Branch Waveguide Research Articles

Design of spin-orbit controlled plasmonic circuits for selectively transporting photons

Abstract The manipulation of spin-related photons is crucial for developing next-generation integrated circuits. However, the spin-orbit interaction of light is typically very weak at nanoscale due to the diffraction limit. Here, a dielectric-loaded plasmonic nanocircuit is proposed, utilizing a chiral cylindrical structure, to directionally couple and guide plasmonic waves through dual-branch waveguides. Optimized results reveal that the waveguide modes excited by circularly polarized light with different spin states can be selectively coupled to one of the two targeted branch waveguides, with a calculated unidirectional coupling efficiency as high as 0.95. The proposed structure could provide avenues for realizing on-chip integrated nanocircuits and developing advanced multifunctional nanocircuits with enhanced degrees of freedom.

Spectrally narrowband simultaneous dual-wavelength emission from Y-branch DBR diode lasers at 785 nm

Y-branch distributed Bragg reflector (DBR) diode lasers with a stable narrowband emission in simultaneous dual-wavelength operation with spectral distances below 3.2 nm are presented. The Y-branch laser consists of two laser branches with different DBR gratings serving as wavelength-selective rear-side mirrors. Therefore, two emission wavelengths with a spectral distance defined by the DBR grating periods can be generated simultaneously. A Y-coupler combines the two ridge waveguide (RW) branches into a single straight output RW. Devices with a spectral distance of 0.6 nm and 2.0 nm emitting around 785 nm are manufactured. Selecting the operation parameters carefully, stable narrowband emission for both wavelengths is obtained. Resistors serving as heaters implemented next to the DBR gratings allow for wavelength adjustment and a tuning of the spectral distance. At an optical output power of 100 mW, the spectral distance can be shifted from 0 to 1.55 nm (0–0.76 THz) for the former device or from 1.00 to 3.15 nm (0.49–1.54 THz) for the latter device, respectively. This makes the Y-branch DBR diode laser particularly interesting for the generation of THz beat-note signals, needed to generate THz radiation via photo-mixing.

Modeling and experimental characterization of a compact Mach–Zehnder electro-optic modulator on the SOI

The Mach–Zehnder electro-optic modulator (MZM) plays a crucial role in photonics integration technology during signal transmission. We propose the design and fabrication of a silicon-based electro-optic modulator based on the M-Z structure and design a modulator using silicon as the waveguide core layer on a silicon dioxide substrate. The detailed design involves a 1×2 splitter, branch waveguides, modulating arm waveguides, and a 2×1 combiner. The MZM fabrication and characterization results reveal that the half-wave voltage of the silicon-based MZM is 2 V, with an optical loss of −2.464dB and a device core size of 450µm×2800µm. The experimental results indicate that the MZM with a low half-wave voltage, a low loss, and high integration has significant value. The proposed MZM exhibits considerable improvements, featuring a low half-wave voltage and a low loss, and this device may serve as a fundamental component in wearable large-scale photonic integrated circuits for weak ECG real-time detection.

Branch Waveguide Couplers with a frequency of 510 GHz for Terahertz Transmit/Receive Isolation Applications.

To address the requirement of functioning as a transmit/receive isolation device in terahertz transceiver systems, in this paper, we present two high-isolation multi-branch waveguide directional couplers operating at a center frequency of 510 GHz. One is a high-performance five-branch directional coupler, and the other is a new type of three-branch waveguide coupler with lower processing difficulty. Both couplers were fabricated using low-cost CNC milling technologies. The performance of these couplers was verified through measurement results, demonstrating high isolation at the center frequency.

Misaligned Waveguide-Based Branch Waveguide Structure for Amplitude Imbalance Improvement in Branch-Guide Coupler

Misaligned Waveguide-Based Branch Waveguide Structure for Amplitude Imbalance Improvement in Branch-Guide Coupler

Uniaxially Symmetrical T-Junction OMT with 45° -Tilted Branch Waveguide Ports

Uniaxially Symmetrical T-Junction OMT with 45° -Tilted Branch Waveguide Ports

Terahertz couplers based on branch lines and waveguide resonators

AbstractThis paper presents two waveguide quadrature hybrids in the WR‐3 band, which are designed to be fabricated by computer numerical control milling process with relaxed branch width requirements. An E‐plane four‐branch directional coupler gives an amplitude imbalance less than 0.8 dB and a phase difference between 88° and 94° from 240 to 324 GHz. Another design is an H‐plane bandpass coupler composed of cavity resonators, showing a bandwidth of 2% near 300 GHz.

