Transmission of subcarriers having different modulation formats

Abstract

Consistent with the present disclosure, an optical communication system is provided in which data is carried over optical signals including subcarriers. The subcarriers may be modulated with the standard modulation formats noted above, but the modulation formats are selectively assigned to the subcarriers, such that some subcarriers are modulated with different standard modulation formats than others. As used herein, a “standard modulation format” is one of BPSK, and n-QAM, where n is an integer greater than one. Such n-QAM modulation formats include of 3-QAM, 4-QAM (QPSK), 8-QAM, 16-QAM, 64-QAM, 128-QAM, and 256-QAM. By selecting the number of subcarriers and the types of modulation formats employed, an optical signal with an effective SE that is between that of the standard modulation formats can be generated for transmission over a distances that more closely matches the link distance. Such custom or intermediate SE signals can be tailored to a particular optical link SNR to provide data transmission rates that are higher than the low order modulation formats that would otherwise be employed for optical signals carried by such links. As a result, more efficient data transmission can be achieved.

1 - 45 . (canceled) 
     
     
         46 . An apparatus, comprising:
 a laser that supplies an optical signal;   a modulator that receives the optical signal; and   a transmission circuit that supplies at least one electrical signal to the modulator, the modulator modulating the optical signal based on said at least one electrical signal to provide a plurality of optical subcarriers, one of said plurality of optical subcarriers having a first modulation format and a second one of the plurality of optical subcarriers having a second modulation format different than the first modulation form, each of the plurality of optical subcarriers being a Nyquist pulse-shaped optical subcarrier, such that each of the plurality of optical subcarriers does not spectrally overlap with one another.   
     
     
         47 . An apparatus in accordance with  claim 46 , wherein the first modulation format is a binary phase shift keying (BPSK) modulation format, and the second modulation format is an n-quadrature amplitude modulation (QAM) modulation format, where n is an integer. 
     
     
         48 . An apparatus in accordance with  claim 46 , wherein the first modulation format is a quadrature phase shift keying (QPSK) modulation format, and the second modulation format is an n-quadrature amplitude modulation (QAM) modulation format, where n is an integer. 
     
     
         49 . An apparatus in accordance with  claim 46 , wherein the first modulation format is a first quadrature amplitude modulation (QAM) modulation format and the second modulation format is a second QAM modulation format. 
     
     
         50 . An apparatus in accordance with  claim 46 , wherein the first and second ones of the plurality of subcarriers have first and second frequencies, respectively, and third and fourth ones of the plurality of subcarriers having third and fourth frequencies, respectively, the third and fourth frequencies are both higher than the first frequency and less than the second frequency, such that third and fourth subcarriers have modulation formats that are a higher order than both the first and second modulation formats. 
     
     
         51 . An apparatus in accordance with  claim 46 , wherein each of a first group of the plurality of subcarriers has a respective one of a first plurality of modulation formats, the first modulation format being one of the first plurality of modulation formats, and a second group of the plurality of subcarriers has a respective one of a second plurality of modulation formats, the second modulation format being one of the second plurality of modulation formats, wherein each of the first group of the plurality of subcarriers has a respective one of a first plurality of frequencies and each of the second group of the plurality of subcarriers has a respective one of a second plurality of frequencies, each of the plurality of first frequencies being less than a frequency associated with the optical signal supplied by the laser, and each of the plurality of second frequencies being greater than the frequency associated with the optical signal supplied by the laser. 
     
     
         52 . An apparatus in accordance with  claim 46 , wherein the first and second ones of the plurality of subcarriers have first and second frequencies, respectively, the first and second frequencies being less than a frequency of the optical signal supplied by the laser. 
     
     
         53 . An apparatus in accordance with  claim 46 , wherein the first and second ones of the plurality of subcarriers have first and second frequencies, respectively, the first and second frequencies being greater than a frequency of the optical signal supplied by the laser. 
     
     
         54 . An apparatus in accordance with  claim 46 , wherein the first and second ones of the plurality of subcarriers have first and second frequencies, respectively, the first frequency being greater than a frequency of the optical signal supplied by the laser, and the second frequency being less than the frequency of the optical signal supplied by the laser. 
     
     
         55 . An apparatus in accordance with  claim 54 , wherein the first modulation format has a higher order than the second modulation format. 
     
     
         56 . An apparatus in accordance with  claim 54 , wherein the first modulation format has a lower order than the second modulation format. 
     
     
         57 . An apparatus in accordance with  claim 50 , wherein a power level of the third and fourth ones of the plurality of subcarriers is greater than a power level of the first and second ones of the plurality of subcarriers. 
     
     
         58 . An apparatus in accordance with  claim 46 , wherein the modulator includes a plurality of Mach-Zehnder modulators. 
     
     
         59 . An apparatus in accordance with  claim 46 , further including a forward error correction encoder circuit that supplies encoded data, wherein the electrical signal is based on the encoded data. 
     
