TM-pass Polarizer Research Articles

Ultrabroadband Compact Graphene–Silicon TM-Pass Polarizer

Graphene is treated as an anisotropic material because it is one atom thick and its π electrons cause electric conduction in its plane. Based on the polarization-dependent absorption, we design compact broadband transverse-magnetic (TM)-pass polarizer by exploiting a graphene–silicon horizontal slot waveguide structure on silicon-on-insulator (SOI) platforms. The interaction between light and graphene is greatly enhanced by placing the double-layer graphene sheets adjacent to the slot waveguide. The selection of the geometric parameters (e.g., waveguide width, silicon, and Si3N4 thicknesses) is discussed. We study the mode properties, extinction ratio (ER), bandwidth, and insertion loss. The graphene–silicon slot waveguide based polarizer offers the performance of high extinction ratio, low insertion loss, broad bandwidth, small footprints, and compatibility with an SOI platform. By employing a 150 μ m long graphene–silicon horizontal slot waveguide, the ER is higher than 40 dB, and the insertion loss is less than 3 dB over the 1450–1650 nm wavelength range. We also analyze the impacts of practical fabrication imperfections on the operation performance, i.e., fabrication error tolerance, and give the possible fabrication process of graphene–silicon horizontal slot waveguide based polarizer.

Low Loss, Compact TM-Pass Polarizer Based on Hybrid Plasmonic Grating

A low-loss, compact TM-pass polarizer is demonstrated based on hybrid plasmonic grating on silicon-on-insulator platform. Since the large mode distribution mismatch and plasmonic effect significantly influence the transmission and reflection spectrum of the device, the traditional theory of Bragg grating cannot fully explain this phenomenon. Here, we proposed an analysis method which takes effective index and mode overlap together into consideration to design this polarizer. A compact length of $2.5~\mu \text{m}$ with extinction ratio over 25 dB is realized simultaneously. Moreover, the insertion loss is only 0.088 dB, which is comparable to dielectric-based devices.

Analysis of the resonant layer effect in multilayer nanostructured optical waveguides

The resonant layer effect (RLE) is investigated for a multilayer structure with iron nanoinclusions. The RLE tuning and strength are analyzed as a function of nanoinclusion filling factor and resonant, cladding and guiding layers thicknesses. Crossing, splitting, and quasidegeneration of modes in the structure dispersion diagram are discussed, along with its relation to the RL effect detuning and structure-coupling regime. For the range of parameters considered, multiple resonances are tunable in the multilayer structure. Optimized RLE TE and TM polarizers are proposed for operation at 1550 nm based on modal loss and field confinement calculations. For the TE-pass polarizer, a 201.1-dB rejection ratio and 3.85-dB/cm insertion loss are obtained, while for the TM-pass polarizer, a 95.6-dB rejection ratio and 4.41-dB/cm insertion loss are achieved.

Titanium Nitride-Based CMOS-Compatible TE-Pass and TM-Pass Plasmonic Polarizers

TE-pass and TM-pass polarizers based on silicon-on-insulator platform are proposed and analyzed. The suggested structures for both the polarizers are truly CMOS-compatible relying on the titanium nitride as an alternative plasmonic material for its favorable properties. The analysis predicts 0.0635-dB insertion loss (IL) and 20-dB extinction ratio (ER) for the TE-pass polarizer at 3.5-μm active device length. The TM-pass polarizer has an IL of 1 dB and an ER of 20 dB at 2.84-μm-long device, at a central wavelength of 1.55 μm.

Graphene Based Waveguide Polarizers: In-Depth Physical Analysis and Relevant Parameters.

Optical polarizing devices exploiting graphene embedded in waveguides have been demonstrated in the literature recently and both the TE- and TM-pass behaviors were reported. The determination of the passing polarization is usually attributed to graphene’s Fermi level (and, therefore, doping level), with, however, no direct confirmation of this assumption provided. Here we show, through numerical simulation, that rather than graphene’s Fermi level, the passing polarization is determined by waveguide parameters, such as the superstrate refractive index and the waveguide’s height. The results provide a consistent explanation for experimental results reported in the literature. In addition, we show that with an accurate graphene modeling, a waveguide cannot be switched between TE pass and TM pass via Fermi level tuning. Therefore, the usually overlooked contribution of the waveguide design is shown to be essential for the development of optimized TE- or TM-pass polarizers, which we show to be due to the control it provides on the fraction of the electric field that is tangential to graphene.

