Optical device with an optical coupler for effecting light branching and/or combining and an optical amplifier

Claim 2

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier arranged on said first light guiding means between said first and second positions is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means.

Claim 3

An optical device according to claim 1, further comprising a semiconductor substrate, and wherein said first, second and third light guiding means respectively comprise channel waveguides monolithically integrated with said light branching and light combining means, and said optical amplifier on said semiconductor substrate.

Claim 4

An optical device according to claim 1, wherein said first light guiding means comprises an active layer.

Claim 5

An optical device according to claim 1, wherein said light branching and light combining means respectively comprise etched grooves for splitting a wave front of the light wave at least with respect to a horizontal direction of said first light guiding means.

Claim 6

An optical device according to claim 4, wherein said first light guiding means comprises an active layer and said etched grooves respectively extend in a depth direction beyond said active layer.

Claim 7

An optical device according to claim 4, wherein said etched grooves respectively comprise two end surfaces forming right angles relative to each other and said end surfaces respectively extend in the horizontal direction of said first light guiding means from a central point of said first and second positions forming angles of 45 degrees relative to opposite propagation directions of the wave light in said first light guiding means.

Claim 8

An optical device according to claim 4, wherein said etched grooves are respectively formed deviated from a central line of said first light guiding means extending along a propagation direction of the light wave in said first light guiding means.

Claim 9

An optical device according to claim 1, wherein each of said second and third light guiding means is connected to said first light guiding means in a T-shaped configuration and a Y-shaped configuration, respectively.

Claim 10

An optical device according to claim 1, further comprising a receiver portion for receiving the light wave propagated through said second light guiding means, and wherein said light branching couples the light waves propagated through said first light guiding means in opposite directions to said second light guiding means at equal branching ratios.

Claim 11

An optical device according to claim 1, further comprising a transmitter portion for transmitting the light wave propagated through said third light guiding means, and wherein said light combining means couples the light wave propagated through said third light guiding means to said first light guiding means in opposite directions at equal branching ratios.

Claim 12

An optical device according to claim 10, wherein said transmitter portion comprises a semiconductor laser.

Claim 13

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, said optical amplifier comprising a semiconductor laser which operates by a current injection below threshold, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity.

Claim 14

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, said optical amplifier comprising a semiconductor laser which operates by a current injection below threshold, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity.

Claim 15

An optical device comprising: first light guiding means for guiding a light wave; antireflection coatings formed on opposite ends of said first light guiding means; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity.

Claim 16

An optical device comprising: first light guiding means for guiding a light wave; antireflection coatings formed on opposite ends of said first light guiding means; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity.

Claim 17

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity; and a receiver portion for receiving the light wave propagated through said second light guiding means, and wherein said light branching means couples the light waves propagated through said first light guiding means in opposite directions to said second light guiding means at equal branching ratios, said receiver portion comprising a photodetector having a semiconductor laser structure which operates by applying a reverse bias voltage.

Claim 18

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are guided into said second light guiding means with the same intensity; and a receiver portion for receiving the light wave propagated through said second light guiding means, and wherein said light branching means couples the light waves propagated through said first light guiding means in opposite directions to said second light guiding means at equal branching ratios, said receiver portion comprising a photodetector having a semiconductor laser structure which operates by applying a reverse bias voltage.

Claim 19

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave; fourth light guiding means for guiding a light wave, said fourth light guiding means being connected to said third light guiding means at a second position different from said first position; fifth light guiding means for guiding a light wave, said fifth light guiding means extending between said first and second positions; light combining means arranged near said first position; light combining means arranged near said second position; and an optical amplifier arranged on said fifth light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first and third light guiding means from opposite directions are guided into said second light guiding means with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said fifth light guiding means.

Claim 20

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave; fourth light guiding means for guiding a light wave, said fourth light guiding means being connected to said third light guiding means at a second position different from said first position; fifth light guiding means for guiding a light wave, said fifth light guiding means extending between said first and second positions; light combining means arranged near said first position; light combining means arranged near said second position; and an optical amplifier arranged on said fifth light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first and third light guiding means from opposite directions are guided into said second light guiding means with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said fifth light guiding means.

