JPH0682663A - Method for machining end surface part of optical fiber - Google Patents

Abstract

PURPOSE:To precisely and stably machine a spherical tip lens part which has, for example, a 5mum tip radius and low coupling loss without reference to changes in discharge state when a convex curved surface lens part is formed atop of an optical fiber by a discharge fusing method. CONSTITUTION:For the machining method which fuses a conic vertex part formed atop of the optical fiber 1 by arc discharge, light emitted by the fusing of the conic vertex part is monitored with a photodetector 7 installed at the other end part of the optical fiber 1. The output of this photodetector 7 is fed back to a discharger power source 5 and a limiter circuit 9 stops the discharge to control the shape of the fused end part, i.e., tip radius R. The light emitted from the fused end part shows the heating temperature and heated part length of the fused end part and the discharge is stopped on the basis of the monitored light intensity to obtain a desired tip radius R at all times regardless of changes in the discharge state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing an end face portion of a spherical optical fiber used for optical coupling with a semiconductor optical device such as a semiconductor laser or a semiconductor switch in the fields of optical communication and optical information processing. is there.

[0002]

2. Description of the Related Art For example, output light from a light emitting portion of a semiconductor laser spreads at an angle of several tens of degrees. Therefore, it is necessary to focus this output light and efficiently couple it to an optical fiber.
For such optical coupling between the semiconductor laser and the optical fiber,
There are an individual lens system in which a focusing lens is arranged between a semiconductor laser and an end of an optical fiber, or a tip lens system in which a lens is integrally formed at the tip of an optical fiber.

FIG. 5 shows an example of a tip lens type optical fiber 1 (front spherical optical fiber) in which a convex curved hemispherical lens portion 2 is formed at the tip processed into a conical shape. Since such a spherical optical fiber 1 has an advantage that it can be directly connected to the optical fiber without interposing an individual lens in connection with the semiconductor laser 3 and is easy to mount, it is used as a component for a semiconductor laser module with a fiber. Widely used.

In a module composed of a general-purpose InGaAsP semiconductor laser 3 and a 1.3 μm zero-dispersion single mode optical fiber 1 (core diameter of about 10 μm), a spherical optical fiber having a tip radius R = 10 μm is usually used. The coupling loss between the optical fiber 1 and the optical fiber 1 is 3 dB. on the other hand,
In a theoretical calculation example of the coupling loss, it has been reported that the coupling loss becomes 1 dB or less if the tip radius R = 5 μm can be achieved (for example, the 1990 National Conference of the Institute of Electronics, Information and Communication Engineers C-262 “Pulverized Beam”). LD using magnifying fiber
-Examination of SMF coupling system "Kazuo Shiraishi, Yoshizo Aizawa, Shojiro Kawakami).

For manufacturing such a spherical optical fiber, a melting method, which is one of the manufacturing methods, has been conventionally used. This melting method uses the discharge melting method which is also used when the end faces of the optical fibers are permanently connected. In this discharge melting method, an optical fiber whose tip is processed into a conical shape in advance is installed so that the tip is located in the arc discharge region of a pair of electrodes, and the cone apex and its vicinity are melted by discharge. Is. The melted end portion is rounded by the surface tension, whereby a minute lens portion 2 is formed at the tip end portion. The radius R of the tip spherical surface of the lens portion 2 is
The control was performed under previously determined conditions such as the installation position of the tip in the discharge area.

[0006]

According to the discharge melting method as described above, a relatively large tip spherical surface having a radius R of 10 μm or more can be manufactured. However, if the radius R is set to 10 μm or less in order to improve the coupling loss, it becomes difficult to manufacture the tip with a desired tip radius. This is because the atmospheric discharge depends on the state of the atmosphere (weather), and the discharge electrode is repeatedly worn and deformed by the discharge, and the discharge state fluctuates every moment. In the conventional melting method, R = 10 μm or less. Moreover, it was impossible to obtain reproducibility of heating conditions to control the tip shape. Therefore, the laser module using the spherical optical fiber has an advantage that the number of parts is small, but has a problem that the coupling loss is only 3 dB.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to improve the controllability of the radius R of the tip of an optical fiber in the conventional melting method, regardless of fluctuations in the discharge state. , Always relatively small tip radius (5 μm
The present invention provides a method of processing a front-end fiber end surface portion that can accurately and stably process a front-end lens portion having a low coupling loss, and can be achieved with a relatively simple device configuration. .

