Search

We demonstrate a complementary metal–oxide–semiconductor (CMOS)-compatible optical parametric Bragg amplifier on an ultra-silicon-rich nitride chip. The amplifier design incorporates advantageous group index properties in a nonlinear Bragg grating to circumvent phase matching limitations arising from the bulk material and waveguide dispersion. The grating structure further augments the effective nonlinear parameter of 800 W−1/m, considerably lowering the power required for the observation of strong parametric gain. On/off optical parametric gain of 20 dB is achieved using a low peak power of 1.6 W, in good agreement with numerical calculations. This represents a 7 dB improvement in the parametric gain compared to the absence of grating enhancement which is attributed to the Bragg grating induced superior phase matching.

We demonstrate slot waveguides on ultra-silicon-rich nitride designed for optimal high group index birefringence $( > 1)$ . High speed characterization using 30Gb/s non-return-to-zero and 56Gb/s pulsed amplitude modulation 4 data are performed on fabricated waveguides showing error-free performance.

Three-dimensional monolithically integrated polymer microtoroid resonator-waveguide system and nested-double-spiral waveguides are fabricated and characterized. Transmission of 30Gb/s non-return-to-zero data and 28Gb/s pulse amplitude modulation-4 data is demonstrated.

Infrared (IR)-emitting RE doped materials have been extensively used to fabricate active components of integrated optical devices in various fields, such as fiber amplifiers, telecommunications, optoelectronics, and waveguides. Among various RE elements, trivalent erbium ions (Er 3+) are of great interest since their emissive behavior span the low loss telecommunication window of 1300–1650 nm. In this paper, we report two types of polymeric waveguide amplifiers. 8 cm long, lithographically patterned spiral waveguides provide 8 dB of gain using a 980 nm pump power of 95 mW. Gain is observed from 1530 to 1590 nm. We further report the first demonstration of polymeric waveguide amplifiers fabricated using 3D printing methods based on two-photon lithography, paving the way for rapid prototyping of active 3D printed devices and active photonic devices which may transcend planar limitations.

Optical pulses are fundamentally defined by their temporal and spectral properties. The ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology, high speed optical communications and attosecond science. Here, we report 11× temporal compression of 5.8 ps pulses to 0.55 ps using a low power of 13.3 W. The result is accompanied by a significant increase in the pulse peak power by 9.4×. These results represent the strongest temporal compression demonstrated to date on a complementary metal–oxide–semiconductor (CMOS) chip. In addition, we report the first demonstration of on-chip spectral compression, 3.0× spectral compression of 480 fs pulses, importantly while preserving the pulse energy. The strong compression achieved at low powers harnesses advanced on-chip device design, and the strong nonlinear properties of backend-CMOS compatible ultra-silicon-rich nitride, which possesses absence of two-photon absorption and 500× larger nonlinear parameter than in stoichiometric silicon nitride waveguides. The demonstrated work introduces an important new paradigm for spectro-temporal compression of optical pulses toward turn-key, on-chip integrated systems for all-optical pulse control.

Bragg solitons are solitary waves which form as a result of the nonlinearity in the medium and the dispersion induced by a Bragg grating. We present recent results covering the dynamics of Bragg solitons. Temporal compression, fission and enhanced, coherent supercontinuum generation and tunable spectral broadening are experimentally demonstrated.

Nonlinear integrated optics leveraging platforms with high nonlinear figure of merit offer energy efficient optical signal processing capabilities. Over the last five years, CMOS-compatible ultra-silico-rich nitride (USRN) has emerged as a promising platform on which to implement various nonlinear optics functions. Bandgap engineered to maximize the Kerr nonlinearity while maintaining two-photon absorption free behavior at telecommunications wavelengths, USRN possesses a nonlinear refractive index that is 100× larger than that in stoichiometric silicon nitride. In this article, we review the recent progress made in USRN-based nonlinear integrated optics devices. The impacts it has made spanning from high gain optical parametric amplification and observations of soliton effects in photonic waveguides and photonic crystal waveguide structures will be discussed. Finally, we assess the future outlook of CMOS-compatible USRN-based nonlinear optics.

