Multilevel pulse position modulation for efficient fiber optic communication
First Claim
1. A method for decreasing the transmitted power in a channel of an optical fiber communication system while maintaining a channel bandwidth, the method comprising the steps of:
- receiving a digital input signal, comprising a series of input pulses, each input pulse having one of two pulse levels;
creating a digital input word having n bits from the digital input signal;
converting each digital input word to a corresponding output symbol representing one of 2n distinct values;
wherein the output symbol comprises a multilevel pulse position modulated symbol; and
generating an output signal comprising a series of output symbols wherein the output signal has an aggregate data rate equal to a data rate of the input signal, and wherein the output signal has a lower transmitted power than an on-off modulated signal transmitting a series of on-off modulated output symbols at the aggregate data rate.
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Accused Products
Abstract
Decreasing the average transmitted power in an optical fiber communication channel using multilevel amplitude modulation in conjunction with Pulse Position Modulation (PPM). This multilevel PPM method does not entail any tradeoff between decreased power per channel and channel bandwidth, enabling a lower average transmitted power compared to On/Off Keying (OOK) with no reduction in aggregate data rate. Therefore, multilevel PPM can be used in high-speed Dense Wavelength Division Multiplexed (DWDM) systems where the maximum number of channels is traditionally limited by nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), stimulated Brillouin scattering (SBS), and stimulated Raman scattering (SRS). This modulation technique can enable an increased number of channels in DWDM systems, thereby increasing aggregate data rates within those systems.
301 Citations
16 Claims
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1. A method for decreasing the transmitted power in a channel of an optical fiber communication system while maintaining a channel bandwidth, the method comprising the steps of:
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receiving a digital input signal, comprising a series of input pulses, each input pulse having one of two pulse levels; creating a digital input word having n bits from the digital input signal; converting each digital input word to a corresponding output symbol representing one of 2n distinct values;
wherein the output symbol comprises a multilevel pulse position modulated symbol; andgenerating an output signal comprising a series of output symbols wherein the output signal has an aggregate data rate equal to a data rate of the input signal, and wherein the output signal has a lower transmitted power than an on-off modulated signal transmitting a series of on-off modulated output symbols at the aggregate data rate. - View Dependent Claims (2, 3, 4)
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5. An optical fiber communication system comprising:
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a multilevel pulse position modulation transmitter for combining n input signals for transmission over an optical fiber communication link as an encoded output signal; wherein the encoded output signal comprises a series of multilevel pulse position modulated symbols, each symbol representing one of 2n unique values; and
wherein a first transmission power required to transmit the encoded signal over the optical fiber communication link at a predetermined data rate is less than a second transmission power required to transmit an on-off modulated output signal over the optical fiber communication link at the predetermined data rate. - View Dependent Claims (6, 7, 8)
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9. A method for encoding n on-off keyed input signals into a single multilevel pulse position modulated output signal, the method comprising the steps of:
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combining at least two of the n input signals into a multilevel signal; representing at least two other of the n input signals as chip positions in a four position pulse position modulation signal; and modifying at least one amplitude level of the four position pulse position modulation signal in accordance with at least one amplitude level of the multilevel signal to generate the single multilevel pulse position modulated output signal. - View Dependent Claims (10, 11, 12, 13)
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14. A transmitter for use in an optical fiber communications system, comprising:
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a multilevel pulse position modulation encoding circuit operative to encode at least four on-off keyed input signals into a single multilevel pulse position modulated output signal; a pulse shaping module for processing the output signal to maximize a dispersion distance of the output signal; and an optical source for transmitting the output signal over a link of the optical fiber communications system, wherein the encoding circuit is operative to combine at least two of the on-off keyed input signals into a multilevel signal. - View Dependent Claims (15, 16)
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Specification