[0008]

In order to achieve the above-mentioned object, the present invention provides a processing method for forming a convex curved lens at the apex of a cone processed at the end of an optical fiber by a melting method as follows. It was configured. That is, the characteristic difference from the conventional one is that the light generated by melting of the apex of the cone is monitored by a light receiver installed at the end of the optical fiber on the side opposite to this melting end, and the output from this light receiver is monitored. Is returned to the melting device to control the shape of the melting end. The processing procedure is as follows: While holding the optical fiber in the vicinity of the conical end so that its optical axis is parallel to the direction of gravity and the conical apex of this end is located below the direction of gravity, Asymptotically approaching the electric discharge machining area, and the light generated by melting of the apex of the cone is monitored by a light receiver installed at the end of the optical fiber on the side opposite to this melting end, and the output from this light receiver is The process consists of stopping the discharge when a predetermined value is reached. Further, the processing method of the present invention is mainly applied to a silica single mode fiber for communication, and an optical filter for blocking a shorter wavelength side than the primary mode cutoff wavelength of the optical fiber is installed on the monitor side of the optical fiber. It is provided between the end of and the light receiver.

[0009]

In the structure as described above, the fused end of the optical fiber is heated by the discharge to generate light. The generated strength becomes stronger as the temperature at the melting end is higher and the heating area is wider. Although light is generated isotropically, light is generated within the core of the optical fiber, and the light included in the opening angle propagates through the fiber and reaches the opposite end. Therefore,
If this light intensity is monitored by a light receiver, the heating temperature and heating length of the melting end can be known, and by controlling the melting device based on this monitored light intensity, the atmospheric conditions during discharge and the discharge electrode It is possible to obtain the desired shape of the melting end, that is, the tip radius R having a small diameter, accurately and stably regardless of the worn state. In addition, if the monitor light intensity reaches a predetermined value with a limiter circuit etc. in the melting device, if the discharge is stopped, the optical fiber will only be brought closer to the arc discharge region and the discharge will occur when the predetermined melting state is reached. Therefore, it is possible to automatically obtain a spherical optical fiber having a predetermined tip radius R regardless of the change in the discharge state.
The reason why the apex portion of the cone is arranged downward in the direction of gravity (vertical direction) is to cool and solidify the shape of the apex portion of the melted cone into a hemispherical shape symmetrical with respect to the optical axis of the optical fiber. Further, by using the optical filter, the monitor light is only single mode light with low propagation loss, and it becomes possible to control the melting end portion and the tip radius R more precisely regardless of the length of the processed fiber.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to an illustrated embodiment. FIG. 1 is a schematic view showing an electric discharge melting apparatus for carrying out the processing method of the present invention. The optical fiber 1 is a silica single mode optical fiber for communication with a zero-dispersion wavelength of 1.3 μm (core diameter: 10 μm). The tip 1a is conical with a tip angle of 85 ° and the apex is on the central axis of the core C. Is processed to match. The discharge melting device includes a pair of discharge electrodes 4 arranged horizontally opposite to each other, a discharge power source 5 connected to the pair of discharge electrodes 4, and an optical fiber 1.
Is provided with a moving device 6 for moving back and forth with respect to the discharge electrode 4.

The moving device 6 is located above the discharge electrode 4 and holds the processed end of the optical fiber 1 so that the optical axis thereof is parallel to the vertical direction and the conical apex is vertically downward, It is a device that moves in a predetermined stroke in a predetermined direction. The distance between the discharge electrodes 4 is 1.3 mm, and the center of the arc discharge area A by the discharge electrodes 4 is set to be located on the central axis of the optical fiber 1 set in the moving device 6.

