JPS60165605A - Optical star coupler - Google Patents

Abstract

PURPOSE:To enable uniform maintenance of the intensity distribution of signal light at an output end by forming the core part of a mixer having a high refractive index into a aquare column and covering the remaining four faces except the two faces to be connected with fiber arrays by clad parts consisting of glass having a low refractive index. CONSTITUTION:A core part 11 of a mixer 18 having a high refractive index is made to a square column and the remaining four faces except the two faces to be connected with fiber arrays are covered by the 2nd clad parts 17 consisting of glass having a low refractive index so that the side faces of the core parts are not exposed to air. Joint surfaces 19 indicate the joint surfaces between the core parts 11 and the clad parts 12 and joint surfaces 20 indicate the joint surfaces between the conventional mixer and the 2nd clad parts. The exposure of the side walls of the core parts 11 is obviated by such constitution and therefore dew condensation is obviated, the condition for total reflection is maintained and the signal light having a uniform intensity distribution is obtd. from the exit end.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention has a plurality of input terminals and a plurality of output terminals,
An optical star coupler that has the function of equally distributing an optical signal input from any input terminal to all output terminals, and is particularly characterized by improved uniformity in the distribution of optical signals to the output terminals. It is.

[Prior art]

An optical star coupler is an optical circuit component that connects terminals in a star network constructed using optical fiber cables, and has an input section that inputs signals, and mixes input signals and distributes them equally to all output terminals. It consists of a mixer that outputs a signal, and an output section that outputs a signal. Generally, the mixer section is a passive type that does not regenerate or relay signals, but when a large number of output terminals are used, an optical-to-electrical converter, a regenerator/repeater, and an electrical-to-optical converter are required to compensate for distribution loss. The mixer part, which is an electric circuit consisting of a mixer, is sometimes divided into two parts and inserted into an active type.

FIG. 1 is a schematic diagram depicting the light guide section of the passive optical star coupler that has the lowest loss among conventionally developed passive optical star couplers. In the figure, (1) is an optical connector or input terminal for inputting signals from an external optical circuit, (2) is a fiber array in which optical fibers are arranged in a straight line and the end faces are polished to enable cross-connection to a mixer, which will be described later. (3)
is an optical fiber whose one end is arranged in a straight line to form a fiber array (2) and whose other end is connected to input terminal +11, (4) is an input section composed of these three parts, (
5) outputs the optical signal inputted from any optical fiber (3) of the fiber array (2) by butt connection from the input side end face with almost no loss through multiple total reflections within itself. The mixer (6) is the same in shape as the fiber array (2) mentioned above, or is tightly connected to the output surface of the mixer (5), and is connected to the output surface of the mixer (5). The second fiber array (7) distributes the optical signal reaching the surface to the output optical connector, (7) is the output optical connector, that is, the output terminal, (
8) is an optical fiber whose one end constitutes the second fiber array and whose other end is connected to the output terminal (7).

(9) is an output section whose components include a second fiber array (6), an output optical connector (7), and an optical fiber (8), and Ql is a casing that houses the above-mentioned elements. Fig. 2 is a diagram showing the details of the mixer (5), Fig. 2(a) is a view seen from the input section (5) side, and Fig. 2(b) is a side view seen from the direction perpendicular to it. , FIG. 2(C) shows the output section (9
), and FIG. 2(d) is a top view.

In Fig. 2, Qll is a core portion made of a material transparent to the signal light (one side is a cladding portion made of a material transparent to the signal light and has a somewhat lower refractive index than the core portion Q13). Yes, the core part (the thickness of the first part is the optical fiber (3) and (8)
), the width of mixer (5) is approximately equal to the array width of fiber arrays (2) and (6), and the length of mixer (5) is approximately equal to the diameter of the core of mixer (5). The value ranges from 10 to 20 times the width. Due to the above-described structure of the mixer (5), the signal light incident on the core section α from any optical fiber (3) constituting the fiber array (2) is also connected to the core section a''lJ and the Clarade section H. The fiber array (6
), and enters the optical fiber (8) constituting the output fiber array (6) closely connected thereto. FIG. 3 schematically shows the progress of light rays inside the mixer (5), with one of the central optical fibers (3) on the input side being arranged in a row. Figure 4 shows the distribution of signal light at the output end face of the fiber array (8) when observing it with the same aperture area and acceptance angle as the optical fiber (8).
6) is the sequence direction dependence.

