Coupled-resonator-induced Transparency Research Articles

New cross-coupled resonator induced shifted absorption (CRISA) in double microring resonators using a cross-coupling-structure technique

We report, for the first time to the best of our knowledge, a technique that employs ′cross-coupling structure’ in the cascaded microring resonators (MRRs) to bring new optical analogues of quantum coherence phenomena. The new configuration resembles a standard double resonator (SDR) but uses cross-coupled–based directional couplers (DCs) instead of the typical direct-coupled–based DCs. One of its unique features is that it does not exhibit the typical SDR’s signature quantum coherence analogue effects like coupled-resonator induced transparency (CRIT) or coupled-resonator induced absorption (CRIA). On the contrary, it produces a new very narrow reflection dip positioned at single-pass phase shift θ = − π/2 which we refer to as cross-coupled resonator induced shifted absorption (CRISA). We compare extensively CRISA’s characteristics with the CRIT, CRIA, and Autler-Townes splitting (ATS) found in SDR. The technique opens up new configurations with richer optical behaviours that could find potentially still unexplored applications.

Reversible fast to slow-light transition originating in the optical analog of EIA-EIT transformation in optical resonators

Coupled-resonator-induced transparency (CRIT) and coupled-resonator-induced absorption (CRIA) are the all-optical analogs of electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA), and enable an optical pulse to propagate subluminally and superluminally in integrated photonic systems, respectively. Here, we describe the results of a theoretical study, which reveals a reversible CRIA-CRIT transition using coupled optical ring resonators. Analogous to the dispersion reversal occurring in the EIA-EIT transition, the dispersion also reverses during the CRIA-CRIT transition. Besides the EIA-EIT crossover analogy, we describe additional analogs of the coherent atomic phenomena arising in the CRIA-CRIT transition. We also discuss the specific conditions that lead to strongly enhanced dispersion. Furthermore, in contrast to the previous studies on coupled resonators, we reveal acquiring a critically and undercoupled slow-light CRIT from an overcoupled fast-light CRIA. Our experimentally viable study provides a route for the dynamic control and reversal of dispersion, which, among other, is important for quantum information technology, the Fresnel light dragging effect, temporal cloaking, and enhanced performance of the optical devices.

Transition between coupled-resonator-induced transparency and absorption

Electromagnetically induced transparency and absorption in atomic systems have applications such as slow-light generation. Coupled-resonator-induced transparency (CRIT) and absorption (CRIA) are the optical analogy to them. Here we theoretically and experimentally study CRIT and CRIA in two directly coupled whispering-gallery-mode microresonators. The theoretical results give conditions for observing CRIT and CRIA, and predict that a transition between them will happen if we change the coupling strength between the two microresonators or the coupling strength between the fiber taper and the first microresonator. The experimental results demonstrate the transitions between CRIT and CRIA using a microsphere coupled to a sausagelike microresonator. The obtained results give some guidelines to observe CRIT and CRIA.

Regulation of fast and slow light characteristics of the add-drop ring-resonator employing an assisted ring.

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 performance of CROW structures on detection of virus nanoparticles

Coupled resonator optical waveguide (CROW) structures were investigated as a whispering gallery mode optical resonator for biosensing applications. A single mode optical fiber taper was used to evanescently couple light into the microspheres. We have simulated the theoretical model of the crow structure with two and three microspheres. The coupled-resonator-induced transparency (CRIT) phenomenon was observed in the crow structures. In this paper, two crow structures and a single microsphere resonator are compared with each other. We have reported the high sensitivity of the crow structures compared to a single microsphere. We have demonstrated apparent shifts of CRIT transparent peak when the virus nanoparticles are placed on the surface of the microsphere. As a result, these crow structures can be used as a biosensing sensor with high sensitivity. The theoretical simulation was carried out at the operating wavelength of 1550 nm.

