Saving fast fourier transform (fft) plot to image

I have a code that tries to plot the fast Fourier transform of an image. When I use imshow function, the result looks fine, but when I try to save the result into an image using imwrite function, it's not just the same thing! Do I lack some other parameters in order to save the actual result? Here is the code below:

 %%INITIALIZE

 c = 299792458; %speed of light
 la = 633e-9; %wavelength
 k = 2*pi/la; %wavenumber
 L = .008; %side length(m)%.004
 W = L; %width
 M = 2^10; %number of samples 1024
 N = M;
 dx = L/M; %src sample interval
 dy = W/N;
 x = -L/2:dx:L/2-dx; %src coords
 y = -W/2:dy:W/2-dy; %src coords
 [X,Y]= meshgrid(x,y);
 Z = X+1i*Y;
 rho = sqrt(X.^2+Y.^2);
 rho0 = 0.00005; %threshold in forming 2D boolean matrix
 D = X.^2+Y.^2 <= rho0^2;%Binarize image, 0 kapag less than chosen rho.
 phi = angle(Z)+pi;%+pi angle returns phase angle of complex elements

 %%MAKE LAGUERRE-GAUSS BEAM
 for i = -5:5
    l = i;
    f = 0.5;
    u=D.*(rho.^abs(l)).*exp(1i*l*phi)+ D.*(rho.^abs(l)).*exp(1i*-l*2*phi);%Laguerre-Gauss

    %Fast fourier transform (FFT)x
    DP =fftshift(fft2(u));
    DM = abs(DP).^2;

    figure(1)
    imagesc(DM)
    axis image

    imwrite(DM,[num2str(l),'fft.bmp'])
 end

Any help and/or suggestion will be much appreciated. Thanks.