Space division multiplexing (SDM) is currently widely investigated in order to provide enhanced capacity thanks to the utilization of space as a new degree of multiplexing freedom in both optical fiber communication and on-chip interconnects. Basic components allowing the processing of spatial modes are critical for SDM applications. Here we present such building blocks implemented on the silicon-on-insulator (SOI) platform. These include fabrication tolerant wideband (de)multiplexers, ultra-compact mode converters and (de)multiplexers designed by topology optimization, and mode filters using one-dimensional (1D) photonic crystal silicon waveguides. We furthermore use the fabricated devices to demonstrate on-chip point-to-point mode division multiplexing transmission, and all-optical signal processing by mode-selective wavelength conversion. Finally, we report an efficient silicon photonic integrated circuit mode (de)multiplexer for few-mode fibers (FMFs).
A method for fabricating scalable antireflective nanostructures on polymer surfaces (polycarbonate) is demonstrated. The transition from small scale fabrication of nanostructures to a scalable replication technique can be quite challenging. In this work, an area per print corresponding to a 2-inch-wafer, is presented. The initial nanopatterning is performed on SiC in a 2-step process. Depending on the nanostructures the transmission of the SiC surface can be increased or suppressed (average height of nanostructures ~300nm and ~600nm, respectively) while the reflectance is decreased, when compared to a bare surface. The reflectance of SiC can be reduced down to 0.5% when the ~600nm nanostructures are applied on the surface (bare surface reflectance 25%). The texture of the green SiC color is changed when the different nanostructures are apparent. The ~600nm SiC nanostructures are replicated on polymer through a process flow that involved hot embossing and galvanization. The resulted polymer structures have similar average height and exhibit more rounded edges than the initial SiC nanostructures. The polymer surface becomes antireflective and hydrophobic after nanostructuring. The contact angle changes from 68 (bare) to 123 (nanostructured) degrees. The optical effect on the polymer surface can be maximized by applying a thin aluminum (Al) layer coating on the nanostructures (bare polymer reflectance 11%, nanostructured polymer reflectance 5%, Al coated nanostructured polymer reflectance 3%). The optical measurements were performed with an integrating sphere and a spectrometer. The contact angles were measured with a drop shape analyzer. The nanostructures were characterized with scanning electron microscopy.
Surface-patterning technologies have enabled the improvement of currently existing light-emitting diodes (LEDs) and can be used to overcome the issue of low quantum efficiency of green GaN-based LEDs. We have applied nanosphere lithography to fabricate nanopillars on InGaN/GaN quantum-well LEDs. By etching through the active region, it is possible to improve both the light extraction efficiency and, in addition, the internal quantum efficiency through the effects of lattice strain relaxation. Nanopillars of different sizes are fabricated and analyzed using Raman spectroscopy. We have shown that nanopillar LEDs can be significantly improved by applying a combination of ion-damage curing techniques, including thermal and acidic treatment, and have analyzed their effects using x-ray photoelectron spectroscopy.
White light-emitting diodes (LEDs) consisting of a nitride-based blue LED chip and phosphor are very promising
candidates for the general lighting applications as energy-saving sources. Recently, donor-acceptor doped fluorescent
SiC has been proven as a highly efficient wavelength converter material much superior to the phosphors
in terms of high color rendering index value and long lifetime. The light extraction efficiency of the fluorescent
SiC based all semiconductor LED light sources is usually low due to the large refractive index difference between
the semiconductor and air. In order to enhance the extraction efficiency, we present a simple method to fabricate
the pseudo-periodic moth-eye structures on the surface of the fluorescent SiC. A thin gold layer is deposited
on the fluorescent SiC first. Then the thin gold layer is treated by rapid thermal processing. After annealing,
the thin gold layer turns into discontinuous nano-islands. The average size of the islands is dependent on the
annealing condition which could be well controlled. By using the reactive-ion etching, pseudo-periodic moth-eye
structures would be obtained using the gold nano-islands as a mask layer. Reactive-ion etching conditions are
carefully optimized to obtain the lowest surface reflection performance of the fabricated structures. Significant
omnidirectional luminescence enhancement (226.0 %) was achieved from the angle-resolved photoluminescence
measurement, which proves the pseudo-periodic moth-eye structure as an effective and simple method to enhance
the extraction efficiency of fluorescent SiC based white LEDs.
