JP2005292843A - Optical transmission device and optical pulse tester - Google Patents

Abstract

【Task】
An optical branching coupler for bidirectional transmission capable of efficiently guiding received light from an optical fiber to a photodetector.
[Solution]
The optical fiber junction 44 is branched into two, a detector coupling optical waveguide 40 and a branch coupling optical fiber 80. The cross-sectional area of the detector coupling optical waveguide 40 is changed from the optical fiber junction 44 to the photodetector. The optical fiber 80 for branching and coupling is provided substantially perpendicularly to the end face of the optical fiber joint 44.
[Selection] Figure 1

Description

  The present invention relates to an optical branching coupler, an optical transmission device, and an optical pulse tester, and more particularly, to an optical branching coupler for multiplexing and separating light in two-way communication using an optical fiber, and the optical branching coupler. The present invention relates to optical transmission equipment and optical pulse testing machines.

  Patent Document 1 discloses a synthetic resin optical branching coupler that has a tapered shape and a straight shape that are narrowed according to the direction in which light is coupled, and that has a light-emitting end surface of a transmission path that branches light has a lens shape. Yes.

  In addition, there is a bidirectional data link that inputs and outputs light using an optical branching coupler and performs bidirectional communication using one optical fiber. For example, Non-Patent Document 1 is cited as a related device of this type.

Furthermore, Non-Patent Document 2 discloses that a polarization beam splitter is used as the optical coupling separation element and a wavelength of 532 is used as the light source.
An optical pulse tester that measures the transmission loss of a plastic optical fiber (hereinafter POF) using a Q-switched YAG laser of nm has been announced.

JP-A-9-159863 "Applied technology of plastic optical fiber" p.82-87 (Denki Shoin, 1988) Proceeding of Plastic Optical Fibers Confernce 98, 290-295

  A conventional optical branching coupler has a tapered waveguide end face as a coupling portion with a light emitting element, and is provided with a taper so that light incident from the light emitting element to the optical branching coupler is narrowed down. In the taper shape, it is joined to the straight waveguide portion on the narrowed side. However, when the light is narrowed down using a tapered shape like a conventional optical branching coupler, the incident angle to the interface between the core and the cladding increases each time the light is reflected by the tapered portion, which exceeds the critical angle. Light leaks out of the core, causing loss. In addition, when the cross-sectional shape of the light guide portion on the light receiving side is larger than the light detection portion of the photodetector, the amount of light incident on the light detection portion is reduced. In the conventional optical branching coupler, the light exit end face has a lens shape and collects light and guides it to the photodetector. However, the shape of the optical branching coupler becomes complicated, and the optical branch coupler is manufactured. There was also a problem that became difficult.

  Further, the conventional bidirectional data link has a problem in that the transmission distance is shortened due to a large optical loss in the optical branching coupler. For example, when an optical fiber that branches light in a ratio of 1: 1 is used, 50% of the light transmitted through the optical fiber is simply branched in a direction different from the branch to the detection side. Further, if the loss due to the coupler itself is included, the amount of light that can be detected is 50% or less of the light transmitted through the optical fiber. Furthermore, when a conventional optical branching coupler is used, a part of the light beam that has entered the optical fiber from the light emitting element through the optical waveguide section is larger than the critical angle of the optical fiber, and thus a loss occurs.

  As described above, in the conventional bi-directional data link using the optical branching and coupling, there is a problem that the optical loss becomes large as a whole because optical loss occurs in both transmission and reception. . Furthermore, since the bandwidth is reduced, it is difficult to use for high-speed communication. For this reason, the conventional bidirectional data link has a problem that the communication distance is very short, and it can be used only for low-speed communication over a short distance.

  Furthermore, in the conventional optical branch coupling and the bidirectional data link using the conventional optical branch coupling, the transmission light is incident on the optical fiber obliquely. For this reason, the loss in the optical fiber has increased and the bandwidth has been reduced.

  Further, the conventional optical pulse tester uses PBS for branching and coupling light. Therefore, it is necessary to use a lens in order to couple the detection light from the optical fiber to the photodetector. When PBS is used, more than half of the detection light is lost in PBS. Furthermore, in order to couple light emitted from an optical fiber having a large core diameter and numerical aperture, such as POF, to a photodetector using a lens, a very bright large-diameter lens is required, but such a lens is expensive. Yes, the distance from the optical fiber to the photodetector becomes long, and the device becomes large. Further, even if such a bright lens is used, the light cannot be focused on a sufficiently small spot, and the detection efficiency is lowered. Therefore, when an optical fiber having a large core diameter and numerical aperture, such as POF, is measured with an optical pulse tester, there is a problem that the detection efficiency is low and the measurable distance becomes very short. In the conventional optical pulse testing machine, the measurable distance is lengthened by using a high-power Q-switched YAG laser. However, the Q-switched YAG laser has a problem that it is expensive and has a large apparatus.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide an optical branching coupler for bidirectional transmission that can efficiently guide received light from an optical fiber to a photodetector. Is to provide.

  Another object of the present invention is to provide a high-speed optical transmission apparatus that can increase the transmission distance by using this bidirectional transmission optical branching coupler and further efficiently coupling the transmission light from the light source with the optical fiber.

  It is another object of the present invention to provide a compact optical pulse tester having an improved measurable range using a bi-directional transmission optical branching coupler that can efficiently guide received light from an optical fiber to a photodetector.

In order to achieve the above object, the present invention provides:
In an optical branching coupler having an optical waveguide portion branched into at least a first optical waveguide and a second optical waveguide from the junction, the cross-sectional area of the first optical waveguide is branched from the junction. The second optical waveguide has a configuration of an optical branching coupler provided substantially perpendicularly to the end face of the joint portion.

  Further, the present invention provides a photodetector for detecting a light beam from an optical fiber, and at least a first optical waveguide and a second optical waveguide for joining the optical fiber, the light source, and the photodetector, respectively. The first optical waveguide is joined to the photodetector, and the cross-sectional area of the first optical waveguide is from the optical fiber to the light. The optical transmission device has a tapered shape that decreases in the direction of the detector.

