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
Photonic Integrated Circuits (PICs) enable photons as data carriers at a very high speed. PIC market opportunities call for reduced wafer dimensions, power consumption and cost as well as enhanced reliability. The PIC technology development must cater for the latter relentless traits. In particular, monolithic PICs are sought as they can integrate hundreds of components and functions onto a single chip. InGaAsP/InP laterally-coupled distributed feedback (LC-DFB) lasers stand as key enablers in the PIC technology thanks to the compelling advantages their embedded high-order surface-gratings have. The patterning of the spatial corrugation along the sidewalls of the LC-DFB ridge, has been established to make the epitaxial overgrowth unnecessary thereby reducing the cost and time of manufacturing, and ultimately increasing the yield. LC-DFBs boast a small footprint synonymous of enhanced monolithic integrate-ability. Nonetheless, LC-DFBs suffer from the adverse longitudinal spatial hole burning (LSHB) effects materialized by typically quite high threshold current levels. Indeed, the carrier density longitudinal gradient- responsible for modes contending for the available material gain in the cavity- may be alleviated somewhat by segmenting the LC-DFB electrode into two or three reasonably interspaced longitudinal sections. In this work we report on the realization and performance of various electrode partition configurations. At room temperature, the experimental characterization of many as-cleaved LC-DFB devices provides ample evidence of superior performance such as a narrow linewidth (less than 400 kHz), a wide wavelength tune-ability (over 4 nm) and a hop-free single mode emission (side mode suppression ratio (SMSR) exceeding 54dB).
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.
There has been much interest in developing low-cost laser sources for applications such as photonics integrated circuits
and advanced coherent optical communications. The ultimate objectives in this development include wide wavelength
tunability, a narrow linewidth, and an ease of integration with other devices. For this purpose, semiconductor surface
grating distributed feedback (SG-DFB) lasers have been introduced. SG-DFB manufacturing consists of a unique
sequence of planar epitaxial growth resulting in a major simplification to the fabrication process. SG-DFB lasers are
highly monolithically integrate-able with other devices due to their small footprint.
The segmentation of the built-in top electrode helps to alleviate the adverse spatial-hole burning effects encountered in
single-electrode devices and brings hence significant enhancements to the laser performance. For the first time, we report
here on the design, fabrication, and characterization of InGaAsP/InP multiple-quantum-well (MQW) SG-DFB lasers
with uniform third-order surface grating etched by means of stepper lithography and inductively-coupled reactive-ion.
The uncoated device reported here is 750 μm-long SG-DFB laser whose central and lateral top electrodes are 244 μmlongs
each, separated by two 9 μm-long grooves. The experimental characterization shows stable single mode operation
at room temperature under uniform and non-uniform injection. High side mode suppression ratios (SMSRs) (50-55dB)
under a wide range of injection current have been discerned as well. A relatively broad wavelength tuning (<4nm) has
also been observed. Moreover, a narrow linewidth (<300 kHz) has been recorded for different injection currents.
Laterally-coupled distributed feedback (LC-DFB) lasers offer compelling advantages over standard DFB lasers. The use
of surface grating on the ridge waveguide sidewalls in LC-DFB devices avoids any epitaxial overgrowth. This provides a
considerable simplification in the fabrication process, reducing cost and time of manufacturing, and ultimately increasing
yield. It offers also the potential for monolithic integration with other devices; paving the way towards low-cost and
mass-production of photonics integrated circuits. In this work, we report on the realization of high-order grating
InGaAsP/InP multiple-quantum-well (MQW) LC-DFB lasers at 1.55 μm by means of stepper lithography and
inductively-coupled reactive-ion as well as wet chemical etching. Third-order rectangular-shaped grating has been
lithographically defined on the ridge waveguide sidewalls with a relatively deep etching along the laser cavity. The
preliminary experimental characterization shows interesting results for as-cleaved devices tested in room temperature
under CW operation. A fabricated 1500 μm-long cavity LC-DFB laser shows stable single-mode operation with a side
mode suppression ratio as high as 50 dB. The tested device can emit at power as high as 9 mW, and the measured
threshold current is around 80 mA at room temperature. Moreover, the measured linewidth has been found to be as
narrow as 178 kHz using the delayed self-heterodyne interferometric technique.