Raman mediated solitonic pulse compression

Multi-component gas sensing based on slotted photonic crystal waveguide with liquid infiltration

A transverse-electric (TE)-pass polarization filter based on a slotted photonic crystal waveguide structure is proposed for application in photonic integrated circuits. The silicon-slab-based structure is fabrication-compatible with the standard silicon-on-insulator process technologies. Different structural parameters, such as the r/a ratio of the photonic crystal sections, slab height, slot width, and slot length, are optimized for improved performance. Moreover, the conversion efficiency of a mode of a W1 waveguide to that of a slot waveguide is analyzed for different starting positions of the slot in order to achieve a high extinction ratio of the TE wave over the transverse-magnetic wave. A 3D finite difference time domain simulation methodology, which has been verified against an earlier experimental study made by researchers on another structure, is adopted to evaluate the transmittance of the structure. It shows that the polarization filter, with a footprint of merely 6.28 μm×4.35 μm, offers an extinction ratio in the order of 22 dB; this corresponds to an effective extinction ratio of 3.5 dB μm−1 considering the total length (or 6.5 dB μm−1 considering only the slot length). TE transmittance of the device is calculated as ≈−3 dB at a wavelength of 1550 nm.

To realize a high sensitivity gas sensor, a large wideband, temperature stabilized and large light confinement slow light structure in slotted photonic crystal waveguide (SPCW) is designed. The simulation results indicate that with a proper optimization of the SPCW structure, a very high group index of 105 can be achieved and the electric field enhancement factor would reach to 12. Combined with the correlation spectroscopy for signal processing, the detection limit of 10 ppm is achieved.

A new procedure of designing slotted photonic crystal waveguides is proposed to achieve slow light with improved normalized delay-bandwidth product and low group velocity dispersion that is suitable for both the W1 defect mode and the slot mode. The lateral symmetry of the waveguide in our study is broken by shifting the air holes periodically along the slot axis. The conversion of the "flat band" from band-up slow light to band-down slow light is achieved for the W1 defect mode. The group index curves of the W1 mode change from U-like to step-like and the group indices of 47, 67 and 130 are obtained with the bandwidth over 7.2, 4.8, and 2.3nm around 1550nm, respectively. We also obtain the group indices of 42, 55, and 108 for the slot mode with the bandwidth over 6.2, 5.6, and 2.2nm, respectively. Then the low dispersion slow light propagation is numerically demonstrated by the finite-difference time-domain method.

In this paper, the sensitivity of slotted photonic crystal waveguides (SPCW) with triangular lattice pattern of ring-shaped holes is analyzed in order to realize highly refractive index (RI) sensor devices at mid-infrared wavelengths. The sensing principle is based on the shift of the transmission spectrum edge of these specific ring hole SPCW waveguides giving rise to reinforced light–matter interaction. The 3D simulation results applied to silicon waveguides on membrane show that this guide geometry leads to a very high sensitivity to variations in the ambient environment index, with very dependent trends on the opto-geometric factors of the waveguides. As a matter of example, a $$720 \,\mathrm{nm}$$ wavelength position band edge shift is predicted, corresponding to a sensitivity of more than $$1450 \,\mathrm{nm}$$ per refractive index unit with a device insertion loss level of $$-\,3 \,\mathrm{dB}$$ .

A completely new design for an all‐silicon all‐optical pass switch has been proposed based on the stimulated Raman scattering (SRS) in silicon nanocrystal embedded slotted photonic crystal waveguide (SPCW). Substantial miniaturisation in the device footprint and operating power has been attained by merging the benefits of the giant SRS gain and the ultra‐high optical confinement of the SPCW. The proposed switch offers a tremendously high contrast ratio of between the logic levels and an extraordinary bit rate of 125 Gbps.

Mid infrared silicon photonic integrated components, namely grating couplers, strip and slot waveguides, slotted and un-slotted photonic crystal waveguides, photonic crystal microcavities are experimentally demonstrated in silicon-on-sapphire. Application in trace gas sensing is experimentally demonstrated. Progress towards monolithic integration of lasers and detectors are discussed.

Total internal reflection (TIR) is a ubiquitous phenomenon used in photonic devices ranging from waveguides and resonators to lasers and optical sensors. Controlling this phenomenon and light confinement are keys to the future integration of nanoelectronics and nanophotonics on the same silicon platform. We introduced the concept of relaxed total internal reflection in 2014 to control evanescent waves generated during TIR. These unchecked evanescent waves are the fundamental reason photonic devices are inevitably diffraction-limited and cannot be miniaturized. Our key design concept is the engineered anisotropy of the medium into which the evanescent wave extends thus allowing for skin depth engineering without any metallic components. In this article, we give an overview of our approach and compare it to key classes of photonic devices such as plasmonic waveguides, photonic crystal waveguides and slot waveguides. We show how our work can overcome a long standing issue in photonics nanoscale light confinement with fully transparent dielectric media.

