F Pozzi

1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on Si substrates

III-V semiconductors monolithically grown on Si substrates are expected to be an ideal solution to integrate highly efficient light-emitting devices on a Si platform. However, the lattice mismatch between III-V and Si generates a high density of threading dislocations (TDs) at the interface between III-V and Si. Some of these TD will propagate into the III-V active region and lead to device degradation. By introducing defect filter layers (DFLs), the density of TDs propagating into the III-V layers can be significantly reduced. In this paper, we present an investigation on the development of InGaAs/GaAs strained-layer superlattices as DFLs for 1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on a Si substrate. We compare two broad-area InAs/GaAs quantum-dot lasers with non-optimized and optimized InGaAs/GaAs DFLs. The laser device with optimal DFLs has a lower room-temperature threshold current density of 99 A/cm2 and higher maximum operation temperature of 88 °C, compared with 174 A/cm2 and 68 °C for the reference laser.

Monolithically integrated heterodyne optical phase-lock loop with RF XOR phase detector

We present results for an heterodyne optical phase-lock loop (OPLL), monolithically integrated on InP with external phase detector and loop filter, which phase locks the integrated laser to an external source, for offset frequencies tuneable between 0.6 GHz and 6.1 GHz. The integrated semiconductor laser emits at 1553 nm with 1.1 MHz linewidth, while the external laser has a linewidth less than 150 kHz. To achieve high quality phase locking with lasers of these linewidths, the loop delay has been made less than 1.8 ns. Monolithic integration reduces the optical path delay between the laser and photodiode to less than 20 ps. The electronic part of the OPLL was implemented using a custom-designed feedback circuit with a propagation delay of ~1 ns and an open-loop bandwidth greater than 1 GHz. The heterodyne signal between the locked slave laser and master laser has phase noise below -90 dBc/Hz for frequency offsets greater than 20 kHz and a phase error variance in 10 GHz bandwidth of 0.04 rad2.

Monolithically Integrated Photonic Heterodyne System

This paper presents the results from the first monolithically integrated photonic heterodyne system that allows the two optical sources to be mutually phase locked by locking to an external optical reference. High-spectral-purity signals of up to 50 GHz have been demonstrated from this first fabricated device, where the tuning range was limited by losses in the input waveguide. Successful phase locking was accomplished through short signal propagation delay of less than 2 ns achieved by monolithic integration and custom-made fast loop electronics. The approach can be extended to generate signals at >; 1 THz.

Photonically enabled communication systems beyond 1000 GHz

This paper presents a review of the recent development and research work on InP devices and their associated systems to generate and detect signal beyond 1 THz. The potential of the technology and the remaining challenges are also discussed. The paper will present recent results on laser sources that could be used as the basis of the THz sources as well as a set of potential THz emitters such as the UTC photodiode which has already permitted up to 25 muW to be emitted at 1 THz.

New applications for microwave photonics

A photonic technique for generating high-purity millimetre-wave or terahertz signals based on heterodyne of two phase-locked optical sources is described. Technology requirements and potential applications are discussed.

1.3-um InAs/GaAs quantum-dot lasers monolithically grown on Ge substrate

The realization of semiconductor laser diodes and light-emitting diodes on Si substrates would permit the creation of complex optoelectronic circuits for the first time, enabling chip-to-chip and system-to-system optical communications. Direct epitaxial growth of III-V semiconductor materials on Si or Ge is one of the most promising candidates1 for fabricating electrically pumped light sources on a Si platform. Here, we describe the first quantum-dot laser diode to be realized on a Ge substrate. To fabricate the laser, a single-domain GaAs buffer layer2 was first grown on the Ge substrate using the Ga prelayer technique. A long-wavelength InAs/GaAs quantum-dot structure was then fabricated on the high-quality GaAs buffer layer. Lasing at a wavelength of 1305 nm with the extremely low threshold current density of 55.2 A/cm2 was observed under continuous-wave (CW) current drive at room temperature

A room temperature electrically pumped 1.3-µm InAs quantum dot laser monolithically grown on silicon substrates

We present a room-temperature 1.3-µm InAs/GaAs quantum dot laser monolithically grown on Si(100). The threshold current at 20°C was 725A/cm2 and the emission wavelength was 1.302µm. The laser was operated in pulsed mode. The growth was enabled via the optimisation of the temperature of the initial nucleation layer of GaAs.