Abstract

Wavelength Division Multiplexed (WDM) optical communications systems rely on wavelength selective components, fibers and other devices that must be specified in the transmission band. Currently available broadband sources for characterization in the 1.5 μm region are based on t ungsten lamp, EELED’s or Er-amplified spontaneous emission (ASE) [1]. We propose a very single broadband source suited for characterization of optical components in the 1500 nm to 1640 nm range. The extended band ASE source is realized by combining the forward ASE in a long erbium fiber with backward ASE. As in L-band amplifiers [2], the input portion of the fiber absorbs the pump laser while the far end of the fiber strongly absorbs the ASE emitted in the first portion. The output ASE spectrum is thus shifted to longer wavelengths. The set-up used for the demonstration is shown in Figure 1, it comprises of a 10 m Er-doped fiber (EDF) section followed by and isolator and then a 90 m EDF section. The isolator in between the fiber sections ensures that backward L-band ASE from the long fiber does not shifts the ASE spectrum of the short fiber section. Without this isolator the backward ASE from the longer section would compete against the c-band ASE in the shorter section. The two sections were of the same aluminosilicate Er-codoped fiber having a peak absorption at 1530 nm of 4.1 dB/m, core diameter 2.2 μm and measured mode field diameter (Peterman II) of 4.5 μm. The pump was a multi mode laser diode with a center wavelength of 1464 nm. A standard 1480/1550 nm WDM coupler was used to couple the pump and to collect the backward ASE from the 10 m fiber. This ASE was combined in a 70 % - 30 % coupler with the forward ASE from the 90 m fiber section to form the broad band spectrum of this source Figure 2 shows the output spectrum. A pump power of only 16 mW was used. The backward ASE peaking at 1530 nm and tile forward ASE peaking at 1565 nm are shown for comparison. Conventional Erbium ASE sources utilize only the c-band [1]. Our source covers a much broader spectrum. From Figure 2 we see, for instance, that at a power density level > −40 dBm/nm, the usable band is doubled by combining c- and b-band ASE. By increasing fiber length and pump power more intense sources are easily obtained using this design. The demonstrated source inherently covers the optical communication transmission bands limited by the availability of optical amplifiers, for which the c- and L-band amplifiers are the current options. In conclusion we have demonstrated a simple broad band source suited for characterization of optical components for WDM systems.

© 2000 IEEE