Refractive Index Profile Of Waveguide Research Articles

Low-crosstalk laser-direct-writing FI/FO device for 8×100-Gbps optical interconnection.

Fan-in/fan-out (FI/FO) device with low crosstalk is essential for weakly coupled short-reach optical interconnect based on multicore fibers (MCF), for which the laser-direct-writing (LDW) technique is one of the preferred fabrication schemes. In this paper, the influence of FI/FO crosstalk on short-reach intensity-modulation/direction-detection MCF optical interconnection is firstly evaluated, and the crosstalk related to different refractive-index profiles of waveguides and misalignment is analyzed for LDW-FI/FO devices. Then low-crosstalk compact LDW-FI/FO devices matching 8-core MCF are fabricated, adopting multiple-scan method for waveguides with a flat-top refractive-index profile and aberration correction method for precise alignment. Owing to the low crosstalk, 8×100-Gbps optical interconnection over 10-km MCF is experimentally demonstrated with only 0.5-dB penalty compared to 10-km G.652D single-mode fiber transmission. Simulation results indicate that the transmission reach can be further extended to over 40 km. The proposed prototype system with low crosstalk is promising for high-speed optical interconnection applications.

Extension of an FFT-Based Beam Propagation Method to Plasmonic and Dielectric Waveguide Discontinuities and Junctions

We adapted a fast Fourier transform-based Beam Propagation Method (FFT-BPM) to investigate waveguide discontinuities in plasmonic waveguides. The adaptation of the FFT-BPM to treat transverse magnetic (TM) fields requires the circumvention of two major difficulties: the mixed derivatives of the magnetic field and waveguide refractive index profile in the TM wave equation and the step-like index change at the transverse metal-dielectric boundary of the plasmonic guide and the transverse boundaries of the dielectric waveguide as well. An equivalent-index method is adopted to transform TM fields to transverse electric (TE) ones, thus enabling the benefit of the full power and simplicity of the FFT-BPM. Moreover, an appropriate smoothing function is used to approximate the step-like refractive index profile in the transverse direction. At the junction plane, we used an accurate combined spatial-spectral reflection operator to calculate the reflected field. To validate our proposed scheme, we investigated the modal propagation in a silicon waveguide terminated by air (like a laser facet in two cases: with and without a coating layer). Then we considered a subwavelength plasmonic waveguide (metal-insulator-metal MIM) butt-coupled with a dielectric waveguide, where the power transmission efficiency has been calculated and compared with other numerical methods. The comparison reveals good agreement.

Measurement of the refractive index profile of waveguides using defocusing microscopy.

Defocusing microscopy (DM) is a bright-field optical microscopy technique often used to obtain structural parameters of objects with low difference in refractive index in relation to the surrounding medium (phase objects). We show a use of this technique to measure the refractive index (n) profile of waveguides produced by femtosecond laser micromachining inside the bulk of a sodalime glass. The results are used to analyze the influence of production parameters on n. The methodology requires only a bright-field optical microscope and has proved to be easily applied. Results provide important insights on the waveguide microfabrication process, since translation speed, rather than intensity, has shown to be more important for achieving greater variations in refractive indices. Index of refraction differences between the waveguide and the substrate of the order of 10-4 were measured for a series of straight waveguides fabricated with different parameters. Low sample scan speeds and pulse energies near 1.20μJ used for fabrication showed the highest values of refractive index change for waveguides in sodalime glasses.

Investigation of Carbon ion-implanted waveguides in tungsten bronze (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 single crystal

Planar optical waveguides were fabricated in (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 (CSBN25) crystal by 6.0-MeV C+ ion implantation with fluences of 2, 4 and 6×1014ions/cm2 at room temperature. The mode parameters, refractive indices profiles are measured and the refractive indices behavior in the waveguide region is discussed. The shape of nuclear energy loss distribution of the C+ implantation was similar to those of the waveguide refractive index profiles, which means an inherent relationship between the waveguide formation and the energetic energy deposition. The extraordinary refractive index has a small positive change in the surface region after the implantation.

Reconstruction of refractive index profiles of 3 MeV O2+ ion-implanted MgO-doped LiNbO3 using wet etching and ellipsometry

A planar waveguide is fabricated by 3 MeV O2+ ion-implanted in MgO-doped lithium niobate, and the refractive index profiles of waveguides are reconstructed based on etching and ellipsometry techniques. The SRIM2003 code is used to simulate the damage distribution induced by implantation. The etching rate versus the etching depth is extracted and the relation between the etching rate and the damage profile is discussed. The index profile of this kind of waveguide is determined by etching in combination with the following ellipsometric measurements. Both ordinary and extraordinary index profiles in waveguide are obtained. The influence of damage profile on index profiles in waveguide, as well as that on waveguide properties is analysed.

