JPS5922020A - Optical distributor - Google Patents

Abstract

PURPOSE:To inhibit the output of a light signal to the output terminal of a port supplied with the light signal by reflecting the light signal projected from an input fiber end part of a port group through a reflector consisting of a rod lens and a diffraction grating. CONSTITUTION:Optical fibers 31-35 have input light fiber end parts M1, M2, and T1, and optical fibers 34 and 36 have output fiber end parts M'1, M'2, and R1. The rod lens connected thereto has a refractive index distribution with nearly squarelaw characteristics in the radial direction and is a quarter as long as zigzag pitch of light beam. A diffraction grating 41 with a period l1 and a diffraction grating l2 with a period a half said period are formed on the end surface of the lens on both sides of an x axis; and the half of each grating period is formed of a dielectric film with thickness lambda/4 and no diffracted light of degree 0 is present. Light from the input fiber end parts M1, M2, and T1 is made incident to the diffraction gratings 41 and 42 and primary diffracted light is inputted to the end part of an output fiber other than its projection port and never returns to its projection station.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to the structure of an optical distributor that distributes optical signals from optical fibers.

[Technical background of the invention and its problems]

In general, the distribution of optical signals to a large number of terminals using passive optical circuit elements is particularly important for realizing reliable and economical optical networks.

Conventionally, as such a passive circuit element, a star coupler is known, which outputs an optical signal input to one input terminal to all output terminals, and a star-shaped network centered on this type of coupler is known. ing. However, in such a system, it is necessary to wire optical cables from all stations to the star coupler, and there is a problem in that increasing the number of stations increases the length of the entire required optical couple and increases costs. Furthermore, since many optical cables are connected to one star coupler, the cables become congested and are not necessarily easy to use.

If a plurality of the above star couplers are used and they are connected in cascade, the number of stations connected to each star coupler will be small even if the total number of stations is large, and the above-mentioned problems can be considered to be eliminated. However, with conventional star couplers, a portion of the optical signal is also distributed to the output terminal of the boat where the optical signal is input, resulting in the formation of a closed loop and oscillation, making normal optical transmission impossible. .

That is, as shown in FIG. When the second star couplers (la) and (lb) have the characteristic of outputting the optical signal supplied to the input terminal of each 11ζ-t to the output terminals of all boats, the first star coupler (1a) The optical signal output from the first receiver (2a) and the first transmitter (
3a), passes through the second star coupler (1b), further passes through the second receiver (2b) and the second transmitter (3b), and is input to the first star coupler (1a), and is inputted again to the first star coupler (1a). A portion is sent to the first receiver (2a). In this way, a closed loop is formed and oscillation occurs.

In FIG. 1, (4) is a station consisting of an optical transmitter (4a) and an optical receiver (4b).

The inventors of the present invention previously proposed an optical splitter that is suitable for the above-mentioned system and does not cause oscillations (#Application No. 57-5671
). That is, it is an optical splitter in which no optical signal is output to the output terminal of the boat to which the optical signal is supplied. FIG. 2 shows an example of this type of optical splitter.

This optical splitter is an example of an optical splitter having three boats, where the first boat is an input terminal (lla) and an output terminal (l
Similarly, the second port has an input terminal (1
2a) From the output terminal (12b), the third port consists of an input terminal (13a) and an output terminal (13b), respectively. Input terminals (1], a), (12a) by optical fiber
.

The optical signals input to (13a) are transmitted to the convex lens 141, which is made up of three so-called semicylindrical lens bodies vertically arranged in parallel.
After being given a predetermined phase shift amount in the vertical direction by the convex lens 119 and then being given a phase shift amount change in the horizontal direction by the convex lens 119, the polarization matrix plate 06) having six different planes on the radiation side as shown in the figure is formed. incident.

The deflection matrix plate (17) disposed on the output side of the matrix plate 116) has an optical function completely opposite to that of +16). The optical signal incident on the upper stage of the deflection matrix plate (116) is divided into two parts, the first half and the second half, and enters the lower and middle parts of the deflection matrix plate (171).Similarly, the optical signal enters the middle and lower stages of the deflection matrix plate (16) The optical signals are transmitted to the upper, lower and middle stages of the deflection matrix plate 11''6.

Inject into the upper part. The optical signal that has passed through the deflection matrix plate (+71) passes through convex lenses 1151, 1181.!, 1 sickle, which has the same structure as 1141, and is output to the output terminals (Jlb), (12b), (13b) of each boat.
is output to.

After all, in this optical splitter, the input terminal of the first port (], 1
The optical signal entering a) is the second one. The output terminal of the third boat (1
2b) and (13b), but not to the output can (child (Ilh)) of one port. Therefore, it is an optical distributor with the above characteristics. However, this t/' )
The optical distributor has a complicated structure and is difficult to adjust, and there are problems in reducing optical loss.