Strong temporal compression in an integrated ultra-silicon-rich nitride temporal compressor consisting of separate nonlinear and anomalously dispersive stages is demonstrated. 11× compression of 5.8ps pulses at a low input peak power of 13.3W and 9.4× increase in the pulse peak power is achieved.

Parametric wavelength conversion of 30Gbps Non-Return-Zero data using degenerate four wave mixing was performed in ultra-silicon-rich nitride waveguides. A power penalty of 1.2dB was achieved at a bit error rate of 10-4.

Nonlinear CMOS Photonics allows for seamless integration with CMOS electronics and ease of manufacturability. We discus developments in USRN-based nonlinear optics. We demonstrate 8.7 soliton-effect compression in USRN waveguides, on-chip Bragg-soliton compression and fission.

Temperature tuning of spectral broadening induced by a nonlinear grating is experimentally demonstrated. The bandwidth is observed to decrease as temperature increases, corresponding to a red-shift in the high dispersion region of the Bragg grating.

Supercontinuum generation (SCG) through soliton fission provides high‐brightness, spectrally‐rich light needed for hyperspectral imaging, broadband spectroscopy, and fluorescence microscopy. The prospect of miniaturization has led to many demonstrations of this phenomenon in integrated platforms. However, due to the moderate dispersion and nonlinearity generally available in channel waveguides, femtosecond pulses have typically been required to date, as the use of picosecond pulses would require unpractically long devices to achieve soliton fission. Here, spectral bandwidth enhancement of the supercontinuum process through Bragg grating induced soliton‐effect compression and soliton fission is demonstrated. This approach uses picosecond pulses on a complementary metal oxide semiconductor (CMOS)‐compatible, millimeter‐scale platform, consisting of a monolithically integrated cladding‐modulated Bragg grating with a channel waveguide. The strong dispersion near the stopband of the grating enables compression and fission of picosecond higher‐order solitons, which enhances the spectral broadening in the channel waveguide. A 4.3 spectral bandwidth enhancement is reported, with respect to a reference waveguide of the same length. The output spectra are further studied both through simulations and experiments and determined to possess high spectral coherence. These results highlight a simple route to significantly augment the bandwidth of nonlinear processes such as SCG while maintaining low power and compact footprint.

Broadband Silicon-On-Insulator (SOI) directional couplers are designed based on a combination of curved and straight coupled waveguide sections. A design methodology based on the transfer matrix method (TMM) is used to determine the required coupler section lengths, radii, and waveguide cross-sections. A 50/50 power splitter with a measured bandwidth of 88 nm is designed and fabricated, with a device footprint of 20 μm × 3 μm. In addition, a balanced Mach-Zehnder interferometer is fabricated showing an extinction ratio of >16 dB over 100 nm of bandwidth.

On-chip waveguide amplifiers offer higher gain in small device sizes and better integration with photonic devices than the commonly available fiber amplifiers. However, on-chip amplifiers have yet to make its way into the mainstream due to the limited availability of materials with ideal light guiding and amplification properties. A low-loss nanostructured on-chip channel polymeric waveguide amplifier was designed, characterized, fabricated and its gain experimentally measured at telecommunication wavelength. The active polymeric waveguide core comprises of NaYF4:Yb,Er,Ce core-shell nanocrystals dispersed within a SU8 polymer, where the nanoparticle interfacial characteristics were tailored using hydrolyzed polyhedral oligomeric silsesquioxane-graft-poly(methyl methacrylate) to improve particle dispersion. Both the enhanced IR emission intensity from our nanocrystals using a tri-dopant scheme and the reduced scattering losses from our excellent particle dispersion at a high solid loading of 6.0 vol% contributed to the outstanding optical performance of our polymeric waveguide. We achieved one of the highest reported gain of 6.6 dB/cm using a relatively low coupled pump power of 80 mW. These polymeric waveguide amplifiers offer greater promise for integrated optical circuits due to their processability and integration advantages which will play a key role in the emerging areas of flexible communication and optoelectronic devices.