Ion implanted optical waveguides in nonlinear optical organic crystal

We report for the first time to our knowledge optical waveguiding in an organic crystalline waveguide produced by ion implantation. Using H+ ions a refractive index barrier suitable for waveguiding has been realized in the highly nonlinear optical organic crystal 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST). The refractive index changes in the waveguiding region as a function of the distance from the surface have been measured. Maximal refractive index changes of up to -0.2 and -0.1 at wavelengths of 633nm and 810nm have been realized, respectively. The waveguide refractive index profiles as a function of the ion fluence have been determined. Planar waveguiding has been demonstrated by polishing sharp edges and using conventional end-fire coupling. The measured losses are approximately 7 dB/cm at 1.57mum.

Formation of planar optical waveguide by multi energy Si ion implantation into Nd:YVO 4 crystal

The planar waveguides have been fabricated in Nd:YVO 4 crystals by single and multi energy Si ion implantation. Optically polished Nd:YVO 4 samples were implanted at room temperature by 2.6 MeV Si ions and multi energy (3.0 MeV, 2.6 MeV and 2.2 MeV) Si ions, to the dose of 6 × 10 14 ions/cm 2. The prism-coupling method was carried out to measure the dark modes in the Nd:YVO 4 crystal waveguides by using a model 2010 prism coupler. In both waveguides 3 modes were observed before annealing and after annealing the effective refractive index of all these modes gets smaller. The two waveguides show much similarity in prism-coupling results. Reflectivity Calculation Method was applied to fitting the single energy ion implanted waveguide refractive index profile. TRIM'98 (Transport of Ions in Matter) code was used to simulate the damage profile in Nd:YVO 4 by a single and multi energy ion implantation, respectively. It is found that the electronic energy loss in ion implantation may play an important role in Nd:YVO 4 waveguide formation.

Systematic modeling study of channel waveguide fabrication by thermal silver ion exchange

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device.

Single-Mode Refractive Index Reconstruction Using an NM-Line Technique

A new technique for the measurement of single-mode planar waveguide refractive index profile is developed. This technique, based on the successive etching and effective index measurement, is applied on planar guides fabricated on a glass substrate using K+-Na+ ion exchange where the guide is etched using diluted HF acid and the mode effective index is measured by the well-known M-lines technique. The profile measured by this technique is assisted by modal calculations using a numerical mode solver and a strong agreement is obtained.

Determination of refractive index profiles of Ag^+-Na^+ ion-exchange multimode strip waveguides by variable wavefront shear double-refracting interferometry microinterferometry

The results of experimental determination of multimode strip waveguide refractive index profiles and Ag concentration profiles obtained by using the variable wavefront shear double-refracting interferometry microinterferometer Biolar PI and an electron microprobe are presented. The strip waveguides under investigation are formed in soda lime glass in an external electric-field-assisted Ag+ -Na+ ion-exchange process from the molten AgNO3 salt by use of dielectric masks with channel apertures. A dry electrochemical technique of dielectric mask formation is applied. The influence of waveguide-forming parameters on the shape of Ag concentration profiles and the range of silver diffusion are shown. Changes in the usually assumed boundary conditions of electric-field calculations in ion-exchange numerical modeling are suggested.

Construction of refractive‐index profiles of graded‐index planar waveguides from effective indexes measured with different mode types and external refractive indexes

AbstractA method is presented whereby the refractive‐index profile (RIP) can be reconstructed from sets of effective indexes measured with different mode types and external refractive indexes. Single‐mode waveguide RIP characterization can be easily realized using an index‐matching liquid at a single wavelength. This method is described and demonstrated via numerical examples and experimental results. The method has the advantages of convenient operation and accurate results for the characterization of graded‐index planar waveguides that support both mode types and contain known modal birefringence. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 342–345, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20818

Planar waveguide lasers by proton implantation in Nd:YAG crystals

The performance of CW Nd:YAG waveguide lasers operating at 1.06 microm at room temperature is described. The waveguides were fabricated by proton implantation and the main differences in the process of fabrication were the angle of implantation and the total dose implanted. The characterization of the waveguide refractive index profile induced by proton implantation and the main laser characteristics i.e., slope efficiency and threshold are presented.

Planar waveguides in Ce:SBN and Cu:KNSBN crystals by 6.0 MeV B 3+ ion implantation

Planar optical waveguides were formed in Ce:SBN and Cu:KNSBN crystals, respectively, by means of 6.0 MeV B 3+ ion implantation at a dose of 2×10 14 ions/cm 2 at room temperatures. The prism coupling method was performed to characterize the dark-mode property of the waveguides. The reconstructed refractive index profiles in the waveguides were found to be typical barrier-type distributions. Transport and range of ions in matter (TRIM 98) code was used to simulate the process of the implantations. The shapes of nuclear energy loss distribution of the B 3+ implantation were similar to those of the waveguide refractive index profiles, which means an inherent relationship between the waveguide formation and the energetic energy deposition.

