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...

AI Technical Summary

Benefits of technology

[0016] The present invention generally comprises a sub-wavelength grating reflector utilized in a novel optical resonator cavity that has application in a number of optical devices. An embodiment of one such device is described as a vertical cavity surface emitting laser (VCSEL) that utilizes a monolithic integrated highly-reflective sub-wavelength grating in its optical resonator cavity. In contrast to conventional distributed Bragg reflectors, these sub-wavelength gratings offer superior optical performance and simplicity of fabrication. The sub-wavelength grating can be scaled to form an optical cavity for VCSELs at different operating wavelengths and can be adapted to different material systems. To achieve an extraordinarily broad bandwidth, the sub-wavelength grating is configured to provide a large index contrast surrounding the high index grating segments, particularly the layer below the lines, which marks the major difference from conventional grating design. The embodiments according to the invention can be fabricated on either planar or curved surfaces. For example, the sub-wavelength grating reflector can be fabricated upon curved optical lenses.

[0019] Micro-electro-mechanical systems (MEMS) provide a simple wavelength tuning mechanism for many optoelectronic devices. The major advantages of MEMS-based tunable filters include a large-tuning range, continuous tuning with high precision, a narrow passband and a fast response time (1-10 microseconds). The concept is based on scanning Fabry-Perot (FP) etalon with an integrated MEMS drive to provide precise physical change of the cavity length. A conventional etalon comprises two mirrors separated by a cavity gap. The filter can be tuned by moving one of the mirrors relative to the other, thus changing the dimensions of the air gap. Thus, conventional MEMS-based tunable filters have the advantage of continuous tuning in that variation of the etalon gap size results in the variation in the transmission wavelength. However, existing filters have a limited tuning range (Δλ / λ˜7%) with mechanical structures which are difficult to fabricate and which have a small optical fill factor. The present invention provides a tunable filter using sub-wavelength grating structures as the reflectors that provide a much larger tuning range (Δλ / λ>30%) in the far-infrared wavelength (FIR) regime. It will be seen that the MEMS-based optical filter design is flexible and can be scaled to a wide range of wavelengths by simply changing the dimensions of the reflectors. The design also provides a large optical fill factor over existing designs that will permit the fabrication of two-dimensional arrays that require reasonably low driving voltages.

[0020] The simplicity and versatility of the SWG mirror design facilitates the monolithic integration with a VCSEL, and eventually a tunable VCSEL, for a wide range of wavelengths from visible to far infrared. Furthermore, such a configuration of MEMS tunable VCSEL can potentially increase resonant frequency and tuning range with reduced actuation power.

[0037] Another aspect of the invention is a sub-wavelength grating reflector that can be readily fabricated planar and curved configurations.

[0045] Another aspect of the invention is to provide SWG-VCSEL devices (e.g., lasers and light emitting diodes) which can be readily fabricated across a range of wavelengths, including extending in either direction into the both the IR and UV range.

Problems solved by technology

However, existing filters have a limited tuning range (Δλ / λ˜7%) with mechanical structures which are difficult to fabricate and which have a small optical fill factor.

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