This paper presents the sensor characteristics of highly birefringent polymer side-hole optical fiber. The fiber core with
greater refractive index was made of copolymer PMMA-PS, while the cladding of pure PMMA. The fabricated fiber
showed relatively low losses of the order of 6 dB/m in the visible range. We measured several sensing characteristics in
the fabricated fiber, including birefringence and polarimetric sensitivity to pressure and temperature. The fiber showed
high polarimetric sensitivity to pressure, which is directly related to the presence of two large holes transferring
symmetrical load applied to the cladding into nonsymmetric stress distribution in the core region. This in turn changes
modal birefringence of the investigated fiber and increases the sensitivity to pressure.
Quantum dot-based diode comb lasers can provide a single multi-channel-laser source for short-reach, high-speed WDM interconnects. In this paper, we review the technology and demonstrate for the first time a 15 channel, low RIN comb laser with 80 GHz channel spacing. We show that each of the Fabry-Perot (FP) modes can be externally modulated at 10 Gb/s or all modes directly modulated, at 3.2 Gb/s so far. The latter indicates that the comb laser may be an ideal broadband light source in WDM-PON applications. We further demonstrate that the whole comb laser spectrum can be amplified by a quantum dot SOA without increasing relative density noise (RIN) of the individual channels. The small signal amplification factor was measured up to 30dB and the saturated output power was as high as 15 dBm.
Quantum dot-based diode comb lasers enable a single multi-channel-laser source for short-reach, high-speed WDM
interconnects. In this paper, we demonstrate for the first time a 15 channel low RIN comb laser with 80 GHz channel
spacing. We show that all the FP modes can be simultaneously directly modulated simply by modulating the pump
current at 3.2 Gb/s, which indicates that the comb laser may be an ideal broadband light source in WDM-PON
applications.We demonstrate that the whole comb laser spectrum can be amplified by a quantum dot SOA without
increasing the relative intensity noise (RIN). Small signal amplification factor was measured as high as 30 dB and the
saturated output power was as high as 15 dBm.
We demonstrate a compact trench-based silicon-on-insulator (SOI) rib waveguide ring resonator comprised of trench-based bends and splitters. It has a perimeter of 50 µm and occupies an area of only 25×25 µm. The measured free spectral range (FSR) is 13.2 nm, which the largest reported for an SOI rib waveguide ring resonator. The measured FSR, full width at half maximum, and quality factor match reasonably well with analytical calculations. Further calculation shows that a FSR of 50.8 nm is achievable for an SOI rib waveguide ring resonator with a perimeter of 15 µm.
High-channel-count WDM will eventually be used for short reach optical interconnects since it maximizes link bandwidth and efficiency. An impediment to adoption is the fact that each WDM wavelength currently requires its own DFB laser. The alternative is a single, multi-wavelength laser, but noise, size and/or expense make existing options impractical. In contrast, a new low-noise, diode comb laser based on InAs/GaAs quantum dots provides a practical and timely alternative, albeit in the O-band. Samples are being evaluated in short reach WDM development systems. Tests show this type of Fabry-Perot laser permits >10 Gb/s error-free modulation of 10 to over 50 separate channels, as well as potential for 1.25 Gb/s direct modulation. The paper describes comb laser requirements, noise measurements for external and direct modulation, O-band issues, transmitter photonic circuitry and components, future CMP applications, and optical couplers that may help drive down packaging costs to below a dollar.
We report on edge-emitting InAs/GaAs quantum dot laser promising as multiple wavelength light source for dense
wavelength-division-multiplexing systems in future generation of silicon photonic integrated circuits. Broad and flat gain
spectrum of quantum dots as well as pronounced gain saturation effect facilitate simultaneous lasing via a very large
number of longitudinal modes with uniform intensity distribution (comb spectrum). A very broad lasing spectrum of
about 75 nm in the 1.2-1.28 μm wavelength range with a total output power of 750 mW in single lateral mode regime is
achieved by intentional inhomogeneous broadening of ground state transition peak and contribution of lasing via excited
state transitions. Average spectral power density exceeds 10 mW/nm. A bit error rate less than 10-13 is demonstrated for
ten spectrally filtered and externally modulated at 10 Gb/s Fabry-Perot modes owing to a low (<0.3% in the 0.001-10 GHz range) relatively intensity noise of each individual mode. This result shows aptitude of a multimode quantum dot
laser for high bandwidth wavelength-division-multiplexing systems.