Refractive index profile of waveguide in NdLiP 4O 12 laser crystal formed by MeV He + ion implantation

The fabrication and characterization of a planar waveguide are reported in NdLiP 4O 12 crystal which can be used for low-threshold, miniature laser. The photoluminescence (PL) measurement shows that there are three peaks around 0.911, 1.077 and 1.366 μm for bulk NdLiP 4O 12. Rutherford backscattering/channeling has been used to check the composition and quality of NdLiP 4O 12 crystal. A waveguide laser in NdLiP 4O 12 crystal is formed with MeV He ions. The refractive index profiles, n x , n y and n z in NdLiP 4O 12 waveguide are given. The changes of refractive index profiles n x , n y and n z are 6.11%, 6.51% and 9.37%, respectively. The refractive index change strongly depends on the crystal structure.

Nonconventional characterization of single-mode planar proton-exchanged LiNbO 3 waveguides by Cherenkov second harmonic generation

A nonconventional characterization method for single-mode planar proton-exchanged (PE) LiNbO 3 waveguides is presented. The method exploits the dependence of the output angle of Cherenkov second-harmonic radiation-mode on the boundary conditions of the fundamental guided mode, and thus, in particular, on the cover refractive index. The measurement of this angle in the presence of different liquid covers of known refractive index provides sufficient information to determine both parameters of the waveguide refractive-index profile, i.e., the index change and the optical depth. The experimental results confirm the reliability of the method proposed.

Determination of ordinary refractive index profile for a planar waveguide by transmission spectrum analysis

We introduce a new method to determine the ordinary refractive index profile of a planar waveguide on a crystal plate. The index profile of the planar waveguide can be numerically divided into multilayers; the transmission spectrum of the multilayer waveguide can be calculated and numerically analyzed to fit the measured transmission spectrum. We demonstrated this method on a proton exchanged planar waveguide in z-cut LiTaO3. We found that the ordinary refractive index profile of this waveguide can very well be described by a Fermi–Dirac function. The index profile evolution with proton exchange time and anneal time were obtained together with the diffusion coefficients for the proton exchange and anneal processes. We discovered that, for the proton exchange process in LiTaO3, there exists a surface diffusion phenomenon which has a much smaller diffusion coefficient than that of the bulk diffusion.

Determination of refractive index profiles of gradient optical waveguides by ellipsometry

Ag +-Na + and K +-Na + ion-exchanged optical waveguides in soda-lime glass are characterised by ellipsometry. Refractive index profiles of the waveguides are calculated from ellipsometric multiple angle of incidence data using the Newton-Kantorovitch type iterative procedure and compared with those reconstructed by inverse WKB method. It is demonstrated that such continuous profiles with relatively small index gradient (of the order of 0.1 and 0.01), extending to few micrometers in depth, can be determined by ellipsometric measurements. A good agreement is found between results obtained by ellipsometry and by the inverse WKB method at depths above 500–600 nm, while there is a difference in the subsurface region, where ellipsometry is more sensitive to the quality of the surface. The profiles obtained by the two methods are consistent if the surface thin layer is etched.

Dilute-melt, proton-exchange slab waveguides in LiNbO_3: a new fabrication and characterization method

A method of dilute-melt proton exchange employing a mixture of glycerol and KHSO4 with lithium benzoate added is used to fabricate planar waveguides in c -cut LiNbO3 . With this exchange melt system the waveguide refractive-index profiles can be fabricated with a high degree of reproducibility. In contrast with the traditional dilute-melt method, which uses benzoic acid and lithium benzoate, the need for sealed containers during the exchange process can be avoided when the glycerol, KHSO4 , and lithium benzoate system is used for the exchange process. A new characterization method for determining the waveguide refractive-index profile from the measured-mode indexes is introduced. The main advantage of this characterization method compared with other methods is that it also applies to single-mode waveguides. Using the new characterization method, we investigate in detail the relation between waveguide refractive-index change and composition of this glycerol, KHSO4 and lithium benzoate exchange melt system.

Construction of glass waveguide refractive index profiles by the effective-index finite-difference method

A numerical method is applied to construct the refractive index profiles of optical waveguides from the measured effective indices (EI). The method is based on choosing a proper analytical function for the refractive index profile and searching its unknown parameters using the simplex search algorithm. Simultaneously, the finite-difference method (FDM) is used to solve the semi-vectorial Helmholtz equation for the guided modes effective indices. The method is applied successfully to two particular Ag +Na + ion-exchanged glass slab waveguides. The results are as accurate as those obtained from from commonly used IWKB-based method. The EI-FDM in principle can be applied to both slab and channel waveguides and does not require that the index profiles are monotonically decreasing, like most of IWKB-based methods. The relation between the induced refractive index and silver concentration profile, measured by SIMS, is found to be almost linear.

Improved near-field method for refractive index measurement of optical waveguides

Refractive index profiles of waveguides are deduced from near-field intensity distributions of guided modes. To improve the accuracy of refractive index profiles, some measurements are taken with the center peak of the mode intensity profile blocked, allowing the increase of the optical power at the waveguide boundaries with a corresponding increase in the signal-to-noise ratio. Additional improvements reported here are related to the subsequent signal processing, which is performed mainly in the spatial frequency domain. Smooth and reliable profiles of channel waveguides are obtained, the method being very general and not presuming the functional dependence of n(x, y).