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Recently, Integrated Microwave Photonics (IMWP) on Silicon-on-Insulator (SOI) platform has attracted much attention. SOI as a platform for passive devices has been studied for operation at a wavelength of 1.55 μm. It has been acknowledged that Si suffers from Two-Photon Absorption (TPA) at this wavelength, which potentially limits the dynamic range of microwave photonic links. The TPA effect diminishes at longer wavelengths, and completely vanishes at a wavelength of 2.2 μm. So far, the detailed effects of TPA on the performance of the SOI platform in the context of IMWP have not been well-explored. In this work, a systemic simulation has been performed in order to investigate the effects of nonlinear TPA on the performance of SOI microwave photonic links at 1.55 μm, particularly the dynamic range of the system was studied in-depth. Furthermore, system performance at wavelengths from 1.55 to 2.2 μm was investigated by scaling the device design, where the parasitic effects of TPA are avoided. Based on theoretical analysis, the result showing microwave photonic links at 2.2 μm outperform that at 1.55 μm was obtained as expected. Strip and rib waveguides at 1.55 μm show P1dB points of 3.75 mW and 69.54 mW, respectively, and at 2.2 μm, these waveguides performed linearly throughout the simulated range (up to 1 W of input power) which is due to the dramatically reduced TPA effect. It is noted that the wavelengths at which SOI avoids parasitic TPA match well with the working wavelengths of emerging GeSn lasers and photodetectors.

This theoretical modeling-and-simulation paper presents designs and projected performance of ∼1550-nm silicon-on-insulator beamsteering of a microwave phased array antenna by the use of true time delays. The tunable on-chip optical delay line is a cascade connection of waveguide Bragg grating resonators (WBGRs) separated by a piece of straight waveguide. The notch in the reflectivity spectrum is translated along the wavelength axis by means of a low-power TO heater stripe atop the grating, inducing a time delay that depends upon the line position of the WBGR affected by TO switching. The filter resonator is a new in-guide array of identical Bragg structures, each one comprising N closely coupled phase-shifted Bragg-grating resonators. The length of each grating cavity in an N group is chosen according to the Butterworth filter technique to provide one resonant spectral profile with 40 GHz optical bandwidth. Finally, we examined the performances of the beamformer system operating in the X and Ku bands, respectively. The investigation demonstrated that steering angles up to 48° are feasible by assuming a minimum steering angle of 8° and a minimum WBGR spacing of about 354 and 236 μ m for X and Ku bands, respectively.

We present Stimulated Brillouin Scattering (SBS) process in AlGaN integrated photonic waveguides. The wide bandgap of this III-Nitride material platform allows operating at visible wavelengths enabling large Stokes shifts. For this study, we employ a multiphysics approach that includes electric-photoelastic, magnetic-photoelastic, material interface displacement effects, and for optimal waveguide dimensions to find the Brillouin-active acoustic modes involved in the SBS process. The SBS power gain and the Stokes frequency shift are investigated for both backward and forward scattering processes, and it is shown that stokes shift larger than 50 GHz with high gain are achievable. Moreover, a parametric analysis is presented in order to demonstrate the possibility of realizing Brillouin lasers operating at blue wavelengths.

Spiral waveguides on a new germanium-on-silicon nitride (GON) platform with a wide transparency and a large core-clad index contrast for mid-infrared (mid-IR) sensing applications are demonstrated. Spiral waveguide sensors with a low bending loss on this platform enable compact sensors for mid-IR absorption spectroscopy. A minimum volumetric concentration of 5% isopropanol (IPA) in an IPA-acetone mixture is measured. This detection limit is three times lower than the counterpart waveguide, fabricated on the regular germanium-on-silicon platform with similar propagation loss at 3.73 μm wavelength. This silicon-compatible GON sensor is promising for applications such as environmental studies, industrial leak detection, process control, medical breath analysis, and many more. NRF (Natl Research Foundation, S’pore) Published version