  Further, a modulation unit that converts an input signal to be transmitted into a signal for transmission, a light source, a photodetector, and a drive unit that drives the light source to transmit a signal modulated by the modulation unit, An optical waveguide unit that guides an optical signal from the light source to the outside, and guides an optical signal from the outside to the photodetector, and which joins at least two optical waveguides of the first optical waveguide and the second optical waveguide; and An optical transmission unit having a detection drive unit that drives the photodetector, and a demodulation unit that demodulates the signal detected by the photodetector into an electrical signal, and the cross-sectional area of the first optical waveguide is It has a tapered shape that decreases from the input side of the signal transmitted from the outside toward the photodetector, and the second optical waveguide is in contact with the end face of the joint with the first optical waveguide. It is assumed that the optical communication apparatus is configured substantially vertically.

  Further, a light source, a light detector, a light branching / coupling unit for guiding a light beam from the light source to a measurement object, and a light beam from the measurement object to the light detector, and detected by the light detection unit An optical unit that amplifies a detection signal; an information processing unit that processes a signal amplified by the amplification unit; and a drive unit that drives the light source in response to an instruction from the information processing unit, The section is formed by joining at least the first optical waveguide and the second optical waveguide, and the cross-sectional area of the first optical waveguide is directed from the input side of the signal transmitted from the outside toward the photodetector. The second optical waveguide has a configuration of an optical pulse tester provided substantially perpendicular to a joint end surface with the first optical waveguide.

  As described above, according to the present invention, it is possible to provide an optical branching coupler for bidirectional transmission capable of efficiently guiding received light from an optical fiber to a photodetector.

  In addition, a high-speed optical transmission device that can increase the transmission distance can be provided by using this bidirectional transmission optical branching coupler and further efficiently coupling the transmission light from the light source with the optical fiber.

  Furthermore, it is possible to provide a small optical pulse tester having an improved measurable range by using a bidirectional transmission optical branching coupler that can efficiently guide the received light from the optical fiber to the photodetector.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of an optical branching coupler and an optical transmission apparatus according to the present invention. The optical transmission apparatus according to this embodiment includes an optical branching coupler 20, a semiconductor laser 10 as a light source, a photodetector 12, a drive circuit, a detection circuit, an input terminal, and an output terminal not shown in the figure. The semiconductor laser 10 is connected to the light source junction 46 of the optical branching coupler 20, the photodetector 12 is connected to the photodetector junction 48, and the optical fiber 22 is abutted against the optical fiber junction 44. An optical signal from the semiconductor laser 10 driven by the drive circuit based on the signal input from the input terminal is output to the optical fiber 22 through the optical branching coupler 20. The optical signal transmitted from the partner optical transmission device through the optical fiber 22 is detected by the photodetector 12 through the optical branching coupler 20, processed by the detection circuit, and output from the output terminal.

  In this way, bi-directional communication using one optical fiber reduces the number of optical fibers compared to the case of using one optical fiber for each transmission and reception. Fiber can be laid. In addition, the optical transmission device and the optical connector can be reduced in size.

The optical branching coupler 20 of the present embodiment includes a detector coupling optical waveguide section 40 of the first optical waveguide section and a branch coupling optical fiber 80 of the second optical waveguide section. The branch coupling optical fiber 80 is fitted in a groove portion 82 formed in the detector coupling optical waveguide section 40, and the branch coupling optical fiber 80 and the detector coupling optical waveguide section 40 are joined in the groove section 82. Has been. The signal light from the semiconductor laser 10 is collected by the ball lens 60 and is incident on the branch coupling optical fiber 80. The signal light incident on the branch coupling optical fiber 80 passes through the optical fiber joint 44 and enters the optical fiber 22. The photodetector joint portion 48 of the detector coupling optical waveguide portion 40 is directly joined to the photodetector element 13 in the photodetector 12. Further, the detector coupling optical waveguide section 40 is tapered so that the diameter becomes smaller toward the photodetector 12, and the signal light is efficiently transmitted to the photodetector element 13 having a diameter smaller than that of the optical fiber. Can lead. The photodetector element 13 is encapsulated by the encapsulating resin 14 including the detector coupling optical waveguide portion 40 so as not to be deteriorated by exposure to the atmosphere.

  In this embodiment, a POF having a core diameter of 1 mm is used for the optical fiber 22, and a hard polymer clad fiber (HPCF) having a core diameter of 200 μm and a fiber outer diameter of 230 μm is used for the branching optical fiber 80. Therefore, of the optical signal transmitted through the optical fiber 22, the amount of light lost by branching to the branch coupling optical fiber 80 side is about 5%, and the remaining 95% is the detector coupling optical waveguide section 40. Branch to the side. Therefore, the branching loss due to the optical branching coupler 20 is small, and the amount of received light can be increased. Further, the center line of the branch coupling optical fiber 80 is installed so as to be substantially parallel to the center line of the optical fiber 22 at the optical fiber junction. That is, the transmission light from the branch coupling optical fiber 80 is emitted substantially perpendicular to the surface of the optical fiber joint 44. Therefore, compared to the case where the center line is inclined, the amount of light incident on the detector coupling optical waveguide portion 40 out of the signal light reflected by the end faces of the optical fiber joint 44 and the optical fiber 22 is reduced, and at the time of transmission. Crosstalk is reduced. Furthermore, since an optical fiber is used, handling is easy and the mounting position of the semiconductor laser 10 can be freely determined.

  FIG. 2 shows a procedure for manufacturing the optical branching coupler 20 of this embodiment. First, as shown in FIG. 2 (a), the detector coupling optical waveguide section 40 having the groove 82 matched to the outer shape of the branch coupling optical fiber 80 is injected using polymethacryl methacrylate (PMMA) which is a transparent resin. The core portion was formed by molding. A thin film having a low refractive index was vapor-deposited using barium fluoride on the detector coupling optical waveguide section 40, and a metal film was formed thereon using gold. Next, as shown in FIG. 2 (b), the branch coupling optical fiber 80 was fitted into the groove portion 82, and the end surface thereof was bonded to the surface of the optical fiber joint portion 44.

