Broadband Polarization Splitter Research Articles

Compact and tunable broadband polarization splitter based on nematic liquid crystal infiltrated dual-core photonic crystal fiber

A compact and broadband polarization splitter is proposed based on nematic liquid crystal infiltrated dual-core photonic crystal fiber having a simpler hexagonal platform. The infiltration of the nematic liquid crystal in the properly optimized structure largely increases the mode birefringence (0.013491), which helps the splitter to attain a compact length of 71.35 µm. Also, the proposed splitter has a broad bandwidth of 356 nm (1285 nm to 1641 nm) keeping a better extinction ratio than -20 dB, covering all the O-E-S-C-L-U optical communication bands, and the minimum extinction ratio is -83.34 dB at the wavelength of 1550 nm. Moreover, nematic liquid crystal of E7 material enables temperature tuning of the device within the wavelengths of 1200 nm to 1650 nm; hence, bandwidth is extended to 450 nm. The compact design along with broadband and temperature tuning properties make the device interesting and it may find diverse applications in optical communication.

Broadband and CMOS-compatible polarization splitter and rotator built on a silicon nitride-on-silicon multilayer platform.

A broadband and CMOS-compatible polarization beam splitter and rotator (PSR) built on the silicon nitride-on-silicon multilayer platform is presented. The PSR is realized by cascading a polarization beam splitter and a polarization rotator, which are both subtly constructed with an asymmetrical directional coupler waveguide structure. The advantage of this device is that the function of PSR can be directly realized in the SiN layer, providing a promising solution to the polarization diversity schemes in SiN photonic circuits. The chip is expected to have high power handling capability as the light is input from the SiN waveguide. The use of silicon dioxide as the upper cladding of the device ensures its compatibility with the metal back-end-of-line process. By optimizing the structure parameters, a polarization conversion loss lower than 1dB and cross talk larger than 27.6dB can be obtained for TM-TE mode conversion over a wavelength range of 1450 to 1600nm. For TE mode, the insertion loss is lower than 0.26dB and cross talk is larger than 25.3dB over the same wavelength range. The proposed device has good potential in diversifying the functionalities of the multilayer photonic chip with high integration density.

Broadband Polarization Rotator and Splitter Based on 70 nm-Etched Waveguides on SOI Platform

The standard silicon photonic platforms provide three-step silicon etching, i.e., 220 nm for full etching, 70 nm for shallow etching, and 130 nm (or 150 nm) for slab etching. Previously reported mode-evolution-based polarization rotators and splitters (PSRs) usually employ 130 nm-etched slab waveguides for adiabatic TM0-to-TE1 conversion, however, they are not compatible with the platforms adopting 150 nm-etching techniques. In this paper, we demonstrate a broadband PSR based on 70 nm-etched slab waveguides, which is compatible with all the platforms. The PSR consists of a bi-level taper and an inverse-tapered coupler. The length of the polarization rotator shrinks from hundreds to only thirty microns by employing the 70 nm-etched slab waveguides, while a high efficiency of >95% is achieved, covering an ultra-wide bandwidth from 1250 nm to 1650 nm. The proposed PSR shows superior performance over S, C, and L bands. Low cross-talk of <−20 dB and a loss of <1.5 dB are experimentally confirmed over a wavelength range of 75 nm.

Broadband ultra-compact polarization splitter-rotator using diagonally overlapped bi-layer architecture.

A broadband and ultra-compact polarization splitter-rotator based on diagonally overlapped bi-layer architecture and an asymmetrical directional coupler is proposed on a silicon-on-insulator platform. By leveraging the structure over supermode theory, a 1-dB bandwidth of 220 nm, extinction ratio (ER) of <19dB, and cross talk (XT) of <-15.85dB within the span of 1400-1700 nm and coupling length of 4.62 µm are achieved. In addition, TM0-TE0 conversion loss of ∼0.19dB, ER of 35.88 dB, and XT of -30.46dB can be obtained at 1550 nm. The fabrication tolerances are also analyzed, indicating that the insertion losses remain below 1 dB over 1460-1620 nm in terms of width errors and layer-to-layer misalignments within ±10nm. The results show that the proposed device is very suitable to utilize between fibers and for polarization diversity of on-chip systems for broadband operation as well as ultra-compact integration.

