Showing papers by "Alwyn J. Seeds published in 2013"

InAs/GaAs Quantum-Dot Lasers Monolithically Grown on Si, Ge, and Ge-on-Si Substrates

Abstract: The realization of semiconductor lasers on Si substrates will enable the fabrication of complex optoelectronic circuits. This will permit the creation of the long-dreamed chip-to-chip and system-to-system optical interconnects. This paper reports recent developments in our work on InAs/GaAs quantum-dot (QD) lasers monolithically grown on Si, Ge, and Ge-on-Si (Ge/Si) substrates. A thin AlAs nucleation layer (NL) was first investigated for the growth of InAs/GaAs QDs on Si substrates. The AlAs NL enables more defects to be confined in the interface between the GaAs epitaxial layer and Si substrate, and hence leads to higher photoluminescence intensity for InAs/GaAs QDs. Room-temperature lasing at 1.29 μm with a threshold current density of 650 A/cm2 was demonstrated with the use of an AlAs NL. The growth of InAs/GaAs QDs on Ge and Ge/Si substrates was further studied. A low threshold current density of ~200 A/cm2 for 1-mm long QD lasers has been demonstrated for QD lasers grown on Ge substrates by using Ga prelayer technique. This growth technique has also been explored for Ge/Si substrates. Room-temperature lasing at 1.28 μm with threshold current density of ~164 A/cm2 and lasing operation up to 84°C has been demonstrated for a 3-mm long device.

Coherent terahertz photonics.

Abstract: We present a review of recent developments in THz coherent systems based on photonic local oscillators. We show that such techniques can enable the creation of highly coherent, thus highly sensitive, systems for frequencies ranging from 100 GHz to 5 THz, within an energy efficient integrated platform. We suggest that such systems could enable the THz spectrum to realize its full applications potential. To demonstrate how photonics-enabled THz systems can be realized, we review the performance of key components, show recent demonstrations of integrated platforms, and give examples of applications.

Semiconductor III?V lasers monolithically grown on Si substrates

Abstract: Silicon (Si) photonics is an area that has recently attracted great attention. In order to realize the goal of integrated photonic components on an electronics platform, an electrically pumped laser on a Si substrate is required. The usage of III‐V compounds has enabled such devices to be grown directly on the Si electronics platform that underpins contemporary electronics. In this paper, semiconductor III‐V lasers monolithically grown on Si are reviewed, with quantum well and quantum dot technology being used to obtain lasers operating at wavelengths of 1.05, 1.30, 1.5 and 2 μm, with threshold currents < 1k A cm −2 . In addition, an integrated modulator and laser fabricated by epitaxial regrowth has been demonstrated at 1.05 μm with a modulation depth of 45% at −3 V and 100% at − 5V . 1.3μm lasers grown on Ge and Ge-on-Si substrates with the low continuous wave room-temperature threshold current densities of 55 and 164 A cm −2 , respectively are reviewed as a promising approach to obtaining high performance lasers on Si substrates. These results demonstrate that the direct, monolithic growth of III‐V compounds on a Si platform is a strong contender for the realization of an optical source integrated on an electronics platform. (Some figures may appear in colour only in the online journal)

Terahertz imaging of sub-wavelength particles with Zenneck surface waves

Abstract: Impact of sub-wavelength-size dielectric particles on Zenneck surface waves on planar metallic antennas is investigated at terahertz (THz) frequencies with THz near-field probe microscopy Perturbations of the surface waves show the particle presence, despite its sub-wavelength size The experimental configuration, which utilizes excitation of surface waves at metallic edges, is suitable for THz imaging of dielectric sub-wavelength size objects As a proof of concept, the effects of a small strontium titanate rectangular particle and a titanium dioxide sphere on the surface field of a bow-tie antenna are experimentally detected and verified using full-wave simulations

Semiconductor device and fabrication method

Abstract: A semiconductor device comprising a silicon substrate on which is grown a < 100nm thick epilayer of AlAsor related compound, followed by a compound semiconductor other than GaN buffer layer. Further III-V compound semiconductor structures can be epitaxially grown on top. The AlAs epilayer reduces the formation and propagation of defects from the interface with the silicon, and so can improve the performance of an active structure grown on top.