  Since the branch coupling optical fiber 80 is used, light does not leak to the detector coupling optical waveguide section 40 in the middle, and crosstalk does not occur. In the detector coupling optical waveguide section 40, the low refractive index film becomes a cladding layer, and the signal light incident on the detector coupling optical waveguide section 40 is totally reflected at the interface between the core section and the cladding layer, and is detected by the photodetector 12. Led to. Even if the signal light leaks out, the interface between the core portion and the clad layer is reflected by the outer metal layer and returns to the detector coupling optical waveguide section 40. Most of the signal light incident on the optical waveguide section 40 is detected by the photodetector 12.

  Instead of the branch coupling optical fiber 80 of this embodiment, the optical waveguide portion may be formed integrally with the detector coupling optical waveguide portion 40.

  An embodiment of the optical communication apparatus of the present invention will be described with reference to FIG. FIG. 3 is a configuration diagram of the optical communication apparatus. Bidirectional communication is performed between the optical transmission apparatus 100 and the optical transmission apparatus 101. The optical communication apparatus 102 includes an optical transmission apparatus 100, a modulation circuit 120 that modulates an input signal, and a demodulation circuit 122 that demodulates and outputs a signal detected by the optical transmission apparatus 100. In this embodiment, a plastic optical fiber is used as the optical fiber 22, and the optical fiber 22 and the optical transmission device 100 are coupled by an optical connector 24. An optical signal sent from the optical transmission apparatus 101 to the optical transmission apparatus 100 through the optical fiber 22 is detected by the photodetector 12 through the optical branching coupler 20 and output to the detection circuit 112 as a digital signal whose waveform has been shaped. . The signal from the detection circuit 112 is demodulated by the demodulation circuit 122 according to the format of the electric signal and output. The electrical signal input to the optical communication device 102 is converted into a code suitable for transmission as an optical signal by the modulation circuit 120 and sent to the drive circuit 110. The semiconductor laser 10 is driven by the drive circuit 110, and an optical signal is transmitted to the optical fiber 22 through the optical branching coupler 20. By exchanging between the modulation circuit 120 and the demodulation circuit 122, collision of optical signals in the optical fiber 22 can be detected. That is, at the time of transmission, the signal reflected by the end face of the optical fiber 22 and detected by the photodetector 12 is compared with its own transmission signal. If there is a difference, the signal is also sent from the optical transmission device 101. And can detect a collision. Alternatively, when a light amount larger than the light amount detected by the photodetector 12 is detected during normal transmission, it can be determined that a collision has occurred. When a collision is detected, transmission may be performed again by a predetermined procedure, such as resending after waiting for a certain time.

  In order to detect a collision in this way, the amount of light detected by the photodetector 12 due to the crosstalk of the optical branching coupler 20 is sent from the optical transmission device 101 in consideration of the power budget and margin of the system. What is necessary is just to make it become below the minimum light quantity which comes. When crosstalk is large and a collision cannot be detected, bidirectional communication can be performed by performing time-division communication. On the contrary, full-duplex communication can be performed when the optical data transmitted from the other party can be reproduced even if the transmission is low in crosstalk.

  FIG. 4 is a configuration diagram of another embodiment of the optical branching coupler of the present invention. The optical branch coupler core 30 includes a light source coupling optical waveguide section 38 and a detector coupling optical waveguide section 40, and is embedded in the optical branch coupler cladding 32. The semiconductor laser 10 is coupled to the light source junction 46 of the light source coupling optical waveguide section 38, and the photodetector 12 is coupled to the photodetector junction 48 of the optical waveguide section 40 for detector coupling. Is enclosed. In this embodiment, the light source coupling optical waveguide portion 38 and the detector coupling optical waveguide portion 40 are integrally formed by injection molding. The detector coupling optical waveguide section 40 has a shape in which a part of a cone is cut out, and the diameter increases from the photodetector joint section 48 side to the optical fiber coupling section 44. The light source coupling optical waveguide portion 38 has a cylindrical shape and a substantially constant thickness. The end face of the optical coupling / separation element core 30 is polished, the semiconductor laser element 11 and the photodetector element 13 are joined, and the optical coupling is performed so as to cover the optical coupling / separation element core 30, the semiconductor laser element 11 and the photodetector element 13. A separation element cladding 32 was formed. The semiconductor laser element 11 and the photodetector element 13 input and output electrical signals through terminals not shown.

In this embodiment, the light source coupling optical waveguide section 38 is straight and the central axis is substantially parallel to the central axis of the optical fiber 22, and one end of the detector coupling optical waveguide section 40 is connected to the central axis of the optical fiber 22. It is characterized by being almost parallel. Therefore, the emitted light from the semiconductor laser element 11 does not spread in the light source coupling optical waveguide section 38 and enters the optical fiber 22. A light beam obliquely incident on the optical fiber 22 has a large loss and decreases the band of the optical signal. However, when the signal light is incident straight as in this embodiment, this loss is increased and the band is decreased. Can be suppressed. When light is transmitted to a step index type plastic optical fiber having a length of 50 m and a numerical aperture of 0.3 using the optical branching coupler of this embodiment, the bandwidth of the optical fiber is 275 MHz, but the angle is 7 °. When the incident optical branching coupler was used, the frequency dropped to 200 MHz. By making the signal light incident straight, the occurrence of crosstalk due to reflection at the end face can be reduced. Further, by making one end of the detector coupling optical waveguide section 40 substantially parallel to the central axis of the optical fiber 22, loss caused by the total optical reflection condition being deviated in the detector coupling optical waveguide section 40 can be suppressed. it can. Furthermore, the optical transmission device can be reduced in size by integrating the optical separator / coupler with the semiconductor laser element 11 and the photodetector element 13.