Photonic data routing in optical networks overcomes the limitations of electronic routers with respect to data rate, latency, and energy consumption while suffering from dynamic power consumption, non-simultaneous usage of multiple wavelength channels, and large footprints. Here we show the first hybrid photonic-plasmonic, non-blocking, broadband 5x5 router. The compact footprint (70 Tbps, thus demonstrating key features required by future high data-throughput optical networks., 12 pages, 4 figures

GeSn lasers enable the monolithic integration of lasers on the Si platform using all-group-IV direct-bandgap material. The GeSn laser study recently moved from optical pumping into electrical injection. In this work, we present explorative investigations of GeSn heterostructure laser diodes with various layer thicknesses and material compositions. Cap layer material was studied by using Si 0.03 Ge 0.89 Sn 0.08 and Ge 0.95 Sn 0.05 , and cap layer total thickness was also compared. The 190 nm SiGeSn-cap device had threshold of 0.6 kA / cm 2 at 10 K and a maximum operating temperature ( T max ) of 100 K, compared to 1.4 kA / cm 2 and 50 K from 150 nm SiGeSn-cap device, respectively. Furthermore, the 220 nm GeSn-cap device had 10 K threshold at 2.4 kA / cm 2 and T max at 90 K, i.e., higher threshold and lower maximal operation temperature compared to the SiGeSn cap layer, indicating that enhanced electron confinement using SiGeSn can reduce the threshold considerably. The study of the active region material showed that device gain region using Ge 0.87 Sn 0.13 had a higher threshold and lower T max , compared to Ge 0.89 Sn 0.11 . The performance was affected by the metal absorption, free carrier absorption, and possibly defect density level. The maximum peak wavelength was measured as 2682 nm at 90 K by using Ge 0.87 Sn 0.13 in gain regions. The investigations provide directions to the future GeSn laser diode designs toward the full integration of group-IV photonics on a Si platform.

As one of major integrated microwave photonics (IMWP) platforms, Si photonics exhibits the intensity-dependent Kerr effect and two-photon absorption (TPA) with associated free carrier effects (FCE). At the commonly used 1.55 µm, TPA losses and the associated FCE would eventually limit the dynamic range of Si photonic links. Resonating structures such as ring resonators (RRs) experience enhanced nonlinear effects due to significant intensity buildup. According to the bandgap characteristics of Si, TPA can be eliminated at and beyond 2.2 µm. In this work, a systemic simulation of straight waveguides and RRs is performed at wavelengths from 1.55 to 2.2 µm where the wavelength-dependent TPA loss is investigated. Moreover, the Kerr effect leads to unwanted change of refractive index, which shifts the RR resonant wavelength at both 1.55 and 2.2 µm, thus needing shift compensation. Compensated RRs operating at 2.2 µm could open a new venue for Si photonics towards IMWP applications.

A Si-based monolithic laser is strongly desired for the full integration of Si-photonics. Lasing from the direct bandgap group-IV GeSn alloy has opened a new avenue, different from the hybrid III–V-on-Si integration approach. We demonstrated optically pumped GeSn lasers on Si with broad wavelength coverage from 2 to 3 μm. The GeSn alloys were grown using newly developed approaches with an industry standard chemical vapor deposition reactor and low-cost commercially available precursors. The achieved maximum Sn composition of 17.5% exceeded the generally acknowledged Sn incorporation limits found with similar deposition chemistries. The highest lasing temperature was measured as 180 K with the active layer thickness as thin as 260 nm. The unprecedented lasing performance is mainly due to the unique growth approaches, which offer high-quality epitaxial materials. The results reported in this work show a major advance toward Si-based mid-infrared laser sources for integrated photonics.

