Optical fiber amplifier and dispersion compensating fiber module for optical fiber amplifier

Claim 2

An optical fiber amplifier as set forth in claim 1, characterized in that said reflection means (4) is formed as a Faraday rotation reflecting mirror.

Claim 3

An optical fiber amplifier including a rare earth doped fiber (1), characterized in that it comprises: a pump light source (2); a first optical coupler (3-1) for introducing pump light from said pump light source (2) into one end of said rare earth doped fiber (1); a second optical coupler (3-2) for demultiplexing residual pump light originating from the pump light introduced into the one end of said rare earth doped fiber (1) by way of said first optical coupler (3-1) and arriving at the other end of said rare earth doped fiber (1); a reflecting mirror (4) for reflecting the residual pump light demultiplexed by said second optical coupler (3-2) so as to be introduced back into said rare earth doped fiber (1) by way of said second optical coupler (3-2); and an optical isolator (5) interposed between said pump light source (2) and said first optical coupler (3-1) for preventing unstable operation of said pump light source (2) arising from interference of the residual pump light introduced back into said rare earth doped fiber (1).

Claim 4

An optical fiber amplifier including a first rare earth doped fiber (11-1) and a second rare earth doped fiber (11-2) disposed at front and rear stages, characterized in that it comprises: first means for introducing pump light into one end of one of said first rare earth doped fiber (11-1) and said second rare earth doped fiber (11-2) by way of an optical circulator (15) having three or more ports and a first optical coupler (13-1); second means for demultiplexing residual pump light originating from the pump light introduced into the one end of the one rare earth doped fiber by said first means and arriving at the other end of the one rare earth doped fiber by a second optical coupler (13-2) and reflecting the demultiplexed residual pump light by reflection means (14) so as to be introduced back into the one rare earth doped fiber; and third means for causing the residual pump light reflected from said reflection means (14) and introduced back into the one rare earth doped fiber by said second means to follow, after passing the one rare earth doped fiber, a different optical path by said optical circulator (15) and multiplexing the residual pump light in the different optical path with an output of the other one of said first rare earth doped fiber (11-1) and said second rare earth doped fiber (11-2) by a third optical coupler (13-3).

Claim 5

An optical fiber amplifier including a first rare earth doped fiber (11-1) and a second rare earth doped fiber (11-2) disposed at front and rear stages, characterized in that it comprises: a pump light source (12); a first optical coupler (13-1) provided at one end of one of said first rare earth doped fiber (11-1) and said second rare earth doped fiber (11-2); a second optical coupler (13-2) provided at the other end of the one rare earth doped fiber; a third optical coupler (13-3) provided at one end of the other one of said first rare earth doped fiber (11-1) and said second rare earth doped fiber (11-2); a reflecting mirror (14) for reflecting residual pump light demultiplexed by said second optical coupler (13-2) so as to be introduced back into the one rare earth doped fiber by way of said second optical coupler (13-2); and an optical circulator (15) having three or more ports connected to said pump light source (12), said first optical coupler (13-1) and said third optical coupler (13-3); and wherein pump light from said pump light source (12) is introduced into one end of the one rare earth doped fiber by way of said optical circulator (15) and said first optical coupler (13-1), and residual pump light originating from the pump light introduced into the one end of the one rare earth doped fiber and arriving at the other end of the one rare earth doped fiber is demultiplexed by said second optical coupler (13-2) and reflected by said reflecting mirror (14) so as to be introduced back into the one rare earth doped fiber, whereafter the residual pump light is introduced, after passing the one rare earth doped fiber, into a different optical path by said optical circulator (15) so that the residual pump light is thereafter multiplexed with an output of the other rare earth doped fiber by said third optical coupler (13-3).

Claim 6

An optical fiber amplifier as set forth in claim 5, characterized in that it further comprises an isolator provided at an input port of said optical fiber amplifier to which input signal light is inputted, another isolator provided between an output of said second optical coupler (13-2) and an input of said third optical coupler (13-3), and a further isolator provided at an output port of said optical fiber amplifier from which output signal light is outputted.

