A two-step K+–Na+ and Ag+–Na+ ion-exchange technique is introduced to fabricate single-mode channel waveguides in BK7 glass for the telecom-wavelength region. The dependencies of insertion loss, polarization-dependent loss (PDL), and bending loss of curved waveguides on channel width, diffusion time, and annealing time are investigated. Results show that postannealing is a required process for improving waveguide properties and an optimal annealing time exists. Although relatively narrow mask openings are used in most one-step ion-exchange processes, a wider channel width, to as wide as 10 µm, is preferred for this two-step method. The minimum coupling loss to/from single-mode fiber and the propagation loss is found to be 0.4 dB and 0.3 dB/cm, respectively. For 5-cm-long waveguides the PDL is less than 0.1 dB. For the S-bend structure the cosine curve exhibits apparently a lower bending loss than the double-arc curve.

http://chen-server.mer.utexas.edu/GroupPapers/312.pdf

Two-step K(+)-Na+ and Ag(+)-Na+ ion-exchanged glass waveguides for C-band applications.

Incorporation of planar waveguide technology into a spectroelectrochemical sensor is described. In this sensor design, a potassium ion-exchanged BK7 glass waveguide was over-coated with a thin film of indium tin oxide (ITO) that served as an optically transparent electrode. A chemically selective film was spin-coated on top of the ITO film. The sensor supported five optical modes at 442 nm and three at 633 nm. Investigations on the impact of the ITO film on the optical properties of the waveguide and on the spectroelectrochemical performance of the sensor are reported. Sensing was based on the change in attenuation of light propagated through the waveguide resulting from an optically absorbing analyte. By applying either a triangular or square wave excitation potential waveform, electromodulation of the optical signal has been demonstrated with Fe(CN)6(3-/4-) as a model electroactive couple that partitions into a PDMDAAC-SiO2 film [where PDMDAAC = poly(dimethyldiallylammonium chloride)] and absorbs at 442 nm.

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 9. Incorporation of planar waveguide technology.

Er-doped silica–titania channel waveguide amplifiers are investigated by means of a home-made computer code to test their feasibility. The optical, spectroscopic and geometrical parameters measured on the fabricated slab waveguides, are used in the simulation model, which takes into account the pump and signal propagation, the amplified spontaneous emission, and the secondary transitions pertaining to the ion–ion interactions. By simulation, in the small signal operation, a gain close to 4.6 dB is demonstrated for a channel waveguide 5 cm long, by using a pump power of 200 mW; the signal wavelength being λs=1533 nm, pump and signal co-propagating.

Design of Er3+ doped SiO2–TiO2 planar waveguide amplifier

We report a technique for producing single-mode buried channel waveguide lasers in neodymium-doped SiO2:GeO2:B2O3:Na2O (SGBN) glass. Direct bonding forms the basis of this process, providing a buried waveguide layer in the photosensitive SGBN material into which channel confinement can be directly written with a focused UV beam. Characterization of a 7.5-mm-long device was performed using a Ti:Sapphire laser operating at 808 nm and the resultant 1059 nm channel waveguide laser output exhibited single-mode operation, milliwatt-order lasing thresholds, and propagation losses of <0.3 dB cm–1.

/pdf/direct-uv-written-buried-channel-waveguide-lasers-in-direct-2ava12tc7o.pdf

Direct-UV-written buried channel waveguide lasers in direct-bonded intersubstrate ion-exchanged neodymium-doped germano-borosilicate glass

We report a technique for producing single-step buried K+-Na+ ion-exchanged waveguide lasers in neodymium doped BK-7. Direct bonding is the basis for this process, providing atomic contact between two chemically modified BK-7-type substrates followed by a 350°C treatment suitable for simultaneous annealing and intersubstrate ion-exchange. Characterization of a 6-mm long device was performed using a Ti:Sapphire laser operating at 808 nm. The resultant laser output exhibited TE polarized single-spatial-mode operation with losses of < 0.4 dB /cm and a maximum output power of 8.5 mW for 249 mW of absorbed pump power.

/pdf/buried-laser-waveguides-in-neodymium-doped-bk-7-by-k-na-ion-1ci5o8eutg.pdf

Buried laser waveguides in neodymium-doped BK-7 by K+–Na+ ion-exchange across a direct-bonded interface

We present a systematic study of the changes induced in the
refractive-index profile of different sets of
K+–Na+ ion-exchanged waveguides on soda-lime
and BK7 substrates because of thermal annealing in the presence or
absence of salt vapors. The concentration of potassium is recovered
by secondary ion mass spectrometry, and the propagation losses are
measured by means of the three-prism configuration.

