Ultrafast and widely tuneable vertical-external-cavity surface-emitting laser, mode-locked by a graphene-integrated distributed Bragg reflector

We report a versatile and cost-effective way of controlling the unsaturated loss, modulation depth and saturation fluence of graphene-based saturable absorbers (GSAs), by changing the thickness of a spacer between SLG and a high-reflection mirror. This allows us to modulate the electric field intensity enhancement at the GSA from 0 up to 400%, due to the interference of incident and reflected light at the mirror. The unsaturated loss of the SLG-mirror-assembly can be reduced to$\sim$0. We use this to mode-lock a VECSEL from 935 to 981nm. This approach can be applied to integrate SLG into various optical components, such as output coupler mirrors, dispersive mirrors, dielectric coatings on gain materials. Conversely, it can also be used to increase absorption (up to 10%) in various graphene based photonics and optoelectronics devices, such as photodetectors.

High-order detached eddy simulation, zonal LES and URANS of cavity and labyrinth seal flows

Hybrid numerical large eddy simulation (NLES), detached eddy simulation (DES) and URANS methods are assessed on a cavity and a labyrinth seal geometry. A high sixth-order discretization scheme is used and is validated using the test case of a two-dimensional vortex. The hybrid approach adopts a new blending function. For the URANS simulations, the flow within the cavity remains steady, and the results show significant variation between models. Surprisingly, low levels of resolved turbulence are observed in the cavity for the DES simulation, and the cavity shear layer remains two dimensional. The hybrid RANS-NLES approach does not suffer from this trait.For the labyrinth seal, both the URANS and DES approaches give low levels of resolved turbulence. The zonal Hamilton-Jacobi approach on the other had given significantly more resolved content. Both DES and hybrid RANS-NLES give good agreement with the experimentally measured velocity profiles. Again, there is significant variation between the URANS models, and swirl velocities are overpredicted. © 2013 John Wiley & Sons, Ltd.

Parabolic tapered photonic crystal cavity in silicon

We demonstrate the design, fabrication, transmission and nearfield characterization of a novel parabolic tapered 1D photonic crystal cavity in silicon. The design allows repeatable device fabrication, high quality factor and small modal volume. © 2012 OSA.

Parabolic tapered photonic crystal cavity in silicon

We demonstrate the design, fabrication, transmission and nearfield characterization of a novel parabolic tapered 1D photonic crystal cavity in silicon. The design allows repeatable device fabrication, high quality factor and small modal volume. © OSA 2012.

Parabolic tapered photonic crystal cavity in silicon

We demonstrate the design, fabrication, transmission and nearfield characterization of a novel parabolic tapered 1D photonic crystal cavity in silicon. The design allows repeatable device fabrication, high quality factor and small modal volume. © 2012 OSA.

Parabolic tapered photonic crystal cavity in silicon

We demonstrate the design, fabrication, transmission spectrum measurement, and near-field characterization of a parabolic tapered one-dimensional photonic crystal cavity in silicon. The results shows a relatively high quality factor (∼43 000), together with a small modal volume of ∼ 1. 1 (λ/n) 3. Moreover, the design allows repeatable device fabrication, as evident by the similar characteristics obtained for several tens of devices that were fabricated and tested. These demonstrated 1D PhC cavities may be used as a building block in integrated photonic circuits for optical on-chip interconnects and sensing applications. © 2012 American Institute of Physics.

Parabolic tapered photonic crystal cavity in silicon

We demonstrate the design, fabrication, transmission and nearfield characterization of a novel parabolic tapered 1D photonic crystal cavity in silicon. The design allows repeatable device fabrication, high quality factor and small modal volume. © OSA 2012.

20 Gb/s QPSK transmission using an electro-optically modulated vertical-cavity surface-emitting laser

20 Gb/s QPSK transmission over 100 m of OM3 fibre using an EOM VCSEL under QPSK modulation is reported. Bit-error-ratio measurements are carried out to express the quality of the transmission scheme. © 2011 Optical Society of America.

