JPS61129606A - Optical coupler - Google Patents

Abstract

PURPOSE:To permit easy packaging while maintaining the low coupling loss of a semiconductor light emitting element and optical fiber by constituting an optical coupler of the semiconductor light emitting element, the 1st near parabolic rod lens of which the end face on the side facing said element has a convex curved face and the 2nd near parabolic rod lens. CONSTITUTION:The 1st near parabolic lens of which the end face on the side facing the semiconductor light emitting element 2 is formed to the convex curved face shape and of which the refractive index decreases in an approximately square distribution with respect to the distance from the central axis is disposed in proximity to a light emitting face 3 of said element 2. The 2nd near parabolic rod lens 7 is disposed in such a manner that the 1st end face faces the lens 6 and the 2nd end face 9 contacts with the end face of an optical fiber 10. The focusing parameter and refractive index on the central axis of the 1st lens 6 are made larger than said parameter and refractive index of the 2nd lens 7 and the pitch of the respective lenses is made <=0.25 pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical coupler for optical communication and original information processing for coupling an output light beam of a semiconductor light emitting device to an optical fiber.

[Prior art]

Optical communication systems and optical information processing systems that use semiconductor light-emitting devices as light sources and optical fibers as optical transmission lines have been put to practical use in many fields, including public communications and broadcasting, due to their wide-band characteristics and excellent economic efficiency. It is becoming more and more popular. One of the various optical circuits that make up such optical communication systems and optical information processing systems is a coupling circuit between a semiconductor light emitting device and an optical transmission line.

Conventionally, as a coupling circuit with good performance, for example, Applied Optics 1
1980, Volume 19, page 42578, which uses a tapered tip fiber described in the paper by Mr. Kuwabara,
Utility Model Application No. 54-137440 r-Sphere Focusing Optical Transmitter” and Utility Application Application No. 59-136824. A device using a converging rod lens with a spherical tip described in the application filed on September 10, 1980, ``Optical coupler using a rod lens with a convex curved surface,'' is proposed. It is already known that these coupling circuits can considerably improve the coupling efficiency between a semiconductor device element, particularly a semiconductor laser, and an optical transmission line, particularly an optical fiber. When a single mode fiber is used as the optical fiber, 3.5 dB and L7d, respectively.
The output light beams from the semiconductor lasers are combined with a coupling loss of B.

However, in a coupling circuit using a tapered spherical fiber, the tapered spherical fiber is connected to a semiconductor light emitting device, for example, a semiconductor laser, by a few μm in the optical axis direction.
It is necessary to implement with positional accuracy within μm. For this reason,
Mounting a tapered spherical fiber is not always easy, and in some cases, there is a risk that the light emitting surface may be damaged and deteriorated due to contact with a semiconductor light emitting element, such as a semiconductor laser, during mounting. Therefore, if this woodcutter's coupling circuit is made into a module, the coupling loss will be 2 to 3 dB more than when adjusting.
The problem was that it was increasing.

On the other hand, a converging rod lens with a spherical tip, which is easier to implement than a tapered spherical fiber, utilizes the refraction of light at the spherical tip surface to direct a significant proportion of the output light beam from the semiconductor light emitting device to the periphery of the lens. can pass through the lens without being affected by lens aberrations. Therefore, the coupling loss between a semiconductor light emitting element, such as a semiconductor laser, and an optical transmission line, such as an optical fiber, can be significantly reduced compared to a rod lens whose end face is not rounded. However, although it is easy to install, it is difficult to install the optical fiber in the direction perpendicular to the optical axis.
It is necessary to implement the device with a positional accuracy within μm, which poses some problems in increasing mass productivity.

Therefore, there has been a demand for the development of an optical coupler that can be mass-produced and can be mounted with a positional accuracy comparable to that of a multimode 7-eyeper even when the optical fiber is a single mode fiber.

[Purpose of the invention]

An object of the present invention is to provide an optical coupler that eliminates the above-mentioned drawbacks, maintains low coupling loss between a semiconductor light emitting device and an optical fiber, is easy to implement, and is suitable for mass production.

