Measurement of intensity noise correlation between lines of spatially distributed multi-wavelength fiber lasers

Abstract

Photoinscription of superstructured Bragg gratings in Er-Yb codoped fiber is a promising and cost-effective approach to produce high-quality multi-wavelength fiber lasers for various applications like radio-over-fiber systems, fiber-optic sensors or low-cost WDM testing source. However, a good understanding of the noise properties of the laser source is required before these applications can be addressed. Previous modeling has shown that these devices are similar to compact cascades of single wavelength DFB fiber lasers in which the modes at each wavelength are almost nonoverlapping along the fiber. In this paper, we further examine the independence of each channel by performing relative intensity noise (RIN) measurements on a multi-wavelength fiber laser, a dual-polarization fiber laser and a dualwavelength fiber laser. In each case, we estimate the correlation between the laser lines. From RIN measurements performed on each channel of a multi-wavelength laser, as well as on the full spectrum, we compute an average degree of correlation between the RIN of neighboring lines and observed no correlation in most of the cases. Moreover, each channel displays a single relaxation frequency which is different from those of the other channels. On the other hand, we observed strong partition noise, with negative correlation, between polarization modes of a single wavelength fiber laser. Finally, we measured the RIN of the two modes of a dual-wavelength fiber laser with modes having a greater overlap than the multi-wavelength laser. The results show that the lines share two common relaxation frequencies, an indication of a dynamic link between them.