MIRRORLESS OPTICAL PARAMETRIC OSCILLATORS

We have considered two novel configurations for optical parametric osc illators (OPO's): transversely-pumped counter-propagating and nondegen erate backward OPO's due to the distributed feedback provided through the opposite propagation directions of the signal and idler. In both c onfigurations, by changing the incident angle of the pump beam, one ca n tune the output frequency in a large range. The threshold pump power s for the oscillation can be as low as similar to 10 W for the transve rsely-pumped counter-propagating OPO's and 44 W for the nondegenerate backward OPO's. The quasi-phase matching is achieved by spatially modu lating second-order susceptibility along the growth direction based on semiconductor alternating thin layers or asymmetric quantum-well doma in structures or by electric-field poling in conventional second-order nonlinear materials. The nondegenerate backward OPO's offer the most efficient conversion among all the configurations for the OPO's having the same threshold pump power. The transversely-pumped counter-propag ating OPO's have the optimal pump power.