Tunable microwave output over a wide RF region generated by an optical dual-wavelength fiber laser

Abstract

The dual-wavelength fiber laser provides a compact, robust and stable platform for the generation of microwave signals. Two approaches towards generating microwave emissions using dual wavelengths are explored in this work, with both exploiting the heterodyning beat technique. Both approaches are based on a ring fiber laser with an erbium-doped fiber, having absorption coefficients of 16.0–20.0 dBm at 1531 nm and 11.0–13.0 dBm at 980 nm, serving as the active gain medium. A 10 cm long photonic crystal fiber with a solid core diameter of 4.37 μm and surrounded by air holes of 5.06 μm diameter with a separation of 5.52 μm between them serves to create the desired dual-wavelength output. A tunable band pass filter with bandwidth of 0.8 nm serves as a tuning mechanism together with a polarization controller. Channel spacings as narrow as 0.00043 nm can be realized, giving a microwave output of about 671.9 MHz. Furthermore, the channel spacing can be extended to as large as 0.03631 nm, giving a microwave emission in excess of 4.59 GHz. The output is highly stable, with little change in power or wavelength observed over a test period of 22 min.