Based on a hypothetical 51.2 Tbps switch using co-packaged optics, we discuss key optical connectivity considerations and lay out different cabling options. Means are discussed to relax the length-accuracy requirements for fiber jumpers while maintaining a crossing-free cable layout for ease of assembly and serviceability. A key consideration is the mechanical stress in the fiber terminations which can lead to a degradation in the polarization integrity of external laser sources.
Hybrid injection-molded ferrules are presented which consist of a polymer body and an over-molded glass insert. The average coefficient of thermal expansion observed at the front face of the ferrules is 8 ppm/C from room temperature to 100 C. This design could be applicable for direct heterogeneous re-matable connections between fiber ribbons and photonic integrated circuits which exhibit low thermal expansion and operate at elevated temperatures.
Silica glass exhibits a permanent anisotropic response, referred to as polarization induced birefringence (PIB), when
exposed to short wavelength, polarized light. The magnitude of the PIB has been empirically correlated with the OH
content of the glass. Our recent studies pertaining to PIB have focused on careful characterization of PIB, with particular
emphasis on understanding all of the contributions to the measured birefringence signal and finally extracting only that
signal associated with birefringence arising from exposure to a polarized light beam. We will demonstrate that a critical
contributor to the total birefringence signal is birefringence that comes from exposure beam inhomogeneities. After
subtracting beam profile effects we are able to show that PIB is proportional to the OH content of the glass. Polarized
infrared (IR) measurements were performed on glasses that developed PIB as a consequence of exposure to polarized
157-nm light. These studies reveal that there is preferential bleaching of a specific hydroxyl (OH) species in the glass
with OH aligned parallel to the incident polarization undergoing more bleaching than those perpendicular. Further, we
observe a very strong correlation between the measured PIB of these samples and the anisotropic bleaching. From these
studies we propose a mechanism that can explain the role of hydroxyl in PIB.
Fused silica, when exposed to excimer laser light, exhibits permanent anisotropic birefringence and wavefront changes. These laser-induced changes depend on the silica composition and processing conditions. The optical anisotropy is most clearly observed in samples that are exposed with linear polarization. This polarization-induced effect has been known for several years, but has become much more important with the advent of immersion lithography and its associated very high numerical apertures. High numerical aperture optics require controlled polarization, notably linear polarization, in order to maintain phase contrast at the image. When birefringence and wavefront changes are induced by laser exposure, the image contrast at the wafer deteriorates. We interpret the changes in optical properties in terms of permanent anisotropic strain induced by laser damage, and the associated strain-induced optical effects. This is accomplished using the mathematics of tensors to account for anisotropic strain and optical anisotropy, and using finite element analysis to calculate the strain fields taking the sample and exposure geometries into account. We report the relations between underlying density and strain anisotropy changes and the induced birefringence and wavefront for a given experimental sample geometry. We also report some examples of the different degree of laser damage from silica with different compositions and processing conditions.
A method capable of measuring the internal transmittance Ti of fused silica @193 nm with a precision better than 0.01 %/cm (3σ) is presented. The basic idea is to vary the optical pathlength during the measurement within one and the same prism-shaped sample by moving the latter through the optical test beam. In comparison to the standard multiple-sample experiment this greatly relaxes the requirements for the repeatability of surface preparation. Lack of any standards makes it currently impossible to determine the absolute accuracy experimentally. However, calculations indicate that it is very likely within 0.02 %/cm (3σ). The application to materials and wavelengths other than what were chosen here for demonstration is straightforward.
Birefringence mapping of fused silica samples is used to measure density change in the material after exposure to excimer laser radiation. The proper techniques and methods that should be used to perform the exposure of the samples and the analysis of the birefringence results will be discussed. The quantitative analysis of birefringence measurements includes the correct subtraction of the initial birefringence of the sample and the comparison with a theoretical birefringence map calculated for a 1 ppm unconstrained density change under consideration of material and exposure parameters. Proper experimental conditions include the use of samples with low initial birefringence and a round circularly polarized laser beam with top-hat intensity profile.
The nonlinear optics of excitons in ZnSe-based heterostructures is investigated by means of fast femtosecond and narrow-band picosecond differential transmission spectroscopy. Pulse lengths amount to 100 fs and 1 ps, respectively. Results taken at Zn1-xCdxSe/ZnSe quantum wells, ZnSe layers with ZnSxSe1-x cladding, and ZnSe epilayers are presented and discussed. Because of strain relaxation the usual bleaching of the excitonic absorption observed in quantum wells and waveguide-type structures reverses into an induced absorption in case of thick ZnSe epilayers. This phenomenon is discussed by use of a simple empirical model for the optical absorption of a set of inhomogeneously broadened Lorentz oscillators which react on the local exciton density with a nonlinear damping and a reduction of the oscillator strength. Additionally, a very fast change in transmission observed in the waveguide-type structures is discussed in terms of the resonant optical Stark effect.
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