[Structure of the invention]

According to the present invention, a semiconductor light emitting device and a semiconductor light emitting device having a convex curved surface whose end face facing the semiconductor light emitting device is formed in a convex curved shape and whose refractive index decreases with a substantially square distribution with respect to the distance from the central axis. The second focusing rod lens has a first end face facing the first focusing rod lens and a second end face close to the optical fiber. Moreover, the focusing parameter and the refractive index on the central axis of the first focusing rod lens with a convex curved surface are larger than those of the second focusing rod lens, and each lens angle is 0.2.
An optical coupler characterized in that it is 5 or less pins is obtained.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

First, before explaining the present invention in detail, the principle and operation of the present invention will be explained.

In the present invention, the end face of the semiconductor light emitting device, for example, the side facing the semiconductor laser, is formed in a convex curved shape, and the first end face has a convex curved surface whose refractive index decreases approximately in proportion to the square of the distance from the central axis. In the focusing rod lens and the second focusing rod lens with a flat end surface, the refractive index at the central axis is no, and the distance from the central axis is r.

When the focusing parameter is a, the refractive index n within the lens is given by n (r) = no (1 - upper a r'').The distance between the semiconductor light emitting element, for example a semiconductor laser, and the first focusing rod lens is The vicinity excluding the focal length.

This is because the second focusing rod lens is placed several degrees away from the first focusing rod lens, and it also expands the spot size of the output light beam when it enters the second focusing rod lens. This is to save money. The second focusing rod lens and the optical fiber are fixed such that their end surfaces are close to each other.

Figure 2 is a diagram to explain these reasons in an easy-to-understand manner, and shows the light emitted from the first focusing rod lens when the end surfaces of the optical fiber and the second focusing rod lens are integrated. The calculated value of the spot size when the light is incident on the second focusing rod lens is shown by changing the lens pitch of the second focusing rod lens. Spot size is second. The larger the lens pitch of the convergent rod lens, the wider it becomes. For example, with a 0.2 pitch lens,
Subo.

This is suitable for coupling an output light beam from a semiconductor light emitting device, such as a semiconductor laser, to an optical fiber with an apparent spot size of 16 μm. This is just like coupling the output light beam from a semiconductor laser into a multimode fiber! They are equivalent and extremely easy to implement. The distance between the first focusing rod lens and the second focusing rod lens is adjusted according to the image magnification. Here, the focusing parameters and refractive indexes on the central axis of the two focusing rod lenses are such that the first focusing rod lens is large and the second focusing rod lens is small, in order to further facilitate implementation. There is a need. In the first focusing rod lens, in order to incorporate as much of the output light beam from the semiconductor light emitting element into the lens as possible, a lens with a large numerical aperture, a focusing parameter, and a large refractive index on the central axis must be used. . On the other hand, in the second focusing rod lens, although the spot size has apparently expanded, the numerical aperture of the optical fiber itself is small, so it is necessary to focus the incident output light beam as gently as possible. Therefore, a lens with a small focusing parameter and a small refractive index on the central axis must be used. In addition, it is preferable that the two converging rod lenses be non-confocal lenses to prevent reflected light, and if the lens pitch is within 0.25 pitch, the image magnification can be adjusted arbitrarily depending on the relative positional relationship between the lenses. The size can be adjusted.

FIG. 1 is a side view showing an embodiment of the present invention, and FIG. 3 is a diagram showing an example of the results of measuring the allowable axis misalignment range of the optical fiber in the embodiment shown in FIG. To make the explanation easier to understand, use the X and Y axes.

Define the Z axis as shown. The Y-axis is oriented perpendicular to the plane of the paper.

In the figure, a semiconductor laser 2 having a bonded surface 1 is fused and fixed on a heat sink 5 so that an optical axis 51 of an output light beam 4 from its light emitting surface 3 is parallel to the Z axis. The first focusing rod lens 6 whose refractive index distribution is approximately given by n (r+) = net (1 - atri'') has a spherical tip on the side disposed close to the light emitting surface 3 of the semiconductor beep 2. Polished. Here, no is the refractive index on the central axis 52 +
al is the focusing parameter of the first focusing rod lens 6 +
rl is the distance from the central axis 52 of the first focusing Rondo lens 6, respectively. The second focusing rod lens has a first end surface 8 facing the first focusing rod lens 6 and a second end surface 9 in contact with the end surface of the optical fiber 0. In particular, the second focusing rod lens 7 and the optical fiber 0 are both fixed as one body. Regarding the refractive index distribution of the second focusing rod lens 7, n (r z ) = 111! It is given by (1ia!r:). Two focusing rod lenses are a+>a
21 noi>no2, the first focusing rod lens 6 is configured to have a large numerical aperture, and the second focusing rod lens 7 is configured to gently focus the output light beam 4.