     
         60 . An apparatus, comprising:
 a laser that supplies an optical signal;   a modulator that receives the optical signal; and   a plurality of engine circuits, each of which supplying a corresponding one of a plurality of outputs, each of the plurality of outputs being indicative of a corresponding one of a plurality of modulation formats, a first one of the plurality of modulation formats being different than a second one of the plurality of modulation formats;   a plurality of filter circuits, each of which receiving a corresponding one of a plurality of inputs, each of the plurality of inputs being indicative of a respective one of the plurality of outputs, such that, based on each of the plurality of inputs, each of the plurality of filter circuits supplies a respective one of a plurality of filter outputs; and   a plurality driver circuits supplying a plurality of drive signals to the modulator based on the plurality of filter outputs, the modulator providing a plurality of optical subcarriers based on the plurality of drive signals, one of said plurality of optical subcarriers having the first one of the plurality of modulation formats and a second one of the plurality of optical subcarriers having the second one of the plurality of modulation formats, each of the plurality of optical subcarriers being a Nyquist pulse-shaped optical subcarrier, such that each of the plurality of optical subcarriers does not spectrally overlap with one another.   
     
     
         61 . An apparatus in accordance with  claim 60 , wherein the first modulation format is a binary phase shift keying (BPSK) modulation format, and the second modulation format is an n-quadrature amplitude modulation (QAM) modulation format, where n is an integer. 
     
     
         62 . An apparatus in accordance with  claim 60 , wherein the first modulation format is a quadrature phase shift keying (QPSK) modulation format, and the second modulation format is an n-quadrature amplitude modulation (QAM) modulation format, where n is an integer. 
     
     
         63 . An apparatus in accordance with  claim 60 , wherein the first modulation format is a first quadrature amplitude modulation (QAM) modulation format and the second modulation format is a second QAM modulation format. 
     
     
         64 . An apparatus in accordance with  claim 60 , further including a forward error correction encoder circuit that supplies encoded data, wherein the electrical signal is based on the encoded data. 
     
     
         65 . An apparatus, comprising:
 a demultiplexer circuit having a plurality of first outputs;   a plurality of engine circuits, each of which supplying a corresponding one of a plurality of second outputs based on a corresponding one of the plurality of first outputs, each of the plurality of second outputs being indicative of a corresponding one of a plurality of modulation formats, a first one of the plurality of modulation formats being different than a second one of the plurality of modulation formats;   a plurality of fast Fourier transform (FFT) circuits, each of which supplying a corresponding one of a plurality of frequency domain outputs based on a respective one of the plurality of second outputs; and   a plurality of filter circuits, each of which supplying a corresponding one of a plurality of filter outputs based on a respective one of the plurality of frequency domain outputs.   
     
     
         66 . An apparatus in accordance with  claim 65 , further comprising:
 a plurality driver circuits supplying a plurality of drive signals based on the plurality of filter outputs;   a laser that supplies an optical signal; and   a modulator providing a plurality of optical subcarriers based on the plurality of drive signals, a first one of said plurality of optical subcarriers having the first one of the plurality of modulation formats and a second one of the plurality of optical subcarriers having the second one of the plurality of modulation formats, each of the plurality of optical subcarriers being a Nyquist pulse-shaped optical subcarrier, such that each of the plurality of optical subcarriers does not spectrally overlap with one another.   
     
     
         67 . An apparatus in accordance with  claim 65 , wherein the first modulation format is a binary phase shift keying (BPSK) modulation format, and the second modulation format is an n-quadrature amplitude modulation (QAM) modulation format, where n is an integer. 
     
     
         68 . An apparatus in accordance with  claim 65 , wherein the first modulation format is a quadrature phase shift keying (QPSK) modulation format, and the second modulation format is an n-quadrature amplitude modulation (QAM) modulation format, where n is an integer. 
     
     
         69 . An apparatus in accordance with  claim 65 , wherein the first modulation format is a first quadrature amplitude modulation (QAM) modulation format and the second modulation format is a second QAM modulation format. 
     
     
         70 . An apparatus in accordance with  claim 65 , further including a forward error correction encoder circuit that supplies encoded data, wherein the demultiplexer receives a demultiplexer input, the demultiplexer input being based on the encoded data. 
     
     
         71 . An apparatus in accordance with  claim 65 , further including:
 a multiplexer circuit that provides a multiplexed output based on the plurality of filter outputs.   
     
     
         72 . An apparatus in accordance with  claim 71 , further including:
 an inverse FFT circuit that provides a time domain output based on the multiplexed output.   
     
     
         73 . An apparatus, comprising:
 a plurality of engine circuits, each of which supplying a corresponding one of a plurality of outputs based on a corresponding one of a plurality of inputs, the plurality of inputs being based on data input to the apparatus, each of the plurality of outputs being indicative of a corresponding one of a plurality of modulation formats, a first one of the plurality of modulation formats being different than a second one of the plurality of modulation formats, the plurality of modulation formats including: a binary phase shift keying (BPSK) modulation format, a quadrature phase shift keying (QPSK) modulation format, and at least one of n-quadrature amplitude modulation (QAM) formats, where n is an integer, the first one of the plurality of modulation formats and a second one of the plurality of modulation formats for modulating first and second optical subcarriers, respectively, each of the first and second optical subcarriers being a Nyquist pulse-shaped optical subcarrier, such that the first and second optical subcarriers do not spectrally overlap with one another; and   a plurality of filter circuits, each of which supplying a corresponding one of a plurality of filter outputs based on a respective one of the plurality of outputs from the plurality of engine circuits.