  FIG. 5 is a block diagram of still another embodiment of the optical branching coupler of the present invention. The signal light incident on the light source coupling optical waveguide 38 from the light source junction 46 is reflected by the reflecting surface 42 and then enters the optical fiber. This optical branching coupler 20 was produced using photolithography. First, a clad layer was formed on a substrate, and a core layer was formed thereon. The core layer was formed into a waveguide shape by photolithography. A clad layer was again formed thereon, and a reflective surface 42 was formed again by photolithography. In this embodiment, the core cross section has a quadrangular shape. The light source coupling optical waveguide section 38 and the detector coupling optical waveguide section 40 have the same height, but the detector coupling optical waveguide section 40 becomes narrower as it approaches the light source side. The waveguide portion 38 maintains substantially the same width. Since photolithography is used, it can be manufactured in large quantities at the same time.

  In this embodiment, since the light source and the light detector can be installed apart from each other, the light source and the light detector do not interfere with each other even when the light source and the light detector are large or when the optical branching coupler 20 is small. can do. As in this embodiment, since the detector coupling optical waveguide section 40 is tapered so that the diameter decreases toward the photodetector side, the light source coupling optical waveguide section 38 and the detector coupling optical waveguide are provided. Both of the waveguide portions 40 can have the central axis parallel to the central axis of the optical fiber. Thus, by making the central axis of the detector coupling optical waveguide section 40 parallel to the central axis of the optical fiber, the loss due to reflection in the detector coupling optical waveguide section 40 can be minimized.

  In addition to the above-described embodiments, the light source, the photodetector, and the optical branching coupler can be coupled using an optical fiber, so that the interval between the light sources or the photodetectors can be widened and the mounting can be facilitated. it can. Or you may give a curvature to the optical waveguide part for light source coupling | bonding.

Here, the relationship between the taper-shaped dimension of the photodetector joint 48 and the optical constant will be described with reference to FIG. In the present embodiment, light is focused using a tapered optical waveguide so that light can be efficiently guided to a photodetector having a small area even when a large core optical fiber is used. . Here, for the sake of simplicity, the case where the diameter of the optical fiber joint 44 is the same as the core diameter of the optical fiber 22 and the optical axes of the photodetector joint 48 and the optical fiber 22 coincide will be described. Since the light beam propagating through the optical fiber 22 propagates while causing total reflection at the interface between the core 34 and the clad 36 of the optical fiber 22, only the light beam that forms an angle within a certain range with respect to the optical fiber 22. 22 can be passed. Assuming that the numerical aperture of the optical fiber 22 is NA _f and the refractive index of the core of the optical fiber is n _cf , where ψ is the maximum angle of the light beam that can be transmitted through the optical fiber 22 with respect to the optical fiber 22,

It is expressed as Here, the numerical aperture NA of the optical fiber and the optical branching coupler is defined as follows, where n _{core is} the refractive index of the _core and n _clad is the refractive index of the cladding.

It is represented by Conditions under which the light propagating at the maximum angle ψ with respect to the optical fiber 22 is totally reflected and propagates in the tapered photodetector joint 48 until reaching the photodetector. When the angle of the taper portion of the detector coupling optical waveguide section 40 is α, the incident angle of the light beam on the optical waveguide interface is
π- (ψ + α)
It becomes. Therefore, when the numerical apertures of the optical fiber and the optical waveguide are equal, this light beam does not cause total reflection, and most of the light is transmitted through the optical waveguide interface. The present invention is characterized in that the numerical aperture of the optical waveguide is made larger than the numerical aperture of the optical fiber. The incident angle to the optical waveguide interface at the n-th reflection at the optical coupler interface is
π− {ψ + (2n−1) α}
It becomes. In order for this ray to cause total reflection at the optical waveguide interface, if the refractive index of the core is n _cw and the numerical aperture is NA _w ,

It is necessary to satisfy. In order for the number of reflections of light propagating at an angle ψ to the optical fiber 22 to be n or less, the length l of the detector coupling optical waveguide section 40 is:

It is necessary to satisfy. However, if the radius of the optical fiber joint 44 is R, d _i is

Is required. The radius r of the photodetector joint 48 when the length of the detector coupling optical waveguide 40 is l is:

(Equation 6)
r = R-ltanα (6)
It becomes. It is desirable to set α and l so that r is as small as possible. By selecting the shape of the optical waveguide and the optical constant so as to satisfy the expressions (3) and (4), ideally, all the light beams incident from the optical fiber 22 to the optical waveguide unit 40 for detector coupling are detector coupled. Since light is totally reflected at the interface of the optical waveguide section 40 and reaches the photodetector, the light use efficiency can be increased. The effect of improving the photodetection sensitivity by reducing the beam diameter using this taper shape is larger when the core diameter is larger. Usually, it is bonded to a plastic optical fiber having a core diameter of 0.5 mm or more, especially the core diameter of about 1 mm. When used, the effect is great.

FIG. 8 shows the taper angle α of the optical waveguide portion and the reduction ratio of the diameter of the tapered optical waveguide calculated using the equations (1) to (6). It can be seen that in order to obtain the same reduction ratio, the taper angle α can be reduced as the number of reflections n increases. A smaller taper angle α is desirable because an optical branch coupler can be easily manufactured. FIG. 9 shows the numerical aperture NA _W of the optical branching coupler calculated using the equations (1) to (6) and the reduction ratio of the diameter of the tapered detector coupling optical waveguide portion. In the calculation, NA _f = 0.3, NA _w = 0.5, n _cf = n _cw = 1.5, and a value that maximizes l was used. From the figure, it is seen that a large numerical aperture NA _w of the optical waveguide is large, the effect of beam reduction. About n = 2 and 3, the same characteristic is shown. A smaller number of reflections is desirable because loss due to reflection is less likely to occur. Therefore, the desirable number of reflections n is 1 to 3, and it can be said that n = 2 is particularly desirable. When NA _f = 0.3, NA _w = 0.5, n _cw = 1.5, R = 0.5 mm, and n = 2, l = 4.5 mm and r = 0.29 mm, and the beam diameter is 58 %, So that the energy density of light is improved three times. From FIG. 9, when the numerical aperture of the optical branching coupler is 1.5 times or more the numerical aperture of the optical fiber to be joined, the area ratio is preferably 0.4 or less. Furthermore, if the numerical aperture of the optical fiber is set to be twice or more, it is more preferable that the reduction ratio of the beam diameter is 0.5 or less and the area ratio is 0.25 or less. A plastic optical fiber having a numerical aperture of 0.3 is used for high-speed communication. Therefore, the numerical aperture of the optical waveguide is preferably 0.45 or more, preferably 0.6 or more. The wavelength normally used for optical communication is about 570 nm to 1550 nm, and it is sufficient that the wavelength used is within this range as long as the numerical aperture.

