A current micro-optical system project at Sandia National Laboratories employs an array of resonant subwavelength gratings (RSGs). An RSG functions as an extremely narrow wavelength and angular band reflector, or mode selector. Theoretical studies predict that the infinite, laterally-extended RSG can reflect 100% of the resonant light while transmitting the balance of the other wavelengths. Experimental realization of these remarkable predictions has been impacted primarily by fabrication challenges. Even so, we will present large area (1.0mm) RSG reflectivities as high as 100.2%, normalized to deposited gold. Broad use of the RSG will only truly occur in an accessible micro-optical system. The program at Sandia is a normal incidence array configuration of RSGs where each array element resonates with a distinct wavelength to act as a dense array of wavelength- and mode-selective reflectors. Because of the array configuration, RSGs can be matched to an array of pixels, detectors, or chemical/biological cells for integrated optical sensing. Micro-optical system considerations impact the ideal, large area RSG performance by requiring finite extent devices and robust materials for the appropriate wavelength. Experimental measurements are presented that demonstrate the component response as a function of decreasing RSG aperture dimension and off-normal input angular incidence.

The challenge in designing a complex optical system for the deep-UV regime is a consequence of the limited material selection combined with the demand of cement free optical groups. Especially for optical mask inspection where the presence of a protecting pellicle requires a long working distance an all-refractive solution for a high NA objective seems to be critical. The combination of diffractive and refractive components to a hybrid optical system offers the advantageous possibility to overcome the addressed limitations. Here we present the realization of a hybrid microscope objective with a working distance of 7.8 mm and a numerical aperture of 0.65 for 193 nm mask evaluation. Despite the relative large bandwidth of 0.5 nm the use of calcium fluoride is not necessary but all components are based on fused silica. The small number of employed optical elements leads to a compact volume concept. The realized objective fits in a conventional mask evaluation tool. Classical refractive approaches didn't succeed in the simultaneous realization of all these critical specifications. For the realization of the diffractive optical element as the most determining element, a sophisticated holographic lithography process with a subsequent ion-etching technique was introduced.

We demonstrate a novel type of self-aligned optofiber/waveguide connector with integrated V-grooves and diffractive optical elements. The self-alignment is achieved by connecting micro-structures which have originally been formed in silicon and later replicated in concave and convex forms. V-grooves hold the optical fibers and the light is coupled out through diffractive optical elements (DOEs). A manufacturing process has been developed which allows both deep micro-structures (V-grooves and alignment structures) and shallow surface reliefs (diffractive elements) to be realized on the same substrate. The self-alignment using microstructures allows a positioning accuracy of about ±5μm. Two different fan-out DOEs have been optically characterized.

With an emphasis on the design and implementation of a miniature multi-element objective lens, this paper discusses the issues and challenges relating to hardware developed to demonstrate the viability of simultaneously writing and reading multiple-channels on phase-change media. A linear array of 850 nm single-mode vertical cavity surface emitting lasers (VCSELS) is used as a source for the noncontact phase-change on tape by means of an F/0.7 NA objective lens. The multichannel design and media characteristics required that an objective lens be developed having a full-field angle of 3 degrees and diffraction-limited performance of Strehl ratio > 0.88. Additionally, during the design process, simultaneous read-back through the same objective lens with 780 nm light, required consideration of the dispersive properties of glass. Because longitudinal and lateral movement of the objective lens in an actuator actively maintains focus, weight minimization related to material choices and mounting was also considered in the design. A successful breadboard implementation of the hardware was constructed demonstrating the capability for simultaneous high-speed writing and reading of multiple channels on tape. The breadboard also demonstrated the feasibility for fabricating a multi-element, molded aspheric, objective lens assembly meeting the unique requirements of the lightweight, high-numerical aperture, finite-field objective lens.

The old adage "Work Smarter, Not Harder" is certainly applicable in today's competitive marketplace for Optical MEMS. In order to survive the current economic conditions, high volume manufacturers must get optimum performance and yield from each design and manufactured component. Wafer bonding, and its numerous variants, is entering mainstream production environments by providing solutions throughout the production flow. For example, SOI (silicon on insulator) and other laminated materials such as GaAs/Si are used as cost effective alternatives to molecular epitaxy methods for Bragg mirrors, rf resonators, and hybrid device fabrication. Temporary wafer bonding is used extensively to allow fragile compound semiconductors to be attached to rigid support wafers. This allows for front side and backside processing with a reduction in wafer breakage and increases in thickness uniformity results after backgrind operations. Permanent wafer bonding is used to attach compound semiconductors to each other or silicon to completely integrate optical components and logic or MEMS components. Permanent hermetic sealing is used for waveguide formation and, when combined with vacuum sealing, higher performance is achieved for RF resonators. Finally, many of the low temperature solders and eutectic alloys are finding application in low temperature wafer-to-wafer level packaging of optical devices to ceramic packages. Through clever application of these bonding methods, throughput increases and reduction in fabrication complexity givs a clear edge in the market place. This presentation will provide guidelines and process overviews needed to adopt wafer-to-wafer bonding technologies into the high volume-manufacturing environment.

