An automated cell detection and sorting system was developed, combining both the optofluidic intracavity spectroscopy
(OFIS) technique and dielectrophoresis (DEP). The OFIS method utilizes a microfluidic channel as a Fabry-Perot cavity
to produce characteristic transmission spectra of individual cells. The concept behind optical detection is that a decrease
in spectral intensity beyond a threshold indicates that a cell is present. Upon detection, an RF voltage is automatically
applied to electrodes, trapping the cell with DEP forces. The system then sorts the cell into one of two microfluidic
channels based on resulting optical analysis. A further advantage is that RF joule heating can be measured from known
dn/dT values of the medium, which is useful for investigating cell viability issues.
The label-free technique of optofluidic intracavity spectroscopy (OFIS) uses the optical transmission spectrum of a cell
in a microfluidic optical resonator to distinguish cancerous and non-cancerous cells. Based on their distinctive
characteristic transmission spectra, canine hemangiosarcoma (HSA) cancer cells and normal peripheral blood
mononuclear cells (PBMCs) have been differentiated using the OFIS technique with high statistical significance (p<10-
6). 95% sensitivity and 98% specificity were achieved simultaneously. A cell lens model explains trends in the transverse
mode pattern in the transmission spectra of HSA cells and allows extraction of cell focal length.
1.3 μm VCSELs have been under development for several years. In this work, we discuss several requirements and
characteristics that allow a device to be manufacturable in high volume with excellent yield.
This paper reviews the recent advances made in monolithic GaAs based, directly modulated, 1.3micrometers VCSEL array technology. Such VCSEL arrays are poised to begin occupying a large telecommunications application space. We present data demonstrating 1.3 micrometers VCSELs having ~ 1mW optical power across a wide temperature range of 10 to 90 degree(s)C while operating with low voltages of less than 2.5V. The data includes performance on typical 8 and 12 element arrays at the die level as well in the module. We also present very encouraging preliminary reliability results.
The Near-Field Scanning Optical Microscope (NSOM) is a tool that combines the spatial resolution of scanning probe microscopy with optical characterization techniques. Using this technique, we have generated high-resolution spatial intensity maps of the output from vertical-cavity surface-emitting lasers (VCSELs) in the near-field region of the facet as a function of operating current. The VCSELs studied were proton implanted, gain guided devices designed to operate at ~850nm. Optical signals that have been spatially imaged include total intensity, the spectrally resolved intensity of individual transverse modes, and the derivative of intensity with respect of operating current. Deviations from expected mode patterns in the devices have been qualitatively linked to unacceptable levels of noise in operating lasers. These deviations can be observed at operating currents below the actual onset of unacceptable noise. We have also found that derivative spectroscopy can be used to sensitively detect the cutoff points of transverse modes. Using the spatial intensity profile at the cutoff point of an allowed mode, a first approximation to the index of refraction profile can be made that is in good agreement with prior work. A series of index profile estimates from the cutoff points of a VCSEL can provide information on the evolution of the index profile and the thermal lens as the power is ramped up.
VCSELs operating at 1.3 microns are the ideal laser source for meeting the exploding demand for bandwidth in local area and metro area networks. NCSELs will eventually replace the vast majority of 1.3 micron FP and DFB edge emitting lasers currently used in these applications, since they offer lower manufacturing cost, on wafer testability, extremely narrow linewidth, a circular output beam, high speed direct modulation, and the ability to be integrated into arrays. The primary challenge in 1.3 micron VCSELs has been to find an active region material that can be grown directly on high thermal conductivity and high reflectivity GaAs/AlGaAs distributed Bragg reflectors DBRs. In this work, we have developed MBE grown InGaAsN quantum wells that can be grown directly on GaAs substrates and integrated directly into high performance oxide VCSEL structures. We have demonstrated record room temperature CW single mode output powers in excess of 1 mW at an emission wavelength of 1287 nm. CW lasing has been observed as high as 125 degree(s)C, illustrating the excellent thermal performance of both the InGaAsN quantum wells and the GaAs/AlGaAs DBRs. Open eye diagrams were observed at 10 Gb/s, paving the way for OC-192 SONET and 10 Gb/s Ethernet applications.
High bit rate communication links are placing increasing demands on the performance and cost of semiconductor laser diodes. VCSELs are uniquely suited to meeting the requirements of 10 Gb/s and higher applications. The laser requirements include high temperature operation, high bandwidth, high reliability, short rise and fall times, low RIN, low jitter, low RMS linewidth, and drive circuit compatibility. We will discuss the major challenges to achieving these goals as well as approaches that have been successful to date.
This paper summarizes recent in situ x-ray analyses of the growth of GaAs by organometallic vapor phase epitaxy (OMVPE). This growth was carried out using tertiarybutylarsine (TBAs) and trimethylgallium (TMG) as the source materials. Examples of in situ x-ray measurements are given including x-ray absorption studies of gas phase behavior and x-ray scattering studies of layer-by-layer growth.
Using a new in situ analysis tool, grazing incidence x-ray scattering, we have studied the surface reconstructions present prior
to and during growth of ZnSe by organometallic vapor phase deposition. We have established that the GaAs native oxide is
chemically reduced by the hydrogen ambient present during pre-growth heating. Following this cleaning procedure, the
growth of ZnSe was found to occur in the presence of a p(2x1) reconstruction, characteristic of an array of Se dimers. This
new technique can easily be extended to other growth systems.