Fig. 1. Schematic diagram of phase correction by introducing optical path difference through perturbations on reflecting surface

Fig. 2. Non-quadratic function contour for the phase correction mirror

Fig. 3. Field distribution of the reflected wave (a) normalized amplitude, (b) normalized phase

Fig. 4. Propagation process of wave entering the cavity and converging on a caustic surface

Fig. 5. The structure and geometric parameters of the open resonant cavity

Fig. 6. Cavity model of the mode generator

Fig. 7. Schematic diagram of quasi-optical mode generator system (a) overall model, (b) position relationship

Fig. 8. Comparison of the ideal field distribution and the simulation field distribution of TE_28,8 mode (a) ideal electric field distribution, (b) simulation result of electric field distribution, (c) E_x component of ideal electric field distribution, (d) simulation result of E_x component of electric field distribution, (e) E_y component of ideal electric field distribution, (f) simulation result of E_y component of electric field distribution

Fig. 9. Picture of assembled quasi-optical mode generator

Fig. 10. Tested results of the field distribution on the cross section at 100 mm from the phase correction mirror (a) field amplitude distribution, (b) phase distribution

Fig. 11. Cold test system (a) overall block diagram, (b) photo of the test site

Fig. 12. Frequency test result of the mode generator

Fig. 13. Measurement of the resonant frequency and Q factor for the TE_28，8 mode

Fig. 14. Measurements of the output field of quasi-optical mode generator (a) Electric field distribution of E_xcomponent, (b)eElectric field distribution of E_y component

Fig. 15. Phase distribution of E_x component

Fig. 16. Total electric field distribution in the cross section