Thermo-optic tunable optical filters with GHz-bandwidth and flat-top passband on thin film lithium niobate platform

Abstract

Lithium niobate on insulator (LNOI) is a new photonic integrated platform that provides high optical confinement and retains the inherent excellent properties of lithium niobate (LN). Tunable filters are one of the indispensable devices for integrated optics. Here we design and fabricate a thermo-optic (TO) tunable optical filter using two cascaded racetrack microring resonators (MRRs) based on LNOI. The filter shows a narrow and flat top passband with intra band ripple less than 0.3 dB, 3 dB bandwidth of 4.8 GHz and out-of-band rejection of about 35 dB. The insertion loss of the filter is about −14 dB, including grating coupling loss about −6.5 dB and on-chip loss less than −1 dB. The heating power for center wavelength shift of the filter is about 89.4 mW per free spectral range (FSR). Relevant applications of such filters include optical information processing and microwave photonics.

Microwave photonic sideband selector based on thin-film lithium niobate platform

“…Due to the high performance of components of the microwave photonic sideband selector, it supports working bandwidth up to 40 GHz, with undesired sidebands effectively suppressed by more than 25 dB. The related design methods and principles have been reported by our research team previously [25][26][27][28] . The insertion loss of a packaged microwave photonic sideband selector is approximately 11 dB, occupying a volume of 35 mm × 10 mm × 5 mm.…”

High-Speed Optical Mode Switch in Lithium Niobate on Insulator

“…22,23 Various devices have been demonstrated in the LNOI platform, including high-speed electro-optic modulators, 24−26 optical mode (de)multiplexers (MMUX), 27,28 and optical filters. 29,30 Although optical mode switches have also been demonstrated in the LNOI platform, 31 the switching time of the device was surprisingly slow (about 30 ns) due to the high capacitance of the chosen electrode configuration, which does not make full use of the high-speed electro-optic material property of the lithium niobate.…”

“…Recently, the lithium niobate on insulator (LNOI) has emerged as a tantalizing platform for realizing high-speed photonic integrated circuits, due to its tight modal confinement and lithium niobate’s attractive material properties such as its strong electro-optic effect. , Various devices have been demonstrated in the LNOI platform, including high-speed electro-optic modulators, − optical mode (de)­multiplexers (MMUX), , and optical filters. , Although optical mode switches have also been demonstrated in the LNOI platform, the switching time of the device was surprisingly slow (about 30 ns) due to the high capacitance of the chosen electrode configuration, which does not make full use of the high-speed electro-optic material property of the lithium niobate.…”

Anisotropic Thermo‐Optic Mach–Zehnder Interferometer on LNOI for Polarization Handling and Multiplexing

“…In recent years, thin-film lithium niobate (LN) on insulator (LNOI) is emerging as a promising integrated photonic platform for on-chip scalable optical signal manipulation and processing that provides large refractive index contrast, strong electro-optic (EO), thermo-optic (TO), and nonlinear effects across a wide transparency window. [1][2][3][4][5][6][7][8][9] Currently, a series of high-performance integrated devices on LNOI, based on Mach-Zehnder interferometers (MZIs), [10] microring [11] and racetrack resonators, and photonic crystal structures, have been reported for applications in modulators, [12][13][14][15][16][17][18][19] filters, [20][21][22] polarization controllers, [23] and frequency combs. [24][25][26][27][28] While EO phase shifters are indispensable for highspeed applications, they often suffer from stability issues for low-speed and static applications, such as modulator bias control and photonic switches.…”

“…[14] Although extensively investigated for silicon photonics, [32][33][34][35][36][37][38] the TO effect, especially the anisotropic TO effect on the LNOI platform has been much less explored. [22,31,[39][40][41] The birefringent refractive indices n o and n e of LN feature quadratic temperature dependence from 300 to 500 K, [42] which is the pertinent temperature range for general TO devices. Near the telecom C band, the TO coefficients (TOCs) for n e and n o are on the order of 10 −5 and 10 −6 K −1 , respectively, differing by nearly an order of magnitude.…”