英語(yǔ)翻譯
SIMULATION IN OPTISYSTEM SOFTWARE
OptiSystem is an innovative optical communication system simulation package that designs,tests,and optimizes virtually any type of optical link from the physical layer to the transport layer according OSI model [6].OptiSystem is a stand-alone product that does not rely on other simulation frameworks.It is a system level simulator based on the realistic modeling of optic communication systems.It possesses a powerful new simulation environment and a truly hierarchical definition of components and systems.Its capabilities can be extended easily with the addition of user components,and can be seamlessly interfaced to a wide range of tools.
In this program there was created a FSO link.At the start there was CW laser with wavelength 850 nm (1550 nm) and optical power 0dBm.Pseudo-random bit sequence generator produced data which were modulated on the optical carrier wave by using external modulator.It was used NRZ modulation.This signal was transferred by the atmosphere,the FSO link length was set 1 km.At the end was placed PIN photodetector.PIN fotodetector converts optical signal back to the data.PIN photodetector was set subsequently:responsivity 1 A/W,dark current 10 nA,thermal noise 100e- 24.
Other parameters of FSO link were subsequent.Transmitter aperture diameter was 5 cm,receiver aperture diameter 10 cm,beam divergence 0.25 mrad.
The FSO component in OptiSystem allows calculate the turbulence attenuation only by Andrews’s method [6],therefore in this article there are compared the theoretical
values and measured values according Andrews’s method.It is not possible to compare other methods,because the software includes only Andrews’s method.
range of tools
RESULTS
At first it was set the wavelength 850 nm,the atmospheric attenuation coefficient 0 dB/km and the index refraction structure Cn 2 10-15 m-2/3.This low index refraction structure means very low or no turbulences.Then it was measured the optical power at the end of FSO link.The obtained value was not zero because the beam was attenuated by propagation attenuation.But the turbulence attenuation was practically
zero,because the index refraction structure was very low.The obtained received power was used as a reference value for other optical powers by varying index refraction structure parameter.The results for wavelength 850 nm are in the table
and are displayed in Fig.5.The red curve is result from OptiSystem,the blue curve are calculated values.
The same procedure was used for wavelength 1550 nm.All parameters were set the same,only the wavelength was changed from 850 nm to 1550 nm.The results for wavelength 1550 nm are in the table and are displayed in Fig.6.The red
curve is result from OptiSystem,the blue curve are calculated values.