best laser for FSO

hi umer
you should choose class 1 type of laser with power < 10 mw for 1550 nm and < .22 mw for 850 nm( these all for eye saftey)

Hello Umer,

Mostly semiconductor lasers are used for FSO. There are several advantages of semiconductor lasers for free space optics (FSO) compared to LEDs: Better optical spectrum, high optical output, advantages for beam shaping, and so on. There are several atmospheric transmission windows and high quality semiconductor lasers with a suitable wavelength for these windows are available.
One big advantage of FSO is the possibility to install a link within hours because there are no construction permits and time consuming construction work necessary.
There are disadvantages as well: The availability of the link is less than 100% especially in regions with fog, sand storms, and so on. A work around is the combination of a FSO link with a microwave link. It increases the availability of the link to nearly 100%.

I hope this would give you some idea.

Regards
Burhan

Hello Umer,
I would also like to mention that semiconductor laser , for instance VCSEL array has been proposed as a concept of a compact FSO communications terminal thanks to their high reliability and high-speed modulation (2.5 Gb/s) under high optical power operation (Advanced Free Space Optics (FSO))
also some attractive features of semiconductor lasers, for instance the chaotic dynamics with and without an external perturbation make them an attractive devices and have become widely use in FSO system.Most commonly used lasers in today’s commercial FSO products are:
– Edge Emitting Lasers
– VCSEL
VCSEL is easier to modulate, but generally much lower in power, which limits link budgets, beamwidths and useful operational distances.
This is why most successful long range FSO devices use edge emitting lasers.
There are also some novel types of lasers considered including VECSEL, which we collaborated on two recent projects which were aimed to develop the actual devices.

I hope it will be of some help to you.
Regards
Burhan

Hello umer ashraf wani

Well yeah… safety is a major concern. But wavelengths greater than 1400 nm help us avoid health hazards due to laser power because at these wavelengths the absortion coefficient by the eye is very high..so negligible amount of laser power is able to reach the cornea.

Regards
Naazira Badar

Dear friend;
Mostly semiconductor lasers are used for FSO. There are several advantages of semiconductor lasers for free space optics (FSO) compared to LEDs: Better optical spectrum, high optical output, advantages for beam shaping, and so on. There are several atmospheric transmission windows and high quality semiconductor lasers with a suitable wavelength for these windows are available.
One big advantage of FSO is the possibility to install a link within hours because there are no construction permits and time consuming construction work necessary.

Hi
I agree with Mr Burhan. You should keep the bandwidth restricted to 15 GHz. I understand your concern about bandwidth of channels but Burhan is right the bandwidth of mux is bandwidth of filter actually. I agree to the point that if the bandwidth is reduced, many signals with higher frequencies get distorted as they fall out of the pass band of the filter. This means they cannot be correctly detected at the receiver.
So i will suggest to use 5 GHz more than the default value.
Hope this will be of some help.
Thanks

I am not sure about channel spacing. You may refer to few threads here that mention channel spacing be it equal channel spacing or unequal channel spacing.
Here are few links. You may refer to them
http://link.springer.com/chapter/10.1007%2F978-1-4020-8741-7_1#page-1
https://www.researchgate.net/publication/261320396_Duobinary_modulation_format_and_unequal_channel_spacing_integration_to_suppress_four-wave_mixing_crosstalk_in_WDM_systems
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5876926&abstractAccess=no&userType=inst

Also go through these threads https://optiwave.com/forums/topic/bande-width/

signal bandwidth

Hope this will be useful.

Regards

Burhan

You are welcome. Cheers

Hello Umer Ashraf Wani.

You could use 10 Ghz as well. we have had a number of discussion over wdm MUX bandwidth over here but a conclusive statement could not be reached as to should the BW of WDM-MUX be n x10Ghz , where n is the no. of channels.

Links to few relevant discussions: https://optiwave.com/forums/topic/bandwidth-parameter-for-each-component/

DWDM system

About channel spacing, i believe you need to just change the wavelength to modify the channel spacing, or is it something else that you are asking?

Best Wishes
Naazira Badar

Hello Naazira,

Yes i remember this was discussed previously as well and no conclusion was reached but yeah in my opinion it is the bandwidth of the filter in multiplexer and what confuses us here is that we think the bandwidth should be large enough to accommodate the channels ( be it 4 channels or 8 channels) and we think the bandwidth should be as large as possible but i don’t think it is the case.
Anyway i hope the discussed stuff will help Umer Ashraf in one way or other.

Regards

Burhan

You are welcome anytime. The forum is a platform for the same.
Healthy discussions are always welcome.

Regards

Hello everyone,
As mentioned by other forum members about this topic being discussed already i would like to add here that the bandwidth of a Multiplexer or a demultiplexer refers to the bandwidth of the filters used for each channel of the implemented WDM system, whereas the bandwidth in some other components such as amplifiers is the bandwidth of operation of that specific component. There was a lot of confusion regarding this topic and as mentioned by naazira no conclusion was reached. I would suggest you to look at the links and go through them. May be these can help you.

Bandwidth parameter for each component

DWDM system

bande width

signal bandwidth

I Hope this will be helpful in some or the other way.
Regards

Hello,
As far as Lasers for FSO are concerned, Free-space laser communication offers an attractive alternative for transferring high-bandwidth data when fiber optic cable is neither practical nor feasible. However, there are a variety of deleterious features of the atmospheric channel that may lead to serious signal fading, and even the complete loss of signal altogether. Physical obstructions—such as birds, insects, tree limbs, or other factors—can temporarily or permanently block the laser line-of-sight. Platform/building motion due to wind, differential heating and cooling, or ground motion over time can result in serious misalignment of fixed-position laser communication systems. But most importantly of all, absorption and scattering due to particulate matter in the atmosphere may significantly decrease the transmitted optical signal, while random atmospheric distortions due to optical turbulence can severely degrade the wave-front quality of a signal-carrying laser beam, causing intensity fading and random signal losses at the receiver.
You may refer to http://link.springer.com/chapter/10.1007/978-0-387-28677-8_2

Regards

Most commonly used lasers in today’s commercial FSO products are:
Edge Emitting Lasers
VCSEL
A vertical-external-cavity surface-emitting-laser (VECSEL) is a small semiconductor laser similar to a vertical-cavity surface-emitting laser (VCSEL). VECSELs are used primarily as near infrared devices in laser cooling and spectroscopy, but have also been explored for applications such as telecommunications.
One of the most interesting features of any VECSEL is the thinness of the semiconductor gain region in the direction of propagation, less than 100 nm. In contrast, a conventional in-plane semiconductor laser entails light propagation over distances of from 250 µm upward to 2 mm or longer. The significance of the short propagation distance is that it causes the effect of “antiguiding” nonlinearities (the same phenomenon is coincidentally quantified by the linewidth enhancement factor relating to Mooradian’s above-mentioned earlier work) in the diode laser gain region to be minimized. The result is a large-cross-section single-mode optical beam which is not attainable from in-plane (a.k.a. “edge-emitting”) diode lasers.
I hope it wiil be helpful
Regards

kyo pure forum ki barah baza rahi? please don’t make irrelevant post

Hi all,

Please do not repeat what has been already posted. I appreciate your efforts but it is irritating at times.
Thank you

Regards

Burhan