Tunable Coupled-Resonator Induced Transparency Based on Asymmetrical Self-Interference Ring Resonators

Tunable coupled resonator induced transparency (CRIT) is observed based on two asymmetrical self-interference ring resonators (SIRRs). The phase shift of the left feedback arm will regulate the output CRIT lineshape, whereas the right FA does not influence the output lineshape. The transmission spectra of the left SIRR will be greatly reshaped with different cross-coupling coefficients, this characteristic is of great use both for optical sensing and designing output lineshape. Instead of adding ring resonators or tuning the uncontrolled multimodes of the whisper gallery resonator, we realize two transparency windows via changing the cross-coupling coefficients of couplers, which provides a convenient and controllable approach for the multichannel filter in optical devices. Moreover, the number of transparency window can be extended via adding more resonators. The proposed structure provides a potential application in the optical filter, optical sensing, slow light, and optical storage.

Superposed Transparency Effect and Entanglement Generation with Hybrid System of Photonic Molecule and Dipole Emitter**Supported by the National Natural Science Foundation of China under Grant Nos 11547258, 11647129 and 11405052, the Hunan Provincial Natural Science Foundation of China under Grant Nos 2018JJ3006, 2017JJ3005 and 2016JJ3006, the Scientific Research Fund of Hunan Provincial Education Department under Grant Nos 16B036 and 15A028,

We theoretically investigate the transparency effect with a hybrid system composed of a photonic molecule and dipole emitter. It is shown that the transparency effect incorporates both the coupled resonator-induced transparency (CRIT) effect and the dipole-induced transparency (DIT) effect. It is found that the superposed transparency windows are consistently narrower than the CRIT and DIT transparency windows. Benefiting from the superposed transparency effect, the photonic Faraday rotation effect could be realized in the photonic molecule system, which is useful for entanglement generation and quantum information processing.

Tunable Coupled-Resonator-Induced Transparency in a Photonic Crystal System Based on a Multilayer-Insulator Graphene Stack.

We achieve the effective modulation of coupled-resonator-induced transparency (CRIT) in a photonic crystal system which consists of photonic crystal waveguide (PCW), defect cavities, and a multilayer graphene-insulator stack (MGIS). Simulation results show that the wavelength of transparency window can be effectively tuned through varying the chemical potential of graphene in MGIS. The peak value of the CRIT effect is closely related to the structural parameters of our proposed system. Tunable Multipeak CRIT is also realized in the four-resonator-coupled photonic crystal system by modulating the chemical potentials of MGISs in different cavity units. This system paves a novel way toward multichannel-selective filters, optical sensors, and nonlinear devices.

Coupled resonator-induced transparency on a three-ring resonator**Project supported by the National Natural Science Foundation of China (Grant Nos. 61771434, 91123036, 61178058, 61275166, and 61076111) and the National Science Fund for Distinguished Young Scholars, China (Grant No. 51225504).

The coupled resonator-induced transparency (CRIT) phenomenon, which is analogous to electromagnetically induced transparency in atomic systems, can occur in an original integrated optical resonator system due to the coherent interference of the coupled optical resonators. The system was composed of three ring resonators on silicon, each with the same cavity size, and the optical coupling to the input and output ports was achieved using grating with a power coupling efficiency of 36%. A CRIT resonance whose spectrum shows a narrow transparency peak with a low group velocity was demonstrated. The quality factor of the ring resonator can attain a value up to 6 × 104, and the harmonic wavelength can be controlled by adjusting the temperature. The through and drop transmission spectra of the resonator are reconciled well with each other and also consistent well with the theoretical analysis.

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

Tunable Fano and coupled-resonator-induced transparency resonances in the waveguide-coupled inverted nested ring resonator

A waveguide-coupled inverted nested ring resonator structure is proposed and theoretically investigated. The effects of the parameters of such a structure on its transmission properties are demonstrated. Results show that both Fano resonance and coupled-resonator-induced transparency (CRIT) spectra can be produced within this structure, depending on the length ratio of the feedback waveguide and ring. In addition, the slope of the Fano resonance can be tuned and reversed by varying coupling coefficients and effective refractive index. Besides, CRIT-based tunable group delay can be obtained with high transmittance. Therefore, this structure has potential applications in optical sensors and optical communication.

