A new laser system is suggested and experimentally verified as a chaotic transmitter for a secure optical communication system. The laser source kind is a distributed feedback with a peak wavelength 1310nm and maximum power 5mW. A doubly external cavity with 85cm of length is constructed via air.
Chaotic signal is achieved successfully after the laser reach of coherence collapse, with a very wide band spectrum (12GHz). This value is capable to increase subjecting to several parameters based on optical feedback (OFB) such as laser current operating level, beam focusing, polarization control, etc. In order to test a message hiding possibility, a frequency message is modulated directly into the laser, which is connected with the laser source using a bias tee. For the free running (solitary) semiconductor laser, the maximum available direct current modulation is: 3GHz/mA, while this value can be increased by this technique. This gives the possibility for very high modulation values and increasing data package volume that can send securely in the applications that requires immunity.
A new simple technique for narrow-linewidth and wavelength-tunable laser is experimentally satisfied. The technique is based on employing nonlinearities arise with laser feedback and injection. The main effect observed and controlled is the mode hopping (MH) within other nonlinearities. In this situation mixed optoelectronical feedback (OEFB) and optical injection from another identical type laser simultaneously, plays the role of controller. These results show that no need of using a Fiber Bragg Grating. As a well-known alternative technique used earlier to build a tunable laser. The map of validity for this effect and parameters affecting the laser output are all investigated. This technique enhances modulation index for the slave laser to be 100% and employs mode hoping generated in it for tuning output lasing frequency. This is by controlling either master laser detuning or injection strength or both. Also, by controlling slave laser optoelectronic feedback time delay (by a variable RF attenuator) or (and) nonlinear contribution for this by introducing a nonlinear function into the detected signal. Bidirectional (mutual) and unidirectional injection systems are experimented. In the first system both lasers multi-lasing in general synchronization manner, while in the last system, injector (master) laser stays immune from slave dynamics.
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