High Contrast Waveguides Research Articles

Sensing performance of Bragg fibers having a defect layer utilizing confinement loss analysis for brain cancer cells detection

The sensing performance of the Bragg fiber having a defect layer in the cladding region is optimized for brain cancer cell detection using the refractive index of brain lesions fluids. The optimization is achieved by comparing the confinement loss of low contrast and a high contrast defected Bragg fiber with similar standard Bragg fiber. Using the transfer matrix method and matching the fields at various interfaces equation of confinement loss is obtained in presence of a defect layer. It is observed that the sensing performance of low contrast waveguide is better than high contrast waveguide in the absence of the defect layer but the situation become reversed in presence of a defect layer. Wavelength interrogation shows high sensing performance with the variation of defect layer refractive index while intensity interrogation shows high sensing performance with the variation of core refractive index. Here wavelength interrogation of high contrast defected Bragg fiber is demonstrated to detect normal and abnormal brain tissues due to its feasibility. Our analysis shows that the respective maximum sensitivity, detection accuracy, and quality parameters are 12.1519 nm/RIU, 4365.7235, and 41.6161 RIU−1 in the benign stage corresponding to the wall of brain and 11.0233 nm/RIU, 4242.7191 and 38.8281 RIU−1 in the malignant stage corresponding to low-grade glioma.

Silicon photonics for telecom and data-com applications

In recent decades, silicon photonics has attracted much attention in telecom and data-com areas. Constituted of high refractive-index contrast waveguides on silicon-on-insulator (SOI), a variety of integrated photonic passive and active devices have been implemented supported by excellent optical properties of silicon in the mid-infrared spectrum. The main advantage of the silicon photonics is the ability to use complementary metal oxide semiconductor (CMOS) process-compatible fabrication technologies, resulting in high-volume production at low cost. On the other hand, explosively growing traffic in the telecom, data center and high-performance computer demands the data flow to have high speed, wide bandwidth, low cost, and high energy-efficiency, as well as the photonics and electronics to be integrated for ultra-fast data transfer in networks. In practical applications, silicon photonics started with optical interconnect transceivers in the data-com first, and has been now extended to innovative applications such as multi-port optical switches in the telecom network node and integrated optical phased arrays (OPAs) in light detection and ranging (LiDAR). This paper overviews the progresses of silicon photonics from four points reflecting the recent advances mentioned above. CMOS-based silicon photonic platform technologies, applications to optical transceiver in the data-com network, applications to multi-port optical switches in the telecom network and applications to OPA in LiDAR system.

Michelson interferometer modulator based on hybrid silicon and lithium niobate platform

We propose and demonstrate a hybrid silicon and lithium niobate Michelson interferometer modulator (MIM) with a reduced half-wave voltage-length product compared to a Mach-Zehnder modulator. The modulator is based on seamless integration of a high-contrast waveguide based on lithium niobate—a widely used modulator material—with compact, low-loss silicon circuitry. The present device demonstrates a half-wave voltage-length product as low as 1.2 V cm and a low insertion loss of 3.3 dB. The 3 dB electro-optic bandwidth is approximately 17.5 GHz. The high-speed modulations are demonstrated at 32 Gbit/s and 40 Gbit/s with the extinction ratio of 8 dB and 6.6 dB, respectively. The present device avoids absorption loss and nonlinearity in conventional silicon modulators and demonstrates the lowest half-wave voltage-length product in lithium niobate modulators. The hybrid MIM demonstrates high-speed data modulation showing potential in future optical interconnects.

