IP Library › Granted Patent US 12,560,832
Granted Patent B2
US 12,560,832 · App. 17/605,202 · Granted Feb 24, 2026

High gyrotropy photonic isolators directly on substrate

Inventors: Karthik Srinivasan (Minneapolis, MN); Bethanie Joyce Hills Stadler (Shoreview, MN)
Assignee: Regents of the University of Minnesota
G02F1/0955G02B6/1225G02B6/4208
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Quick Facts
Patent No.
US 12,560,832
App. No.
17/605,202
Granted
Feb 24, 2026
Kind
B2
Abstract

A method of fabricating a gyrotropic device (e.g., an optical isolator) includes: providing a substrate comprising a waveguide layer and forming an optical isolator active layer on the waveguide layer of the substrate. Forming the optical isolator active layer includes, for a specified composition of the optical isolator active layer, deriving at least one sputtering process parameter, performing sputtering of a plurality of targets according to the at least one sputtering process parameter to deposit the optical isolator active layer on the waveguide layer of the substrate, measuring an initial value of a bias voltage at a first target of the plurality of targets; and throughout deposition of the optical isolator active layer, maintaining the bias voltage at the initial value to within a predetermined threshold of the initial value.

Claims (26)

1 . A method of fabricating a gyrotropic device, the method comprising:

providing a substrate; and

forming an optical isolator active layer on the substrate, wherein forming the optical isolator active layer comprises:

for a specified composition of the optical isolator active layer, deriving at least one sputtering process parameter;

performing radio-frequency sputtering of at least one target according to the at least one sputtering process parameter to deposit the optical isolator active layer on the substrate;

measuring a first value of a bias voltage at a first target of the at least one target;

during deposition of the optical isolator active layer, monitoring the bias voltage; and

in response to the monitored bias voltage, adjusting a sputtering process parameter distinct from the bias voltage, wherein the adjustment maintains the bias voltage within a target range that includes the first value.

2 . The method of claim 1 , wherein adjusting the sputtering process parameter comprises (a) adjusting a forward power associated with sputtering the first target of the at least one target, (b) closing a shutter to prevent deposition of material from the first target on the substrate, or (c) adjusting the forward power associated with sputtering the first target and closing the shutter to prevent deposition of material from the first target on the substrate.

3 . The method of claim 1 , wherein the optical isolator active layer has a magnitude of Faraday rotation greater than 3000°/cm for a predetermined wavelength of light.

4 . The method of claim 1 , wherein the substrate comprises a waveguide layer and the optical isolator active layer is a cladding to the waveguide layer.

5 . The method of claim 1 , wherein the optical isolator active layer comprises doped garnet.

6 . The method of claim 5 , wherein the doped garnet is a waveguide layer.

7 . The method of claim 1 , wherein the optical isolator active layer comprises doped terbium iron garnet.

8 . The method of claim 7 , wherein the doped terbium iron garnet is doped with cerium.

9 . The method of claim 1 , wherein forming the optical isolator active layer comprises annealing the optical isolator active layer.

10 . The method of claim 9 , wherein annealing the optical isolator active layer is performed at a temperature between about 850 and about 970 degrees Celsius.

11 . The method of claim 1 , wherein forming the optical isolator active layer comprises performing the radio-frequency sputtering in an oxygen environment.

12 . The method of claim 1 , wherein the at least one target comprises a cerium target, a terbium target, and an iron target.

13 . The method of claim 1 , wherein at least one of the at least one target comprises an alloy of terbium and iron.

14 . The method of claim 1 , wherein at least one of the at least one target comprises cerium.

15 . The method of claim 1 , further comprising forming a silicon nitride layer on the optical isolator active layer.

16 . The method of claim 1 , wherein adjusting the sputtering process parameter comprises increasing a forward power associated with sputtering the first target until the bias voltage satisfies a condition.

17 . The method of claim 1 , wherein, during the radio-frequency sputtering, the bias voltage exhibits a drop to a value less than the first value, and, after the drop, a rise to a value greater than the first value.

18 . The method of claim 1 , wherein the first target comprises cerium.

19 . The method of claim 1 , wherein the optical isolator active layer has a magnitude of Faraday rotation greater than 500°/cm for a predetermined wavelength of light.

Assignments (2)
CONFIRMATORY LICENSE Recorded May 13, 2025
From: REGENTS OF THE UNIVERSITY OF MINNESOTA TECHNOLOGY COMMERCIALIZATION
To: NATIONAL SCIENCE FOUNDATION
Reel/Frame 071270/0777 →
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded Nov 9, 2021
From: SRINIVASAN, KARTHIK; STADLER, BETHANIE JOYCE HILLS
To: REGENTS OF THE UNIVERSITY OF MINNESOTA
Reel/Frame 058059/0457 →
Continuity (2)
Provisional Application 62837461 · Apr 23, 2019
Related Publication 20220214568A1 · Jul 7, 2022
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