Widely tunable 2.3μm III-V-on-silicon Vernier lasers for broadband spectroscopic sensing

Heterogeneously integrating III-V materials on silicon photonic integrated circuits has emerged as a promising approach to make advanced laser sources for optical communication and sensing applications. Tunable semiconductor lasers operating in the 2–2.5 μm range are of great interest for industrial and medical applications since many gases(e.g., CO_2, CO, CH_4) and biomolecules(such as blood glucose) have strong absorption features in this wavelength region. The development of integrated tunable laser sources in this wavelength range enables low-cost and miniature spectroscopic sensors. Here we report heterogeneously integrated widely tunable III-V-on-silicon Vernier lasers using two silicon microring resonators as the wavelength tuning components. The laser has a wavelength tuning range of more than 40 nm near 2.35 μm. By combining two lasers with different distributed Bragg reflectors, a tuning range of more than 70 nm is achieved. Over the whole tuning range, the side-mode suppression ratio is higher than 35 dB. As a proof-of-principle, this III-V-on-silicon Vernier laser is used to measure the absorption lines of CO. The measurement results match very well with the high-resolution transmission molecular absorption(HITRAN) database and indicate that this laser is suitable for broadband spectroscopy.

Time-domain compact macromodeling of linear photonic circuits via complex vector fitting

In this paper, a novel baseband macromodeling framework for linear passive photonic circuits is proposed, which is able to build accurate and compact models while taking into account the nonidealities,such as higher order dispersion and wavelength-dependent losses of the circuits. Compared to a previous modeling method based on the vector fitting algorithm, the proposed modeling approach introduces a novel complex vector fitting technique. It can generate a half-size state-space model for the same applications, thereby achieving a major improvement in efficiency of the time-domain simulations. The proposed modeling framework requires only measured or simulated scattering parameters as input,which are widely used to represent linear and passive systems. Three photonic circuits are studied to demonstrate the accuracy and efficiency of the proposed technique.

Quantum dot lasing from a waterproof and stretchable polymer film

Colloidal quantum dots(QDs)are excellent optical gain materials that combine high material gain,a strong absorption of pump light,stability under strong light exposure and a suitability for solution-based processing.The integration of QDs in laser cavities that fully exploit the potential of these emerging optical materials remains,however,a challenge.In this work,we report on a vertical cavity surface emitting laser,which consists of a thin film of QDs embedded between two layers of polymerized chiral liquid crystal.Forward directed,circularly polarized defect mode lasing under nanosecond-pulsed excitation is demonstrated within the photonic band gap of the chiral liquid crystal.Stable and long-term narrow-linewidth lasing of an exfoliated free-standing,flexible film under water is obtained at room temperature.Moreover,we show that the lasing wavelength of this flexible cavity shifts under influence of pressure,strain or temperature.As such,the combination of solution processable and stable inorganic QDs with high chiral liquid crystal reflectivity and effective polymer encapsulation leads to a flexible device with long operational lifetime,that can be immersed in different protic solvents to act as a sensor.