KEYWORDS: Transducers, Chemical elements, Finite element methods, 3D modeling, Wave propagation, Oscillators, Resonators, Signal attenuation, Instrument modeling, Ultrasonics
Finite element modeling is being adopted in the design of ultrasonic transducers and imaging arrays. Impetus is accelerated product design cycles and the need to push the technology. Existing designs are being optimized and new concepts are being explored. This recent acceptance follows the convergence of improvements on many fronts: necessary computer resources are more accessible, lean, specialized algorithms replacing general-purpose approaches, and better material characterization The basics of the finite element method (REM) for the coupled piezoelectric-acoustic problem are reviewed. We contrast different FEM formulations and discuss the implications of each: time-domain versus frequency domain, implicit versus explicit algorithms, linear versus nonlinear. Beyond discussions of the theoretical underpinnings of numerical methods, the paper also examines other modeling ingredients such as discretization, material attenuation, boundary conditions, farfield extrapolation, and electric circuits. Particular emphasis is placed on material characterization, and this is discussed through an actual "modelbuild-test" validation sequence, undertaken recently. Some applications are also discussed. Keywords: Arrays, Attenuation, Finite Element Method, Imaging, Piezoelectric, Transducer, Ultrasound
The current image-theoretical basis for phase shifting masks (PSMs) relies on the scalar and Kirchhoff approximations, which neglect vector wave and edge diffraction effects around the mask. In this paper we use EMFlex finite element modeling to quantify vector diffraction effects, and show a method for modeling broadband illumination using the code's transient (optical pulse) capability and the Fourier transform in time. Simulations indicate that: the Kirchhoff approximation applied to etched quartz PSMs can lead to unacceptable errors due to a dark boundary layer on the quartz sidewall; diffraction produces relatively strong vector wave fields near feature edges but their contribution to the lithographic image is negligible; and the paraxial partial coherence approximation is generally valid for 4x or 5x projection systems. We discuss examples illustrating needs for better PSM metrology and phase measurements.
Optical modeling on the computer can aid R&D efforts to enhance metrology methods, and similarly for lithography, alignment, and particulate monitoring. However, full exploitation of optical modeling is hindered by the lack of appropriate benchmarks for verifying algorithms and evaluating approximations. To help remedy this situation we describe a preliminary set of scalar, 2-D numerical reference models (NRMs). These include isolated thin and thick lines, periodic lines, and an isolated trench. Scattered fields are compared for three different solution methods, based on time-domain finite elements, boundary integrals, and a waveguide model. Correlation is good in general, although important differences are seen in both code accuracy and performance. NRM generalizations are suggested that accommodate 3-D effects, imaging, and experimental verification.
This paper describes a three-dimensional computer modeling technique for alignment system simulation, and some example calculations. The technique has been developed to address issues of alignment and overlay accuracy for future generation VLSI technology. The analytical basis is a general finite element electromagnetic wave propagation code, EMFlex, that rigorously simulates light scattering from the 3-D alignment mark. Using the Nikon Laser Step Alignment (LSA) system as a model instrument, the overlay error and signal shape are simulated. Examples of an idealized asymmetric metal mark are studied. Preliminary results suggest that the rigorous simulations are substantially different from the one-dimensional Fresnel approximations that have been used previously.
IC fabrication problems grow as nominal feature sizes shrink, due in large part to fundamental optical diffraction limits. Currently, one of the most pressing needs is robust critical dimension measurement. However, optical methods must be refined for this scale of submicron metrology, particularly in the case of thick features. This paper examines the problem of reflected light microscopy for nominal 1 micron high lines on silicon using 2-D, time-domain finite element simulations. The experimental basis is a prototype line width standard that is characterized using optical, contact, and SEM measurements. Microscope and simulated images are compared for 1 and 3 micron wide lines. Good first-order correlation is found between real and synthetic images but model uncertainties need to be reduced and microscope aberrations need to be quantified before second-order differences can be eliminated. Numerical experiments are used to relate images to resonance patterns in the feature; determine the strength of evanescent waves near the line; and contrast isolated and periodic line images as a function of pitch.
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