Abstract

Measurement of wind speed, one of the most basic meteorological variables, is becoming increasingly important for improving weather forecasts. Although Coherent doppler wind lidars (CDWLs) [1,2] provide us with a wind profile having high resolution and good precision, the maximum measurement distance is limited by a pulse energy of their laser system. Several groups have reported high-energy and single-frequency pulse laser systems at 1.5 µm based on all-fibre master oscillator power amplifier (MOPA) systems which employ large mode area (LMA) Er-doped fibre amplifiers (EDFA) with a several milli-joule output energies [3,4]. However, the gain fibre length must be shortened to suppress stimulated Brillouin scattering in the fibre, which leads to low gain. And higher Er ion doping in the fibre to obtain higher gains per unit length does not work well due to photodarkening. To solve these problem, a planar waveguide amplifier (PWA) made of Er,Yb:glass has been also reported in our group [5]. The PWA achieves both high gain due to a multi-bounce optical path configuration and high energy output due to its large mode area. However, the output energy of the PWA reaches saturation fluence which depends on the waveguide size. Moreover, it is difficult to obtain higher gain by increasing the reflection frequency inside the PWA since most of the increased propagation path passes through the gain-consumed region.

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