  A bias-free source-independent quantum random number generator scheme based
on the measurement of vacuum fluctuation is proposed to realize the effective
elimination of system bias and common mode noise introduced by the local
oscillator. Optimal parameter settings are derived to avoid the system
recording two canonically conjugate quadratures simultaneously in each
measurement. In particular, it provides a new approach to investigate the
performance difference between measuring two quadratures of equal and unequal
intensity. It is experimentally demonstrated that the system supports 4.2 Gbps
bias-free source-independent random number generation, where its common mode
rejection ratio reaches 61.17 dB. Furthermore, the scheme offers an all-optical
method facilitating the integration of source-independent quantum random number
generators into compact chips.