Claim 21

An optical communication system comprising: a plurality of optical nodes each comprising an optical device comprising a first light waveguide for guiding a light wave, a second light waveguide for guiding a light wave which is connected to said first light waveguide at a first position, a third light waveguide for guiding a light wave which is connected to said first light waveguide at a second position different from the first position, a light combining device arranged near the first position, a light branching device arranged near the second position, and an optical amplifier arranged on said first light waveguide between the first and second positions for compensating for a light loss of the light wave caused by each of said light branching device and said light combining device, a light transmission line for connecting said nodes, said light transmission line being connected to said first light waveguide, and further optical amplifiers respectively arranged at opposite ends of the first light guiding means, wherein an amplification factor of said optical amplifier arranged on said first light waveguide between the first and second positions is set so that the light waves entering said first light waveguide from opposite directions are guided into said second light waveguide with the same intensity.

Claim 22

An optical communication system comprising: a plurality of optical nodes each comprising an optical device comprising a first light waveguide for guiding a light wave, a second light waveguide for guiding a light wave which is connected to said first light waveguide at a first position, a third light waveguide for guiding a light wave which is connected to said first light waveguide at a second position different from the first position, a light combining device arranged near the first position, a light branching device arranged near the second position, and an optical amplifier arranged on said first light waveguide between the first and second positions for compensating for a light loss of the light wave caused by each of said light branching device and said light combining device, a light transmission line for connecting said nodes, said light transmission line being connected to said first light waveguide, and further optical amplifiers respectively arranged at opposite ends of the first light guiding means, wherein an amplification factor of said optical amplifier arranged on said first light waveguide between the first and second positions is set so that the light waves entering said first light waveguide from opposite directions are guided into said second light waveguide with the same intensity.

Claim 23

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means.

Claim 24

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means.

Claim 25

An optical device according to claim 17, further comprising a semiconductor substrate, and wherein said first, second and third light guiding means respectively comprise channel waveguides monolithically integrated with said light branching means and light combining means, and said optical amplifier on said semiconductor substrate.

Claim 26

An optical device according to claim 17, wherein said first light guiding means comprises an active layer.

Claim 27

An optical device according to claim 17, wherein said light branching means and light combining means respectively comprise etched grooves for splitting a wave front of the light wave at least with respect to a horizontal direction of said first light guiding means.

Claim 28

An optical device according to claim 20, wherein said first light guiding means comprises an active layer and said etched grooves respectively extend in a depth direction beyond said active layer.

Claim 29

An optical device according to claim 20, wherein said etched grooves respectively comprise two end surfaces forming right angles relative to each other and said end surfaces respectively extend in the horizontal direction of said first light guiding means from a central point of said first and second positions forming angles of 45 degrees relative to opposite propagation directions of the wave light in said first light guiding means.

Claim 30

An optical device according to claim 20, wherein said etched grooves are respectively formed deviated from a central line of said first light guiding means extending along a propagation direction of the light wave in said first light guiding means.

Claim 31

An optical device according to claim 17, wherein each of said second and third light guiding means is connected to said first guiding means in a T-shaped configuration and a Y-shaped configuration, respectively.

Claim 32

An optical device according to claim 17, further comprising a receiver portion for receiving the light wave propagated through said second light guiding means, and wherein said light branching means couples the light waves propagated through said first light guiding means in opposite directions to said second light guiding means at equal branching ratios.

Claim 33

An optical device according to claim 17, further comprising a transmitter portion for transmitting the light wave propagated through said third light guiding means, and wherein said light combining means couples the light waves propagated through said third light guiding means to said first light guiding means in opposite directions at equal combining ratios.

Claim 34

An optical device according to claim 26, wherein said transmitter portion comprises a semiconductor laser.

Claim 35

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, said optical amplifier comprising a semiconductor laser which operates by a current injection below threshold; wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity.

Claim 36

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, said optical amplifier comprising a semiconductor laser which operates by a current injection below threshold; wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity.

Claim 37

An optical device comprising: first light guiding means for guiding a light wave; antireflection coatings formed on opposite ends of said first light guiding means; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means; and wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity.

Claim 38

An optical device comprising: first light guiding means for guiding a light wave; antireflection coatings formed on opposite ends of said first light guiding means; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light branching and light combining means; and wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity.

Claim 39

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity; and a receiver portion for receiving the light wave propagated through said second light guiding means, and wherein said light branching means couples the light waves propagated through said first light guiding means in opposite directions to said second light guiding means at equal branching ratios, wherein said receiver portion comprises a photodetector having a semiconductor laser structure which operates by applying a reverse bias voltage.