Broadband and Short-Length Polarization Splitter on Dual Hollow-Core Antiresonant Fiber

We present a compact polarization splitter on a dual hollow-core antiresonant fiber with broad bandwidth covering two well-known communication wavelengths of <inline-formula> <tex-math notation="LaTeX">$1.31~\mu \text{m}$ </tex-math></inline-formula> and 1.55 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>. It can achieve excellent polarization splitting performances in a simpler optimized single-layer geometry compared to the related splitters and for the first time, simultaneously offers a very short splitter length of 21.52 mm and a broad bandwidth of 340 nm by maintaining an extinction ratio higher than 20 dB. It also achieves the highest extinction ratio of 140 dB at <inline-formula> <tex-math notation="LaTeX">$1.55~\mu \text{m}$ </tex-math></inline-formula> and maintains a standard single mode performance. Therefore, the proposed splitter has the potentiality to be a promising candidate for the integrated optical devices in communication systems.

Fabrication-tolerant and CMOS-compatible polarization splitter and rotator based on a compact bent-tapered directional coupler

In this paper, we demonstrate a broadband, low-loss, compact, and fabrication-tolerant polarization splitter and rotator (PSR) on a silicon-on-insulator platform. The PSR is based on an asymmetric directional coupler (ADC), which is covered with SiO2 from the top to make it compatible with the standard metal back end of line (BEOL) process. Conventional ADC-based PSRs suffer from stringent fabrication requirements and relatively low bandwidth, while the proposed bent-tapered design is highly insensitive to the fabrication errors (＞70 nm tolerance on the coupling gap) with an enlarged bandwidth and a compact footprint of 53 µm × 7 µm. It yields a polarization conversion loss less than 0.7 dB, a transverse electric (TE) insertion loss better than 0.3 dB, an ultra-low crosstalk with the TE extinction better than 30 dB, and the transverse magnetic extinction better than 25 dB, over a 200 nm wavelength range (1.5 µm–1.7 µm), in both ports. At the 1.55 µm wavelength, the calculated ultra-low polarization conversion loss and TE insertion loss are 0.27 dB and 0.08 dB, respectively.

Design of a compact and broadband terahertz polarization splitter based on gradient dual-core photonic crystal fiber

We report a broadband polarization splitter based on polyethylene photonic crystal fiber with microstructured dual refractive index gradient cores. These dual cores consist of a properly optimized arrangement of air holes such that for individual fibers $x$x-polarized modes have large effective indices difference, while this index difference is almost zero for their $y$y-polarized modes, leading to efficient coupling between the $y$y-polarized modes. We have shown that by proper optimization of gradience created in the arrangement of air holes, efficient polarization splitting can be achieved for a broad range of terahertz frequencies. Device length and extinction ratio have been calculated numerically for the proposed configuration. Device length of $\sim{1.96}$∼1.96 to $\sim {60}\;{\rm cm}$∼60cm was found to be appropriate for frequencies in the 0.4-1.0 THz range to have high extinction ratios: $ - {38}$-38 to $ - {49}\;{\rm dB}$-49dB and $ - {15}$-15 to $ - {23}\;{\rm dB}$-23dB for the $x$x and $y$y polarizations, respectively. The bending loss for the proposed design is quite low: $\sim{0.05}\;{\rm dB/m}$∼0.05dB/m at 1 THz for the bend radius of 1 cm. These results suggest that a compact, low-loss, and broadband polarization splitter with very high extinction ratios can be achieved by wrapping the fiber around a small mandrel.

