Abdessamad Benhsaien

Narrow Linewidth 1550 nm Corrugated Ridge Waveguide DFB Lasers

We report on the design and characterization of InP-based multiple quantum well corrugated ridge waveguide distributed feedback diode lasers operating at 1550 nm. Third-order gratings have been etched along the sidewalls of the ridge waveguide using the standard I-line stepper lithography technique with an inductively coupled reactive ion etching process. An as-cleaved 1500-μm-long laser diode shows stable continuous wave single-mode operation at 1550 nm with high side-mode suppression ratios (>50 dB), a temperature-dependent wavelength shift dλ/dT ~0.095 nm/°C, and output powers ≥7 mW at 25 °C. Linewidth determination has been carried using the delayed self-heterodyne interferometric technique. Narrow linewidths (≤250 kHz) have been observed for a wide range of current injection, with a minimum of 184 kHz at 300 mA.

O-band semiconductor optical amplifier design for CWDM applications

A broadband semiconductor optical amplifier (SOA) has been realized for the coarse WDM (CWDM) based systems operating over the O-band range. The SOA exhibits low polarization sensitivity, 23 dB gain and low noise based on the asymmetric multi-quantum well (AMQW) technique. Reflective SOAs (for modulating the upstream data in passive optical networks (PONs)) as well as in-line or booster amplifiers in CWDM systems are some of the applications of such a SOA.

Narrow linewidth two-electrode 1560 nm laterally coupled distributed feedback lasers with third-order surface etched gratings

We report on the design and characterization of a re-growth free InGaAsP/InP multiple quantum well two-electrode laterally coupled distributed feedback (LC-DFB) lasers. Third-order surface etched gratings have been defined on the ridge sidewalls along the laser cavity by means of stepper lithography. The lasers oscillate in single-mode around 1560 nm with high side mode suppression ratios (>52 dB), a wavelength tuning (≥ 3nm), an output power (≥ 6 mW), and narrow linewidth (<170 kHz) under various current injection ranges at room temperature. A minimum linewidth of 94 kHz has been recorded for 1500 µm-long two-electrode LC-DFB laser while providing non-uniform current injection through the two electrodes. The effect of the width of the inter-electrode gap on these different performance measures is also studied.

Time-Domain Analysis of Third-Order Quantum-Dot-Based Laterally-Coupled Distributed Feedback Lasers Using Travelling-Wave Approach

In this paper, we present a time-domain (TD) coupled model suitable to investigate high-order λ/4 phase-shift grating quantum-dot (QD) based laterally-coupled distributed feedback (LC-DFB) laser. First, by integrating the Streifers coefficients, we include the effects of radiation and evanescent modes into the TD coupled wave equations, and hence we investigate the effect of the radiation modes. Then, via a well-established set of rate equations coupled with the travelling field propagation equations, population dynamics in the QD region are modeled and the homogeneous and inhomogeneous broadening of, respectively, the whole QD ensemble and each QD inter-band transition are properly taken into account in the model. Finally, we consider the coupling between forward and backward electric fields due to the grating via the travelling-wave approach. This approach advances the impact of radiating partial waves in high-order QD-LC-DFB lasers. It is shown that, in particular for third-order rectangular grating, longitudinal spatial hole-burning is highly reduced, high single mode suppression ration (60 dB) is obtained and larger frequency modulation is achieved thanks to the fine engineering of the grating features and the particular properties of QD. Eventually, such results highlight the beneficial effect of considering high-order grating QD-LC-DFB lasers for better longitudinal-mode discrimination and high device performances.

The impact of laterally coupled grating microstructure on effective coupling coefficients

Lithographic fabrication may be used to define laterally coupled gratings of high refractive index contrast on waveguide ridges, eliminating the need for regrowth steps in such distributed feedback lasers. These may be made more amenable to fabrication by employing higher-order gratings. Reliable exploration of the laser design space requires that the radiating partial waves be accurately incorporated in numerical simulations. We modify the coupled-mode approach to fully consider the two-dimensional cross section, analyzing rectangular, sinusoidal, triangular and trapezoidal grating shapes. Effective coupling coefficients are determined for grating orders from first to third. We show that, by tailoring the grating microstructure, effective coupling coefficients up to double that of a 0.5 duty cycle rectangular grating can be achieved. The actual grating microstructure of an as-fabricated grating was analyzed and its effective coupling coefficient predicted as [Formula: see text]. This was found to be in excellent agreement with the value extracted from the amplified spontaneous emission spectrum, [Formula: see text].

Narrow linewidth 1560 nm InGaAsP split-contact corrugated ridge waveguide DFB lasers.

We demonstrate a split-contact corrugated ridge waveguide InGaAsP distributed feedback laser at 1560 nm. The laser cavity has been defined with uniform third-order gratings etched along the sidewalls of the ridge waveguide. The gratings were fabricated using a standard I-line stepper lithography technique along with an inductively coupled reactive ion-etching process. Stable single-mode operation has been achieved with side-mode suppression ratios ≥50  dB, output powers ≥7  mW, a wavelength tuning range ≥2.3  nm, and narrow linewidths (≤140  kHz) for different biasing conditions, with a minimum of 70 kHz. The effect of p-contact partition on device performance is also studied.

