ABSTRACT
Microscopic single-mode lasers with low power consumption, large modulation bandwidth, and ultra-narrow linewidth are essential for numerous applications, such as on-chip photonic networks. A recently demonstrated microlaser using an optical Fano resonance between a discrete mode and a continuum of modes to form one of the mirrors, i.e., the so-called Fano laser, holds great promise for meeting these requirements. Here, we suggest and experimentally demonstrate what we believe is a new configuration of the Fano laser based on a nanobeam geometry. Compared to the conventional two-dimensional photonic crystal geometry, the nanobeam structure makes it easier to engineer the phase-matching condition that facilitates the realization of a bound-state-in-the-continuum (BIC). We investigate the laser threshold in two scenarios based on the new nanobeam geometry. In the first, classical case, the gain is spatially located in the part of the cavity that supports a continuum of modes. In the second case, instead, the gain is located in the region that supports a discrete mode. We find that the laser threshold for the second case can be significantly reduced compared to the conventional Fano laser. These results pave the way for the practical realization of high-performance microlasers.
ABSTRACT
We demonstrate all-optical switching using a multi-mode membranized photonic crystal nanocavity exploiting the free-carrier induced dispersion in InP and the sharp asymmetric lineshape of Fano resonances. A multi-mode cavity is designed to sustain two spatially overlapping modes with a spectral spacing of 18 nm. The measured transmission spectrum of the fabricated device shows multiple asymmetric Fano resonances as predicted by optical simulations. The capabilities of the device are benchmarked by comparing a wavelength conversion from 1538.2 nm to 1565.2 nm with a single-mode wavelength conversion at 1566.2 nm on the same device. The results show an improvement in signal quality with a 5.6 dB power penalty reduction at the receiver as well as in energy efficiency with a reduction of the pump power from 534 fJ/bit to 445 fJ/bit.
ABSTRACT
A tunable integrated terahertz (THz) filter is one of the basic elements for realizing integrated reconfigurable THz communication systems. The state-of-the-art tunable THz filters are discrete or vertically pumped for integrated devices. Here, we propose and demonstrate voltage-actuated thermally tunable on-chip THz bandpass and bandstop filters based on a whispering gallery mode resonator. The quality factors of the bandpass and bandstop filters attain 1867 and 1909, respectively, at approximately 0.4795 THz. Widely continuous tunability is realized by adjusting the voltage applied to a micro-heater. As far as we know, this is the first Letter on on-chip tunability in the THz domain. It provides a simple and reliable tuning method for on-chip THz devices. Furthermore, the implementation of tunable bandpass and bandstop filters plays an important role in THz signal processing.
ABSTRACT
We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry-Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 µm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40 dB and a peak loss as low as 0.6 dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption, and higher contrast, compared to that involving Lorentzian resonance. For example, under signal trains of 2.5 Gb/s, switching energy with a contrast of 3 dB for the Fano case is 113 fJ, which is 8 dB smaller than that for the Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67 dB to 9.53 dB.
ABSTRACT
We propose and demonstrate four-channel all-optical switches based on silicon photonic crystal (PhC) nanobeam cavities, with an area of only 31 µm2 per channel. For these switches, signal extraction and rejection functions have been successfully demonstrated while the signal speed is limited to 2.5 Gb/s due to the slow switching recovery process in silicon. In order to improve the signal speed, first, a blue-detuned filtering method is employed to suppress the slow switching recovery tails of the output signal light based on passive resonant devices. The suppressing mechanism relies on the extraction of the large blue-chirped component in the fast rising edge, while suppressing the red-chirped component in the slow switching recovery tail. A detailed theoretical model is established to analyze the improvement mechanism of the switching dynamic characteristics in the silicon PhC nanobeam cavity. Moreover, the simulated and experimental results have both shown that the switching recovery time of the output signal light is greatly reduced from 500 ps to 50 ps. Thus, the processing of 10-Gb/s optical signals has been experimentally demonstrated with the help of the blue-detuned filtering method.
ABSTRACT
An integrated vertical coupler that transfers light from the lower passive waveguide to the upper active waveguide in an asymmetric twin-waveguide integration structure (in InGaAsP/InP material system) is designed using transformation optics (TO). The length of the coupler is as short as 3 µm, which is two orders of magnitude shorter than that of traditional tapered couplers. According to three-dimensional full-wave simulations, the designed optimized coupler has a high coupling efficiency of 94.9%, and a low reflection at the wavelength of 1.55 µm. Subsequently, quasi-conformal mapping is employed to reduce the material complexity and to make it possible to realize the coupler by purely using an isotropic dielectric material. Applying TO to integrated photonic devices may motivate new applications, and improve integration density on the InP platform.
