Mode Splitter Research Articles

Compact Variable ${\rm TE}$-${\rm TM}$ Polarization Splitter Based on Simplified Coherent Coupling in Lithium Niobate

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.

Variable Transverse-Electric and Transverse-Magnetic Mode Splitter Using Nickel Diffusion and Annealed Proton-Exchange Lithium Niobate Waveguides

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.

Coupling between long range surface plasmon polariton mode and dielectric waveguide mode

Coupling of TM mode between long range surface plasmon polariton (LRSPP) mode and conventional dielectric waveguide mode is demonstrated numerically with finite element method. The characteristics of a hybrid coupler, which consists of the LRSPP waveguide and conventional single mode dielectric waveguide, are analyzed. The high efficient coupling shows a possible route for integrating the SPP device and conventional dielectric optical devices together and a method to excite LRSPP mode with dielectric waveguide. Because the coupling just occurs on TM mode, this kind of the hybrid coupler can be used as polarization mode splitter and combiner.

Analysis of hollow optical fiber couplers using the compact two-dimensional finite-difference time-domain method

The coupling characteristics of newly proposed hollow optical fiber (HOF) couplers are rigorously analyzed using the compact 2-D finite-difference time-domain (FDTD) method. The FDTD-simulated coupling efficiency as a function of the coupling length, and the transverse electric field distributions of the higher-order mode converted by the HOF couplers, are investigated. We propose that the designed HOF couplers can be used for various optical devices such as side-pumping double-clad fibers, mode splitters, and power monitors.

Mode splitter based on triple-core waveguide

The mode index and mode field of a triple-core waveguide are simulated by the compact supercell method and the FEM method. The coupling property of LP(11) mode is analyzed, for the first time to our knowledge, which is similar to that of LP(01) mode except the different coupling length. Both LP(01) and LP(11) modes can be separated based on their different coupling lengths in the waveguide. When both modes are put into the central port, they will come out on different ports by optimizing the coupler length, and the mode extinction ratio can approach 30dB.

Coupling Characteristics of Fiber Optic Couplers Consisting of Two Circular Core Dual Mode Fibers

Coupling characteristics of a directional coupler consisting of two circular-core dual mode fibers are studied. In the case of a coupler fabricated with polished half-block technology, the coupling lengths corresponding to two degenerate LP11 modes LP11evenand LP11odd I are found to be very much different from each other. The two coupling lengths can, however, be made equal to each other if the coupler is fabricated using fusion technique and the two fibers are twisted with respect to each other by an angle equal to mπ/2, m being an integer. This means a mode splitter using two identical dual mode fibers would be extremely difficult to realize using the polished half-block technique, and should be fabricated using the fused-coupler technique.

Mode-order converter in a multimode waveguide

A novel device that converts the order of modes in an integrated-optic multimode waveguide was proposed and fabricated. The device consists of two mode splitters and tapered waveguides. Its operation at a wavelength of 1.55 microm was confirmed by observation of the output mode profiles. The cross talk measured by an indirect method was >10.2 dB. The excess loss with reference to a straight multimode waveguide was 1.5 dB, compared with the propagation loss of a straight multimode waveguide.

1.55 μm Ti:LiNbO3광도파로의 두 모드 간섭을 이용한 편광모드 분리기

두 모드 간섭 현상을 기초로 해서 1.55 <TEX>$\mu\textrm{m}$</TEX> 파장대역에서 동작하는 편광모드 분리기를 Ti: x-cut LiNbO<TEX>$_3$</TEX>광도파로 구조를 이용하여 설계, 제작한 다음, TE, TM 입사 모드에 따른 소자의 동작 특성을 측정하였다. 광도파로 폭, 분기각도와 간섭영역 길이를 8<TEX>$\mu\textrm{m}$</TEX>, 0.55<TEX>$^{\circ}$</TEX>, 470<TEX>$\mu\textrm{m}$</TEX>로 제작된 소자의 분리 비는 TE, TM 입사 모드 각각에 대해서 16.18 dB, 21.25 dB로 측정되었으며, 누화는 -16.28 dB, -21.28 dB로 측정되었다. 삽입 손실은 TE, TM 각각에 대하여 2.24 dB/cm, 2.41 dB/cm로 측정되었으며. 30 nm 파장 범위 내에서 비교적 균일한 분리 비가 관찰되었다. Passive polarization mode splitters at λ= 1.55 <TEX>${\mu}{\textrm}{m}$</TEX> were designed and fabricated based on Ti:x-cut LiNbO<TEX>$_3$</TEX> single-mode optical waveguide and two-mode interference theory. The splitting ratio with waveguide width 8 <TEX>${\mu}{\textrm}{m}$</TEX>, branching angle 0.55<TEX>$^{\circ}$</TEX> and interfering length 470 <TEX>${\mu}{\textrm}{m}$</TEX> showed 16.18 dB, 21.25 dB for TE and TM input polarization modes, respectively. Polarization cross-talk of -16.28 dB and -21.28 dB for TE and TM modes was achieved. Total insertion losses of 2.24 dB/cm (TE) and 2.41 dB/cm (TM) were also measured. The devices operated nearly wavelength independently over a range or 30 nm.

Two-wavelength planar add/drop WDM filter employinga three-mode coupling Bragg grating

A novel six-port planar waveguide device for adding and dropping two wavelengths from a wavelength division multiplexing singlemode fibre using a single blazed grating is presented. By writing a Bragg grating into a multi-moded core at a particular angle to the waveguide propagation direction, power can be coupled from the fundamental mode into only the backward-propagating higher-order modes, which are then separated using an adiabatic mode splitter. Modelling results indicate that &gt; 99.9% of the power in the fundamental can be transferred to the higher-order modes at their respective Bragg wavelengths, with crosstalk between channels of &lt; –30 dB.