In this embodiment, the first focusing rod lens 6 is a flo lens.
t=L63, a1=α175w s rt =0
．． 9mm + lens beam, chi 0.23 pitch, second focusing rod lens 7, no=1.59, a=0.10
7m sr 2 = 0.9■! Lens pitch 0.2
A 0 pitch one was used. In addition, the core diameter of 10 optical fibers is 10 μm.

Single mode fiber with a cutoff wavelength of 1.1μm.

The semiconductor laser 2 used had an oscillation wavelength of 1.3 μm. The coupling loss at this time was 2-7 dB, which was about the same low loss as when using only the spherical focusing rod lens.

Furthermore, since the optical fiber 10 is integrated with the second converging rod lens 7, the spot size becomes relatively large and coupling with the output light beam 4 becomes easy.

Further, as shown in FIG. 3, the degree of increase in loss due to axis deviation of the optical fiber 10 is slower than in the conventional example in which a converging rod lens with a spherical tip is used alone. Loss increase amount is 1d
Comparing the conventional example and this example at point B, the result is 3.4.
It can be seen that the allowable axis misalignment amount has expanded twice as much.

In this embodiment, several modifications can be made in addition to the typical embodiment described above. In the above embodiment, the semiconductor laser 2
．． 1st. Second focusing rod lens 6.7. Although the parameters of the optical fiber 0 have been specified, it goes without saying that the present invention is not limited to these values. Further, in this embodiment, the optical fiber 10 and the second focusing rod lens 7 are integrated in contact with each other, but as long as they are integrated, they may be fixed with a slight interval between them. Further, in the above-described embodiment, the first converging rod lens 6 having a spherical tip was used as the convex curved surface, but it is also possible to use an aspheric shape such as a hyperboloid, which is said to have a small spherical aberration.

As described above, according to the present invention, it is possible to realize a coupling circuit with low loss and in which the amount of increase in loss due to axis misalignment of optical fibers during mounting is 3.4 times less than in the prior art. Furthermore, by configuring the semiconductor laser, the first focusing rod lens, the second focusing rod lens, and the optical fiber fiber as one block, an optical coupler can be realized for mass production.

[Brief explanation of drawings]

FIG. 1 is a side view showing an embodiment of the present invention, and FIG. 2 is a diagram showing the spot size relative to the lens pitch when the second focusing rod lens and the original fiber are integrated, in order to explain the present invention in an easy-to-understand manner. FIG. 3 is a diagram showing the calculation results, and FIG. 3 is a diagram showing the measurement results of the amount of loss increase with respect to the amount of axial deviation of the original fiber in the embodiment of the present invention and the conventional example. 1... Junction surface, 2... Semiconductor laser,
3... Light emitting surface, 4... Output light beam,
5...Heat sink, 6°°°゛°°first focusing rod lens, 7...second focusing rod lens, 8...first end surface , 91990. . Second end face, 10... Optical fiber, 51...
...Optical axis, 52... Central axis. Figure 1 Figure 3 Lens hand Figure Z

Claims (1)

[Claims] a semiconductor light emitting element; and a first focusing rod with a convex curved surface whose end face facing the semiconductor light emitting element is formed in a convex curved shape and whose refractive index decreases with a substantially square distribution with respect to the distance from the central axis. a second focusing rod lens having a first end face facing the end face of the first focusing rod lens with the convex curved surface and a second end face close to the optical fiber; An optical coupling characterized in that the focusing parameter and the refractive index on the central axis of the first focusing rod lens are larger than those of the second focusing rod lens, and the pitch of each lens is 0.25 pitch or less. vessel.