Design and realization of polarisation insensitive semiconductor optical amplifiers with low forward current

Polarisation insensitive semiconductor travelling wave amplifiers (TWA's) with high internal gain at low bias current are of great importance for the development of future optical fiber transmissions systems. During the last year, an important effort was carried out worldwide and significant improvements have already been achieved from a better design and fabrication of the active waveguide [1-4]. More recently, we have obtained polarisation insensitive GaInAsP/InP TWA's realized by gas source molecular beam epitaxy (GSMBE) with a high internal gain (28 dB) and a gain wavelength ripple of 3 dB for both TE and TM modes at a very low forward current of only 50 mA [5]. We present consolidated measurements on a large number of TWA'S with different structures, and in order to evaluate the tolerances on the technological parameters, we illustrate with a simple model, the variation of the polarisation sensitivity with gain.