Formation of negative-index-change waveguide lenses in LiNbO(3) by using ion milling

Kinoform microlenses for focusing into microfluidic channels

Optical detection in microflow cytometry requires a tightly focused light beam within a microfluidic channel for effective microparticle analysis. Integrated planar lenses have demonstrated this function, but their design is usually derived from the conventional spherical lens. Compact, efficient, integrated planar kinoform microlenses are proposed for use in microflow cytometry. A detailed design procedure is given and several designs are simulated. A paraxial kinoform lens integrated with a microfluidic channel was then fabricated in a silicate glass material system and characterized for focal position and spotsize, in comparison with light emerging directly from a channel waveguide. Focal spotsizes of 5.6 μm for kinoform lenses have been measured at foci as far as 56 μm into the microfluidic channel.

Modified integrated optic Fresnal lens for waveguide-to-fiber coupling

The traditional design procedure for the waveguide Fresnel lens was carried over from those of bulk optics and micro-optics. In this design it is assumed that the lens thickness is negligibly small with respect to the focal length. This criterion does not hold for many integrated optic devices, in particular those with small mode-index modulations and long wavelengths. Under these conditions, the focal properties of the lens become unpredictable and the lens efficiency is reduced, both of which severely limit the usefulness of the lens as a waveguide-to-fiber coupler. To correct for this shortcoming, the standard Fresnel lens design procedure was modified to acocunt for the thickness of the lens explicitly. Both the standard and the modified Fresnel lens designs are outlined. A comparison of the limitations of the two lenses predicts better performance for the modified Fresnel lens. This is supported through computersimulation results for a pair of test lenses.

High-efficiency diffractive waveguide lenses by parametric optimization

The first-order diffraction efficiency of a waveguide diffraction grating is maximized, for a wide range of grating periods, by optimization of the effective-index modulation profile. Three different values of effective-index modulation in the range of 0.02-0.11 are considered. The analysis is performed with the thin-grating-decomposition method. The results are verified by electromagnetic grating theory and applied to the construction of diffractive waveguide lenses with an improved overall efficiency. In the neighborhood of the optical axis, the optimized lens structure is a close approximation of a gradient-thickness Fresnel lens. Significant deviations from this shape appear when the local grating period reduces below ~ 15-25λ, where ~ is the wavelength of the guided mode. Near the edges of a high-numerical-aperture lens, where the local period is ~ 3-6λ, an approximate Bragg grating structure is obtained.

Integrated acousto-optic heterodyning device modules in LiNbO(3) substrate

This paper reports the realization of integrated acousto-optic (AO) device modules that combine a wideband AO Bragg cell, an ion-milled Bragg diffraction grating, and a titanium-indiffused protonexchanged waveguide lens in a Y-cut LiNbO(3) substrate, 1 x 8 x 16 mm(3) in size, to perform optical heterodyning, and their application to rf signal processing. These integrated AO heterodyne modules have demonstrated the capabilities for channelized detection of the amplitude, the frequency, and the phase of wideband rf signals and thus the capability to perform interferometric rf spectral analysis with significantly improved performances over the conventional AO Bragg cells. The single-unit (basic) modules have provided single-tone simultaneous and two-tone third-order spurious-free dynamic ranges of 51 and 40 dB, respectively, and a bandwidth of 205 MHz centered at 350 MHz at the optical wavelength of 0.6328 microm, the optical power of 1.0 mW, and the drive power of 50 mW/rf signal input. Furthermore the dual-unit modu es that consist of a pair of identical basic heterodyne devices in the same LiNbO(3) waveguide substrate, also 1 x 8 x 16 mm(3) in size, have been constructed and used to measure the angle of arrival of the rf signals.

Integrated acoustooptic circuits and applications

The recent development of titanium-indiffusion proton-exchange (TIPE) microlenses and lens arrays has made possible the construction of a variety of single- and multichannel integrated acoustooptic (AO) and acoustooptic-electrooptic (EO) circuits in LiNbO(3) channel-planar waveguides 0.1x1.0x2.0 cm(3) in size. These hybrid AO and AO-EO circuits can be fabricated through compatible and well-established technologies. The most recent realization of ion-milled microlenses and lens arrays together with the recent development of gigahertz AO Bragg modulators and EO Bragg modulator arrays have also paved the way for construction of similar but monolithic AO and AO-EO GaAs/GaAlAs waveguides of comparable size. Both types of integrated AO and AO-EO circuits suggest versatile applications in communications signal processing, and computing. Efficient and simultaneous excitation of the channel waveguide array using an ion-milled planar microlens array has facilitated the demonstration of some of these applications.

Achromatic waveguide lenses

An investigation of the chromatic properties of waveguide lenses is described. In general, the focal length of mode-index and Fresnel zone (diffractive) lenses will be a function of wavelength. As a result, these lenses will have high optical quality over only a relatively small wavelength range. A method is given to correct for this chromatic dispersion by forming a hybrid mode-index/diffractive doublet. Using this approach, the various lens parameters can be chosen so that the chromatic dispersion of the diffractive element will cancel the dispersion of the refractive element. In certain conditions, the power of the diffractive element in the hybrid achromatic doublet can be shown to go to zero producing an achromatic mode-index lens. It was found that, with typical waveguide materials, a 10-mm focal length, f/5 hybrid mode-index/diffractive lens can be made that has a usable wavelength range of approximately 80 nm. This is over an order of magnitude improvement compared with that obtained with conventional mode-index and diffractive lens types.