Tunable Fano resonance analysis in plasmonic waveguide side-coupled multiple Taiji resonators

In this paper, we first propose and analyze tunable Fano resonance based on indirect interaction between two Taiji resonators which both side-couple with a MIM (metal–insulator–metal) waveguide. An S-shaped branch waveguide embedded in the Taiji ring can tailor the propagating modes and then varying the number of whispering-gallery (WG) modes in the Taiji resonator, leading to the convenient tuning of Fano resonance lineshape. By covering monolayer graphene on the waveguide, Fano resonance lineshape can be all-optically tuned with relatively low pump intensity because of the optical Kerr effect of graphene; by coating UV-glue on the proposed structure, temperature sensing with high sensitivity of −0.23 nm/°C is obtained because of large negative thermo-optic coefficient of UV-glue. Furthermore, up to 16 Taiji resonators are designed and coupled with a common MIM waveguide to observe and analyze Fano lineshape variation, finally realizing the optical band-stop filter with maximal bandwidth of 49.5 nm and optical band-pass filter with maximal bandwidth of 45.3 nm. This ultra-compact micro-structure of plasmonic waveguide coupling multiple Taiji resonators demonstrates good potential applications in the nonlinear optics, optical modulation, and high-sensitivity biochemical sensors.

Unsaturated polyester resin/polymethylmethacrylate waveguide-based refractive index sensor with dual-wavelength temperature compensation

This paper demonstrates an optical waveguide based- refractive index (RI) sensor using the temperature compensation method. The optical waveguide was formed using a polymethylmethacrylate sheet as the cladding material and unsaturated polyester resin as the core material. The sensor design consists of two input waveguide branches, a sensing area and an output branch. Two light emitting diodes with wavelength of 530 nm and 660 nm were used as light sources. In this work, temperature compensation was done by dual-wavelength technique in which RI and temperature sensitivities were measured at two different wavelengths at 530 nm and 660 nm. Based on the RI and temperature sensitivities, temperature compensation was implemented. Experimental findings indicated that the average relative error of the uncompensated measurement using the light source of 530 nm and 660 nm were 0.4372% and 0.2749%, respectively. Meanwhile, the average error of the temperature compensation method was 0.0344%. Hence, the temperature compensation method provides measurement error up to 92% lower compared to the uncompensated method. As such, the proposed dual-wavelength compensation method could effectively improve the RI measurement accuracy.

On Chip Polarization Beam Splitter Based on Inverse Design

With the gradual improvement of optical interconnection technology’s requirements for high-speed broadband transmission of data, multidimensional multiplexing technology must be used to meet the application scenarios. Among them, polarization multiplexing technology has opened up a higher multiplexing dimension, and the application prospects are very broad. Polarization beam splitters have received a lot of attention as a key device in polarization multiplexing technology. The polarization multiplexer designed by traditional design methods with the help of classical theory and empirical calculation generally has deficiencies such as excessive volume and complex design, which is not conducive to large-scale integration, and the introduction of inverse design can effectively solve this problem and improve design efficiency. In this paper, the polarization beam splitter is implemented by using the inverse design, which can realize the output of the modes TE0 and TM0 in the bus waveguide from the respective regional waveguides, and the integration of TE0 and TM0 in the respective branch waveguides into the fusion transmission in the bus waveguide, with a size of only 2.4μm × 2μm. At the same time, simulation experiments show that the insertion loss of the device in the operating wavelength range of 1520nm to 1580nm is less than 1.4dB, and the crosstalk value between channels is almost negligible because the core layer of 220nm is difficult to achieve polarization rotation.

Hierarchical Integration of Organic Core/Shell Microwires for Advanced Photonics.

The combination of multiple components or structures into integrated micro/nanostructures for practical application has been pursued for many years. Herein, a series of hierarchical organic microwires with branch, core/shell (C/S), and branch C/S structures are successfully constructed based on organic charge transfer (CT) cocrystals with structural similarity and physicochemical tunability. By regulating the intermolecular CT interaction, single microwires and branch microstructures can be integrated into the C/S and branch C/S structures, respectively. Significantly, the integrated branch C/S microwires, with multicolor waveguide behavior and branch structure multichannel waveguide output characteristics, can function as an optical logic gate with multiple encoding features. This work provides useful insights for creating completely new types of organic microstructures for integrated optoelectronics.

