Advances in lithium niobate photonics:development status and perspectives

Lithium niobate(LN)has experienced significant developments during past decades due to its versatile properties,especially its large electro-optic(EO)coefficient.For example,bulk LN-based modulators with high speeds and a superior linearity are widely used in typical fiber-optic communication systems.However,with everincreasing demands for signal transmission capacity,the high power and large size of bulk LN-based devices pose great challenges,especially when one of its counterparts,integrated silicon photonics,has experienced dramatic developments in recent decades.Not long ago,high-quality thin-film LN on insulator(LNOI)became commercially available,which has paved the way for integrated LN photonics and opened a hot research area of LN photonics devices.LNOI allows a large refractive index contrast,thus light can be confined within a more compact structure.Together with other properties of LN,such as nonlinear/acousto-optic/pyroelectric effects,various kinds of high-performance integrated LN devices can be demonstrated.A comprehensive summary of advances in LN photonics is provided.As LN photonics has experienced several decades of development,our review includes some of the typical bulk LN devices as well as recently developed thin film LN devices.In this way,readers may be inspired by a complete picture of the evolution of this technology.We first introduce the basic material properties of LN and several key processing technologies for fabricating photonics devices.After that,various kinds of functional devices based on different effects are summarized.Finally,we give a short summary and perspective of LN photonics.We hope this review can give readers more insight into recent advances in LN photonics and contribute to the further development of LN related research.

Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform

Optical color filters are widely applied in many areas including display,imaging,sensing,holography,energy harvest,and measurement.Traditional dye-based color filters have drawbacks such as environmental hazards and instability under high temperature and ultraviolet radiation.With advances in nanotechnology,structural color filters,which are based on the interaction of light with designed nanostructures,are able to overcome the drawbacks.Also,it is possible to fabricate structural color filters using standard complementary metal-oxide-semiconductor(CMOS)fabrication facilities with low cost and high volume.In this work,metasurface-based subtractive color filters(SCFs)are demonstrated on 12-inch(300-mm)glass wafers using a CMOS-compatible fabrication process.In order to make the transmissive-type SCF on a transparent glass wafer,an in-house developed layer transfer process is used to solve the glass wafer handling issue in fabrication tools.Three different heights of embedded silicon nanopillars(110,170,and 230 nm)are found to support magnetic dipole resonances.With pillar height and pitch variation,SCFs with different displayed colors are achieved.Based on the resonance wavelength,the displayed color of the metasurface is verified within the red-yellow-blue color wheel.The simulation and measurement results are compared and discussed.The work provides an alternative design for high efficiency color filters on a CMOS-compatible platform,and paves the way towards mass-producible large-area metasurfaces.