4-membered ring compound and optical phase optical retardation plate using the same

A 4-membered ring compound represented by the following formula (I):

• (in the formula, X1 and X2 each independently represent an oxygen atom, a sulfur atom or a substituted or unsubstituted imino group, Y1 and Y2 each independently represent a single bond, an oxygen atom or a substituted or unsubstituted imino group, B1 and B2 each independently represent an optionally substituted aliphatic group, aliphatic carbonyl group, aromatic group or aromatic carbonyl group, having 1-20 carbon atoms, two of the benzene rings directly bonding to the cyclobutane ring each may have a substituent on the rings, and A1 and A2 each independently represent a group represented by the following formula (II):
• (in the formula, Ar1, Ar2 and Ar3 each independently represent a cyclic group having 5-14 carbon atoms, which may have a substituent on the ring, L1 and L2 each independently represent a single bond or a divalent linking group, p represents an integer of 0-2, and when p is 2, two of Ar2 and two of L2 may be identical to or different from each other)).