Coupled Fabry-Perot Resonators Research Articles

Bias Reconfigurable Photoresponse of an Infrared Nanocrystal Film Integrated into a Coupled Fabry-Perot Resonator

The coupling of a photonic structure to a nanocrystal film enables light focusing over a distance compatible with the charge diffusion length. This strategy has been implemented in infrared sensors based on nanocrystal films to maximize their absorption. Here, we demonstrate that the photonic structure can be further exploited to generate a bias-reconfigurable photoresponse. To reach this goal, we use a coupled Fabry-Perot structure that can be seen as a periodic grating with two different cavities per period. The two cavities are coupled and a resonance appears, increasing the effective absorption coefficient by a factor of 30 compared to standard interdigitated electrodes. When connected in the appropriate configuration, this device enables the turning-on and -off of part of the spectral response (over a factor of 25 in magnitude) simply by tuning the applied bias (<1 V). Finally, we also demonstrate that this resonator geometry is promising for integration at the focal plane array level since the resonance is maintained for a pixel size as small as 10 μm.

All-fiber optical nonreciprocity based on parity-time-symmetric Fabry-Perot resonators

Nonreciprocal light transmission in an all-fiber platform is critical in modern optical communication systems, which can avoid the packaging and integration process required in current devices based on magneto-optical or nonlinear materials. Here we propose and demonstrate an all-fiber device with remotely tunable isolation ratio and switchable isolation direction by constructing two mutually coupled Fabry-Perot (FP) resonators with identical geometry and balanced gain and loss. By controlling the pumping power, strong optical nonreciprocity is achieved due to gain saturation nonlinearity that is enhanced by the broken parity-time symmetry. Nonreciprocal light transmission with an isolation ratio of 8.58 dB at 1550 nm and an insertion loss of 2.5 dB is demonstrated. The isolation bandwidth is 125 MHz, which is determined by the bandwidths of the two coupled FP resonators. The proposed approach provides an all-fiber solution for a remotely tunable and optically controlled isolator, which may find applications in software-defined optical networks.

Optical mode conversion in coupled Fabry-Perot resonators.

Low-loss conversion among a complete and orthogonal set of optical modes is important for high-bandwidth quantum and classical communication. In this Letter, we explore tunable impedance mismatch between coupled Fabry-Perot resonators as a powerful tool for manipulation of the spatial and temporal properties of optical fields. In the single-mode regime, frequency-dependent impedance matching enables tunable finesse optical resonators. Introducing the spatial dependence of the impedance mismatch enables coherent spatial mode conversion of optical photons at near-unity efficiency. We experimentally demonstrate a NIR resonator whose finesse is tunable over a decade, and an optical mode converter with efficiency >75% for the first six Hermite-Gauss modes. We anticipate that this new perspective on coupled multimode resonators will have exciting applications in micro- and nano-photonics and computer-aided inverse design.

Accessing the Exceptional Points in Coupled Fabry–Perot Resonators through Hybrid Integration

Parity-time (PT) symmetric coupled microresonators with judiciously modulated loss and gain have been widely studied to reveal many non-Hermitian features in optical systems. The phase transition a...

Fabry–Perot resonators with transverse coupling on SOI using loop mirrors

A novel integrated transversely coupled Fabry–Perot resonator using loop mirrors as the end reflectors are demonstrated via simulations and experiments on the silicon-on-insulator (SOI) platform. The resonator is formed by connecting two loop mirrors to the two output ports of a directional coupler to form the resonant cavity and utilizing the other two ports as the input and the output. Depending on which two ports of the directional coupler are mirrored, two configurations of the resonator can be achieved. The impacts of varying the cavity length and the coupling coefficient of the directional coupler on the output characteristics of the resonators are analyzed. A Q-factor of 28086 and an extinction ratio of 10.04 dB with an insertion loss of 1.9 dB is achieved experimentally for a 1038μm cavity length and an extinction ratio of 18.14 dB and a Q-factor of 5120 with an insertion loss of 2.12 dB is obtained for a cavity length of 376μm. The reported resonator offers additional freedom to tune the spectral characteristics.

Transversely coupled Fabry-Perot resonators with Bragg grating reflectors.

We design and demonstrate Fabry-Perot resonators with transverse coupling using Bragg gratings as reflectors on the silicon-on-insulator (SOI) platform. The effects of tailoring the cavity length and the coupling coefficient of the directional coupler on the spectral characteristics of the device are studied. The fabricated resonators achieved an extinction ratio (ER) of 37.28dB and a Q-factor of 3356 with an effective cavity length of 110μm, and an ER of 8.69dB and a Q-factor of 23642 with a 943μm effective cavity length. The resonator structure presented here has the highest reported ER on SOI and provides additional degrees of freedom compared to an all-pass ring resonator to tune the spectral characteristics.

