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Compact lithium niobate polarization-independent electrooptic modulators using integration of polarization splitters and mode converters are presented. Experimental results show polarization-dependent loss as low as 0.04 dB can be achieved for devices fabricated on Z -cut substrates with an applied voltage of 26 V. The electrode lengths required for electrooptic modulation are 10 and 6 mm for TE and TM modes, respectively, and the total device length is only 1.6 cm. Moreover, only one diffusion step is required that greatly simplifies the fabrication process.

Polarization splitters with zinc–nickel and gallium indiffusion optical waveguides fabricated on Z-cut lithium niobate substrates are presented. The device fabrication process needs only one diffusion step and, therefore, is greatly simplified. Experimental results show that, at 1.55- $\mu \text{m}$ wavelength, the extinction ratios for the TE and TM modes are 27.8 and 24.5 dB, respectively.

Multimode interference (MMI) power splitters with various truncated-and-raised interference regions near the input edge are proposed. Simulation results show that ridge width decreasing is more effective for the reduction of non-uniformity and device length, whereas the ridge height increasing is more advantageous for the increase of the total transmitted power. Based on these results, MMI power splitter with a truncated-and-raised interference region is proposed. Simulation results show that the proposed power splitter can have both negligible non-uniformity and larger transmitted power.

A compact-sized electrically tunable TE-TM mode splitter composed of a mode converter and an asymmetric Y-branch structure is presented. The asymmetric Y-branch consists of a straight and a bent waveguides to split two polarization modes based on the mode-sorting effect. To shorten the device length, a simplified coherently coupled-bending structure is utilized for the bent waveguide. Experimental results show that the device length is reduced about 52%, extinction ratios of both TE and TM modes are higher than 25 dB, yet the applied voltage is not significantly increased.

The wavelength sensitivities of three kinds of nanostructures (nanoslits, nanoholes, and concentric circles) with various aperture sizes were compared in water environment. These nanostructures were made on a 110-nm-thick gold film with a period of 600 nm. Surface plasmon resonances in these nanostructures produce transmission dips near the phase-matching conditions while peaks at longer wavelengths. The wavelength sensitivities measured at dips are close to theoretical predictions and about 1.5 times larger than those measured at peaks. Such sensitivity difference is attributed to various surface plasmon distributions, as illustrated by the finite-difference time-domain calculations. In addition, the sensitivity decreases with the increase of aperture size. The nanoslit array and concentric circles have better sensitivities than the nanohole array due to the no cut-off transmission.

A novel variable transverse-electric and transverse-magnetic (TE–TM) mode splitter using nickel diffusion and annealed proton-exchange waveguides for the TE and TM branches of the splitter is presented. Due to the single-polarization property of the annealed proton-exchange waveguide, the measured polarization extinction ratio for the TE mode is higher than that reported. The measured polarization extinction ratio for the TM mode is as good as that reported, yet the fabrication process of single nickel diffusion is much simpler than that of double zinc-and-nickel diffusions. Moreover, the tunabilities of both TE and TM modes are found to be higher than those reported.

Multimode interference (MMI) couplers with a width of arbitrary-exponent binomial function are proposed. The proposed structure includes the conventional, butterfly, and parabolic structure such that the proposed MMI device can be used for equal and unequal power splitting. With a proper choice of the exponent of a binomial function, several equal and unequal optical powers splitting ratio can be obtained. For comparison, the optical power splitting ratios, total transmission, and coupler length of the proposed MMI couplers are discussed.

Buried-type benzocyclobutene (BCB) optical waveguides fabricated by UV pulsed-laser illumination are proposed and comprehensively characterized in this paper. The fabrication process is greatly simplified as compared to conventional dry-etched ridge-type BCB waveguides. The measured propagation loss at 1548 nm is as low as 0.6 dB/cm due to the buried waveguide structure. And the produced refractive index change is dependent upon the number of laser shots such that single-mode waveguides with different mode sizes can be tailored for efficient coupling. Furthermore, rigorous analyses of surface damage threshold, rms roughness, and chemical characteristics under different illumination conditions are presented to illustrate the design considerations and the chemical mechanism of the UV-induced BCB waveguides