An on-chip Coarse wavelength Division Multiplexing (CWDM) has been designed, fabricated and experimentally measured, yielding 9 multiplexed wavelength channels spanning S+C+L band. The average channel crosstalk is −25 dB. All channels cover the CWDM central wavelengths stipulated by ITU standard.

Nonlinear phenomena at the 1550nm wavelength are studied in ultra-silicon-rich nitride devices. Photonic crystals in one are demonstrated to introduce 1000x enhancement in the group velocity dispersion properties and a 40x increase in the nonlinear parameter. The large Kerr nonlinearity and negligible two-photon absorption allow strong nonlinear effects including 42.5dB optical parametric gain and Bragg soliton based temporal compression to be demonstrated.

Nonlinear photonics devices are designed and fabricated on bandgap engineered ultra-silicon-rich nitride (USRN). The USRN films are compositionally engineered to possess a bandgap of 2.1 eV to eliminate two-photon absorption at $1.55 \mu{\mathrm{m}}$ while maintaining a large linear and nonlinear refractive index of 3.1 and 2.8 × 10−13 cm2/ W respectively. We present nanopho-tonic devices periodic in one and two dimensions that introduce an engineered group index profile. The devices are designed to possess a specific dispersion profile that enables slow-light behavior and augmented waveguide nonlinear parameters to be observed. Photonic crystal waveguides with flat band region engineered at the $1.55 \mu{\mathrm{m}}$ region show a ×40 enhancement increase in the nonlinear parameter, providing an effective nonlinear parameter of 1.97 × 104 W−l/m. One-dimensional photonic crystals are designed with effective index modulation effected in the device cladding, and demonstrated to exhibit augmented anomalous dispersion on the band edge while maintaining high transmission. Consequently, the reduced dispersive length combined with the large intrinsic nonlinearity in the material enables time and spectrally resolved characterizations of soliton formation, temporal compression and soliton fission to be experimentally observed. This represents one of the first observations of Bragg solitons on a chip, with the largest soliton-effect pulse compression to date with a compression factor of × 4.

We demonstrate pulse compression using ultra-silicon-rich nitride grating devices. Frequency chirp from a waveguide is temporally synchronized by a dispersive grating to achieve temporal compression by a factor of 4.3. When reversed, spectral compression of 2.3× is achieved.

We demonstrate the optical pulse compression of 2ps laser down to 230fs pulse resulting in 8.7 times compressed using a USRN waveguide. The process is facilitated by high-order soliton formation arising from a large nonlinear parameter and anomalous group velocity dispersion.

Energy bands in AB-stacked bilayer graphene are featured by the co-presence of trigonal warping and a Mexican hat structure around each Dirac point, and electrically modulatable band edges with the modulation valley-dependent (valley-independent) in the case of in-plane (vertical) fields. This theoretical work takes into account the foregoing realistic features and exploits them for valleytronic applications. Specifically, it investigates in detail electrical valley transport in the armchair direction, in AB-stacked bilayer graphene lateral quantum structures with an interface, a single barrier, and double barriers, respectively, and demonstrates that due to the band structure features as well as an involved interplay among them, such structures harbor an interesting potential for valley filtering. An analysis of transmitted current valley polarization is provided. Optimization of the structures for the polarization is explored. The thermal effect on valley filtering is examined. Sizable polarizations of 88% (97%) and 23% (27%) at low and room temperatures, respectively, are shown to be achievable in the case of one-barrier (double-barrier) structures.

