single-mode optical fiber (core diameter 10 μm, cladding diameter 125 μm) is used as the optical fiber 10, and is cut by a fiber cutter perpendicular to the central axis thereof, and a core end portion 51 is formed on the cut surface. Similarly, different optical fibers are cut into the optical fiber 10, and the cut surface of the optical fiber 10 and the end surface of the different optical fiber are abutted and melted and connected by the optical fiber melting device 2. Here, the different optical fibers to be connected are
Optical fibers without a core are preferred. The melting condition at this time is that the discharge current as the discharge power is 15.1 mA,
The discharge time is 2.5 seconds. Then, about 1 mm on the different fiber side is cut from the fusion-spliced position with a fiber cutter provided in the optical fiber melting device 2. The tip of this connected 1 mm-long optical fiber is melted and heated to slightly raise the ball, and then the LED of the light source device 1 (wavelength:
The signal light 40 of 1.3 μm) was introduced and emitted from the ball-up end. Then, for example, an electrical reference signal 41 from the light source device 1 is introduced into the photodetecting device 3, and the photodetection optical fiber 11 having a focal length connected to the photodetecting device 3 is introduced.
Was set on the optical axis of the optical fiber melting device 2 at a position about 1 mm away from the position where the front ball was formed. 1 mm
When the focal length of 1 was obtained, the discharge current as the discharge power was set to 19.3 mA, and the cut surface was discharge-heated to be spherical as shown in FIG. 2 (a). In this case, the light emitted from the tip sphere has a focal point on the optical axis, but the average radius of curvature R is still small, so the distance L from the tip of the tip sphere to the core end portion 51 is 3 of the average radius of curvature R of the tip sphere. It is longer than twice, and the light receiving intensity depends on the discharge time as can be seen from the graph of the light receiving intensity with respect to the discharge time in FIG. When the light is melted with a constant discharge current, the intensity of the received light gradually increases, and the light has a peak at a certain time (tf). At this time, as shown in FIG. 2B, the light emitted from the tip of the front sphere has a focus on the end face of the optical fiber 11 for detecting light having a focal length, is guided to the core 52, and is focused in the present embodiment. When the distance is set to 1 mm, the intensity of light coupled to the optical fiber 11 for light detection shows the maximum (about 0.2 μW), and at this time, the electric feedback signal 42 controls the discharge to stop. did. As a result, the front spherical fiber lens 20 having a focal length of about 1 mm could be produced. At this time, if the light detecting optical fiber 11 is set on the optical axis of the optical fiber melting device 2 at a position sufficiently distant from the position where the front sphere is formed, it is possible to obtain a parallel light beam. When the discharge is further continued, the average radius of curvature R is as shown in FIG.
Since the distance L from the tip of the front sphere to the end of the core 51 becomes shorter than three times the average radius of curvature R, the light emitted from the front sphere diverges and the received light intensity is as shown in FIG. Will decrease.

[0014]

[Embodiment 2] FIG. 4 shows another structural diagram of an apparatus used for carrying out the present invention. The fibers used are the same as in Example 1. Moreover, although the creation method is almost the same, the detection method of the focal length is different. Here, the optical fiber 1 for transmitting an optical signal from the LED of the light source device 1
3 is connected to the beam splitter 5, the signal light 40 is branched, and one of them is cut to produce an optical fiber 10 for producing a spherical lens.
Is introduced at the other end (40A) and emitted from the cut surface. Then, the other is introduced into the optical fiber 12 that transmits an optical signal to form the signal light 40B. Then, the signal light 40B is introduced into the photodetector 4 and converted into a reference signal 41 such as an electric signal. Then, the reference signal 41 is introduced into the photodetector 3. In addition, the optical fiber 11 for light detection having the focal length connected to the light detection device 3 was set on the optical axis of the optical fiber melting device 2 at a position about 5 mm away from the position where the front sphere was formed. The discharge current was set to 19.3 mA and the cut surface was melted and heated to be spherical. Then, when the light intensity reaches the maximum (about 0.2 μW), for example, the electric feedback signal 42 is controlled so that the discharge is stopped. As a result, the front spherical fiber lens 20 whose area that can be regarded as a parallel light beam is up to about 5 mm could be produced.

In the above embodiment, the optical fiber 1 for photodetection is used.
Although 1 was used as an optical slit having a predetermined opening area, although not shown here, an optical slit such as a pinhole is actually formed and introduced into the optical sensor through a bandpass filter that passes signal light. Is also good.

While particular embodiments of the present invention have been illustrated and illustrated herein, it will be appreciated by those skilled in the art that modifications and changes can be readily made. Therefore, the claims are intended to be construed to cover such modifications and equivalents other than the above-described embodiments.