A surface plasmon resonance (SPR) waveguide immunosensor fabricated by germanium-doped silicon dioxide was investigated in this study. The designed waveguide sensor consisted of a 10 microm SiO(2) substrate layer (n=1.469), a 10 microm Ge-SiO(2) channel guide (n=1.492) and a 50 nm gold film layer for immobilization of biomolecules and SPR signal detection. The resultant spectral signal was measured by a portable spectrophotometer, where the sensor was aligned by a custom-designed micro-positioner. The results of the glycerol calibration standards showed that the resonance wavelength shifted from 628 to 758 nm due to changes of refractive index from 1.36 to 1.418. Flow-through immunoassay on waveguide sensors also showed the interactions of protein A, monoclonal antibody (mAb ALV-J) and avian leucosis virus (ALVs) resulted in wavelength shifting of 4.17, 3.03 and 2.18 nm, respectively. The SPR dynamic interaction could also be demonstrated successfully in 4 min as the sensor was integrated with a lateral flow nitrocellulose strip. These results suggest that SPR detection could be carried out on designed waveguide sensor, and the integration of nitrocellulose strip for sample filtering and fluid carrier would facilitate applications in point-of-care portable system.

By adding lithium carbonate into a mixture of benzoic and adipic acids as the proton-exchange source, the wet-etched ridge structure in x-cut LiNbO3 is successfully fabricated. Both the etched depths and profiles are demonstrated to be outperformed those of the traditional wet etching method using pure benzoic acid, which is diluted by lithium benzoate. Meanwhile, the etched surfaces are shown to be very smooth. The proposed wet etching method can be further applied to fabricate high-quality components with ridge structure in x-cut LiNbO3. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2108–2111, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21874

We propose and demonstrate a polarization splitter, in which the power ratio between transverse electric (TE) and transverse magnetic (TM) modes at two output arms can be electrically controlled. The mode-sorting effect and off-diagonal electrooptic coefficient of LiNbO/sub 3/ are utilized for polarization splitting and conversion, respectively. To simplify design and fabrication processes, we apply a newly developed zinc and nickel codiffusion technique in LiNbO/sub 3/, by which TE-, TM-, and randomly polarized waveguides can all be made by simply using different fabrication parameters. To lower the applied voltage, ridge structure is used to increase the overlap integral between electric and optical fields. Measured extinction ratios of polarization splitting are higher than 21 dB for TE mode and 18 dB for TM mode, and the applied voltage can be reduced by a factor of one-third with a ridge of height 3 /spl mu/m. Finally an application example is proposed for future study.

This paper presents a novel wet etching method for LiNbO/sub 3/ using electric-field-assisted proton exchange. By applying voltage with appropriate polarity on designed electrodes placed on both sides of substrate, the induced electric-field distribution can effectively suppress or enhance proton diffusion in the lateral and depth directions. Thus, the proton-exchanged range in LiNbO/sub 3/ can be expertly manipulated. Because the proton-exchanged region can be removed by using a mixture of HF/HNO/sub 3/ acids, the proposed wet-etching method can effectively control the shape of the etched region in the LiNbO/sub 3/ substrate. Under appropriate electrode and proton-exchange parameters, a vertical sidewall with smooth surface is successfully produced, which makes fabricating reflection mirrors and T-junctions in LiNbO/sub 3/ possible. By utilizing the proposed wet-etching method, optical integrated circuits with higher integration density can be fabricated in LiNbO/sub 3/.

An abrupt bend structure with a corner reflector on LiNbO3 is proposed. In the proposed structure, a region whose refractive index is higher than that of the substrate is placed at the corner of the bend. The interface between the substrate and the high index region is used as a reflector for the guided wave. The calculated normalized transmission power is about 94% even when the bend angle is 10∘.

A novel Ni-diffused abrupt waveguide bend on LiNbO/sub 3/ using proton-exchanged microprism is presented. With the phase delay caused by the microprism, the guided wavefront can be appropriately tilted such that most of the optical power can be kept within the waveguide after passing through the bend corner. The simulated normalized transmitted power of the proposed waveguide bend can be as high as 93.33% for a bend angle of 10/spl deg/. The effects of microprism parameters are also discussed to facilitate the optimal design of the proposed waveguide bend. The experimental results show that the proton-exchanged microprism on LiNbO/sub 3/ does significantly enhance the transmitted power.

