High-index Waveguides Research Articles

Vertical cavity devices as wavelength selective waveguides

We show that novel wavelength-sensitive devices can be fabricated by coupling a semiconductor vertical cavity resonator to a low index waveguide. The optical mode in the resonator propagates at an angle, and the resonator resembles a high index waveguide. A taper in the thickness of the resonator allows different parts of the waveguide to operate at different wavelengths. These structures are analyzed using both thin film equations and waveguide normalism. Concentrating on a waveguide demultiplexer, simple design equations are derived, and a demonstration device is fabricated for TE mode at 0.75 /spl mu/m operation. Using AlGaAs/AlAs multilayers and a polymer top waveguide, the spectrometer exhibited a dispersion of 29 nm/cm, a wavelength resolution of better than 1 nm, and an intrinsic device efficiency of about 90%. A similar structure containing a light-emitting quantum well operated as a multiwavelength light source by modifying the spontaneous emission into the polymer waveguide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polarizing properties of a high index birefringent waveguide on top of a polished fiber coupler

The polarizing properties of a device made up of a high-index birefringent planar waveguide and a polished-type fiber coupler are analyzed. Approximate analytical formulas are derived for the width and the relative spacing of the TE and TM coupling resonances between the fiber and the waveguide. Experimental results are also shown and a practical in-line fiber polarizer based on this principle is demonstrated. >

Double ion exchange for high-index waveguides in LiTaO 3

The Letter describes the fabrication and properties of optical waveguides formed in Y-cut LiTaO3 by simultaneous processing of zinc–lithium, proton–lithium and zinc–proton exchange in the melts K2SO4–Na2SO4–ZnSO4–LiSO4–KHSO4 at 540°C. A surface increase of the refractive index of 0.14 was observed for the extraordinary polarisation and 0.11 for the ordinary polarisation. The dynamics of the process is discussed.

A molded polymeric resin-filled coupler

A novel type of molded polymeric resin-filled coupler has been built with the goal of making a low cost and manufacturable 1*N multimode optical coupler. The coupler consists of a low index thermoplastic molded cladding piece part containing an optically finished waveguide channel. The channel is covered with a flat lid of the same material and is filled with a high index resin to form a mode mixing waveguide. Optical fibers are inserted into both ends of the channel before it is filled to complete the pigtailed device. The design accomplished all required tasks with just two materials: the molded low index structural part which provides the waveguide cladding, and the high index waveguide core part which provides the adhesive to hold the fibers in place and the optial refractive index matching to reduce reflections. Two different material systems have been used to construct 1*23 couplers. Typical coupler excess losses are less than 2 dB, and the uniformity among all fibers is better than a 1 dB standard deviation. >

Direct measurement of the effective refractive indices of GaAs/AlGaAs slab waveguides: a new technique

A new method is presented for accurately and nondestructively measuring the effective refractive indices of GaAs slab waveguides. The experimental setup is extremely simple. This method is particularly applicable for buried waveguides and high refractive index waveguides that cannot be measured by prism couplers. It is also suitable for glass and LiNbO(3) waveguides.

Waveguide coupling efficiency in thin-film homogeneous lenses

Homogeneous thin-film lenses for integrated optical signal processing devices consist of alternating regions of high and low index waveguide. Boundary losses depend on coupling efficiency between fundamental modes in the two regions. Coupling efficiency has been calculated for various assumed index profiles, and also for measured optical field profiles in glass and lithium niobate waveguides. The glass system showed poor performance, but a system consisting of Ti-indiffused and annealed proton-exchanged waveguides had well matched modes between which the coupling efficiency calculated from measured field profiles was 99%.

Low-index embedded waveguide lenses in GaAs substrates

An integrated optical lens structure which embeds a low-index waveguide lens region in a high-index host waveguide is discussed. The lens has been realized on a GaAs/GaAlAs waveguide using an embedded low-index lens structure of glass/SiO/sub 2/. At an f-number of 2 and a wavelength of 1.152 mu m, the focal spot size is 2.8 mu m. The throughput efficiency is 45% and the angular field of view is 10 degrees .< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A fiber-based crosspoint switch using high-refractive index interlay materials

A switch principle is described which relies on the coupling between two polished fiber coupler blocks through a high-index interlay waveguide whose refractive index is higher than the effective mode index of the fibers. Switching is effected by the input radiation coupling through the interlay waveguide into the second fiber (cross-coupled state) or recoupling into the first fiber (straight-through state). The half-coupler blocks were constructed with a nominal radius of curvature of 25 cm and the top surfaces polished close to the edge of the fiber core. Accurate glass and polymer ribbon spacers were used to separate the two blocks by from 5-20 mu m and align them in parallel. The interstice was filled with a film of transparent high-index oil to form a slab waveguide. >

Exposed-core single-mode-fiber channel-dropping filter using a high-index overlay waveguide

Using the coupling between a standard single-mode fiber and single higher-order modes in a high-index overlay waveguide, we demonstrate a wavelength-filtering device with a channel-dropping response. Two types of filter are described. One uses a thin overlay waveguide, giving a single tunable dropped band response in the 1.2-1.6-microm wavelength region with rejection greater than 20 dB and an insertion loss of about 0.5 dB. The other uses a thick overlay waveguide and gives a comb-filter response with a dropped channel spacing of 13 nm with 20-dB rejection and an insertion loss of between 1 and 4 dB.