Now, regarding the optical star coupler according to the conventional invention.

Core portion G' shown in a top view in FIG. 2! The two planes of J are in close contact with each other through the cladding (1), so they are not affected by dew condensation caused by sudden changes in outside temperature and humidity; Since it is not covered with II, condensation may occur, and it may adsorb dust floating in the air and become absorbent to the signal light, or small parts of the dew may evaporate, increasing the impurity concentration. In this case, mixer (5)
A change occurs in the direction and phase of the light reflected by the side wall that arrives at the output end of the optical fiber (8), and as a result, the state of the interference effect with the direct light that arrives without being reflected changes, and the light distributed to the optical fiber (8) changes. The uniformity of the images sometimes varied greatly.

FIG. 5 shows the location dependence of the arriving light observed in the same manner as FIG. 4, and it can be seen that the uniformity is disturbed.

[Summary of the invention]

This invention focuses on the fact that the drawback of the conventional device described above is caused by minute changes in the intensity and phase of the reflected light on the side surface of the mixer (5), and the present invention
The optical star coupler is coated with a material that is transparent to the signal light and has a refractive index lower than that of the optical star coupler, thereby improving the performance of the optical star coupler.

FIG. 6 is a diagram showing the shape of the improved mixer of the optical star coupler according to the present invention. In the figure (lη is the second cladding part newly added to prevent the side surface of the core part θB of the conventional mixer (5) from contacting the air and getting dirty, and H is the cladding part between the core part 0υ and the first cladding part. This is an improved mixer whose constituent elements include a cladding section 0 and a new second cladding section 0η.

Incidentally, numerals indicate the joint surfaces between the core part 09 and the cladding part (1). The joint surface with the cladding part 0 is shown. Also, the 6th (
Figure a) is a sectional view of the improved mixer q8 viewed from the direction of the input section (4), and Figure 6(b) is a side view viewed from the direction in which the fiber arrays (2) and (6) are arranged at right angles thereto. , 6th (
c) The figure is a sectional view of the improved mixer 0υ seen from the direction of the output part (9), and FIG. 6(d) is a top view.

Note that the material for the second cladding θη should be selected to have the same refractive index as the first cladding aS and transparency for signal light, and the two bonding surfaces OI and (4) should have total reflection. It is preferable to fill the adhesive material with an adhesive that is transparent to the refractive index E signal light and not disturb the conditions of E, or to bond the core portion 0υ and the cladding portion 0 to be bonded. To take an example of an adhesive, it is used because its viscosity is low and no air bubbles remain during bonding, and therefore the bonding surface is highly uniform, and its refractive index is higher than that of the glass used as the core part Qll. This is because the refractive index is appropriately low (and it is non-absorbent to signal light), and curing only occurs when UV rays are irradiated in an oxygen-free atmosphere, so take enough time to align it. Loctite's anaerobic ultraviolet curing adhesive LO-8 has been used because of its high adhesive properties and beautiful finish.
There are 12. In addition, because of its non-absorption property for signal light, the small number of scattering centers, and the good refractive index matching between the optical fibers (3) and (8), it is possible to use LL-7 glass as the glass of the core part (I9) for refraction with this core part 00. Because of its good rate matching, appropriate softening point, and non-absorption of signal light, L is used as the glass for the cladding part.
Mention may be made of LF7 glass. When the glass is selected in this way, the joint part Q1. The joining method suitable for Tht21 is welding for the joining members with emphasis on the loss of the signal light, and filling of the joining members with adhesive with emphasis on workability.

Now, this is how the mixer is configured.

There is a gap in the housing OI that houses the light guide part of the optical star coupler that allows air to flow in, so that there is so-called breathing, which can cause condensation on the side walls of the improved mixer due to sudden changes in the environmental temperature. However, since the side wall of the core part I is not exposed, no condensation occurs, and the light rays entering from the optical fiber (3) undergo repeated total reflection without being disturbed, giving a uniform intensity distribution to the output end. Characteristics as a star coupler can be maintained over a long period of time.

It should be noted that in the above explanations, the deviation in the total reflection condition simply due to dew condensation on the peripheral wall of the core portion αD has been emphasized.

Another reason for the uniformity of signal light distribution due to not exposing the surface of the core portion 0υ to air is that the specular surface changes to a diffusive surface due to sublimation of atoms constituting the glass from the exposed surface. The latter reason is essential to maintaining long-term stability of the optical star coupler.