Claim 7

An optical fiber amplifier including a first rare earth doped fiber (21-1) and a second rare earth doped fiber (21-2) disposed at front and rear stages, characterized in that it comprises: first means for branching pump power at a ratio of n:1, n being a real number equal to or greater than 1, by an optical branching element (23), multiplexing the pump light from a port of said optical branching element (23) by a first optical coupler (24-1) and introducing the multiplexed light into one end of one of said first rare earth doped fiber (21-1) and said second rare earth doped fiber (21-2); second means for extracting residual pump power originating from the pump light introduced into the one end of the one rare earth doped fiber by said first means and arriving at the other end of the one rare earth doped fiber by a second optical coupler (24-2) connected to the other end of the one rare earth doped fiber, multiplexing the extracted residual pump power by a third optical coupler (24-3) and introducing the multiplexed power into one end of the other one of said first rare earth doped fiber (21-1) and said second rare earth doped fiber (21-2); and third means for multiplexing the pump power from another port of said optical branching element (23) branched by said optical branching element (23) and introducing the multiplexed power into the other end of the other rare earth doped fiber by a fourth optical coupler (24-4).

Claim 8

An optical fiber amplifier including a first rare earth doped fiber (21-1) and a second rare earth doped fiber (21-2) disposed at front and rear stages, characterized in that it comprises: a pump light source (22); an optical branching element (23) for branching pump power from said pump light source (22) at a ratio of n:1, n being a real number equal to or greater than 1; a first optical coupler (24-1) for multiplexing the pump light from a port of said optical branching element (23) and introducing the multiplexed light into one of said first rare earth doped fiber (21-1) and second rare earth doped fiber (21-2); a second optical coupler (24-2) for extracting residual pump power outputted from the one rare earth doped fiber; a third optical coupler (24-3) for multiplexing the residual pump power extracted by said second optical coupler (24-2) and introducing the multiplexed power into the other one of said first rare earth doped fiber (21-1) and said second rare earth doped fiber (21-2); and a fourth optical coupler (24-4) for multiplexing the pump power from another port of said optical branching element (23) branched by said optical branching element (23) and introducing the multiplexed power into the other rare earth doped fiber.

Claim 9

An optical fiber amplifier as set forth in claim 8, characterized in that it further comprises an isolator provided at an input port of said optical fiber amplifier to which input signal light is inputted, another isolator provided between said pump light source (22) and said optical branching element (23), a further isolator provided between said second optical coupler (24-2) and a signal port of said third optical coupler (24-3), and a still further isolator provided at an output port of said optical fiber amplifier from which output signal light is outputted.

Claim 10

An optical fiber amplifier including a rare earth doped fiber (31), characterized in that it comprises: a pump light source (32); an optical circulator (33) having three or more ports one of which is connected to said pump light source (32); a first optical coupler (34-1) for multiplexing pump light introduced thereto from said pump light source (32) by way of said optical circulator (33) and introducing the multiplexed light into one end of said rare earth doped fiber (31); a second optical coupler (34-2) for demultiplexing residual pump light originating from the pump light introduced into the one end of said rare earth doped fiber (31) by said first optical coupler (34-1) and arriving at the other end of said rare earth doped fiber (31); a reflecting mirror (35) for reflecting the residual pump light demultiplexed by said second optical coupler (34-2) so as to be introduced back into said rare earth doped fiber (31) by way of said second optical coupler (34-2); a residual pump light detector (36) for detecting the residual pump light introduced back into said rare earth doped fiber (31) by said reflecting mirror (35) and inputted from the one end of said rare earth doped fiber (31) to said optical circulator (33) by way of said first optical coupler (34-1); and a controller (37) for controlling said pump light source (32) so that the residual pump light detected by said residual pump light detector (36) may be constant.

Claim 11

An optical fiber amplifier as set forth in claim 3, 5 or 10, characterized in that a Faraday rotation reflecting mirror is used for said reflecting mirror (4; 14; 35).

Claim 12

An optical fiber amplifier as set forth in claim 3, 5, 8 or 10, characterized in that it further comprises an optical circulator through which input signal light is inputted to said optical fiber amplifier and through which output signal light of said optical fiber amplifier is outputted.

Claim 13

An optical fiber amplifier as set forth in claim 10, characterized in that it further comprises an isolator provided at an input port of said optical fiber amplifier to which input signal light is inputted and another isolator provided at an output port of said optical fiber amplifier from which output signal light is outputted.

Claim 14

An optical fiber amplifier, characterized in that a rare earth doped fiber optical amplification element formed from a rare earth doped fiber (51; 61; 71) and a Raman optical amplification element which is pumped with pump light to cause Raman amplification to occur are connected in cascade connection.

Claim 15

An optical fiber amplifier, characterized in that a rare earth doped fiber optical amplification element formed from a rare earth doped fiber (61; 71) and a Raman optical amplification element which is pumped with pump light, which is capable of pumping said rare earth doped fiber optical amplification element, to cause Raman amplification to occur are connected in cascade connection; and that a pump light source (63; 73) for supplying pump light for pumping said rare earth doped fiber optical amplification element and said Raman optical amplification element is provided.

