J. Daleiden

Ultralow biased widely continuously tunable fabry-Perot filter

Optical filters capable of single control parameter-based wide tuning are implemented and studied. The surface micromachined Fabry-Perot filter consists of two InP-air-gap distributed Bragg reflectors and shows a wavelength tuning of more than 140 nm using only a single voltage of up to 3.2 V at currents below 0.2 mA. The membrane-based filter is designed to block all wavelengths in the whole range of 1250-1800 nm apart from its transmission wavelength.

Modeling of ultrawidely tunable vertical cavity air-gap filters and VCSELs

Tunable vertical cavity devices including an air-gap integrated in the cavity have been designed, fabricated, and investigated. The ultrawide wavelength tuning is realized by micromechanical actuation of Bragg mirror membranes. Based on optical and mechanical model calculations, the air-gap filters and vertical cavity surface emitting lasers (VCSELs) are designed for investigating mainly the optical tuning efficiency. In our research, we focus on two different mirror material systems, dielectric Si/sub 3/N/sub 4//SiO/sub 2/ and InP/air-gap Bragg mirrors and on two tuning concepts, respectively. For the dielectric mirrors, continuous tuning is achieved by thermal actuation of the Si/sub 3/N/sub 4//SiO/sub 2/ mirror membranes, and for InP/air-gap mirrors, electrostatic actuation of the InP membranes is used. To verify the optical and mechanical simulations, InP/air-gap filters are characterized by measuring reflectance spectra and the tuning behavior. The measured results agree with the simulations used to optimize the micromechanical and optical characteristics of air-gap filters and VCSELs for optical communication applications.

Tuning efficiency and linewidth of electrostatically actuated multiple air-gap filters

We investigated the tuning efficiency of electrostatically actuated multiple air-gap filters fabricated in InP for dense wavelength division multiplex applications by comparing measured tuning curves with the results of optical and mechanical simulations. These filters exhibit a record tuning range of 127 nm at 7.3 V tuning voltage. The filters were measured in reflection using standard single mode fiber. The subsequent analysis is based on a one-dimensional electromechanical and optical model providing a reasonable estimation for the pull-in voltage. Optical simulations show that the filter linewidth does not affect the tuning efficiency.

Surface micromachined optical low-cost all-air-gap filters based on stress-optimized Si3N4 layers

A new surface micromachining approach based on a multiple Si3N4- and silicon-layer stack is presented. The fabrication process is implemented by plasma-enhanced chemical vapour deposition of stress-optimized films, reactive ion etching using SF6/CHF3/Ar, wet chemical etching of the sacrificial silicon layers by KOH and critical point drying. Using this approach, the fabrication of an optical all-air-gap vertical-cavity Fabry–Perot filter is demonstrated. The surface micromachined filter consists of two DBR mirrors, each having five 590 nm thick Si3N4 membranes separated by 390 nm wide air gaps. The distance between the mirrors (cavity) is 710 nm. The optical characterization and a white light interferometer measurement document the accuracy of the layer positioning and the performance of this low-cost approach. The filter shows the designed filter dip at 1490 nm, the full width at half maximum (FWHM) of the filter is 1.5 nm and the insertion loss is just 1.3 dB. The process is compatible with a variety of materials, e.g. III–V compounds, silicon, as well as organic materials, facilitating a huge application spectrum for sensors.

A novel low-cost tunable dielectric air-gap filter

Dense wavelength division multiplex (DWDM) systems is a promising technology for long-haul networks using the established fiber networks. Tunable devices such as optical filters, highly selective photodetectors, as well as lasers are considered to be key components for dynamic WDM systems. A novel low-cost tunable dielectric filter consisting of an air-gap cavity embedded by two DBRs is presented. A FWHM of 8 nm and a tunability of 15 nm/mA at 2 k/spl Omega/ heating resistance is obtained.