  As described above, it is desirable that the numerical aperture, that is, the refractive index difference between the core portion and the clad portion is large, because the effect of optical confinement becomes large. In order to increase the numerical aperture, a low refractive index dielectric film may be formed at the interface between the core portion and the cladding portion. Furthermore, if a metal film is further formed at the interface between the dielectric film and the clad, the beam diameter that exceeds the numerical aperture and the beam that has passed through the dielectric film is reflected back by the metal film. It becomes.

  As an example of the optical branching coupler, polystyrene (refractive index 1.59) was used as the core material, and polymethylpentene (refractive index 1.46) was used as the cladding material. At this time, the numerical aperture is 0.63 at a wavelength of 650 nm. Therefore, as obtained from FIG. 9, using n = 2, the diameter reduction ratio becomes 0.4 and the area ratio becomes 0.16.

  The case where the optical axes of the photodetector joint 48 and the optical fiber 22 coincide with each other has been described above. However, the photodetector joint 48 can be provided inclined with respect to the optical fiber 22. Although the loss is caused by tilting the photodetector joint 48, the photodetector joint 48 and the optical fiber 22 are less than an angle at which one side of the photodetector joint 48 is parallel to the optical axis of the optical fiber 22. This is desirable because no significant increase in loss occurs from the case where the optical axes of the two coincide. Further, it is possible to prevent loss by reducing the taper angle.

  Next, with reference to FIG. 7, the inclination of the light source coupling optical waveguide section 38 will be described under the condition that all rays incident on the optical fiber from the light source coupling optical waveguide section 38 are totally reflected at the optical fiber interface. The spread angle θ of the light beam when the light beam of the spread angle Θ from the light source enters the optical fiber is

It becomes. If the inclination of the light source coupling optical waveguide 38 is β, this light ray is totally reflected at the interface of the optical fiber.

It is necessary to satisfy. If β is increased, the distance between the light source and the photodetector can be increased, so that the mounting of the light source and the photodetector becomes easy. In that case, it is necessary to make θ smaller than the equation (8). A semiconductor laser has a smaller divergence angle θ than a light emitting diode. One example of a light source that is particularly suitable as a light source for use in the optical transmission device of the present invention is a surface emitting semiconductor laser. Usually, the spread angle of a surface emitting semiconductor laser is about 5 ° in 1 / e ² half angle, and NA _s is about 0.09. If NA _f = 0.3, NA _s = 0.1, n _cf = 1.5, β may be 7.7 ° or less, and if the radius of the light source coupling optical waveguide section 38 is s, NA _{When w} = 0.5, n _cw = 1.5, R = 0.5 mm, r = 0.29 mm, s = 0.125 mm, l = 4.3 mm, and n = 2, the light source junction 46 and light detection The distance from the instrument joint 48 is 0.5 mm. For a plastic optical fiber having a numerical aperture of 0.3 for high-speed communication, the distance between the light source coupling optical waveguide section 38 and the detector coupling optical waveguide section 40 can be widened by setting sinΘ to 0.1 or less. desirable. A pinhole for limiting the divergence angle between the light source and the light source coupling optical waveguide 38 when the divergence angle of the light source is large, as in the case where an edge-emitting semiconductor laser or a light emitting diode is used as the light source. May be provided. Alternatively, the light source coupling optical waveguide 38 may be tapered so that the cross-sectional area increases from the light source joint 46 to the optical fiber joint 44. If the light from the light source has an intensity distribution, the 1 / e ² half angle of the intensity distribution may be used as Θ in equation (10).

  Thus, even if the light source coupling optical waveguide 38 is disposed obliquely with respect to the optical fiber, the signal light can be efficiently incident on the optical fiber. However, when light is incident obliquely on the optical fiber, the transmission loss in the optical fiber increases and the transmission band also decreases. Therefore, it is desirable that the inclination between the light source coupling optical waveguide section 38 and the optical fiber is small. An almost parallel arrangement is most desirable.

By making the diameter of the light source coupling optical waveguide section 38 smaller than the diameter of the optical fiber joint section 44, the light quantity incident on the optical branching coupler 20 from the optical fiber 22 is branched to the detector coupling optical waveguide section 40. The ratio of the amount of light that is generated can be increased. Since the branching ratio is substantially proportional to the area of each optical waveguide section, for example, when the diameter of the light source coupling optical waveguide section 38 is ¼ of the diameter of the optical fiber joint section 44, the light source coupling optical waveguide section 38 and the detection are detected. The ratio of the ratio of the amount of light branched into the optical coupling 40 for coupling is approximately 1: 9. Thus, by setting the diameter of the light source coupling optical waveguide portion 38 to ¼ or less of the diameter of the optical fiber joint portion 44, the optical loss is desirably 10% or less. By making the diameter of the light source coupling optical waveguide section 38 to be 1/10 or less of the diameter of the optical fiber joint section 44, the optical loss is more preferably 1% or less. Therefore, when a plastic optical fiber having a core radius of 0.5 mm is used, the radius of the light source coupling optical waveguide section 38 is 0.125 mm or less, preferably 0.15 mm, compared to the radius of 0.5 mm of the optical fiber joint 44. It is desirable to set it to 05 mm or less.