Ultra-broadband dual hollow-core anti-resonant fiber polarization splitter

Abstract A dual hollow-core anti-resonant fiber is proposed and numerically investigated. Two elliptical tubes are introduced to separate the core into two symmetrical cores; further nested tubes are adopted to achieve good single mode performance. Mode coupling takes place in the proposed fiber through an air gap between the two cores; the coupling strength can be controlled by adjusting fiber parameters. A broadband polarization splitter can be constructed by selecting a suitable fiber length. Numerical results show that a polarization splitter based on the proposed fiber has a length of 6.75 cm and a bandwidth of 310 nm, covering the wavelength range from 1.41 μm to 1.72 μm with an extinction ratio as low as −20 dB. The ratio of higher order mode to fundamental mode loss is great than 100, implying that the proposed polarization splitter also possesses effective single mode performance.

Design of a Broadband Polarization Splitter Based on Anisotropy-Engineered Tilted Subwavelength Gratings

Polarization management is of paramount importance in integrated optics, particularly for highly birefringent photonic platforms such as silicon-on-insulator. In this paper, we present a polarization beam splitter based on a multimode interference coupler incorporating tilted subwavelength gratings. The tilt provides accurate control of the structural anisotropy and enables independent selection of the beat length for two orthogonal polarization states. As a result, device length is reduced to less than 100 μm while simultaneously achieving broadband operation through subwavelength grating dispersion engineering. Insertion losses below 1 dB and an extinction ratio higher than 20 dB are demonstrated through three-dimensional FDTD simulation in a 131-nm bandwidth.

Ultra-short and broadband polarization splitter based on PCF and metal surface plasmons resonance

An ultra-short and broadband polarization splitter based on PCF and metal surface plasmons resonance is proposed by designing a new structure and filling gold wire into certain air holes. The introducing of gold wire aims to couple with the basic modes. Then high birefringence is obtained to improve the splitter’s performances including length, bandwidth and maximal extinction ratio. The numerical results demonstrate that the splitter can be the shortest length of 100 μm (to our knowledge) and the broad bandwidth is 470 nm simultaneously. And when the splitter’s length is set as 104 μm, the widest bandwidth reaches the maximum 575 nm (to our knowledge) which covers almost all the E, S, C, L, and U communication band. In addition, the structure is relatively simple, so it is easy to fabricate using available methods. These properties will help designing splitter in the optical communication and sensing system.

Demonstration of an on-chip broadband polarization splitter and rotator using counter-tapered coupler

Abstract A broadband and fabrication-tolerant polarization splitter and rotator (PSR) using a counter-tapered coupler is proposed and demonstrated on silicon-on-insulator (SOI) platform. Compared to previously reported PSRs based on a conventional directional coupler, which suffer from relatively low bandwidth and stringent fabrication requirements, the introduced counter-tapered structure can be used to enlarge the bandwidth and fabrication tolerance. The proposed PSR can be fabricated through a single step of lithography and etching, with a total length of 170 μ m . The measured results show that the fundamental transverse magnetic (TM0) to fundamental transverse electric (TE0) polarization conversion loss is less than 0.8 dB, while the TE0-TE0 insertion loss is less than 0.5 dB, over the wavelength range from 1520 to 1580 nm. The polarization crosstalk is lower than -20/-18 dB for TE0/TM0 mode, respectively.

Ultrahigh Suppression Broadband Polarization Splitter Based on an Asymmetrical Directional Coupler

Polarization-beam-splitters with both broadband operation window and high extinction ratio are highly desirable in optical communication systems. In this paper, a compact noncascaded-directional-couplers PBS with an ultrahigh extinction ratio and low excess loss is proposed. The PBS utilizes an asymmetrical directional coupling structure consisted of a TE-pass-polarizer waveguide and a TE- and TM-pass waveguide. The simulation results show that the extinction ratio is up to 35.41 dB and the excess loss is only 0.11 dB around the central wavelength 1550 nm for both polarizations (TE and TM). Meanwhile, when the extinction ratio is 30, 25, and 20 dB, the corresponding bandwidth is 72, 145, and 188 nm, respectively. Also, the EL is 1 and 0.5 dB in a bandwidth of ∼73 and ∼48 nm, respectively. A fabrication tolerance of ±10 nm for the waveguide width is also achieved.

