Shailendra Bansropun

InP based lasers and optical amplifiers with wire-/dot-like active regions

Long wavelength lasers and semiconductor optical amplifiers based on InAs quantum wire-/dot-like active regions were developed on InP substrates dedicated to cover the extended telecommunication wavelength range between 1.4 and 1.65 µm. In a brief overview different technological approaches will be discussed, while in the main part the current status and recent results of quantum-dash lasers are reported. This includes topics like dash formation and material growth, device performance of lasers and optical amplifiers, static and dynamic properties and fundamental material and device modelling. (Some figures in this article are in colour only in the electronic version)

Gain and noise saturation of wide-band InAs-InP quantum dash optical amplifiers: model and experiments

We present a theoretical model for gain and noise saturation in quantum dash (QDash) semiconductor optical amplifiers. The model is based on the density matrix formalism and addresses static saturation spectra. The calculations are confirmed by a series of experiments which highlight the unique properties of these amplifiers. We demonstrate a high gain, a wide bandwidth, and high saturation power. The saturation spectrum is shown to be asymmetric, emphasizing saturation at short wavelength. The asymmetry stems from the high energy tail of the density of state function in those quantum wire (QWire) like gain media as well as from the interactions with the wetting layer.

Optimization of an inductively coupled plasma etching process of GaInP∕GaAs based material for photonic band gap applications

In this article, we investigate the dry etching of GaInP∕GaAs based material system using an inductively coupled plasma (ICP) etching system. In a view to develop a suitable ICP process for the etching of aluminum-free material, ridge waveguides have been fabricated and the effects of the ICP parameters have been assessed. The coil power and the platen power have been varied at constant pressure and temperature for a chlorine-based process. The surface quality, sidewall profile, and selectivity have been reported. We also demonstrate the optimization of the chlorine-based process for deep etching and its subsequent implementation in photonic band gap device fabrication for 1.55μm optical applications. The optimized process has been shown to provide a high aspect ratio and a good selectivity for 250nm diam holes with a depth of 3μm in the GaInP∕GaAs material system. The influence of the ICP parameters on this material system have been analyzed mainly by scanning electron microscopy with particular attentio...

Simulations of radical and ion fluxes on a wafer in a Cl2/Ar inductively coupled plasma discharge: Confrontation with GaAs and GaN etch experiments

A two-dimensional fluid model is used to study an industrial Ar/Cl2 inductively coupled plasma discharge designed to etch III-V samples. The effect of rf power, gas pressure, and chlorine content on the fluxes of reactive species reaching the wafer is numerically investigated. To understand how the etch process is influenced by the discharge conditions, simulation results are confronted with GaAs and GaN etch experiments performed in the same reactor geometry. When the source power is increased, the measured etch rate increase is consistent with the Cl radical and ion fluxes increase shown in the simulation, as well as the ion energy decrease due to the constant value of the wafer-holder power. Increasing the gas pressure results in a moderate increase in the etch rate due to the lower magnitude, lower mean energy, and anisotropy of the ion flux at high pressure. When the chlorine content is increased, the total ion flux decreases while Cl and Cl2 neutral fluxes increase significantly. A good correlation is obtained between calculated fluxes and etch characteristics, analyzed with scanning electron microscope images of etch profiles.A two-dimensional fluid model is used to study an industrial Ar/Cl2 inductively coupled plasma discharge designed to etch III-V samples. The effect of rf power, gas pressure, and chlorine content on the fluxes of reactive species reaching the wafer is numerically investigated. To understand how the etch process is influenced by the discharge conditions, simulation results are confronted with GaAs and GaN etch experiments performed in the same reactor geometry. When the source power is increased, the measured etch rate increase is consistent with the Cl radical and ion fluxes increase shown in the simulation, as well as the ion energy decrease due to the constant value of the wafer-holder power. Increasing the gas pressure results in a moderate increase in the etch rate due to the lower magnitude, lower mean energy, and anisotropy of the ion flux at high pressure. When the chlorine content is increased, the total ion flux decreases while Cl and Cl2 neutral fluxes increase significantly. A good correlation ...

High-power Al-free active region (λ = 852nm) DFB laser diodes for atomic clocks and interferometry applications

We have developed single frequency and single spatial mode laser structures with high optical power, using an aluminium free active region, which are to our knowledge the first demonstration for Cs pumping at 852 nm.

