higher NA fibers "collect" more light, this is more noticable in LED lighting as it's a more divergent beam.

Are you going to use the same lasers?

No the laser I was using is blue one 473 nm, Now I will use a green laser 534 nm.

Can you check your NA value for the given wavelength you are using. Are you using high NA but longer wavelength ones. I checked Thorlabs website, but could not find the NA value as you mentioned as 0.22 NA. Are they 0.28 NA but 1100 nm to 1600 nm working wavelength SM fibers?

Since the wavelength is very small, even in green. So the high NA fiber is unlikely work at this wavelength as it confines the optical mode so tight than the regular SM silica core fiber. So I don't think the fiber itself really matters for 0.22 (assume it exists) for 532 nm. You can't find higher NA fiber working at the wavelength you are using. Unless you have to use a microscope objective. Then it matters only for the choice of objective NA rather than fiber.

there should be no problem using the same fiber.

higher NA is not needed

Thanks for your ansers.

Zhizhong Yan here is a link to the thorlab wesite where there is the 0.22 NA optical fiber https://www.thorlabs.de/thorproduct.cfm?partnumber=FG200UEA.

Khalki, I thought it was single mode fiber, you are using multimode instead. I recommend using some fiber lens or microscope objective if you think the intensity is not sufficient, otherwise just stay with the same multimode fiber as you used before.

In the same optical fiber, changing wavelength from λ=473nm to λ=534nm will change the v-number of the optical fiber. The v-number of a fiber is defined as v=2πɑ/λ x N.A. Here ɑ is the diameter of the fiber and N.A is 0.22, both are same for the same fiber. Here, the v-number will change due to change in wavelength λ and it will get reduced. Lower v-number here will not allow higher mode numbers to pass.

Stick with the 0.22 NA fibre. Any increase in NA makes the light coming out the end scatter more, decreasing your effective stimulation distance. Doesn't matter which wavelength you are using, or whether it's lasers or LED's. Yes, even LED's, because with a higher NA fibre you need ridiculously high light output to maintain your stimulation depth.

For example, in a typical experiment with a 200um fibre and requiring an irradiance of 1mW/mm^2 to activate ChR2, if you wanted to have effective stimulation for 1 mm from the end of your fibre, you would need approximately 4.6 mW from a 0.22 NA fibre. But if you used a 0.50 NA fibre, you would need 16.2 mW. I ran these calculations based on the Aravanis model, and using my online optogenetics power calculator at: https://nicneuro.net/power-calculator/