Correlated photon pair generation is demonstrated using ultra-silicon-rich nitride waveguides. Waveguides with a length of 10 mm, nonlinear parameter of 530 W−1/m and anomalous dispersion are used to achieve spontaneous four-wave mixing. A generated coincidence rate of 2.40 × 105 counts per second is achieved, and derived from a measured coincidence rate of ∼ 1 counts per second at the maximum coupled power of 5 mW, in line with the expected quadratic dependence of spontaneous four-wave mixing efficiency on power. Utilizing picosecond pulses as the pump, we achieve a measured coincidence rate of up to 1.8 counts per second, resulting in a generated coincidence rate of 2.20 × 10−2 counts per pulse at the maximum peak power of 8.33 W. 2.3 times larger coincidence-to-accidental ratio is also obtained using a pulsed pump compared to that achieved with a continuous-wave pump. Further enhancements via the use of ring resonators may be adopted.

We present a library of high-performance passive and active silicon photonic devices at the C-band that is specifically designed and optimized for edge-coupling-enabled silicon photonics platform. These devices meet the broadband (100 nm), low-loss (< 2dB per device), high speed (≥ 25 Gb/s), and polarization diversity requirements (TE and TM polarization extinction ratio ≤ 25 dB) for optical communication applications. Ultra-low loss edge couplers, broadband directional couplers, high-extinction ratio polarization beam splitters (PBSs), and high-speed modulators are some of the devices within our library. In particular, we have designed and fabricated inverse taper fiber-to-waveguide edge couplers of tip widths ranging from 120 nm to 200 nm, and we obtained a low coupling loss of 1.80±0.28 dB for 160 nm tip width. To achieve polarization diversity operation for inverse tapers, we have experimentally realized different designs of polarization beam splitters (PBS). Our optimized PBS has a measured extinction ratio of ≤ 25 dB for both the quasiTE modes, and quasi-TM modes. Additionally, a broadband (100 nm) directional coupler with a 50/50 power splitting ratio was experimentally realized on a small footprint of 20×3 μm2 . Last but not least, high-speed silicon modulators with a range of carrier doping concentrations and offset of the PN junction can be used to optimise the modulation efficiency, and insertion losses for operation at 25 GHz.

High-performance silicon polarization beam splitters were experimentally demonstrated for both the C and L bands. Extinction ratio is ≥ ∼40 dB for the entire measured bandwidth of 90 nm, with insertion losses of ∼1 dB.

Nonlinear optics leveraging CMOS-compatible, ultra-silicon-rich nitride devices is presented. Films are engineered to possess high Kerr nonlinearity and negligible two-photon absorption at telecommunications wavelengths. We demonstrate high-gain optical parametric amplifiers, wavelength conversion, supercontinuum sources and slow light enhanced devices.

CMOS-compatible nonlinear optics platforms with negligible nonlinear losses and high nonlinearity are of great merit. Silicon, silicon nitride and Hydex glass have made significant headway in nonlinear optical signal processing, though none of these platforms possesses the highly sought after combination of high nonlinearity and negligible nonlinear losses. In this manuscript, we present a nonlinear optics platform based on silicon-rich nitride, deposited at a low temperature of 250°C compatible with back-end CMOS processing. The silicon-rich nitride is designed and engineered in composition to have a bandgap of 2.05 eV, such that the two-photon absorption edge is well below 1.55 μm. The designed and developed waveguides have a nonlinear parameter of 550 W−1/m, 500 times larger than that in silicon nitride waveguides, while at the same time not possessing two-photon and free-carrier losses. Using 500-fs pulses, we generate supercontinuum exceeding 0.6 of an octave.

We report on the design and experimental demonstration of a broadband silicon polarization beam splitter (PBS) with a high extinction ratio (ER)≥30 dB. This was achieved using triple-bent-waveguide directional coupling in a single PBS, and cascaded PBS topology. For the single PBS, the bandwidths for an ER≥30 dB are 20 nm for the quasi-TE mode, and 70 nm for the quasi-TM mode when a broadband light source (1520-1610 nm) was employed. The insertion loss (IL) varies from 0.2 to 1 dB for the quasi-TE mode and 0.2-2 dB for the quasi-TM mode. The cascaded PBS improved the bandwidth of the quasi-TE mode for an ER≥30 dB to 90 nm, with a low IL of 0.2-2 dB. To the best of our knowledge, our PBS system is one of the best broadband PBSs with an ER as high as ∼42 dB and a low IL below 1 dB around the central wavelength, and experimentally demonstrated using edge-coupling.

