question: How is the degeneracy between two counterpropagating modes revoked in a ring resonator with angular momentum modulation? option 1: By changing the resonance frequency of the cavity through magnetic materials option 2: By changing the modulation frequency of the angular momentum option 3: By applying spatial modulation to the ring resonator option 4: By breaking the time-reversal and spatial-inversion symmetries option 5: By changing the phase constants along the waveguide 