分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Integrated optical filter based on microring resonators plays a critical role in many applications, ranging from wavelength division multiplexing and switching to channel routing. Bandwidth tunable filters are capable of meeting the on-demand flexible operations in complex situations, due to their advantages of scalability, multi-function, and energy-saving. It has been investigated recently that parity-time (PT) symmetry coupled-resonant systems can be applied to the bandwidth-tunable filters. However, due to the trade-off between the bandwidth-tunable contrast ratio and insertion loss of system, the bandwidth-tunable contrast ratio of this method is severely limited. Here, the bandwidth-tunable contrast ratio is defined as the maximum bandwidth divided by the minimum bandwidth. In this work, we show that high bandwidth-tunable contrast ratio and low insertion loss of system can be achieved simultaneously by increasing the coupling strength between the input port and the resonant. System characterizations under different coupling states reveal that the low insertion loss can be obtained when the system initially operates at the over-coupling condition. A high bandwidth-tunable contrast ratio PT-symmetry band-pass filter with moderate insertion loss is shown on the Silicon platform. Our scheme provides an effective method to reduce the insertion loss of on-chip tunable filters, which is also applicable to the high-order cascaded microring systems.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Yanxian Wei
Junwei Cheng
Yilun Wang
Hailong Zhou
Jianji Dong
Dongmei Huang
Feng Li
Ming Li
P. K. A. Wai
Xinliang Zhang
摘要： Thermo-optic microheater is indispensable in silicon photonic devices for smart and reconfigurable photonic networks. Much efforts have been made to improve the metallic microheater performance in the past decades. However, because of the metallic nature of light absorption, placing the metallic microheater very close to the waveguide for fast response is impractical and has not been done experimentally. Here, we experimentally demonstrate a metallic microheater placed very close to the waveguide based on parity-time (PT) symmetry breaking. The intrinsic high loss of metallic heater ensures the system will operate in the PT-symmetry-broken region, which guarantee the low loss of light in the silicon waveguide. Moreover, heating at a close range significantly reduces the response time. A fast response time of ~1 us is achieved without introducing extra loss. The insertion loss is only 0.1 dB for the long heater. The modulation bandwidth is 280 kHz, which is an order of magnitude improvement when compared with that of the mainstream thermo-optic phase shifters. To verify the capability of large-scale integration, a 1*8 phased array for beam steering is also demonstrated experimentally with the PT-symmetry-broken metallic heaters. Our work provides a novel design concept for low-loss fast-response optical switches with dissipative materials and offers a new approach to enhance the performance of thermo-optic phase shifters.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Encircling an exceptional point (EP) in a parity-time (PT) symmetric system has shown great potential for chiral optical devices, such as chiral mode switching for symmetric and anti-symmetric modes. However, the chiral switching for polarization states has never been reported although chiral polarization manipulation has significant applications in imaging, sensing, and communication etc. Here inspired by the anti-PT symmetry, we demonstrate an on-chip chiral polarizer by constructing polarization-coupled anti-PT symmetric system for the first time. The transmission axes of the chiral polarizer are different for forward and backward propagation. A polarization extinction ratio of over 10 dB is achieved for both propagating directions. Moreover, a telecommunication experiment is performed to demonstrate the potential applications in polarization encoding signals. It provides a novel functionality for encircling-an-EP parametric evolution and offer a new approach for on-chip chiral polarization manipulation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Yanxian Wei
Hailong Zhou
Yunhong Ding
Zihao Cheng
Dongmei Huang
P. K. A. Wai
Jianji Dong
Xinliang Zhang
摘要： The integration density of photonic integrated circuits has been limited by light coupling between waveguides. Traditional approaches to layout the waveguide with high density are based on refractive index engineering to suppress the light coupling between waveguides. However, these methods mostly require sophisticated and sensitive structure design, thus lack universality. Herein, we propose high-density multi-mode-multi-core integrated photonic waveguides by inserting high-loss metal strips between waveguides. We have achieved a 10-spatial-channel multi-mode-multi-core waveguide with total occupying spacing of 6.6 um. The multi-mode waveguides have a close spacing of 400 nm. The proposed scheme has high fabrication tolerance, ultra-large bandwidth and good compatibility to the complementary metal-oxide-semiconductor technology. It can be applied to any integration platform, any working waveband and any operating mode, providing a universal solution for high-density photonic circuits.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Thermo-optic (TO) phase shifters are very fundamental units in large-scale active silicon photonic integrated circuits (PICs). However, due to the limitation of microheater materials with a trade-off between heating efficiency and absorption loss, designs reported so far typically suffer from slow response time, high power consumption, low yields, and so on. Here, we demonstrate an energy-efficient, fast-response, and low-loss TO phase shifter by introducing hydrogen-doped indium oxide (IHO) films as microheater, and the optimized electron concentration with enhanced mobility endows the IHO high conductivity as well as high near-infrared (NIR) transparency, which allow it to directly contact the silicon waveguide without any insulating layer for efficient tuning and fast response. The TO phase shifter achieves a sub-microsecond response time (970 ns/980 ns) with a {\pi} phase shift power consumption of 9.6 mW. And the insertion loss introduced by the IHO microheater is ~ 0.5 dB. The proposed IHO-based microheaters with compatible processing technology illustrate the great potential of such material in the application of large-scale silicon PICs.
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