Tuneability of monolithically integrated optical phase lock loop for THz generation

Abstract: This work presents a monolithically integrated optical phase lock loop (OPLL) synchronised to an Optical Frequency Comb Generator (OFCG) without any prior filtering of the comb lines for the first time. The heterodyne phase locking is achieved at a tuneable offset frequency in the range of 2 to 6 GHz, while the optical comb lines are spaced by 12 GHz. This is of particular interest as it allows investigation of the influence of the nearest comb lines on OPLL performance. Moreover, the work discusses continuous tuneability limitations of a photonic THz source based on the single OPLL and proposes a solution to improve the frequency agility. Finally, the spectra of signals ranging from 2.5 up to 21.5 GHz, generated by heterodyning the locked slave laser and the subsequent comb lines, are presented and analysed. Phase noise performance of -80 dBc/Hz at 10 kHz offset across the frequency range is reported.

Long-wavelength III-V quantum-dot lasers monolithically grown on Si substrates

Abstract: Although great effort have been devoted for Si-based light generation and modulation technologies since the 1980s, monolithic growth of electrically pumped laser on Si remains the `holy grail' for Si photonics. In this paper, room temperature lasing near the telecom wavelength of 1300 nm has been demonstrated at room temperature with low threshold current densities for InAs/GaAs quantum-dot lasers grown on both Si and Ge substrates.

InAs/GaAs quantum-dot lasers and detectors on silicon substrates for silicon photonics

Abstract: We present the development of InAs/GaAs quantum-dot devices monolithically grown on Si substrates for silicon photonics. Room-temperature cw lasing at 1.3 μm has been demonstrated for the InAs/GaAs quantum-dot devices on Si substrates.

Near-field probe mapping of the THz electric field distribution on metallic surfaces

Abstract: We demonstrate for the first time the accuracy of the interpretation of images detected by the sub-wavelength aperture near-field THz probe, which enables mapping the distribution of THz electric field on antennas and metallic surfaces.

Simplified wavelength control of uncooled widely tuneable DSDBR laser for optical access networks

Abstract: A simplified control system is described which uses only three point calibration to maintain the wavelength of the ITU channels of an uncooled DS-DBR laser, spaced at 50GHz, over the full C-band. Wavelength is controlled mode-hop free over a temperature range of 15°C to 40°C.

Spatial confinement of broadband THz pulses with a twin-needle probe for THz spectroscopy

Abstract: Spatial confinement of broadband THz pulses to a 10 micrometer spot is achieved using a twin-needle probe. Combined with a THz subwavelength aperture near-field probe, it enables broadband THz spectroscopy of single micrometer-size objects.

Optical Injection Locking of a DFB laser to a 10-GHz Spaced Frequency Comb Signal

Abstract: Optical injection locking of a DFB laser to one line of a frequency comb was investigated for different conditions. The locking range became asymmetrical in reference to the laser free-running frequency for high injected power.

Surface plasmon waves for broadband THz spectroscopy

Abstract: In this presentation we discuss application of broadband terahertz (THz) time-domain spectroscopy for probing subwavelength (micrometer) size objects. The problem of weak coupling between THz waves and sub-wavelength objects, which limits the use of THz spectroscopy to large samples, is mitigated by employing surface plasmon waves. In one implementation, THz surface waves, excited on a broad-band planar THz bow-tie antenna, are used to enhance the interaction with a small particle placed on the antenna surface. The surface field distribution near the particle is mapped with an integrated sub-wavelength aperture THz near-field probe. We demonstrate that imaging and probing of the subwavelength size dielectric particles (TiO2 and SrTiO3) can be realized using the enhanced THz field between the antenna and the probe. We also discuss THz wave confinement using two sharp metallic needles. We demonstrate that in the near-field region of the needle tips, the electric field of THz pulses is concentrated to a volume smaller than (10m) 3 without limiting the THz pulse bandwidth. Application of both methods for high spatial resolution imaging and spectroscopy will be discussed.

III–V quantum-dot laser growth on silicon and germanium

Abstract: We present the studies of the development of room-temperature continuous-wave lasers near 1.3 μm on both silicon and germanium substrates with very low threshold current densities for silicon photonics.