Waveguide-type coupler/splitter

Abstract: A 2-input/2-output directional coupler is arranged as an element coupler/splitter for a first stage (D1), and 1-input/2-output coupler/splitters are used as element coupler/splitters for a second stage (D2) and its subsequent stages (D3...). Output ports of these element coupler/splitters are concatenated with input ports of other element coupler/splitters to form a 2-input/multi-output coupler/splitter. An optical signal can be inputted through one input port (d1) of the first-stage 2-input/2-output directional coupler, and an optical signal for optical line monitoring can be inputted through the other input port (d3). It is unnecessary, therefore, to use an (d3) optical wavelength division multiplexer/demultiplexer or other optical part which conventionally is connected at the time of optical line monitoring.

Description: The present invention relates to waveguide-type coupler/splitters effectively used in an optical fiber communication system and optical sensor system, and more particularly, to waveguide-type coupler/splitters which need not be connected with any other optical parts, such as an optical wavelength division multiplexer/demultiplexer, at the time of optical line monitoring in these systems. In an optical fiber communication system, such as the one shown in Fig. 1, a signal transmitted from one parent station 1 is divided into N number of signals by means of a 1-input/N-output waveguide-type coupler/splitter 2, and the individual signals are distributed to N number of child stations 4 1 , 4 2 , . . . 4 N by means of N number of fiber lines 3 1 , 3 2 , . . . 3 N , respectively. Referring now to Figs. 2 to 7, 1-input/16-output versions of the coupler/splitter 2 adapted to be used in this system will be described by way of example. A coupler/splitter A of the type shown in Fig. 2 uses, as each of its element coupler/splitters, a 1-input/2-output Y-branch waveguide I in which two output ports I b and I c are continuous with an input port I a , as shown in Fig. 3. The input and output ports I a , I b and I c , of these individual element coupler/splitters are concatenated to one another in four stages in a tournament-list style. A coupler/splitter B of the type shown in Fig. 4 uses, as each of its element coupler/splitters, a 1-input/2-output directional connector II formed of a 1-input/2-output coupler/splitter having a junction II d at which one of two waveguides is continuous and the other is discontinuous, as shown in Fig. 5. Input and output ports II a , II b and II c of these individual element coupler/splitters are concatenated to one another in four stages. A coupler/splitter C of the type shown in Fig. 6 uses, as each of its element coupler/splitters, a 1-input/2-output directional coupler III formed of a 1-input/3-output coupler/splitter having a junction III d at which two waveguides are discontinuous with another waveguide, as shown in Fig. 7. Input and output ports III a , III b and III c of these individual element coupler/splitters are concatenated to one another in four stages. In monitoring the optical fiber lines 3 1 , 3 2 , . . . 3 N without interrupting communication between the parent station and the child stations 4 1 , 4 2 , . . . 4 N , in the optical communication system shown in Fig. 1, it is necessary to connect an optical line monitoring device (e.g., OTDR) 5, which uses light with a monitoring wavelength λ 2 different from a communication wavelength λ 1 , as shown in Fig. 8, to the arrowed spot (Fig. 1) of an optical path connecting the parent station 1 and the 1-input/N-output coupler/splitter 2, through an optical wavelength division multiplexer/demultiplexer 6 for synthesizing and dividing light waves with the wavelengths λ 1 and λ 2 . Thus, when using the 1-input/N-output coupler/ splitter 2 composed of the concatenated 1-input/2-output element coupler/splitters I, II or III of the conventional configuration described above, the interposition of another optical part, such as the optical wavelength division multiplexer/demultiplexer (λ 1 ≠ λ 2 ) or an optical coupler (λ 1 = λ 2 ), is required in connecting the optical line monitoring device 5 between the coupler/splitter 2 and the parent station 1. According to the present invention, there is provided a waveguide-type coupler/splitter comprising a plurality of element coupler/splitters concatenated to one another, input ports of said individual element coupler/splitters being connected to output ports of other element coupler/splitters, thereby forming a linked sequence of coupling/splitting stages, said element coupler/splitter in the first stage being a 2-input/2-output evanescent coupler/splitter, and characterised in that: each of said element coupler/splitter in the second (D 2 ) and any subsequent stages are 1-input/2-output Y-branch waveguides having two output branches which are continuous with an input branch. In the coupler/splitter of the present invention, the first-stage element coupler/splitter is a 2-input/2-output coupler/splitter, and therefore, the input ports thereof can be used separately, one for communication and the other for optical line monitoring. Alternatively, the two input ports may be used individually as a running version and as a stand-by (spare). Thus, there is provided a waveguide-type coupler/ splitter capable of optical line monitoring without the interposition of any other optical part, such as an optical wavelength division multiplexer/demultiplexer or optical coupler. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a schematic view showing an example of an optical fiber communication system; Fig. 2 is a schematic view showing an example of a conventional waveguide-type coupler/splitter; Fig. 3 is a schematic view showing a 1-input/2-output element coupler/splitter of the Y-branch waveguide type used in the coupler/splitter of Fig. 2; Fig. 4 is a schematic view showing another example of the conventional waveguide-type coupler/splitter; Fig. 5 is a schematic view showing a 1-input/2-output element coupler/splitter of the directional connector type used in the coupler/splitter of Fig. 4; Fig. 6 is a schematic view showing still another example of the conventional waveguide-type coupler/ splitter; Fig. 7 is a schematic view showing a 1-input/2-output element coupler/splitter of the directional connector type used in the coupler/splitter of Fig. 6; Fig. 8 is a schematic view showing an optical part interposed for optical line monitoring in the optical communication system of Fig. 1; Fig. 9 is a schematic view showing a 2-input/16-output waveguide-type coupler/splitter according to an embodiment of the present invention; and Fig. 10 is a schematic view showing a 2-input/2-output element coupler/splitter of the directional connector type arranged in the first stage of the coupler/splitter according to the present invention. Fig. 9 is a schematic view showing a 2-input/16-output coupler/splitter. In this coupler/splitter D, the first-stage element coupler/splitter D 1 is a 2-input/2-output coupler/splitter, as shown in Fig. 10. The input port I a of a Y-branch waveguide I (as shown in Fig. 3) is concatenated to each of output ports d 2 and d 4 of the first stage coupler/splitter D 1 , thus forming a second-stage element coupler/splitter group D2 having four output ports. Further, the input port I a of additional Y-branch waveguides I are concatenated to each of the output ports I b and I c of each group-D 2 Y-branch waveguide, thus forming a third-stage element coupler/splitter group D 3 having eight output ports. Likewise, the input port I a of yet further Y-branch waveguides I are concatenated to each of the output ports I b and I c , of each group-D 3 Y-branch waveguide, thus forming a fourth-stage element coupler/splitter group D 4 having sixteen output ports. After the formation of the group D 4 , additional Y-branch waveguides may be successively concatenated in the same manner as aforesaid. If the 1-input/2-output element coupler/splitters are connected in (n - 1) stages in all, the resulting coupler/splitter becomes a 2-input/2 n -output coupler/splitter. In the waveguide-type coupler/splitter according to this invention, the coupler/splitter D 1 as an element coupler/splitter in the first stage is arranged so that a signal with a communication wavelength λ 1 is inputted through the one input port d 1 (or d 3 ), while a light beam for optical line monitoring with a monitoring wavelength λ 2 is inputted through the other input port d 3 (or d 1 ). Preferably, the first stage coupler/splitter D 1 should be one whose branch coupling ratio for light having a wavelength intermediate between the communication wavelength λ 1 and the monitoring wavelength λ 2 is wavelength-independent, that is, a coupler/splitter which is wavelength-flattened between the communication and monitoring wavelengths. As an example of the coupler/splitter of this type, there is an asymmetric Mach-Zehnder interferometer (WINC) which is proposed in Topical Meeting on Integrated Photonic Research 1990, W17. Preferably, the coupler/splitter D 1 is arranged so that a slit is cut in the one input port d 1 , for example, and a filter which transmits light with the communication wavelength λ 1 and reflects light with the monitoring wavelength λ 2 is housed in the slit, and at the same time, another slit is cut in the other input port d 3 , and a filter which reflects light with the communication wavelength λ 1 and transmits light with the monitoring wavelength λ 2 . Thus, according to the present waveguide-type coupler/splitter, the element coupler/splitters used are equal in number to the ones used in the conventional coupler/splitter. Since the first-stage element coupler/splitter is a 2-input/2-output coupler/splitter, however, one of its input ports can be used for optical line monitoring, so that it is unnecessary to use an exclusive optical part for optical line monitoring which conventionally is essential.

