ABSTRACT. Since 1960 California's Sierra Nevada counties have ranked among the regions with the strongest relative population growth in the state. Reassessment of peripheral areas has been the main force driving population and settlement growth in the central Sierra Nevada of California and Nevada, termed “amenity migration” or “counterurbanization.” This study analyzes the impacts of amenity migrants—“urban refugees”—on socioeconomic conditions in high‐mountain regions. We define these regions as the “High Sierra,” comprising zones at elevations more than 1,800 meters above sea level. People who migrate to the High Sierra tend to be white and well educated, with considerable household earnings. Unlike the population in the foothills, these migrants are not senior citizens. Their demand for periodic or permanent residences has caused housing prices to increase enormously. As a result, a majority of homes are now priced well beyond the reach of local salaries, which may lead to potential conflict between locals and newcomers. The massive settlement expansion in high‐mountain areas requires a new approach to land‐use planning, one that takes functional regions into account. Therefore, it is expedient to reassess existing jurisdictional boundaries.

Semiconductor lasers with a wide tuning range can be fabricated with the use of super structure gratings (SSG). In this paper we give a short introduction to SSGs, the technical problem of their realization and the existing techniques to generate SSGs. A method is presented to generate 'true' continuously chirped gratings overcoming the technical restrictions.Furthermore we make a proposal how to characterize SSGs in resist profiles. lithography INTRODUCTIONTunable lasers with a wide wavelength range are key components for high-performance optical telecommunication systems. Unfortunately state-of-the-art lasers with Bragg gratings of a fixed periodicity exhibit a rather narrow tuning range of only a few nanometers due to the limits in the change of the refractive index' achievable by current injection. Simulations and first experimental results have shown that the tuning range of a semiconductor laser can be extended to about 100 nm by the use of super structure gratings (SSG)2'3. Similar to conventional DBR gratings the SSG consists of repeating bars, the pitch however being continuously slightly changed ('chirped'). Usually the pitch of a SSG linearily chirps from a Bragg period AA to a period AB over the distance of the super period As. This arrangement is repeated several times in a regular (see Fig. 1) or irregular manner. Pitch As z A5 AA N NN AA AB a)ABN' b)fl J1J__l:x Fig. 1 Concept of a linearily chirped SSG demonstrated in a) the frequency range and b) the space rangeWhereas a conventional distributed Bragg reflector shows a single reflection peak, the SSG reflector exhibits multiple reflection peaks due to the periodical super structure arrangement5. The oscillation wavelength of a DBR laser can be adjusted by selecting a mode from among these peaks. Several mechanisms for wavelength tuning with SSGs have been decscribed, e. g. for tuning with multiple-phase-shift SSGs5. The main drawback of generating 'true' continuously chirped gratings is the required positioning accuracy of down to a few tenths of Angstroms. Typical values for AA = 245 nm, AB = 230 nm and A = 61.600 pm result in a medium pitch variation of about 0.05 nm which has to be addressed in the electron-beam writer (e-beam). Several simplified versions of SSGs have been fabricated: sampled gratings2 consist of short regions of a conventional grating seperated by non-structured sections, discretely chirped gratings3 use steps of the utmost minimal resolution of the electron-beam writer, multiple-phase-shift SSGs4 comprise additionally inserted phase shifters at appropriate positions in an uniform grating.We present a method to generate SSGs with almost no limitation by the beamwriters resolution and give a proposal to characterize SSGs realized in resist. 204 ISPIE Vol. 2437 0-8194-1785-8/95/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

The paper describes the procedures and preliminary results of accelerated life tests performed in the frame of an evaluation programme under ESA -contract. For the calculation of activation energy and median life time, and in order to investigate the drift behaviour ofoptical parameters, a conventional three temperature ageing test at 30°C, 50°C and 70°C is being performed on 80 laser diodes in total, split into two subgroups operating under quaternary pulse position modulation (QPPM) and non return to zero (NRZ) modulation at l6Mbitis with a PN-code length 2-1. The hermetically sealed diodes of the three selected laser types are operated for 3500hrs under automatic average power control with lO4mWpeak/3OmWaverage for QPPM and SlmWpeak/42mWaverage power for NRZ. The failure criterion is 30%-increase ofthe bias current, continuously monitored by computer. Intermediate measurements of the lasers PJI-curves, V/I-characteristics, far field patterns and spectra for purpose of s-calculation are performed. leasurements before and upon completion of the ageing tests consist of Pa/I-curves, V/I-characteristics, photo diode tracking ratios, spectra, mode hopping behaviours, far field patterns, wave front errors and astigmatisms and linear polarization ratios.

No abstract