JPS58209710A - Multistage optical demultiplexing and multiplexing circuit - Google Patents

Abstract

PURPOSE:To perform optical redemultiplexing and remultiplexing, by arranging plural light guides having a uniform cross section nearly in a semicircle shape in parallel at intervals, arranging a couple of substrates so that their light guide exposure surfaces face each other, while a partially reflective and transmissive layer is interposed and closely arranged over the entire surfaces or necessary parts of the light guides and connecting a prescribed optical fiber to each light guide end part. CONSTITUTION:In an optical demultiplexing circuit, a light beam 14 from an input fiber 7 to a light guide 4A travels in a sine curve, and reaches the surface of a substrate 2A at an about 1/4-pitch position, where 50% of the beam is reflected by a semitransparent film 6; and the reflected beam travels in the same light guide and enters the other directly-connected fiber 12. The remaining light transmitted through the semitransparent film 6 travels in a light guides and then enters the other directly-connected fiber 13. The light entering the fiber 12 enters a light guide 3A and further travels similarly and is divided into two by the semitransparent film 6; and they enters optical fibers 10 and 11 respectively. The light entering the fiber 13, on the other hand, travels in a light guide 5B and is divided by the semitransparent film 6 into two, which enter output fibers 8 and 9 respectively.

Description

[Detailed Description of the Invention] The present invention is suitable for manually branching light transmitted through seven optical fibers into multiple optical fibers equally, or for inputting separate optical fibers for each specific wavelength. This invention relates to a light splitting circuit.

Conventionally, this type of device is known in which a cylindrical gradient index lens is cut in half, a partially transparent layer is interposed between the halves, and one end of optical fibers for input and output are connected to both end surfaces of the lens. .

Here, the function of the partially transparent layer differs depending on the function of the device, and in the case of a branching/merging circuit where the nine bars sent through one optical fiber are equally distributed and input to multiple optical fibers, or vice versa, they are merged. In the case of L, a semi-transparent film with a reflectance of SO% or a total reflection film covering half of the emission area of the light beam is used as the partially transparent layer.

In addition, mixed light containing light of two or more wavelengths can be divided into light of each wavelength and manually connected to separate optical fibers, or conversely, light of each wavelength can be combined to form mixed light. In the multiplexing circuit, an interfering film filter is used as the partially transparent layer, which selectively transmits only light of a specific wavelength and reflects light of other wavelengths.

Hereinafter, in this specification, unless otherwise specified, the above-mentioned branching and splitting will be referred to as light splitting, and the branching functional layer and the splitting functional layer will be referred to as a "partially transparent layer".

In the conventional light splitting circuit using the halved cylindrical gradient index lens described above, it is difficult to process with high precision because it requires polishing a very small fibrous lens.
Assembly work such as optical axis alignment is also very complicated and requires skill. Therefore, when building a multiple division circuit that divides the light that has been divided once once again and even more times, it requires an extremely large number of man-hours to manufacture. In short, there was a problem that it was not very practical.

The present invention solves the above-mentioned conventional problems and provides a novel multi-stage light splitting/combining circuit that is very easy to manufacture, can be highly accurate, and can be made very compact as a whole. With the goal.

In other words, the light splitting and merging circuit of the present invention has a transparent substrate made of glass or synthetic resin with parallel planes, the refractive index of which is greater than that of the substrate, and whose refractive index is the highest at the substrate surface in a cross section perpendicular to the direction of light propagation. A number of parallel light guide paths KFj are provided at intervals, and have a distribution that gradually decreases toward the inside, and have a uniform refractive index and a substantially semicircular cross section in the direction of movement of the light beam.
The pair of substrates are closely arranged with the exposed surfaces of the light guide facing each other, and a partially reflective transparent layer is interposed over the entire area or main part of the surface of the light guide, and an optical fiber is connected to one end of the light guide,
One end of the direct coupling optical fiber is connected to the other end of the light guide or (and) the other end of the light guide opposite the light guide, and the other end is connected to the end of the adjacent light guide on the same side of the board. This is a light splitting/combining circuit characterized in that the light is divided or recombined thereby.

According to the configuration described in Section 2, the light flux introduced into one light guide path in the substrate through the input light 7 eyeper travels in a sine curve, and travels a specific distance determined by the refractive index distribution in the optical path. At this point, the light reaches the substrate surface, some of the light passes through the partially transparent layer provided on this surface and enters the other opposing light guide path, and the rest is reflected by the partially transparent layer.
Proceeds within the same light guide path.

The light thus divided is guided to a direct-coupled optical fiber connected to the other end of one of the light guides mentioned above, and is input into the other adjacent light guide on the same side of the substrate [III, as described above. It will be re-divided through the process of

Then, the re-divided light is taken out through the output fiber connected to the light guide path or the light guide path Kl' opposite thereto.

Alternatively, a second relay fiber is connected here, and the other end of this relay fiber is connected to a third adjacent light guide path on the same side of the substrate to repeat the division of light.

