Multifocal system with polarization-independent focusing

A multifocal system for focusing an incoming light beam to form an outgoing light beam, the system comprising:

• a polarization beam splitter (PBS) arranged to split the incoming light beam into first and second linearly-polarized (LP) light beams mutually orthogonal to each other in polarization orientation;
• a variable-focusing module for focusing an input LP light beam to form an output LP light beam, the variable-focusing module having a first end and a second end such that the input LP light beam is allowed to enter into the variable-focusing module through one of the two ends to generate the output LP light beam leaving from another one of the two ends, a forward propagation direction being defined as a direction from the first end towards the second end, a backward propagation direction being defined as a direction from the second end towards the first end, the variable-focusing module comprising:
• a front-end quarter waveplate (QWP) located at the first end for converting the input LP light beam received at the first end into an incident circularly-polarized (CP) light beam, both the input LP light beam and the incident CP light beam traveling in the forward propagation direction;
• an optical assembly configured to provide an optical power for focusing the incident CP light beam to form an exit CP light beam, the optical assembly being formed with a stack of optical elements including at least one geometric phase lens (GPL), the optical assembly being electrically reconfigurable for supporting multifocal focusing;
• a rear-end QWP for converting the exit CP light beam to a first intermediate LP light beam;
• and
• a rear-end liquid crystal (LC) half waveplate (HWP) located at the second end for transforming the first intermediate LP light beam into the output LP light beam leaving from the second end, the rear-end LC HWP being electrically reconfigurable to either maintain or 90°-rotate a polarization orientation of the first intermediate LP light beam in forming the output LP light beam;
• first and second mirrors both arranged such that:
• the first mirror reflects the first LP light beam emitted from the PBS to the first end, causing the first LP light beam to travel along the forward propagation direction in the variable-focusing module to thereby form a third LP light beam leaving from the second end;
• the second mirror reflects the third LP light beam emitted from the second end to the PBS;
• the second mirror reflects the second LP light beam emitted from the PBS to the second end, causing the second LP light beam to travel in the backward propagation direction in the variable-focusing module to thereby form a fourth LP light beam leaving from the first end;
• and
• the first mirror reflects the fourth LP light beam leaving from the first end to PBS;
• and
• an electronic controller configured:
• to configure the optical assembly to provide a desired optical power in focusing the incident CP light beam traveling in the forward propagation direction, whereby the first LP light beam is focused in the variable-focusing module with the desired optical power;
• and
• to configure the rear-end LC HWP such that the first and third LP light beams are orthogonal to each other in polarization orientation so that the second and third LP light beams are same in polarization orientation, causing the second LP light beam to be focused in the variable-focusing module with the same desired optical power in forming the fourth LP light beam with the second and fourth LP light beams being orthogonal to each other in polarization orientation, thereby allowing the variable-focusing module to be reused in simultaneously focusing the first and second LP light beams;
• wherein the PBS is further arranged to combine the received third and fourth LP light beams to form the outgoing light beam, whereby radiation power of the incoming light beam is fully utilized in creating the outgoing light beam while allowing the desired optical power in focusing the incoming light beam to be variable and selectable to support multifocal focusing.