Single-mode asymmetric Y-branches using microprisms are proposed. With a bend prism designed by the bend phase compensation rule (bend PCR) and a pair of Y-branch prisms designed by the Y-branch PCR, the phase front mismatch at the branching point is greatly eliminated, resulting in wide-angle low-loss 3-dB asymmetric Y-branches. Furthermore, control of power-splitting ratios is fulfilled through varying the lengths of prisms for a fixed branching angle and a fixed prism index. Finally, cascades of the proposed structures are studied. It is shown that the construction of a satisfactory 1/spl times/N tree power divider based on the cascaded structures is possible.

A ridge-type Mach-Zehnder modulator on X-cut LiNbO/sub 3/ is fabricated by wet etching with proton-exchange pretreatment. Experimental results show that, with the assistance of the ridge structure, the drive voltage of the proposed modulator is reduced. The enhancement of overlap integral caused by ridge structure is also validated from numerical simulation. Moreover, an improved design to further reduce the drive voltage of the ridge-type Mach-Zehnder is proposed by a proper placement of waveguide relative to the electrode.

Diffusion characteristics of a joint-proton source for proton exchange in LiNbO3 are presented. With a concentration-dependent diffusivity derived from experimental results, the diffusion process is simulated to estimate the proton-exchanged wet-etched depth. Good agreement between simulated and measured depth is obtained. In addition, an S-shaped ridge waveguide is fabricated to demonstrate the improvement in power transmission efficiency. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2736–2738, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23752

Mach-Zehnder modulators fabricated by gallium diffusion in y-cut lithium niobate (LiNbO) are presented. The measured halfwave voltages are 6.2 and 3.2 V when the electrode lengths are 0.4 and 0.8 cm, respectively. By calculating the overlap integral between the modulating electric and the guided optical fields, the value of the electrooptic coefficient is found in good agreement with that of the bulk LiNbO, which indicates no significant degradation in is induced by the in-diffused gallium atoms.

Gamma-ray irradiation-enhanced wet-etching of proton-exchanged Z-cut Y-propagating LiNbO3 is presented. The etched ridge height of a sample with gamma-ray irradiation of intensity 650 krad/h on a LiNbO3 substrate for 30 min is three times larger than that without. Moreover, experimental results show the propagation loss values of Ti-indiffused LiNbO3 waveguides fabricated on the irradiated ridge structures are only slightly larger than those on the nonirradiated ones.

Benzocyclobutene directional couplers and 1times2 multimode interference (MMI) power splitters fabricated by ultraviolet (UV) pulsed-laser illumination are presented. With an accurate control of the fabrication process, the measured coupling lengths of the directional couplers are in good agreement with those simulated by the beam propagation method. In particular, accurate power splitting ratios of the directional couplers can be achieved by controlling the number of laser shots to obtain the required index changes. Moreover, MMI power splitters with accurate interference lengths and low imbalances can be successfully fabricated. All those reveal that UV pulsed-laser illumination is an accurate and controllable technique for the device fabrication.

Cyclic arrayed waveguide grating (AWG) devices with flat-top passband and uniform spectral response are proposed. Each access waveguide of the proposed cyclic AWG consists of a multimode interference region and a taper waveguide. Simulation results show that the 1-dB bandwidth of the proposed device is larger than 0.44 times the channel spacing and the corresponding nonuniformity is smaller than 1 dB.

Gallium oxide used as a diffusion source for the fabrication of lithium niobate optical waveguides is presented. The optical waveguide properties are investigated and the behavior of the in-diffused gallium is characterized by the secondary ion mass spectroscopy. Single-mode single-polarization optical waveguides with low propagation loss at 632.8 and 1550 nm can be obtained. For reference, the diffusion constant and activation energy of the in-diffused gallium atoms are also obtained.

Transmission characteristics of gamma-irradiated LiNbO3 waveguides, made by five different methods, are measured and studied. All samples were irradiated with a dosage of 800 krad/h to a total amount of 10 Mrad. With the increasing gamma-irradiation intensity, the annealed proton-exchange waveguide shows the most anti-irradiative ability and the lowest transmission loss, where the measurements were carried out at a wavelength of 633 nm in a harsh gamma-irradiative environment.