Digital data transmission using electro-optically modulated vertical-cavity surface-emitting laser with saturable absorber

An electro-optically (EO) modulated oxide-confined vertical-cavity surface-emitting laser (VCSEL) containing a saturable absorber in the VCSEL cavity is studied. The device contains an EO modulator section that is resonant with the VCSEL cavity. A type-II EO superlattice medium is employed in the modulator section and shown to result in a strong negative EO effect in weak electric fields. Applying the reverse bias voltages to the EO section allows triggering of short pulses in the device. Digital data transmission (return-to-zero pseudo-random bit sequence, 27-1) at 10Gb/s at bit-error-rates well below 10-9 is demonstrated. © 2014 AIP Publishing LLC.

A Single-Fundamental-Mode Photonic Crystal Vertical Cavity Surface Emitting Laser

Single-fundamental-mode photonic crystal (PhC) vertical cavity surface emitting lasers (VCSEL) are produced and their single-fundamental-mode performances are investigated and demonstrated. A two-dimensional PhC with single-point-defect structure is fabricated using UV photolithography and inductive coupled plasma reactive ion etching on the surface of the VCSEL's top distributed Bragg-reflector. The PhC VCSEL maintains single-fundamental-mode operating with output power 1.7 mW and threshold current 2.5 mA. The full width half maximum of the lasing spectrum is less than 0.1 nm, the far field divergence angle is less than 10 degrees and the side mode suppression ratio is over 35 dB. The device characteristics are analyzed based on the effective index model of the photonic crystal fiber. The experimental results agree well with the theoretical expectation.

Small-Signal Equivalent-Circuit Model and Characterization of 1.55-mu m Buried Tunnel Junction Vertical-Cavity Surface-Emitting Lasers

The work was supported in part by the National Natural Science Foundation of China under Grant 60536010, Grant 60606019, Grant 60777029, and Grant 60820106004, and in part by the National Basic Research Program of China under Grant 2006CB604902, Grant 2006CB302806, and Grant 2006dfa11880.

Low threshold lasing of GaN-based vertical cavity surface emitting lasers with an asymmetric coupled quantum well active region

We have fabricated and characterized GaN-based vertical cavity surface emitting lasers (VCSELs) with a unique active region structure, in which three sets of InGaN asymmetric coupled quantum wells are placed in a half-wavelength (0.5 lambda) length. Lasing action was achieved under optical pumping at room temperature with a threshold pumping energy density of about 6.5 mJ/cm(2). The laser emitted a blue light at 449.5 nm with a narrow linewidth below 0.1 nm and had a high spontaneous emission factor of about 3.0x10(-2). The results indicate that this active region structure is useful in reducing the process difficulties and improving the threshold characteristics of GaN-based VCSELs.

A traveling-wave electroabsorption modulator with a large optical cavity and intrastep quantum wells

This paper reports a novel traveling-wave electroabsorption modulator (TWEAM) with a large optical cavity waveguide and an intrastep quantum well structure designed to achieve a high bandwidth, high saturation power and better fiber-matched optical profile, which is good for high coupling efficiency. The optical mode characteristic shows a great improvement in matching the circular mode of the fiber and the saturation power of 21 dBm, and a 3 dB bandwidth of 23 GHz was achieved for the fabricated TWEAM.

Blue-green optically pumped GaN-based vertical cavity surface emitting laser

Blue-green GaN-based vertical cavity surface emitting lasers (VCSELs) were fabricated with two dielectric Ta2O5/SiO2 distributed Bragg reflectors. Lasing action was observed at a wavelength of 498.8 nm at room temperature under optical pumping. Threshold energy density and emission linewidth were 189 mJ/cm(2) and 0.15 nm, respectively. The result demonstrates that blue-green VCSELs can be realised using III-nitride semiconductors.

Design of novel three port optical gates scheme for the integration of large optical cavity electroabsorption modulators and evanescently-coupled photodiodes

This paper presents a novel scheme to monolithically integrate an evanescently-coupled uni-travelling carrier photodiode with a planar short multimode waveguide structure and a large optical cavity electroabsorption modulator based on a multimode waveguide structure. By simulation, both electroabsorption modulator and photodiode show excellent optical performances. The device can be fabricated with conventional photolithography, reactive ion etching, and chemical wet etching.