Tetrahedron Equation and Quantum R Matrices for Modular Double of $${{\varvec{{U_q(D^{(2)}_{n+1})}}, \varvec{{U_q (A ^{(2)}_{2n})}}}}$$ U q ( D n + 1 ( 2 ) ) , U q ( A 2 n ( 2 ) ) and $$\varvec{{U_q(C^{(1)}_{n})}}$$ U q ( C n ( 1 ) )

We introduce a homomorphism from the quantum affine algebras $U_q(D^{(2)}_{n+1}), U_q(A^{(2)}_{2n}), U_q(C^{(1)}_{n})$ to the $n$-fold tensor product of the $q$-oscillator algebra ${\mathcal A}_q$. Their action commute with the solutions of the Yang-Baxter equation obtained by reducing the solutions of the tetrahedron equation associated with the modular and the Fock representations of ${\mathcal A}_q$. In the former case, the commutativity is enhanced to the modular double of these quantum affine algebras.