One option is to pay for a subscription to WolframAlpha Pro which allows you to upload much larger expressions.
Another option is to make use of substitutions to shorten your expression.
Since you use 2(A^2-B^2+A) in several places you can start with n=2(A2-B2+A), followed by the rest of your expression where you replace all 2(A^2-B^2+A) with n.
Then you can shorten all your multiple character variable names down to single character names, but avoid using variable names that WolframAlpha will assume have predefined mathematical meaning.
With that it appears to be possible to get your expression down within the string length limitation of WolframAlpha.
d=.05,k=.002,h=3300,m=1760,g=1.465*10^-7,n=2(A2-B2+A),l=n/(n+1),p=2B(2A+1)/(n+1)^2,B=o/(4 pi g m),A=h/(4 pi m),(s(2j d)(1+(k p)^2))/(cosh(2j d)±sqrt(1-(s(2j d)k p)^2))+l=0
Unfortunately, even though it appears that it might be short enough now, WolframAlpha cannot understand what you now want it to do with this long expression.
Sometimes it is possible to do a problem in two steps when using WolframAlpha. To do that you try to find a way to get a partial answer to your problem in one step, copy and paste that answer to form part of the rest of your final question. Can you see any way to divide your question into two parts that might be smaller?
Even with that I don't know what you are expecting the values of sh or eta to be.