Simulation of a short and broadband polarization splitter based on photonic crystal fiber filled with tellurite glass

A polarization splitter based on dual-core photonic crystal fiber filled with tellurite glass in the central hole is proposed. The characteristics are studied by finite element method. The influences of the parameters \(d_{1}, d_{2}, \varLambda\) on the coupling length and coupling length ratio (CLR) are analyzed. The curves of coupling lengths of X-polarization, Y-polarization light dependence on the operable wavelength \(\lambda\) are flat under the optimized structural parameters which is helpful to realize broadband polarization splitter. The simulation results indicate that the CLR could reach to 2.006 at the wavelength of \(1.55\,\upmu {\hbox {m}}\). The fiber length is only 510 \(\upmu {\hbox {m}}\) and the bandwidth of extinction ratio greater than 20 dB is 284 nm, i.e., from 1461 to 1745 nm which could be widely used in the large-capacity, broad-bandwidth and integrated optical communication systems. As the fiber length decreases, we find the bandwidth increases. But the extinction ratio at 1.55 \(\upmu {\hbox {m}}\) is lower than 20 dB as the fiber length is less than 510 \(\upmu {\hbox {m}}\).

A Low Crosstalk and Broadband Polarization Rotator and Splitter Based on Adiabatic Couplers

A low crosstalk and broadband polarization rotator and splitter (PRS) consisting of a bi-level adiabatic taper, a symmetric micro Y-junction and adiabatic couplers is proposed and demonstrated using a silicon-on-insulator platform. Due to the principle of mode evolution, the proposed PRS exhibits superior performance over a broad bandwidth. The waveguide with a thin ridge layer is introduced to reduce the crosstalk from TM0 mode and increase the coupling strength of TE0 mode. The proposed PRS is experimentally demonstrated with a loss about 1 dB and a crosstalk about −14 dB over a wavelength range of 100 nm.

Plasmonic Broadband Polarization Splitter Based on Dual-Core Photonic Crystal Fiber with Elliptical Metallic Nanowires

We design two kinds of plasmonic broadband polarization splitters based on dual-core photonic crystal fiber (DC-PCF) with elliptical Au or Ag nanowire in this paper. It is analyzed for the polarization independent characterestics of the designed DC-PCF by the finite element method (FEM). In order to excite the surface plasmon resonance (SPR), the metal Au and Ag are filled into elliptical central air hole. The resonance coupling between the fourth- or fifth-order surface plasmon modes (SPMs) and core-guided modes (CGMs) are founded by this numerical simulation. The device lengths of the designed splitters with Au nanowire are 2937 and 827 μm at the wavelength of 1.31 and 1.55 μm, respectively. As the extinction ratios are better than −20 dB, its bandwidths are better than 94 and 103 nm. For the designed Ag nanowire splitter, the device lengths are 3066 or 809 μm at 1.31 or 1.55 μm, respectively. The bandwidths with the extinction ratio better than −20 dB are 66 and 104 nm, respectively.

Ultra-small and broadband polarization splitters based on double-slit interference

An ultra-small and broadband polarization splitter is numerically and experimentally demonstrated based on the double-slit interference in a polymer-film-coated double-slit structure. The hybrid slab waveguide (air-polymer-Au) supports both the transverse-magnetic and transverse-electric modes. The incident beam from the back side can excite these two guided modes of orthogonally polarized states in the hybrid structure. By exploiting the difference slit widths and the large mode birefringence, these two guided modes propagate to the opposite directions along the front metal surface. Moreover, the short interference length broadens the operation bandwidth. Experimentally, a polarization splitter with a lateral dimension of only about 1.6 μm and an operation bandwidth of 50 nm is realized. By designing the double-slit structure in a hybrid strip waveguide, the device dimension can be significant downscaled to about 0.3 × 1.3 μm2. Such an ultra-small and broadband polarization splitter may find important applications in the integrated photonic circuits.

