Small, high power optical isolator
An optical isolator for use with high power, collimated laser radiation includes an input polarizing optical element, at least one Faraday optical element, at least two reflective optical elements for reflecting laser radiation to provide an even number of passes through said at least one Faraday optical element, at least one reciprocal polarization altering optical element, an output polarizing optical element, at least one light redirecting element for remotely dissipating isolated or lost laser radiation. The isolator also includes at least one magnetic structure capable of generating a uniform magnetic field within the Faraday optical element which is aligned to the path of the collimated laser radiation and a mechanical structure for holding said optical elements to provide thermal gradients that are aligned to the path of the collimated laser radiation and that provide thermal and mechanical isolation between the magnetic structure and the optical elements.
1. An optical isolator for collimated laser radiation, comprising:
an optic holder;
a Faraday optic having a front side and a back side, a first surface region of the front side being mounted to an end of the optic holder, the back side facing away from the end of the optic holder;
a magnetic structure for generating a magnetic field within the Faraday optic, the magnetic structure surrounding but being separated from the Faraday optic;
an input polarizing optical element mounted to the optic holder and configured to separate two orthogonally polarized components of the collimated laser radiation and forward at least one of the two orthogonally polarized components to the front side of the Faraday optic as forward-going laser radiation;
high-reflection coatings on the back side and the first surface region of the front side for reflecting the forward-going laser radiation, received via the front side, to provide an even number of passes of the forward-going laser radiation between the front and back sides;
an output polarizing optical element mounted to the optic holder to intercept the forward-going laser radiation when propagating away from the front side of the Faraday optic after the even number of passes;
a reciprocal polarization altering optical element mounted to the optic holder and arranged to intercept the forward-going laser radiation between the input and output polarizing optical elements;
a light redirecting element mounted to the optic holder and arranged to remotely dissipate isolated reverse-going laser radiation; and
a mechanical structure for holding the optic holder and the magnetic structure.
2. The optical isolator of claim 1 , further comprising a mechanical structure for holding the optic holder and the magnetic structure.
3. The optical isolator of claim 2 , wherein the magnetic structure is separated from the Faraday optic by an air gap.
4. The optical isolator of claim 2 , further comprising a pliable layer between the optic holder and the mechanical structure.
5. The optical isolator of claim 1 , wherein:
the Faraday optic and the magnetic field are configured to rotate polarization of forward-going laser radiation by a total of 45 degrees in a first rotation direction; and
the reciprocal polarization altering optical element is configured to rotate polarization of the forward-going laser radiation by an additional 45 degrees in the first rotation direction.
6. The optical isolator of claim 1 , wherein:
the input polarizing optical element is arranged to direct the forward-going laser radiation to a second surface region of the front side adjacent the first surface region; and
the Faraday optic has an irregular hexagon shape that causes the forward-going laser radiation to exit the Faraday optic via a third surface region of the front side adjacent the first surface region.
7. The optical isolator of claim 6 , wherein the input polarizing optical element and the Faraday optic are arranged such that the propagation direction of the forward-going laser radiation is perpendicular to the first surface region both (a) when incident on the front side upon entry into the Faraday optic and (b) when propagating away from the front side upon exiting the Faraday optic.
8. The optical isolator of claim 6 , wherein:
each of the first, second, and third surface regions of the front side is planar;
the first surface region is between the second and third surface regions; and
each of the second and third surface regions is at an oblique angle to the first surface region.
9. The optical isolator of claim 6 , wherein:
the first, second, and third surface regions are coplanar;
the first surface region is between the second and third surface region; and
the back side includes a plurality of planar surface regions that are at oblique angles to each other.
10. The optical isolator of claim 1 , wherein:
the input polarizing optical element is a first birefringent displacer configured to forward both of the two orthogonally polarized components as the forward-going laser radiation; and
the output polarizing optical element is a second birefringent displacer configured to combine the two orthogonally polarized components into a single output beam.
11. The optical isolator of claim 10 , wherein the light redirecting element is a rejection mirror disposed in an input propagation path of the collimated laser radiation toward the first birefringent displacer, the rejection mirror (a) having an inner aperture for passage of the collimated laser radiation to the first birefringent displacer and (b) being arranged to deflect reverse-going laser radiation displaced from the input propagation path.
12. The optical isolator of claim 10 , further comprising a rejection mirror disposed in an output propagation path of the single output beam, the rejection mirror (a) having an aperture for passing the single output beam and (b) being arranged to deflect forward-going laser radiation not combined by the second birefringent displacer.
13. The optical isolator of claim 10 , further comprising:
an optical fiber for receiving and transmitting the single output beam; and
a lens for coupling the single output beam into the optical fiber and directing, into a cladding of the optical fiber, forward-going laser radiation not combined by the output polarizing optical element.
14. The optical isolator of claim 1 , wherein:
the input polarizing optical element is a first polarizing beam splitter cube configured to transmit only a selected one of the two orthogonally polarized components to the Faraday optic; and
the output polarizing optical element is a second polarizing beam splitter cube configured to transmit the selected polarized component.
15. The optical isolator of claim 1 , wherein the Faraday optic includes potassium terbium fluoride.
16. The optical isolator of claim 1 , wherein the reciprocal polarization altering optical element is selected from the group consisting of a quartz rotator and a half-wave plate.
17. The optical isolator of claim 1 , wherein the mechanical structure forms a housing for the magnetic structure, the optic holder, and the optical elements mounted to the optic holder.
18. The optical isolator of claim 1 , wherein the optical isolator is configured for fiber coupling to an input fiber and an outgoing fiber.