Ring resonators on silicon rich nitride for potential use as rare-earth doped amplifiers pumped at 1310 nm with amplification at telecommunications-band are designed and characterized. The ring resonators are fabricated on 300 nm and 400 nm silicon rich nitride films and characterized at both 1310 nm and 1550 nm. We demonstrate ring resonators exhibiting similar quality factors exceeding 10,000 simultaneously at 1310 nm and 1550 nm. A Dysprosium-Erbium material system exhibiting photoluminescence at 1510 nm when pumped at 1310 nm is experimentally demonstrated. When used together with Dy-Er co-doped particles, these resonators with similar quality factors at 1310 nm and 1550 nm may be used for O-band pumped amplifiers for the telecommunications-band.

We characterize the nonlinear optical properties of GeSbS chalcogenide glasses with fiber-based experiments. A waveguide nonlinear parameter of 7 W−1/m and nonlinear refractive index of 3.71 × 10−18 m2/W are estimated by self-phase modulation. A GeSbS waveguide could also generate a supercontinuum from 1280 to 2120 nm at the −30 dB level for maximum coupled power of 340 W, showing a 14 fold spectral broadening of the input spectrum explained by cascaded stimulated Raman scattering.

We study ultrafast spectral characteristics of our ultra-short ultra-slicon rich nitride (USRN) waveguide with large Kerr nonlinearity (γ∼550W−1/m) and negligible nonlinear loss. The output spectra of USRN ring resonator and short-length waveguide broaden around 2 times and 4 times wider than that in 500 fs input pulses, respectively. Negligible nonlinear loss including two-photon absorption at near-infrared wavelength rages is proven by the linear increase in both the output bandwidth and power versus input peak power up to 100 W. The bandwidth broadens by 200 nm per millimeter of USRN waveguide implying that our ultra-short USRN waveguide acquires higher spectra-broaden efficiency compared other CMOS-platforms operating at telecommunication bands.

We have successfully fabricated and measured our silicon bridge waveguide polarization beam splitter (PBS). Our proposed PBS is based on a bend directional coupler with a bend bridge waveguide and is experimentally realized using silicon waveguide thickness of 220 nm and 250 nm, which are the commonly used silicon thickness for silicon photonics manufacturing. Our experimental results demonstrated high extinction ratio of > 20 dB for the TE-like mode, and > 15 dB for the TM-like mode across a broad bandwidth of 90 nm that covers the entire C-band with a small footprint of ~18×9 μm2. On-chip high performance PBS is important for polarization diversity in integrated photonics, and for communication applications such as dual-polarization quadrature phase-shift keying (DP-QPSK) modulation.

GeSbS ridge waveguides have recently been demonstrated as a promising mid – infrared platform for integrated waveguide – based chemical sensing and photodetection. To date, their nonlinear optical properties remain relatively unexplored. In this paper, we characterize the nonlinear optical properties of GeSbS glasses, and show negligible nonlinear losses at 1.55 μm. Using self – phase modulation experiments, we characterize a waveguide nonlinear parameter of 7 W[subscript −1]/m and nonlinear refractive index of 3.71 × 10[superscript −18] m[superscript 2]/W. GeSbS waveguides are used to generate supercontinuum from 1280 nm to 2120 nm at the −30 dB level. The spectrum expands along the red shifted side of the spectrum faster than on the blue shifted side, facilitated by cascaded stimulated Raman scattering arising from the large Raman gain of chalcogenides. Fourier transform infrared spectroscopic measurements show that these glasses are optically transparent up to 25 μm, making them useful for short – wave to long – wave infrared applications in both linear and nonlinear optics., SUTD-MIT International Design Centre (IDC)

The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation to be attributed to the USRN waveguide’s large nonlinearity and negligible two-photon absorption at 1550 nm.The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation...