  The core and clad materials of the optical branch coupler of the present invention are acrylic, methacrylic, carbonate, amorphous olefin, sulfone, silicone, vinyl, fluorine, so as to have a desired numerical aperture. These compounds can be used in appropriate combination. Since the optical branching coupler of the present invention is characterized by its shape, the material is not limited to an organic material, and a transparent inorganic material such as glass, silicon oxide, or silicon nitride, or a thin film material may be used. In addition, the manufacturing method is appropriately selected, such as a method of manufacturing an optical waveguide such as an injection shaping method, an ultraviolet curing method, a wet etching method, a reactive ion etching method, a photopolymerization method, or a method of joining optical fibers. A branch coupler may be manufactured.

  The cross-sectional shape of the optical branching coupler of the present invention is not necessarily the same as the optical fiber to be joined, and for example, a quadrangular cross-sectional shape may be used. In the case of a square cross-sectional shape, the length of one side of the optical fiber joint is made larger than the diameter of the optical fiber, and the light source coupling optical waveguide unit 38 is all circularly emitted from the light source coupling optical waveguide unit 38. What is necessary is just to shift and join from a light source junction part so that it may inject into this optical fiber. By shifting in this way, light can be efficiently coupled to an optical fiber having a circular cross-sectional shape even when a rectangular cross-sectional shape is used.

  So far, the optical branching coupler branched into two has been described, but the present invention is not limited to two, but can be applied to the case where two or more branches are branched.

FIG. 10 is a configuration diagram of an embodiment of the optical pulse testing machine of the present invention. The optical pulse tester 150 of this example uses an optical time domain reflectometry (OTDR). The semiconductor laser 10 is pulse-driven by the drive circuit 130 and emits pulsed light. The pulsed light is collected by the ball lens 60, passes through the optical fiber 84, adjusts the light amount by the optical attenuator 66, and enters the optical branching coupler 20. The light enters the optical fiber 22 to be measured from the optical branching coupler 20. The detection light scattered and reflected in the optical fiber 22 returns to the optical fiber 86 from the optical branching coupler 20 and is detected by the photodetector 12. The signal detected by the photodetector 12 is amplified by the amplifier 132 and taken into the processor 136. The signal processed by the processor 136 is displayed on the display. The processor performs processing such as signal integration, smoothing, peak detection, loss measurement, time distance conversion, and switching between Rayleigh scattering and Fresnel reflection measurement based on input from a panel (not shown). The start / end of light pulse generation and the light pulse width of the drive circuit 130 are controlled by the processor 136. The trigger signal output from the drive circuit 130 in synchronization with the generation of the optical pulse is delayed by a predetermined time by the delay circuit 134 and input to the processor 136. The processor 136 starts capturing the signal from the amplifier 132 based on the trigger signal from the delay circuit 134. Further, the transmittance of the optical attenuator 66 and the gain of the amplifier 132 are controlled so that the signal from the amplifier 132 becomes a predetermined level.

  In this embodiment, the semiconductor laser 10 having a wavelength of 650 nm is used, and the photodetector 12 is a silicon avalanche photodiode. The gain of the signal can also be adjusted by controlling the voltage applied to the avalanche photodiode.

FIG. 11 shows an embodiment of the optical branching coupler and optical system used in this embodiment. As the optical branching coupler 20, the one already described in FIG. 4 is used. The pulsed light from the semiconductor laser 10 is collected by the ball lens 60 and enters the optical fiber 84 using a hard polymer clad fiber (HPCF) having a core diameter of 100 μm. The amount of light of the optical pulse is adjusted by an optical attenuator 66 provided in the middle of the optical fiber 84, enters the light source coupling optical waveguide unit 38 from the light source junction 46 of the optical branching coupler 20, and is coupled to the optical fiber 22. Is done. The optical fiber 22 is connected to the optical pulse tester 150 using the optical connector 24 so as to come to a predetermined position. The detection light scattered and reflected in the optical fiber 22 is collected by the detector coupling optical waveguide section 40 of the optical branching coupler 20 and guided to the optical fiber 86. The photodetector element 13 is coupled to the other end of the optical fiber 86, and the photodetector element 13 is sealed with a sealing resin including the optical fiber 86 so as not to be deteriorated by exposure to the atmosphere. . The optical fibers 84 and 86 are coupled and fixed to the optical branching coupler 20. In this embodiment, a POF having a core diameter of 0.5 mm and a numerical aperture of 0.6 is used for the optical fiber 84. Moreover, the diameter of the optical fiber joint end was 1.1 mm. Therefore, an OTDR measurement can be efficiently performed for an optical fiber having a core diameter of 1.1 mm or less. In this embodiment, the position of the optical branching coupler 20 can be moved so that pulsed light can be efficiently incident on an optical fiber having a small diameter. The optical branching coupler 20 is moved with respect to the optical fiber 22 so that the detected light quantity becomes maximum. That is, for an optical fiber with a small diameter, the optical branching coupler 20 may be moved upward in the figure. By moving in this way, in this embodiment, even in an optical fiber having a core diameter of 150 μm, more than half of the detection light from the optical fiber can be coupled to the photodetector. That is, an optical fiber having a core diameter of 1.5 times or more the diameter of the light source coupling optical waveguide section 38 can be measured efficiently.

  In this embodiment, since the optical branching coupler 20, the semiconductor laser 10, and the photodetector 12 are connected using an optical fiber, handling is easy and the mounting position can be freely determined. Therefore, a light source and a photodetector can be freely selected, and a high-output light source and a highly sensitive photodetector 12 can be used. Further, as in this embodiment, the optical branching coupler 20 can be moved. The optical branch coupler 20 used in the optical pulse tester of the present invention is not limited to this embodiment, and all the optical branch couplers of the present invention can be used.