Designs and theoretical analysis are presented for a room temperature resonant-cavity-enhanced GeSn LED whose emission peaks at the 2 $\mu$m wavelength. The Ge/GeSn/Ge PIN hetero-diode of length 1 $\mu$m is embedded in a rib-type Ge-on-Si nanobeam having either 24 or 36 air holes. The maximum LED modulation bandwidth $f_{3\text{dB}}$ is proportional to the Purcell factor and is inversely proportional to $\tau _{s\,p0}$ the GeSn bulk spontaneous emission lifetime. For an emission linewidth of 200 nm and $\tau _{s\,p0}$ of 10 ns, an $f_{3\text{dB}}$ of 1.6 GHz is predicted.

Palladium germanide thin films were investigated for infrared plasmonic applications. Palladium thin films were deposited onto amorphous germanium thin films and subsequently annealed at a range of temperatures. X-ray diffraction was used to identify stoichiometry, and Scanning Electron Micrographs, along with Energy Dispersive Spectroscopy (EDS) was used to characterize composition and film quality. Resistivity was also measured for analysis. Complex permittivity spectra were measured from 0.3 to 15 µm using IR ellipsometry. From this, surface plasmon polariton (SPP) characteristics such as propagation length and mode confinement were calculated and used to determine appropriate spectral windows for plasmonic applications with respect to film characteristics. Films were evaluated for use with on-chip plasmonic components.

Using the strip-guided “manufacturable” SOI/GeSn group-IV integrated-photonics platform operating at 1550 nm, we propose an optical-to-electrical-to-optical (O-E-O) device that can work either as a...

We studied the design of SiGeSn/GeSn/SiGeSn multiple-quantum-well active regions and the gain threshold needed to achieve lasing. The enhancement of optical confinement factor was demonstrated by introducing a SiGeSn cap.

GeSn DHS and QW lasers and photoconductors have been investigated. For laser, the maximum operation temperature of 270 K and wavelength of 3.5 µm were achieved; for detector, spectral cut-off was measured at 3.6 µm.

The development of low-loss optical phase change materials (O-PCMs) promises to enable a plethora of nonvolatile integrated photonic applications. However, the relatively large optical constants change between different states of calls for a set of new design rationales. Here we report a non-perturbative design that enables low-loss device operation beyond the traditional figure-of-merit limit. The basic design rationale is to engineer the light propagation path through the OPCMs when it is in the low-loss amorphous state, and divert light away from the lossy crystalline state leveraging the large mode modification induced by the O-PCM phase transition. Following this approach, we demonstrate broadband photonic switches with significantly enhanced performances compared to current state-of-the-art.

The emerging SiGeSn heterostructure photonics technology has its roots in my early silicon-photonics results (1985-1991) and SiGeSn bandgap theory (1991). I shall review the real and potential applications of SiGeSn OE chips in the 2 to 5 micron range, monolithic chips hopefully for foundry manufacture.

The difference between transverse electric (TE) and transverse magnetic (TM) mode-effective indices in a wave-guided angled multimode interferometer structure is found to produce practical polarization splitting (PS) in the silicon-on-insulator platform at 1550 nm. Simulations show that this PS offers competitive performance in low insertion loss (0.4 dB for TE and 0.8 dB for TM), high extinction ratio (ER) (27.6 dB for TE and 26.5 dB for TM), low cross talk (−27.3 dB for TE and −28.0 dB for TM), and a 53-nm bandwidth for ER>20 dB. The compact footprint (∼25 μm2), the identical single-mode input/output waveguides for integration without altering the cross section, and the simplicity in implementation are prominent advantages compared with prior art designs.