Record wavelength tuning of 127 nm for vertical cavity Fabry-Perot filter

Demonstrated micromechanically tunable Fabry-Perot filters with record electromechanical and optical performance. Wavelength tuning of 127nm applying only 7.3V is achieved. The stop-band of these filters is extremely wide (1250nm - 1800nm). These results open new application fields for micromechanically tunable filters, such as spectrometry for environmental and process analysis, medical diagnostics and colorimetry.

Wide continuously tunable 1.55µm vertical air-cavity wavelength selective elements for filters and VCSELs using micromachined actuation

Tailored scaling allows the effectiveness of physical effects and mechanical stability to be enhanced. This is shown for micromachined 1.55μm vertical-resonator-based filters and VCSELs, capable of wide, continuous, and kink-free tuning by a single control parameter. Tuning is achieved by mechanically actuating one or several membranes in a vertical air-gap resonator including two highly reflective DBR mirrors. Electrostatically actuatable single-chip filters including InP/air-gap DBRs (3.5 periods) reveal a continuous tuning up to 14% of the absolute wavelength. Varying a reverse voltage (U=0 .. -3.2V) between the membranes (almost flat in the unactuated condition) a tuning range up to 142nm was obtained. Varying a reverse voltage (U=0 .. -28V) between the membranes (strained and curved in the unactuated condition) a tuning range up to 221nm was obtained. Optically pumped and continuously tunable 1.55μm VCSELs show 26nm spectral tuning range, 400μW maximum output power, and 57dBm SMSR. This two-chip VCSEL has a movable top mirror membrane, which is precisely designed to obtain a specific air-gap length and a tailored radius of curvature in order to efficiently support the fundamental optical mode of the plane-concave resonator. The curved top mirror DBR membrane consists of periodically alternating differently stressed silicon nitride and silicon dioxide multilayers. The lower InP-based part consists of the InP/GaInAsP bottom DBR and the GaInAsP active region.

Wide continuously tunable 1.55μm vertical air-cavity wavelength selective elements for filters and VCSELs using micromachined actuation (Invited Paper)

Tailored scaling allows the effectiveness of physical effects and mechanical stability to be enhanced. This is shown for micromachined 1.55μm vertical-resonator-based filters and VCSELs, capable of wide, continuous, and kink-free tuning by a single control parameter. Tuning is achieved by mechanically actuating one or several membranes in a vertical air-gap resonator including two highly reflective DBR mirrors. Electrostatically actuatable single-chip filters including InP/air-gap DBRs (3.5 periods) reveal a continuous tuning up to 14% of the absolute wavelength. Varying a reverse voltage (U=0 .. -3.2V) between the membranes (almost flat in the unactuated condition) a tuning range up to 142nm was obtained. Varying a reverse voltage (U=0 .. -28V) between the membranes (strained and curved in the unactuated condition) a tuning range up to 221nm was obtained. Optically pumped and continuously tunable 1.55μm VCSELs show 26nm spectral tuning range, 400μW maximum output power, and 57dBm SMSR. This two-chip VCSEL has a movable top mirror membrane, which is precisely designed to obtain a specific air-gap length and a tailored radius of curvature in order to efficiently support the fundamental optical mode of the plane-concave resonator. The curved top mirror DBR membrane consists of periodically alternating differently stressed silicon nitride and silicon dioxide multilayers. The lower InP-based part consists of the InP/GaInAsP bottom DBR and the GaInAsP active region.

Multiple air-gap InP-based VCSELs and filters with ultra-wide wavelength tuning-flexibility and shape of the membranes

Vertical cavity devices that comprise of multiple air-gaps and extremely thin InP membranes implemented by surface micromachining is presented. Both, for the tunable cavity and for the distributed Bragg reflector (DBR) mirrors the material module InP/air is applied. This design facilitates improved opto-mechanical device performance. With the same technological concept, a 1.55 /spl mu/m micromachined optical filter with an ultracontinuous wavelength tuning is fabricated and characterized. An 8-air-gap 1.55 /spl mu/m VCSEL structure is also implemented.