All-optical tunable wavelength converter with improved extinction ratio and low power penalty for 10 Gbps transmission using a singe mode fabry-perot laser diode

Abstract

Novel applications of Fabry-Perot laser diode (FP-LDs) are presented for wavelength division multiplexing (WDM) network. A tunable single mode laser is obtained using a weakly coupled cavity structure assembled into a co-axially packaged FP-LD. The cleaved end-facet of the coupling fiber becomes an optical reflector and forms an external cavity with a laser facet. The single mode oscillation condition is controlled and stabilized by tuning the operating temperature. The only additional component is a thermo-electric cooler (TEC) module used to tune the mode matching condition. This tunable single mode laser can be used to other applications due to its inherent multi mode characteristics. When the external pump beam of $\lambda_{pump}$ , which is close to one longitudinal mode of the solitary FP-LD, is injected into this single mode FP-LD, the single mode operation at $\lambda_{probe}$ collapses. This is because the injection locking on the selected mode by the pump beam causes the change of carrier density that results in the red shift of laser cavity modes and, thus, the mode matching condition of the coupled cavities is disturbed. As a result, the probe beam at $\lambda_{probe}$can be modulated by the pump beam which carries digital data. In the experiment to verify the performance, a power penalty was less than 2.5 dB at 2.5 Gbps NRZ wavelength conversion and less than 4 dB at 5 Gbps NRZ wavelength conversion. Furthermore, the $2\times2$ wavelength converter at 2.5 Gbps using above results is presented. An additional CW assistance beam was used to overcome the speed limit of the proposed wavelength conversion scheme which involves in only one single mode FP-LD is proposed and demonstrated. The power penalties in this experiment are achieved less than 0.2 dB at 2.5 Gbps conversion, 2 dB at 5 Gbps conversion, and 3.9 dB at 10Gbps conversion, respectively. To use the CW assistance beam is a good solution to increase the performance of the wavelength converter u...