Ultra-compact resonant tunneling-based TE-pass and TM-pass polarizers for SOI platform.

We investigate the polarization-dependent resonance tunneling effect in silicon waveguides to achieve ultra-compact and highly efficient polarization fitters for integrated silicon photonics, to the best of our knowledge for the first time. We hence propose simple structures for silicon-on-insulator transverse electric (TE)-pass and transverse magnetic (TM)-pass polarizers based on the resonance tunneling effect in silicon waveguides. The suggested TE-pass polarizer has insertion losses (IL), extinction ratio (ER), and return losses (RL) of 0.004dB, 18dB, and 24dB, respectively; whereas, the TM-pass polarizer is characterized by IL, ER, and RL of 0.15dB, 20dB, and 23dB, respectively. Both polarizers have an ultra-short device length of only 1.35 and 1.31μm for the TE-pass and the TM-pass polarizers which are the shortest reported lengths to the best of our knowledge.

Graphene-Coated Surface Core Fiber Polarizer

In this paper, we propose and numerically analyze a graphene-coated surface core fiber (SCF) polarizer. The loss characteristics of TE- and TM-modes are investigated. The results show that the graphene-coated SCF polarizer can produce either TE- or TM-polarized wave that can be tuned via altering the chemical potential with the external electric field. When the length of graphene sheet is 3 mm, the extinction ratios of 25.1 and 26.0 dB can be achieved at the wavelength of 1550 nm for TE- and TM-pass polarizer, respectively. The SCF has a high mechanical strength and can be made directly by chemical modifications on the core surface without destroying the fiber structure. The proposed polarizer provides a potential way to manipulate the polarization of light in all fiber-integrated devices and highly integrated optical circuits.

Proposal of an Ultracompact CMOS-Compatible TE-/TM-Pass Polarizer Based on SoI Platform

An all-dielectric transverse electric (TE)-/transverse magnetic (TM)-pass polarizer based on silicon-on-insulator (SoI) is proposed and analyzed. The symmetric etching of the silicon nanowire with specific values allows the cutoff of the undesired polarization state while the other is propagated with minimal losses. The proposed SoI polarizer can achieve 26- and 30-dB extinction ratios and 0.4-dB insertion losses for both TE- and TM-pass polarizers, respectively, with a very compact device length as short as 2.5 μm. The polarizer maintains 20-dB extinction ratio over a wide wavelength range of 1.454-1.68 μm. Fabrication of the introduced device is compatible with standard CMOS fabrication process.

Low-loss ultracompact transverse-magnetic-pass polarizer with a silicon subwavelength grating waveguide.

An ultracompact and low-loss TM-pass polarizer on silicon is proposed and demonstrated experimentally with a subwavelength-grating (SWG) waveguide. The SWG waveguide is designed to support Bloch mode for TM polarization so that the incident TM-polarized light goes through the SWG waveguide with very low excess loss. On the other hand, for TE polarization, the SWG waveguide works as a Bragg reflector, and consequently the incident TE-polarized light is reflected. For a fabricated ∼9 μm long polarizer (with the period number N=20), the measured extinction ratio is ∼27 dB and the excess loss is ∼0.5 dB at the central wavelength 1550nm. The bandwidth to achieve an extinction ratio of 20dB is about 60nm (from 1520 to 1580nm). When increasing the period number to N=40, the measured extinction ratio is up to 40dB (which is not as high as the expected theoretical value 65dB due to the limit of the measurement system).

Polarizers in an Asymmetric Twin Waveguide Based on Resonant Coupling

A polarization filter based on resonant coupling in an asymmetric twin waveguide (ATG) is demonstrated for the first time. A special taper design of the upper waveguide cladding enables power transfer from the fundamental input to the first higher order mode and causes mode beating. A power extinction ratio (PER) of the TE-relative to the TM-polarization of (3.1 ± 0.4) dB is measured at 1610 nm for two consecutive TM-pass polarizers. A TM/TE-PER of (1.4±0.4) dB is observed for a second device with a similar configuration also at 1610 nm. A single polarizer has a length of only 372 μm. Multiple polarizers can be easily placed in series to increase the PER. In addition, the input waveguide acts as a spot size converter to enable improved coupling to a lensed fiber.

