Optical Polarization Splitter Research Articles

Intelligent design of large angle deflection beam splitter based on method of moving asymptotes

Photonic chip is a kind of integrated device that uses light as a carrier for information transportation and processing. Owing to its advantages of small size, lightweight, and low power consumption, photonic chip has become the most popular research topic nowadays. The beam splitter is a vital part of on-chip integration. For conventional beam splitting elements, Y-type and tree-branch output are the main elements, which are usually realized by interference principles. However, it is appropriate only for simple conventional beam splitter because the propagation direction of light cannot achieve large angle deflection. In the case of relay loading, optical amplification, pumping, and frequency upconversion, the vertical loading is often required without affecting the main optical path. To complete the large-angle deflection beam splitting, one needs to add a mirror to realize it or use a right-angle mirror structure for geometric double-sided reflection and splitting in traditional ways, but these structures are relatively complicated and difficult to complete on-chip integration. Based on previous work on inversely designed multi-channel wavelength routers and wide spectrum efficient focusing devices by using the intelligent algorithm, and combining the years of research on the coherent superposition theory of multi-scattering of the disordered medium, a large angle beam splitter that can realize from the near-infrared band is designed through using the intelligent algorithm. The beam splitter structure is based on AMTIR-1 glass, the part to be etched is air. The composition of AMTIR-1 is Ge<sub>33</sub>As<sub>12</sub>Se<sub>55</sub>. And the size of the structure is only 1 μm × 2 μm. The beam splitter can achieve 180° linear separation of beams in a range from 800 nm to 1100 nm, the beam splitting ratio of the entire waveband is approximately 1∶1, and the gross beam splitting efficiency is stable between 85% and 92%. Compared with several conventional structures with the same size, the efficiency of the beam splitter designed by this algorithm is higher. At the same time, the algorithm has the advantages of fast computation speed and small computation amount, and it can be completed only by ordinary personal computers without the support of hardware such as workstations. This intelligent algorithm can also be applied to the design of various passive photonic devices such as optical polarization splitters, routers, optical isolators, etc., providing an idea and reference for the design of integrated micro-nano photonic devices on high-density sheets.

On-chip broadband ultra-compact optical couplers and polarization splitters based on off-centered and non-symmetric slotted Si-wire waveguides

In this work, we propose novel schemes to design on-chip ultra-compact optical directional couplers (DC) and broadband polarization beam splitters (PBS) based on off-centered and asymmetric dielectric slot waveguides, respectively. Slot dimensions and positions are optimized to achieve maximum coupling coefficients between two symmetric and non-symmetric slotted Si wire waveguides through overlap integral method. We observe >88% of enhancement in the coupling coefficients when the size-optimized slots are placed in optimal positions, with respect to the same waveguides with no slot. When the waveguides are parallel, in that case, a coupling length as short as 1.73 μm is accomplished for TM mode with the off-centered and optimized slots. This scheme enables us to design optical DC with very small footprint, Lc ∼ 0.9 μm in the presence of S-bends. We also report a compact (Lc ∼ 1.1 μm) on-chip broadband PBS with hybrid slots. Extinction ratios of 13 dB and 22.3 dB are realized with very low insertion loss (0.055 dB and 0.008 dB) for TM and TE modes at 1.55 μm, respectively. The designed PBS exhibits a bandwidth of 78 nm for the TM mode (C-and partial L-bands) and >100 nm for the TE mode (S + C + L wavelength bands). Such on-chip devices can be used to design compact photonic interconnects and quantum information processing units efficiently. We have also investigated the fabrication tolerances of the proposed devices and described the fabrication steps to realize such hybrid devices. Our results are in good agreement with 3D FDTD simulations.