Hierarchical Integration of Organic Core/Shell Microwires for Advanced Photonics

AbstractThe combination of multiple components or structures into integrated micro/nanostructures for practical application has been pursued for many years. Herein, a series of hierarchical organic microwires with branch, core/shell (C/S), and branch C/S structures are successfully constructed based on organic charge transfer (CT) cocrystals with structural similarity and physicochemical tunability. By regulating the intermolecular CT interaction, single microwires and branch microstructures can be integrated into the C/S and branch C/S structures, respectively. Significantly, the integrated branch C/S microwires, with multicolor waveguide behavior and branch structure multichannel waveguide output characteristics, can function as an optical logic gate with multiple encoding features. This work provides useful insights for creating completely new types of organic microstructures for integrated optoelectronics.

Multichannel Adjustable Single-Photon Router Based on Large Detuning

Quantum router as a key device in quantum information processing always attracts researchers' attention. This work suggests a single-photon (SP) router based on one bus-waveguide side coupled to numerous Jaynes-Cummings emitters (JCEs). Each JCE connects with a semi-infinite branch waveguide as an output channel. Different from the commonly used scheme that the JCEs are set in the tuning regime, we here let them work in the large-detuning regime. This change brings about the following amazing benefits for the SP router. Firstly, the number of channels can reach more than a thousand. Secondly, the router is adjustable, that is, the SP can be routed into any output channel on demand. Thirdly, the router has a remarkable monochromaticity. Fourthly, such a SP router can also depress the influence of cavity losses and interferential levels in atoms. Finally, the routing probability can reach approximately $100\mathrm{%}$ for each channel by adding a mirror and a phase shifter to the end of the bus waveguide. This work takes the Rydberg atoms ${}^{87}\mathrm{Rb}$ whose levels can be adjusted by an external electrostatic field as an example to demonstrate the feasibility of the router, which can be applied to quantum informatics.

Spin–Orbit-Engineered Selective Transport of Photons in Plasmonic Nanocircuits with Panda-Patterned Transporters

The spin–orbit coupling of light, which can be utilized to manipulate the polarization and spatial degrees of freedom of photons, has shown unprecedented potential in realizing on-chip integrated nanocircuits and quantum information processing. Particularly, this chiral coupling mechanism can result in unidirectional transport of spin-dependent light at a subwavelength scale by designing specific nanostructures. Here we propose and demonstrate a dielectric-loaded plasmonic nanocircuit with a panda-patterned transporter to directionally couple and guide plasmonic waves through two-branched waveguides. Both simulation and experimental results reveal that the waveguide modes excited by circularly polarized light with different spin states can be selectively coupled to one of two branching waveguides, with a measured unidirectionality efficiency up to 0.95. The proposed configuration may open up more possibilities in developing multifunctional nanocircuits that could be utilized for exploiting chiral manipulation with flexible degrees of freedom.

Ultra low loss broadband 1 × 2 optical power splitters with various splitting ratios

We designed Si-based all-dielectric 1 × 2 TE and TM power splitters with various splitting ratios by combining the use of the inverse design of adjoint and numerical 3D finite-difference time-domain methods. The structure of the designed Si-based power splitters contains two Si waveguide branches on a SiO2 substrate that is compatible with CMOS fabrication technology. The proposed devices exhibit ultra-high transmission efficiency above 98 and 99%, and excess losses below 0.1 and 0.035 dB, for TE and TM splitters, respectively. The merits of these devices include a minor footprint of 2.2 × 2.2 µm2 and a flat-broad operating bandwidth of 200 nm with a center wavelength of λ = 1.55 µm. Also, the other advantage of these optical power splitters is the very short optimization time of 2 h for each device. Because of the aforementioned merits, the optimized devices can be crucial candidates for optical integrated circuits.

