Wavelength tunable GHz repetition rate picosecond pulse generator using an SBS frequency comb

Abstract

We have developed a new system to generate GHz repetition rate tunable pulses in the picosecond regime at any wavelength by using self-phase-locked stimulated Brillouin scattering (SBS). The phase-locked comb at any required wavelength is generated using a single length of fiber in a ring cavity, seeded by an amplified single frequency CW pump laser. We demonstrate a coherent phase relationship between multiple cascaded Stokes waves in the cavity, which directly leads to a highly stable pulse regime. This scheme does not require the matching of frequency components to the cavity, as the frequency components are generated by SBS and not oscillating modes. The coherent pulses in the time domain are in the order of ~10 ps. The nature of the fiber leads to a stable SBS frequency shift, which is directly correlated to the repetition frequency and which is in the order of tens of GHz. Since the process is governed by SBS, it is self-starting and has a linear dependence with temperature (1 MHz/°C), which could be used for fine adjustments. Such a laser is therefore suitable for high-speed optical clocks and optical communication system, amongst other applications. This system allows the ultra-short pulses to be generated at any wavelength by simply tuning the wavelength of the seed laser. The pump power allows the pulse width to be tuned in steps, by generating additional Stokes orders. The repetition rate is altered by the choice of fiber cavity or by the choice of the orders of the SBS shifted frequencies.