Claim 40

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; light combining means arranged near said first position; light branching means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, wherein an amplification factor of said optical amplifier is set so that the light waves from said third light guiding means are guided into said first light guiding means in opposite directions with the same intensity; and a receiver portion for receiving the light wave propagated through said second light guiding means, and wherein said light branching means couples the light waves propagated through said first light guiding means in opposite directions to said second light guiding means at equal branching ratios, wherein said receiver portion comprises a photodetector having a semiconductor laser structure which operates by applying a reverse bias voltage.

Claim 41

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave; fourth light guiding means for guiding a light wave, said fourth light guiding means being connected to said third light guiding means at a second position different from said first position; fifth light guiding means for guiding a light wave, said fifth light guiding means extending between said first and second positions; light combining means arranged near said first position; light branching means arranged near said second position; and an optical amplifier arranged on said fifth light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, wherein an amplification factor of said optical amplifier is set so that the light waves from said fourth light guiding means are guided into said first and third light guiding means in opposite directions with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said fifth light guiding means.

Claim 42

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave; fourth light guiding means for guiding a light wave, said fourth light guiding means being connected to said third light guiding means at a second position different from said first position; fifth light guiding means for guiding a light wave, said fifth light guiding means extending between said first and second positions; light combining means arranged near said first position; light branching means arranged near said second position; and an optical amplifier arranged on said fifth light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said light combining and light branching means, wherein an amplification factor of said optical amplifier is set so that the light waves from said fourth light guiding means are guided into said first and third light guiding means in opposite directions with the same intensity; and further optical amplifiers respectively arranged at opposite ends of said fifth light guiding means.

Claim 43

An optical communication system comprising: a plurality of optical nodes each comprising an optical device comprising first light waveguide for guiding a light wave, a second light waveguide for guiding a light wave which is connected to said first light waveguide at a first position, a third light waveguide for guiding a light wave which is connected to said first light waveguide at a second position different from the first position, a light combining device arranged near the second position, and an optical amplifier arranged near the first position, a light branching device arranged on said first light waveguide between the first and second positions for compensating for a light loss of the light wave caused by each of said light combining device and light branching device; a light transmission line for connecting said nodes, said light transmission line being connected to said first light waveguide; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means, wherein an amplification factor of said optical amplifier arranged near the first position is set so that the light waves from said third light waveguide are guided into said first light waveguide in opposite directions with the same intensity.

Claim 44

An optical communication system comprising: a plurality of optical nodes each comprising an optical device comprising first light waveguide for guiding a light wave, a second light waveguide for guiding a light wave which is connected to said first light waveguide at a first position, a third light waveguide for guiding a light wave which is connected to said first light waveguide at a second position different from the first position, a light combining device arranged near the second position, and an optical amplifier arranged near the first position, a light branching device arranged on said first light waveguide between the first and second positions for compensating for a light loss of the light wave caused by each of said light combining device and light branching device; a light transmission line for connecting said nodes, said light transmission line being connected to said first light waveguide; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means, wherein an amplification factor of said optical amplifier arranged near the first position is set so that the light waves from said third light waveguide are guided into said first light waveguide in opposite directions with the same intensity.

Claim 45

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; first light combining means arranged near said first position; second light combining means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means; further optical amplifiers respectively arranged at opposite ends of said first light guiding means, wherein an amplification factor of said optical amplifier arranged on said first light guiding means between said first and second positions is set so that the light waves entering said first light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 46

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; first light combining means arranged near said first position; second light combining means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means; further optical amplifiers respectively arranged at opposite ends of said first light guiding means, wherein an amplification factor of said optical amplifier arranged on said first light guiding means between said first and second positions is set so that the light waves entering said first light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 47

An optical device according to claim 33, further comprising a semiconductor substrate, and wherein said first, second and third light guiding means respectively comprise channel waveguides monolithically integrated with said first and second light combining means, and said optical amplifier on said semiconductor substrate.

Claim 48

An optical device according to claim 33, wherein said first light guiding means comprises an active layer.

Claim 49

An optical device according to claim 33, wherein said first and second light combining means respectively comprise etched grooves for splitting a wave front of the light wave at least with respect to a horizontal direction of said first light guiding means.

Claim 50

An optical device according to claim 36, wherein said first light guiding means comprises an active layer and said etched grooves respectively extend in a depth direction beyond said active layer.

