Electromagnetically induced transparency-like effect in microring-Bragg gratings based coupling resonant system.

An all-pass microring-Bragg gratings (APMR-BG) based coupling resonant system is proposed and experimentally demonstrated to generate electromagnetically induced transparency (EIT)-like transmission for the first time. The coupling between two light path ways in the micro-ring resonator and the Fabry-Pérot (F-P) resonator formed by two sections of Bragg gratings gives rise to the EIT-like spectrum. This system has the advantage of a small footprint consisting of only one microring resonator and one bus waveguide with Bragg gratings. It also has a large fabrication tolerance as the overlap requirement between the resonance wavelengths of the microring and the F-P resonator is more relaxed. The two most important properties of the EIT-like transmission namely the insertion loss (IL) and the full-width-at-half-maximum (FWHM) have been analytically investigated by utilizing the specially developed model based on the transfer matrix method. The APMR-BG based coupling resonant system was fabricated on a silicon-on-insulator (SOI) platform. The EIT-like transmission with an extinction ratio (ER) of 12 dB, a FWHM of 0.077 nm and a quality factor (Q factor) of 20200 was achieved, which agree well with the simulated results based on our numerical model. A slow light with a group delay of 38 ps was also obtained.

Recent progress in GeSi electro-absorption modulators.

Electro-absorption from GeSi heterostructures is receiving growing attention as a high performance optical modulator for short distance optical interconnects. Ge incorporation with Si allows strong modulation mechanism using the Franz-Keldysh effect and the quantum-confined Stark effect from bulk and quantum well structures at telecommunication wavelengths. In this review, we discuss the current state of knowledge and the on-going challenges concerning the development of high performance GeSi electro-absorption modulators. We also provide feasible future prospects concerning this research topic.

23 GHz Ge/SiGe multiple quantum well electro-absorption modulator.

We report on high speed operation of a Ge/SiGe multiple quantum well (MQW) electro-absorption modulator in a waveguide configuration. 23 GHz bandwidth is experimentally demonstrated from a 3 µm wide and 90 µm long Ge/SiGe MQW waveguide. The modulator exhibits a high extinction ratio of more than 10 dB over a wide spectral range. Moreover with a swing voltage of 1 V between 3 and 4 V, an extinction ratio as high as 9 dB can be obtained with a corresponding estimated energy consumption of 108 fJ per bit. This demonstrates the potentiality of Ge/SiGe MQWs as a building block of silicon compatible photonic integrated circuits for short distance energy efficient optical interconnections.

Quantum-confined Stark effect at 1.3 µm in Ge/Si(0.35)Ge(0.65) quantum-well structure.

Room-temperature quantum-confined Stark effect in a Ge/SiGe quantum-well structure is reported at the wavelength of 1.3 µm. The operating wavelength is tuned by the use of strain engineering. Low-energy plasma-enhanced chemical vapor deposition is used to grow 20 periods of strain-compensated quantum wells (8 nm Ge well and 12 nm Si(0.35)Ge(0.65) barrier) on Si(0.21)Ge(0.79) virtual substrate. The fraction of light absorbed per well allows for a strong modulation around 1.3 µm. The half-width at half-maximum of the excitonic peak of only 12 meV allows for a discussion on physical mechanisms limiting the performances of such devices.