Internally-loaded ring resonator configuration for optical filter applications

We study on-chip Wavelength Division Multiplexing (WDM) application of ring resonators on Silicon-on-Insulator (SOI) platform. Though WDM devices have been demonstrated earlier, there are certain challenges which are yet to be tackled. Large FSR and narrow line width requirement for a WDM device cannot be fulfilled in a conventional WDM device as the requirement for both the metrics demand opposing structural requirements from a ring resonator. A larger FSR demands for a smaller resonator length whereas smaller line width requires a large resonator length device. We overcome this using an embedded type ring resonator configuration. The structure is made of a racetrack type ring resonator with another ring embedded inside it (loading the external ring). Such structures are capable of showing coupled resonator induced transparency (CRIT) which can result in a very narrow line-width. We present initial experimental demonstration of CRIT in an internally loaded micro ring resonator fabricated on SOI material platform. The structures were optimized using 3D-FDTD analysis and coupling-matrix method.

Coupled-resonator-induced transparency in two microspheres as the element of angular velocity sensing**Project supported by the National Natural Science Foundation of China (Grant Nos. 51225504, 61171056, and 91123036) and the Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi Province, China.

We proposed a two-coupled microsphere resonator structure as the element of angular velocity sensing under the Sagnac effect. We analyzed the theoretical model of the two coupled microspheres, and derived the coupled-resonator-induced transparency (CRIT) transfer function, the effective phase shift, and the group delay. Experiments were also carried out to demonstrate the CRIT phenomenon in the two-coupled microsphere resonator structure. We calculated that the group index of the two-coupled sphere reaches ng = 180.46, while the input light at a wavelength of 1550 nm.

Control of dispersion in fiber coupled resonator-induced transparency structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61307076 and 61275066), the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAF14B11), and the Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province, China (Grant No. LBH-Q14042).

Induced transparency phenomena and strong dispersion can be produced in a coupled resonator induced transparency (CRIT) structure. In this paper, we investigate the influences of structure parameters, such as amplitude reflection coefficient and loss, on transmission spectrum and dispersion of CRIT structure, and further study the control of dispersion in the structure. The results show that in the CRIT structure, adjusting the loss of resonators is an effective method of controlling dispersion and producing simultaneous normal and abnormal dispersion. When we choose approximate amplitude reflection coefficients of the two couplers, the decrease of transmittance due to loss could be effectively made up. In the experiment, we achieve the control of dispersion and simultaneous strong normal and abnormal dispersion in the CRIT structure comprised of fiber. The results indicate the CRIT structure has potential applications in optical signal processing and optical communication.

Tunable multimode plasmon-induced transparency with graphene side-coupled resonators

We investigate a plasmonic graphene waveguide system based on monolayer graphene and two side-coupled graphene rings. The system exhibits multimode plasmon-induced transparency (PIT) effects in the mid-IR region. The dark-bright coupling mechanisms and coupled-resonator-induced transparency (CRIT) theory are both utilized to explain the electromagnetic responses, and the explanation is verified by simulation results of the finite-element method (FEM). By varying the Fermi level of graphene or the coupling gap, we have a means to dynamically manipulate the PIT system.