High-performance hybrid silicon and lithium niobate Mach–Zehnder modulators for 100 Gbit s−1 and beyond

Optical modulators are at the heart of optical communication links. Ideally, they should feature low insertion loss, low drive voltage, large modulation bandwidth, high linearity, compact footprint and low manufacturing cost. Unfortunately, these criteria have only been achieved on separate occasions.Based on a Silicon and Lithium Niobate hybrid integration platform, we demonstrate Mach-Zehnder modulators that simultaneously fulfill these criteria. The presented device exhibits an insertion loss of 2.5 dB, voltage-length product of 2.2 Vcm, high linearity, electro-optic bandwidth of at least 70 GHz and modulation rates up to 112 Gbit/s. The high-performance modulator is realized by seamless integration of high-contrast waveguide based on Lithium Niobate - the most mature modulator material - with compact, low-loss silicon circuits. The hybrid platform demonstrated here allows for the combination of 'best-in-breed' active and passive components, opening up new avenues for enabling future high-speed, energy efficient and cost-effective optical communication networks.

100-Gb/s Electro-Absorptive Duobinary Modulation of an InP-on-Si DFB Laser

100-Gb/s single-channel optical data communication transceivers can provide a compact and cost-effective solution for the exponentially growing data-center traffic. One of the enabling technologies is electro-absorption-modulated single-mode lasers which are very compact, efficient, and fast. In this letter, such a transmitter integrated on a silicon photonics platform is demonstrated. While low loss and high contrast waveguides are provided by Si photonics, the gain and efficient electro-absorption are provided by the InP-based multi-quantum-well structure. A lumped electro-absorption modulator integrated with a distributed feedback laser is designed and fabricated in this platform. The epitaxial stack is identical for the laser and the modulator, which eases the fabrication process considerably. In this way, we successfully demonstrate 100-Gb/s single-channel electrical duobinary optical data transport over ~100 m of fiber with a bit error rate of 1.6e-3.

Ultra-low loss photonic circuits in lithium niobate on insulator.

Lithium niobate on insulator (LNOI) photonics promises to combine the excellent nonlinear properties of lithium niobate with the high complexity achievable by high contrast waveguides. However, to date, fabrication challenges have resulted in high-loss and sidewall-angled waveguides, limiting its applicability. We report LNOI single mode waveguides with ultra low propagation loss of 0.4 dB/cm and sidewall angle of 75°. Our results open the route to a highly efficient photonic platform with applications ranging from high-speed telecommunication to quantum technology.

3D laser-written silica glass step-index high-contrast waveguides for the 3.5 μm mid-infrared range.

We report on the direct laser fabrication of step-index waveguides in fused silica substrates for operation in the 3.5 μm mid-infrared wavelength range. We demonstrate core-cladding index contrasts of 0.7% at 3.39 μm and propagation losses of 1.3 (6.5) dB/cm at 3.39 (3.68) μm, close to the intrinsic losses of the glass. We also report on the existence of three different laser modified SiO₂ glass volumes, their different micro-Raman spectra, and their different temperature-dependent populations of color centers, tentatively clarifying the SiO₂ lattice changes that are related to the large index changes.

Stimulated Brillouin scattering in integrated photonic waveguides: Forces, scattering mechanisms, and coupled-mode analysis

Recent theoretical studies of Stimulated Brillouin Scattering (SBS) in nanoscale devices have led to an intense research effort dedicated to the demonstration and application of this nonlinearity in on-chip systems. The key feature of SBS in integrated photonic waveguides is that small, high-contrast waveguides are predicted to experience powerful optical forces on the waveguide boundaries, which are predicted to further boost the SBS gain that is already expected to grow dramatically in such structures because of the higher mode confinement alone. In all recent treatments, the effect of radiation pressure is included separately from the scattering action that the acoustic field exerts on the optical field. In contrast to this, we show here that the effects of radiation pressure and motion of the waveguide boundaries are inextricably linked. Central to this insight is a new formulation of the SBS interaction that unifies the treatment of light and sound, incorporating all relevant interaction mechanisms --- radiation pressure, waveguide boundary motion, electrostriction and photoelasticity --- from a rigorous thermodynamic perspective. Our approach also clarifies important points of ambiguity in the literature, such as the nature of edge-effects with regard to electrostriction, and of body-forces with respect to radiation pressure. This new perspective on Brillouin processes leads to physical insight with implications for the design and fabrication of SBS-based nanoscale devices.

