Optical transmitting apparatus, optical transmission system and optical transmission method

1 . An optical transmitter comprising:

a first modulator configured to generate an optical modulated signal through intensity modulation of an optical signal;

a second modulator configured to generate an optical modulated signal through phase/frequency modulation of the optical signal; and

a modulation scheme switcher configured to switch a modulator of the optical signal to one of the first and second modulators,

wherein the modulation scheme switcher switches the modulator to a modulator corresponding to a device of a connection destination between the first and second modulators,

the second modulator realizes phase/frequency modulation of the optical signal by modulating a bias current to be applied to a light source that emits the optical signal to a modulated signal related to the modulator, and

the first modulator realizes intensity modulation of the optical signal by applying a bias current at a current value larger than a bias current applied to the light source by the second modulator.

2 . The optical transmitter according to claim 1 , wherein the first modulator realizes intensity modulation of the optical signal by an electro-absorption modulator or a Mach-Zehnder modulator.

3 . The optical transmitter according to claim 1 , wherein the communication scheme switcher determines, by negotiation, a modulation scheme to be used for communication with the device of the connection destination during initial communication with the device of the connection destination.

4 . An optical transmission system comprising:

one or more user devices including the optical transmitter according to claim 3 and an optical receiver configured to detect an optical signal in conformity with a direct detection scheme or a digital coherent detection scheme;

one or more network node devices accommodating the one or more user devices; and

a route control device configured to control a communication route formed by the one or more network node devices,

wherein the optical transmitter exchanges information related to the negotiation performed with a user device of a communication partner via the route control device.

5 . The optical transmission system according to claim 4 ,

wherein, when a first user device performs communication with a second user device accommodated in the same network node device as the first user device including an optical receiver of a direct detection scheme, an optical transmitter of the first user device communicates with the optical receiver of the second user device in conformity with an intensity modulation scheme, and

wherein, when the first user device performs communication with a third user device via a relay by the one or more network node devices, the optical transmitter of the first user device communicates with an optical receiver of a digital coherent detection scheme included in a network node device relaying communication between the first and third user devices, in conformity with a phase/frequency modulation scheme.

6 . An optical transmission method comprising:

modulating an optical signal by one of a first modulator that generates an optical modulated signal through intensity modulation of the optical signal and a second modulator that generates an optical modulated signal through phase/frequency modulation of the optical signal; and

switching a modulator of the optical signal to either the first or second modulator,

wherein, in the switching, the modulator is switched to a modulator corresponding to a device of a communication partner between the first and second modulators,

the second modulator realizes phase/frequency modulation of the optical signal by modulating a bias current to be applied to a light source that emits the optical signal to a modulated signal related to the modulator, and

the first modulator realizes intensity modulation of the optical signal by applying a bias current at a current value larger than a bias current applied to the light source by the second modulator.