Claim 51

An optical device according to claim 36, wherein said etched grooves respectively comprise two end surfaces forming right angles relative to each other and said end surfaces respectively extend in the horizontal direction of said first light guiding means from a central point of said first and second positions forming angles of 45 degrees relative to opposite propagation directions of the wave light in said first light guiding means.

Claim 52

An optical device according to claim 36, wherein said etched grooves are respectively formed deviated from a central line of said first light guiding means extending along a propagation direction of the light wave in said first light guiding means.

Claim 53

An optical device according to claim 33, wherein each of said second and third light guiding means is connected to said first guiding means in a T-shaped configuration and a Y-shaped configuration, respectively.

Claim 54

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; first light combining means arranged near said first position; second light combining means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means, said optical amplifier comprising a semiconductor laser which operates by a current injection below threshold, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 55

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; first light combining means arranged near said first position; second light combining means arranged near said second position; an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means, said optical amplifier comprising a semiconductor laser which operates by a current injection below threshold, wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 56

An optical device comprising: first light guiding means for guiding a light wave; antireflection coatings formed on opposite ends of said first light guiding means; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; first light combining means arranged near said first position; second light combining means arranged near said second position; and an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means; wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 57

An optical device comprising: first light guiding means for guiding a light wave; antireflection coatings formed on opposite ends of said first light guiding means; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave, said third light guiding means being connected to said first light guiding means at a second position different from said first position; first light combining means arranged near said first position; second light combining means arranged near said second position; and an optical amplifier arranged on said first light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means; wherein an amplification factor of said optical amplifier is set so that the light waves entering said first light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 58

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave; fourth light guiding means for guiding a light wave, said fourth light guiding means being connected to said third light guiding means at a second position different from said first position; fifth light guiding means for guiding a light wave, said fifth light guiding means extending between said first and second positions; first light combining means arranged near said first position; second light combining means arranged near said second position; an optical amplifier arranged on said fifth light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means; and further optical amplifiers respectively arranged at opposite ends of said fifth light guiding means, wherein an amplification factor of said optical amplifier arranged on the fifth light guiding means is set so that the light waves entering said first and third light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 59

An optical device comprising: first light guiding means for guiding a light wave; second light guiding means for guiding a light wave, said second light guiding means being connected to said first light guiding means at a first position; third light guiding means for guiding a light wave; fourth light guiding means for guiding a light wave, said fourth light guiding means being connected to said third light guiding means at a second position different from said first position; fifth light guiding means for guiding a light wave, said fifth light guiding means extending between said first and second positions; first light combining means arranged near said first position; second light combining means arranged near said second position; an optical amplifier arranged on said fifth light guiding means between said first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining means; and further optical amplifiers respectively arranged at opposite ends of said fifth light guiding means, wherein an amplification factor of said optical amplifier arranged on the fifth light guiding means is set so that the light waves entering said first and third light guiding means from opposite directions are respectively guided into said second and third light guiding means with the same intensity.

Claim 60

An optical communication system comprising: a plurality of optical nodes each comprising an optical device comprising first light waveguide for guiding a light wave, a second light waveguide for guiding a light wave which is connected to said first light waveguide at a first position, a third light waveguide for guiding a light wave which is connected to said first light waveguide at a second position different from the first position, a first light combining device arranged near the first position, a second light combining device arranged near the second position, and an optical amplifier arranged on said first light waveguide between the first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining devices; a light transmission line for connecting said nodes, said light transmission line being connected to said first light waveguide; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means, wherein an amplification factor of said optical amplifier arranged on said first light waveguide between the first and second positions is set so that the light waves entering said first light waveguide from opposite directions are respectively guided into said second and third light waveguides with the same intensity.

Claim 61

An optical communication system comprising: a plurality of optical nodes each comprising an optical device comprising first light waveguide for guiding a light wave, a second light waveguide for guiding a light wave which is connected to said first light waveguide at a first position, a third light waveguide for guiding a light wave which is connected to said first light waveguide at a second position different from the first position, a first light combining device arranged near the first position, a second light combining device arranged near the second position, and an optical amplifier arranged on said first light waveguide between the first and second positions for compensating for a light loss of the light wave caused by each of said first and second light combining devices; a light transmission line for connecting said nodes, said light transmission line being connected to said first light waveguide; and further optical amplifiers respectively arranged at opposite ends of said first light guiding means, wherein an amplification factor of said optical amplifier arranged on said first light waveguide between the first and second positions is set so that the light waves entering said first light waveguide from opposite directions are respectively guided into said second and third light waveguides with the same intensity.