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Sub-wavelength grating integrated vcselRelated Patent Categories: Coherent Light Generators, Particular Active Media, Semiconductor, Injection, Monolithic Integrated, Laser Array, With Vertical Output (surface Emission)Sub-wavelength grating integrated vcsel description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070153860, Sub-wavelength grating integrated vcsel. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from, and is a 35 U.S.C. .sctn. 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. 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 copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. .sctn. 1.14. BACKGROUND OF THE INVENTION [0005] 1. Field of the Invention [0006] This invention pertains generally to broadband mirrors, and more particularly to high reflectivity gratings. [0007] 2. Description of Related Art [0008] Semiconductor light emitting diodes and lasers are used in a wide range of applications, such as telecommunication, display, solid-state lighting, sensing, surveillance and imaging. For many of these applications it is desirable to have devices having light emission normal to the surface of the wafer. The surface emitting topology facilitates array fabrication, integration with other devices and wafer-scale testing during and after processing. One form of these light emitting devices requires integration of mirrors with high reflectivity. [0009] Broadband mirrors (.DELTA..lamda./.lamda.>15%) with very high reflectivity (R>99%) are essential for numerous applications, including telecommunications, surveillance, sensors and imaging, ranging from 0.7 .mu.m to 12 .mu.m wavelength regimes. For example, in optical integrated circuits, electro-optic modulators play an important role in switching and signal encoding. Ideally, electro-optic modulators have low insertion loss and wide bandwidth. Mirrors are key components and the performance of many modulators would be substantially improved if they incorporated a low insertion loss, broad bandwidth, mirror. In the case of surface-emitting semiconductor light-emitting diodes and lasers, the broadband mirrors are required in the construction of optical cavity resonators to achieve large quality (Q) factors. [0010] Among the candidates for mirrors are metal mirrors and dielectric mirrors. Metal mirrors have comparatively large reflection bandwidths but lower reflectivities (R), as they are limited by absorption loss. As a result, they are not suitable for fabricating transmission-type optical devices such as etalon filters. [0011] Dielectric mirrors on the other hand have a lower loss than metal mirrors and therefore can achieve a higher reflectivity. However, the available deposition methods are often not precise enough to readily provide these high reflectivities. It should be appreciated that dielectric mirrors are composed of multi-layer dielectric materials with different dielectric indices. Distributed Bragg Reflectors (DBR) consist of multiple periods of alternating high and low refractive index layers. The tuning range for a tunable filter made with DBR mirrors is determined by the DBR mirror bandwidth and the maximum allowable mechanical movement, whichever is smaller. These mirrors have low absorption loss, but the modulation depth, bandwidth and band location depend on the refractive index contrast of the constituent materials as well as on the control over the layer thickness. [0012] In order to minimize interface disorder and strain in the multilayer structures, typical combinations of materials often have small refractive index differences, thus resulting in very limited bandwidths (.DELTA..lamda./.lamda..apprxeq.3-9%). As a result of this narrow bandwidth, the tuning range of electro-optic modulators, such as etalon type devices, has been severely limited. [0013] For tunable etalon type devices, such as micro-electro-mechanical (MEM) vertical cavity surface emitting lasers (VCSEL), filters and detectors, the tuning range is often limited by semiconductor based distributed Bragg reflectors (DBRs) to .DELTA..lamda./.lamda..apprxeq.3-9%. Conventional designs have not provided a mirror with broadband reflection, low loss and compatibility with optoelectronic processing. Semiconductor-based DBRs have been widely used for vertical cavity surface emitting lasers (VCSEL), detectors, and filters because of their higher thermal and electrical conductivities. A typical VCSEL requires an optical resonant cavity having two DBRs, wherein one DBR is positioned on each side of a cavity layer. In the center of the cavity layer resides an active region. In one implementation the active region comprises at least one layer of quantum wells or quantum dots. Current is injected into the active region through a current guiding structure such as provided by either an oxide aperture or proton-implanted surroundings. The laser emission wavelength of the structure is determined by the Fabry-Perot resonance wavelength of the cavity and DBRs, as well as the active region gain bandwidth. The use of semiconductor DBRs within devices limits the emission wavelength, wherein a mirror with high reflectivity and broad bandwidth is desired. [0014] One of the major difficulties in the current status of VCSEL fabrication, especially for long wavelength components around 1.55 .mu.m regimes, concerns the realization of high quality reflective p-type VCSEL mirror. This fabrication difficulty is primarily a result of the limited choice of materials available for the material growth process. In conventional semiconductor-based DBR (e.g., Al.sub.xGa.sub.1-xAs) devices, the refractive index contrast is low, such as somewhere between the high and low index material. Consequently, an excess number of DBR pairs is required to achieve >99% reflectivity, thus increasing the difficulty in achieving high quality material growth. This has been a major bottleneck for 1.3-1.55 .mu.m VCSEL fabrication and remains a problem for blue-green and 2-3 .mu.m wavelength regimes. The shortcomings of this prior approach are even more pronounced with regard to the fabrication of wavelength-tunable VCSELs, in which the requirements on mirror bandwidth and reflectivity become even more stringent. [0015] Accordingly, there is a need for vertical cavity surface emitting lasers which can be readily fabricated across a range of wavelengths as well as for wavelength-tunable devices. The present invention satisfies that need, as well as others, and generally overcomes the limitations of the art. BRIEF SUMMARY OF THE INVENTION [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. [0017] The structure of the sub-wavelength grating generally comprises a one dimensional grating structure with lines made of high refractive index material sandwiched between two low refractive index materials on top and bottom. The index difference between the high and low index materials determines the bandwidth and modulation depth. The larger difference in refractive indices gives rise to wider reflection bands. The reflection is sensitive to parameters such as the grating period, the grating thickness, the duty cycle of the grating, the refractive index and the thickness of the low index layer underneath the grating. [0018] Several examples are provided to illustrate the functionality of the sub-wavelength grating reflector. The bandwidth of a reflector is defined by the stopband wavelength range over the center wavelength (.DELTA..lamda./.lamda.) for a given minimum reflectivity (e.g., R>99%). Typical bandwidth of distributed Bragg Reflector has a bandwidth of .DELTA..lamda./.lamda..apprxeq.3-9%. In contrast to this, one example embodiment of sub-wavelength grating according to the present invention describes a reflector with R>99% with .DELTA..lamda./.lamda.>30% for a wavelength range centered at 1.55 .mu.m. [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 (.DELTA..lamda./.lamda..about.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 (.DELTA..lamda./.lamda.>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. Continue reading about Sub-wavelength grating integrated vcsel... Full patent description for Sub-wavelength grating integrated vcsel Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Sub-wavelength grating integrated vcsel patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Sub-wavelength grating integrated vcsel or other areas of interest. ### Previous Patent Application: Semiconductor component and laser device Next Patent Application: Vertical cavity surface emitting laser Industry Class: Coherent light generators ### FreshPatents.com Support Thank you for viewing the Sub-wavelength grating integrated vcsel patent info. 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