A low-loss large-angle waveguide bend structure utilizing a low-index microprism is proposed. Using the principle of phase front compensation, a simple and efficient rule for the low-index prism is derived. Field distortion due to the prism is discussed and an optimized prism design is also proposed. Simulated normalized transmission efficiency of the proposed waveguide bend is as large as 99.1% for a bend angle of 10/spl deg/. Moreover, waveguide bends with high- and low-index prisms are compared for reference.

By mixing benzoic and adipic acids as the source of proton exchange, wet etched ridge waveguides are fabricated in Z-cut LiNbO3. Under appropriate adipic-benzoic acid concentration ratios, the joint proton source can suppress the proton diffusion in the lateral directions, and thus, the sidewalls are much more vertical than the usual. The etched depths are also enhanced for more than 30%. And meanwhile, the fabricated ridge waveguides possess smooth surfaces and the scattering losses are lower than that of the conventionally produced samples

Surface plasmon resonance (SPR) sensors made by multimode silica-on-silicon channel waveguides are investigated theoretically and experimentally. Promising sensing characteristics, with sensitivity up to 4547 nm/RIU, are observed over a wide detection range without a conventional tuning-layer design. The Si-based device-fabrication process offers great potential for high-level sensor integration. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 955–957, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21531

Process-dependence characteristics of Zn-diffused waveguides on a y-cut, x-propagation LiNbO3 substrate at 1.55-μm wavelength are presented for the first time. The experimental results show that a single-mode waveguide of extraordinary polarization is easily fabricated and can serve as an effective TE-pass waveguide polarizer. The best polarization extinction ratio of 32 dB/cm and the corresponding propagation loss of 0.9 dB/cm are obtained. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2312–2314, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21923

Optical waveguides fabricated by nickel indiffusion on lithium niobate are reviewed. In particular, the fabrication process, index change versus concentration, wavelength dispersion, process-dependent polarization, propagation loss, and electro-optic modulation of the nickel indiffusion waveguide are discussed. To improve the confinement of single-ordinary polarization waveguide fabricated by nickel indiffusion, a novel waveguide made by zinc and nickel indiffusion is presented for the first time. Though the measured propagation loss of the waveguide is larger, the measured output power contours are found more symmetric. Moreover, several TE-TM mode splitters using one or more nickel indiffusion waveguides for the complete mode sorting effect are discussed.

An improved multigrid technique for the quasi-TEM analysis of a microstrip line embedded in an inhomogeneous anisotropic dielectric medium is presented. A general finite-difference form for the inhomogeneous anisotropic medium is derived by the finite-volume discretization of Gauss's theorem. By the analogy between the quasi-TEM and the steady current problems, this general form can be interpreted by Kirchhoff's current law. Then, the electric potential distribution in this complicated dielectric structure can be regarded as that on a resistive network, which makes the formulation easier. The resulting matrix equation for the potential distribution on the finest grid is solved by the improved multigrid iteration, where the coarse-grid operator is derived directly from the finest grid operator by the help of an equivalent resistive network. Three numerical examples show that the convergence rate is hardly dependent of the number of unknowns and the complexity of the dielectric media. Moreover, the numerical results are in good agreement with those by the other method when special cases are considered.

By the technique of nickel indiffusion proton exchange (NIPE) and the technique of buffered proton exchange (PE) melt, wet-etched ridge waveguides in y-cut LiNbO/sub 3/ are fabricated for the first time. The fabricated ridge waveguides have smooth surfaces and are good enough for low-loss waveguides. Moreover, a ridge waveguide Mach-Zehnder modulator in y-cut LiNbO/sub 3/ is fabricated. The measured half-wave voltage is about 30% lower than that of a conventional modulator. The wet-etched ridge waveguides in y-cut and z-cut substrates are also characterized for comparison.

A novel three-branch optical power divider with a diamondlike microprism of low index is proposed. The input power can be equally distributed to three output waveguides at large branching angles. The total transmitted power is as high as 97.7% at θ = 3°, which is higher than that reported. Furthermore, by simply varying the size or refractive index of the microprism, the percentages of the power entering the central and the outer branches can be adjusted. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 145–147, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20750

Ridge structures are fabricated on gamma-ray irradiated lithium niobate substrates to modify the modal field distributions of titanium-diffused waveguides. Experimental results show the measured modal field distributions are very close to that of a fiber.