A silicon nanocrystal embedded Nonlinear Slotted Photonic Crystal Waveguide (NSPhCW) is proposed to reduce the length of the nonlinear section required in a typical all-optical switching device. Phase-variation of a pulse due to the effect of self-phase modulation and cross-phase modulation has been calculated and analysed under slow-light regime using a modified Nonlinear Schrodinger Equation (NSEs). A 180-degree phase shift is observed in a sub-hundred micrometer length of the NSPhCW even without the effect of XPM. Also, the addition of a control signal increases the change in phase shift more drastically and a same phase shift is attained in a smaller length.

A high-speed compact silicon modulator based on the lateral capacitor configuration is experimentally demonstrated with low-power consumption and 3 dB modulation depth. The capacitor layout is introduced to scale down the total modulator capacitance to 30x10(-15) F, which effectively reduces the rf power consumption to 0.54 pJ/bit. Exploiting the slow group velocity of light in the slot photonic crystal waveguides, the device reported herein exhibits higher modulation efficiency than conventional capacitor modulator and provides a V(pi)L figure of merit of 0.18 Vcm at the wavelength of 1548 nm.

In an on-chip silicon-organic hybrid electro-optic (EO) modulator, the mode overlap with EO materials, in-device effective r33, and propagation loss are among the most critical factors that determine the performance of the modulator. Various waveguide structures have been proposed to optimize these factors, yet there is a lack of comprehensive consideration on all of them. In this Letter, a one-dimensional (1D) photonic crystal (PC) slot waveguide structure is proposed that takes all these factors into consideration. The proposed structure takes advantage of the strong mode confinement within a low-index region in a conventional slot waveguide and the slow-light enhancement from the 1D PC structure. Its simple geometry makes it robust to resist fabrication imperfections and helps reduce the propagation loss. Using it as a phase shifter in a Mach-Zehnder interferometer structure, an integrated silicon-organic hybrid EO modulator was experimentally demonstrated. The observed effective EO coefficient is as high as 490 pm/V. The measured half-wave voltage and length product is less than 1 V·cm and can be further improved. A potential bandwidth of 61 GHz can be achieved and further improved by tailoring the doping profile. The proposed structure offers a competitive novel phase-shifter design, which is simple, highly efficient, and with low optical loss, for on-chip silicon-organic hybrid EO modulators.

We experimentally demonstrate topological slow light waveguides in valley photonic crystals (VPhCs). We employed a bearded interface formed between two topologically-distinct VPhCs patterned in an air-bridged silicon slab. The interface supports both topological and non-topological slow light modes below the light line. By means of optical microscopy, we observed light propagation in the topological mode in the slow light regime with a group index ng over 30. Furthermore, we confirmed light transmission via the slow light mode even under the presence of sharp waveguide bends. In comparison between the topological and non-topological modes, we found that the topological mode exhibits much more efficient waveguiding than the trivial one, demonstrating topological protection in the slow light regime. This work paves the way for exploring topological slow-light devices compatible with existing photonics technologies.

Free-carrier absorption (FCA) has proven to be an important obstacle in the development of a silicon-based laser; however, FCA may serve as a potential advantage in active silicon-based switches or modulators. In this work, we present FCA modulation in slot waveguides with silicon nanocrystals (Si-ncs) embedded in SiO(2) as the low-index slot material. Slot waveguides were fabricated with and without Si-ncs, and the presence of Si-ncs was shown to increase the pump-induced FCA loss in the waveguides by a factor of 4.5. We modeled the Si-nc material using a four-level rate equation analysis to estimate the excited population of Si-ncs, allowing us to extract a value of 2.6 × 10(-17) cm(2) for the FCA cross section of the Si-nc material.

A silicon nitride horizontal slot waveguide with silicon dioxide cladding is designed to achieve flat negative dispersion (<; -600 ps/(nm · km)) over an octave-spanning bandwidth (782 to 2100 nm). Simulations show that, when a 10-fs pulse with 1-W peak power is input into a 5-cm long waveguide, the pulse width becomes 448 times wider and its peak power is reduced to 2.23×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> W. After passing through another ideal positive dispersion element, we find that the output pulse peak power can be recompressed close to 1 W in the case of different input pulse widths. Moreover, for the input pulse with a much higher peak power, the pulse width of the output pulse can be compressed to a much narrower level because of the spectral broadening introduced by optical nonlinearity. A 100-fs input pulse with 10-kW peak power can be compressed to 12.5 fs with a peak power of 63 kW. Considering the time-domain broadening and the peak power reduction, such a slot waveguide with a flat negative dispersion could be used as a time stretcher for 10-fs level pulse in on-chip chirped pulse amplification (CPA) system.

We report thorough investigations of photonic crystal waveguide properties in the slow light regime. The transmission and the group index near the cutoff wavelengths oscillate in phase in close analogy with the 1D photonic crystal behavior. The influence of having a finite number of periods in the photonic crystal waveguide is addressed to explain the spiky character of both the transmission and group index spectra. The profile of the slow-light modes is stretched out into the first and second rows of the holes closest to the waveguide channel. One of our strategies to ameliorate the design of photonic crystal devices is to engineer the radii of holes in these rows. A topology optimization approach is also utilized to make further improvements. The results of the numerical simulations and the optical characterization of fabricated devices such as straight waveguides with bends and couplers are presented. A nice match is found between theory and experiment.