| 1. |
- Carlsson, Christina, 1975
(författare)
-
Design and Evaluation of Vertical Cavity Surface Emitting Lasers for Microwave Applications
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the rapid developments of wireless communication networks such as cellular systems for mobile communication and wireless local area networks, as well as developments in radars and defence systems, there is an increasing demand for efficient and cost-effective transmission and distribution of RF and microwave signals. In this respect, fiber optics provide advantages such as low loss, mechanical flexibility, low weight, and natural immunity to electromagnetic interference, enabling densely spaced and electrically isolated transmission paths. Semiconductor lasers are used as light sources in such links where modulation of the RF signal onto the optical carrier is most easily achieved by directly modulating the laser. With increasing demand for cost-effective solutions, it is also of interest to find low cost components. For short range transmission of digital signals in local area networks and interconnects, the vertical cavity surface emitting laser (VCSELs) has established itself as a low cost, high performance alternative to edge-emitting lasers. As the requirements on the light source used in analog systems differ in some respects from the requirements on a light source in digital systems, especially in terms of noise and linearity, it is the purpose of the work presented in this thesis to investigate whether VCSELs also fulfill basic performance requirements for analog fiber optic links in the low-GHz range. Different GaAs based VCSEL designs are investigated with respect to their high frequency modulation characteristics in order pin-point limitations and to find the optimum design. Fiber optic RF links using VCSELs and multimode fibers are also assembled and evaluated to demonstrate that potentially low cost and high performance links can be constructed. It is found that optimised single mode VCSELs provide the highest performance and that the performance of links using VCSELs and high bandwidth multimode fibers satisfies the requirements in a number of applications, including radars, mobile communication systems, and wireless local area networks. The performance is also comparable to that of more sophisticated single mode fiber links using edge emitting lasers. However, the cost of a link using a VCSEL and a multimode fiber should be lower due to lower component costs and larger misalignment tolerances.
|
|
| 2. |
|
|
| 3. |
- Carlsson, Christina, 1975, et al.
(författare)
-
RF transmission over multimode fibers using VCSELs-comparing standard and high bandwidth multimode fibers
- 2004
-
Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 22:7, s. 1694-1700
-
Tidskriftsartikel (refereegranskat)abstract
- Fiber-optic radio-frequency links have been assembled using oxide-confined vertical-cavity surface-emitting lasers (VCSELs) and multimode fibers. Links with single and multimode VCSELs and with standard and high-bandwidth fibers have been evaluated and compared in the frequency range of 0.1-10 GHz. The best results were obtained for links with a multimode VCSEL and a high-bandwidth fiber. For a 500-m-long link, a spurious free dynamic range of 104 dB. HZ(2/3) at 2 GHz and 100 dB (.) Hz(2/3) at 5, GHz were obtained while allowing for a VCSEL-fiber misalignment of +/-12 mum. Corresponding numbers for the intrinsic link gain and noise figure are -29 and -33 dB, and 39 and 42 dB at 2 and 5 GHz, respectively. Inferior performance Was observed for the standard fiber link due to a larger variation in modal group velocities. This paper also presents a detailed link analysis to identify performance limitations and to suggest modifications for improved performance.
|
|
| 4. |
- Frih, Anna-Karin, 1975-
(författare)
-
Flickan i medicinen : ungdom, kön och sjuklighet 1870-1930
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main purpose of this thesis is to study and analyze how concepts of childhood and adolescence were constructed in scientific medicine during the period 1870 to 1930. The focus in the first part of the thesis is to study the sick girl as a stereotype in 1870–1900. In the late nineteenth-century, the poor health of girls was a popular topic in Swedish medical discourse. It was a well-established opinion that a substantial number of Swedish girls suffered from various diseases and ailments. Mass- and coeducation was under debate and physicians became interested in the impact of schools and schooling on children’s health. It is here shown that children, and in particularly adolescents, were de-fined as gendered creatures. The doctors emphasized the universal nature of adolescence and conceptualized pu-berty as a traumatic and risky stage of life and they also tended to focus on middle-class girls. Pubescent girls were seen as most vulnerable to external stress such as mental strain and physical demands. Physicians claimed that ill health inevitably followed when girls were educated in the same way as boys. However, boys and their health were discussed too. The most common ailments for both girls and boys were overstudy, anemia, headaches and disor-dered digestion. It was also shown in various studies, that poorer children were substantially inferior in weight as well as in height. Chlorosis was a common theme in late nineteenth-century medical discourse. Although it appeared mainly as a girls’ disease in medical books and in most sanitary journals, health studies for example, showed that chlorosis could also be a boys’ disease. However, sick boys were rarely spoken of. Medical opinions on overstudy, chlorosis and dress reform could be interpreted as a concern for unhealthy girls as future mothers of the nation. It is not my intention to advertise doctors as vicious oppressors, as opponents of female emancipation. In fact, the doctors often pointed out social factors and unequal circumstances of childhood and adolescence for girls and boys. In early twentieth-century, the scientific opinion of girls changed. Even though gendered notions of children and youths persisted all through the period studied, more and more some doctors, Karolina Widerström, for example, began to question them. The new girl was not weak and ill, but rather healthy and active. However, a dividing line between those who claimed the weakness of girls and those who emphasized the new, healthy girl became more evident after 1900. In this thesis, this disparity is discussed in terms of popular medical discourse and scientific medi-cal discourse. In the latter, girls were still described as more sensitive and more frail than boys and as unfit for higher education and strenuous schoolwork. Thus, the new girl – vivid, healthy and equal to the boy – was above all a con-struction in popular medicine. The uniform medical discourse on girls from the late nineteenth-century thus dissolved. A number of changes in the medical discourse on sickness and health of girls and boys during in this period occurred. First, concepts of sickness and health were modified over time and fewer schoolchildren were considered sick. Fi-nally, in the beginning of the period studied, girls were sicker than boys were, but in the end, in the 1930s, there was no obvious gender difference. Both sexes seemed equally sick (or healthy).
|
|
| 5. |
|
|
| 6. |
|
|