A Novel Ultrawideband Branch Waveguide Coupler With Low Amplitude Imbalance

In this article, we present a novel ultrawideband branch waveguide coupler (BWC) with low amplitude imbalance. This novel design is based on a new structure of branch waveguide obtained by symmetrically increasing the waveguide width. The coupling degree can be independently controlled by the height and width of the new branch waveguide, which significantly increases the design flexibility. In addition, this structure can produce a transmission zero (TZ), and a concept to improve the fractional bandwidth of the BWC with out-of-band TZ is proposed. Based on the analysis, the design guidelines for the novel BWC are provided. For a given center frequency, an n-branch novel BWC can be easily designed. Moreover, because of the larger branch waveguide height, this novel design has greatly eased the machining difficulty. Finally, to verify the design concept, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band eight-branch prototype is processed and measured. In full <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band, the amplitude imbalance is less than 0.52 dB, the phase imbalance is less than 2.5°, the return loss (RL) is greater than 21.4 dB, and the isolation is greater than 20.5 dB. The simulation and experimental results are in good agreement.

Design of Compact and Easy-to-Fabricate Power Coupling Structures for Sub-Terahertz Sheet Beam Traveling Wave Amplifiers

The great challenge in fabrication is one of the most significant factors for hindering the development of subterahertz sheet beam traveling wave amplifiers (SB-TWAs). Therefore, it is in great demand to develop power coupling structures and slow wave structures with easy-to-fabricate and compact geometries for SB-TWAs. In addition, it is desirable that their heights are as small as possible, thus conducive to the focusing of the sheet electron beam. In this article, two novel power coupling structures are designed, which are based on an <inline-formula> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula>-plane short-slot and multiple branch waveguides, respectively. The former one is highlighted by its compactness, and the latter one has a wider frequency bandwidth. Two proof-of-concept prototypes of the proposed power coupling structures were microfabricated and tested, showing excellent agreement between experimental measurements and design simulations. Reflection coefficient &#x003C;&#x2212;13.6 dB, isolation coefficient &#x003C;&#x2212;15.4 dB, and transmission coefficient &#x003E;&#x2212;2.2 dB were experimentally obtained across the band of 220.0&#x2013;273.4 GHz (53.4 GHz). Hopefully, a wider measured frequency bandwidth will be obtained if the operating frequency range of the vector network analyzer could be extended to lower frequencies.

Novel In-Line Microstrip-to-Waveguide Transition Based on E-Plane Probe T-Junction Structure

In this letter, a novel in-line E-plane probe microstrip-to-waveguide (M2W) transition is proposed. The proposed in-line transition structure consists of a waveguide T-junction which has two short-circuited branch waveguides with a quarter-wavelength difference in length and a microstrip line fed probe that is in line with the main waveguide. A W-band in-line M2W transition is designed based on the proposed structure. Back-to-back measured results show that the reflection coefficient is better than -10 dB and the insertion loss is less than 1 dB over the full W-band. The measurements agree well with the simulations.

A mathematical model for sidelobe level optimization of variable inclination continuous transverse stub antenna

AbstractA mathematical model of variable inclination continuous transverse stub (VICTS) antenna for low sidelobe design is proposed in this paper. VICTS antenna is an antenna with continuous transverse stubs on the parallel-plate waveguide and additional branches attached to the transverse stubs to generate radiation. The antenna using this technique has high aperture efficiency and keeps a significant solution for high-gain antenna. However, the sidelobe level (SLL) of this antenna is relatively high and increases continuously as the pitch angle decreases. This paper presents a fast calculation model for the SLL of VICTS antennas using leaky-wave theory and antenna array theory. The full-wave simulation results and model calculation results are in good agreement, so this model can be used for SLL suppression of VICTS antennas in different frequency bands. By controlling the aperture field distribution to be tapered, the SLL is suppressed to − 23.7 dB using this mathematical model.

Ultrabroadband, compact, polarization independent and efficient metasurface-based power splitter on lithium niobate waveguides.

We propose a metasurface-based Lithium Niobate waveguide power splitter with an ultrabroadband and polarization independent performance. The design consists of an array of amorphous silicon nanoantennas that partially converts the input mode to multiple output modes creating multimode interference such that the input power is equally split and directed to two branching waveguides. FDTD simulation results show that the power splitter operates with low insertion loss (< 1dB) over a bandwidth of approximately 800 nm in the near-infrared range, far exceeding the O, E, S, C, L and U optical communication bands. The metasurface is ultracompact with a total length of 2.7 µm. The power splitter demonstrates a power imbalance of less than 0.16 dB for both fundamental TE and TM modes. Our simulations show that the device efficiency exhibits high tolerance to possible fabrication imperfections.