LE-1200 Erbium doped Fiber Laser

The pump laser diode (LD) has a so called single mode fiber pigtail, terminated with a fiber connector and is directly connected with a fiber patch cable (PC) to the EDF fiber The light inside the fiber is partially reflected at each end face due to Fresnel reflections. Despite the low reflectivity of 4% laser oscillation is built up between the two end faces of the EDF due to the high gain. A collimator (CO) with short focal length forms an almost parallel beam and an InGaAs photodetector (PD) is used to detect the emission of the fiber The interference filter (IF) is mounted to an adjustment holder and passes only the 1.55 µm radiation. With its front face reflectivity of about 10% it serves also as an external cavity mirror to study the effect of a coupled optical cavity. The pump laser diode is connected to a controller (LD) with adjustable injection current and modulation. This allows to study the amplified spontaneous emission (ASE) below and above the laser threshold. By using the modulation of the injection current the lifetime of the excited state as well as impressive laser spiking is displayed and measured on an oscilloscope (OS). In the ring laser setup, the pump radiation is injected by a wavelength division multiplexer (WDM) into the ring structure which consists out of the EDF, a 4 port fiber coupler and an optical diode or just a fiber patch cable. The optical diode is used to force the ring laser either to the clockwise (cw) or counter clockwise (CCW) operation. Exchanging the optical diode against a fiber the ring laser oscillates in both directions. The 4 port fiber coupler is used to extract about 10% of the internal power of the cw and ccw ring laser mode for measurement purposes. Including the optical diode into the ring structures only cw or ccw oscillation occurs. By using an electronic spectrum analyser the beat frequency of the longitudinal ring resonator modes is measured and set into relation to the resonator length for the 2, 4 or 8 m long EDF.

A. Visible green Emission created by two photon absorption
 Increasing the pump power the fiber starts to "glow" in green color. This is due to a two two photon excitation with subsequent green emission.