[Purpose of the invention]

An object of the present invention is to provide an optical distributor installed in an optical transmission system having many stations, that is, an improved optical distributor having a characteristic that no optical signal is output to the output terminal of a boat to which the optical signal is supplied. With the goal.

[Outline and summary of the invention]

The present invention relates to a boat group consisting of a plurality of boats arranged in parallel at predetermined positions each consisting of an input fiber terminal and an output fiber end, each of which inputs and outputs an optical signal, and a boat that is emitted from each input fiber end of these boats. a reflector that reflects the optical signal and makes it incident on the output fiber end of a boat other than the boat in the input section 774761M from which the optical signal was emitted; This is a light distributor consisting of a rod lens or an optical system equivalent to the rod lens. A feature of the present invention is that the reflector has a diffraction grating structure.

〔Effect of the invention〕

In the present invention, a reflector having a diffraction grating structure is used, and an optical splitter having a simple structure and suitable for an optical transmission system having many stations can be obtained.

FIG. 3 shows the overall configuration of an optical transmission system to which the optical splitter of the present invention is applied. (, υ will be explained in detail later. For example, it is an optical distributor according to the present invention having 3 ports. Each optical distributor (: 1st to 3rd ports) c41)
, · 2) , +23). Each optical distributor (2
The 1M 1st second board 2υ1122 is connected to the adjacent optical distributor (2i1), and the third boat (G) is connected to the station (9).Each station (2 is the optical It consists of an optical transmitter r2Q that transmits a signal and an optical receiver (2η) that receives an optical signal.

Each optical splitter (21) has characteristics as shown in the schematic diagram in Figure 4. Each boat consists of an input optical fiber end for inputting an optical signal and an output optical fiber end for outputting an optical signal. .1st bow) +′,! 1) is the input optical fiber end (
Ml) and the output optical fiber end (Ml'), the second
The port (the second side consists of the input optical fiber end (Ml), the output optical fiber end (Ml), and the output optical fiber (M2'). Also, the third boat 12 moat consists of the input optical fiber end (T).
1) and an output optical fiber end (R+) 3, and the optical signal entering each powered optical fiber end passes through this optical splitter and enters all output optical fiber ends except that boat. . For example, the first boat L! The optical signal entering the input optical fiber end (Ml) of +1 is transmitted to the second. 3rd boat +23,
1. Output optical fiber end (Mz), (R+
). This optical distributor has the characteristic that optical signals are distributed in the same manner.

FIG. 5 shows the structure of an embodiment of the present invention having the above characteristics. In the same figure, fibers 31) to (, 3 have their ends connected to input light 7 fiber ends (Ml), (Ml), (
T1) is an optical fiber having 1. E ~ son-in-law) connects its end to the output optical fiber end (M4), (Ml)
, (R+).

+4U is a rod lens, which has a refractive index distribution of approximately square-law characteristics in the radial direction, and its length is set to 1/4 of the meandering pitch of the light beam. This rod lens ((40)) One end face is in contact with the end faces of the above-mentioned original fibers: 11) to (;you), and the other end face is made of two glazes with the X axis as the border. A diffraction grating (411, T42) is provided.

The diffraction grating (41) has a grating structure with a period of 11, so that the first-order diffracted light is coupled to both sides of the original fiber in the The above a1 is selected in the diffraction grating 11L5.
The grating period 12 of is selected to be equal to 11/2, and the first-order diffracted light is coupled to an optical fiber located two cycles of the fiber arrangement in the X direction from the optical fiber to which it would be coupled if the O-order diffracted light exists. do.

This connection relationship will be explained in detail below. The above diffraction grating f
,llll, +47! J has a cross-sectional structure as shown in FIG. That is, half of the grating period (l<l+ or 12) is a dielectric layer whose thickness is the optical path length of λ/4 (λ is the wavelength used).
Encased N membrane (consisting of 4 shallow layers. In this example, 5i02
uniformly forming a thin film on the end of the rod lens Lll;
A diffraction grating with a period l and a width e/2 was created by photolithography. Thereafter, a thin gold film (44) was deposited on the entire surface to form four reflectors having a diffraction grating structure.

In this type of reflector (45), the O-order diffracted light becomes zero. That is, in Fig. 6, the parallel light beam ('+1, 62 is the direction of mirror reflection,
That is, the second-order light wave +531 diffracted in the direction of the 0th-order diffracted light,
The phase relationship of (54) is that the luminous flux 6υ is 8102 with a thickness of λ/4
Since the light travels back and forth through the thin film and is reflected, a phase delay of λ/2 occurs compared to the light flux (1). Therefore, at a distance, the 0th-order diffracted light no longer exists in this phase grating because they cancel each other by 4"J due to interference.

