Polarization-independent directional coupler and polarization beam splitter based on asymmetric cross-slot waveguides

Ultra-broadband and high extinction ratio polarization splitter based on triple-tapered directional couplers

The design and numerically investigation of a silicon polarization splitter (PS) is proposed using triple-tapered directional couplers (DCs).The proposed device consists of a triple-tapered DC, a triple-bent DC at through port, and a tapered waveguide at cross port. The coupling length of the device is 20.5 µm. At the 1550 nm wavelength, the realized PS exhibits the extinction ratio (ER) values of 35.7 dB and 37.35 dB as well as the insertion loss values of < 0.58 dB and < 0.4 dB for the TE and TM polarization modes, respectively. Furthermore, the device's bandwidth for ER > 20 dB and ER > 25 dB are 170 nm and 136 nm, respectively.

Polymer-based three-waveguide polarization beam splitter with reduced crosstalk for optical circuitry

Polarization beam splitters are pivotal in manipulating polarized light within photonic integrated circuits for various optical applications. This study introduces a single-mode polarization beam splitter comprising three waveguides realized with polymer materials. The device optimization process employed the beam propagation method, explicitly using the RSoft CAD BeamProp solver. Our proposed beam splitter performs exceptionally well with 99% complete and null light transmission efficiency. In particular, it demonstrates minimal insertion loss (0.04 dB for complete transmission and 0.07 dB for null transmission) and low coupling loss (0.03 dB and 0.04 dB for complete transmission, 21.9 dB and 36.3 dB for null transmission from input to bridge and bridge to output waveguides, respectively). Additionally, the beam splitter showcases significantly reduced crosstalk: -27d B and -26.98d B for TE modes during complete light transfer, and -36.28d B and -33.61d B for TM modes during null light transfer. These results underscore its potential for advancing integrated optical systems.

Compact and efficient three-mode (de)multiplexer based on horizontal polymer waveguide couplers

A compact and efficient polymer three-mode (de)multiplexer with two cascaded waveguide directional couplers fabricated on the same substrate along the horizontal direction is proposed. Three waveguides formed two couplers, where two narrower waveguides were placed on either side of the central waveguide. By optimizing the core height and width, the two couplers can ensure that the E11x mode of the two narrower waveguides are highly coupled into the E21x and E31x modes of the central waveguide at a wavelength of 1310 nm. The structural size of the fabricated three-mode (de)multiplexer using ultraviolet (UV) lithography technology is in agreement with the designed value. The fabricated device, which is 35 mm long, exhibits coupling ratios of 98.07% and 95.43% for the two couplers, respectively. The insertion losses of the three waveguides are 5.23 dB, 8.58 dB, and 14.39 dB, respectively. The device can achieve the multiplexing of three modes in two dimensions, which can increase the channel capacity of optical communication.

Polarization-Insensitive Beam Splitter with Variable Split Angles and Ratios Based on Phase Gradient Metasurfaces

The beam splitter is a common and critical element in optical systems. Traditional beam splitters composed of prisms or wave plates are difficult to be applied to miniaturized optical systems because they are bulky and heavy. The realization of the nanoscale beam splitter with a flexible function has attracted much attention from researchers. Here, we proposed a polarization-insensitive beam splitter with a variable split angle and ratio based on the phase gradient metasurface, which is composed of two types of nanorod arrays with opposite phase gradients. Different split angles are achieved by changing the magnitude of the phase gradient based on the principle of Snell’s law of refraction, and different split ratios are achieved by adding a phase buffer with different areas. In the designed four types of beam splitters for different functions, the split angle is variable in the range of 12–29°, and the split ratio is variable in the range of 0.1–1. The beam splitter has a high beam splitting efficiency above 0.3 at the wavelength of 480–600 nm and a weak polarization dependence. The proposed beam splitter has the advantages of a small size and easy integration, and it can be applied to various optical systems such as multiplexers and interferometers for integrated optical circuits.