Claim 16

An optical fiber amplifier, characterized in that a rare earth doped fiber optical amplification element formed from a rare earth doped fiber (51; 61; 71) and a Raman optical amplification element formed from a dispersion compensating fiber (52; 62; 72) which is pumped with pump light to cause Raman amplification to occur are connected in cascade connection at two front and rear stages.

Claim 17

An optical fiber amplifier as set forth in claim 16, characterized in that said Raman optical amplification element is disposed as a front stage amplification element while said rare earth doped fiber optical amplification element is disposed as a rear stage amplification element.

Claim 18

An optical fiber amplifier as claimed in claim 16, characterized in that said rare earth doped fiber optical amplification element is formed as an optical amplification element having a low noise figure and is disposed as a front stage amplification element while said Raman optical amplification element is disposed as a rear stage amplification element.

Claim 19

An optical fiber amplifier as claimed in any one of claims 14 to 16, characterized in that a pump light source (53-2; 63; 73) for pumping said Raman optical amplification element includes a pair of pump light sources and a polarizing multiplexer for orthogonally polarizing and multiplexing pump light from said pump light sources.

Claim 20

An optical fiber amplifier as claimed in any one of claims 14 to 16, characterized in that a pump light source (53-2; 63; 73) for pumping said Raman optical amplification element includes a combination of a pump light source and a depolarizer by which pump light is depolarized.

Claim 21

An optical fiber amplifier as claimed in any one of claims 14 to 16, characterized in that a pump light source (53-2; 63; 73) for pumping said Raman optical amplification element produces modulated pump light.

Claim 22

An optical fiber amplifier, characterized in that it comprises: a rare earth doped fiber (51) and a dispersion compensating fiber (52) disposed at two front and rear stages; a first pump light source (53-1) for producing pump light of a first wavelength band for said rare earth doped fiber (51); a first optical coupler (54-1) for introducing the pump light from said first pump light source (53-1) into said rare earth doped fiber (51); a second pump light source (53-2) for producing pump light of a second wavelength band for said dispersion compensating fiber (52); and a second optical coupler (54-2) for introducing the pump light from said second pump light source (53-2) into said dispersion compensating fiber (52); said dispersion compensating fiber (52) being pumped with the pump light of the second wavelength band from said second pump light source (53-2) to cause Raman amplification to occur.

Claim 23

An optical fiber amplifier as set forth in claim 22, characterized in that said rare earth doped fiber (51) is formed from an erbium-doped-fiber, and the wavelength band of the pump light produced by said first pump light source (53-1) is a 0.98 µm band while the wavelength band of the pump light produced by said second pump light source (53-2) is a 1.47 µm band.

Claim 24

An optical fiber amplifier, characterized in that it comprises: an erbium-doped-fiber (61) and a dispersion compensating fiber (62) disposed at two front and rear stages; a pump light source (63) for producing pump light; and an optical coupler (64) for introducing the pump light from said pump light source (63) into said erbium-doped-fiber (61); said dispersion compensating fiber (62) being pumped with residual pump light from said erbium-doped-fiber (61) to cause Raman amplification to occur.

Claim 25

An optical fiber amplifier, characterized in that it comprises: an erbium-doped-fiber (71) and a dispersion compensating fiber (72) disposed at two front and rear stages; a pump light source (73) for producing pump light; and an optical coupler (74) for introducing the pump light from said pump light source (73) into said dispersion compensating fiber (72); said erbium-doped-fiber (71) being pumped with residual pump light from said dispersion compensating fiber (72).

Claim 26

An optical fiber amplifier, characterized in that it comprises: a dispersion compensating fiber (81) doped with a rare earth element; a pump light source (82) for producing pump light for said dispersion compensating fiber (81); and an optical coupler (83) for introducing the pump light from said pump light source (82) into said dispersion compensating fiber (81).

Claim 27

An optical fiber amplifier, characterized in that it comprises: an erbium-doped-fiber (91) and a dispersion compensating fiber (92) disposed at two front and rear stages; a pump light source (93) for producing pump light for said erbium-doped-fiber (91); an optical coupler (94) for introducing the pump light from said pump light source (93) into said erbium-doped-fiber (91); and an optical filter (95) interposed between said erbium-doped-fiber (91) and said dispersion compensating fiber (92) for intercepting residual pump light coming out from said erbium-doped-fiber (91).

