Investigation of Tolerable Laser Linewidth for Different Modulation Formats in CO-OFDM Systems

Abstract

The ideal behavior of communication system requires a single frequency carrier. In optical communication system, light is used as a carrier. Practical laser source has a finite linewidth due to variations in the frequency of operation, hence, resulting in undesired phase perturbations in the signal whereas the ideal requirement is the delta function spectral shape at the carrier frequency. The spectral shape gets broadened due to phase noise and is modeled as lorentzian shape. Linewidth is a measure of stability of laser phase noise with time. Coherent Optical Orthogonal frequency division multiplexing (CO-OFDM) along with the spectrally efficient Quadrature Amplitude Modulation (QAM) formats is emerging as one of the best solutions for future high speed fiber transmission systems. Though the coherent, receivers have advantages in terms of sensitivity and selectivity, laser phase noise is the main limitation of such systems as the laser phase noise further causes common phase rotation of all the subcarriers per symbol and also results in inter carrier interference. QAM formats are also susceptible to laser phase noise. Phase noise in coherent systems is governed by laser linewidth. Hence, it is very important to investigate the impact of laser linewidth in CO-OFDM systems. This paper investigates the tolerable laser linewidths for different QAM formats in a 40 Gbps COOFDM system.

Characterization and Direct Modulation of a Multi-Section PIC Suited for Short Reach Optical Communication Systems

“…We anticipate that there will be a second generation of this device, which could be expected to give improved performance and linewidth results. However, the reduced linewidth as a result of the injection can still enable the device to be used with higher order modulation formats at high baud rates [24].…”

Phase Noise Characterization of a Mode-Locked Quantum-Dot Coherent Optical Frequency Comb Source Laser

“…Thus, the large phase noise exhibited by megahertz linewidth lasers is not suitable for coherent optical communications. This led to a refinement in laser technology which now allows the TLSs employed in coherent optical communication systems to exhibit optical laser linewidths on the order of 100 kHz [21].…”

Laser frequency noise characterization using high-finesse plano–concave optical microresonators

“…This is manifested as frequency noise, which is typically measured as the power spectral density ( PSD ν ). Frequency noise is a key performance indicator of a laser as it can be used to describe its stability and to analytically derive a laser linewidth [ 1 ], which is fundamental to determining the resolution in frequency metrology [ 2 ], sensitivity of an optical coherent sensing system [ 3 ], and the spectrum efficiency in coherent optical communications [ 4 ].…”