This paper presents the passively aligned Wavesetter (PAWS) locker: a micro-optic subassembly for use as an internal wavelength locker. As the wavelength spacing in dense wavelength division multiplexing (WDM) decreases, the performance demands placed upon source lasers increase. The required wavelength stability has led to the use of external wavelength lockers utilizing air-spaced, thermally stabilized etalons. However, package constraints are forcing the integration of the wavelength locker directly into the laser module. These etalons require active tuning be done during installation of the wavelength locker as well as active temperature control (air-spaced etalons are typically too large for laser packages). A unique locking technique will be introduced that does not require an active alignment or active temperature compensation. Using the principles of phase shifting interferometry, a locking signal is derived without the inherent inflection points present in the signal of an etalon. The theoretical background of PAWS locker will be discussed as well as practical considerations for its implementation. Empirical results will be presented including wavelength accuracy, alignment sensitivity and thermal performance.

We report the design, fabrication, and testing of a novel imaging micro-spectrometer system for the 500-1000 nm wavelength range. The space-variant design incorporates a linear array of MEMS mirrors in order to vary the dispersion spatially on a pixel-by-pixel basis. A planar-optics geometry is used so that the spectrometer optics are contained on a single piece of bulk fused silica. The object to be investigated is imaged onto a linear array of tilting MEMS mirrors that define the spectrometer slit. Each individual MEMS mirror tilts to send the light to one of three blazed gratings of differing dispersive powers. Depending on the wavelength and selected grating the spectral resolution is between 5 and 20 nm. The collimating and focusing mirrors of the spectrometer are fabricated in standard photoresist via grayscale photolithography with a custom high-energy beam-sensitive (HEBS) photomask. A reflow at 70 degrees Celsius for 40 hours is necessary to achieve diffraction-limited performance. The blazed gratings are fabricated in SU-8 via direct-write electron beam lithography. Spectrometer results with a variety of lasers and gaseous discharge tubes are presented and indicate that system performs as expected.

An integrated fiber-optic displacement sensor based on multimode interference is characterized through analysis of experimental performance in comparison to the expected behavior that is theoretically predicted. Multimode interference and re-imaging theory applied to the specific fiber properties and geometry of the device can be used to design and predict the performance of the device. Essentially, the sensor consists of a multimode fiber of a specific length fusion spliced to a single mode fiber used in conjuction with an 80/20 splitter, source, and detector that are used to inject and detect reflected signals from targets. The sensor is fabricated into a robust, compact, and single arm device capable of operating as a calibrated displacement sensor over a large displacement range. This is achieved through analysis of power reflected off of a surface and back through the device over a finite wavelength range.

Organic laser dye doped Zirconia-Titania-ORMOSIL waveguide thin films with refractive index from 1.55 to 1.59 were prepared by the sol-gel method. The thickness can be varied from 0.97 μm to 10 μm by changing coating speed. Distributed feedback waveguide lasing with multi-wavelength were observed with a periodic gain modulation induced by a frequency-doubled Nd:Yttritium-aluminum-garnet (YAG) laser. Wavelength tuning typically from 597 nm to 602 nm was demonstrated in Rhodamine 6G doped multiple mode waveguiding ZrO₂-TiO₂-ORMOSIL thin films DFB configuration by varying the temperature from 20°C to 120°C. The thermal coefficients of DFB waveguide laser wavelength and the refractive index of the film were deduced. This compact DFB laser device can be applied to measure the thermal coefficients of refractive index of the active films, and used as a remote temperature sensor.

Metrology is one of the critical enabling technologies for realizing the full market potential for micro-optical systems. Measurement capabilities are currently far behind present and future needs. Much of today’s test equipment was developed for the micro-electronics industry and is not optimized for micro-optic materials and geometries. Metrology capabilities currently limit the components that can be realized, in many cases. Improved testing will be come increasingly important as the technology moves to integration where it will become important to “test early and test often” to achieve high yields. In this paper, we focus on micro-refractive components in particular, and describe measurement challenges for this class of components and current and future needs. We also describe a new micro-optics metrology research program at UNC Charlotte under the Center for Precision Metrology and the new Center for Optoelectronics and Optical Communications to address these needs.

This effort describes a design method used to develop a binary-phase Fourier grating that generates an incoherent array of output source points with nonuniform user-defined intensities, symmetric about the zeroth order. Like the Dammann fanout grating approach, the binary-phase Fourier grating uses only two phase levels in its grating surface profile to generate the output array. Unlike the Dammann fanout grating approach, this method provides for the generation of nonuniform, user-defined intensities within the final fanout pattern. The process employs both simulated annealing and nonlinear optimization algorithms to locate solutions to the specified grating design problem. Because the desired grating output is incoherent, each source point of the grating response is assessed in terms of intensity, from which an overall efficiency is calculated. Efficiencies are calculated for each solution and are used to evaluate the relative value of each solution. A final design solution that produces an incoherent, symmetric, user-defined nine spot array is presented.

