Sub-wavelength grating integrated VCSEL

Abstract

A vertical cavity surface emitting laser (VCSEL) is described using a sub-wavelength grating (SWG) structure that has a very broad reflection spectrum and very high reflectivity. The grating comprises segments of high and low refractive index materials with an index differential between the high and low index materials. By way of example, a SWG reflective structure is disposed over a low index cavity region and above another reflective layer (either SWG or DBR). In one embodiment, the SWG structure is movable, such as according to MEMS techniques, in relation to the opposing reflector to provide wavelength selective tuning. The SWG-VCSEL design is scalable to form the optical cavities for a range of SWG-VCSELs at different wavelengths, and wavelength ranges.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from, and is a 35 U.S.C. § 111(a) continuation-in-part of, co-pending PCT international application serial number PCT / US2005 / 001416, filed on Jan. 14, 2005, incorporated herein by reference in its entirety, which designates the U.S., and which claims priority from U.S. provisional application serial number 60 / 536,570 filed on Jan. 14, 2004, incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with Government support under a grant from DARPA (Center for Bio-Optoelectronic Sensor Systems [BOSS]), Contract No. MDA9720010020. The Government has certain rights in this invention.INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

[0003] Not Applicable NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

[0004] A portion of the material in this patent document is subject to copyright protection under the copy...

Examples

example 1

[0084]FIG. 2A through FIG. 2D illustrate simulated mirror reflectivity for linear polarized light in the direction perpendicular to the grating lines with results shown as a function of wavelength for the sub-wavelength grating structure shown in FIG. 1. FIG. 2A compares simulated reflectivity using both a Rigorous Coupled Wave Analysis (RCWA) and confirmed by finite difference time domain electromagnetic propagation using TEMPEST®. The two methods are in excellent agreement and both illustrate the broadband and highly reflective properties of the sub-wavelength grating. It can be seen that the sub-wavelength grating provides a very broadband mirror Δλ / λ>30%, with R>0.99, for wavelengths centered around 1.55 μm, over the range 1.33 μm to 1.80 μm, as depicted by FIG. 2A. The reflection bandwidth of the mirror is also very broad for a higher reflectivity R>0.999 (1.40 μm to 1.67 μm or Δλ / λ>17%).

[0085] The parameters used in the simulation were: Si substrate (n=3.48), grating period Λ...

example 2

[0096] In order to demonstrate the functionality of the design, several single wavelength grating structures according to FIG. 1 were fabricated. The 1D grating structures were formed with stripes of high index material disposed on two low index layers. The high index material was poly-Si (nh)=3.48, and the low index material within the grating was air (n=1). The low index material under the grating was SiO2 with (nL)=1.47 and a thickness (tL)=0.58 μm and (tg)=0.4 μm. The grating period was varied from 0.7 μm to 0.9 μm and the grating duty cycle was varied 40-80%. The duty cycle is defined as the ratio of the width of the high index material to the total period length. Fabrication was conducted on a silicon wafer and e-beam lithography on PMMA was used for lift off of metal as to mask the top oxide layer, which was etched by RIE. The grating is polarization sensitive and light polarized along the grating lines will not see the band gap. However, if the grating has a two-dimensional ...

example 3

[0101] A simple one-dimensional (1D) grating was simulated to illustrate the scalability of the single wavelength grating structures and the dependence of reflectivity spectrum on various parameters. A very broadband mirror with reflectivity larger than 99%, is obtained over the range of 1.4 μm to 1.7 μm (Δλ / λ>19%). The simulation calculations were performed based on Rigorous

[0102] Coupled Wave Analysis (RCWA) and confirmed by time-domain electromagnetic propagation using TEMPEST®. The high index material was poly-Si (nh)=3.48, and the low index material within the grating was air (n=1). The low index material under the grating was SiO2 with (nL)=1.47 and a thickness (tL)=0.5 μm and (tg)=0.46 μm. The fill factor was 0.75 and the grating period was 0.7 μm. The index of refraction was considered constant along the coverage range.

[0103] It can be seen that the period of the grating in the simulation is sub-wavelength (but not half wavelength) and a scalable constant. Accordingly, the...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from, and is a 35 U.S.C. § 111(a) continuation-in-part of, co-pending PCT international application serial number PCT / US2005 / 001416, filed on Jan. 14, 2005, incorporated herein by reference in its entirety, which designates the U.S., and which claims priority from U.S. provisional application serial number 60 / 536,570 filed on Jan. 14, 2004, incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with Government support under a grant from DARPA (Center for Bio-Optoelectronic Sensor Systems [BOSS]), Contract No. MDA9720010020. The Government has certain rights in this invention.INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

[0003] Not Applicable NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

[0004] A portion of the material in this patent document is subject to copyright protection under the copy...

Examples

example 1

[0084]FIG. 2A through FIG. 2D illustrate simulated mirror reflectivity for linear polarized light in the direction perpendicular to the grating lines with results shown as a function of wavelength for the sub-wavelength grating structure shown in FIG. 1. FIG. 2A compares simulated reflectivity using both a Rigorous Coupled Wave Analysis (RCWA) and confirmed by finite difference time domain electromagnetic propagation using TEMPEST®. The two methods are in excellent agreement and both illustrate the broadband and highly reflective properties of the sub-wavelength grating. It can be seen that the sub-wavelength grating provides a very broadband mirror Δλ / λ>30%, with R>0.99, for wavelengths centered around 1.55 μm, over the range 1.33 μm to 1.80 μm, as depicted by FIG. 2A. The reflection bandwidth of the mirror is also very broad for a higher reflectivity R>0.999 (1.40 μm to 1.67 μm or Δλ / λ>17%).

[0085] The parameters used in the simulation were: Si substrate (n=3.48), grating period Λ...

example 2

[0096] In order to demonstrate the functionality of the design, several single wavelength grating structures according to FIG. 1 were fabricated. The 1D grating structures were formed with stripes of high index material disposed on two low index layers. The high index material was poly-Si (nh)=3.48, and the low index material within the grating was air (n=1). The low index material under the grating was SiO2 with (nL)=1.47 and a thickness (tL)=0.58 μm and (tg)=0.4 μm. The grating period was varied from 0.7 μm to 0.9 μm and the grating duty cycle was varied 40-80%. The duty cycle is defined as the ratio of the width of the high index material to the total period length. Fabrication was conducted on a silicon wafer and e-beam lithography on PMMA was used for lift off of metal as to mask the top oxide layer, which was etched by RIE. The grating is polarization sensitive and light polarized along the grating lines will not see the band gap. However, if the grating has a two-dimensional ...

example 3

[0101] A simple one-dimensional (1D) grating was simulated to illustrate the scalability of the single wavelength grating structures and the dependence of reflectivity spectrum on various parameters. A very broadband mirror with reflectivity larger than 99%, is obtained over the range of 1.4 μm to 1.7 μm (Δλ / λ>19%). The simulation calculations were performed based on Rigorous

[0102] Coupled Wave Analysis (RCWA) and confirmed by time-domain electromagnetic propagation using TEMPEST®. The high index material was poly-Si (nh)=3.48, and the low index material within the grating was air (n=1). The low index material under the grating was SiO2 with (nL)=1.47 and a thickness (tL)=0.5 μm and (tg)=0.46 μm. The fill factor was 0.75 and the grating period was 0.7 μm. The index of refraction was considered constant along the coverage range.

[0103] It can be seen that the period of the grating in the simulation is sub-wavelength (but not half wavelength) and a scalable constant. Accordingly, the...

Images