Circumferentially isotropic phase plate, method of making the same, method of forming bundle of rays using the same, and polarization measuring apparatus and method using the same

A method of making a circumferentially isotropic phase plate, said method comprising:

• a first step of depositing a first material on a transparent substrate so as to form a first material layer;
• a second step of drawing a plurality of boundaries in concentric circles around a predetermined axis in said first material layer within a plane orthogonal to said predetermined axis;
• a third step of selectively eliminating any of a plurality of regions held between the plurality of boundaries in said first material layer so as to form a plurality of first material layers in concentric circles around said predetermined axis;
• a fourth step of depositing, on said transparent substrate, a second material having a refractive index different from that of said first material so as to form a plurality of second material layers in concentric circles around said predetermined axis, filling a space between the plurality of said first material layers;
• and
• a fifth step of polishing the plurality of said first and second material layers such that each layer thickness of the plurality of said first and second material layers along a direction of said predetermined axis becomes uniform along a circumferential direction of said concentric circles, thereby constituting said first and second material layers, as a whole, as a form birefringent body which is isotropic in the circumferential direction of said concentric circles.

A method of forming a bundle of rays by use of a circumferentially isotropic phase plate, said method comprising:

• a first step of setting a circumferentially isotropic phase plate into an optical path of a bundle of rays, said phase plate comprising a plurality of first material layers which are formed by a first material on a transparent substrate and disposed in concentric circles around a predetermined axis within a plane orthogonal to an incident direction of the bundle of rays and a plurality of second material layers which are formed by a second material having a refractive index different from that of said first material and disposed in concentric circles around said predetermined axis so as to fill a space between the plurality of said first material layers, wherein the plurality of said first and second material layers are formed such that each layer thickness along the incident direction of said bundle of rays is uniform along a circumferential direction of said concentric circles, thereby constituting, as a whole, a form birefringent body which is isotropic in the circumferential direction of said concentric circles;
• and
• a second step of transmitting through said phase plate a bundle of rays having a uniform polarization state within a plane orthogonal to the incident direction with respect to said phase plate so as to form, as elliptically polarized light in which at least one of ellipticity and principal-axis azimuth continuously changes along the circumferential direction of the concentric circles of said phase plate, a bundle of rays having a polarization distribution which changes according to the circumferential direction of the concentric circles of said phase plate.

A polarization measuring apparatus equipped with a circumferentially isotropic phase plate, said apparatus comprising:

• a stationary polarization optical system which is spatially fixed and includes a radial phase plate whose azimuth of optic axis is radially disposed around an optical axis of said apparatus;
• and
• a rotary polarizing device which is disposed in one of an upstream and a downstream direction with respect to said polarization optical system and is supported so as to be rotatable around the optical axis of said apparatus;
• wherein, in a state where a bundle of rays to be measured is made incident on said stationary polarization optical system and said rotary polarizing device while said rotary polarizing device is rotated, when, of said bundle of rays transmitted through both said stationary polarization optical system and rotary polarizing device, any of circumferential directions around the optical axis of said apparatus attains an extinction state, a polarization state of said bundle of rays being incident on said stationary polarization optical system and said rotary polarizing device is measured according to a direction of the optic axis of said rotary polarizing device and the direction of the extinction state of said bundle of rays.

A polarization measuring method using a circumferentially isotropic phase plate, said method comprising:

• a first step of making a bundle of rays to be measured incident on a polarization measuring apparatus comprising a stationary polarization optical system which is spatially fixed and includes a radial phase plate whose azimuth of optic axis is radially disposed around an optical axis of said apparatus, and a rotary polarizing device which is disposed in one of an upstream and downstream direction with respect to said polarization optical system and is supported so as to be rotatable around the optical axis of said apparatus;
• a second step of rotating said rotary polarizing device around the optical axis of said apparatus so as to make, of said bundle of rays transmitted through both said stationary polarization optical system and rotary polarizing device, any of circumferential directions around the optical axis of said apparatus attain an extinction state;
• and
• a third step of measuring, based on a direction of the optic axis of said rotary polarizing device and the direction of the extinction state of said bundle of rays, a polarization state of said bundle of rays being incident on said stationary polarization optical system and said rotary polarizing device.