Claim 28

An optical fiber amplifier, characterized in that a rare earth doped fiber optical amplification element formed from a rare earth doped fiber (102; 111) and a Raman optical amplification element formed from a silica-type-optical-fiber (101; 112) which causes, when pumped with pump light, Raman amplification to occur are connected in cascade connection at two front and rear stages.

Claim 29

An optical fiber amplifier as set forth in claim 28, characterized in that said Raman optical amplification element is disposed as a front stage amplification element while said rare earth doped fiber optical amplification element is disposed as a rear stage amplification element.

Claim 30

An optical fiber amplifier as claimed in claim 28, characterized in that said rare earth doped fiber optical amplification element is formed as an optical amplification element having a low noise figure and is disposed as a front stage amplification element while said Raman optical amplification element is disposed as a rear stage amplification element.

Claim 31

An optical fiber amplifier, characterized in that it comprises: a silica-type-optical-fiber (101) and an erbium-doped-fiber (102) provided at a front stage and a rear stage, respectively; a silica-type-optical-fiber pump light source (103-1) for producing pump light of a wavelength band for said silica-type-optical-fiber (101); an optical coupler (104-1) for introducing the pump light from said silica-type-optical-fiber pump light source (103-1) into said silica-type-optical-fiber (101); an erbium-doped-fiber pump light source (103-2) for producing pump light of a wavelength band for said erbium-doped-fiber (102); and another optical coupler (104-2) for introducing the pump light from said erbium-doped-fiber pump light source (103-2) into said erbium-doped-fiber (102); said silica-type-optical-fiber (101) being pumped with the pump light from said silica-type-optical-fiber pump light source (103-1) to cause Raman amplification to occur.

Claim 32

An optical fiber amplifier, characterized in that it comprises: an erbium-doped-fiber (111) having a low noise figure and a silica-type-optical-fiber (112) provided at a front stage and a rear stage, respectively; a silica-type-optical-fiber pump light source (113-2) for producing pump light of a wavelength band for said silica-type-optical-fiber (112); an optical coupler (114-2) for introducing the pump light from said silica-type-optical-fiber pump light source (113-2) into said silica-type-optical-fiber (112); an erbium-doped-fiber pump light source (113-1) for producing pump light of a wavelength band for said erbium-doped-fiber (111); and another optical coupler (114-1) for introducing the pump light from said erbium-doped-fiber pump light source (113-1) into said erbium-doped-fiber (111); said silica-type-optical-fiber (112) being pumped with the pump light from said silica-type-optical-fiber pump light source (113-2) to cause Raman amplification to occur.

Claim 33

An optical fiber amplifier as set forth in claim 31 or 32, characterized in that it further comprises a pump light source which produces pump light and serves both as said silica-type-optical-fiber pump light source (103-1; 113-2) and said erbium-doped-fiber pump light source (103-2; 113-1).

Claim 34

An optical fiber amplifier, characterized in that it comprises: a rare earth doped fiber optical amplification element formed from a rare earth doped fiber (121-1; 131-1) and having a low noise figure, said rare earth doped fiber optical amplification element being disposed as a front stage amplification element; a Raman optical amplification element for causing Raman amplification to occur when pumped with pump light, said Raman optical amplification section being disposed as a middle stage amplification element; and another rare earth doped fiber optical amplification element formed from a rare earth doped fiber (121-2; 131-2) and disposed as a rear stage amplification element.

Claim 35

An optical fiber amplifier as set forth in claim 34, characterized in that said Raman optical amplification element is formed as an optical amplification element formed from a dispersion compensating fiber (132).

Claim 36

An optical fiber amplifier as set forth in claim 34, characterized in that said Raman optical amplification element is formed as an optical amplification element formed from a silica-type-optical-fiber (122).

Claim 37

An optical fiber amplifier, characterized in that it comprises: a first erbium-doped-fiber (131-1) having a low noise figure, a dispersion compensating fiber (132) and a second erbium-doped-fiber (131-2) provided at a front stage, a middle stage and a rear stage, respectively; a first erbium-doped-fiber pump light source (133-1) for producing pump light of a wavelength band for said first erbium-doped-fiber (131-1); an optical coupler (134-1) for introducing the pump light from said first erbium-doped-fiber pump light source (133-1) into said first erbium-doped-fiber (131-1); a dispersion compensating fiber pump light source (133-2) for producing pump light of a wavelength band for said dispersion compensating fiber (132); another optical coupler (134-2) for introducing the pump light from said dispersion compensating fiber pump light source (133-2) into said dispersion compensating fiber (132); a second erbium-doped-fiber pump light source (133-3) for producing pump light of a wavelength band for said second erbium-doped-fiber (131-2); and a further optical coupler (134-3) for introducing the pump light from said second erbium-doped-fiber pump light source (133-3) into said second erbium-doped-fiber (131-2); said dispersion compensating fiber (132) being pumped with the pump light from said dispersion compensating fiber pump light source (133-2) to cause Raman amplification to occur.