A Broadband Polarization-Insensitive Graphene Modulator Based on Dual Built-in Orthogonal Slots Plasmonic Waveguide

A broadband polarization-insensitive graphene modulator has been proposed. The dual built-in orthogonal slots waveguide allows polarization independence for the transverse electric (TE) mode and the transverse magnetic (TM) mode. Due to the introduction of metal slots in both the vertical and horizontal directions, the optical field as well as the electro-absorption of graphene are enhanced by the plasmonic effect. The proposed electro-optic modulator shows a modulation depth of 0.474 and 0.462 dB/μm for two supported modes, respectively. An ultra-low effective index difference of 0.001 can be achieved within the wavelength range from 1100 to 1900 nm. The 3 dB-bandwidth is estimated to be 101 GHz. The power consumption is 271 fJ/bit at a modulation length of 20 μm. The proposed modulator provides high speed broadband solutions in microwave photonic systems.

Polarization-independent, lithium-niobate-on-insulator directional coupler based on a combined coupling-sections design

We have proposed a polarization-independent directional coupler (DC) by using sections with optimal coupling strength designs on the lithium-niobate-on-insulator platform. With this design, arbitrary polarization-independent coupling ratio ranging from 0% to 100% can be achieved by tuning the length of the identical coupling region. The DC exhibits ultralow excess losses (<0.1dB) and polarization-dependent losses (<0.05dB for the complete coupling) over a bandwidth of 100 nm. Moreover, the proposed DC is compact in size, simple in structure, and easy to fabricate.

Compact cross-slot waveguide polarization beam splitter using a sandwich-type coupler

A compact silicon-based cross-slot waveguide (CSW) polarization beam splitter (PBS) utilizing a sandwich-type coupler is proposed. The coupler consists of two identical CSWs separated by a horizontal slot waveguide (HSW), and S-bend sections at each end of the coupling section are introduced to decouple and separate the light. Owing to the strong birefringence of the HSW, the coupling length ratio between two different polarized modes (TE and TM) is adjustable in a suitable range by simply changing the gap width between the CSW and the HSW. The coupling length of the TM mode can be easily made half of that of the TE mode with a proper gap width, which is a favorable condition to realize a short PBS. Then, by making the length of the coupling section equal to the coupling length of the TE mode, the TE and TM modes are split. The PBS has the advantages of a small footprint and a high polarization extinction ratio (PER) and may be useful in the polarization management of a CSW-based on-chip optical system. Numerical results indicate that a PBS of ∼12µm with an insertion loss (IL) of 0.17 (0.53) dB, PER of 24.12 (21.14) dB for the TM (TE) mode is achieved at the wavelength of 1.55 µm, with a bandwidth covering the full C band for keeping PER>15dB and IL<1dB.

Compact polarization beam splitter assisted by subwavelength grating in triple-waveguide directional coupler

A polarization beam splitter (PBS) is one of the key components for manipulating different polarization states in the areas of optical interconnection and communication. In this paper, a PBS with two coupling regions using a subwavelength grating (SWG) waveguide as a bridge is proposed and investigated on a 340-nm silicon-on-insulator platform. The PBS is designed with a triple-waveguide directional coupler consisting of two identical silicon waveguides and an SWG waveguide sandwiched between them. The tailorable dispersion relation of the SWG waveguide offers a flexible design freedom. With the optimized grating period and duty ratio, the input TE mode will experience efficient coupling between the silicon waveguide and the SWG waveguide, while the TM mode can directly pass through without influence. The results show that with a device length of 6.5 μm, the extinction ratios and insertion losses of the two modes are higher than 27 dB and lower than 0.3 dB at a wavelength of 1550 nm, respectively.

Polarization beam splitter based on a silicon nitride-silica-silicon horizontal slot waveguide

A novel compact polarization beam splitter (PBS) based on a silicon nitride-silica-silicon horizontal slot waveguide is numerically proposed, to the best of our knowledge. In the slot waveguide, the transverse electric (TE) mode propagates through the silicon layer, while the transverse magnetic (TM) mode is confined in the slot region. By utilizing an asymmetric directional coupler (DC) and bent directional coupler (bent DC) consisting of a slot waveguide and a thin silicon waveguide, PBSs with 14.6 μm (DC) and 5.2 μm (bent DC) coupling regions are obtained. Without cascading other structures, the DC PBS shows a low insertion loss (IL) of 0.4 (0.2) dB and high extinction ratio (ER) of 31.56 (24.61) dB for a TE (TM) port around 1.55 μm, while the IL and ER of the bent DC PBS are 0.4 (0.15) dB and 35.83 (21.74) dB, respectively. The proposed PBSs also have a good fabrication tolerance and broad bandwidth (>40  nm) for an ER of >20  dB.