Semiconductor lasers in use today rely on mirrors based on the reflection at a cleaved facet or Bragg reflection from a periodic stack of layers. Here, we demonstrate an ultra-small laser with a mirror based on the Fano resonance between a continuum of waveguide modes and the discrete resonance of a nanocavity. The Fano resonance leads to unique laser characteristics. Since the Fano mirror is very narrow-band compared to conventional lasers, the laser is single-mode and in particular, it can be modulated via the mirror. We show, experimentally and theoretically, that nonlinearities in the mirror may even promote the generation of a self-sustained train of pulses at gigahertz frequencies, an effect that was previously only observed in macroscopic lasers. Such a source is of interest for a number of applications within integrated photonics.Keywords: Laser, Photonic-crystal, Fano resonance, Nonlinear optics, Nanocavity, Self-pulsation Conventional semiconductor lasers mirrors are based on a cleaved facet [1] or a Bragg grating, or a two-dimensional grating resonance [2][3][4][5][6][7][8]. In this work, we demonstrate a new concept for lasers, an ultra-small laser with a mirror based on the Fano resonance between a continuum of waveguide modes and the discrete resonance of a nanocavity. The rich physics of Fano resonances [9] has recently been explored in a number of different photonic and plasmonic systems [10,11]. The Fano resonance leads to unique laser characteristics and furthermore represents a very rich dynamical system, which is still to be explored. In particular, since the Fano mirror is very narrow-band compared to conventional lasers, the laser is single-mode and it can be modulated via the mirror. We show, experimentally and theoretically, that nonlinearities in the mirror may even promote the generation of a self-sustained train of pulses at gigahertz frequencies, an effect that was previously only observed in macroscopic lasers [12][13][14][15].The photonic crystal Fano laser (FL) concept is illustrated in Fig. 1(a). The laser cavity is composed of a linedefect waveguide in a photonic crystal (PhC) membrane and two mirrors. The left mirror is a conventional PhC mirror, realized by blocking the PhC waveguide (WG) with air holes [16]. In contrast, the right mirror is due to a Fano interference between the continuum of waveguide modes and the discrete resonance of a side-coupled nanocavity [17]. At resonance, the paths of light through the nanocavity and through the waveguide interfere destructively, leading to a high reflectivity, see Fig. 1(b). If the quality factor (Q-factor) of the nanocavity is dominated by its coupling to the waveguide, rather than by intrinsic losses, the maximum reflectivity of the Fano mirror approaches unity, which is the basis for its use as a laser mirror (see Appendix A.1.). This FL concept was suggested in [18] where it was highlighted that, if such a laser could be realized, it should enable modulation not limited by the relaxation oscillations generic to lasers. Here, we ...
The threshold properties of photonic crystal quantum dot lasers operating in the slow-light regime are investigated experimentally and theoretically. Measurements show that, in contrast to conventional lasers, the threshold gain attains a minimum value for a specific cavity length. The experimental results are explained by an analytical theory for the laser threshold that takes into account the effects of slow light and random disorder due to unavoidable fabrication imperfections. Longer lasers are found to operate deeper into the slow-light region, leading to a trade-off between slow-light induced reduction of the mirror loss and slow-light enhancement of disorder-induced losses.PACS numbers: 42.55. Tv, 42.70.Qs, Slow light in photonic crystal (PhC) line-defect waveguides [1] enhances the interaction between the propagating light wave and the material of the waveguide, and has enabled the demonstration of increased material nonlinearity [2], enhanced spontaneous emission into the propagating mode [3,4], and enhanced material gain [5]. Such engineering of fundamental materials properties is important for the development of integrated photonic circuits, with applications in classical as well as quantum information technology. Microcavity lasers can be realized in the same PhC membrane structure by exploiting highquality point-defect cavities and in the past decade significant progress was made [6][7][8], culminating in recent demonstrations of high-speed electrically pumped structures [9]. Such PhC lasers allow the exploration of new operation regimes, such as single emitter lasing [10] and ultra-high speed modulation [11]. However, while it was shown that slow light in combination with random spatial disorder leads to very rich physics [12][13][14][15][16][17][18], the role of slow light on lasers realized using defect cavities has apparently not been systematically investigated. For the case of passive point-defect cavities, it is well known that disorder is an important factor limiting the quality factor [19][20][21][22] but the role of slow light in extended active cavities is not well understood.In this paper, we report experimental results on PhC quantum dot lasers with variable cavity length and show that these attain a minimum threshold gain for a certain cavity length, in stark contrast to conventional lasers, where the threshold gain decreases monotonically with cavity length. We derive a rate equation including the effect of slow-light propagation and show that the experimental observations may be explained when taking into account disorder-induced losses. These results show that disorder may lead to fundamental limitations on the performance of nanostructured lasers, but the results also demonstrate a promising platform for investigating disorder effects in active structures, such as the competition between deterministic cavity modes and random modes formed by Anderson localization [18]. . The PhC structure has a lattice constant of a = 438 nm and an air-hole radius of 0.25a. A so-called LN cavity [25...