Selectively coupling core pairs in multicore photonic crystal fibers: optical couplers, filters and polarization splitters for space-division-multiplexed transmission systems

Selective coupling a single pair of cores in a photonic crystal fiber with multiple, initially decoupled, cores is demonstrated through the use of a technique to locally post-process the fiber cross section. Coupling occurs when the hole between the selected core pair is collapsed over a short fiber section, which is accomplished by heating the section while the hole is submitted to an air pressure that is lower than that applied to all other holes in the microstructure. The demonstrated couplers present an estimated insertion loss of ~1 dB and exhibit spectral modulations with a depth of up to 18 dB and a high polarization sensitivity that can be exploited for polarization splitting or filtering in space-division-multiplexed optical interconnection and telecommunication links.

Design and fabrication of a three-dimensional polymer optical waveguide polarization splitter

We present a design and fabrication of a three-dimensional polymer optical waveguide polarization splitter by taking into consideration of the induced birefringence effect of the polymer. We show that it is not possible to couple TM light from one waveguide to the other but evanescent coupling for TE light is possible. Hence the polarization splitter can be designed by considering TE mode coupling alone. This has an advantage of short interaction length of the device. Based on this consideration, we fabricated a polarization splitter with a TE extinction ratio of 15 dB and TM extinction ratio of 21 dB.

Design of optical polarization splitters in a single-section deeply etched MMI waveguide

The design of a single-section polarization splitter in a deeply etched semiconductor MMI waveguide is presented. Numerically simulated results indicate that the semiconductor MMI exhibits considerable polarization dependence and, utilizing this effect, a compact 1.6-mm-long polarization splitter may be fabricated to yield more than 8-dB polarization separation and only 0.11-dB optical loss, using a very simple design-approach.

A study of wet oxidized Al/sub x/Ga/sub 1-x/As for integrated optics

An investigation of wet oxidized Al/sub x/Ga/sub 1-x/As layers in integrated optical applications is reported. Refractive index and thickness shrinkage of wet oxidized Al/sub x/Ga/sub 1-x/As layers are measured using spectroscopic ellipsometry. A Cauchy fit to the refractive index is found in the wavelength range between 0.3 and 1.6 μm. The refractive index at 1.55 μm is found to be 1.66/spl plusmn/0.01 with little dispersion around 1.55 μm. Very low loss single-mode waveguides with metal electrodes showing very low polarization dependence of loss coefficient are fabricated using wet oxidized Al/sub x/Ga/sub 1-x/As layers as upper cladding. Optical polarization splitters are also designed and fabricated from the same type of waveguides taking advantage of increased birefringence. Designs utilizing wet oxidized Al/sub x/Ga/sub 1-x/As are compared with conventional designs using only compound semiconductor heterostructures.

Integrated optical polarization splitter based on photobleaching-induced birefringence in azo dye polymers

An integrated optical polarization splitter has been fabricated by utilizing the photobleaching-induced birefringence in an azo dye polymer. It consists of a Y-branch waveguide formed by the reactive ion etching with one of the two arms photobleached. The refractive index of the photobleached arm is decreased for the TE mode and increased for the TM mode. The performance of the splitter was measured as a function of the energy of the photobleaching beam and compared to a wave propagation simulation of the device. The measured cross talks are less than -28 dB for the TM mode and -24 dB for the TE mode at a wavelength of 1310 nm. The measured excess losses for the TE and TM modes, which measure the effect of the Y branch and the photobleaching, are 0.3 and 0.4 dB, respectively. The insertion loss was 5 dB, which includes the input fiber to waveguide coupling loss.

Directional coupler based on radiatively coupled waveguides

We investigate a system of two waveguides with leaky modes sharing a common substrate (radiatively coupled waveguides). The main advantage of such a system is the possibility of remote coupling. A perturbation theory is developed for both TE and TM polarization. Numerical calculations of dispersion curves and of the coupling length allow us to determine the limitations of the perturbation theory. We study the influence of multimode interference on the process of beating by considering the propagation of a given initial field. Finally, we propose a new design for an effective, integrated optical TE-TM polarization splitter.