High power, very low noise and long term ageing 1.55 /spl mu/m InP-based Fabry-Perot quantum dash lasers under CW operation

Under continuous wave operation at room temperature, 50 mW per facet output power, -162 dB/Hz wide spectrum relative intensity noise and 6500 hours accelerated ageing with no failure of quantum dash Fabry-Perot lasers are presented.

High-power and low-noise 1.55 μm InP-based quantum dash lasers

The explosion of internet traffic, the increase in data or multimedia transmission are the main reasons for a huge rise in demand for transmission bandwidth especially in dense wavelength division multiplexing (DWDM) systems. Nowadays this technique must be developed in the 1.4 μm to 1.65 μm wavelength range to follow the progress of new low-loss fibres. A decade ago, a new class of gain material, based on quantum dot was intensively studied. For three years, researchers have succeeded in growing new elongated nano-structures based on InP, called quantum dashes, for applications beyond the wavelength limit of 1.3 μm using GaAs-based quantum dots. These great strides in the elaboration of these new gain materials could meet this gain bandwidth. In the framework of the European project, BIGBAND, we have developed 1.55 μm quantum dash Fabry-Perot lasers based on InP using a ridge waveguide operating in continuous wave at room temperature. These devices have reached the power of 40 and 50mW per facet in p side up and down configurations respectively and have shown a low relative intensity noise (RIN) of -162 dB/Hz ± 1.6 dB in 0.1-13 GHz range.

Lasers and amplifiers based on quantum-dot-like gain material

Semiconductor lasers and amplifiers were developed based on self-assembled quantum-dot gain material. This paper gives an overview about the recent work on GaAs- and InP-based quantum-dot devices mainly dedicated for telecom applications. The major advantage of quantum-dot like gain material, i.e. the possibility to tailor the spectral and spatial gain properties of an amplifying material, was used to optimize different device aspects, like low threshold current, broad band amplification or low temperature sensitivity. High performance GaAs-based continuous wave (cw) operating quantum-dot lasers could be fabricated with threshold currents of about 2 mA (L = 400 μm). Single mode emitting devices with emission wavelengths > 1.3 μm were realized by laterally coupled feedback gratings with threshold currents below 5 mA, output powers > 5 mW and cw operation temperatures up to 85 °C. Modulation frequencies of up to 7.5 GHz were obtained for standard device structures. For long wavelength telecom applications quantum-dot like material with dash geometry was developed on InP substrates with basic properties in the transition region between quantum-dot and -wire systems. A very large tuning range of the emission wavelength between 1.2 and 2.0 μm (room temperature) was obtained which allow the realization of material with ultra-wide gain bandwidth. Quantum-dash laser structures reaches threshold current densities < 1 kA/cm2. Ridge waveguide lasers with a cavity length of 1.9 mm show cw threshold currents of about 100 mA and maximum output powers > 40 mW per facet. With 300 μm long facet coated devices cw threshold currents of 23 mA and maximum operation temperatures in pulsed mode of 130 °C were achieved. Semiconductor optical amplifiers were fabricated by using broad band quantum-dash material. For a 1.9 mm long device, up to 22 dB gain was obtained with a three times larger spectral range than in comparable quantum well devices. High speed nearly pattern free signal amplification up to 10 GBit/s could be demonstrated and wavelength conversion experiments were performed.

Narrow spectral linewidth of al-free active region DFB laser diodes operating at 852nm

We have developed single frequency and single spatial mode laser structures with stable narrow linewidth (<1MHz) and high optical power (40mW), using an aluminium free active region for Cs pumping at 852nm.

Ultra-low noise over wide-bandwidth of 1.55 μm InP-based quantum-dash Fabry-Perot lasers for microwave systems

During the European project, BIGBAND, we have developed 1.55 μm quantum dash Fabry-Perot lasers based on InP using a ridge waveguide operating in continuous wave at room temperature. These devices have not only reached a high power of 50mW per facet but also have shown an ultra low relative intensity noise (RIN) of -162 dB/Hz ± 1.6 dB/Hz in 0.1-13 GHz range for the first year. At the end of the project we have succeeded in obtaining a very low RIN of -160 dB/Hz ± 2 dB/Hz over a wide bandwidth from 50 MHz to 18 GHz. This paper deals with the analysis of the experimental results, obtained with quantum dash Fabry Perot lasers, especially those relating to noise performances and also the first results of reliability demonstrating the suitability of these new devices for microwave optical links.