Analysis of induced-transparency in an original three-order resonator system

For the application requirements of resonant micro-cavity, an original three-ring resonant micro-cavity structure is proposed in this paper. Like electromagnetically induced transparency in an atomic system, the coupled resonator-induced transparency (CRIT) phenomenon in a new optical micro-cavity system is proven experimentally. Up to now, most of the resonators based on CRIT are just in the theoretical exploration stage, and the analysis of the double-ring structure has been relatively common. The CRIT effect of a resonator has a significant relationship with the coupler insertion loss, the ring circumference, and the multiples of the rings, which need high requirements in the structural design and preparation process. In order to reduce the difficulty in design and preparation, we propose a new three-ring cascade resonator structure with the same cavity size on silicon. According to the transfer matrix method and coupled mode theory, we find a CRIT effect after theoretical analysis. Our devices are fabricated on an SOI wafer. By using the micro-cavity measurement platform to repeat and analyze the tests of single ring and three-ring cascade resonator structure, we obtain a grating coupler efficiency of 30%. By applying the antireflection coating, the coupling efficiency of the grating coupler is up to 34%. During the test, the mutual interference between annular cavities of the three-ring resonators produces two transmission peaks, the output spectrum of the resonator with a narrow transparency peak at a low group velocity, which is verified in CRIT phenomenon. Compared with the traditional single-ring structure, the resonator has a quality factor increasing four times, reaching a value of up to 0.65×105, the through and drop transmission spectra of the resonator are reconciled well with each other. At the same time, in order to obtain the sensitivity of the resonator to temperature, we conduct tuning tests of the resonator temperature characteristics, the resonant peak is moved to the large wavelength direction with temperature increasing, and detuning wavelength of the resonance can be controlled by changing temperature, which is called red-shift. Therefore, the original three-ring cascaded resonators have significant applications in the rotation sensing, optical filters, optical storage and temperature sensing elements.

Coupled resonator induced transparency in surface plasmon polariton gap waveguide with two side-coupled cavities

We investigate theoretically the generation process of coupled resonator-induced transparency (CRIT) in surface plasmon polariton gap waveguide system containing two side-coupled cavities, which locate at a symmetric position. The CRIT is original from the destructive interference of the two detuned cavities. In contrast with the existing electromagnetically induced transparency (EIT) schemes, the occurrence of the CRIT is caused by the two radiative cavities in waveguide, instead of interference between a dark cavity and radiative cavity. This behavior mimics the quantum interference between two direct excitation pathways in a three-level V-type atom. The transmission lineshape can be tuned between an EIT-like resonant peak and a Lorentzian-like resonant dip by tailoring the detuning of the two cavities. Moreover, we also find that the transparency peak moves to high frequency with a line shift and its Q factor decreases with the increase of coupling distance between the cavities and waveguide.

Experimental demonstration of induced-transparency based on a novel resonator system

We experimentally demonstrate that coupled-resonator-induced-transparency (CRIT) phenomenon results from classical destructive interference whose spectrum has a narrow transparency peak with low group velocity. In this work, a CRIT resonance with a quality factor of 0.72×105 is demonstrated with the same cavity sizes. The through and drop transmission spectra are reconciled well with each other which are in good agreement with the theoretical analysis. Simultaneously, the resonant wavelength can be controlled by changing the temperature.

Induced-transparency in silicon-on-insulator based novel resonator systems

The coupled-resonator-induced-transparency (CRIT) phenomenon in a novel optical resonator system is experimentally demonstrated. The system is composed of a four-ring resonator with a 20 μm diameter on silicon, whose spectrum has a narrow transparency peak with low group velocity. The CRIT effect is observed in the optical coupled-resonator because of classical destructive interference. In this reported work, a CRIT resonance with a quality factor of 7.2 × 104 is demonstrated with the same cavity size and the power coupling of the system is 60%, which agree well with the theoretical analysis. Then, through and drop transmission spectra of the resonator coincide well with each other. Simultaneously, the detuning resonant wavelength can be controlled by changing the temperature.

Power enhancement and phase regimes in embedded microring resonators in analogy with electromagnetically induced transparency

Coupled microresonators exhibit great potential for nonlinear applications. In the present work, we explore the nonlinear performance of an embedded ring resonator analogous to an electromagnetically induced transparency (EIT) medium, also known as coupled resonator induced transparency (CRIT). Interestingly, an EIT-like amplitude response can have a remarkably different power enhancement factor that varies by more than one order of magnitude, which is attributed to the different phase regimes of the embedded micro-ring resonators. In addition to the non-monotonic phase profile reported in atomic EIT systems, the phase responses featuring 2 π and 4 π monotonic transitions are identified and analyzed. We also present an interesting phenomenon, in which the power enhancement changes greatly, even with the same transfer function (both intensity and phase responses). This reveals that wisely choosing the operating regime is critical to optimize nonlinear performance of the embedded double resonator system, without adding to design or fabrication difficulty.