Optical Sources

Hi Salwa! Can you, please, clarify what are you using LED in your scheme for?

If I understood you right, you are trying to calculate the bandwidth of your CW-laser source without modulation with given central/carrier frequency, right?

hi salwa,
i) for your first question check it out the following link to get the answer
http://en.wikipedia.org/wiki/Laser_linewidth
ii) PIN diode is sufficient for optical reception. if u need further amplification at detector it self mean go for APD. APD is optional one for your different requirements

In general line width of the system is defined by trans. bit-rate in a channel. The line width of the system combines from line width of its channels + filtering. As far as optical pulses from CW-laser are Gaussian, you can use Gaussian pulse relations to determine its width.

All has the function of photo detectors convert light into electrical current has to be polarized to reverse form. Regardless of the type of fiber PIN detectors generally operate in the area between 850 to 1310 µm. advantages: more robust that the APL detectors, technology and application less costly, less semiconductor material, useful life greater than other detectors. Disadvantages: power to low power signals detection unless the APD detectors, response time is smaller than the other detectors, the signal-to-noise ratio detriment this type of detector. APD-“Avalanche Phodiode”: The APD Photodetectors are Photodetectors that combine optical signal detection with amplification (gain) of the photocurrent. Its main advantage is a high signal-to-noise ratio, especially at high bit rates. The photo-detector PIN is enough for your project primarily, has best features as linearity, lifetime, response time and the circuits of polarizations are simpler.

If you have more questions, please provide the requirements for your system so we can better help you!