Claim 38

An optical fiber amplifier, characterized in that it comprises: a first erbium-doped-fiber (121-1) having a low noise figure, a silica-type-optical-fiber (122) and a second erbium-doped-fiber (121-2) provided at a front stage, a middle stage and a rear stage, respectively; a first erbium-doped-fiber pump light source (123-1) for producing pump light of a wavelength band for said first erbium-doped-fiber (121-1); an optical coupler (124-1) for introducing the pump light from said first erbium-doped-fiber pump light source (123-1) into said first erbium-doped-fiber (121-1); a silica-type-optical-fiber pump light source (123-2) for producing pump light of a wavelength band for said silica-type-optical-fiber (122); another optical coupler (124-2) for introducing the pump light from said silica-type-optical-fiber pump light source (123-2) into said silica-type-optical-fiber (122); a second erbium-doped-fiber pump light source (123-3) for producing pump light of a wavelength band for said second erbium-doped-fiber (121-2); and a further optical coupler (124-3) for introducing the pump light from said second erbium-doped-fiber pump light source (123-3) into said second erbium-doped-fiber (121-2); said silica-type-optical-fiber (122) being pumped with the pump light from said silica-type-optical-fiber pump light source (123-2) to cause Raman amplification to occur.

Claim 39

A dispersion compensating fiber module for an optical fiber amplifier, characterized in that it comprises a dispersion compensating fiber (141), and a pump light source (142) for pumping said dispersion compensating fiber (141) to cause Raman amplification to occur.

Claim 40

An optical fiber amplifier including a dispersion compensating fiber (141), characterized in that it comprises: a pump light source (142); and an optical coupler (143) for introducing pump light from said pump light source (142) into said dispersion compensating fiber (141); said dispersion compensating fiber (141) being pumped with pump light from said pump light source (142) to cause Raman amplification to occur.

Claim 41

An optical fiber amplifier as set forth in claim 40, characterized in that it further comprises an optical circulator through which input signal light is inputted to said optical fiber amplifier and through which output signal light of said optical fiber amplifier is outputted.

Claim 42

An optical fiber amplifier as set forth in claim 40, characterized in that it further comprises an isolator provided at an input port of said optical fiber amplifier to which input signal light is inputted and/or another isolator provided at an output port of said optical fiber amplifier from which output signal light is outputted.

Claim 43

An optical fiber amplifier including a silica-type-optical-fiber (151), characterized in that it comprises: a pump light source (152); and an optical coupler (153) for introducing pump light from said pump light source (152) into said silica-type-optical-fiber (151); said silica-type-optical-fiber (151) being pumped with the pump light from said pump light source (152) to cause Raman amplification to occur.

Claim 44

An optical fiber amplifier as set forth in claim 43, characterized in that it further comprises an optical circulator through which input signal light is inputted to said optical fiber amplifier and through which output signal light of said optical fiber amplifier is outputted.

Claim 45

An optical fiber amplifier, characterized in that it comprises: a rare earth doped fiber optical amplification element (154) formed from a rare earth doped fiber (61); and an optical fiber attenuation element (155) formed from an optical fiber or an optical fiber with an optical isolator for suppressing unstable operation of said rare earth doped fiber optical amplification element (154).

Claim 46

An optical fiber amplifier, characterized in that it comprises: an optical amplification unit including a front stage optical amplification element (156-1) and a rear stage optical amplification element (156-2) each formed as a rare earth doped fiber optical amplification element formed from a rare earth doped fiber (121-1, 121-2); and an optical fiber attenuation element (157) formed from an optical fiber or an optical fiber with an optical isolator interposed between said front stage optical amplification element (156-1) and said rear stage optical amplification element (156-2) of said optical amplification unit for suppressing unstable operation of said optical amplification unit.

Claim 47

An optical fiber amplifier as set forth in claim 45 or 46, characterized in that said optical fiber attenuation element (155; 157) serves also as a Raman optical amplification element which is pumped with pump light to cause Raman amplification to occur.