Switching-wavelength picosecond pulses and their applications in photonic processing of high-speed analog and digital signals

A new optical source capable of generating high-repetition-rate switching-wavelength pulses is successfully developed using either a fiber laser or a semiconductor laser diode. Through the techniques of dispersion compensation and sub-harmonic gating of pulses, relatively stable and uniform switching-wavelength pulses are generated. Our approach allows tunability in the number of wavelengths by minimal adjustment in the operating parameters of the simple laser configuration. The source has been applied to illustrate photonic sampling of microwave signals in a photonic analog-to-digital converter and multicasting of digital signals.; Switching-wavelength picosecond pulses are firstly generated from a mode-locked erbium doped fiber ring laser. The principles of a dispersion-managed fiber cavity and sub-harmonic gating of pulses are exploited in a fiber ring laser. By cooling the erbium doped fiber (EDF) in a liquid nitrogen bath, the homogeneous gain broadening effect is suppressed. A switching-wavelength pulse source has been successfully constructed. To remove the constraint on the use of liquid nitrogen cooling, a semiconductor optical amplifier is used to replace the EDF, thus providing an inhomogeneous gain medium. With a similar system configuration, switching-wavelength pulses are generated from a semiconductor optical amplifier (SOA) based fiber laser at room temperature. Gain modulation of a 1.55 μm SOA is used together with sub-harmonic gating of pulses in the cavity. The laser switches among different wavelength components with less than 1.1 dB variation in power.; To have a higher suppression of the background noise, a self-seeded semiconductor Fabry-Perot laser diode (FP-LD) is also employed for the generation of switching-wavelength pulses. Wavelength tuning has been performed using the compensated dispersion tuning approach. A 10-channel switching-wavelength pulse source is achieved by sequential self-seeding of a single FP-LD. The peak powers at different wavelengths are relatively uniform with less than 3% variation, and a pulse-to-pulse timing jitter below 286 fs is obtained. With the techniques of pulse compression and time division multiplexing, the pulse train is multiplied to operate at 20 GHz.; A photonic analog to digital converter (ADC) is realized using our uniform switching-wavelength sampling pulse source. A 20 Gsample/s photonic ADC has been demonstrated and is used to sample an arbitrary microwave signal. By making use of wavelength division of the photonic signal, different channels are demultiplexed and are individually sampled by an electronic ADC at a relatively low sampling rate. Thus, the overall system throughput can be significantly increased while employing relatively low-speed electronic components.; Multicasting of high-speed digital signals is successfully demonstrated with a new approach. The data is copied to the switching-wavelength pulses through cross-absorption modulation in an electro-absorption modulator. The scheme not only can multicast the signal to different wavelengths, but also converts the data format to return-to-zero. Hence, a negative power penalty can be obtained in the conversion process.