Silicon-based optoelectronic devices have long been desired owing to the possibility of monolithic integration of photonics with high-speed Si electronics and the aspiration of broadening the reach of Si technology by expanding its functionalities well beyond electronics. To overcome the intrinsic problem of bandgap indirectness in the group-IV semiconductors such as Si and Ge, a new group-IV based material, GeSn alloy, has attracted increasing interests. The group-IV GeSn alloy has been demonstrated to become direct bandgap material with more than 8% Sn incorporation, which opens a new opportunity towards a Si-based light source with fully complementary metal-oxide-semiconductor (CMOS) compatibility. The GeSn laser contributes strongly to the progress of optoelectronic integration towards next-generation photonic integrated circuit on the Si platform, as it fills the deficiency of the efficient group-IV band-to-band lasers. Moreover, due to the tunable bandgap of GeSn, the lasing operation wavelength covers broad near- and mid-infrared range. Recently, the GeSn optically pumped lasers based on direct bandgap GeSn alloys have been demonstrated. In this work, the following aspects have been investigated: i) the novel growth strategy to obtain high Sn compositions based on spontaneous-relaxation-enhanced (SRE) Sn incorporation and the GeSn virtual substrate (VS) approaches. The maximum Sn composition of 22.3% was achieved; ii) the demonstration of GeSn optically pumped heterostructure lasers. The operation wavelength covers from 2 to 3 µm and the maximum lasing temperature is 265 K; iii) the demonstration of GeSn quantum well laser. The significantly reduced lasing threshold compared to heterostructure laser was achieved.

We present the first bistable 2 × 2 crossbar switches using dual suspended nanobeams with phase changing Ge2Sb2Se4Te1 (GSST) cladding material. The dual suspended nanobeam configuration gives a higher-temperature pulse that will efficiently change the phase of a nanoscale GSST cladding on each nanobeam cavity region. The compact resonant 2 × 2 Mach–Zehnder switch has stable cross and bar states corresponding to the amorphous and crystalline phases of the GSST, respectively. We have optimized the nanobeam design using 3D FDTD and have made detailed numerical simulations that predict low insertion loss and low crosstalk with ∼100 GHz bandwidth. Finally, the application of this device to N x N x Mλ wavelength cross-connect switching is presented. The unique integration of switch design elements presented in this paper enables, for the first time, the combination of nonvolatile resonant behavior, low switching power, low insertion loss and crosstalk, wide bandwidth, and fast switching times, for WDM switching applications.

Germanium-tin (GeSn) films with Sn compositions from 5% to 11% were grown on Ge-buffered Si using a reduced pressure chemical vapor deposition system with low-cost SnCl4 and GeH4 precursors. Material characterization showed that relaxed GeSn layers with thicknesses ranging from 400 nm to 1 μm were achieved. The strong photoluminescence (PL) intensity and the low defect density indicated very high material quality. In addition, temperature-dependent 10–300 K photoluminescence spectra showed that, due to strain relaxation of the material, the emission wavelength is longer than that of strained GeSn thin film samples (t < 200 nm) having the same Sn composition. At 300 K, the PL peak at 2520 nm was observed from the sample with a 1-μm-thick GeSn layer and 11% Sn composition.

We demonstrate accurate control of mode symmetry in suspended dual-nanobeam resonators on a silicon-on-insulator chip. Each nanobeam consists of a Fabry–Perot nanocavity bounded by tapered 1-D photonic crystals. Even and odd cavity-modes are formed due to lateral evanescent coupling between the two nanobeams. The odd cavity-mode can be excited by mode-symmetry-transforming Mach–Zehnder couplers. Modal contrasts over 27 dB are measured in fabricated structures. The influence of the optical field in the middle air slot on the background transmission and quality factors is discussed. The observed peak wavelength separations of the modes at various nanobeam spacings are in good agreement with simulation results. These nanobeam resonators are potentially useful in applications, such as ultrafast all-optical modulation, filtering, and switching.

Buffer-free GeSn and SiGeSn films have been deposited on Si via a cold-wall, ultra-high vacuum chemical vapor deposition reactor using in situ gas mixing of deuterated stannane, silane and germane. Material characterization of the films using x-ray diffraction and transmission electron microscopy shows crystalline growth with an array of misfit dislocation formed at the Si substrate interface. Energy dispersive x-ray maps attained from the samples show uniform incorporation of the elements. The Z-contrast map of the high-angle annular dark-field of the film cross section shows uniform incorporation along the growth as well. Optical characterization of the GeSn films through photoluminescence technique shows reduction in the bandgap edge of the materials.

