Sasan Fathpour

The role of Auger recombination in the temperature-dependent output characteristics (T0=∞) of p-doped 1.3 μm quantum dot lasers

Temperature invariant output slope efficiency and threshold current (T0=∞) in the temperature range of 5–75 °C have been measured for 1.3 μm p-doped self-organized quantum dot lasers. Similar undoped quantum dot lasers exhibit T0=69K in the same temperature range. A self-consistent model has been employed to calculate the various radiative and nonradiative current components in p-doped and undoped lasers and to analyze the measured data. It is observed that Auger recombination in the dots plays an important role in determining the threshold current of the p-doped lasers.

High-speed quantum dot lasers

The modulation bandwidth of conventional 1.0–1.3 µm self-organized In(Ga)As quantum dot (QD) lasers is limited to ~6–8 GHz due to hot carrier effects arising from the predominant occupation of wetting layer/barrier states by the electrons injected into the active region at room temperature. Thermal broadening of holes in the valence band of QDs also limits the performance of the lasers. Tunnel injection and p-doping have been proposed as solutions to these problems. In this paper, we describe high-performance In(Ga)As undoped and p-doped tunnel injection self-organized QD lasers emitting at 1.1 and 1.3 µm. Undoped 1.1 µm tunnel injection lasers have ~22 GHz small-signal modulation bandwidth and a gain compression factor of 8.2 × 10−16 cm3. Higher modulation bandwidth (~25 GHz) and differential gain (3 × 10−14 cm2) are measured in 1.1 µm p-doped tunnel injection lasers with a characteristic temperature, T0, of 205 K in the temperature range 5–95°C. Temperature invariant threshold current (infinite T0) in the temperature range 5–75°C and 11 GHz modulation bandwidth are observed in 1.3 µm p-doped tunnel injection QD lasers with a differential gain of 8 × 10−15 cm2. The linewidth enhancement factor of the undoped 1.1 µm tunnel injection laser is ~0.73 at lasing peak and its dynamic chirp is <0.6 A at various frequencies and ac biases. Both 1.1 and 1.3 µm p-doped tunnel injection QD lasers exhibit zero linewidth enhancement factor (α ~0) and negligible chirp (< 0.2 A). These dynamic characteristics of QD lasers surpass those of equivalent quantum well lasers.

Heterogeneous lithium niobate photonics on silicon substrates

A platform for the realization of tightly-confined lithium niobate photonic devices and circuits on silicon substrates is reported based on wafer bonding and selective oxidation of refractory metals. The heterogeneous photonic platform is employed to demonstrate high-performance lithium niobate microring optical resonators and Mach-Zehnder optical modulators. A quality factor of ~7.2 × 10⁴ is measured in the microresonators, and a half-wave voltage-length product of 4 V.cm and an extinction ratio of 20 dB is measured in the modulators.

Prospects for Silicon Mid-IR Raman Lasers

This paper presents the case for the silicon Raman laser as a potential source for the technologically important midwave infrared (MWIR) region of the optical spectrum. The mid-IR application space is summarized, and the current practice based on the optical parametric oscillators and solid state Raman lasers is discussed. Relevant properties of silicon are compared with popular Raman crystals, and linear and nonlinear transmission measurements of silicon in the mid-IR are presented. It is shown that the absence of the nonlinear losses, which severely limit the performance of the recently demonstrated silicon lasers in the near IR, combined with unsurpassed crystal quality, high thermal conductivity and excellent optical damage threshold render silicon a very attractive Raman medium, even when compared to the very best Raman crystals. In addition, silicon photonic technology, offering integrated low-loss waveguides and microcavities, offers additional advantages over todays bulk crystal Raman laser technology. Using photonic crystal structures or microring resonators, the integrated cascaded microcavities can be employed to realize higher order Stokes emission, and hence to extend the wavelength coverage of the existing pump lasers. Exploiting these facts, the proposed technology can extend the utility of silicon photonics beyond data communication and into equally important applications in biochemical sensing and laser medicine

Silicon-on-nitride waveguides for mid- and near-infrared integrated photonics

Silicon-on-nitride ridge waveguides are demonstrated and characterized at mid- and near-infrared optical wavelengths. Silicon-on-nitride thin films were achieved by bonding a silicon handling die to a silicon-on-insulator die coated with a low-stress silicon nitride layer. Subsequent removal of the silicon-on-insulator substrate results in a thin film of silicon on a nitride bottom cladding, readily available for waveguide fabrication. At the mid-infrared wavelength of 3.39 μm, the fabricated waveguides have a propagation loss of 5.2 ± 0.6 dB/cm and 5.1 ± 0.6 dB/cm for the transverse-electric and transverse-magnetic modes, respectively.

High-speed 1.3 μm tunnel injection quantum-dot lasers

1.3μm tunnel injection quantum-dot lasers are demonstrated. The laser heterostructures are grown by molecular-beam epitaxy. The InAs self-organized quantum dots are p doped to optimize the gain. The lasers are characterized by Jth=180A∕cm2, T0=∞, dg∕dn≈1×10−14cm2, f−3dB=11GHz, chirp of 0.1A, and zero α parameter.

Mn-doped InAs self-organized diluted magnetic quantum-dot layers with Curie temperatures above 300 K

The magnetic and structural properties of InAs:Mn self-organized diluted magnetic quantum dots grown by low-temperature (∼270°C), solid-source molecular-beam epitaxy using a very low InAs growth rate (<0.1ML∕s) are investigated. A Curie temperature (TC) of ∼350K is measured in a sample grown with a Mn∕In flux ratio of 0.15. Electron energy-loss spectroscopy confirms that most of the Mn remains within the InAs quantum dots. We propose as a possible explanation for this high TC the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms amongst the InAs quantum dots.

High-speed 1.3μm tunnel injection quantum-dot lasers

1.3μm tunnel injection quantum-dot lasers are demonstrated. The laser heterostructures are grown by molecular-beam epitaxy. The InAs self-organized quantum dots are p doped to optimize the gain. The lasers are characterized by Jth=180A∕cm2, T0=∞, dg∕dn≈1×10−14cm2, f−3dB=11GHz, chirp of 0.1A, and zero α parameter.

Energy harvesting in silicon wavelength converters

Nonlinear loss is the central problem in silicon devices that operate using nonlinear optical effects. Wavelength converters are one example of such devices, wherein high optical intensities required for nonlinear interactions cause two-photon absorption and severe free-carrier absorption. In this paper, we report the first demonstration of nonlinear photovoltaic effect in silicon wavelength converters. This useful phenomenon allows us to eliminate the nonlinear loss caused by free-carrier absorption, while harvesting the optical power that is normally consumed by two-photon absorption.

Limitations of active carrier removal in silicon Raman amplifiers and lasers

The lifetime of two-photon generated carriers has been established as the critical parameter that determines the performance of silicon Raman lasers and amplifiers since it determines the optical loss. Here, we investigate the intensity dependence of the carrier lifetime in the case where the carriers are swept out by means of a p‐n junction. Numerical simulations show that at sufficiently high pump intensities, the generated carriers screen the applied electric field and therefore result in a higher lifetime and hence a lower net Raman gain. We also quantify the electrical power dissipation necessary to maintain low optical losses.