In the discharge melting apparatus having such a structure,
A light receiver 7 is connected to the other end of the optical fiber 1 via an optical filter 8, and a limiter circuit 9 is added to the discharge power supply 5. The light receiver 7 is a photodiode that receives light from the processed end of the optical fiber 1 and outputs a voltage proportional to the amount of light, and the head has a sensitivity wavelength range of 0.75 to 1.7 μm.
m, an InGaAs light receiving element having an optical power measuring range of 1 pW to 1 mW is used.

The optical filter 8 is a filter that blocks wavelengths shorter than the primary mode cutoff wavelength, for example, wavelengths of 1.2 μm or less, and allows only single-mode light with low propagation loss of monitor light to pass. . Limiter circuit 9
Is a commonly used comparator that is electrically connected to the photodetector 7, compares the output voltage from the photodetector 7 with a set value, and turns off the discharge power supply 5 when the output voltage exceeds the set value. Circuit.

With the above structure, processing is performed as follows. (1) An optical fiber having an 85 ° cone processed at one end is attached to the moving device 6, and the other end is connected to the light receiver 7 via the optical filter 8. (2) For example, the monitor light intensity, that is, the light-receiver output, at which the tip radius R of 5 μm is obtained, is obtained in advance, and this is set in the limiter circuit 9 as a limiter setting value. (3) The moving device 6 is lowered at a predetermined speed, and the optical fiber 1
The tip of the is gradually approached to the arc discharge region A, and the apex of the cone is melted. (4) When the predetermined melting state is reached, the output of the photodetector exceeds the limiter setting value and the discharge stops. The light receiver output, that is, the monitor light intensity, represents the heating temperature of the melting portion and the heating portion length, and is always the desired melting state, that is, the tip radius R of 5 μm, regardless of the atmospheric state at the time of discharge and the worn state of the discharge electrode 4.
Is obtained.

Next, a numerical example of actual processing using the above-mentioned apparatus will be shown. While the arc discharge is generated by the pair of discharge electrodes 4, the moving device 6 causes the conical tip end of the optical fiber 1 to approach at a speed of 0.3 mm / sec, and the limiter circuit 9 works to cause the discharge. The relationship between the output of the light receiver (intensity of monitor light) when stopped and the tip radius R of the lens portion 2 formed by melting processing was examined.

FIG. 2 shows the time dependence of the monitor light output when the limiter set value of the discharge power source 5 is set to 26 pW in terms of monitor light intensity conversion. From this FIG. 2, the monitor light intensity increases as the fiber tip approaches the arc discharge region A, and when it reaches 26 pW, the discharge stops, and thereafter,
It can be seen that the temperature gradually decreases as the temperature of the fusion zone of the fiber tip decreases. The tip radius R at this time was 5 μm ± 1 μm as a result of measurement with a laser microscope.

FIG. 3 is a graph of the tip radius R obtained when the limiter value is set to various values from 19.5 pW to 42 pW in terms of monitor light intensity conversion. The tip radius R is
It was possible to control from 3 μm to 10 μm with an accuracy of ± 1 μm or less. When the monitor light intensity during the limit operation was 19 pW or less, the tip portion did not become a hemisphere although there was a trace of melting.

Next, in order to confirm the effect of the present invention, the optical coupling characteristics between the spherical optical fiber 1 and the semiconductor laser 3 produced as described above were examined. The laser 3 used for the characteristic measurement is the full width at half maximum θ _V , θ in the vertical and horizontal directions of the emission angle
InG with 1.3 μm output where _H is 35 ° and 25 ° respectively
aAsP laser. As shown in FIG. 4, the minimum loss of 0.9 dB was obtained at the tip radius of 5 μm ± 1 μm.