Analysis of a novel intersection waveguide‐type optical polarization splitter using birefringence of GaInAsP/InP superlattice

AbstractA novel intersection waveguide‐type polarization splitter based on total reflection using the birefringence of the GaInAsP/InP superlattice waveguide is proposed and analyzed in this paper. The semivectorial finite difference beam propagation method (FD‐BPM) (which handles both TE and TM modes) is used in the analysis. The waveguide structure including the GaInAsP/InP superlattice is designed; and it is shown that, although with a superlattice core the refractive index for the TM mode is reduced by approximately 0.4 percent, there is no change for the TE mode. Based on this result, the optimal structural parameters such as superlattice layer number, rib height (h), intersecting angle (θ), and port separation length (Lsp) are investigated using a 1.55μm wavelength. It is found that the TE and TM modes can be separated with an insertion loss of less than 0.4 dB for both modes and a crosstalk of less than −35 dB using an intersecting angle of 5° and a device length of approximately 0.9 mm. It is shown that compared to conventional devices, the device length in the proposed device structure can be reduced by using total reflection. The wavelength dependence of the device is also analyzed.

Analytical and experimental study of waveguide optical polarization splitter with Langmuir-Blodgett cladding layer

The waveguide-type optical polarization splitter, which utilizes birefringence of a Langmuir-Blodgett cladding layer, is studied theoretically and experimentally. By means of the beam propagation method based on Galerkin's principle, characteristics of the polarization splitter are analyzed. Results of the numerical calculation predict excellent polarization splitting properties with a crosstalk of -30 dB and an insertion loss of less than 0.1 dB for both TE and TM polarization. Successful operation of the polarization splitter was demonstrated in an experimental device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Numerical analysis of passive integrated-optical polarization splitters: comparison of finite-element method and beam-propagation method results

We compare results obtained from the application of a scalar finite-element method and a three-dimensional beam-propagation method to passive integrated optical polarization splitters (IOPS’s) in Ti-indiffused LiNbO3. A comparison of calculated channel waveguide modes is given. Results reveal good agreement for the two methods. The IOPS is explained in terms of local normal modes. Results obtained by the finite-element and the beam-propagation methods are then used in the two-mode interference picture in order to design several IOPS’s. For adiabatic transitions the phase difference of the two lowest-order modes in each polarization at the output of the IOPS is obtained from Δβ as a function of waveguide separation. In the same way the conditions for polarization-independent operation can be obtained. The validity of results obtained by the finite-element method with local normal modes for two modes is limited to extremely slowly varying waveguide separations. Otherwise a method is needed that calculates the complete field, including coupling to radiation. Mode coupling, including coupling to radiation modes, is studied in detail for one type of IOPS by means of the beam-propagation method.

High extinction guided-wave optical polarization splitter

Conventional guided-wave optical polarization splitters exhibit poor polarization extinction characteristics because of the necessity of controlling waveguide parameters. In order to improve the characteristics, an electrical control scheme was investigated in an alternating Delta beta directional coupler. Polarization-dependent electrooptic as well as polarization-independent plasma effects were employed to produce high extinction for two orthogonal polarizations independently. As a result, an extinction ratio as high as 32 dB was obtained with a fabricated GaAs-GaAlAs device. This is the highest value ever reported with a channel waveguide device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Broad-band optical directional couplers and polarization splitters

A method is described for designing broadband optical directional couplers. The basic idea is to determine an optimum distance between the waveguides where wavelength dependence of the coupling coefficient vanishes at a given wavelength. The method is applied to design directional coupler polarization splitters. As an example the computer design of a polarization splitter made of single-mode twin-core optical fiber is presented. The extinction ratio obtained for waves with undesired direction of polarization is better than -20 dB within a wavelength range of 80 nm. The sensitivity of the design to variations of the main parameters caused by the production process is discussed for characteristic examples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>