Isolator-free DFB laser for analog CATV applications

Fiber-pigtailed Distributed Feedback (DFB) laser diode modules often employ isolators to reduce the optical feedback induced intensity noise and distortion, and to meet the requirements imposed on the DFB lasers in analog optical transmission systems such as Cable Television (CATV). For some situations however, isolators could be avoided to reduce cost and simplify laser module manufacture while maintaining the desired DFB laser's performance.; In this thesis, Fabry Perot (FP) and DFB laser diode rate equations were augmented to include the effect of optical back-reflections. The proposed laser model was implemented in software and used as the basis for linearity and noise simulations in which the effect of the reflected optical power on the laser diode performance was studied. The model's results were verified experimentally using an tunable induced back-reflection setup.; Results suggest that it is beneficial to operate unisolated DFB laser diodes in feedback Regime V. This was achieved by attaching appropriate FBG to DFB laser. Two telecommunications wavelengths, 1310 nm and 1550 nm, were used to examine the performance of a DFB laser coupled to an Fiber Bragg Grating (FBG). A stable spectrum was showed and low Relative Intensity Noise (RIN) comparable to that of the isolated DFB laser was achieved for both wavelengths.; A pre-distorter model including optical back-reflection effects was derived, implemented in software, and cascaded to the laser model to compensate for the laser nonlinearity. Simulation results showed that at 0.10 modulation index, average improvements of 45 dB in second order harmonic distortion, 55 dB in third order harmonic distortion, and 40 dB in different intermodulation distortions can be achieved using the proposed pre-distortion technique. Furthermore, at a modulation index of 0.04, the predistorter was found to reduce the second order harmonic distortion and two-tone third order intermodulation distortion levels to less than -75 dB and -100 dB respectively. This hence renders the laser suitable for CATV applications.; Our proposed pre-distorter constitutes a contribution to the state-of-the-art as it enhances the precision of currently used models by adding the effect of the optical feedback.