Experimental demonstration of a transparent graphene millimetre wave absorber with 28% fractional bandwidth at 140 GHz

The development of transparent radio-frequency electronics has been limited, until recently, by the lack of suitable materials. Naturally thin and transparent graphene may lead to disruptive innovations in such applications. Here, we realize optically transparent broadband absorbers operating in the millimetre wave regime achieved by stacking graphene bearing quartz substrates on a ground plate. Broadband absorption is a result of mutually coupled Fabry-Perot resonators represented by each graphene-quartz substrate. An analytical model has been developed to predict the absorption performance and the angular dependence of the absorber. Using a repeated transfer-and-etch process, multilayer graphene was processed to control its surface resistivity. Millimetre wave reflectometer measurements of the stacked graphene-quartz absorbers demonstrated excellent broadband absorption of 90% with a 28% fractional bandwidth from 125–165 GHz. Our data suggests that the absorbers' operation can also be extended to microwave and low-terahertz bands with negligible loss in performance.

Spectral characteristics of single and coupled microresonator lasers comprising a replica-molded Bragg grating and dye-doped polymer

Visible microlasers consisting of 80±20 nm thick, dye-doped polymer resonators mated to a second-order, distributed feedback grating having a period of 410 nm exhibit longitudinal mode and spectral characteristics that can be manipulated by microresonator design. Resonators in the form of a square, ring (annulus), or a ring with an intentionally introduced defect (π/2 section removed) have been examined with respect to the output spectrum, pump energy threshold, and relative slope efficiency of the corresponding microlaser. Although the emission of single rings and arrays of nonoverlapped rings is generally a single mode, the square geometry resonator exhibits a spectrum rich in mode structure, which is attributed partially to degeneracies associated with two coupled Fabry–Perot resonators. Similarly, arrays of coupled (overlapped) rings produce multimode spectra that are skewed toward the blue. For a fixed pump fluence, an array of coupled rings generates output energies at least 50% higher than those for its uncoupled counterpart.

Diffractively coupled Fabry-Perot resonator with power-recycling

We demonstrate the optical coupling of two cavities without light transmission through a substrate. As the all-reflective coupling component, we use a dielectric low-efficiency 3-port diffraction grating. In contrast to a conventional transmissive coupling component, such an all-reflective coupler avoids all thermal effects that are associated with light absorption in the substrate. An all-reflective scheme for cavity coupling is of interest in the field of gravitational wave detection. In such detectors light that is resonantly enhanced inside the so-called power-recycling cavity is coupled to (kilometre-scale) Fabry-Perot resonators representing the arms of a Michelson interferometer. We realized such an all-reflective coupling in a table-top experiment. Our findings are in qualitative agreement with the theoretical model incorporating the characteristics of the 3-port grating used, and therefore encourage the application of all-reflective cavity couplers in future gravitational wave detectors.

Slowing light with Fabry-Perot resonator arrays

We analyze the transmission of light through coupled-resonator optical waveguides in the form of evanescently coupled Fabry-Perot resonator arrays. We develop a transfer matrix method to calculate the amplitude and phase responses of the arrays. We also discuss the inclusion of optical gain in the system to compensate for losses in these structures. Owing to the compact length along the propagation direction in evanescently coupled arrays, large slowing factors of the order of 102-103 can be achieved even with a weak index contrast of ∼0.1%. The large slowing factor, coupled with weak index contrast, makes this structure a promising candidate for artificial slow light system.

Design of 10-to-40 GHz and higher pulse-rate multiplication by means of coupled Fabry–Perot resonators

Limitations of a general autoregressive multistage-coupled filter for repetition rate multiplication are addressed. With only two or three stages, the useable filter passband is broadened by more than two orders of magnitude compared to single-stage (e.g. Fabry–Perot) filters thereby improving the robustness of the device to frequency detuning. Multi-stage filters also show improved performance in the pulse-to-pulse power uniformity.

Symmetric optical switches using coupled Fabry–Perot resonators

An analysis is made of the feasibility of using two identical nonlinear Fabry–Perot resonators, coupled weakly by a shared electromagnetic field, as all-optical logic elements of optical computers. The functional capabilities of such resonators are identical with the capabilities of known devices, but the replacement of an electrical feedback mechanism with an electromagnetic one should make it possible to increase considerably the switching frequency.

Tristability and self-oscillations in a double resonator system

A system consisting of two coupled Fabry-Perot resonators, one of them nonlinear, with an additional feedback between them is studied experimentally and theoretically. The dependence between the phase shift δφ of the resonator 2 and the laser-induced thermal load Q applied to the resonator 1 is essentially nonlinear. This nonlinearity of the additional feedback in the double resonator system is shown to make possible its self-oscillations and the existence of the tristable 8-shaped hysteresis curves. The frequencies of the observed self-oscillations are in the range from 100 Hz to 100 kHz, their shapes varying from sinusoidal to square and sawtooth.