TE/TM-Pass Polarizer Based on Lithium Niobate on Insulator Ridge Waveguide

We propose a TE/TM-pass polarizer based on a shallow X-cut lithium niobate-on-insulator (LNOI) ridge waveguide. In shallow X-cut LNOI ridge waveguides, the leaky mode is interchanged between TE and TM polarization waves depending on the ridge waveguide height. The phenomenon does not occur in silicon-on-insulator ridge waveguides. We use this special loss mechanism for TE/TM-pass polarizers. We evaluate structural and wavelength dependencies of polarizers by a vectorial finite-element method. The extinction ratios of 108 dB/mm and 27 dB/mm are obtained for TE-pass and TM-pass polarizers.

Integrated optic TE/TM pass polarizers using resonant coupling between ITO thin film lossy modes and dielectric waveguide modes

The resonant coupling between the lossless dielectric waveguide modes and the lossy modes supported by the absorbing indium–tin oxide (ITO) film is analyzed theoretically. It is observed that by changing the thickness of an ITO cladding layer placed above the planar dielectric waveguide, the TE or TM propagating modes may be selectively attenuated. This polarization effect can be used to design a TE or TM pass polarizer. Further it is also proposed that an electro-optic buffer layer inserted between the waveguide and ITO film can be used to design a high extinction ratio integrated optic polarizer at wavelength of 1.3μm. A polarizer (both TE and TM pass) with extinction ratio of about 254dB and insertion loss of about 10dB can be easily designed for a 1mm of its length.

Analysis of CMOS Compatible Cu-Based TM-Pass Optical Polarizer

A transverse-magnetic-pass (TM-pass) optical polarizer based on Cu complementary metal-oxide-semiconductor technology platform is proposed and analyzed using the 2-D method-of-lines numerical model. In designing the optimum configuration for the polarizer, it was found that the metal-insulator-metal (MIM) polarizer structure is superior compared to the insulator-metal-insulator polarizer structure due to its higher polarization extinction ratio (PER) and low insertion loss. An optimized MIM TM-pass polarizer exhibits simulated long wavelength pass filter characteristics of >;~1.2 μ.m, with fundamental TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode transmissivity of >;70% and <;5%, respectively, and with PER ~11.5 dB in the wavelength range of 1.2-1.6 μ.m. The subwavelength and submicrometer features of this TM-polarizer are potentially suitable for compact and low power photonics integrated circuit implementation on silicon-based substrates.

Improvement of polarization extinction in silicon waveguide devices

The SOI based waveguide devices are found to be highly polarization sensitive. Unwanted polarization excitations can be attenuated by integrating a TE- or TM-pass polarizer. A large attenuation of TM-polarized light has been observed when a thin film of metal is coated on the top of silicon rib waveguide, while TE-polarized light remains almost unaffected. The attenuation of TM-polarized light is attributed to the plasmonic absorption of the evanescent field in the metal cladding. Typically, with an Al cladding of thickness ∼100nm and a length of 1mm on top of a single-mode (λ∼1550nm) SOI rib waveguide structure, TE vs TM extinction ratio of ∼15dB has been obtained. Integrating such waveguide polarizers in a directional coupler and MZI based DWDM channel interleaver, we have also achieved an improvement in polarization extinction by ∼15dB.

Compact hybrid TM-pass polarizer for silicon-on-insulator platform

Hybrid waveguides consisting of a metal plane separated from a high-index medium by a low-index spacer have recently attracted a lot of interest. TM and TE modes are guided in two different layers in these structures and their properties can be controlled in different manners by changing the waveguide dimensions and material properties. We examine the effects of different parameters on the characteristics of the two modes in such structures. We show that by properly choosing the dimensions, it is possible to cut off the TE mode while the TM mode can still be guided in a well-confined manner. Using this property of the hybrid guide, we propose a TM-pass polarizer. The proposed device is very compact and compatible with the silicon-on-insulator platform. Finite-difference time-domain simulation indicates that such a polarizer can provide a high extinction of the TE mode for a reasonable insertion loss of the TM mode.

