Lithographic wavelength control of an external cavity laser with a silicon photonic crystal cavity-based resonant reflector

Abstract

We report the experimental demonstration of a new design for external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier (SOA) with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises an SU8 polymer bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and side-mode suppression ratios of more than 25 dB. © 2015 Optical Society of America Over the past few years, Silicon (Si) Photonics technology has emerged as a potential solution for the realization of low-cost, high performance components and Photonic Integrated Circuits (PIC) that can be used to meet the increasing bandwidth demands of chip-scale and on-chip optical interconnections [1][2][3][4]. A key feature of PICs is their ability to support Wavelength Division Multiplexing (WDM), a technique offering the parallelism necessary for high bandwidth and high density chips. Cheap, compact, efficient and Silicon compatible wavelength-tunable laser sources with precise wavelength control are thus crucial elements to facilitate the generation of WDM optical interconnects [5].Although Silicon-On-Insulator (SOI) has proven itself to be a most appealing platform for light propagation and manipulation, practical efficient, electrically pumped lasers directly in Si or other group IV elements are still absent from the Silicon Photonics tool kit, owing to the indirect bandgap that these materials exhibit. Consequently, the use of III-V elements as gain material in lasers for WDM optical interconnects is dictated -a challenging task, as direct growth of III-V semiconductors on IV semiconductors is difficult due to lattice constant mismatch and compatibility issues.A popular solution to the above problem is the heterogeneous integration of III-V parts on top of SOI PICs by means of direct wafer bonding [6]. An alternative approach suggests the deployment of Reflective Semiconductor Optical Amplifiers (RSOAs) and external Si-based reflectors for the formation of External-Cavity (EC) lasers. The latter approach has lately attracted significant attention as it allows independent design, fabrication and optimization of the active and the passive regions, and makes the most effective use of the III-V materials [5,7]. Up to now, devices that use Bragg gratings [7][8][9], ring resonators [10,11] and Sagnac interferometers [12] as Si reflectors have been demonstrated in this platform.The concept of using grating cavity resonant mirrors for Tx Rx heterogeneously integrated lasers has been introduced in [13, 14]. In this Letter, we present an EC laser design employing as a resonant reflector a PhC cavity coupled to a low-index waveguide [15,16], which lays the first stone towards EC laser source architectures with small footprint, high Side-Mode Suppression Ratio (SMSR), and the highly precise wavelength control required for WDM applications [5]. The Si-based reflector is simply a d...

Theory of Self‐pulsing in Photonic Crystal Fano Lasers

“…The realization of ultra‐compact lasers that generate short optical pulses are of interest for applications, e.g., in on‐chip optical signal processing. Fano resonances in photonic crystal membrane structures have previously been used to demonstrate improved optical switching characteristics and non‐reciprocal transmission and the use of narrow‐band mirrors for lasers was also demonstrated in hybrid platforms . In this paper we develop a theory for the photonic crystal Fano laser, which successfully accounts for the self‐pulsations observed experimentally and clarifies the physics of the self‐pulsing dynamics.…”

“…Fano resonances in photonic crystal membrane structures have previously been used to demonstrate improved optical switching characteristics [12] and non-reciprocal transmission [13] and the use of narrowband mirrors for lasers was also demonstrated in hybrid platforms. [14,15] In this paper we develop a theory for the photonic crystal Fano laser, which successfully accounts for the self-pulsations observed experimentally [8] and clarifies the physics of the self-pulsing dynamics. Different regimes of laser operation are identified via extensive phase diagrams, and the laser material and design parameters that are important for the laser characteristics are identified.…”

Hybrid photonic crystal lasers

“…The laser cavity is formed by butt-coupling a short Reflective Semiconductor Optical Amplifier (RSOA) to SOI chips containing tunable Photonic Crystal (PhC) cavity-based resonant reflectors, similar to those of [14], providing a route to accessing the advantages of resonant modulation without the wavelength matching issues. PhC cavities provide very precise control of their resonant wavelengths by lithographic tuning [17], significantly assists channel scalability. Hybrid integration provides a means to combine the III-V and silicon components.…”

“…The Si passive chip was fabricated on a 220-nm SOI platform and comprised an SU8 polymer bus waveguide vertically coupled to a Dispersion Adapted (DA) PhC cavity, with a p-i-n junction extending in the PhC defect as described in [14]. The physical principle behind the functionality of the latter component as a resonant reflector is described in [17,19]. The bus waveguide height and width were ~2.1 μm and ~3.5 μm, respectively for better matching with the emitted mode of the RSOA.…”

Hybrid External Cavity Laser with an Amorphous Silicon-Based Photonic Crystal Cavity Mirror

“…The hybrid external cavity photonic crystal laser has been previously demonstrated with c-Si as the medium in which the 2D PhC cavities were fabricated [15]. The laser uses a polymer bus waveguide concept to optimize coupling between the SOA and the PhC cavity [16]; this approach has the advantage of minimizing the propagation losses associated with a-Si.…”