FIG. 1 is a diagram showing a second example of a mixer employed in the optical star coupler according to the present invention. In the figure, αυ is the core part, Qυ is the core part (the cladding part is made of glass with a slightly lower refractive index than Ill and has an approximately circular outer shape, and cta is the core part aυ and the cladding part (20 is the constituent element). This is a mixer.The specific dimensions of this mixer are as follows: The fiber array (2) connected to the mixer
When the number of optical fibers (3) and (8) making up (6) and (6) is 10, the width of the core part is approximately 630 ut and the height is approximately 4
The 0i+ms length is approximately 8 dragons. The manufacturing method for this mixer@ is to first make a quartz glass rod (mother rod; MoTnmRROD) with a cross-sectional dimension about 25 times the above dimensions, and then draw the rod while partially melting it in a bath. . Cladding part c in the mother rod! 1) is manufactured by dividing it into several parts, placing them close to each other, pressing them together in a high-temperature furnace, and then cutting the outer periphery into a circular shape to obtain the cross-sectional shape of the core part I after drawing, as shown in Fig. 6. This is suitable for keeping the shape rectangular.

In this embodiment, quartz glass is used as the glass trap for both the core part 00 and the cladding part 04, but it is clear from the development process of the optical fiber that this results in lower loss than the use of conventional optical glass in the first embodiment. It is clear from looking at. Also 9
If quartz glass is used as the core part 00 and the cladding part c20, the fiber array (2) that should be matched with it
Since the thermal expansions of the optical fibers (3) and (8), which are the constituent elements of (6) and (6), can be matched, the temperature characteristics can be improved, which is advantageous.

〔Effect of the invention〕

As described above, in the optical star coupler using the mixer having the thin plate-like core according to the present invention, by shielding the entire peripheral wall of the core from the outside air, interference fringes on the output side end face of the mixer can be reduced. This makes it possible to maintain a uniform intensity distribution and maintain long-term stability of the performance of the optical star coupler.

[Brief explanation of the drawing]

Figure 1 shows the structure of a star coupler, and Figure 2 shows the structure of a mixer used in a conventional star coupler that was thought to have the highest efficiency and the smallest variation in distributed signal light. Diagram showing. Figure 3 is a schematic diagram showing how the signal light is distributed in the optical star coupler using the mixer shown in Figure 2, and Figure 4 is the signal light at the output end of the mixer shown in Figure 2. Figure 5 shows the signal at the output end of the mixer shown in Figure 2, which is generated when the side surface of the mixer becomes dirty due to condensation of moisture in the atmosphere or becomes scattering due to sublimation of constituent atoms. FIG. 6 is a diagram showing the disordered distribution of light, and FIG. 6 is a diagram showing an example of a mixer used in the optical star coupler according to the present invention. FIG. 7 is a diagram showing another example of the mixer used in the optical star coupler according to the present invention. It is a diagram. In the figure, (1) and (7) are optical connectors, the former serving as an input terminal and the latter serving as an output terminal. (2) and (6) are fiber arrays, (3) and (
8) is an optical fiber, (4) is an input section, (5) is a mixer,
(9) is the output part, Ql is the housing, Ql) is the core part, and 0 is the cladding part. Ol is the core part of the optical fiber, (I4 is the clad part of the optical fiber, (1!9 is the distribution of signal light at the output end of the mixer, and ae is the same (the distribution of signal light at the output end is uniform). Type 0 is the mixer adopted in the optical star coupler according to the present invention, I7) is the core part that has been withdrawn, and QIhCll is the joint surface between the core part and the cladding part or the cladding part and the cladding part. , at+ is the cladding part of the second mixer employed in the optical star coupler according to the present invention, and (c) is the second mixer. Note that the same or equivalent parts in the two figures are given the same reference numerals. (12) @4 Figure Ji5 Side 1 1 1

Claims (1)

[Claims] An optical connector that inputs and outputs signals from an external optical circuit. A fiber array in which a plurality of optical fibers are arranged in a straight line and optically polished to enable side-to-side connection with a mixer, a source fiber whose one end is terminated by an optical connector and the other end constitutes a fiber array, and the above-mentioned fiber array. In an optical star coupler that uses a mixer as a light guide component, which is connected to both ends of the mixer, the high refractive index region of the mixer, that is, the core part, has a square prism shape, and the remaining surfaces except for the two faces to which the fiber array is connected are An optical star coupler characterized in that its four faces are covered with glass having a low refractive index, that is, a cladding part.