Strength of homophonic substitution ciphers

For example, given $\mathcal{A}=\{x,y\}$, $H(x)=\{00,10\}$, and $H(y)=\{01,11\}$. The plaintext $xy$ would encrypt to one of $0001,0011,1001,1011$.

However in this cipher, multiple-letter patterns still survive in the ciphertext as each element of plaintext affects only one element of ciphertext. We look at two methods to lessen extent to which the structure survives in the ciphertext: Playfair cipher and Vigenère cipher.