Ultra-broadband and compact polarization splitter based on gold filled dual-core photonic crystal fiber

A polarization splitter based on gold filled dual-core photonic crystal fiber (DC-PCF) that can work from 1420 nm to 1980 nm (560 nm bandwidth) is proposed in this work. The splitter has an extinction ratio lower than −20 dB over a large bandwidth with a total length of 254.6 μm. The key principle of operation of the splitter is the induced change in the refractive index of the y-odd mode when it is coupled to the second order plasmonic mode, while other supermodes are weakly affected by the plasmonic mode. The proposed broadband and compact polarization splitter may find applications in communications and sensing, being capable of working in the infrared and mid-infrared wavelength ranges.

Fabrication tolerant and broadband polarization splitter and rotator based on a taper-etched directional coupler.

We propose a fabrication tolerant polarization splitter and rotator (PSR) on the silicon-on-insulator platform based on the mode-coupling mechanism. The PSR consists of a silicon wire waveguide coupled to a taper-etched waveguide. Compared to previously reported PSRs based on directional couplers which are sensitive to fabrication variations, the partially etched taper structure can compensate for fabrication inaccuracies. In addition, the taper-etched geometry breaks both the horizontal and vertical symmetries of the waveguide, introducing an additional degree of design freedom to accommodate different upper cladding layers. The proposed PSR can be readily integrated in a planar waveguide circuit using e.g. SiO(2) cladding, making it compatible with typical metal back-end-of-line processes. Our simulation results show that the PSR has a low TM-to-TE polarization conversion loss of -0.09 dB in the C-band (or a conversion efficiency of 98%). A low TE-to-TE through insertion loss (-0.07 dB) and a very low polarization crosstalk (-30 dB) over a wide wavelength range exceeding 160 nm with a large fabrication tolerance (>50 nm) are numerically demonstrated.

Integrated Broadband Polarization Splitters Made by Ion-Exchange on Glass

In this letter, we present the design, fabrication, and characterization of a broadband polarization splitter working in the 1550-nm transmission window. The device is an asymmetric Y-junction realized by Ag <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion exchange on glass. The transverse electric (TE) output branch of the device filters out the residual transverse magnetic (TM) mode by radiation. Measurements show cross-talks better than (31.1±0.4) dB in TE and better than (32.7±0.4) dB in TM mode over a 70-nm bandwidth limited by the characterization source. Optimal values of, respectively, (33.6±0.4) dB and (37.2±0.4) dB were measured at 1540 nm. At this wavelength, the insertion losses are, respectively, (6.0±0.4) dB and (5.5±0.4) dB in TE and TM modes while the function losses are (0.65±0.12) dB and (0.35±0.12) dB, respectively.

Terahertz polarization splitter based on orthogonal microstructure dual-core photonic crystal fiber

A broadband polarization splitter operating in the terahertz (THz) band is proposed based on dual-core photonic crystal fiber with orthogonal microstructure in the core regions. The Index Converse Matching Coupling method is presented to design the THz polarization splitter for the first time, which exhibits several advantages, such as short splitting length, high extinction ratio, low loss, and broad operation bandwidth. By numerical simulation, it has been found that the strong coupling occurs within a frequency range of 0.4-0.7 THz. The operation bandwidth is more than 0.15 THz (equal to 138 μm). The shortest splitting length is only 1.83 cm at 0.4 THz. The extinction ratios for both of x and ypolarization are better than -15 dB when the frequency is larger than 0.51 THz. The lowest material absorption loss is only 0.34 dB at 0.4 THz. Moreover, this structure is simple to design and easy to fabricate over its counterparts in the communication band. Our research offers an effective method to design a broadband THz device and would be of significance for future relevant applications.