TriPleX: a versatile dielectric photonic platform

Abstract Photonic applications based on planar waveguide technology impose stringent requirements on properties such as optical propagation losses, light coupling to optical fibers, integration density, as well as on reliability and reproducibility. The latter is correlated to a high level of control of the refractive index and waveguide geometry. In this paper, we review a versatile dielectric waveguide platform, called TriPleX, which is based on alternating silicon nitride and silicon dioxide films. Fabrication with CMOS-compatible equipment based on low-pressure chemical vapor deposition enables the realization of stable material compositions being a prerequisite to the control of waveguide properties and modal shape. The transparency window of both materials allows for the realization of low-loss waveguides over a wide wavelength range (400 nm–2.35 μm). Propagation losses as low as 5×10-4 dB/cm are reported. Three basic geometries (box shell, double stripe, and filled box) can be distinguished. A specific tapering technology is developed for on-chip, low-loss (<0.1 dB) spotsize convertors, allowing for combining efficient fiber to chip coupling with high-contrast waveguides required for increased functional complexity as well as for hybrid integration with other photonic platforms such as InP and SOI. The functionality of the TriPleX platform is captured by verified basic building blocks. The corresponding library and associated design kit is available for multi-project wafer (MPW) runs. Several applications of this platform technology in communications, biomedicine, sensing, as well as a few special fields of photonics are treated in more detail.

Femtosecond laser inscribed cladding waveguides in Nd:YAG ceramics: Fabrication, fluorescence imaging and laser performance

We report on the fabrication of depressed cladding waveguide lasers in Nd:YAG (neodymium doped yttrium aluminum garnet, Nd:Y3Al5O12) ceramics microstructured by femtosecond laser pulses. Full control over the confined light spatial distribution is demonstrated by the fabrication of high contrast waveguides with hexagonal, circular and trapezoidal configurations. The confocal fluorescence measurements of the waveguides reveal that the original luminescence features of Nd3+ ions are well-preserved in the waveguide regions. Under optical pump at 808 nm, cladding waveguides showed continuous wave efficient laser oscillation. The maximum output power obtained at 1064.5 nm is ~181 mW with a slope efficiency as high as 44%, which suggests that the fabricated Nd:YAG ceramic waveguides are promising candidates for efficient integrated laser sources.

High-contrast waveguides in sputtered pure TeO,_2 glass thin films

We present a technological approach to the realization of channeled optical waveguides, starting from reactively sputtered tellurite glass thin films, grown on silica-coated 4" Si wafers. In particular, optical lithographic process and etching recipes have been developed to overcome the solubility of TeO(2) films in aqueous solutions, and to process them into high-index contrast structures with minimized post-etch roughness. Optical tests on preliminary rib waveguide geometries feature 6.3 dB/cm propagation loss for fundamental TE mode at lambda = 1.5 microm.

광섬유 수동정렬을 위한 단일 모드 대형 코어 폴리머 광도파로

정력 오차 허용 범위를 증가 시켜서 효과적인 수동정렬이 가능토록 하기 위한 단일 모드 대형 코어 폴리머 광도파로를 구현하였다. 대형 코어 광도파로는 TEC(thermally expanded core) 광섬유의 모드와 일치하는 큰 도파모드를 가진다. 이로 인해 광섬유와 도파로의 정렬오차로 인한 모드 결합 손실을 줄일 수 있게 된다. 코어와 클래딩의 굴절률 차이가 5 <TEX>${\times}$</TEX> <TEX>$10^{-4}$</TEX> 인 폴리머 재료를 이용하여 25 <TEX>${\times}$</TEX> 25 <TEX>$\mu\textrm{m}$</TEX><TEX>$^2$</TEX> 크기의 정사각형 광도파로를 제작하였으며 도파모드 관측결과 단일모드로 동작함을 확인하였다. 이와 같이 두꺼운 형태의 광도파로 구조 제작을 위하여 자외선 경화를 이용한 인젝션 몰딩(injection molding) 공정을 사용하였다. 제작된 광도파로 소자를 TEC 광섬유와 정렬연결을 할 때 정렬오차가 4.5 <TEX>$\mu\textrm{m}$</TEX> 까지 증가하더라도 삽입손실 증가는 0.5 dB 이하고 유지됨을 확인하였다. To increase the tolerance for passive fiber alignment, a single mode polymer waveguide with a large core structure is demonstrated. The large core waveguide is designed to have a mode profile comparable to that of a thermally expanded core (TEC) fiber, and it can be connected to a high-contrast waveguide through an adiabatic transition taper structure. From a waveguide with a rectangular core of 25 <TEX>${\times}$</TEX> 25 <TEX>${\mu}{\textrm}{m}$</TEX><TEX>$^2$</TEX>, a single mode propagation is observed when the index contrast is as low as 0.0005. A UV-cured injection molding method is used to fabricate the thick core structure. Due to the large mode size, the insertion loss of the device is below 0.5 dB until the lateral displacement of the TEC fiber is 4.5 <TEX>${\mu}{\textrm}{m}$</TEX>. The low insertion loss is important for reproducible passive alignment.

Fabrication of large-core single-mode polymer waveguide connecting to a thermally expanded core fiber for increased alignment tolerance

To increase the fiber alignment tolerance for the passive alignment with a high-contrast waveguide, a single-mode polymer waveguide with a large core structure is proposed. The large core waveguide is designed to have a mode profile comparable to that of a thermally expanded core (TEC) fiber, and it can be connected to a high-contrast waveguide through an adiabatic transition taper structure. From a waveguide with a rectangular core of 25×25 μm2, a single-mode propagation is observed when the index contrast is as low as 0.0005. A UV-cured injection molding method is used to fabricate the thick core structure. Due to the large mode size, the insertion loss of the device is below 0.5 dB until the lateral displacement of the TEC fiber is 4.5 μm, that is important for reproducible passive alignment.

AWG Technologies for Dense WDM Applications

This paper reviews the recent technologies supporting arrayed waveguide gratings (AWGs) based on planar lightwave circuits. From the practical point of view, I describe new technologies such as an athermalization and the high-contrast waveguide that includes the mode field transfer needed for low connection loss with conventional optical fiber. As AWG applications, I present new types of AWG modules such as a dynamic gain equalizer and a variable optical attenuator (VOA) MUX/DEMUX. Both of these will play an important role for next-generation wavelength-division multiplexing networks.

A new higher order finite-difference approximation scheme for the method of lines

A new 5-point and a 7-point nonuniform mesh finite-difference scheme is introduced to approximate the second-derivative operator. The scheme is applied using the method of lines. The necessary interface conditions for the TE and TM fields at an index discontinuity are appropriately included in the derivation. This scheme can model lossy dielectrics as well as metallic layers in a unified way. Numerical results are given for the fundamental TE and TM modes of a high-contrast waveguide and for a metal/dielectric single interface TM surface-plasmon mode showing excellent convergence behavior to the analytical results.

Optical switching with gain in waveguide-modulator structures

Optical switching with gain realised with monolithic waveguide-based smart pixels is reported. In this smart pixel a high-power light beam propagating in a waveguide structure is controlled by small surface-normal optical input beams incident on a reference diode and a threshold switch. A photoconductive switch, a reference diode and a high-contrast waveguide modulator have been fabricated monolithically from the same GaAs/AlGaAS double-hetero-p–i–n structure grown on a semi-insulating GaAs substrate. Even with this first nonoptimised structure an optical gain larger than 150 has been achieved. The contrast ratio of the output signal was greater than 17 dB. The switching energy is 2 pJ, corresponding to 5 fJ/µm2.