Optical device, wavelength division multiplexing transmitter, wavelength division multiplexing receiver, and wavelength division multiplexing transmission and receiving system

• US 10,718,899 B2
• Filed: 03/29/2019
• Issued: 07/21/2020
• Est. Priority Date: 03/30/2018
• Status: Active Grant

• Current Assignee: Fujikura Limited
• Original Assignee: Fujikura Limited
• Inventors: Goi, Kazuhiro
• Primary Examiner(s): Pak, Sung H
• Application Number:
  US16/370,421
• Publication Number:
  US 20190302363A1
• Time in Patent Office: 480 Days
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/29341 Loop resonators operating in a whispering gallery mode evanescently coupled to a light guide, e.g. sphere or disk or cylinder evanescent coupling for sensing fluorescence G01N21/648
• CPC Class Codes: G02B 6/29355 Cascade arrangement of interferometers
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/3576 Temperature or heat actuation thermal forces controlling reflecting elements in general G02B26/0866; thermo-optic devices G02F1/0147
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: H04J 14/0297 Optical equipment protection

Abstract

An optical device includes: a first port group P including n ports P_i; a second port Q; and a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q. In a case where light beams L_i of predetermined different n wavelengths λ_i corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, the wavelength multiplexer/demultiplexer combines the light beams L_i into light L and outputs the light L to the second port Q. In a case where light L′ is inputted to the second port Q, the wavelength multiplexer/demultiplexer separates the light L′ into light beams L′_i of the wavelengths λ_i and outputs the light beams L′_i to the corresponding ports P_i.

Claims

1. An optical device according comprising:

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q;

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q;

wavelength splitters WD_i (i=1, 2, . . . , n) disposed between the corresponding ports P_i and the wavelength multiplexer/demultiplexer;

a wavelength combiner WM disposed between the second port Q and the wavelength multiplexer/demultiplexer; and

a switch disposed between the wavelength splitters WD_i and the wavelength combiner WM and arranged in parallel to the wavelength multiplexer/demultiplexer, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q,

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S,

each of the wavelength splitters WD_i couples a corresponding one of the light beams L_i or a corresponding one of the light beams L′

_i between a corresponding one of the ports P_i and the wavelength multiplexer/demultiplexer, and couples the light beam L_SP or the light beam L′

_SP between a corresponding one of the ports P_i and the switch,

the wavelength combiner WM couples the light L or the light L′

between the wavelength multiplexer/demultiplexer and the second port Q, and couples the light beam L_SP or the light beam L′

_SP between the switch and the second port Q, and

the switch, under control from an external member, selects a wavelength splitter corresponding to the selected port P_S as a selected wavelength splitter from among the wavelength splitters WD_i, and couples the light beam L_SP or the light beam L′

_SP between the selected wavelength splitter and the wavelength combiner WM.

2. The optical device according to claim 1, wherein

the first port group P further comprises a port P_n+1 in parallel to the ports P_i and connected directly to the wavelength multiplexer/demultiplexer,

the wavelength combiner WM is a wavelength selective switch,

the wavelength multiplexer/demultiplexer, in a case where the light beams L_i (i=1, 2, . . . , n) are inputted to the corresponding ports P_i (i=1, 2, . . . , n) and a light beam L_n+1 of a wavelength λ

_n+1 different from the wavelengths λ

_i (i=1, 2, . . . , n) and λ

_SP is inputted to the port P_n+1, multiplexes the light beams L_i (i=1, 2, . . . , n, n+1) to emit the light L and outputs the light L to the second port Q, and

the wavelength multiplexer/demultiplexer, in a case where the light L′

is inputted to the second port Q, demultiplexes the light L′

to emit the light beams L′

_i (i=1, 2, . . . , n, n+1) of the wavelengths λ

i (i=1, 2, . . . , n, n+1) and outputs the light beams L′

_i to the corresponding ports P_i (i=1, 2, . . . , n, n+1),

the wavelength selective switch, in a case where one port is selected as the selected port P_S from among the ports P_i (i=1, 2, . . . , n, n+1), couples the light beams L_i (i=1, 2, . . . , n, n+1) between the wavelength multiplexer/demultiplexer and the second port Q,

the wavelength selective switch, in a case where one port is selected as the selected port P_S from among the ports P_i (i=1, 2, . . . , n), couples the light beam L_SP or L′

_SP between the switch and the second port Q under control from the external member, and

the wavelength selective switch, in a case where the port P_n+1 is selected as the selected port P_S, couples the light beam L_SP or L′

_SP between the wavelength multiplexer/demultiplexer and the second port Q under control from an external member.

