Zhiping Zhou

Subwavelength-grating-assisted broadband polarization-independent directional coupler.

This Letter presents both numerical and experimental results of a polarization-independent directional coupler based on slot waveguides with a subwavelength grating. The measured coupling efficiency is 97.4% for TE and 96.7% for TM polarization at a wavelength of 1550 nm. Further analysis shows that the proposed subwavelength grating directional coupler has a fabrication tolerance of ±20u2009u2009nm for the grating structure and that the coupling efficiencies for the two polarizations are both higher than -0.5u2009u2009dB (∼89%), exceeding the entire C-band (1525-1570 nm) experimentally.

Manipulation of beat length and wavelength dependence of a polarization beam splitter using a subwavelength grating.

A polarization beam splitter assisted by a subwavelength grating (SWG) is proposed. The SWG enables nearly 20-fold beat length reduction for TE, which makes the high extinction ratio (ER) possible. On the other hand, the embedded SWG preferably affects the refractive index of the even mode in the coupling region and broadens the bandwidth of the splitter. As a result, the ER of 28.7xa0dB (24.8xa0dB) for TE (TM) is obtained, while the insertion loss is only 0.10xa0dB (0.11xa0dB) at the wavelength of 1550xa0nm. The ER is more than 10xa0dB in the wavelength range of 1450-1625xa0nm for TE and 1495-1610xa0nm for TM.

Room-temperature near-infrared up-conversion lasing in single-crystal Er-Y chloride silicate nanowires.

Near-infrared up-conversion lasing in erbium(Er)-yttrium(Y) chloride silicate nanowires was demonstrated when pumped by 1476u2009nm laser at room temperature. The emission covers a very wide wavelength range (400–1000u2009nm). A clear threshold for 985u2009nm peak was observed at a launched average pump power of approximately 7u2009mW. Above threshold, the intensity increases linearly when turning up the pump power. The full width at half maximum at 985u2009nm decreases from 1.25u2009nm to 0.25u2009nm when reducing the measurement temperature from 30u2009K to 7u2009K, which is the narrowest linewidth of 980u2009nm micro-lasers to date. Our demonstration presents a possible novel method of utilizing up-conversion mechanism in Er-Y nanowire to achieve tunable near-infrared laser, which breaks new ground in the exploration of nanoscale optoelectronic devices operating at near-infrared wavelength.

Low Loss, Compact TM-Pass Polarizer Based on Hybrid Plasmonic Grating

A low-loss, compact TM-pass polarizer is demonstrated based on hybrid plasmonic grating on silicon-on-insulator platform. Since the large mode distribution mismatch and plasmonic effect significantly influence the transmission and reflection spectrum of the device, the traditional theory of Bragg grating cannot fully explain this phenomenon. Here, we proposed an analysis method which takes effective index and mode overlap together into consideration to design this polarizer. A compact length of

Athermal and flat-topped silicon Mach-Zehnder filters

2.5~mu text{m}

Manipulating the effective index of the hybrid plasmonic waveguide based on subwavelength grating

with extinction ratio over 25 dB is realized simultaneously. Moreover, the insertion loss is only 0.088 dB, which is comparable to dielectric-based devices.

An ultra-compact MMI-based wavelength diplexer employing subwavelength grating

Athermal and flat-topped transmissions are the two main requirements for a silicon WDM filter. A Mach-Zehnder (MZ) filter which simultaneously satisfies these two requirements has been experimentally demonstrated in this paper. A combination of strip waveguide and hybrid strip-slot waveguide is introduced for athermalization, and two-stage interference is utilized for flat-topped transmission. The temperature dependent wavelength shift is measured to be ~-5 pm/K while the best 1 dB bandwidth is 5.5 nm with 14.7 nm free spectral range (FSR). The measured minimum insertion loss is only 0.4 dB with a device dimension of 170 μm × 580 μm. Moreover, Such a MZ filter is compatible with the state-of-art CMOS-fabrication process and its minimum feature size is as large as 200 nm.

High-performance Ge-on-Si photodetector with optimized DBR location

In this paper, we propose and numerically study a subwavelength grating based hybrid plasmonic waveguide. The metal layer on top of the waveguide enables unique features compared with conventional silicon based waveguide. Since the field distribution in this structure is different, traditional homogeneous medium approximation is not applicative. Therefore, we develop a new effective index calculation method. This method is suitable for metal-existing waveguide as well as structures with multiple medium. Effective index of this waveguide depends on grating period, duty ratio and width, respectively. By modifying duty ratio and period of the waveguide, the relationship between effective index and waveguide width can be concave function or convex function and the slope can be similar to TM mode of silicon based waveguide, which opens up possibilities for SPPs based applications.

Refractive index engineering of high performance coupler for compact photonic integrated circuits

Through the refractive index engineering of the subwavelength grating, an ultra-compact multimode interference based diplexer is proposed and demonstrated. It is 43.4 μm in length, only ~30% of its conventional counterpart and displays a wide 1dB bandwidth >120nm.

Plasmonic-Assisted Polarization Beam Splitter Based on Bent Directional Coupling

We investigated the Ge-on-Si photodetectors performance enhancement by optimizing the detector length, therefore, the location of the distributed Bragg reflector (DBR). Since the unabsorbed signal light in the photodetector oscillates between the germanium and silicon layers, but the DBR is on the silicon layer, the optimized location of the DBR will result in shorter devices, with increased bandwidth, reduced dark current, and consistent responsivity. The 5xa0μm long photodetector with an optimized DBR location shows responsivity of 0.72xa0A/W, at least 31.7xa0GHz 3xa0dB bandwidth; the dark current is only 7xa0nA at 1550xa0nm.