How to make image interpolate to subplot size matplotlib

Question

I have the following subplot in my code -

import matplotlib.pylab as plt

fig, axes = plt.subplots(3, 6, figsize=(20, 9), sharex=True, sharey=True)

for i in range(6):
    ax = axes[1, i]
    ax2 = axes[2, i]
    ..

    ax.imshow(im_pool, cmap='gray')
    ax2.imshow(get_fft_plot(im_sp[0]), cmap='gray',interpolation='bilinear')

    if not i:
        ax.set_ylabel('Spectral Pooling', fontsize=16)
        ax2.set_ylabel('Fourier Transform', fontsize=16)

It prints the following plot:

All images displayed on ax are size nXn. The images displayed on ax2 are size pooled images of the original n X n image and hence smaller in size than n X n.These images are not getting interpolated to fit the frame of the subplot even after using interpolation = 'bilinear' in imshow. How to interpolate the images to the size of the subplot frames?

Thanks in advance for any help.