  Heralded single photon source (HSPS) is an important way in generating
genuine single photon, having advantages of experimental simplicity and
versatility. However, HSPS intrinsically suffers from the trade-off between the
heralded single photon rate and the single photon purity. To overcome this, one
can apply multiplexing technology in different degrees of freedom to enhance
the performance of HSPS. Here, by employing spectral multiplexing and active
feed-forward spectral manipulating, we demonstrate a HSPS at 1.5 {\mu}m
telecom-band. Our experimental results show that the spectral multiplexing
effectively erases the frequency correlation of pair source and significantly
improves the heralded single photon rate while keeping the g{^(^2^)}(0) as low
as 0.0006{\pm}0.0001. The Hong-Ou-Mandel interference between the heralded
single photons and photons from an independent weak coherent source indicates a
high indistinguishability. Our results pave a way for scalable HSPS by spectral
multiplexing towards deterministic single photon emission.
