Optical E-field modulation using a Mach-Zehnder interferometer
AssigneeNortel Networks Limited
InventorsDouglas McGhan, Maurice O'Sullivan, Yves Beaulieu
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Abstract
A method for modulating the E-field of an optical carrier signal utilizes a Mach-Zehnder modulator having a pair of independently controllable branches. A pair of independent branch drive signals VL(t) and VR(t) are derived. Each branch of the MZ modulator is driven with a respective one of the independent branch drive signals. By this means, a low cost conventional MZ modulator (interferometer) can be used to perform complex modulation of the E-field of the optical carrier. In some embodiments, this functionality is used to facilitate precompensation of optical impairments of an optical communications system.
Claims12
A method of modulating the E-field of an optical carrier signal using a Mach-Zehnder modulator having a pair of independently controllable branches, the method comprising steps of:
- calculating respective phase and amplitude values φ(n) and S(n) of a desired optical E-field;
- scaling the calculated phase and amplitude values φ(n) and S(n) to obtain respective scaled phase and amplitude values φ′(n) and S′(n);
- using a phase response of the MZ modulator to calculate a phase signal component value Vφ(n) required to produce the scaled phase value φ′(n);
- using an amplitude response of the MZ modulator to calculate the amplitude signal component value VS(n) required to produce the scaled amplitude value S′(n);
- calculating corresponding values of a pair of independent branch drive signals VL(t) and VR(t) in accordance with:
- VL(t)=Vφ(t)+VS(t) and
- VR(t)=Vφ(t)−VS(t)
- and
- driving each branch of the Mach-Zehnder modulator with a respective one of the independent branch drive signals VL(t) and VR(t).
A system for modulating the E-field of an optical carrier signal, the system comprising:
- a Mach-Zehnder (MZ) modulator having a pair of independently controllable branches;
- and
- a complex driver for deriving a pair of independent branch drive signals VL(t) and VR(t) based on a stream of successive digital sample values representative of In-Phase and Quadrature components of a desired optical E-field, the complex driver comprising:
- a digital filter for generating the stream of successive digital sample values, based on an input data stream x(t);
- a non-linear compensator for computing respective drive signal values VL(n) and VR(n) based on the stream of successive sample values generated by the digital filter;
- and
- a respective Digital-to-Analog converter for penetrating each of the drive signals VL(t) and VR(t) based on a corresponding one of the drive signal values VL(n) and VR(n)
- wherein each branch of the MZ modulator is driven with a respective one of the independent branch drive signals.
Dependencies are inferred from the claim text.