Similarly, it is possible to perform serial light splitting in three or more stages.

According to the above configuration, multiple stages of light splitting circuits are integrated on a common substrate, so there is no need for the complicated work of arranging and fixing individual small elements in the correct relative positional relationship as in the past. It is very easy to connect the relay fiber that connects the divided circuits, and since it is flat, it is easy to handle and assemble with other parts, making it suitable for in-house production. The present invention will now be described in detail with reference to embodiments shown in the drawings.

FIG. 1 is a perspective view of an optical branch circuit to which the present invention is applied;
FIG. 2 is a cross-sectional view of the same.

The branch circuit/is three light guide paths 3A having a substantially semicircular cross section.

A transparent substrate A in which 9A and 5A are arranged parallel to each other at intervals, and three light guide paths JB and i in a similar arrangement.

Another transparent substrate-B provided with a transparent substrate B is closely placed with the exposed surfaces of the light guides facing each other with an SO% reflective semi-transparent film interposed therebetween as a partially reflective transparent layer 6. It is constructed by connecting a predetermined optical fiber to the

More specifically, as shown in FIG. 1, each light guide path 3A, 11A, 3A, which is provided with its side surface exposed on one side of a transparent substrate 2A made of glass or synthetic resin, has a refractive index that is lower than the refractive index ns of the substrate. is also large, and in Figure 5 /T(
The refractive index at the center in the width direction on the substrate surface is no.
The distribution has a maximum value of n=no(/-4J2r2)-(1), and gradually decreases toward the inside in a cross section perpendicular to the direction of travel of the light.

Here, r is the distance from the center on the substrate surface, and A is a distribution constant.

Further, the refractive index distribution within the light guide path is constant in the direction in which the light travels.

In order to form a light guide path having a refractive index distribution as described in 1-7 in a substrate, for example, titanium or the like is deposited on one side of a glass substrate having parallel planes by sputtering to cover the entire surface. A metal thin film is made, and one or more stripe-shaped openings are made in this thin film K at intervals.

When using photolithography technology, a photoresist film is applied on top of the thin film, a mask with striped openings is placed, the photoresist film is exposed, and after development and etching, the metal film is etched. This is etched to form striped openings, and the resist film is removed to serve as a mask for preventing ion transmission during the subsequent ion exchange treatment.

Next, the mask surface of this substrate is brought into contact with a high-temperature molten salt, and one or more monovalent ions, such as Tl+, Os+, or Ag10, are diffused through the openings of the mask to form a high refractive index portion inside the glass. A light guide with the desired smooth refractive index distribution, by forming and further high temperature heat treatment in air? A, 4(A, tA can be made.

Alternatively, it can be made using plastic as a base material, for example, by diffusing a monomer with a relatively low refractive index into the substrate from around a mask provided on a required portion of the surface of the substrate having a relatively high refractive index, and causing a polymerization reaction.

A partially transparent layer 6 is formed by attaching a thin film to one or both surfaces of the substrates -A and -B obtained as described above by sputtering or the like.

This partially transparent nine layer B does not necessarily need to be provided over the entire surface of the substrate, and the light guide path, tA (jB), l (4El
), 5A (3B), or may be further limited to only the area through which the luminous flux is transmitted (reflected).

Then, a pair of light guide paths 4 (A, 41B) located in the center of the total of six light guide paths #1' is connected to the optical fiber 7 for human power use toward the end of the light guide path 9A, and is adjacent to each other on the same side of the board. 3B and 3A for each pair of light guide paths 3.

Output optical fibers are provided on each end face of the SB, 9, 10.
//Connect each.

In addition, on the other side IIu fljl of the board, both ends of the Flf, Mt41 optical fiber/, 2 made as short as possible are connected to each end face of the light guide path +A to which the human power fiber 7 is connected and the adjacent light guide path 3A. .

Furthermore, both ends of another +ti coupling fiber/30 are connected to the end face of the light guide path 4 to which the input fiber 7 is connected (light guide path 4<B opposite to A and the adjacent light guide path jB in the same substrate). do.

Here, the length L of the substrate in the light traveling direction is selected to be approximately 2/period length (pitch) K.

The above pitch P and the refractive index distribution constant A in the above equation (1)
There is a relationship between P=-π/VK... (-).

In the light splitting circuit/with the above structure, the light t@iy that is emitted from the input fiber 7 and enters the light guide path 111 travels in a sine curve, and reaches the surface of the substrate at a point of about q/l pinch. After 50% of the light is reflected by the semi-transparent film t and travels within the same light guide path, it enters the direct-coupled fiber /-.

Further, the light that has passed through the semi-transparent film g travels through the light guide path 3B and then enters another direct-coupled fiber 73.

Directly connected fiber saw light is connected to light guide path 3A. After going through the same process as described above, we made #transparent film 6! The output fibers are split and input into output fibers 10 and/or 2, respectively.

Further, the light that has entered the other direct-coupled fiber /3 travels through the light guide path 5B and is divided into parts by the semi-transparent film 6, and then enters the output fibers 9, respectively.

