A new class of planar optics has emerged using subwavelength gratings with a large refractive index contrast, herein referred to as high-contrast gratings (HCGs). This seemingly simple structure lends itself to extraordinary properties, which can be designed top-down based on intuitive guidelines. The HCG is a single layer of high-index material that can be as thin as 15% of one wavelength. It can be designed to reflect or transmit nearly completely and with specific optical phase over a broad spectral range and/or various incident beam angles. We present a simple theory providing an intuitive phase selection rule to explain the extraordinary features. Our analytical results agree well not only with numerical simulations but also experimental data. The HCG has made easy fabrication of surface-normal optical devices possible, including vertical-cavity surface-emitting lasers (VCSELs), tunable VCSELs, and tunable filters. HCGs can be designed to result in high-quality-factor (Q) resonators with surface-normal output, which is promising for wafer-scale lasers and optical sensors. Spatially chirped HCGs are shown to be excellent focusing reflectors and lenses with very high numerical apertures. This field has seen rapid advances in experimental demonstrations and theoretical results. We provide an overview of the underlying new physics and the latest results of devices.

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High-contrast gratings for integrated optoelectronics

We discuss a new concept of dielectric subwavelength grating leveraging high index contrast to manipulate light to achieve ultra broad band reflector, high-Q resonator, planar high numerical aperture lens and reflector, and hollow-core integrated optics.

High contrast gratings for integrated optoelectronics

The vertical-cavity surface-emitting laser (VCSEL) has become a light source of great importance for industrial and consumer applications. This includes communication and sensing in particular, where dynamics and optical mode behavior are key performance characteristics. This tutorial treats relevant VCSEL basics, performance requirements and recent progress toward higher speed, higher single-mode power, and polarization control.

Advances in VCSELs for Communication and Sensing

We report the fabrication of a wavelength tunable optical filter using surface micromachining technology. The center wavelength is 1.517 /spl mu/m and the transmission bandwidth is 5 nm. The device with a 50-/spl mu/m diameter aperture has an optical loss of about 5 dB. A continuous wavelength tuning of 60 nm has been demonstrated. This device may find applications in optical sensing and wavelength division multiplexing systems, and can be readily integrated with surface emitting lasers, modulators, and detectors.

Surface micromachined fabry-perot tunable filter

Surface-emitting semiconductor lasers have been widely used in data communications, sensing, and recently in Face ID and augmented reality glasses. Here, we report the first achievement of an all-epitaxial, distributed Bragg reflector (DBR)–free electrically injected surface-emitting green laser by exploiting the photonic band edge modes formed in dislocation-free gallium nitride nanocrystal arrays, instead of using conventional DBRs. The device operates at ~523 nm and exhibits a threshold current of ~400 A/cm2, which is over one order of magnitude lower compared to previously reported blue laser diodes. Our studies open a new paradigm for developing low-threshold surface-emitting laser diodes from the ultraviolet to the deep visible (~200 to 600 nm), wherein the device performance is no longer limited by the lack of high-quality DBRs, large lattice mismatch, and substrate availability.

An electrically pumped surface-emitting semiconductor green laser

A single-mode continuous tuning range of 76 nm is realized using a bulk-micromachined vertical-cavity surface-emitting laser (VCSEL) operating at wavelengths around 1.55 mum. The bulk-micromachined upper mirror is optimized for dielectric material and manufactured separately from the half-VCSEL. The VCSEL is tuned by an electrothermal actuation of a concave bended membrane. The tuning range characteristics in dependence on the bias of the VCSEL are investigated. It is determined that the tuning range saturates by increasing the current of the VCSEL and a further increase causes a multimode behavior within the tuning range.

Bulk-Micromachined VCSEL At 1.55 $\mu$ m With 76-nm Single-Mode Continuous Tuning Range

InAlGaAs bulk micromachined tunable Fabry–Pérot filter for dense WDM systems

GaAs/AlAs micromachined tunable Fabry-Pérot filters with long resonant cavity

Mikromechanische, abstimmbare optische Filter wurden hauptsächlich für Anwendungen in Wellenlängenmultiplex(WDM)-Systemen entwickelt. Zwei unterschiedliche, von uns im Hinblick auf die Spezifikationen solcher Systeme entwickelte Filtertypen können auch für die Gasspektroskopie interessante Anregungen liefern, um die Empfindlichkeit des Sensors bei begrenztem Volumen und geringer Leistungsaufnahme zu verbessern. Das zugrunde liegende Prinzip besteht darin, einen der beiden Bragg-Spiegel, die einen Mikroresonator bilden, als Membran auszuführen. Diese kann dann durch elektrostatische Kräfte oder durch Wärmezufuhr aufgrund eines aufgeprägten Stromflusses ausgelenkt werden. So kann Abstimmbarkeit über den gesamten freien Spektralbereich des Filters implementiert werden. Ein stabiles, halbsymmetrisches Resonatordesign verbessert deutlich die Filtergüte und Verlustfreiheit bei geringerem Produktionsaufwand. Allerdings ist dann verstärkt auf die Unterdrückung lateraler Nebenmoden zu achten.

Ein neues, kostengünstiges Konzept für abstimmbare Mikroresonatoren (A New and Cost Effective Concept for Tunable Microcavities)

For the first time a vertical-cavity surface-emitting laser (VCSEL) with a single-mode wavelength-tuning over 102 nm in the range of 1550 nm is demonstrated. The fiber-coupled optical output power has a maximum of 3.5 mW and is > 2 mW over the entire tuning range. The sidemode suppression ratios are > 45 dB. The wavelength tuning is achieved with the micro-electro mechanical actuation of a mirror membrane fabricated with surface micro-machining for on-wafer mass production. The mirror membrane consists of low cost dielectric materials (SiOx/SiNy) deposited with low temperature (< 100°C) Plasma Enhanced Chemical Vapor Deposition (PECVD).

Surface micromachined tunable 1.55 μm-VCSEL with 102 nm continuous single-mode tuning.

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