  Light in which the mounting position of the light source coupling optical waveguide section 38 is shifted so that the light source coupling optical waveguide section 38 is inclined and the light emitted from the light source coupling optical waveguide section 38 passes through the center of the optical fiber joint section 44. When the branch coupler 20 is used, OTDR measurement of an optical fiber with a small diameter is possible even if the optical branch coupler 20 is fixed.

  As described above, the optical branch coupler of the present invention has been described using the embodiment in which the optical fiber joint of the optical branch coupler and the optical fiber are directly abutted, but the optical fiber is joined to the optical fiber joint, An optical fiber and a fiber for communication or measurement may be connected using an optical connector.

The optical pulse tester according to the present invention is suitable for an optical fiber having a large core diameter in which detection light is difficult to be separated, and is therefore effective when used for a plastic optical fiber having a large core diameter. Since the core diameter of plastic optical fiber that is usually used is about 0.5 mm or more and 2 mm or less, the diameter of the connection part on the optical pulse testing machine side is particularly 0.5.
It is desirable to set it to mm or more and 2 mm or less.

  Here, the relationship between the OTDR position resolution and the bandwidth and length of the optical fiber to be measured will be described. If the refractive index n of the optical fiber core is known, the scattering position z is determined from the time t until the incident light is scattered and returned.

(Equation 9)
z = ct / 2n (9)
It can be obtained more. At this time, if the position resolution Δz is W as the pulse width before the optical fiber transmission, F as the transmission band in the unit length, and L as the transmission distance,

It is expressed. OTDR measurement of an optical fiber having a large transmission loss such as POF and used in a short distance is desired to have high resolution. FIG. 12 shows the relationship between the fiber length and the resolution. The case of the fiber band is 10, 20, 100 MHz · km, and the pulse width is 0, 0.1, 0.5, 1.0 ns. When the bandwidth is narrow, the resolution is degraded by the bandwidth of the optical fiber even when a short pulse is used, and at 10 MHz / km, when transmitting 50 m or more, there is almost no difference between the pulse width of 0.1 ns and 0.5 ns. . Conversely, it can be seen that a pulse width of about 0.1 ns is necessary in order not to degrade the resolution at 100 MHz · km. FIG. 13 shows the relationship between the bandwidth of the fiber and the resolution when the pulse width is 0.1 to 3.0 ns. For example, in a band of 10 MHz · km corresponding to a step index plastic optical fiber having a numerical aperture of 0.3, the length corresponding to 50 m is 200 MHz, and in this band, the resolution is 175 mm even when the incident pulse width is zero. . From the figure, it can be seen that if the pulse width is 1 ns, the resolution is not deteriorated so much and 202 mm can be obtained. In order to suppress the resolution to α times or less of the resolution inevitably determined by the optical fiber, the incident pulse width W is

It is necessary to satisfy. Therefore, when the band F and length L of the optical fiber are known in advance,

If the maximum pulse width W that satisfies the above is selected, the degradation of resolution remains at 50% or less, and the measurement dynamic range can be maximized. By measuring the delay time and pulse width of the pulse reflected and returned from the output end of the optical fiber in the Fresnel reflection mode, the band F and length L of the optical fiber can be measured. Using the band F and length L of the optical fiber, the optical pulse tester can automatically select the optimum pulse width.

  FIG. 14 shows the results of measuring a step index (SI) type POF with NA 0.3, core diameter 1 mm, and length 100 m using the optical pulse tester of this example. The semiconductor laser used had a pulse width of 70 ps, a power of 160 mW, a maximum repetition frequency of 1 MHz, and a wavelength of 654 nm. Under this condition, a resolution of 9.5 cm or less can be obtained with a POF length of 25 m. As a result of 10,000 times of integration, it was possible to measure a length of 50 m or more.

  As in this embodiment, by using the optical separator / coupler of the present invention, the amount of light that can be coupled to the photodetector can be made larger than that of the conventional optical pulse tester using PBS, and the measurement dynamics can be increased. The range can be widened. Therefore, even if a semiconductor laser is used as a light source and a photodiode or an avalanche photodiode is used as a photodetector, OTDR measurement of a plastic optical fiber having a practical length can be performed.

  If a photon counter is used for the photodetector, the dynamic range can be further widened, and a longer distance can be measured. The dynamic range can also be widened by increasing the number of integrations.

  FIG. 15 shows an OTDR signal when five loops having a radius of 15 mm are formed in the optical fiber. Corresponding to the position where the loop was formed, the peak of the OTDR signal was observed. FIG. 16 shows the reciprocal of the radius of curvature, the peak height, and the loss due to the loop. The loss is per loop. Both the peak intensity and the logarithm of loss change in proportion to 1 / R. The step index optical fiber can be converted into the curvature of the optical fiber by measuring the peak height of the OTDR signal in this way. The optical pulse testing machine of the present embodiment has a function of measuring the height of the peak and converting it from the size into the curvature of bending.

  FIG. 17 is a configuration diagram of an embodiment of an optical system used in the optical pulse tester of the present invention. The beam from the semiconductor laser element 11 mounted on the mount 72 has its divergence angle reduced by the lens 62 and is incident on the polarization beam splitter (PBS). In this embodiment, a thin PBS is used, and the PBS film 70 may be formed on the entire joint surface of the PBS. Therefore, the fabrication is easier than forming the PBS film on a part of the prism. The pulsed light reflected by the PBS film 70 is collected at the center of the lens 64 and enters the optical fiber 22. The beam that has not been reflected by the PBS film 70 is absorbed by the absorbing member 76. Since the detection light from the optical fiber 22 is wider than the spread angle of the incident pulse light, it passes through a wide area of the lens 64, is reflected by the total reflection mirror 78, and is detected by the photodetector element 13. Of the detected light that has passed through the PBS film 70, about half of the light is reflected by the PBS film 70 and lost. However, since the area is smaller than the area occupied by the detection light, the loss in the PBS film 70 is small with respect to the total detected light quantity. Although not shown in the figure, the entire optical system was hermetically sealed.

