Fast tunable lasers with a broad tuning range are desirable for Bragg-grating-based fiber-optic sensors and optical coherence tomography. Most tunable fiber lasers or diode lasers use mechanical, rotatable diffraction gratings, mirrors, or filters, limiting tuning speed. But, by varying modulation frequency and chromatic dispersion in the laser cavity (and thus eliminating mechanically moving parts), researchers at the University of Tokyo (Tokyo, Japan) have demonstrated a fast wavelength-tunable modelocked fiber laser that tunes across a range of 100 nm (around a 1330 nm center wavelength) with a sweep rate as high as 200 kHz.
By using an active-modelocking technique in which short pulse trains are generated by directly modulating the injection current to the semiconductor optical amplifier, a predictable wavelength shift can be achieved. The technique-also called dispersion tuning-requires a length of dispersion-compensating fiber (DCF). By adjusting the DCF length, the tuning range and sensitivity of the fiber laser can be modified. The sweep rate of the tunable laser is limited by the cavity length, and could be increased by using a shorter dispersive element. Contact Shinji Yamashita at [email protected].