3. An optical device comprising:

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q;

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q; and

a switch group disposed between the wavelength multiplexer/demultiplexer and the second port Q, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q,

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S,

the wavelength multiplexer/demultiplexer comprises n ports p_i (i=1, 2, . . . , n) connected directly to the ports P_i (i=1, 2, . . . , n) and n ports q_i (i=1, 2, . . . , n) connected to the second port Q via the switch group,

the wavelength multiplexer/demultiplexer, in a case where the light beams L_i are inputted to the corresponding ports P_i, multiplexes the light beams L_i to emit the light L and couples the light L to a predetermined port q_Q of the ports q_i,

the wavelength multiplexer/demultiplexer, in a case where the light L′

is inputted to the port q_Q, demultiplexes the light L′

to emit the light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i, and

the wavelength multiplexer/demultiplexer selectively couples the light beam L_SP or L′

_SP between the ports p_i and the ports q_i, and

the switch group, under control from an external member, couples the light beam L_SP or L′

_SP between one port q_i (i is any of 1, 2, . . . , n) selectively coupled to the selected port P_S and the second port Q.

4. An optical device comprising:

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q;

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q; and

a switch group disposed between a port P_j (j is any of 1, 2, . . . , n) that is one of the ports P_i and the wavelength multiplexer/demultiplexer, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q,

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S,

the wavelength multiplexer/demultiplexer comprises n ports p_i (i=1, 2, . . . , n) connected directly or via the switch group to the ports P_i (i=1, 2, . . . , n) and n ports q_i (i=1, 2, . . . , n),

the wavelength multiplexer/demultiplexer, in a case where the light beams L_i are inputted to the corresponding ports P_i, multiplexes the light beams L_i to emit the light L and couples the light L to a predetermined port q_Q of the ports q_i,

the wavelength multiplexer/demultiplexer, in a case where the light L′

is inputted to the port q_Q, demultiplexes the light L′

to emit the light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i, and

the wavelength multiplexer/demultiplexer selectively couples the light beam L_SP or L′

_SP between the ports p_i and the ports q_i and couples the light beam L_SP or L′

_SP between a port p_j, of the ports p_i, corresponding to the port P_j and the port q_Q, and

the switch group, under control from an external member, couples the light beam L_SP or L′

_SP between one port q_i (i is any of 1, 2, . . . , n) selectively coupled to the selected port P_S and the port p_j.

5. An optical device comprising:

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q;

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q; and

n wavelength selective combiners WSM_i (i=1, 2, . . . , n) that constitute the wavelength multiplexer/demultiplexer and that are inserted in series with a main bus having one end as the second port Q, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q,

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S,

the ports P_i (i=1, 2, . . . , n) are connected directly to the corresponding wavelength selective combiners WSM_i,

each of the wavelength selective combiners WSM_i is constituted by a combination of a corresponding one of wavelength combiners WM_i (i=1, 2, . . . , n) and a corresponding one of wavelength selective switches WSS_i (i=1, 2, . . . , n),

in a case where the light beams L_i are inputted to the corresponding ports P_i, the wavelength combiners WM_i couple the light beams L_i to the main bus so that the wavelength multiplexer/demultiplexer emits the light L into which the light beams L_i are multiplexed and outputs the light L to the second port Q,

in a case where the light L′

is inputted to the second port Q, the wavelength combiners WM_i separate the light L′

into light beams L′

_i so that the wavelength multiplexer/demultiplexer emits the light beams L′

_i into which the light L′

is demultiplexed and outputs the light beams L′

_i to the corresponding ports P_i, and

one of the wavelength selective switches WSS_i (i is any of 1, 2, . . . , n) corresponding to the selected port P_S couples the light beam L_SP or L′

_SP between the selected port P_S and the main bus under control from an external member.

6. An optical device comprising:

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q;

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q,

n wavelength combiners WM_i (i=1, 2, . . . , n) that constitute the wavelength multiplexer/demultiplexer and that are inserted in series with a main bus having one end as the second port Q; and

wavelength selective switches WSS_i (i=1, 2, . . . , n) connected to the corresponding wavelength combiners WM_i (i=1, 2, . . . , n) are inserted in series with a secondary bus in parallel to the main bus, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q,

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S,

the secondary bus has a first end connected to a preceding stage or a subsequent stage of the wavelength multiplexer/demultiplexer when viewed from a second port Q side,

the ports P_i are connected directly to the corresponding wavelength combiners WM_i,

each of the wavelength combiners WM_i couples a corresponding one of the light beams L_i or L′

_i between a corresponding one of the ports P_i and the main bus and couples the light beam L_SP or L′