  By using the lens 62, the area lost in the PBS film 70 in the detection light can be reduced, and the loss in the PBS film 70 can be reduced. In addition, since each beam is incident perpendicular to the surface of the optical component, it is easy to couple light to the photodetector without increasing aberration. In the present embodiment, it is desirable that the numerical aperture of the optical fiber is large because the amount of detected light lost in the PBS film 70 is reduced.

The block diagram which shows the Example of the 1st optical branching coupler of this invention. Explanatory drawing of the preparation procedure of a 1st optical branch coupler. The block diagram which shows the Example of the optical communication apparatus of this invention. The block diagram which shows the Example of the 2nd optical branch coupler of this invention. Explanatory drawing of the shape of the light-receiving side optical waveguide part. Explanatory drawing of the shape of a transmission side optical waveguide part. The block diagram which shows the Example of the 3rd optical branch coupler of this invention. The relationship between the taper angle α of the optical waveguide portion and the reduction ratio of the diameter of the tapered optical waveguide. Relationship between the numerical aperture of the optical branching coupler and the reduction ratio of the diameter of the optical waveguide part for detector coupling. The block diagram which shows the Example of the optical pulse tester of this invention. The block diagram of the Example of the 1st optical system of an optical pulse testing machine. The relationship between optical fiber length and resolution. The relationship diagram of the transmission band and resolution of an optical fiber. Measurement example using an optical pulse tester. The measurement example which measured the optical fiber which has a loop-shaped defect using an optical pulse testing machine. Measurement example of curvature, loss, and peak intensity of optical fiber. The block diagram of the Example of the 2nd optical system of an optical pulse testing machine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Semiconductor laser, 11 ... Semiconductor laser element, 12 ... Photodetector, 13 ... Photodetector element, 14 ... Resin for encapsulation, 20 ... Optical branch coupler, 22 ... Fiber, 24 ... Optical connector, 30 ... Branch coupling Optical fiber core, 36 ... optical fiber cladding, 38 ... optical waveguide part for light source coupling, 40 ... optical waveguide part for detector coupling, 42 ... reflective surface, 44 ... optical fiber Junction, 46 ... light source junction, 48 ... detector junction, 60 ... ball lens, 62, 64 ... lens, 66 ... optical attenuator, 68 ... prism, 70 ... PBS film, 72 ... mount, 74 ... substrate, 76 ... Absorbing member, 78 ... Total reflection mirror, 80 ... Optical fiber for branching and coupling, 82 ... Groove, 84, 86 ... Optical fiber, 100 ... Optical transmission device, 102 ... Optical communication device, 110 ... Drive circuit, 112 ... Detection circuit, DESCRIPTION OF SYMBOLS 14 ... Input terminal, 116 ... Output terminal, 120 ... Modulation circuit, 122 ... Demodulation circuit, 130 ... Drive circuit, 132 ... Amplifier, 134 ... Delay circuit, 136 ... Processor, 138 ... Display, 140 ... Optical attenuator, 150 ... Optical pulse testing machine.

Claims (9)

In the optical branching coupler having the optical waveguide portion branched into at least the first optical waveguide and the second optical waveguide from the joint portion,
The cross-sectional area of the first optical waveguide has a tapered shape that decreases in the branch direction from the joint,
The second optical waveguide is an optical branching coupler provided substantially perpendicular to the end face of the joint. In the optical branching and coupling part of claim 1,
An optical branching coupler in which the second optical waveguide is an optical fiber, and the second optical waveguide is joined to a groove provided in the first optical waveguide. The optical branching coupler according to claim 1,
An optical branching coupler in which the cross-sectional area of the second optical waveguide is smaller than the cross-sectional area of the first optical waveguide at the junction. A light source;
A photodetector for detecting light from the optical fiber;
An optical branching coupler having one optical waveguide portion branched into at least a first optical waveguide and a second optical waveguide for joining the optical fiber, the light source, and the photodetector, respectively;
The first optical waveguide is joined to the photodetector, and the cross-sectional area of the first optical waveguide is a tapered shape that decreases from the optical fiber toward the photodetector. The optical transmission device according to claim 4.
The second optical waveguide is bonded to the light source, and is provided in an approximately vertical direction with respect to a joint end surface with the first optical waveguide. The optical transmission device according to claim 4 or 5,
The optical detector is an optical transmission device having a photodetecting element bonded to an end surface portion of the first optical waveguide. A modulator that converts an input signal to be transmitted into a signal for transmission;
A light source, a light detector, a drive unit for driving the light source to transmit a signal modulated by the modulation unit, a light signal from the light source to the outside, and a light signal from the outside to the light detection An optical transmission unit having an optical waveguide unit that joins at least two optical waveguides, i.e., the first optical waveguide and the second optical waveguide, and a detection driving unit that drives the photodetector;
A demodulator that demodulates the signal detected by the photodetector into an electrical signal;
The cross-sectional area of the first optical waveguide has a tapered shape that decreases from the input side of a signal transmitted from the outside toward the photodetector, and the second optical waveguide is the first optical waveguide. An optical communication device provided substantially perpendicular to the end face of the joint with the optical waveguide. A light source;
A photodetector;
A light branching and coupling unit that guides a light beam from the light source to a measurement object, and guides a light beam from the measurement object to the photodetector;
An amplifying unit for amplifying a detection signal detected by the photodetecting unit;
An information processing unit for processing the signal amplified by the amplification unit;
A drive unit that drives the light source according to an instruction from the information processing unit,
The optical branching and coupling part is formed by joining at least a first optical waveguide and a second optical waveguide, and the cross-sectional area of the first optical waveguide is detected from the input side of a signal transmitted from the outside. An optical pulse tester having a taper shape that decreases in the direction of the vessel, and wherein the second optical waveguide is provided substantially perpendicular to a joint end surface with the first optical waveguide. The optical pulse tester according to claim 8,
An optical pulse tester in which a diameter of a joint portion between the measured object and the optical branching coupling portion is 0.5 mm or more and 2 mm or less.

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