Properties, formation, and interpretation of stimulated resonance raman scattering spectra of dyes

talline quartz obtained by irradiation with helium ions," Pis'ma Zh. Tekh. Fiz., ~, No. 15, 927-930 (1981). 28. V. L. Smirnov and A. V. Shmal'ko, "Optical channel and strip microwaveguides: methods of manufacture, analysis, and elements of integrated optical systems," Zarubezh. Radioelektron., No. ii, 73-84 (1981). 29. I. G. Voitenko and V. P. Red'ko, "A three-channel electrooptical waveguide switch," Pis'ma Zh. Tekh. Fiz., ~, 418,421 (1981). 30. H. Kogelnic, "Current trends in integrated optics," Conference on Optical Communication, Copenhagen (1981), pp. 1-4. 31. B. L. Spoori, W. S. Chang, and C. M. Phillips, "A new method for the efficient interconnection of high-index planar waveguides to low-index transitional waveguides," Appl. Phys. Left., 29, 800-802 (1976). 32. S. A. Gurevich, E. L. Portnoi, N. V. Pronina, and V. I. Skopina, "Effective monolithic-hybrid joint of an injection heterolaser with a film waveguide of chalcogenide glass," Pis'ma Zh. Tekh. Fiz., 8, No. 14, 193-197 (1982). 33. P. K. Tien, "Integrated optics and new wave phenomena in optical waveguides," Rev. Mod. Phys., 49, No. 2, 361-419 (1977).

Proton exchange for high-index waveguides in LiNbO3

We describe the fabrication and characterization of optical waveguides formed in LiNbO3 by proton exchange in benzoic acid melts at 200–250 °C. Proton exchange, in LiNbO3 the replacement of lithium ions with protons, takes place when the substrate is immersed in the molten acid. We observe a surface increase in the refractive index of 0.12, for the extraordinary polarization only, with a step function index profile. This is the highest index increase obtainable to date for LiNbO3. Measured diffusion rates for x-cut crystals are 1.37 μm2/h at T = 249 °C and 0.37 μm2/h at T = 217 °C, so that very deep guides can be formed in short times. Diffusion is somewhat slower in the z direction. The process as described is not useful for y-cut crystals, since it damgaes this surface. Losses, measured on x-cut samples, were &amp;lt;0.5 dB/cm. All measurements were made at 0.633 μm.

Efficient optical waveguide coupler

A new method for high-efficiency interconnection of two planar optical waveguides is described. This technique is based on mode-matched coupling and is particularly useful when the difference between the refractive indices of the individual guides is large. The method consists of etching a deep vertical step in the highindex waveguide followed by the deposition of low-index waveguide on the etched section so that the two guides remain connected end to end. A theoretical treatment for the design of the coupler and for determination of fabricational tolerences is given. Couplers were fabricted using high-index waveguides like GaAs and LiNbO(3) and low-index waveguides made up of glass or solution-deposited (polyurethane or photoresist) films on SiO(2) substrate. It is shown that by controlling the junction profile, efficiencies close to theoretical values can be obtained. Some applications of such a coupler are given.

A new method for the efficient interconnection of high-index planar waveguides to low-index transitional waveguides

An efficient method for interconnecting two planar optical waveguides on the same substrate is described. Efficiencies better than 80% have been obtained in coupling from high-index GaAs and LiNbO3 waveguides to low-index AZ 1350 and polyurethane waveguides. This method is important for the coupling of high-index waveguides to optical fibers.

Optical grating coupling between low-index fibers and high-index film waveguides

Grating couplers between low-refractive-index (n ≈1.5) optical fibers and high-refractive-index (n ≈2.2) electro-optic planar guides have been analyzed and demonstrated. Coupling efficiencies of 6% between single modes of a film and a fiber have been observed. Efficiencies of approximately 86% between single-mode fibers and films using blazed backward-wave gratings are predicted. In addition, low-loss low-optical-aperture multimode fibers may be coupled to single-mode films with efficiencies greater than 50% and angular spreads less than 0.5°.