_SP between a corresponding one of the ports P_i and a corresponding one of the wavelength selective switches WSS_i,

each of the wavelength selective switches WSS_i, when selected under control from an external member, couples the light beam L_SP or L′

_SP between a corresponding one of the wavelength combiners WM_i and the secondary bus,

the wavelength multiplexer/demultiplexer is configured such that;

in a case where the light beams L_i are inputted to the corresponding ports P_i, the wavelength combiners WM_i couple the light beams L_i to the main bus so that the wavelength multiplexer/demultiplexer emits the light L into which the light beams L_i are multiplexed and outputs the light L to the second port Q; and

in a case where the light L′

is inputted to the second port Q, the wavelength combiners WM_i separate the light L′

into light beams L′

_i so that the wavelength multiplexer/demultiplexer emits the light beams L′

_i into which the light L′

is demultiplexed and outputs the light beams L′

_i to the corresponding ports P_i, and

one of the wavelength selective switches WSS_i (i is any of 1, 2, . . . , n) connected to a corresponding one of the wavelength combiners WM_i (i is any of 1, 2, . . . , n) corresponding to the selected port P_S couples the light beam L_SP or L′

_SP between the corresponding one of the wavelength combiners WM_i and the secondary bus under control from an external member.

7. The optical device according to claim 6, wherein

the first end of the secondary bus is connected directly to the subsequent stage of the wavelength multiplexer/demultiplexer when viewed from the second port Q side, and

the wavelength multiplexer/demultiplexer couples the light beam L_SP or L′

_SP between the first end of the secondary bus and the second port Q.

8. The optical device according to claim 6, further comprising another wavelength combiner disposed between the wavelength multiplexer/demultiplexer and the second port Q,

wherein the first end of the secondary bus is connected, via the another wavelength combiner, to the preceding stage of the wavelength multiplexer/demultiplexer when viewed from the second port Q side, and

the another wavelength combiner couples the light beams L_i between the wavelength multiplexer/demultiplexer and the second port Q and couples the light beam L_SP or L′

_SP between the secondary bus and the second port Q.

9. An optical device comprising:

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q; and

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q, and

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S,

the selected port P_S is a first selected port P_S1,

the wavelength λ

_SP is a wavelength λ

_SP1,

the light beam L_SP of the wavelength λ

_SP is a light beam L_SP1,

each of m ports (m is an integer that satisfies 1≤

m<

n) selected from among the ports P_i and different from the first selected port P_S1 is a j-th selected port P_Sj (j=2, 3, . . . , m+1),

light beams of different wavelengths λ

_SPj different from the wavelengths λ

_i and λ

_SP1 are light beams L_SPj and L′

_SPj,

in a case where the light beam L_SPj is inputted to the j-th selected port P_Sj, the light beam L_SPj is outputted to the second port Q, and

in a case where the light beam L′

_SPj is inputted to the second port Q, the light beam L′

_SPj is outputted to the j-th selected port P_Sj.

10. The optical device according to claim 9, further comprising:

first wavelength splitters WD_1i (i=1, 2, . . . , n) disposed between the corresponding ports P_i and the wavelength multiplexer/demultiplexer;

second wavelength splitters WD_2i (i=1, 2, . . . , n) disposed between the corresponding ports P_i and the wavelength multiplexer/demultiplexer;

a first wavelength combiner WM_a disposed between the second port Q and the wavelength multiplexer/demultiplexer;

a second wavelength combiner WM_b disposed between the second port Q and the wavelength multiplexer/demultiplexer;

a first switch disposed between the first wavelength splitters WD_1i and the first wavelength combiners WM_a and arranged in parallel to the wavelength multiplexer/demultiplexer; and

a second switch disposed between the second wavelength splitters WD_2i and the second wavelength combiner WM_b and arranged in parallel to the wavelength multiplexer/demultiplexer,

wherein each of the first wavelength splitters WD_1i couples a corresponding one of the light beams L_i or a corresponding one of the light beams L′

_i between a corresponding one of the ports P_i and the wavelength multiplexer/demultiplexer, and couples a light beam L_SP1 or a light beam L′

_SP1 between a corresponding one of the ports P_i and the first switch,

each of the second wavelength splitters WD_2i couples a corresponding one of the light beams L_i or a corresponding one of the light beams L′

_i between a corresponding one of the ports P_i and the wavelength multiplexer/demultiplexer, and couples a light beam L_SP2 or a light beam L′

_SP2 between a corresponding one of the ports P_i and the second switch,

the first wavelength combiner WM_a couples the light beams L_i or the light beams L′

_i between the wavelength multiplexer/demultiplexer and the second port Q, and couples the light beam L_SP1 or the light beam L′

_SP1 between the first switch and the second port Q,

the second wavelength combiner WM_b couples the light beams L_i or the light beams L′

