70 dB long-pass filter on a nanophotonic chip.

Integrated quantum photonic chips are promising for scalable, photonic based quantum information processing. Although on-chip quantum photon sources and single photon detectors have been demostrated separately, the full integration of these components on single chip is hindered by the background photons from the strong classical pump light. Here we design and fabricate an on-chip long-pass filter which can provide 70 dB attenuation for visible light near 775 nm with less than 3 dB insertion loss for light in the telecom C-band near 1550 nm. The adiabatic design makes this device broadband and robust against fabrication errors as well as working conditions. Combined with the previously demonstrated non-classical on-chip source based on spontaneous parametric down conversion on the same material system, this platform could enable 100 dB suppression of pump light and holds promise in realizing fully integrated quantum photonic chips where the sources, filters and detectors are monolithically integrated.