Field distributions of 1-to-N multimode interference optical power splitters with two cascaded multimode interference regions are calculated. An improved objective function is presented for the optimization of the proposed devices.

A novel Y-branch waveguide for variable-ratio power dividing and transverse electrical-transverse magnetic (TE-TM) mode splitting depending on the applied voltage is presented. The Y-branch waveguide is formed by two closely coupled waveguides tabricated by nickel indiffusion (NI) and by magnesium-oxide induced lithium outdiffusion (MILO) in a y-cut lithium niobate (LiNbO3) substrate. The TE component of the randomly polarized light is tuned between these two waveguides, such that the device can be either a power divider or a mode splitter depending on the applied voltage. The measured TE mode extinction ratio is about 20 dB.

A new wide-angle low-loss abrupt bend is presented. A prism-like region of index equal to that of the substrate is placed at the bend corner to compensate the phase mismatch caused by the bend. The novel abrupt bend has been fabricated on a LiNbO/sub 3/ substrate by proton exchange. The experimental result shows that the normalized transmitted power is 63% with a bend angle of 10/spl deg/, which is quite close to the simulated result.

Optical waveguides based on benzocyclobutene polymer are fabricated by electron-beam direct writing without etching. The propagation losses of waveguide measured at 1.55 μm for both TE and TM polarizations are 0.76 and 0.86 dB/cm, respectively. Moreover, the characteristics of waveguide bends are discussed for comparison. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 208–210, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20254

Zn-diffused Mach–Zehnder intensity modulators operating at 1.55-μm wavelength are demonstrated on a z-cut and a y-cut LiNbO3 substrate for the first time. The switching voltages are measured and the corresponding values of switching voltage-length product are 9.6 V-cm and 13.5 V-cm for the z-cut and y-cut modulators, respectively. Both the modulated extinction ratios are about 20 dB. The results show that the Zn-diffused modulators not only have electro-optic tunability as great as that of the Ti-diffused ones, but also have more flexibility for device fabrication. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 142–144, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20401

By using micro-prisms, improved three-dimensional (3-D) bends of the embedded and buried waveguides of step-index profile are proposed. A simple phase compensation rule for the optimal design of the micro-prism is also presented. Through the simulation of 3-D semivectorial finite-difference beam propagation method, the transmission characteristics of the improved bends are shown to have been enhanced dramatically as compared with those of the conventional ones. Even for a bend angle of as large as 10/spl deg/, the normalized transmitted power can still be greater than 95%. These results of 3-D bends are then compared with those of the two-dimensional (2-D) ones which are simplified from 3-D structures by the effective index method, and physical explanation of the discrepancy between the 3-D and 2-D results is introduced. The influences of waveguide structures and prism parameters on the transmission characteristics are discussed in detail. Some criteria for the design of large-angle low-loss 3-D improved bends are also accessed. >

A novel large-angle low-loss direction-coupler type power divider with designed ratio between output waveguides is proposed. The radiation loss is greatly reduced by using a micro-prism at the bend corner to compensate the phase mismatch due to bending. A normalized transmitted power of the power divider with a bend angle of 10/spl deg/ simulated by the semivectorial beam propagation method is about 93%, which is much larger than those were reported for single-mode waveguides. Application of more micro-prisms is also shown. The calculated loss of a symmetric large-angle 3-dB directional coupler with eight micro-prisms is less than 0.953 dB. >

The nanoscaled tris-(8-hydroxyquinoline) aluminum (AlQ3) crystalline film was synthesized by vapor condensation. It was stacked with nanometer-sized rods, approximately 100 nm wide and 1 μm long, and had a surface roughness of about 100 nm. The vibronic progression with several separated peaks was observed in the photoluminescence spectrum at room temperature. It is attributed to the crystallinity of AlQ3 and the coupling of vibrations of the individual ligands to the fluorescence transition. The emission current was also observed with a turn-on field of 12.0 V/μm, and a current density of about 0.8 mA/cm2 at 22 V/μm. Therefore, the AlQ3 crystalline film provides a choice for field emission.