An 8-channel coarse wavelength division multiplexer (CWDM) based on coupled vertical gratings has been designed, fabricated and characterized. The devices are implemented on the ultra-silicon-rich nitride (USRN) platform. The demonstrated device possesses 8 CWDM channels. The absence of free spectral range (FSR) enabled the overall multiplexed bandwidth to span across the S + C + L bands. The CWDM channels meet the specifications stipulated by the International Telecommunications Union G.694.2 standard. The average channel crosstalk is -25dB. Pseudo-Random Bit Sequence 231-1 Non-Return-Zero data at 30Gb/s was launched into the device and a clear eye diagram was obtained. The device was further used with a USRN waveguide generating supercontinuum to create a multi-wavelength source emitting light at 8 CWDM wavelengths.

We theoretically study the valley aspect of lateral tunneling transport in valleytronic materials, using AB-stacked (Bernal-stacked) bilayer graphene as a material example. A lateral structure with multiple well/barrier interfaces is considered. A full-zone tight-binding method is employed, allowing for the study of intervalley mixing in electron states. We study the degree of tunneling current valley contrast under the condition of a source-drain bias or barrier asymmetry. For a single-barrier structure, it is found that the intervalley mixing is negligible, and the contrast is positively correlated with the barrier width and height. For a double-barrier structure, the effect of resonant tunneling is investigated. The intervalley mixing is shown to be significantly enhanced at resonant tunneling. In addition, the resonant levels are found valley split, and a proposal is given which exploits the splitting for the generation of a sizable tunneling current valley polarization. Based on a simple model using momentum-shifted thermal distribution for obliquely incident electrons, the temperature dependence of tunneling current valley polarization is also examined. An interesting crossover from the valley-orbit interaction-dominant polarization to the warping-dominant polarization is found to occur as the temperature is increased.We theoretically study the valley aspect of lateral tunneling transport in valleytronic materials, using AB-stacked (Bernal-stacked) bilayer graphene as a material example. A lateral structure with multiple well/barrier interfaces is considered. A full-zone tight-binding method is employed, allowing for the study of intervalley mixing in electron states. We study the degree of tunneling current valley contrast under the condition of a source-drain bias or barrier asymmetry. For a single-barrier structure, it is found that the intervalley mixing is negligible, and the contrast is positively correlated with the barrier width and height. For a double-barrier structure, the effect of resonant tunneling is investigated. The intervalley mixing is shown to be significantly enhanced at resonant tunneling. In addition, the resonant levels are found valley split, and a proposal is given which exploits the splitting for the generation of a sizable tunneling current valley polarization. Based on a simple model using ...

High performance silicon-on-insulator polarization beam splitter with a small footprint of ∼18 × 9 μm2 is demonstrated using a bend directional coupler with a bridge waveguide. High extinction ratio of > ∼20 dB over the entire C band is achieved for both TE-like and TM-like polarizations.

CMOS-compatible nonlinear optics platforms with high Kerr nonlinearity facilitate the generation of broadband spectra based on self-phase modulation. Our ultra – silicon rich nitride (USRN) platform is designed to have a large nonlinear refractive index and low nonlinear losses at 1.55 μm for the facilitation of wideband spectral broadening. We investigate the ultrafast spectral characteristics of USRN waveguides with 1-mm-length, which have high nonlinear parameters (γ ∼ 550 W−1/m) and anomalous dispersion at 1.55 μm wavelength of input light. USRN add-drop ring resonators broaden output spectra by a factor of 2 compared with the bandwidth of input fs laser with the highest quality factors of 11000 and 15000. Two – fold self phase modulation induced spectral broadening is observed using waveguides only 430 μm in length, whereas a quadrupling of the output bandwidth is observed with USRN waveguides with a 1-mm-length. A broadening factor of around 3 per 1 mm length is achieved in the USRN waveguides, a value which is comparatively larger than many other CMOS-compatible platforms.

