B Boudewijn Docter

Discretely Tunable Laser Based on Filtered Feedback for Telecommunication Applications

A novel discretely tunable laser based on filtered feedback is presented. The semiconductor device consists of a Fabry-Perot laser with deeply etched broadband distributed Bragg reflector mirrors. Single-mode operation is achieved by using feedback from an integrated filter. This filter contains an arrayed waveguide grating wavelength router and a semiconductor optical amplifier gate array. Design, simulation, and the first characterization results of this new integrated filtered-feedback tunable laser device are presented. It shows a combination of a simple and robust switching algorithm with good wavelength stability. A rate equation model predicts that a properly designed device can switch within 1 ns. The fast switching and reduced control complexity makes the device very promising for various advanced applications in optical telecommunication networks.

Semiconductor Ring Laser With On-Chip Filtered Optical Feedback for Discrete Wavelength Tuning

We introduce a novel concept of discretely tunable semiconductor lasers with on-chip filtered optical feedback. The integrated device is based on a semiconductor ring laser that can sustain two counter-propagating modes. By means of a directional coupler, part of the light emitted by the laser is coupled out to a feedback section integrated on the same chip. The feedback section contains two arrayed waveguide gratings and a set of semiconductor optical amplifiers to provide filtering of particular longitudinal modes sustained by the ring cavity. By controlling the current injected into the semiconductor optical amplifiers, single mode operation in both directions is achieved. In this paper, the design, characterization, and modeling of the device is presented.

Deep Etched DBR Gratings in InP for Photonic Integrated Circuits

A novel fabrication process was developed to realize high quality SiOx masks for CI2 based ICP etching of InP. First order DBR mirrors, 3 mum deep, were realized that can be used in photonic circuits. The process can be used in combination with conventional optical lithography, reducing production cost.

Transmission of pillar-based photonic crystal waveguides in InP technology

Waveguides based on line defects in pillar photonic crystals have been fabricated in InP∕InGaAsP∕InP technology. Transmission measurements of different line defects are reported. The results can be explained by comparison with two-dimensional band diagram simulations. The losses increase substantially at mode crossings and in the slow light regime. The agreement with the band diagrams implies a good control on the dimensions of the fabricated features, which is an important step in the actual application of these devices in photonic integrated circuits.

Short Cavity DBR Laser Using Vertical Groove Gratings for Large-Scale Photonic Integrated Circuits

We present a novel compact distributed Bragg reflector (DBR) laser using InP-InGaAsP deep ridge waveguides with vertical groove gratings. Stable single-mode laser operation was achieved with an active cavity length down to 25 mum and a threshold current of 14 mA. The devices are promising building blocks in large-scale photonic integrated circuits because of their simple structure and low power consumption.

Monolithically integrated widely tunable laser source operating at 2 μm

We present a widely tunable extended cavity ring laser operating at 2 μm that is monolithically integrated on an indium phosphide substrate. The photonic integrated circuit is designed and fabricated within a multiproject wafer run using a generic integration technology platform. The laser features an intracavity tuning mechanism based on nested asymmetric Mach–Zehnder interferometers with voltage controlled electro-refractive modulators. The laser operates in a single-mode regime and is tunable over the recorded wavelength range of 31 nm, spanning from 2011 to 2042 nm. Its capability for high-resolution scanning is demonstrated in a single-line spectroscopy experiment using a carbon dioxide reference cell.

Three level masking for improved aspect ratio InP-based photonic crystals

A three-level masking technique is used to improve the aspect ratio of InP-based photonic crystals. The masking consists of a ZEP/Cr/SiOx stack where the ZEP layer is used to open the Cr which on its turn is a good mask for opening the 500 nm thick SiOx layer. Subsequently InP is etched in an ICP process using Cl2:O2. Very high aspect ratios could be achieved in holes ranging from 130 up to 270 nm in diameter. A maximum aspect ratio of >20 is obtained with the narrowest holes having diameters of 180 and 130 nm.

Trends in High Speed Interconnects: InP Monolithic Integration

InP PIC technologies offer unsurpassed optoelectronic performance and are a key enabler for high-performance optical transceivers. InP lasers are the default solution for the communications lasers operating in the 1300–1600 nm wavelength window. As integration technologies continue to mature and information rates scale up, increasingly sophisticated monolithic techniques are deployed for both discrete devices and integrated circuits for longer-reach networking and higher data rates. The possibility to engineer the band gap across the wafer delivers a rich range of functions in an ever-decreasing footprint. Lasers are combined with additional devices such as modulators, multiplexers, detectors and hybrids within the same chip. Wafer scale production offers a proven route to cost-effective, high-volume production. Monolithic integration reduces cost through reduced test time and simplified assembly and packaging. This chapter reviews the techniques, capabilities and future potential for InP-integrated photonics with a particular reference to requirements in the rapidly evolving data interconnect market, driven in particular by data centres, where energy efficiency, bandwidth and volume production are crucial.

Monolithic photonic integration technology platform and devices at wavelengths beyond 2μm for gas spectroscopy applications

In this paper a generic monolithic photonic integration technology platform and tunable laser devices for gas sensing applications at 2 μm will be presented. The basic set of long wavelength optical functions which is fundamental for a generic photonic integration approach is realized using planar, but-joint, active-passive integration on indium phosphide substrate with active components based on strained InGaAs quantum wells. Using this limited set of basic building blocks a novel geometry, widely tunable laser source was designed and fabricated within the first long wavelength multiproject wafer run. The fabricated laser operates around 2027 nm, covers a record tuning range of 31 nm and is successfully employed in absorption measurements of carbon dioxide. These results demonstrate a fully functional long wavelength photonic integrated circuit that operates at these wavelengths. Moreover, the process steps and material system used for the long wavelength technology are almost identical to the ones which are used in the technology process at 1.5μm which makes it straightforward and hassle-free to transfer to the photonic foundries with existing fabrication lines. The changes from the 1550 nm technology and the trade-offs made in the building block design and layer stack will be discussed.

Long wavelength monolithic photonic integration technology for gas sensing applications

Progress on the development of a long wavelength (~2 μm) generic monolithic photonic integration technology on indium phosphide substrate and a novel concept of a tunable laser realized as a photonic integrated circuit using such technology are presented. Insights into the development of active and passive waveguide structures which are used to define a limited set of on-chip functionalities in the form of building blocks will be given. A novel tunable laser was proposed and designed using such predefined set of basic building blocks. The laser geometry features an intra-cavity wavelength tuning mechanism based on asymmetric Mach-Zehnder interferometers in a nested configuration. The photonic integrated circuit chip was fabricated within the first long wavelength multi-project wafer run. The experimental evaluations of the fabricated device show a record tuning range of 31 nm around 2027 nm and successful measurements of a 0.86 GHz wide absorption line of carbon dioxide. These results provide a demonstration of a fully functional photonic integrated circuit operating at wavelengths that are much longer than those in the typical telecommunication windows as well as the use of indium phosphide based generic photonic integration technologies for gas sensing applications.