Effects of thermal annealing on the optical characteristics of k(+)-na(+) waveguides.

The effects of double Ti and Mg diffusion into lithium niobate couplers exploiting cascaded second-order nonlinearity are theoretically investigated. We demonstrate that this technology may be employed to optimize the performance of a new type of coupler made by uniaxial crystal having an unusual dielectric tensor configuration, i.e. equatorial. An extended version of the simple effective index method is developed in order to take into account the complex nature of hybrid modes. A home-made computer code is utilized in the electromagnetic analysis of rotated anisotropic channel waveguides. As an example, the simulation results show that a magnesium diffusion, made in the external region of a Ti : LiNbO 3 coupler which induces negative extraordinary and ordinary changes of the refractive indices of LiNbO 3 Δ n e ( Mg ) =−0.002 and Δ n o(Mg) =−0.001, decreases the linear coupling length from L c =73 to 44 mm.

Performance enhancement of nonlinear lithium niobate couplers via double titanium and magnesium diffusion

The effects of anisotropic coupling on the nonlinear behavior of different LiNbO3 waveguides and couplers employing cascaded second-order nonlinearity are analyzed and the importance of leaky mode effect is shown. A set of practical coupling structures made of both symmetric and asymmetric waveguides is investigated and their performance is compared. The home-made computer-code, based on coupled wave theory and anisotropic mode propagation in the complex domain, allows an exact electromagnetic investigation of devices, taking into account both guided and leaky propagation in structures which exhibit losses, the generated second harmonic wave having leaky nature. As an example, for the well-investigated slab three layer waveguide, by taking into account the leaky nature of the generated second harmonic, the modal mismatch Δβ = 333 m−1 is obtained at the azimuthal angle θm ≅ 61.9∘ (between the crystal optical c-axis and the propagation direction) while the angle found via the conventional approach is θm ≅ 63.5∘. Moreover, the calculated second harmonic wave exhibits an attenuation equal to 7.44 × 10−1dB/cm that strongly influences the whole cascaded second-order phenomenon. The simulation results, for those structures in which it is possible to neglect the hybrid and leaky nature of the propagation modes, are compared with the literature data and an excellent agreement is found.

Exact analysis of cascaded second-order nonlinearity in rotated Ti:LiNbO3 Couplers

We report on a new model for simulating wave propagation in two-dimensional photonic crystals (PhCs) by means of Green’s functions rearranged to fit on the geometrical and physical properties of the structure under investigation. The model can take into account physical effects occurring when the PhC is excited by either a point-like source, for the analysis of extended crystals with line and point defects, or a plane wave coming from infinite, to investigate mirrors and microlenses. The model has been used for studying a Fabry–Perot cavity to evaluate its response in presence of a Hankel source or a plane wave excitation. A parametric investigation of the filter response as a function of the cavity length has been carried out and the best conditions to obtain an increase of quality factor of each resonant cavity mode have been determined.

Investigation of a point-like and plane-wave excitation in 2D photonic bandgap microcavities using Green’s function method

In this paper, a 3-D model based on the Green's function for analyzing wave propagation in 2-D guided-wave photonic crystals (PhCs) is proposed. The model allows analysis all the physical effects occurring when a source field propagates in a multilayered structure with a periodic arrangement of scatterers, by taking into account both physical and geometrical parameters. Numerical results for PhC waveguides are compared with those obtained using the well-known finite-difference time-domain algorithm and the 3-D multiple-scattering technique already proposed in the literature, showing a very good agreement and some remarkable advantages, in terms of faster determination of electromagnetic field distributions and band diagrams and capability to analyze both in-plane and out-of-plane scattering losses.

C. Ciminelli

Papers

Effects of thermal annealing on the optical characteristics of k(+)-na(+) waveguides.

Performance enhancement of nonlinear lithium niobate couplers via double titanium and magnesium diffusion

Exact analysis of cascaded second-order nonlinearity in rotated Ti:LiNbO3 Couplers

Investigation of a point-like and plane-wave excitation in 2D photonic bandgap microcavities using Green’s function method

Fast and Accurate Investigation of 2-D Multilayered Photonic Crystals by a 3-D Model Based on the Green's Function