In this thesis, a novel bi-directional optical add-drop module (OADM), composed of an arrayed waveguide grating (AWG) with asymmetric fold-back optical paths, has been proposed and demonstrated. In a bi-directional transmission system, the relative intensity noise (RIN) caused by Rayleigh backscattering or optical reflections at connection points could degrade the system's performance. This is mainly because the reflection-induced RIN degrades the receiver sensitivity and restricts the maximum gain of bi-directional amplifiers, as the optical isolators are not allowed to ensure the bi-directional transmission. To overcome this problem, it has been previously proposed to implement bi-directional OADM modules with either optical bandpass filters or wavelength interleaving techniques. When the optical bandpass filters were used, these additional components would restrict the use of the AWG's periodic property (which could be used for increasing the number of wavelength channels). When the wavelength channels were interleaved for eliminating Rayleigh back scattering, the bi-directional OADM module could utilize only one half of the AWG ports. In addition, the bi-directional network implemented by using such interleaved OADM modules could suffer from lasing. On the other hand, in the proposed bi-directional OADM module, the multiplexing ports of the AWG are arranged asymmetrically by folding back (N/2-1) port instead of N/2 port in fold-back architecture. Thus, the proposed OADM module could avoid RIN (by sending the reflected signals to the absorber) and multi node lasing path at the expense of only one channel reduction in each direction. The proposed module could still suffer from RIN due to AWG's crosstalk. However, it would be negligible if the AWG's crosstalk was less than 45dB.
To evaluate the performance of the proposed OADM module, we compared the proposed module with the AWG in basic fold-back scheme in a bi-directional transmission system. The AWG in basic fold back scheme represents the optical band pass filter omitted OADM module from previous optical band pass filtered bi-directional OADM module. Thus, this module would inevitably suffer from both RIN and multi-node lasing path. In a single-node transmission experiment, the receiver sensitivity of the proposed module was 0.2 dB better than the AWG in basic fold-back scheme since Rayleigh back scattering was eliminated. To confirm the effect of multi-node lasing path elimination, we experimented with two nodes. In this case, the receiver sensitivity of the proposed module was 1.5 dB better than the AWG in basic fold-back scheme.