In this theoretical work, we design elemental and higher-order wavelength-division-multiplexed cross-connects (WXCs): nonblocking space-and-wavelength routing switches to be constructed in a monolithic, industry-standard, silicon-on-insulator (SOI) chip operating at a center wavelength of 1550 nm. Each multi-spectral multi-crossbar 2×2 x Mλ “element” of the network switch is an M-fold cascade connection of λ-diverse SOI Mach-Zehnder interferometers (MZIs), each of which utilizes a nanobeam cavity in each MZI arm. Within the element, each MZI has an electro-optically (EO) controlled local PN-junction “depleter” embedded in each cavity. The cavity voltage commands are (0,0) or (V,V) where V is a “small” reverse bias. Each element can be reconfigured in 2 to 5 ps, depending on Q, with few-fJ/bit switching energy. For the M = 3 case, a compact 6-element 4×4×3λ WXC is presented. In addition, compact new designs are given for a 12-element 8×8×3λ WXC and for 16×16×8λ WXCs employing either 56 or 72 elements.

Monolithic lasers on Si have long been anticipated as an enabler of full photonic integration, and significant progress in GeSn material development shows promise for such laser devices. While there are many reports focused on optically pumped lasers, in this work, we demonstrate electrically injected GeSn lasers on Si. We grew a GeSn/SiGeSn heterostructure diode on a Si substrate in a ridge waveguide laser device and tested it under pulsed conditions, giving consideration to the structure design to enhance the carrier and optical confinement. The peak linewidth of 0.13 nm (0.06 meV) and injection current curves indicated lasing, which was observed up to 100 K with emission peaks at 2300 nm. We recorded a threshold of 598 A / c m 2 at 10 K. The peak power and external quantum efficiency were 2.7 mW/facet and 0.3%, respectively. The results indicate advances for group-IV-based lasers, which could serve as a promising route for laser integration on Si.

We report an investigation of a planar GeSn p–i–n diode for a high-detectivity photodetector based on an undoped GeSn film. By fabricating n- and p-type regions on the plane of the GeSn film using the complementary metal–oxide–semiconductor technology of ion implantation, a low dark current density is revealed and attributed to the low defect density of the film and current flow suppression around the diode periphery. This yields a specific 1550-nm detectivity of ∼1010 cm Hz1/2 W−1, an order of magnitude higher than that of conventional vertical GeSn-based diodes and comparable to that of commercially available Ge-based diodes. This work provides an alternative approach for achieving a high-detectivity GeSn photodetector that may facilitate its potential applications.

The 2 µm wavelength band has recently gained increased attention for potential applications in next-generation optical communication. However, it is still challenging to achieve effective photodetection in the 2 µm wavelength band using group-IV-based semiconductors. Here we present an investigation of GeSn resonant-cavity-enhanced photodetectors (RCEPDs) on silicon-on-insulator substrates for efficient photodetection in the 2 µm wavelength band. Narrow-bandgap GeSn alloys are used as the active layer to extend the photodetection range to cover the 2 µm wavelength band, and the optical responsivity is significantly enhanced by the resonant cavity effect as compared to a reference GeSn photodetector. Temperature-dependent experiments demonstrate that the GeSn RCEPDs can have a wider photodetection range and higher responsivity in the 2 µm wavelength band at higher temperatures because of the bandgap shrinkage. These results suggest that our GeSn RCEPDs are promising for complementary metal-oxide-semiconductor-compatible, efficient, uncooled optical receivers in the 2 µm wavelength band for a wide range of applications.

