Yi Yu

Demonstration of a self-pulsing photonic crystal Fano laser

Fano interference and nonlinearity are exploited to achieve self-pulsing of a laser at gigahertz frequencies. The semiconductor lasers in use today rely on various types of cavity, making use of Fresnel reflection at a cleaved facet1, total internal reflection between two different media2, Bragg reflection from a periodic stack of layers3,4,5,6,7,8, mode coupling in a high contrast grating9,10 or random scattering in a disordered medium11. Here, we demonstrate an ultrasmall laser with a mirror, which is based on Fano interference between a continuum of waveguide modes and the discrete resonance of a nanocavity. The rich physics of Fano resonances12 has recently been explored in a number of different photonic and plasmonic systems13,14. The Fano resonance leads to unique laser characteristics. In particular, because the Fano mirror is very narrowband compared to conventional laser mirrors, the laser is single mode and 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 has previously been observed only in macroscopic lasers15,16,17,18. Such a source is of interest for a number of applications within integrated photonics.

Pulse carving using nanocavity-enhanced nonlinear effects in photonic crystal Fano structures

We experimentally demonstrate the use of a photonic crystal Fano resonance for carving-out short pulses from long-duration input pulses. This is achieved by exploiting an asymmetric Fano resonance combined with carrier-induced nonlinear effects in a photonic crystal membrane structure. The use of a nanocavity concentrates the input field to a very small volume leading to an efficient nonlinear resonance shift that carves a short pulse out of the input pulse. Here, we demonstrate shortening of ∼500u2009u2009ps and ∼100u2009u2009ps long pulses to ∼30u2009u2009ps and ∼20u2009u2009ps pulses, respectively. Furthermore, we demonstrate error-free low duty cycle return-to-zero signal generation at 2xa0Gbit/s with energy consumption down to ∼1u2009u2009pJ/bit and power penalty of ∼2u2009u2009dB. The device physics and limitations are analyzed using nonlinear coupled-mode theory.

Signal reshaping and noise suppression using photonic crystal Fano structures

We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10-9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.

Large signal simulation of photonic crystal Fano laser

We numerically investigate small and large signal modulation of a photonic crystal laser with a mirror based on Fano interference between continuum modes of a waveguide and a discrete mode of a nanocvaity. Our simulation shows that the instantaneous optical frequency of the laser signal can be modulated at frequencies exceeding 1 THz which is much higher than its corresponding relaxation oscillation frequency. Large signal simulation of the Fano laser is also investigated based on pseudorandom bit sequence at 0.5 Tbit/s. It shows eye patterns are open at such high modulation frequency, verifying the large bandwidth of the laser.

Lasers, switches and non-reciprocal elements based on photonic crystal Fano resonances

We discuss the realization of active photonic devices exploiting Fano resonances in photonic crystal membranes.

Theory and simulations of self-pulsing in photonic crystal Fano lasers

A detailed theoretical and numerical investigation of the dynamics of photonic crystal Fano lasers is presented. It is shown how the dynamical model supports self-pulsing, as was recently observed experimentally, and an in-depth analysis of the physics of the self-pulsing mechanism is given. Furthermore, it is demonstrated how different dynamical regimes exist, and these are mapped out numerically, showing how self-pulsing or continuous-wave output may be controlled through the strength of the pump and the detuning of the nanocavity. Finally, laser phase transitions through dynamical perturbations are demonstrated.

Optical time domain demultiplexing using fano resonance in InP photonic crystals

Ultra-compact photonic structures that perform high-speed low-energy optical signal processing are essential for enabling integrated photonic chips that can meet the growing demand for information capacity [1]. Here, we demonstrate all-optical 40 Gbit/s to 10 Gbit/s demultiplexing of an optical time domain multiplexed (OTDM) signal using an InP photonic crystal switch. The device is realized using a membrane structure, where a point-defect nanocavity is side coupled to a photonic crystal line-defect waveguide as shown in Fig. 1(a). The discrete cavity mode interacts with continuum modes of the waveguide creating a Fano resonance [2]. By placing a partially transmitting element (PTE) in the waveguide, the coupling between the waveguide and the cavity can be controlled [3]. The Fano lineshape is characterized by a large on-off transmission ratio with small spectral separation making it suitable for switching applications (Fig. 1(b)).

Fabrication and experimental demonstration of photonic crystal laser with buried heterostructure

Development of ultra-small and efficient laser sources for photonic integrated circuits is one of the main cornerstones in achieving the requirements imposed for on-chip optical interconnects [1]. The InP photonic crystal (PhC) platform with selectively embedded gain medium [2] is a promising way of separating active light amplification regions from passive regions for light propagation without induced absorption losses and surface recombination. The main focus of this work is the fabrication and experimental demonstration of a buried heterostructure (BH) photonic crystal laser bonded to a silicon wafer, illustrating the effective single-platform active-passive material integration method.

Experimental demonstration of a Fano laser based on photonic crystals

Conventional semiconductor laser mirrors are based on Fresnel reflection [1], Bragg reflection [2, 3] or total internal reflection [4]. Here we demonstrate a new laser concept using photonic crystals (PhC), with a mirror based on Fano interference between a waveguide continuum and a discrete resonance of a nanocavity [5]. We show that the very narrowband feature of the Fano resonance [6] can lead to single mode lasing. In addition, when combined with optical nonlinearity, the highly dispersive feature of the Fano resonance can promote self-pulsations at gigahertz frequencies [7], which was previously observed only in macroscopic lasers [8].

Photonic crystal Fano resonances for realizing optical switches, lasers, and non-reciprocal elements

We present our work on photonic crystal membrane devices exploiting Fano resonance between a line-defect waveguide and a side coupled nanocavity. Experimental demonstration of fast and compact all-optical switches for wavelength-conversion is reported. It is shown how the use of an asymmetric structure in combination with cavity-enhanced nonlinearity can be used to realize non-reciprocal transmission at ultra-low power and with large bandwidth. A novel type of laser structure, denoted a Fano laser, is discussed in which one of the mirrors is based on a Fano resonance. Finally, the design, fabrication and characterization of grating couplers for efficient light coupling in and out of the indium phosphide photonic crystal platform is discussed.