Optical Launch Power Research Articles

Optical Comb Sources for High Dynamic-Range Single-Span Long-Haul Analog Optical Links

We present a new technique for achieving high spurious-free dynamic range in long-haul analog optical links. Our technique utilizes an optical comb as the optical carrier in an externally intensity-modulated direct-detection link architecture. By distributing the optical carrier power over the comb (in contrast to concentrating it in a single continuous-wave laser, as in a conventional link), this technique circumvents the optical power limitations imposed by stimulated Brillouin scattering allowing a substantial increase in optical launch power. Increased launch power translates directly to decreased optical amplification requirements at the link terminus and results in a significantly lower noise floor than may be achieved in a conventional link architecture. To our knowledge, the dynamic range of SFDR=105.5 dB (1-Hz bandwidth, L=50 km link) is the highest reported to date for a single-span long-haul analog optical link.

Nonlinear Distortion Due to Cross-Phase Modulation in Microwave Fiber-Optic Links With Optical Single-Sideband or Electrooptical Upconversion

A new analytical model is presented to study nonlinear distortion due to cross-phase modulation in dispersive and nonlinear wavelength-division-multiplexing microwave fiber-optic links. The model is not based on the pump-probe approach. Hence, it can be used to analyze a larger variety of links, including, in particular, electrooptical upconversion links. Our simulations and experiments show that the model predicts the nonlinear distortion due to cross-phase modulation quite accurately, even when the modulating microwave frequency is in tens of gigahertz and the fiber length is in tens of kilometers. Detailed analyses of the distortion due to cross-phase modulation for links with optical single-sideband modulation are presented. Measured results for optical single-sideband are shown to match our theoretical predictions very well. Our results show that the nonlinear distortion due to cross-phase modulation can be a limiting factor for optical launch power in wavelength-division-multiplexing microwave fiber-optic links; moreover, the maximum possible nonlinear distortion level for a higher frequency may be lower than that for a lower frequency. Also presented are some simple approximations for a quick estimate of the level of the nonlinear distortion

Optical feedback-induced noise in pigtailed laser diode modules

The sensitivity of commercially available pigtailed laser diode modules to optical feedback, in terms of laser relative intensity noise, is investigated. A pigtailed laser diode model which is based on multimode rate equations, Langevin operators, and optical feedback terms in used to predict that operation in the coherence collapse region can be avoided in high-speed, short-haul, optical data links by trading off optical launch power into the pigtail with decreased laser/fiber coupling efficiency. Experimental results for three pigtailed laser diode modules indicate that with a laser/fiber coupling efficiency of 4%, an external feedback level of between -15 and -17 dB can be tolerated before the laser enters the coherence collapse region. Good correlation between these results and predictions from the numerical model is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>