Broadband silicon-on-insulator (SOI) 2 × 2 power splitters are designed based on curved asymmetric waveguide coupler sections. A 50/50 power splitter with a footprint of ∼20 × 3 μm2 and ±1dB bandwidth >100 nm is designed and fabricated.

In this study, we report a method to quantify the helium distribution in the SiC f /SiC composites, which are used as the first-wall materials of fusion reactor. The helium-bubble formation in Hi-Nicalon Type-S (HNS) was observed in the irradiated SiC f /SiC composites at a level of 100 dpa and at 800 °C and 1000 °C, respectively. We applied transmission electron microscopy and electron energy loss spectroscopy to investigate the helium-gas-bubbles-formation mechanisms. To simulate the practical first-wall environment of Deuterium–Tritium (D–T) fusion reactor, a dual-ion beam (6 MeV Si 3+ and 1.13 MeV He + ) was performed to irradiate the SiC f /SiC composites. The relationship between the energy shift of He K-edge and the radius of the bubble of the SiC composites was estimated by electron energy loss spectroscopy analysis. The results show that all of the helium atoms irradiated at 1000 °C and formed the bubbles. On the other hand, at 800 °C, only 25.5% of the helium atoms form the helium bubbles. A clear thermal-dependent formation mechanism is found.

The generation of broadband light within the telecommunication band has been instrumental to the design and characterization of advanced optical devices and systems. In this paper, stimulated degenerate four-wave mixing of an ultra-silicon rich nitride waveguide is investigated using a pulsed pump at 1.555 μm and incoherent broadband sources emitting in the 1.65 μm wavelength region as a signal. The waveguide possesses a large nonlinear parameter of 330 W−1/m as well as anomalous dispersion, required for phase matched parametric processes. The broadband idler ranging from 1.43 μm to 1.52 μm is generated using a coupled peak power of 4.6 W, spanning ∼100 nm at the −20 dB level, which is sufficient to cover parts of the E- and S-bands. The spectral span of the generated idler also agrees well with the calculation based on the phase-matching condition governing degenerate four-wave mixing. Cascaded incoherent four-wave mixing is also observed. Using a supercontinuum pump spanning from 1.1 to 1.7 μm with a co...

Multiplexing of optical modes in waveguides is demonstrated using coupled vertical gratings. The device utilizes sinusoidally corrugated waveguides of different widths with a period designed to multiplex information at 1.55 µm. The design, fabrication and characterization of devices is performed. Multiplexing of modes is demonstrated in optical structures which support 3 and 5 quasi-TE modes. The design utilizes counter-propagating modes in periodic structures, thus enabling the device to combine its mode division multiplexing capabilities with wavelength division multiplexing functionalities to further augment the multiplexing capacity of the device.

Mode division multiplexing of modes in a silicon waveguide supporting three optical modes is demonstrated in the silicon on insulator platform. Cross-talk suppression of 17dB and 12dB are obtained for the zeroth and second order modes respectively. The extinction bandwidth is observed to increase with the mode order indicating a stronger cross coupling coefficient as the mode order is increased. The extinction ratio is also observed to increase from 5 dB to 15dB and >25dB as the mode order is increased, implying an increasing cross coupling coefficient.

NiFe/NiMn exchange field was manipulated by an underlayer NiFeCr or by C ion irradiation. Underlayer NiFeCr significantly promoted (1 1 1) texture growth, leading to a higher exchange field. However, the threshold annealing temperature required to reach a large value of exchange field was raised. This can be attributed to well aligned orientations between NiFe and NiMn at the interface, which stabilizes the FCC γ phase of NiMn and increases the nucleation energy. C ion irradiation with the dosage of 3.7×1015/cm2 prior to the annealing increases the exchange field by 21% without altering the blocking temperature (>400°C). The enhancement of the exchange field by irradiation can be related to the increase of defect sites in NiMn or (and) to the new phase NiMn(C) formation having c/a ratio significantly less than NiMn.