Claims: A waveguide-type coupler/splitter (D) comprising a plurality of element coupler/splitters (D 1 , D 2 , D 3 , D 4 ...) concatenated to one another, input ports of said individual element coupler/splitters being connected to output ports of other element coupler/splitters, thereby forming a linked sequence of coupling/spletting stages said element coupler/splitter in the first stage being a 2-input/2-output evanescent coupler/splitter (D 1 ), and characterised in that: each of said element coupler/splitter in the second (D 2 ) and any subsequent stages (D 3 , D 4 ...) are 1-input/2-output Y-branch waveguides having two output branches which are continuous with an input branch. A waveguide-type coupler/splitter according to claim 1, comprising two input ports and sixteen output ports. A waveguide-type coupler/splitter according to claim 1 or 2, wherein the branch coupling ratio of said first stage element coupler/splitter (D 1 ) is wavelength-independent for light having a wavelength within a predetermined range. A waveguide-type coupler/splitter according to claim 3, arranged so that said predetermined range is the wavelength range intermediate between a communication signal wavelength (λ 1 ) inputted through a first input port (d 1 ) and a monitoring wavelength (λ 2 ) inputted through a second input port (d 3 ). A waveguide-type coupler/splitter according to any preceding claim, wherein one of the input ports (d 1 ; d 3 ) of said first stage element coupler/splitter (D 1 ) is provided with a filter adapted to transmit light with a communication wavelength (λ 1 ) and reflect light with a monitoring wavelength (λ 2 ), and the other input port (d 1 ; d 3 ) is provided with a filter adapted to reflect light with the communication wavelength (λ 1 ) and transmit light with the monitoring wavelength (λ 2 ).

Inventors: NAKAMURA SHIRO, OYAMA ISAO, SHIMIZU TAKEO, YANAGAWA HISAHARU, NAKAMURA, SHIRO, OYAMA, ISAO, SHIMIZU, TAKEO, YANAGAWA, HISAHARU
Applicants: FURUKAWA ELECTRIC CO LTD, THE FURUKAWA ELECTRIC CO., LTD.
Application year: 1991
Main classification: G02B6
IPC codes: G02B6