Optical data transmitting apparatus and method
AssigneeNEC Corporation
InventorYutaka Yano
Life of this patent
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Abstract
An optical data transmitting apparatus and method allows data transmission over a distance that surpasses a limit previously experienced in the prior art and which has been imposed due to group velocity dispersion (GVD) and self phase modulation (SPM) effects within an optical fiber. This has been accomplished by allocating trinal duobinary symbols to optical 1, P, −1 symbols. These optical symbols have the same intensity, but the +1 and −1 symbols have inverted optical phases from each other, and are orthogonally polarized from each other between the +1 and P symbols. At the receiver, a conventional polarization shift keying receiver can be used to restore the original binary data stream.
Claims6
An optical data transmitting apparatus comprising:
- a code encoder transforming a binary input data signal to obtain a duobinary signal having a center level and two extreme levels;
- carrier source of a carrier light;
- an optical modulator modulating phase and polarization of said carrier light in response to said duobinary signal to obtain a modulated output light,
- said modulated output light having a first polarization state that corresponds to said center level of said duobinary signal, and second and third polarization states that correspond to said two extreme levels, respectively,
- said second and third polarization states sharing a common plane of polarization that is orthogonal to a plane of polarization of said first polarization state,
- said second and third polarization states having phases that are inverted to each other.
An optical data transmitting apparatus comprising:
- a code converter transforming a binary input data signal to obtain a pair of mutually complementary duobinary signals;
- a carrier source of a carrier light;
- an intensity modulator separating said carrier light into first and second carrier lights, altering phases of said first and second carrier lights in response to said pair of mutually complementary duobinary signals, respectively, combining said phase altered first and second carrier lights to obtain a pair of mutually complementary interference output lights;
- and
- means for combining said pair of mutually complementary interference output light beams in a mutually orthogonal polarized relationship,
- whereby an envelope of intensity of a resulting output light signal is kept constant to thereby suppress SPM-GVD effects.
An optical data transmitting method comprising the steps of:
- transforming a binary input data signal to obtain a duobinary signal having a center level and two extreme levels;
- and
- modulating a phase and polarization of a carrier light in response to said duobinary signal to obtain a modulated output light,
- said modulated output light having a first polarization state that corresponds to said center level of said duobinary signal, and second and third polarization states that correspond to said two extreme levels, respectively,
- said second and third polarization states sharing a common plane of polarization that is orthogonal to a plane of polarization of said first polarization state,
- said second and third polarization states having phases that are inverted from each other.
An optical data transmitting method comprising the steps of:
- transforming a binary data signal to obtain a pair of mutually complementary duobinary signals;
- separating a carrier light into a first carrier light and a second carrier light;
- modulating phases of said first and second carrier lights in response to said pair of mutually complementary duobinary signals, respectively, to obtain phase modulated first and second carrier lights;
- combining said phase modulated first and second carrier lights to interfere with each other to obtain a pair of mutually complementary interference output lights;
- and
- combining said pair of mutually complementary interference output lights in a mutually orthogonal polarized relationship,
- whereby an envelope of intensity of a resulting output light signal is kept constant to thereby suppress SPM-GVD effects.
Dependencies are inferred from the claim text.