Entanglement is one of the most important resources for quantum information processing. This Lab is actively involved in developing compact and robust high brightness optical entanglement systems for various experiments, including the on-board test of entanglement in a satellite. Using spontaneous parametric down-conversion in a periodically poled, we have demonstrated the entangled photon source with spectral brightness as high as ~0.41±0.02 MHz/mW/nm. The source can be fitted in a foot-print of 10 cm x 10 cm and a weight of 1 kg including the drivers and electronics. Similarly, we are also developing high brightness hybrid entangled photon source that can be used for quantum communication experiments. We are working on the manipulation of the spatial structure of the single-photon source to explore the possibility of moderately long-distance (>1 km) (in comparison to the dimension of the laboratory experiments) free-space propagation of the photons without divergence. In this case, we might be able to avoid the bulky telescope for beam launching. Since we are involved in the development of high brightness single-photon sources, we are using such sources for various quantum sensing and metrology experiments, including the measurement of rotation (Gyroscopic effect) and nano- or pico- displacement. We are also studying the nonlinear interaction of single-photon for possible quantum switches.