Let \( e_1 \) be the eccentricity of the hyperbola \(\displaystyle \frac{x^2}{16}-\frac{y^2}{9}=1 \) and \( e_2 \) be the eccentricity of the ellipse \(\displaystyle \frac{x^2}{a^2}+\frac{y^2}{b^2}=1, a>b \), which passes through the foci of the hyperbola. If \( e_1 e_2=1 \), then the length of the chord of the ellipse parallel to the \( x \)-axis and passing through \( (0,2) \) is:
