Total Insertion Loss Research Articles

Management of lateral misalignment loss and total insertion loss with beam waist control in high contrast single mode coupling fibers

Abstract This paper has illustrated the management of lateral misalignment loss and total insertion loss with beam waist control in high contrast single mode coupling fibers. The beam waist variations are clarified versus the fiber coupler wavelength and coupling length variations for the silica glass/fluoride glass fiber coupler with the optimum incident beam angle of 60°. Besides, the coupling loss is demonstrated against the fiber coupler wavelength and coupling length variations for the silica glass/fluoride glass fiber coupler with the optimum incident beam angle of 60°. The optimum beam waist and optimum coupling loss are deeply studied against the fiber coupler core radius variations for the silica/fluoride glass fiber coupler with the optimum incident beam angle of 60° and wavelength of 1,550 nm.

Low-loss, compact, fibre-integrated cell for quantum memories

We present a low-loss, compact, hollow core optical fibre (HCF) cell integrated with single mode fibre (SMF). The cell is designed to be filled with atomic vapour and used as a component in photonic quantum technologies, with applications in quantum memory and optical switching. We achieve a total insertion loss of 0.6(2) dB at 780 nm wavelength via graded index fibre to ensure efficient mode matching coupled with anti-reflection coatings to minimise loss at the SMF-HCF interfaces. We also present numerical modelling of these interfaces, which can be undertaken efficiently without the need for finite element simulation. We encapsulate the HCF core by coupling to the SMF inside a support capillary, enhancing durability and facilitating seamless integration into existing fibre platforms.

Tailorable ITO thin films for tunable microwave photonic applications

Tunability is a fundamental prerequisite for functional devices and forms the backbone of reconfigurable microwave photonic (MWP) signal processors. In this paper, we explore the use of indium tin oxide (ITO) thin films, notable for their combination of optical transparency and electrical conductivity, to provide tunability for integrated MWP devices. We study the impacts of post-thermal annealing on the structural, electrical, and optical properties of ITO films. The annealed ITO microheater maintains a low total insertion loss of just 0.1 dB while facilitating the tunability of the microring across the entire free spectral range (FSR) using less than half the voltage required by its non-annealed counterpart. Furthermore, the post-annealed ITO film exhibits a 30% improvement in response time, enhancing its performance as an active voltage-controlled microheater. Leveraging this advantage, we employed the post-annealed device to demonstrate continuous tunable radio frequency (RF) phase shifts from 0–330° across a frequency range spanning 15 GHz to 40 GHz with only 5.58 mW of power. The flexibility in modifying the ITO thin film properties effectively bridges the gap between achieving low-loss and high-speed thermo-optic based microheaters.

Two Structural Designs of Broadband, Low-Loss, and Compact TM Magneto-Optical Isolator Based on GaAs-on-Insulator.

Integrated optical isolators are important building blocks for photonic integrated chips. Despite significant advances in isolators integrated on silicon-on-insulator (SOI) platforms, integrated isolators on GaAs-on-insulator platforms are rarely reported. In this paper, two structural designs of optical isolators based on the TM basic mode of GaAs-on-insulator are proposed. The non-reciprocal phase shift (NRPS) of GaAs/Ce:YIG waveguides with different geometric structures are calculated using numerical simulation. The isolators achieve 35 dB isolation bandwidths greater than 53.5 nm and 70 nm at 1550 nm, with total insertion losses of 2.59 dB and 2.25 dB, respectively. A multi-mode interferometric (MMI) coupler suitable for these two structures is proposed. In addition, suitable manufacturing processes are discussed based on the simulated process tolerances.

Semi-embedded slot waveguide electro-optic modulator.

Electro-optic modulators are essential devices on silicon photonic chips in modern optical communication networks. This paper presents a compact, low-loss electro-optic modulator. The modulation efficiency is greatly improved by embedding the lower half of the slot waveguide into the buried oxide layer and inserting graphene at the junction. The interaction of graphene with an optical field in a waveguide is studied using the finite element method. The functions of phase modulation and absorption modulation are realized by changing the gate voltage to change the chemical potential of graphene. The semi-embedded slot waveguide optical modulator has a length of 50µm. After simulation verification, it can be used as an electro-absorption modulator and can achieve a modulation depth of 26.38dB and an insertion loss of 0.60dB. When used as an electro-refractive modulator, it can be realized with a linear change of phase from zero to π; the total insertion loss is only 0.59dB. The modulator has a modulation bandwidth of 79.6GHz, and the energy consumption as electro-absorption and electro-refraction modulation are 0.51 and 1.92pj/bit, respectively. Compared with common electro-optic modulators, the electro-optic modulator designed in this paper has a higher modulation effect and also takes into account the advantages of low insertion loss and low energy consumption. This research is helpful for the design of higher-performance optical communication network devices.

Large group delay and low loss optical delay line based on chirped waveguide Bragg gratings.

On-chip optical delay lines (ODLs) based on chirped waveguide Bragg gratings (CWBG) have attracted much attention in recent years. Although CWBGs are well developed, the CWBG which have large group delay (GD), large delay-bandwidth product and low loss while is circulator-free have little been investigated so far. In this work, we propose and experimentally demonstrate such a CWBG-based ODL. This device is fabricated on a low-loss 800-nm-height silicon nitride platform, combining 20.11-cm long index-chirped multi-mode spiral waveguide antisymmetric Bragg gratings with a directional coupler. The bandwidth of this circulator-free ODL is 23 nm. The total GD is 2864 ps and the delay-bandwidth product is 65.87 ns·nm, which both are the largest values achieved by on-chip CWBG reported to our knowledge. Its loss is 1.57 dB/ns and the total insertion loss of the device is 6 dB at the central wavelength near 1550 nm. This integrated CWBG can be explored in practical applications including microwave photonics, temporal optics, and optical communication.

Simulation of hybrid silicon nitride/polymer Mach-Zehnder optical modulator beyond 170 GHz

In this paper, a hybrid Mach-Zehnder optical modulator is proposed based on silicon nitride/organic polymer waveguides, which is expected to break through the performance bottleneck of the silicon-based optical modulator by exploiting the low-loss optical transmission property of silicon nitride waveguides and the excellent modulation performance of organic polymers. For reduction of the optical loss and ease of photonic packaging, perfectly vertical silicon nitride bidirectional grating couplers are utilized for both input/output optical coupling and power splitting/combining. Thus, a Mach-Zehnder interferometer can be constructed with a back-to-back configuration of such grating couplers. With grating apodization, the coupler can achieve a simulated coupling efficiency of 70%. To bridge the silicon nitride waveguides and the polymer waveguides, a longitudinal adiabatic mode-spot converter with a transmission efficiency of 99.2% was designed. In this paper, high-β donor-π bridge-accepter molecule YLD-124 combined with HD-BB-OH as the host polymer is utilized for a design example. The polymer waveguides with inverted ridge structure can be realized through the processes of silica cladding etching, spin coating or microfluidic trench filling of polymer. Following this design, we numerically demonstrate a hybrid silicon nitride-polymer Mach-Zehnder modulator with modulation efficiency of 1.57 Vcm and Electric-Optical bandwidth of 174 GHz. The total insertion loss is less than 5.74 dB, including two grating coupler losses of about 3.08 dB.

Manufacture of Three-Dimensional Optofluidic Spot-Size Converters in Fused Silica Using Hybrid Laser Microfabrication

We propose a hybrid laser microfabrication approach for the manufacture of three-dimensional (3D) optofluidic spot-size converters in fused silica glass by a combination of femtosecond (fs) laser microfabrication and carbon dioxide laser irradiation. Spatially shaped fs laser-assisted chemical etching was first performed to form 3D hollow microchannels in glass, which were composed of embedded straight channels, tapered channels, and vertical channels connected to the glass surface. Then, carbon dioxide laser-induced thermal reflow was carried out for the internal polishing of the whole microchannels and sealing parts of the vertical channels. Finally, 3D optofluidic spot-size converters (SSC) were formed by filling a liquid-core waveguide solution into laser-polished microchannels. With a fabricated SSC structure, the mode spot size of the optofluidic waveguide was expanded from ~8 μm to ~23 μm with a conversion efficiency of ~84.1%. Further measurement of the waveguide-to-waveguide coupling devices in the glass showed that the total insertion loss of two symmetric SSC structures through two ~50 μm-diameter coupling ports was ~6.73 dB at 1310 nm, which was only about half that of non-SSC structures with diameters of ~9 μm at the same coupling distance. The proposed approach holds great potential for developing novel 3D fluid-based photonic devices for mode conversion, optical manipulation, and lab-on-a-chip sensing.

Cascaded all-optical quantization employing step-size MMI and shape-optimized power splitter

As a key unit of future high-throughput communications, optical analog to digital converter (OADC) with all-optical quantizer element that simultaneously possesses high resolution, large bandwidth and compact size is highly promising. A pending issue of conventional OADC methods is that a higher resolution is always accompanied with dramatically increased system size and complexity, consequently magnified impact of system error on the performance index such as bandwidth, which fails the inherent superiority of OADC. In this paper, we propose and numerically investigate a cascaded optical quantization (COQ) solution aiming to address the wavelength sensitivity issue of integrable optical phase-shifted quantizers at high resolution (>= 5-bit). Harnessing a step-size multimode interference coupler and a shape-optimized power splitter, we predict the operation bandwidth for 1-bit degradation can be up to 20 nm, 15.8 nm and 11.9 nm for the quantization resolution of 5-, 6- and 7-bit respectively, indicating a bandwidth improvement of >1 THz compared to those without COQ. Meanwhile, the total insertion loss can be maintained below −1 dB. This proposed quantizer is CMOS-compatible, which can be monolithically integrated on the silicon-on-insulator (SOI) platform and fabricated through a commercial Multi-Project Wafer (MPW) run. It paves the path to achieve high-resolution and large bandwidth OADC chips in a cost-effective way.

Numerical modeling and field test of sonic crystal acoustic barriers.

The rapid development of highway traffic has gradually deteriorated the acoustic environment along the line. Sonic crystal theory provides new ideas for traffic acoustic barrier. However, the lack of practical numerical models and field test verifications has restricted the promotion and application of sonic crystal acoustic barriers (SCABs). In this study, a field test was conducted to study the noise reduction performance of SCAB. The SCAB exhibits excellent wave attenuation in the band gap, when compared with concrete acoustic barriers (CABs) along highways, the noise reduction performance in the band gap is improved by 0.5-2.1dB(A), especially at the local peak in the highway noise spectrum. However, from the perspective of total insertion loss, CAB performs better than SCAB in all distances in the protected area. Next, the 3D FEM model is established based on the highway site and validated by the measured results. Compared with the commonly used 2D model, the 3D FEM model is more practical for considering the top diffraction and ground reflection, which influence the noise reduction performance a lot and need to be considered. To improve the noise reduction performance of SCAB, three types of optimization measures are explored. The gradient combination of scatterers can effectively improve the noise reduction effect in the low-frequency band gap, especially the high- to low-gradient layout. Besides, not only the porous sound-absorbing material but also the microperforated plates can improve the noise reduction effect, especially outside the band gap. The larger perforation rates and smaller apertures of microperforated plate are preferred in SCAB. This work provides field test support and promotes the application of SCABs in traffic noise control.

Antiresonant Hollow-Core Inline Fiber Polarizer

The unique characteristics of hollow core fibers lead to low non-linearity and reduced sensitivity to environmental influences, making them attractive platform for designing inline fiber optic devices. Among these, an inline fiber polarizer would be most desired for applications such as gyroscopes, interferometric sensors and telecommunication. Hollow-core fiber polarizers, demonstrated to date, suffer from high insertion loss (>5 dB) for the pass polarization, and typically require tens of meters long nested antiresonant fiber to achieve a meaningful polarization extinction ratio (PER) >20 dB. We report a novel approach that makes use of intricate modal loss spectrum within a resonant band of single-ring antiresonant fiber to realize the first high-performance, discrete hollow-core fiber polarizer. The compact device comprising only 6 cm long fiber offers a high PER of >25 dB with <1 dB transmission loss for the pass polarization. In the present form, the polarizing action takes place over 14 nm and 7 nm bandwidth in the 2 μm and 1 μm wavelength range, but the simplicity of design principles makes it straightforward to shift the operating wavelengths to practically any wavelength band. The device can be fusion spliced with a standard antiresonant hollow-core fiber and a large mode area solid-core fiber with splice loss of 0.14 dB and 0.45 dB respectively. Complete integration of the proposed device into an all hollow-fiber setup would lead to a total insertion loss of 1.3 dB including both input and output splicing, which is the lowest for a discrete hollow-core fiber polarizer reported so far. The results encourage the development of other hollow-core fiber components by exploiting the unique characteristics cultivated in a resonant band of an antiresonant fiber.

Passive polarization splitter using zero-gap directional coupler in LiNbO3

Low-crosstalk zero-gap directional coupler (ZDC) based TE-TM polarization splitter/combiner was designed at 1.55 µm transmitting wavelength using titanium indiffused LiNbO3 technology and effective-index based matrix method (EIMM). Single mode waveguides and ZDC were designed from its fabrication parameters. The coupling length of ZDC was optimized to 1826 µm to achieve a splitter crosstalk around −60 dB for both polarizations. At input and output ends of ZDC low-loss cosine-generated S-bent waveguides were used. For proof-of-concept, the device was fabricated and tested. Details of fabrication technology of the device are discussed. DC sputtering process was adopted for titanium film deposition, and wet-oxygen ambient was used during high-temperature diffusion of titanium into LiNbO3 to suppress lithium out-diffusion. Our first experiment with the splitter yields crosstalk values −10.79 dB for TE and −10.21 dB for TM mode. The measured fiber-device total insertion losses were 3.13 dB and 5.15 dB for TE and TM polarizations. The higher crosstalk values of the fabricated polarization-splitter can be significantly lowered by using optical detector of higher efficiency, and coupling length compensation during mask-data generation.

SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material.

Numerical analysis of optical phase modulator operating at 2 μm wavelength using graphene/III–V hybrid metal-oxide-semiconductor capacitor

We propose an optical phase modulator with a hybrid metal-oxide-semiconductor (MOS) capacitor, consisting of single-layer graphene and III–V semiconductor waveguide. The proposed modulator is numerically analyzed in conjunction with the surface conductivity model of graphene. Since the absorption of graphene at a 2 μm wavelength can be suppressed by modulating the chemical potential of graphene with the practical gate bias, the phase modulation efficiency is predicted to be 0.051 V·cm with a total insertion loss of 0.85 dB when an n-InGaAs waveguide is used, showing the feasibility of the low-loss, high-efficiency graphene/III–V hybrid MOS optical phase modulator, which is useful in the future 2 μm optical fiber communication band.

Fiber-Chip Bi-Wavelength Multiplexing With Subwavelength Single-Etch Grating Coupler and Diplexer

We propose a silicon photonicgrating coupling scheme for dual-band multiplexing in optical fibers. By utilizing subwavelength grating effective refractive index engineering, a dual-band operating grating coupler and a wavelength-polarization diplexer are designed. Both devices are fabricated on a 220-nm silicon-on-insulator and require only one 220-nm full etch step to facilitate cost-effective production. The subwavelength grating coupler guides S-band and O-band lights from a single-mode fiber into a waveguide as transverse-electric and transverse-magnetic modes, while the subwavelength diplexer separates the two signals into two waveguides. Experimentally, our proposed scheme for coupling and multiplexing can achieve a total insertion loss of –4.26 dB at near 1490 nm and –5.86 dB at near 1310 nm.

90°-bent graded-index core polymer waveguide for a high-bandwidth-density VCSEL-based optical engine.

In this paper, we present a low-loss optical assembly utilizing a 90°-bent graded-index (GI) core polymer optical waveguide on vertical cavity surface emitting laser (VCSEL) based optical transceivers. The proposed assembly can replace conventional components such as mirrors and lenses for realizing subminiature optical engines applicable to on-board integration. To minimize the total insertion loss of the waveguide when connected to a high-speed VCSEL and a GI-core multimode fiber (MMF) at each end, the characteristics of the beam emitted from VCSELs are measured and taken into consideration for the waveguide design. In order to confirm the effect of insertion loss reduction by the waveguide numerical aperture control, 90°-bent GI-core polymer waveguides are fabricated applying the Mosquito method. The fabricated waveguide exhibits a total insertion loss as low as about 2 dB at 850-nm wavelength, which includes the coupling losses at both ends, bending, and propagation losses. We also investigate a way to reduce the insertion loss when a gap exists between the waveguide and VCSEL chip. We theoretically and experimentally confirm that filling the gap with a high index resin can reduce the coupling loss by 5 dB.