[0017]

According to the present invention, the discharge current of the optical fiber melting device 2 is used to make the light beam emitted from the front-end fiber into a substantially parallel light beam or to form the front-end fiber lens 20 having a predetermined focal length. Also, by adjusting the discharge time and the like, it can be easily and highly accurately prepared.

Further, it is possible to provide the front spherical fiber lens 20 according to the use such as connecting the fiber to devices such as various sensors, and the range of application thereof is expanded.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus used for carrying out the present invention, in which a signal light 40 from a light source device 1 is emitted from a tip sphere of an optical fiber 10 and is received by a photodetector device 3, and at the same time, the light source device 1 is used. A reference signal 41 such as an electric signal from the optical fiber is introduced into the photo-detecting device 3, and the signals are synchronized to the optical fiber melting device 2 so that the discharge is stopped at the maximum light intensity.
Send a feedback signal 42.

FIG. 2 is a diagram illustrating a relationship among a distance L, an average radius of curvature R, and a focal length f when the front spherical fiber lens 20 is formed. (A) When the distance L is longer than three times the average radius of curvature R at the initial stage of melting of the front ball and the focal length f is between the front fiber lens 20 and the optical fiber 11. (B) When the melting time of the tip ball is adjusted and the distance D from the tip of the tip ball to the optical fiber 11 is equal to the focal length f due to the relationship between the distance L and the average radius of curvature R. (C) When the melting time of the front sphere is too long, the distance L is shorter than three times the average radius of curvature R, has a negative focal length, and the light diverges.

FIG. 3 shows the relationship between the received light intensity I and the discharge time t in the detection optical fiber (the discharge power is constant). When t = tf, the received light intensity becomes maximum.

FIG. 4 is another configuration diagram of an apparatus used for carrying out the present invention, in which a signal light 40 from a light source device 1 is branched by a beam splitter 5 and one is emitted from a tip sphere of an optical fiber 10. (Signal light 40A), the detection device 3 receives the light,
The other (signal light B) is simultaneously introduced into the photodetector 4, converted into a reference signal 41 such as an electric signal, and introduced into the photodetector 3. Then, a feedback signal 42 is sent to the optical fiber melting device 2 by synchronizing the signals so that the discharge is stopped at the maximum light intensity.

[Explanation of symbols]

 1. Light source device 2. Optical fiber melting device 3. Photodetector 4. Photodetector 5. Beam splitter 10. Optical fiber 11. Optical fiber 12. Optical fiber 13. Optical fiber 20. Tip spherical fiber lens 30. Electric discharge machining needle 40. Signal light 40A. Signal light 40B. Signal light 41. Reference signal 42. Feedback signal 50. Core of the spherical fiber 51. 52. End of the core of the spherical fiber 52. Optical fiber core

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisayuki Miyagawa Kitagawa Harayama, Kawauchi, Kawasaki, Shibata-gun, Miyagi Prefecture 228 Tohoku Nakataniuchi Co., Ltd. (72) Koji Endo Kawasaki, Shibata-cho, Miyagi Prefecture 228 Tohoku Nakatani Co., Ltd.

Claims (6)

[Claims] 1. A method for producing a front-end fiber lens in which the tip of an optical fiber is melted and balled up to form a lens, which is used as a lens, in which the tip of the optical fiber (10) is discharge-heated and balled up. The melting device (2), the light source device (1), and light from the light source device (1) are introduced into the other end of the optical fiber (10), and this light is emitted from the ball-up end of the optical fiber (10). The optical fiber melting device (2) is provided with a photodetector (3) that emits light and detects the emitted light to determine the focal length, and feeds back the signal from the photodetector (3) to the optical fiber melting device (2). Then, the discharge power, discharge time, etc. of the optical fiber melting device (2) are adjusted so that a predetermined focal length can be obtained. 2. A light source device (1) to an optical fiber (1
The method for producing a front spherical fiber lens (20) according to claim 1, wherein the light introduced into 0) is signal light. 3. An electric or optical signal synchronized with a signal from the light source device (1) is used as a reference signal.
A method for producing the described spherical fiber lens (20). 4. The front spherical fiber lens according to claim 1, further comprising a photodetector (3) provided with an optical sensor behind an optical slit having a predetermined opening area so as to obtain a predetermined focal length. 20) How to create. 5. The method for producing a front spherical fiber lens (20) according to claim 4, wherein an optical fiber (11) is used as an optical slit having a predetermined opening area. 6. A method in which two or more optical fibers are used, at least one of which is arranged on the optical axis of an optical fiber lens (20), and the focal length is determined from information of light passing through these optical fibers. Item 5. A method for producing a spherical lens (20) having a spherical tip.