Optical transmitter for transmitting a multilevel amplitude-shift-keying modulated signal

• US 9,621,276 B2
• Filed: 06/21/2013
• Issued: 04/11/2017
• Est. Priority Date: 07/19/2012
• Status: Active Grant

• Current Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Original Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Inventors: Renaudier, Jeremie, Charlet, Gabriel, Mardoyan, Haik
• Primary Examiner(s): Jacob, Oommen
• Application Number:
  US14/413,071
• Publication Number:
  US 20150207570A1
• Time in Patent Office: 1,390 Days
• Field of Search: 398140, 398115, 398147
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04B 10/54 Intensity modulation
• CPC Class Codes: H04B 10/564 Power control

Abstract

An optical transmitter for transmitting a multilevel amplitude-shift-keying modulated signal includes an optical modulator for modulating an optical signal with a multilevel amplitude-shift-keying modulation, and a spectral filter adapted to increase a high-frequency component of the modulated optical signal relatively to a central frequency component. The multilevel ASK modulation is quaternary ASK and the symbol rate of the optical modulator is above 40 Gbaud. An optical link connects the optical transmitter to a quadratic direct detection optical receiver.

Claims

1. An optical transmitter for transmitting a multilevel amplitude-shift-keying modulated signal, comprising:

an optical modulator for modulating an optical signal with a multilevel amplitude-shift-keying modulation;

a spectral filter adapted to increase a high-frequency component of the modulated optical signal relatively to a central frequency component; and

a feedback loop further comprising a quality measurement module for measuring a quality of the transmitted optical signal and a feedback controller for reconfiguring the spectral filter as a function of the measured quality.

2. An optical transmitter in accordance with claim 1, wherein the multilevel ASK modulation is quaternary ASK.

3. An optical transmitter in accordance with claim 1, wherein the symbol rate of the optical modulator is above 40 Gbaud.

4. An optical transmitter in accordance with claim 1, wherein the high-frequency component of the modulated optical signal comprises a frequency higher than f₀+0.5R, wherein f₀ is a central frequency of the optical signal and R is the symbol rate of the optical modulator.

5. An optical transmitter in accordance with claim 4, wherein the high-frequency component of the modulated optical signal comprises a frequency equal to f₀+0.7R.

6. An optical transmitter in accordance with claim 1, wherein the spectral filter further comprises a Feed Forward filter arranged to filter a baseband electrical signal that drives the optical modulator.

7. An optical transmitter in accordance with claim 6, wherein the Feed Forward filter further comprises a single delay-tap with a negative configurable delay-tap coefficient.

8. An optical transmitter in accordance with claim 6, wherein the Feed Forward filter further comprises a plurality of delay-taps with a plurality of configurable delay-tap coefficients.

9. An optical transmitter in accordance with claim 1, wherein the spectral filter further comprises an optical spectral equalizer for equalizing the modulated optical signal.

10. An optical transmitter in accordance with claim 1, wherein the quality measurement module is adapted to measure an eye-diagram opening of the transmitted optical signal.

11. An optical transmitter in accordance with claim 1, wherein the quality measurement module is adapted to measure a power ratio between the high-frequency component of the transmitted optical signal and the central frequency component of the transmitted optical signal.

12. An optical transmitter in accordance with claim 10, wherein the spectral filter further comprises a Feed Forward filter arranged to filter a baseband electrical signal that drives the optical modulator and the feedback controller is adapted to increase the absolute value of a negative delay-tap coefficient of the Feed Forward filter in response to the measured eye-diagram opening or power ratio being lower than a target value.

13. An optical transmitter in accordance with claim 10, wherein the spectral filter further comprises an optical spectral equalizer for equalizing the modulated optical signal and the feedback controller is adapted to increase the gain of a high-frequency channel of the optical spectral equalizer in response to the measured eye-diagram opening or power ratio being lower than a target value.

14. A optical communication system comprising:

an optical transmitter further comprising;

an optical modulator for modulating an optical signal with a multilevel amplitude-shift-keying modulation;

a spectral filter adapted to increase a high-frequency component of the modulated optical signal relatively to a central frequency component; and

a feedback loop further comprising a quality measurement module for measuring a quality of the transmitted optical signal and a feedback controller for reconfiguring the spectral filter as a function of the measured quality;

an optical receiver, and

an optical link connecting the optical receiver to the optical transmitter in the optical domain, wherein the optical receiver is a direct detection receiver and wherein a range of the optical communication system is shorter than 100 km.