Integrated polarized light emitting diode with a built-in rotator

• US 9,362,460 B2
• Filed: 07/19/2011
• Issued: 06/07/2016
• Est. Priority Date: 07/19/2010
• Status: Active Grant

• Current Assignee: Rensselaer Polytechnic Institute
• Original Assignee: Rensselaer Polytechnic Institute
• Inventors: Lin, Shawn-Yu, Kim, Yong Sung, Hsieh, Mei-Li
• Primary Examiner(s): Tran, Minh-Loan
• Assistant Examiner(s): KHAN, FARID H
• Application Number:
  US13/810,380
• Publication Number:
  US 20130161677A1
• Time in Patent Office: 1,785 Days
• Field of Search: 257/13
• US Class Current: 1/1
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 5/30 Polarising elements light-modulating devices with active elements G02F1/00
• CPC Class Codes: G02B 5/3008 comprising dielectric particles, e.g. birefringent crystals embedded in a matrix
• CPC Class Codes: G02B 5/3058 comprising electrically conductive elements, e.g. wire grids, conductive particles
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: H01L 2933/0083 Periodic patterns for optical field-shaping in or on the semiconductor body or semiconductor body package, e.g. photonic bandgap structures
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/58 Optical field-shaping elements

Abstract

The invention is directed to an integrated polarized light emitting diode device that has a light emitting diode, a metal grating, an oxide layer, and a built-in photonic crystal rotator. Additional teachings include a method for making the integrated polarized light emitting diode, a method for improving the polarization selectivity and energy efficiency of a light emitting diode, and a method for rotating polarization of a light emitting diode.

Claims

1. An integrated polarized light emitting diode device comprising:

a light emitting diode, a metal grating, an oxide layer, and a built-in photonic crystal birefringent polarization rotator, wherein the built-in photonic crystal birefringent polarization rotator comprises a plurality of array layers interleaved with a plurality of layers comprising spacer material, each of the plurality of array layers comprises a plurality of rods parallel to each other and separated from each other by spacer material within the array layer, the plurality of rods comprises gold, silver, or TiO₂, and the plurality of rods in each of the plurality of array layers are rotated ninety degrees relative to the plurality of rods in an immediately successive array layer.

2. The polarized light emitting diode of claim 1, wherein said metal grating is selected from a group consisting of aluminum, iron, and copper.

3. The polarized light emitting diode of claim 1, wherein said oxide layer is made from a single layer of SiO₂.

4. The polarized light emitting diode of claim 1, wherein said rods comprise TiO₂ with a refractive index of about 2.7, and the spacer material comprises SiO₂ with a refractive index of about 1.5.

5. The polarized light emitting diode of claim 1, wherein the metal grating is made of aluminum and the dimensions of the aluminum grating are such that the pitch is approximately 250 nm, the width is approximately 125 nm, and the height is approximately 125 nm.

6. The polarized light emitting diode of claim 1, wherein the thickness of the oxide layer is approximately 100 nm and its refractive index is about 1.5.

7. A method for improving the polarization selectivity and energy efficiency of a light emitting diode, said method comprising:

a. generating light using a light emitting diode device;

b. passing light with one direction of polarization through a metal grating on said light emitting diode device;

c. passing light that does not pass through the metal grating through a photonic crystal birefringent polarization rotator that is built-in as part of said light emitting diode device, wherein the photonic crystal birefringent polarization rotator comprises a plurality of array layers interleaved with a plurality of layers comprising a spacer material, each of the plurality of array layers comprises a plurality of rods parallel to each other and separated from each other by spacer material within the array layer, the plurality of rods comprises gold, silver, or TiO₂, and the plurality of rods in each of the plurality of array layers are rotated ninety degrees relative to the plurality of rods in an immediately successive array layer; and

d. optically rotating the polarization of said light to the desired polarization using the built-in photonic crystal rotator, such that high polarization selectivity is obtained and the energy efficiency of the light emitting diode is improved.

8. The method of claim 7, wherein said method further includes a step of recycling the rotated light such that the energy efficiency of the light emitting diode is improved and more light of the desired polarization exits the light emitting diode device through the metal grating.

9. The method of claim 7, wherein said polarization selectivity is approximately 50:

1 at λ

=550 nm.

10. A method for rotating polarization of a light emitting diode, said method comprising:

a. generating light using a light emitting diode device;

b. passing light with one direction of polarization through a metal grating on said light emitting diode device;

c. passing light that does not pass through the metal grating through a photonic crystal birefringent polarization rotator that is built-in as part of said light emitting diode device, wherein the photonic crystal birefringent polarization rotator comprises a plurality of array layers interleaved with a plurality of layers comprising a spacer material, each of the plurality of array layers comprises a plurality of rods parallel to each other and separated from each other by spacer material within the birefringent layer, the plurality of rods comprises gold, silver, or TiO₂ and the plurality of rods in each of the plurality of array layers are rotated ninety degrees relative to the plurality of rods in an immediately successive array layer; and

optically rotating the polarization of said light to the desired polarization using the built-in photonic crystal rotator.

11. The method of claim 10, wherein said method further includes a step of recycling the rotated light such that more light is polarized to the desired polarization.

12. The method of claim 10, wherein the light is rotated to the desired polarization such that the polarization selectivity is approximately 50:

1 at λ

=550 nm.

13. The method of claim 10, wherein said metal grating is made of aluminum and the dimensions of the aluminum grating are such that the pitch is approximately 250 nm, the width is approximately 125 nm, and the height is approximately 125 nm.

14. A method of making a polarized light emitting diode with a built-in rotator, said method comprising:

a. assembling a birefringent photonic crystal optical rotator by a layer by layer method, wherein assembling comprises depositing a plurality of array layers in alternation with depositing a plurality of layers comprising spacer material and depositing an array layer comprises forming a plurality of rods parallel to each other and separated from each other by spacer material within the array layer, the plurality of rods comprising gold, silver, or TiO₂, and orienting the plurality of rods in each succeeding array layer so as to be rotated ninety degrees relative to the plurality of rods in an immediately preceding array layer;

b. adding a conventional light emitting diode on top of the photonic crystal optical rotator;

c. adding an oxide layer on top of the light emitting diode; and

d. adding a metal grating on top of the oxide layer.

15. The method of claim 14, wherein the layer by layer method of step a) includes spin-coating a 300 nm thick bi-layer polymethyl methacrylate (PMMA) e-beam resist on a double-sided silicon substrate, exposing the resist-coated sample to a dosage of 900 pC/cm² and current of 20 nA, followed by development in a 1:

3 mixture of methyl isobutyl ketone (MIBK) and isopropanol (ISP), and descum in an oxygen plasma.

16. The method of claim 14, wherein said metal grating is selected from a group consisting of aluminum, iron, and copper.

17. The method of claim 14, wherein said oxide layer is made from a single layer of SiO₂.

18. The method of claim 14, wherein said rods comprise TiO₂ with a refractive index of 2.7, and the spacer material comprises SiO₂ with a refractive index of 1.5.

19. The method of claim 14, wherein the metal grating is made of aluminum and the dimensions of the aluminum grating are such that the pitch is approximately 250 nm, the width is approximately 125 nm, and the height is approximately 125 nm.

20. The method of claim 14, wherein the thickness of the oxide layer is approximately 100 nm and its refractive index is 1.5.