Light-emitting diodes (LEDs) are penetrating into the huge market of general lighting because they are energy saving
and environmentally friendly. The big advantage of LED light sources, compared to traditional incandescent lamps and
fluorescent light tubes, is the flexible spectral design to make white light using different color mixing schemes. The
spectral design flexibility of white LED light sources will promote them for novel applications to improve the life quality
of human beings. As an initial exploration to make use of the spectral design flexibility, we present an example: 'no
blue' white LED light source for sufferers of disease Porphyria. An LED light source prototype, made of high brightness
commercial LEDs applying an optical filter, was tested by a patient suffering from Porphyria. Preliminary results have
shown that the sufferer could withstand the light source for much longer time than the standard light source. At last
future perspectives on spectral design flexibility of LED light sources improving human being's life will be discussed,
with focus on the light and health. The good health is ensured by the spectrum optimized so that vital hormones
(melatonin and serotonin) are produced during times when they support human daily rhythm.
This paper explored the feasibility of using a LED-based bulb as the illumination light source for photolithography room.
A no-blue LED was designed, and the prototype was fabricated. The spectral power distribution of both the LED bulb
and the yellow fluorescent tube was measured. Based on that, colorimetric values were calculated and compared on
terms of chromatic coordinates, correlated color temperature, color rendering index, and chromatic deviation.
Gretagmacbeth color charts were used as a more visional way to compare the two light sources, which shows that our
no-blue LED bulb has much better color rendering ability than the YFT. Furthermore, LED solution has design
flexibility to improve it further. The prototype has been tested with photoresist SU8-2005. Even after 15 days of
illumination, no effect was observed. So this LED-based solution was demonstrated to be a very promising light source
for photolithography room illumination due to its better color rendering in addition to energy efficiency, long life time
and design flexibility.
Ge nanostructures embedded in silica matrix are emerging as a promising material for new generation devices due to the
unique electric and photonic properties. In this paper, Ge nanoclusters and nanocylinders with Ge shell were successfully
formed by the high energy electron irradiation in the PECVD deposited glass. In addition, large area Ge nanoclusters
were also created by heat-treatment of PECVD deposited glass film. These nanostructures were characterized in terms of
size, composition, distribution and crystalline state by using TEM, HRTEM, EDS, SEM, Raman spectroscopy, and
SIMS. Waveguides doped with Ge nanoclusters were fabricated and their absorption has been characterized in a
wavelength range from 500nm to 1700nm.
Optical transmission technologies such as Dense-Wavelength Division Multiplexing (DWDM) have emerged in recent years to meet the demand for higher bandwidths and data rates. In order to implement such technologies, accurate determination of channel wavelengths is required. The Fabry-Perot Interferometer (FPI) offers the ability to resolve wavelengths with a 2-5 pm precision in resolution. We present here a novel Generic Lightwave Integrated Chip (GLIC) founded on the FPI. The device has been realised on a Planar Lightwave Circuit (PLC) in SiO<sub>2</sub> on Silicon as a means to achieve the desired rapid wavelength monitoring with high resolution. In this paper, the simulation and characterisation of the device is reported and the advantages of this technology are revealed. The theory is founded on employing the concept of quadrature between 2 phase-shifted signals provided by 2 similar Fabry-Perot cavities to determine the wavelength in question with a sub-microsecond response time. The compact features of the device make it an ideal candidate for application in future silica based PLC DWDM networks. By its generic nature, the device is also an attractive choice for applications in optical sensing and biophotonics.
In future all-optical networks pure optical signal processing, such as switching, routing and signal regeneration is going to be essential. Each of these tasks puts different constraints to the chosen solution regarding speed, wavelength range of operation, noise and polarization properties etc. However, a large fraction of these functionalities may be obtained by utilizing optical components with a strong nonlinear refractive index .
Silica has a very low nonlinear refractive index. Fortunately, silica also has a very low loss. As a consequence of the latter a significant nonlinear phase shift may be accumulated over a large distance i.e. over tens of kilometers of optical fiber. Because of this long length silica is not a viable material when designing compact nonlinear planare lightwave circuits.
Recently, nanostructured materials have been proposed as promising candidates for nonlinear waveguides. More specifically glass based materials doped with nanometer sized clusters of for example metals or semiconductors. In this work we demonstrate processing of waveguides with strong confinement of the electrical field achieved using air trenches and processing of glass doped with germanium nanoclusters. We illustrate how the cluster size may be controlled and we show that realization of nonlinear waveguides may be within reach.