Sudharsanan Srinivasan

Low threshold and high speed short cavity distributed feedback hybrid silicon lasers.

In this paper we investigate reducing threshold and improving the efficiency and speed of distributed feedback hybrid silicon lasers. A low threshold current of 8.8 mA was achieved for a 200 μm cavity at 20 °C. A 3 dB bandwidth of 9.5 GHz as well as 12.5 Gb/s direct modulation of DFB laser diode was achieved on the hybrid silicon platform for the first time.

Heterogeneous Silicon Photonic Integrated Circuits

We review recent breakthroughs in the silicon photonic technology and components, and describe progress in silicon photonic integrated circuits. Heterogeneous silicon photonics has recently demonstrated performance that significantly outperforms native III/V components. The impact active silicon photonic integrated circuits could have on interconnects, telecommunications, sensors, and silicon electronics is reviewed.

Low Threshold Electrically-Pumped Hybrid Silicon Microring Lasers

We report on significantly improved performance of a compact hybrid silicon microring lasers obtained by selectively reducing the volume of active region. This is done by appropriately undercutting the multiple quantum well (MQW) region to force carriers to flow toward the outer edge of the microring for better gain/optical mode overlap. We observe a reduction of the threshold of over 20% and up to 80% output power enhancement. These are primarily due to the improved injection efficiency. We developed a diode laser model that includes nonradiative recombination. The model and the experimental results highlight the benefits, as well as the negative effects from excessive undercutting, including lower MQW confinement, higher modal loss, and higher thermal impedance. A design rule for MQW undercutting is, therefore, provided.

Widely Tunable Narrow-Linewidth Monolithically Integrated External-Cavity Semiconductor Lasers

We theoretically analyze, design, and measure the performance of a semiconductor laser with a monolithically integrated external cavity. A ~4 cm long on-chip cavity is made possible by a low-loss silicon waveguide platform. We show tuning in excess of 54 nm in the O-band as well as significant reduction in laser linewidth due to controlled feedback from the external cavity. The measured linewidth in full tuning range is below 100 kHz and the best results are around 50 kHz. Approaches to further improve the performance of such laser architectures are described.

Optimization of Hybrid Silicon Microring Lasers

In this paper, we review the recent optimization work in hybrid silicon microring lasers. Device structure and fabrication procedures are discussed first, followed by two major improvements in carrier injection and thermal management. A simple, well-controlled quantum well undercut leads to about 20% enhancement of injection efficiency. A silicon-on-diamond (SOD) substrate is demonstrated to fundamentally solve the device heating issue for silicon-on-insulator (SOI)-based active devices. SOD rib waveguides show low propagation loss of 0.74 dB/cm, which is 0.2 dB/cm higher than SOI counterparts. More than 22× reduction of device heating in hybrid silicon microring lasers is projected by simulations.

Quantum dot lasers for silicon photonics (Invited)

We review recent advances in the field of quantum dot lasers on silicon. A summary of device performance, reliability, and comparison with similar quantum well lasers grown on silicon will be presented. We consider the possibility of scalable, low size, weight, and power nanolasers grown on silicon enabled by quantum dot active regions for future short-reach silicon photonics interconnects.

Design of integrated hybrid silicon waveguide optical gyroscope

We propose and analyze a novel highly integrated optical gyroscope using low loss silicon nitride waveguides. By integrating the active optical components on chip, we show the possibility of reaching a detection limit on the order of 19°/hr/√Hz in an area smaller than 10 cm(2). This study examines a number of parameters, including the dependence of sensitivity on sensor area.

Teardrop Reflector-Assisted Unidirectional Hybrid Silicon Microring Lasers

We study directional bistability in hybrid silicon microring lasers and demonstrate a unidirectional laser. Unidirectional emission is achieved by integrating a passive reflector that feeds laser emission back into the laser cavity to introduce an extra unidirectional gain. We show that the length of the passive reflector is a critical parameter in determining the lasing behavior.

Design of phase-shifted hybrid silicon distributed feedback lasers

We present data on the design and performance analysis of phase shifted distributed feedback (DFB) lasers on the hybrid silicon platform. The lasing wavelength for various input currents and temperatures, for devices with standard quarter-wavelength, 60 μm and 120 μm-long phase shift are compared for mode stability and output power. The pros and cons of including a large phase shift region in the grating design are analyzed.

Harmonically Mode-Locked Hybrid Silicon Laser With Intra-Cavity Filter to Suppress Supermode Noise

We present results from two hybrid silicon mode-locked lasers, each with a 2 GHz cavity and one with an intra-cavity ring resonator filter. We compare the performance of the two lasers with respect to the harmonic mode-locking behavior at 20 GHz, i.e., the tenth harmonic. The filter based laser design passively mode-locked at 20 GHz with an electrical spur mode suppression >45 dB. Furthermore, an optical supermode suppression of 55 dB and an RF linewidth of 52 kHz was also observed. Hybrid mode-locking the laser without the filter required 10 dBm input microwave power for 25 dB (electrical) spur mode suppression as opposed to the design with the filter showing >45 dB suppression at 0 dBm input power.