In this case, neither the tip lens portion 2 nor the other coupled light monitor portion is provided with an antireflection coating, and proper antireflection coating is applied to both ends of the spherical optical fiber to eliminate Fresnel loss. Then, a further decrease in coupling loss of 0.3 dB can be expected, and a module with a low coupling loss of 0.6 dB can be obtained. The R value that gives the minimum coupling loss and the coupling loss value at that time are in good agreement with the theoretical trial calculations of the above-mentioned documents, and according to the present invention, ideal control of the tip R is possible.

In the above description, a spherical optical fiber used for optical coupling between a semiconductor laser and a single mode optical fiber has been described, but the present invention is not limited to this, and a spherical optical fiber coupled with other optical elements can also be used. It goes without saying that the invention can be applied. Also, an example has been shown in which the limiter circuit is used to control the melting device to stop the discharge, but the present invention is not limited to this, and other control methods can also be adopted.

[0021]

As described above, according to the present invention, when the end of an optical fiber processed into a conical shape is melt processed, a light receiver is provided at the other end to monitor the melted state, Since the shape of the melting tip is controlled based on the output, it is possible to precisely control the tip radius of a relatively small diameter regardless of the atmospheric conditions during discharge and the wear state of the discharge electrode, and theoretical calculation is required. Stable machining of the optimum tip radius. In addition, the equipment that realizes this is, for example, a general-purpose fiber fusion splicing device is partially modified for the electric discharge melting device,
An optical power meter for the optical communication wavelength range may be used as the light receiver, which can be inexpensively constructed. Therefore, according to the present invention, a semiconductor optical device such as a semiconductor laser and 1d
It is possible to inexpensively supply a high-performance spherical optical fiber that optically couples with an extremely low loss of B or less,
It greatly contributes to the realization of a low-noise semiconductor optical amplifier.

[Brief description of drawings]

FIG. 1 is a schematic view showing an electric discharge melting apparatus for carrying out the processing method of the present invention.

FIG. 2 is a graph showing the time change of the monitor light output during melt processing according to the present invention.

FIG. 3 is a graph showing a relationship between a limiter setting value and a tip radius R according to the present invention.

FIG. 4 is a graph showing a relationship between a tip radius R of a spherical optical fiber and a coupling loss with a semiconductor laser.

FIG. 5 is a schematic view showing an arrangement state of a semiconductor laser and a spherical optical fiber.

[Explanation of symbols]

 1 Optical Fiber 2 Lens Part 3 Semiconductor Laser 4 Discharge Electrode 5 Discharge Power Supply 6 Moving Device 7 Light Receiver 8 Optical Filter 9 Limiter Circuit

Claims (3)

[Claims] 1. A method for processing an end face of an optical fiber in which an end of an optical fiber is processed into a conical shape whose apex coincides with the center of a core, and a convex curved lens portion is formed on the apex of this cone by a melting method, The light generated by the melting of the apex is monitored by a light receiver installed at the end of the optical fiber on the side opposite to this melting end, and the output from this light receiver is returned to the melting device to form the shape of the melting end. A method for processing an end face of an optical fiber, characterized in that 2. A method for processing an end face of an optical fiber, wherein an end of an optical fiber is processed into a conical shape whose apex coincides with the center of a core, and a convex curved lens part is formed at the apex of this cone by a fusion method. A step of making the conical apex part asymptotically closer to the electric discharge machining region while holding the vicinity of the conical apex part such that its optical axis is parallel to the direction of gravity and the conical apex part of this end part is located downward in the direction of gravity. , The light generated by the melting of the apex of the cone is monitored by a light receiver installed at the end of the optical fiber opposite to the melting end, and the discharge is stopped when the output from the light receiver reaches a predetermined value. A method for processing an end face of an optical fiber, comprising the steps of: 3. The optical filter according to claim 1 or 2, wherein an optical filter for blocking a wavelength shorter than a primary mode cutoff wavelength of the optical fiber is provided between the monitor-side end of the optical fiber and the light receiver. A method for processing an end face portion of an optical fiber, characterized in that