A fiber Lyot depolarizer was used to reduce the degree of polarization (DOP) of a laser pump diode. The typical DOP out of the depolarizer is better than 0.2 which should be sufficient to reduce the effect of pump polarization on erbium fiber amplifiers.Index Terms-Optical fiber amplifier, optical fiber birefringence, optical fiber device, polarization, semiconductor laser.

We report on a polarization measurement of inclusive J /ψ mesons in the di-electron decay channel at mid-rapidity at 2 < p T < 6 GeV/c in p + p collisions at √ s = 200 GeV. Data were taken with the STAR detector at RHIC. The J /ψ polarization measurement should help to distinguish between different models of the J /ψ production mechanism since they predict different p T dependences of the J /ψ polarization. In this analysis, J /ψ polarization is studied in the helicity frame. The polarization parameter λ θ measured at RHIC becomes smaller towards high p T , indicating more longitudinal J /ψ polarization as p T increases.The result is compared with predictions of presently available models.