Implementation of wavelength tunability, wavelength conversion and optical flip-flop in injection locked fabry-perot laser diodes

Abstract

Novel applications of Fabry-Perot laser diodes (FP-LDs) are presented for wavelength division multiplexing (WDM) networks. 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 tuning range is about 10 nm with the side mode suppression ratio of more than 27 dB when the temperature changes from 11.5$deg$C to 25$deg$C. Direct modulation characteristics were investigated and the results show that shorter externalcavity can bear deeper modulation depth. For 8 mm external cavity, an error free operation was achieved with extinction ratio (ER) of 3.7 dB, but an error floor was shown at the bit error rate (BER) level of $10^{-8}$ when the corresponding ER is 4.11 dB. For 4 mm external cavity, however, the maximum ER increased to more than 9 dB. 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 3.5 dB at 2.5 Gbit/s NRZ wavelength conversion. Furthermore, a novel scheme of all-...