In this paper, we discussed the theory of the double loop optical buffer (DLOB) based on collinear 3×3 coupler, and put forward 4 types of read-write methods in DLOB: positive optical pulse control, negative optical pulse control, positive electrical pulse control and negative electrical pulse control. We also introduced 0.89π-phase adjusting method. A double loop optical buffer experiment system had been built in which the loop was 63 meter length. The experiment had not only proved 4 types of read-write methods, but also demonstrated that the negative optical pulse control was the only doable method when the optical packets traversed in DLOB exceeding 20 round-trips. In order to suppress the noise, we can enhance the bias current of the control light, the “base” power of the control light was required from 500 μW to 1 mW by the way of enhancing the bias current of the control laser, or injecting a direct light whose wavelength was different from the signal light and control light. In the electrical pulse control, it also needed injecting a direct light to suppress the noise.