Figure 7 shows the positional relationship between the optical fibers +31) and 13fil in the rod lens (upward direction).The input/output relationship of the original signal will be explained using this figure. From the end (Ml) to the rod lens (40
The optical signal that has entered is reflected and enters the output optical fiber 3a, which is normally located at a point symmetrical to the axes of this lens 4C (the inflection points of the X and y axes). However, as mentioned above, in the light reflection by the rod lens (4 (different diffraction grating t, 11), +4Z, there is no 0th order diffracted light, so the optical signal entering the end (Ml) of the output optical fiber 134) is 11 It almost doesn't exist. On the other hand, the input optical fiber (3υ end (M
Of the optical signals incident on the rod lens (41) from l),
The first-order diffracted light by the diffraction grating (41) produces a spot at the end of the output optical fiber (4) (Ml) and the end of the dummy optical fiber L3η. Fiber (, plow end (R1) and dummy optical fiber; produce a spot at the end of the candle).

The light that enters the end of the optical fiber 'm+ (, 1 second) is absorbed so that it does not leak to others.Therefore, the optical signal that enters the rod lens (1) from the end (Ml) is transmitted through the diffraction grating
, +42) and reflected at the end (Ml) , (R1)
will enter.

Similarly, the optical signal that entered the rod lens (formerly from the end (Ml) of the input optical fiber (32) to the diffraction grating +411
.

(It is deflected by four forces and passes through the ends (Ml) and (R4) to the output optical fiber 4) and enters tJIil.

Father, the optical signal incident on the rod lens tli from the end (T1) of the human-powered optical fiber ();9, &yo, the diffraction grating Il+
, 1421 at the end (M+').

(NId) to the output optical fiber +: +0. t,i
■Inject into.

In the end, the optical distributor shown in FIG. 5 has the characteristics shown in FIG. 4.

In the present invention, the optical splitter 41 is realized by a reflector having a diffraction grating structure so that the transmitted signal from the own station does not return to the own station. The optical distributor of the above embodiment is composed only of a fiber array and a reflective phase grating based on a rod lens profile, and has an extremely simple structure and high productivity. According to the present invention, it is possible to connect a plurality of optical distributors using a simple repeater, and a large-scale system can be constructed. At this time, the drawback of the large length of the fiber, which was an economic problem in the conventional star system, can be overcome, and the vibration in the star coupler of the optical cable can be eliminated. Of course, it is also possible to connect a plurality of optical distributors without using a repeater.

Furthermore, there is a collision detection system called Nenotower (C) which does not have a control station.
arrier 5ense Multiple Acc
ess with Collision Detection
on system), collisions can be easily detected by the digital source transmitter. That is, if a signal is received by the own station while the own station is transmitting, it is obvious that this signal is a signal from another station, and it is known that a collision has occurred.

In the above embodiment, a three-boat optical splitter is constructed using a reflector having a structure having two diffraction gratings with different periods, but in general, a (N-1) boat diffraction method is used to construct an N-boat optical splitter. A reflector having a structure having a grating may be used, and the present invention is not limited to the above embodiment.

It is also possible to configure it in a transmission type by using a λ/2 phase grating.

Further, although the above embodiment uses a rod lens with a length of 1/4 pitch, the present invention is not limited to this, and the light may be changed into parallel light (
collimating) or an equivalent optical system having the property of focusing parallel light may also be used.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an optical transmission system using a conventional star coupler, Fig. 2 is a structural diagram of an optical splitter proposed earlier, and Fig. 3 is an optical transmission system using the optical splitter of the present invention. System configuration diagram, Figure 4 is a schematic diagram showing the efficiency of the optical distributor of the present invention, Figure 5 is a perspective view of one embodiment of the present invention, Figure 6 is Qp s.
FIG. 7 is a diagram showing how optical signals are reflected in the reflector of the embodiment shown in the figure, and FIG. 7 is a diagram showing the positional relationship of the input and output optical fibers in the embodiment of FIG. 20... Optical distributor, 21... First boat, 22 ・
・・ a8.2 boat, 23 ・・
3rd boat, 31.32.33...Manpower optical fiber, 34.35.36...Output optical fiber, 4
0...Rod lens, 41.42...Diffraction grating, 4
5... Reflector s MIIM21T1... Input fiber end, Ml. M2 r RI... Output fiber end. 91 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] A boat group consisting of a plurality of boats arranged in parallel at predetermined positions, each consisting of an input fiber end and an output fiber end, each of which inputs and outputs an optical signal, and the trough input fiber ends of these boats. A reflector that reflects an optical signal emitted from the board and directs the optical signal to the output fiber end of a boat other than the board at the end of the input fiber that emitted it; An optical distributor comprising a rod lens or an optical system equivalent thereto for transmitting signals, wherein the reflector is a reflector having a diffraction grating structure.