Nanostructures that feature nonreciprocal light transmission are highly desirable building blocks for realizing photonic integrated circuits. Here, a simple and ultracompact photonic‐crystal structure, where a waveguide is coupled to a single nanocavity, is proposed and experimentally demonstrated, showing very efficient optical diode functionality. The key novelty of the structure is the use of cavity‐enhanced material nonlinearities in combination with spatial symmetry breaking and a Fano resonance to realize nonreciprocal propagation effects at ultralow power and with good wavelength tunability. The nonlinearity of the device relies on ultrafast carrier dynamics, rather than the thermal effects usually considered, allowing the demonstration of nonreciprocal operation at a bit‐rate of 10 Gbit s−1 with a low energy consumption of 4.5 fJ bit−1.
Fano resonances appear in quantum mechanical as well as classical systems as a result of the interference between two paths: one involving a discrete resonance and the other a continuum. Compared to a conventional resonance, characterized by a Lorentzian spectral response, the characteristic asymmetric and "sharp" spectral response of a Fano resonance is suggested to enable photonic switches and sensors with superior characteristics. While experimental demonstrations of the appearance of Fano resonances have been made in both plasmonic and photonic-crystal structures, the control of these resonances is experimentally challenging, often involving the coupling of near-resonant cavities. Here, we experimentally demonstrate two simple structures that allow surprisingly robust control of the Fano spectrum. One structure relies on controlling the amplitude of one of the paths and the other uses symmetry breaking. Short-pulse dynamic measurements show that besides drastically increasing the switching contrast, the transmission dynamics itself is strongly affected by the nature of the resonance. The influence of slow-recovery tails implied by a long carrier lifetime can thus be reduced using a Fano resonance due to a hitherto unrecognized reshaping effect of the nonlinear Fano transfer function. For the first time, we present a system application of a Fano structure, demonstrating its advantages by the experimental realization of 10 Gbit/s all-optical modulation with bit-error-ratios on the order of 10 -7 for input powers less than 1 mW. These results represent a significant improvement compared to the use of a conventional Lorentzian resonance.Ultra-compact photonic structures that perform optical signal processing such as modulation and switching at high-speed with low-energy consumption are essential for enabling integrated photonic chips that can meet the growing demand for information capacity . It remains, however, an important task to identify and demonstrate PhC structures that can meet the low-energy and high-bandwidth requirement. In cavity-based switches an applied control signal changes the refractive index of the cavity, thereby shifting the cavity resonance and modulating the transmission of the data signal. The shape of the transmission spectrum is then very important, since it determines the refractive
We show that the degree of light-speed control in a semiconductor optical amplifier can be significantly extended by the introduction of optical filtering. We achieve a phase shift of approximately 150 degrees at 19 GHz modulation frequency, corresponding to a several-fold increase of the absolute phase shift as well as the achievable bandwidth. We show good quantitative agreement with numerical simulations, including the effects of population oscillations and four-wave mixing, and provide a simple physical explanation based on an analytical perturbation approach.
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