Long-to-short wavelength swept source.

Most swept external cavity diode lasers tune in the short-to-long wavelength direction (red tuning). Lower relative intensity noise (RIN) and higher output power are typically possible in this direction. We show here that long-to-short tuning (blue tuning) is possible for a short, linear cavity laser that has both low noise and high power. This mode of operation is made possible by nonlinear frequency broadening in the semiconductor optical amplifier (SOA) followed by clipping of the red portion of the spectrum by the micro-electro-mechanical systems (MEMS) tunable Fabry-Perot filter. Blue shifting during gain recovery is an important broadening mechanism. There is an approximate 50% advantage in coherence length for the same filter bandwidth for blue over red tuning, which allows deeper imaging in optical coherence tomography (OCT) applications. Calculations contrasting the blue tuning mechanism with red tuning are presented. The accuracy of the blue-tuning model is confirmed by coherence and coherence revival measurements and simulations.