TE-TM mode splitter with heterogeneously coupledTi-diffused and Ni-diffused waveguides on Z-cut lithium niobate

A coupling type mode splitter with an extraordinary polarisation and a random polarisation waveguide made by Ni and Ti indiffusion, respectively, on a Z-cut LiNbO3 substrate is described for the first time. With optimised process parameters, a very small TM mode profile mismatch is obtained due to the similar characteristics of the Ti- and Ni-diffused waveguides. The measured extinction ratios of the TE and TM modes at 1.55 µm wavelength are &gt; 22 dB.

Design and fabrication of wide-angle TE-TM mode splitter in lithium niobate

A novel wide-angle TE-TM mode splitter in a Z-cut lithium niobate is presented. A straight random polarization nickel-indiffused waveguide and a proton-exchanged waveguide bend with substrate prism on the bend corner were combined to form an asymmetric wide-angle Y-branch. The waveguide bend with substrate prism bends the TM wave to the proton-exchanged waveguide with large angle. Hence, the TE wave is left in the straight NI waveguide. The experimental results show that the splitting ratios are 26 dB for the TE mode and 28 dB for the TM mode even at a splitting angle of 7.

Method for calculating the properties of polarisation-maintaining 3D waveguides in very thin multilayered structures

We propose and analyse a new optical three-dimensional waveguide having the function of a single-mode polarisation-maintaining waveguide or TE/TM mode splitter. In the optical waveguide proposed, a multilayer film composed of two dielectric materials with different refractive indices provides confinement in the height direction, and strong mode separation between TE- and TM-like modes, whilst a strip-loaded or rib-type structure provides confinement in the lateral direction. A full analysis of the structure based on a mode-matching method and a familiar equivalent circuit representation of 3D waveguides is presented. We also discuss several fundamental properties of the guided waves supported by the proposed waveguide for various structural parameters.

Determination of eigenmodes by using Cauchy's integralformula

A deterministic method is proposed for the computation of zeros within a complex plane by using Cauchy's theorem. The integrals have been calculated for different numbers of integration points by the Gaussian integration formula. As an example, several eigenmodes of a TE/TM mode splitter have been determined by the proposed method.

Nickel-Indiffusion Waveguide for TE-TM Mode Splitter in Lithium Niobate

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.

Characterization of metal-clad TE/TM mode splitters using the finite element method

A metal-clad directional coupler-based polarizer with two-dimensional (2-D) modal confinement has been designed and its performance has been rigorously computed by using the accurate vector H-field finite element method after taking into consideration the polarization-dependent coupling lengths, phase mismatchings and losses due to metal-cladding of the system involved.

A novel Y-branch waveguide for power dividing and mode splitting

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.

Overlapping-image multimode interference couplers with a reduced number of self-images for uniform and nonuniform power splitting

Overlapping-image multimode interference (MMI) couplers, a new class of devices, permit uniform and nonuniform power splitting. A theoretical description directly relates coupler geometry to image intensities, positions, and phases. Among many possibilities of nonuniform power splitting, examples of 1 × 2 couplers with ratios of 15:85 and 28:72 are given. An analysis of uniform power splitters includes the well-known 2 × N and 1 × N MMI couplers. Applications of MMI couplers include mode filters, mode splitters-combiners, and mode converters.

TE-TM mode splitter using directional coupling between heterogeneous waveguides in LiNbO/sub 3/

We propose and demonstrate a novel passive TE-TM mode splitter using an anomalous directional coupler consisting of Ti-diffused and annealed, proton-exchanged waveguides in LiNbO/sub 3/. The extraordinary wave was successfully power-transferred to the cross output with the extinction ratio of >12 dB in both X- and Z-cut LiNbO/sub 3/. The ordinary wave experienced no power transfer without any excess loss due to side-way diffusion of Ti or proton. The coupler length was only <1 mm at /spl lambda/=0.813 mm, which was short enough for optical integration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fabrication of TE/TM Mode Splitter Using Completely Buried GaAs/GaAlAs Waveguide

A GaAs/GaAlAs-system TE/TM mode splitter using the mode interference principle is described. Single- and double-mode waveguides are patterned by reactive ion etching after the first molecular beam epitaxy. They are then completely buried by liquid-phase epitaxy, which enables low loss propagation due to side-wall smoothness, because of the thermal deformation effect. For achieving low loss characteristics in this mode splitter, the surface treatment process before crystal growth and S-bend waveguide mask formation procedure are also optimized. Propagation loss of the single-mode waveguide is less than 1.0 dB/cm. In order to secure birefringence of the waveguide for mode splitting, upper and lower GaAlAs-cladding mol fractions are different. Finally, the fabricated device achieves the TE/TM mode splitting ratio of 8.2 dB for both polarizations.

A TE-TM mode splitter on LiNbO 3 using an asymmetric Y-junction with a gap region

A new type of TE-TM mode splitter is proposed, which uses an asymmetric Y-junction with a gap region. It does not require external electric field and can be fabricated by only titanium diffusion technique. The transmission characteristics of the splitter are simulated by means of the beam propagation method (BMP). The results show that the power splitting ratios for TE-TM modes are 20.3 dB and 23.5 dB, respectively and the excess losses both are below 0.25 dB.