Low polarization-sensitive asymmetric multi-quantum well semiconductor amplifier for next-generation optical access networks

A broadband and low-polarization-sensitive multi-quantum well semiconductor optical amplifier with an asymmetric structure is reported for operation in the E-band wavelength range. A gain peak of 20 dB for a bandwidth of more than 50 nm is measured for both TE and TM polarizations. A maximum polarization sensitivity of 3 dB is measured for a broad wavelength range from 1340 to 1440 nm.

Metamaterial Lüneburg waveguide lenses for switch fabric on-a-chip applications

Optical information processing has traditionally been demonstrated using 3D free-space optical systems employing bulk optical components. These systems are bulky and unstable due to the stringent alignment tolerances that must be met. Taking advantage of the alignment accuracy offered by planar light circuits, these issues may be overcome by confining the light in a planar slab waveguide. The limitation on scaling, consequent on the loss of one dimension is offset by the nanoscale component footprints attainable in a silicon integration platform. A key component of this free-space-opticson- a-chip concept is a waveguide lens. Waveguide lenses are of general utility but our specific application is their use to implement the complex crossover interconnections of a switch fabric. The graded refractive index of the lens is engineered by patterning the silicon layer of silicon on insulator slab waveguides into a dense distribution of cylinders; either solid (silicon) or voids (air); using a single etch step. The cylinders have variable diameters and are placed on a regular square or hexagonal grid with sub-wavelength pitch. In the case of voids, the patterned silicon may be suspended in air to form the core of a symmetric slab waveguide. Solid cylinders must be supported by the Si02 layer leading to an asymmetric waveguide of reduced effective index range. Advantageously, the patterning of the metamaterial region within the slab-waveguide requires only a single etch step. Photonic wire feeder waveguides at different positions around the lens may be used to launch light into the lenses or collect light from the lenses. A method is developed to determine the local effective media index of a periodic metamaterial in terms of the parameters of its unit cell. This method is used as a calibration to lay out a metamaterial with graded parameters. The operation of a metamaterial Lüneburg lens telescope is verified by FDTD simulations and shown to be capable of near zero insertion loss and crosstalk. The careful approximation of the graded index of the Lüneburg lens by a metamaterial introduces minimal impairments.

Characterization of an Asymmetric InGaAsP/InP Multi Quantum Well Semiconductor Optical Amplifier

An experimental characterization of broadband semiconductor optical amplifiers (SOAs) at 1360 nm is reported. In addition to their inherent small size, fast dynamics, and feasibility of integration with other optoelectronic components, the relevance of the multi quantum well (MQW) asymmetric SOAs here reported relies on the achievement of a flat and broad 3 dB amplification bandwidth. SOAs are composed of nine In1-xGaxAsyP1-y 0.2% tensile strained MQW layers separated by latticed matched InP barriers. The asymmetry of the active region is based on the difference of the molar concentrations, with Ga (x) ranging from 0.46 to 0.47 and As (y) ranging from 0.89 to 0.94. Devices under test have 7 degrees tilt cleaved facets and feature different geometries: ridge widths from 2 to 4 μm in steps of 0.25 μm, and cavity lengths of 600, 900, 1200, and 1500 μm. Fabry-Pérot (FP) lasers with the same material composition as the SOAs and within the same wafer are used as test structures for parameters extraction, providing a feedback mechanism for further design improvement. The ridge width of the FP lasers varies from 2 to 8 μm, in steps of 2 μm. All the devices have been designed and characterized at the Photonics Technology Laboratory, Centre for Research in Photonics, fabrication was done at Canadian Photonics Fabrication Centre (CPFC), Canada and supported by CMC Microsystems. Devices under test are DC-biased and temperature controlled at 25°C. A single pass gain of 13.5 dB is measured for a 3 dB bandwidth of 60 nm centred at 1360 nm. Light-current plots obtained from the FP lasers show that the threshold current varies with the cavity length, with a minimum of 80 mA for a cavity length of 600 μm and a ridge width of 2 μm. A thermal roll-off occurring at high injection currents is observed, especially with the smallest cavity length. In conclusion, asymmetric MQW SOAs featuring different ridge widths and cavity lengths have been

The Linewidth Broadening Factor: A Length-Scale-Dependent Analytical Approach

A first-order frequency-dependent formula of the linewidth broadening factor (α–factor) is derived in terms of scattering rates whilst, a mesoscopic disk approach is used in order to accompany the dimension effect to the spontaneous emission lifetime (inverse of scattering rate). An excitonic correction to the relaxation properties is shown to occur provided the binding energy of the electron and hole is comparable to their eigenenergy-separation. The ensuing analysis is independent of the selected III-V material system and resides upon three simplifying assumptions which allow for analytical formulae to be derived.