Narrow Linewidth Laser

We report spectral linewidth measurements of a 9.1-µm distributed-feedback quantum cascade laser (QCL). The free-running QCL beam was mixed with a waveguide isotopic C18O2 laser onto a high-speed HgCdTe photomixer, and beat notes were recorded from a radio-frequency spectral analyzer. Beating was performed at two operating conditions, first near the QCL laser threshold (beating with the C18O2 R10 line) and then at a high injection current (beating with the C18O2 R8 line). Overall, beat note widths of 1.3 – 6.5 MHz were observed, which proves that a free-running QCL can have a short-term spectral width near 1 MHz.

A single frequency Erbium-doped fiber laser (EDFL) operating at 1552.5 nm has been demonstrated by using a 2 m long of newly developed Zirconia-based Erbium-doped fiber (Zr-EDF) as a gain medium. The Zr-EDF is fabricated by combining Zr and Al to achieve the maximum Erbium ion concentration of 4320 ppm wt. By using a fiber Bragg grating (FBG) in a ring configuration, a laser which operates at 1552.5 nm with signal to noise ratio of 60 dB is generated. The linewidth of the EDFL is measured to be approximately 95 MHz using a heterodyne technique.

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