A new wide-angle 1/spl times/3 optical power divider with variable power splitting using substrate microprisms and two waveguide expanders is experimentally demonstrated by nickel diffusion in LiNbO/sub 3/. The produced substrate microprism with a graded-index profile and a depth-varied size is proved to be effective to produce phase-front tilt and field modification when in operation with two waveguide expanders. Experimental results show that the tuning range of the power splitting ratio can be 0.25/spl sim/1.69 and 0.18/spl sim/>1.09 with low insertion loss for branching angle /spl theta/=3/spl deg/ and 4/spl deg/, respectively. The fabricated devices have the features of low insertion loss, large branching angle, wide power tuning range, and easy fabrication.

Based on a simplified coherent coupling effect, a compact Y-branch power divider with polymer waveguides is presented. The simulated and measured normalized transmitted powers are 0.88 and 0.75 when the effective branching angle is as large as 19.7/spl deg/. For the same transmission efficiency, both theoretical and experimental results show that the length required for the proposed Y-branch is shorter than those for the conventional S-bend configurations. Furthermore, the transmission spectrum shows that the proposed Y-branch is suitable for a dense wavelength-division-multiplexing application.

The variation of thermo-optic coefficient caused by gamma irradiation is investigated for the fiber Fabry-Perot interference (FFPI) sensor. The sensor is formed by fusing fibers with different core diameters, and its thermo-optic coefficient is measured during irradiation up to doses higher than 1 MGy. The method used to measure the thermo-optic coefficient shows excellent agreement with Sellmeier equation with a difference of only 0.2%. Experiments show that the relative change of thermo-optic coefficient increases only by 2.1% and saturates at a total dose of 300 kGy, which suggests that the fiber FFPI sensor is suitable for use in harsh gamma radiation environments.

A new TE-TM mode splitter with an asymmetric Y-junction structure fabricated by diffusing different materials into Y-cut lithium niobate is presented. Randomly polarized light launched into a titanium indiffused waveguide is split into TE and TM modes by two different single-polarization waveguides. The ordinary-polarized waveguide is made by nickel indiffusion and the extraordinary-polarized waveguide by magnesium-oxide induced lithium outdiffusion. The measured extinction ratios are greater than 20 dB for both TE and TM modes. The devices operate over a wide wavelength range and have a large fabrication tolerance. >

The temperature profiles of thermo-optic waveguides are analyzed by the finite element method. The heat generated by a thin-film heater causes the temperature of a nearby waveguide to increase. The analysis results show that thermal coupling is a function of the waveguide spacing and depth. Thermal coupling increases with the waveguide depth but decreases with the waveguide spacing. Thermal coupling could be reduced by placing a cooler on the adjacent waveguide or etching a deep trench between the waveguides. The cooler can reduce the coupling, but it is not effective for deep waveguides. For the trenched structure, the temperature of the heated waveguide increases as the trench depth increases; however, the temperature of the nearby waveguide will decrease.

A new low-loss abrupt bend structure of the microprism type is proposed. This new bend uses a microprism to compensate for the phase difference of the phase front before and after the bend corner, so the entire phase front of the eigenmode is tilted properly, resulting in a very low-loss characteristic. Simulated results show that a normalized transmitted power of greater than 95% is achieved for a bend angle of 10/spl deg/. Moreover, a phase compensation rule and its corrections are presented to determine the optimal prism parameters. Application examples of the microprism to design a very low-loss large-angle Z-bend and two cascaded Z-bends are also shown. >

The modified ray-optics method is used to analyze the coupling efficiency from a Gaussian beam to a rectangular multimode embedded strip waveguide. It is convenient for analyzing the case of a simple waveguide structure because of reduced computation time. The conditions for determining which optical rays can be coupled into the waveguide to become the waveguiding modes, as well as the effective receiving area of the waveguide, are derived in this work. The data obtained by this method are compared with those calculated by the well-known overlap integral theorem and Marcatili's models for investigating the validity of the modified ray-optics method.

In this paper, a new iterative method to solve for the modal indices and field profiles of the supermodes of multichannel waveguide structures is proposed. This method combines the shift inverse power method with the simultaneous iteration method, and can be applied to any longitudinally invariant waveguide couplers problem very efficiently. Using this method, the characteristics of the leading supermodes can be obtained simultaneously. The validity and accuracy of this method are assessed by comparing to other existing methods for symmetric two-channel waveguide couplers. Results are in good agreement. Asymmetric two-channel and symmetric three-channel waveguide couplers are then considered to show the usefulness and versatility of the proposed method. >