A Survivable Optical Network for WDM Access Against Fiber Breakpoint

To avoid the fault occurrence of fiber link, a simple self-restored wavelength-division-multiplexing passive optical network (WDM-PON) is presented. In the demonstration, the additional optical components are included in the optical line terminal (OLT), remote node (RN) and optical network unit (ONU) to produce the alternative fiber path for fault protection. Here, 10 Gb/s on-off keying (OOK) downstream and upstream wavelengths are exploited to measure the bit error rate (BER) performances at the back-to-back (B2B) and through 50 to 51 km fiber transmission, respectively. Moreover, all the modulation signals can achieve enough power budget under the forward error correction (FEC) level to meet with the total insertion loss caused by the various fiber links and additional devices.

Fabrication of low-loss quasi-single-mode PPLN waveguide and its application to a modularized broadband high-level squeezer

A continuous-wave (CW) broadband high-level optical quadrature squeezer is essential for high-speed large-scale fault-tolerant quantum computing on a time-domain-multiplexed continuous-variable optical cluster state. CW THz-bandwidth squeezed light can be obtained with a waveguide optical parametric amplifier (OPA); however, the squeezing level has been insufficient for applications of fault-tolerant quantum computation because of degradation of the squeezing level due to their optical losses caused by the structural perturbation and pump-induced phenomena. Here, by using mechanical polishing processes, we fabricated a low-loss quasi-single-mode periodically poled LiNbO3 (PPLN) waveguide, which shows 7% optical propagation loss with a waveguide length of 45 mm. Using the waveguide, we assembled a low-loss fiber-pigtailed OPA module with a total insertion loss of 21%. Thanks to its directly bonded core on a LiTaO3 substrate, the waveguide does not show pump-induced optical loss even under a condition of hundreds of milliwatts pumping. Furthermore, the quasi-single-mode structure prohibits excitation of higher-order spatial modes and enables us to obtain larger squeezing level. Even with including optical coupling loss of the modularization, we observe 6.3-dB squeezed light from the DC component up to a 6.0-THz sideband in a fully fiber-closed optical system. By excluding the losses due to imperfections of the modularization and detection, the squeezing level at the output of the PPLN waveguide is estimated to be over 10 dB. Our waveguide squeezer is a promising quantum light source for high-speed large-scale fault-tolerant quantum computing.

Low loss hybrid plasmon polariton Mach-Zehnder modulators

We propose a hybrid plasmon polariton (HPP) Mach-Zehnder modulator (MZM) structure that combines the tight optical confinement of plasmonic waveguides and narrow slot waveguides with the low loss feature of photonic waveguides. Compared with conventional surface plasmon polariton (SPP) modulators, the HPP modulator exhibits lower propagation loss and better overall performance. Simulations based on the finite difference time-domain (FDTD) and finite element method (FEM) predict a half-wave voltage-length product of 0.078 V·mm for the HPP modulator. Meanwhile, the propagation loss is only 0.2 dB/μm, which is less than half of that for an SPP modulator. The modulation bandwidth of a 10-μm-long HHP modulator exceeds 650 GHz, while the total insertion loss of the device is estimated to be lower than 4 dB.

Compact and low loss magneto-optical waveguide isolator for TE mode based on lithium niobate on insulator

A novel optical isolator for fundamental transverse electric (TE) mode light based on asymmetric Mach–Zehnder interferometer (MZI) configuration is proposed. Asymmetric Mach–Zehnder interferometer (MZI) configuration is employed to generate nonreciprocal phase shift (NRPS). The optical isolator is implemented by applying Ce: YIG thin film on lithium niobate on insulator (LNOI). The NRPS of LN/Ce: YIG composite waveguides with different geometric sizes are calculated. The 30 dB isolation bandwidth is larger than 48.3 nm and the total simulated insertion loss is as low as 2.736 dB for NRPS waveguides with a length of 504.5μm at a wavelength around 1550 nm. Considering the state-of-art technology, the fabrication tolerances and a suitable process are discussed. Besides, a wavelength-tuning optical isolator is designed to cancel the phase deviation.