Etalons having one surface which is highly reflective have been used for a variety of applications. By varying the coating type and carefully controlling the thicknesses of the coatings on the lower reflectance side, one can obtain interesting and useful properties. One example is a low finesse but highly efficient element having a reflectance which is very sinusoidal with respect to wavelength. By adding additional layers, functions which are asymmetric about the reflectance peak with respect to wavelength can be obtained, including behavior which approximates a sawtooth reflectance as a function of wavelength. Such devices are easily fabricated at the wafer scale, and can be used in wavelength monitoring and control applications such as wavelength lockers for tunable lasers.

Resonant subwavelength gratings (RSGs) may be used as narrow-band wavelength and angular reflectors. Rigorous coupled wave analysis (RCWA) predicts 100% reflectivity at the resonant frequency of an incident plane wave from an RSG of infinite extent. For devices of finite extent or for devices illuminated with a finite beam, the peak reflectivity drops, coupled with a broadening of the peak. More complex numerical methods are required to model these finite effects. We have modeled finite devices and finite beams with a two-dimensional finite difference Helmholtz equation. The effect of finite grating aperture and finite beam size are investigated. Specific cases considered include Gaussian beam illumination of an infinite grating, Gaussian illumination of a finite grating, and plane wave illumination of an apertured grating. For a wide grating with a finite Gaussian beam, it is found that the reflectivity is an exponential function of the grating width. Likewise, for an apertured grating the reflectivity shows an exponential decay with narrowing aperture size. Results are compared to other methods, including plane wave decomposition of Gaussian beams using RCWA for the case of a finite input beam, and a semi-analytical techniques for the case of the apertured grating.

Replication technology is playing an increasingly important role in the production of micro-optical elements and systems. Hot embossing, injection moulding and uv-embossing all can produce high quality optical elements in very cost-effective processes. The development of wafer scale replication technology using uv-curable sol-gel and polymer materials enables refractive and diffractive micro-optical elements to be replicated directly onto glass substrates or onto Si or III-V device wafers. New sol-gel materials allow the combination of replication with lithography to leave selected areas material-free for sawing and bonding. The technology is suitable for the production of both planar micro-optical elements and stacked optical microsystems. Replication techniques are inherently of very high resolution, so that optical nanostructures such as subwavelength structures can also be produced by the same technologies. Grating nanostructures with linewidths less than 100 nm have been replicated into polymer and sol-gel materials for the cost-effective fabrication of large area subwavelength structures for applications such as anti-reflection surfaces, polarisers and certain types of resonant filters.

The mask structured silver sodium ion exchange in glass (MSI) is a powerful tool for the realization of high precision refractive micro optical GRIN components. Commonly the distribution of the silver ions in GRIN elements and thus the index distribution is determined by the laws of thermal diffusion. By the use of a structured metal mask, which defines the areas of contact between the glass and the silver salt melt, an additional degree of freedom in optical design is introduced. A photolithographic pattern generator provides the accuracy of the mask structure to realize wave front optimized micro lens arrays with 100% filling factor in Cartesian, hexagonal and also in nearly any other arbitrary geometrical arrangements for several applications such as high precision Shack-Hartmann systems. In this paper we want to discuss the potential and limits of this technique. We report on the family of optical functions, which can be realized with MSI. Furthermore we give an overview over the actual applications.

In order to form the proper aspherical microlens array profile with larger NA on photosensitive materials, a method is developed based on the characteristics of resist and processing parameters during development, for designing the exposure distribution, an experience formula has been proposed in the paper. Using the moving mask method, the exposure energy distribution function related to the photolithographic mask function can be determined by the experience formula. The profile control procedure is formed especially for the deeper relief profiles, after the binary mask data are slightly modified, the micro-structure with aspherical lens profile can be fabricated on the selected thicker resist, the micro relief profile error can be controlled in a certain range. The micro-profile is farther transferred to fused silica by ICP etching system. By our method, the fast microlens array elements with good fidelity and reasonable roughness have been fabricated and applied to the laser diode collimating system.

A conclusion that a single conventional optical system could not realize fiber coupled high-power laser diode array is drawn based on the BPP of laser beam. According to the parameters of coupled fiber, a method to couple LDA beams into a single multi-mode fiber including beams collimating, shaping, focusing and coupling is present. The divergence angles after collimating are calculated and analyzed; the shape equation of the collimating micro-lenses array is deprived. The focusing lens is designed. A fiber coupled LDA result with the core diameter of 800 um and numeric aperture of 0.37 is gotten.