We report a multi-channel optical frequency synthesizer developed to generate
extremely stable continuous wave lasers directly out of the optical comb of an
Er-doped fiber oscillator. Being stabilized to a high-finesse cavity with a
fractional frequency stability of 3.8×10−15 at 0.1 s, the comb-rooted
synthesizer produces multiple optical frequencies of ultra-narrow linewidth of
1.0 Hz at 1 s concurrently with an output power of tens of mW per each channel.
Diode-based stimulated emission by injection locking is a key mechanism that
allows comb frequency modes to sprout up with sufficient power amplification
but no loss of original comb frequency stability. Channel frequencies are
individually selectable with a 0.1 GHz increment over the entire comb bandwidth
spanning 4.25 THz around a 1550 nm center wavelength. A series of out-of-loop
test results is discussed to demonstrate that the synthesizer is able to
provide stable optical frequencies with the potential for advancing diverse
ultra-precision applications such as optical clocks comparison, atomic line
spectroscopy, photonic microwaves generation, and coherent optical
telecommunications.Comment: 19 pages, 4 figure
