Paul Lambkin

Analysis of Slot Characteristics in Slotted Single-Mode Semiconductor Lasers Using the 2-D Scattering Matrix Method

We use the two-dimensional (2-D) scattering matrix method (SMM) to analyze the slot characteristics in slotted single-mode semiconductor lasers and compare the results with those calculated by the one-dimensional transfer matrix method (TMM). The analysis shows that the 2-D SMM is required to accurately account for the measured results. Using the 2-D SMM simulation, we find that there is almost no reflection at the interface from slot to waveguide while a large reflection exists at the interface from waveguide to slot, and the power loss is much larger than the power reflected. For a single slot, the slot width has little influence on the slot reflectivity, which coincides with the measured results. The reflection and transmission of the slot are found to be exponentially dependent on the slot depth

A Novel Two-Section Tunable Discrete Mode Fabry-PÉrot Laser Exhibiting Nanosecond Wavelength Switching

A novel widely tunable laser diode is proposed and demonstrated. Mode selection occurs by etching perturbing slots into the laser ridge. A two-section device is realized with different slot patterns in each section allowing Vernier tuning. The laser operates at 1.3 mum and achieves a maximum output power of 10 mW. A discontinuous tuning range of 30 nm was achieved with a side mode suppression greater than 30 dB. Wavelength switching times of approximately 1.5 ns between a number of wavelength channels separated by 7 nm have been demonstrated.

A Multiwavelength Low-Power Wavelength-Locked Slotted Fabry–Pérot Laser Source for WDM Applications

Wavelength-locking of a multiwavelength stabilized slotted Fabry-Peacuterot (SFP) laser to a single-mode laser source is experimentally demonstrated. The SFP resonates at channels spaced by ~8 nm between 1510 and 1565 nm over a wide range of temperatures and drive currents. Under low-power (<-20 dBm) external optical injection, wavelength-locking with a sidemode suppression ratio (SMSR) >25 dB is achieved. A locking width of >25 GHz and SMSR >30 dB can be achieved for each locked wavelength channel at injection power >-16 dBm

Fast Wavelength Switching Lasers Using Two-Section Slotted Fabry&#8211;P&#201;rot Structures

Fast wavelength switching of a two-section slotted Fabry-Perot laser structure is presented. The slot design enables operation at five discrete wavelength channels spaced by 10 nm by tuning one section of the device. These wavelengths operate with sidemode suppression ratio in excess of 35 dB, and switching times between these channels of approximately 1 ns are demonstrated

An Integrated Optofluidic Platform for DNA Hybridization and Detection

There has been extensive research into micro total analysis systems (micro-TAS) and lab-on-a-chip research due to the benefits of increased sample throughput, reduced sample consumption, and rapid analysis times. The integration of low-cost fluidic and optical components offers the possibility of complex systems with increased functionality on a single detection platform. For the development of an integrated optofluidic system for DNA hybridization, the key areas are optical/fluidic integration and the efficiency of surface chemistry integration within the system. The impact of fluidic parameters such as flow rate, channel height, and time on hybridization performance is to optimize detection performance over conventional assay (microtiter plate formats). The use of a passive waveguide device means DNA binding events can be monitored using fluorescence excitation or refractive index measurement. The integration of the three areas is enhanced by the robustness of the waveguide material (oxide, nitride), enabling chemical functionalization by initial silanization followed by addition of a linker molecule 1,4 phenylene diisothiocyanate (PDITC) for covalent immobilization of DNA probes together with the possibility to define microfluidics on the waveguide substrate using standard SU8 photolithography. The fluidic design requires 240 nl of analyte to fill the integrated optofluidic system. Here, we report the novel integration and optimization of a covalent surface chemistry with microfluidic channels for fluidic delivery, and a standard resonant mirror (RM) waveguide detection platform. The optofluidic detection platform was tested using fluorescence and refractive index to monitor binding events between target and probe DNA. We describe the detection system, using simulations to explain the response to changes in refractive index and outline a method for covalent attachment of DNA probes surface chemistry protocol to immobilize probe DNA on the sensor surface and the optimization of fluidic design, achieving pM detection limit. We highlight the benefit of optimizing the fluidic component and its benefit in hybridization efficiency an approach often overlooked in sensor design and performance.

Multiwavelength array of single-frequency stabilized Fabry-Perot lasers

We characterize the influence of controlled perturbations (slots) in the ridge waveguide of Fabry-Perot lasers emitting around 1550 nm. The slots are etched simultaneously with the ridge and each slot introduces an additional loss of 2.3 cm/sup -1/. The lasers emit with a single wavelength when more than three slots are introduced, in which case the interslot spacing strongly influences the lasing spectrum. An array of devices with differing slot arrangements are fabricated on a single chip where each laser emits at a single wavelength across a 30-nm band each with side-mode suppression ratios greater than 28 dB. The emission wavelengths are simulated with a model for lossy slots where each slot has an effective in-phase reflectivity of 0.7%.

Reflectivity measurements of intracavity defects in laser diodes

A method for measuring the complex reflectivity associated with a localized defect existing inside a laser diode cavity is presented. It relies on analyzing the magnitudes of resonant peaks in the Fourier transform of a subthreshold laser spectrum. Reflectivities between 0.01 and 0.02 with zero phase have been measured in a laser with a deliberately induced scattering center produced by standard lithographic techniques.

Transition From Perturbed to Coupled-Cavity Behavior With Asymmetric Spectral Emission in Ridge Lasers Emitting at 1.55

We have investigated a series of ridge waveguide lasers with deeply etched slots in the ridges. The slots do not penetrate the active region, but are deep enough to strongly perturb the longitudinal modes. By the addition of slots, a transition between perturbed-mode and coupled-cavity behavior is crossed. With a group of four or more slots, the below-threshold amplified spontaneous emission spectrum from each end of the laser has different periods and the facet-facet oscillations are suppressed indicating that the different sections have become quasi-independent. A model using a distributed emitter in the cavity reproduces this behavior. Above threshold, the single contact coupled cavity lasers are single mode with greater than 30-dB sidemode suppression ratio over a wide range of currents

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A novel facetless laser structure is proposed and demonstrated. The facetless laser is realised by etching deep slots into the mirror sections of a multi section semiconductor laser which provide the feedback for laser operation.

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Tunable laser structures with nanosecond switching time between wavelength channels and low-power injection locking are demonstrated on a low-cost platform. These lasers are suitable as source or slave lasers in WDM passive optical access networks.