In this way, the light transmitted through one optical fiber 7 is divided into 1 equal parts, and the output fiber is divided into 9°10, //
taken from.

FIG. 7 shows another embodiment.

In this example, a total reflection film with half the area is used as the partially transparent nine layer B, and the light is transmitted through the human fiber 7, and the light entering the light guide path IIA reaches the substrate, 2A [mlK, where half of it is After being reflected by the total reflection film 6, the direct coupling fiber /
− is incident.

Further, the light transmitted through the portion where the total reflection film 6 is not provided enters the direct-coupled fiber 73 after traveling through the light guide path 4tB.

FIG. 4 shows an example in which the present invention is applied to an optical demultiplexing circuit.

In this example, a pair of light guide paths 1.3 are provided on the substrates jA and 2B, respectively.
k and <13. jB, one opposing light guide &A and q
An interference film filter tA that reflects light with a specific wavelength λ1 and transmits light with other wavelengths is interposed between the other opposing light guide paths jA and jB, and reflects light with a specific wavelength λ3 and transmits light with other wavelengths. An interference film filter &-IB that transmits light of the same wavelength is interposed.

Then, the input fiber 7 is connected to the end surface of the light guide path 4fB, and the output fiber 10 is connected to the other end surface of this light guide path 44B, and is directly connected to the light guide path A facing this light guide path and the light guide path tA adjacent thereto. Connect both ends of fiber 72. Further, an output fiber cable 9 is connected to the end faces of the light guide paths 5A and jB.

In the above circuit, the wavelength λ1 is passed through the input fiber 7.
．． When the mixed light of λ2 and λ3 is transmitted, the light of wavelength λ1 is reflected by the interference film filter A and travels through the light guide QBtt, and then enters the output fiber 7OK.

The mixed light of wavelengths λ2 and λ3 that has passed through the filter A travels through the light guide path <jA, enters the direct-coupled fiber 72, and is transmitted to the light guide path 5A.

When the light of λ3 travels through the light guide path 5A and reaches the interference film filter 6B, it is reflected there, and after further traveling through the same light guide path, it enters the output fiber.

Further, the light having the wavelength λ2 that has passed through the filter 6B travels through the light guide path 5B and then reaches the output fiber rK.

enter.

In this way, the wavelength λ1. λ2. The mixed light of λ3 is demultiplexed into light of each wavelength and output.

In the example shown in FIG.
3 are provided between adjacent light guide paths on the same substrate, but they may be connected to adjacent light guide paths on the other substrate (for example, from light guide path 1A to light guide path 3B).

It is also possible to provide more pairs of light guide paths to perform light division in three or more stages.

It goes without saying that it can also be used as a merging circuit in which monochromatic light or mixed light of various wavelengths transmitted through a large number of optical fibers is merged into seven optical fibers.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an optical branch circuit to which the present invention is applied. 2 and 3 are cross-sectional views of the main parts of FIG. 7, FIG. 1 is an M view showing the substrate used in the present invention, FIG. 5 is a graph showing the same substrate with no refractive index distribution, and FIG. Fig. 7 is a perspective view showing an example in which the present invention is applied to a full wave circuit, and Fig. 7 is a cross-sectional view of the main part of Fig. 7. C......Light splitting circuit 2AljB...
...Transparent substrate 3A, ,? B l 41A, II
B t 3A l jB...For...Light guide path O...
・・Partially transparent layer 7・・・・・・・Man-powered fiber!
, ri, 10, //river... uJJ cuff eye bar/J, /3... Direct fiber patent applicant Nippon Telegraph and Telephone Public Corporation Figure 1 OF3 Figure 2 Figure 3 S Δ B Figure 4

Claims (1)

[Claims] ]) In a transparent substrate with parallel planes, the refractive index is larger than the substrate and in a cross section perpendicular to the direction of light propagation, the refractive index is maximum at the substrate surface and directed toward the inside. A plurality of parallel VC light guide paths having a gradually decreasing distribution and a uniform refractive index in the traveling direction of the light and a substantially semicircular cross section are provided at intervals. A partially transparent 14 transparent layer is interposed over the entire area or main part of the surface of the light guide and is closely arranged, an optical fiber is connected to one end of the light guide, and an optical fiber is connected to the other end of the light guide or (and) When connecting one end of the direct coupling optical fiber to the other end of the opposing light guide, the other end is connected to the end of the adjacent light guide on the same side of the board, thereby re-splitting or recombining the light. Multi-stage light splitting and merging [[J1 road. 2) The multi-stage light splitting and merging circuit according to claim 1, wherein the partially reflective light transmitting layer is a thin film having a function of transmitting approximately half of the amount of light and reflecting the rest. 3) The partially reflective transparent layer transmits only light of a specific wavelength,
2. The multistage light splitting/merging circuit according to claim 1, wherein the multistage light splitting/merging circuit is a thin film having a function of reflecting light.