_i between the wavelength multiplexer/demultiplexer and the second port Q, and couples the light beam L_SP2 or the light beam L′

_SP2 between the second switch and the second port Q,

the first switch, under control from an external member, selects a wavelength splitter corresponding to the first selected port P_S1 as the first selected wavelength splitter from among the first wavelength splitters WD_1i, and couples the light beam L_SP1 or L′

_SP1 between the first selected wavelength splitter and the first wavelength combiner WM_a, and

the second switch, under control from an external member, selects a wavelength splitter corresponding to the second selected port P_S2 as the second selected wavelength splitter from among the second wavelength splitters WD_2i, and couples the light beam L_SP2 or L′

_SP2 between the second selected wavelength splitter and the second wavelength combiner WM_b.

11. The optical device according to claim 9, further comprising:

wavelength splitters WD_i (i=1, 2, . . . , n) disposed between the corresponding ports P_i and the wavelength multiplexer/demultiplexer;

a wavelength combiner WM disposed between the second port Q and the wavelength multiplexer/demultiplexer; and

a switch disposed between the wavelength splitters WD_i and the wavelength combiner WM and arranged in parallel to the wavelength multiplexer/demultiplexer,

wherein each of the wavelength splitters WD_i couples a corresponding one of the light beams L_i or a corresponding one of the light beams L′

_i between a corresponding one of the ports P_i and the wavelength multiplexer/demultiplexer, and couples the light beam L_SP1 or L′

_SP1 and the light beam L_SP2 or L′

_SP2 between a corresponding one of the ports P_i and the switch,

the wavelength combiner WM couples the light L or the light L′

between the wavelength multiplexer/demultiplexer and the second port Q, and couples the light beam L_SP1 or L′

_SP1 and the light beam L_SP2 or L′

_SP2 between the switch and the second port Q, and

the switch, under control from an external member, selects a wavelength splitter corresponding to the first selected port P_S1 as the first selected wavelength splitter from among the wavelength splitters WD_i selects a wavelength splitter corresponding to the second selected port P_S2 as the second selected wavelength splitter from among the wavelength splitters WD_i, couples the light beam L_SP1 or the light beam L′

_SP1 between the first selected wavelength splitter and the wavelength combiner WM, and couples the light beam L_SP2 or the light beam L′

_SP2 between the second selected wavelength splitter and the wavelength combiner WM.

12. A wavelength division multiplexing transmitter comprising:

an optical device that comprises;

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q; and

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q, wherein

the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q, and

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S;

modulators M_i having respective input ports PI_i (i=1, 2, . . . , n) and respective output ports PO_i, wherein the output ports PO_i are connected to corresponding ports P_i;

optical sources OS_i connected to the corresponding input ports PI_i and that output respective light beams L_i;

a spare optical source OS_SP that outputs a light beam L_SP; and

a spare optical source switch disposed between the spare optical source OS_SP and the input ports PI_i and that selects one input port as a selected input port from among the input ports PI_i under control from an external member and that inputs the light beam L_SP to the selected input port.

13. A wavelength division multiplexing transmission and receiving system comprising:

a wavelength division multiplexing transmitter according to claim 12;

a wavelength division multiplexing receiver comprising;

an optical device comprising;

a first port group P including n ports P_i (i=1, 2, . . . ;

n);

a second port Q; and

a wavelength multiplexer/demultiplexer disposed between the first port group P and the second port Q,

wherein the wavelength multiplexer/demultiplexer, in a case where light beams L_i of predetermined different n wavelengths λ

_i (i=1, 2, . . . , n) corresponding to the respective ports P_i are inputted to the wavelength multiplexer/demultiplexer, combines the light beams L_i into light L and outputs the light L to the second port Q,

the wavelength multiplexer/demultiplexer, in a case where light L′

is inputted to the second port Q, separates the light L′

into light beams L′

_i of the wavelengths λ

_i and outputs the light beams L′

_i to the corresponding ports P_i,

one port is selected as a selected port P_S from among the ports P_i,

in a case where a light beam L_SP of a wavelength λ

_SP different from the wavelengths λ

_i is inputted to the selected port P_S, the light beam L_SP is outputted to the second port Q, and

in a case where a light beam L′

_SP of the wavelength λ

_SP is inputted to the second port Q, the light beam L′

_SP is outputted to the selected port P_S;

photodetectors D_i that comprises respective light receiving elements D_OPi (i=1, 2, . . . , n) coupled to corresponding ports P_i; and

an optical fiber that connects between a second port Q of the wavelength division multiplexing transmitter and a second port Q of the wavelength division multiplexing receiver.