Generation of a multi-wavelength source spanning the entire C-band by nonlinear spectral broadening of dual-carrier electro-optic frequency combs

in OSA Continuum (2020)

We demonstrate a multi-wavelength source with a high repetition rate of 25 GHz, spanning the entire C-band, of which 124 lines lie within 10 dB bandwidth. We exploit the spectral and temporal properties ... [more ▼]

We demonstrate a multi-wavelength source with a high repetition rate of 25 GHz, spanning the entire C-band, of which 124 lines lie within 10 dB bandwidth. We exploit the spectral and temporal properties of dual carrier electro-optic combs to simultaneously enhance self-phase modulation (SPM) based broadening and increase the stimulated Brillouin scattering (SBS) threshold. Dual carrier combs are generated through electro-optic modulation of spectrally separated narrow linewidth carriers. They are spectrally broadened in a highly nonlinear fiber after amplification with an in-house built erbium ytterbium co-doped fiber amplifier. The temporal profile of the dual carrier combs consists of significantly narrow pulses (1.4-1.9 ps FWHM) in comparison to the single laser comb (16.5 ps FWHM), increasing the peak power and enhancing the SPM effects. Further, the spectral power is distributed across the comb lines, increasing the SBS threshold and thus the power scalability of the system. These two factors together boost the bandwidth of the spectrally broadened multi-wavelength source. [less ▲]

Frequency Offset Locked, Dual Carrier Excitation of Phase modulated, Electro-optic Frequency Combs for Bandwidth Scaling and Nonlinear Spectral Broadening

in SPIE (2018, January 29)

DWDM with/without superchannel based photonic networks require the use of optical carriers with equalised amplitudes and frequency stabilization of adjacent carriers to realise reliable high bandwidth ... [more ▼]

DWDM with/without superchannel based photonic networks require the use of optical carriers with equalised amplitudes and frequency stabilization of adjacent carriers to realise reliable high bandwidth optical communication systems with high spectral efficiency and long reach. Cascading of electro-optic (EO) modulators is a versatile method for generating tuneable, high repetition rate frequency combs which can be used as sources for the carriers. However, the number of lines produced with this technique is limited by the number of phase modulators. Nonlinear spectral broadening is an attractive option for bandwidth scaling; however, bandwidth scaling of single carrier combs through four wave mixing suffers from unequal comb lines or power limitations due to Brillouin scattering. A simpler technique to increase the number of comb lines would involve using multicarrier excitations for comb generation which would result in a proportional increase in the comb lines. Further, dual-carrier excitation enables an excellent temporal profile for nonlinear spectral broadening. However, since the two carriers have uncorrelated drifts, the resultant frequency combs would be unsuitable for most applications. This issue can be overcome by frequency offset locking the two lasers. Here, we demonstrate frequency offset locking (MHz accuracy) of two diode lasers spaced by 100GHz by using an optical phase locked loop which locks one laser to a RF harmonic of the other. This allows for the generation of frequency comb lines locked to each other even post nonlinear broadening. Using this technique, we demonstrate a 25GHz frequency comb with >90 lines (2THz) in the C-band. [less ▲]