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International Conference on Photonics and Optical Engineering

Controllable optical quality factor in a two-ring-two-bus structure

Ying Zhang, Qingzhong Huang, Liu Qiang

Published Jan 15, 2021• 2 citations
Publisher

Abstract

Dynamically tuning Q factor in optical resonators is now more feasible in information processing applications, such as light storage and wavelength conversion. This paper proposed and demonstrated a new dynamically tuning Q approach that is realized in coupled two rings structure. One resonator uses an add-drop configuration, coupled to another single micro-ring. The heating causes an increase in the refractive index, which in turn causes resonant wavelength redshift. This shift is a switch to control the coupling between the two rings, to tune the linewidth of light confined in the ring, equivalent to tune the quality factor. And we adjust the detuning and coupling state between the two rings to control the light coupled into the resonator. The Q factor decreases from 56,525 to 16,450 in the transmission spectrum with the different heater power. In this way, we successfully realized a modulation of the Q from high to low states in the structure. Besides, the original coupling spacing between the two rings also has an influence on the Q factor. The larger the coupling spacing, the higher the Q factor. In addition, we also study the changes of phase and delay time in the tunable process. The results show that the change of fast light (high Q) and slow light (low Q) can be realized at the same time, which would enable applications for on-chip adjustable time delay, fast/slow light and light storage.

DOI
10.1117/12.2584964

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Dynamically tuning Q factor in optical resonators is now more feasible in information processing applications, such as light storage and wavelength conversion. This paper proposed and demonstrated a new dynamically tuning Q approach that is realized in coupled two rings structure. One resonator uses an add-drop configuration, coupled to another single micro-ring. The heating causes an increase in the refractive index, which in turn causes resonant wavelength redshift. This shift is a switch to control the coupling between the two rings, to tune the linewidth of light confined in the ring, equivalent to tune the quality factor. And we adjust the detuning and coupling state between the two rings to control the light coupled into the resonator. The Q factor decreases from 56,525 to 16,450 in the transmission spectrum with the different heater power. In this way, we successfully realized a modulation of the Q from high to low states in the structure. Besides, the original coupling spacing between the two rings also has an influence on the Q factor. The larger the coupling spacing, the higher the Q factor. In addition, we also study the changes of phase and delay time in the tunable process. The results show that the change of fast light (high Q) and slow light (low Q) can be realized at the same time, which would enable applications for on-chip adjustable time delay, fast/slow light and light storage.
Optical resonators with controllable Q factors are key components in many areas of optical physics and engineering. We propose and investigate a Q -factor controllable system composed of two directly coupled microring resonators, one of which is tunable and coupled to dual waveguides. By shifting the resonance of the controllable microring, the Q factor of the system as well as the other microring changes significantly. We have demonstrated wide-range controllable Q factors based on this structure in silicon-on-insulator, for example. The influences of spectral detuning and coupling strength between two resonators on the variation of Q factors are studied in detail experimentally. Then, we explore its applications in optical buffering. Tunable fast-to-slow/slow-to-fast light has been carried out by switching the system between the high- Q state and low- Q state. Moreover, optical pulse capture and release are also achievable using this structure with dynamic tuning, and the photon storage properties are investigated. The proposed Q -factor tunable system is simple, flexible, and realizable in various integrated photonic platforms, allowing for potential applications in on-chip optical communications and quantum information processing.
This paper proposes a ring-out-ring structure of coupled optical resonators to yield coupled-resonator-induced transparency (CRIT). Considering the insertion loss of the coupler, it theoretically deduces the transmission and the effective phase shift. The influences of the insertion loss of the coupler on the transmittance, the effective phase shift, the group index and the CRIT linewidth are fully studied. We find that the increase in multiple m can effectively enhance the normal dispersion and the group index of the proposed structure. Moreover, the specific expression of the group index at resonance is theoretically deduced and discussed for the proposed structure with two rings. The result shows that the multiple m between the lengths of ring 1 and ring 2 can enhance the group index to m times that of the structure with two equal-sized rings at resonance. The control of slow light in the proposed structure is important for applications of highly sensitivity gyroscopes, optical delay lines and optical buffers, etc.
High-Q nanophotonic resonators are crucial for many applications in classical and quantum optical processing, communication, and sensing. We achieve ultra-high quality factors via a method previously limited to bulk systems, preparing a highly transparent and strongly dispersive medium within the resonator that causes a reduction in the group velocity and a corresponding increase in the quality factor. We implement this via spectral hole burning in erbium-doped thin-film lithium niobate microring resonators, and show Q-factors enhanced by nearly three orders of magnitude to exceed 108. Additionally, we show dynamic control of the resonances via electro-optic tuning. Finally, we present a theoretical model for our experimentally observed resonator linewidths, which are not well-described by the standard Bloch equations. Our results show a dramatic reduction in the erbium dephasing rate under a strong optical drive, leading to much narrower linewidths than would otherwise be expected given the large circulating intensity in the resonator. Light can be slowed to extreme degrees in engineered media, giving rise to unique behavior. Here, the authors show that slow light enables the formation of ultra-narrow tunable mirroring resonators, introducing a new paradigm for controlling optical responses on a photonic chip.
We demonstrate theoretically and experimentally that the fast and slow light characteristics of the add-drop ring-resonator (ADRR) can be regulated by introducing an assisted ring. This novel geometry is named ring-assisted add-drop ring-resonator (RA-ADRR). When the assisted ring is under-coupled, the fast and slow light characteristics of through and drop ports of the RA-ADRR will be reversed, which is different from the coupled resonator induced transparency (CRIT) studied previously. With the decrease of loss, the dispersion peak (dip) of the two ports will grow up towards the opposite directions and finally the inversion occurs. Meanwhile, we find that by increasing the circumference of the assisted ring, the dispersion of the two ports could be improved proportionally. The experimental results show that the maximum group delays of the through and drop ports are 115 ns and -485 ns, respectively. This novel phenomenon could greatly enhance the sensitivity of slow light interferometers and also has potential applications in optical communication, network, filtering and switching.
The possibility of dynamically controlling the speed of light can be extremely useful in all the optical applications where a variable delay is needed, such as bit and frame synchronization and optical storage. To this aim, coupled resonator slow-wave structures (SWSs) represent a promising approach to slow down the propagation of optical signals with as large bandwidths as required by optical communication systems. We show that by suitably setting the rings' resonances, SWSs can act efficiently as tunable delay lines, with the overall time delay being continuously adjustable from zero to a maximum value, typically limited by the effects of loss and dispersion. Every ring of the structure can be used as an optical gate and optical pulses can also be trapped and released by the SWS, so as to realize an optical memory or buffer. A time delay of 300 ps and a slowing ratio of 7.5 over a 3.3 GHz bandwidth are experimentally demonstrated in SWSs realized in silicon oxynitride technology