Analysis of the ${\rm TE}$-Pass or ${\rm TM}$-Pass Metal-Clad Polarizer With a Resonant Buffer Layer

A metal-clad optical polarizer with a resonant buffer layer has been investigated by the finite-element method in this paper. Important waveguide design parameters, such as the refractive index, thickness, interaction length, fabrication tolerance, and band-stop characteristics, have been analyzed in detail. Mode coupling within the polarizer and the losses due to coupling between the polarizer and the input and output waveguides are considered using the normal mode analysis. The loss behaviors of and modes are explained and the roles of the resonant buffer layer are interpreted. By using ultralow index layers, resonance, as well as its phase-matching conditions and excellent performance, has also been presented and discussed for this structure for the first time. Simulations show that high performance can be achieved in a wide range of the cladding thicknesses (ges 2 mum) and interaction length for both TE-pass and TM-pass polarizers. With optimized parameters under 3-mm length, it is possible to obtain a broadband TE-pass polarizer with an extinction ratio of more than 40 dB and insertion loss below 0.2 dB over 200 nm, and a TM-pass polarizer with an extinction ratio of more than 30 dB and insertion loss below 0.4 dB over 28 nm.

Compact and integrated TM-pass waveguide polarizer

A novel integrated TM-pass waveguide polarizer with a subwavelength-wide slot is introduced and theoretically analyzed. With a proper design of the slot, the waveguide can be used as a single polarization waveguide to guide only TM polarization modes of the light signal. With 26 microm length of this TM-pass polarizer, our computer simulations predict the insertion loss of 0.54 dB for the TM polarization mode with the extinction ratio of 20.3 dB at the wavelength of 1.55 microm.

Polarizing properties of optical coupler composed of single mode side-polished fiber and multimode metal-clad planar waveguide

We report the experimental results for the polarizing properties of an optical coupler made of a single mode side-polished fiber and multimode metal-clad planar waveguide. The experimental results show that the large birefringence of a metal-clad planar waveguide facilitates the effective separation of TE and TM polarization in the spectral domain. Furthermore, through proper control of the planar waveguide parameters, the coupler can be used as either a TE-pass or TM-pass polarizer within a large spectral window (>130 nm). We present an approximated analytical method to calculate resonant wavelengths and demonstrate its validity experimentally.

TM-pass polarizer based on a photobleaching-induced waveguide in polymers

An integrated optical TM-pass polarizer was fabricated by utilizing a photobleaching-induced birefringence in polymers. The polarizer is implemented by integrating a photobleached waveguide supporting only the TM mode between input and output etched rib waveguides supporting both TE and TM modes. The photobleaching has been controlled to reduce the excess loss by closely matching the mode profiles of the waveguides. The measured polarization extinction ratio is 25 dB, and the excess loss is about 0.4 dB at the wavelength of 1.31 μm.

Diode-pumped and packaged acoustooptically tunable Ti:Er:LiNbO/sub 3/ waveguide laser of wide tuning range

Design, fabrication, and properties of an acoustooptically tunable Ti:Er:LiNbO/sub 3/ waveguide laser of up to 31-nm tuning range in the wavelength band 1530 nm</spl lambda/<1575 nm are discussed. The laser cavity is formed by an Au mirror and a dielectric mirror as output coupler, both vacuum-deposited on the polished waveguide endfaces. As tunable intracavity wavelength filter with zero frequency shift, two monolithically integrated single-stage acoustooptical TE-TM-mode converters are used together with two polarization splitters operated as TE- and TM-pass polarizers, respectively. The minimum threshold of about 54 mW (coupled) pump power is obtained at /spl lambda//spl ap/1561-nm emission wavelength for diode laser pumping at /spl lambda//sub p//spl ap/1480 nm. With about 110-mW coupled pump power, up to 320-/spl mu/W output power is achieved; the emission linewidth is 0.3 nm.