Abstract
We study the effects of laser phase noise on a phase diversity coherent optical frequency domain (C-OFD) technique that has been recently proposed to measure passive devices used in dense wavelength division multiplexing (DWDM) systems. Theoretical expressions are provided to calculate the laser phase-noise to intensity-noise conversion in this technique under simplified circumstances. Obtained simulation results for a realistic measurement set-up show the validity of the approximate expressions. It is concluded that this effect is one of the limiting source of error for this measurement technique.
Highlights
Dense wavelength division multiplexing (DWDM) system design puts stringent requirements in amplitude and phase response of passive devices which play a crucial role in these systems
Coherent optical frequency-domain (C-OFD) techniques [1], such as coherent optical frequency-domain reflectometry (C-OFDR) [2], or swept frequency interferometry [3,4], are becoming increasingly important and they are competing with other optical domain techniques such as low coherence interferometry
A new phase diversity C-OFD technique has been proposed [5,6], with promising possibilities. This method is based in the six-port measurement technique, a well established and accurate method to measure complex reflection coefficients at microwave and millimeterwave frequencies which is used by several metrological institutes to determine the complex reflection coefficient of commercial working standards [7], and that has been recently proposed as a direct digital receiver [8]
Summary
Dense wavelength division multiplexing (DWDM) system design puts stringent requirements in amplitude and phase response of passive devices (as, for example, arrayed waveguide gratings or fiber bragg gratings) which play a crucial role in these systems. The core of the proposed technique is a small and rugged planar lightwave circuit (PLC) six-port junction, based on multi-mode interference (MMI) couplers, which was designed and simulated showing an excellent performance in a wide wavelength range. This germinal work has with no doubt open the possibility of extending the six-port measurement technique, so successful at microwave frequencies, up to the optical range, assessment of the optical six-port measurement technique as a whole, must still be carried out. The effects of laser phase noise on six-port power measurement errors is studied and simulated, and simplified expressions are obtained to calculate the power measurement uncertainties from the constituent parts of the setup
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