The design, modeling, micro-fabrication, and characterization of an ultra-broadband Ge-on-Si waveguide polarization rotator are presented. The polarization rotator is based on the mode evolution approach where adiabatic symmetric and anti-symmetric tapers are utilized to convert from the fundamental transverse magnetic to electric mode. The device is shown to be extremely fabrication tolerant and simple to fabricate. The fabricated devices demonstrate a polarization extinction ratio of ≥15 dB over a 2 μm bandwidth (9–11 μm wavelength) with an average insertion loss of

The recent demonstration of the GeSn laser opened a promising route towards the monolithic integration of light sources on the Si platform. A GeSn laser with higher Sn content is highly desirable to enhance the emission efficiency and to cover longer wavelength. This Letter reports optically pumped edge-emitting GeSn lasers operating at 3 μm, whose device structure featured Sn compositionally graded with a maximum Sn content of 22.3%. By using a 1950-nm laser pumping in comparison with a 1064-nm pumping, the local heating and quantum defect were effectively reduced, which improved laser performance in terms of higher maximum lasing temperature and lower threshold.

Energy-efficient tunability is highly desired for silicon photonic devices. We demonstrate a thermo-optic tunable filter with an ultra-high tuning efficiency based on a suspended photonic crystal nanobeam cavity. Attributed to the ultra-small mode volume and free-standing waveguide structure, a tuning efficiency of 21 nm/mW is achieved over a wide single-resonance tuning range of ∼43.9 nm. The 10%-90% switching times are 67.0 μs and 68.8 μs for the rising edge and the falling edge, respectively. The demonstrated energy-efficient tunable device can find applications in reconfigurable photonic integrated circuits.

This theoretical modeling-and-simulation paper presents designs and projected performance of ~1500-nm silicon-on-insulator 2 x 2 Mach-Zehnder interferometer (MZI) optical crossbar switches and tunable filters that are actuated by thermo-optical (TO) means. A TO heater stripe is assumed to be on the top of each waveguided arm in the interferometer. Each strip-waveguide arm contains an inline set of N-fold coupled, phase-shifted Bragg-grating resonators. To implement accurate and realistic designs, a mixed full-vectorial mathematical model based upon the finite-element, coupled-mode, and transfer-matrix approaches was employed. The Butterworth-filter technique for grating length and weighting was used. The resulting narrowband waveguide-transmission spectral shape was better-than-Lorentzian because of its steeper sidewalls (faster rolloff). The metrics of crossbar switching, insertion loss (IL) and crosstalk (CT), were evaluated for choices of grating strength and TO-induced change in the grating-waveguide refractive index. The predicted ILs and CTs were quite superior to those cited in the literature for experimental and theoretical MZI devices based upon silicon nanobeam resonators. This was true for the Type-I and Type-II resonator addressing discussed here. Finally, we examined the TO-tunable composite filter profiles that are feasible by connecting two or more Type-I MZIs in an optical series arrangement. A variety of narrow filter shapes, tunable over ~2 nm, was found.

Responsivity of Ge/GeSn/Ge a heterostructure photodiode was measured and compared to a theoretical model. The responsivity of the device was found to decrease with increasing power from a pulsed laser, and the responsivity showed a peak at 1600 nm.

Nowadays, Quantum Photonics finds a number of significant applications, such as Quantum Computing [1] and Quantum Communication [2]. Silicon on Insulator (SOI) technology has proven its potential for the generation of correlated photon pairs through the spontaneous four wave mixing (SFWM) effect [3-4], but not in the visible wavelength range. In this invited paper we present the physical investigation and design guidelines of AlGaN microring resonators for generating photon entanglement, as induced by SFWM in the visible. The work theoretically demonstrates the possibility of realizing the on-chip generation of correlated pairs of photons within integrated microring resonators based on the AlGaN/AlN technological platform, due to its wide bandgap, crystalline structure and low losses [5]. Furthermore, general physical features are presented by means of a parametric analysis of the biphoton flux and cross correlation as a function of the device parameters, i.e. ring radius, resonator cross section and sizes, pulley coupling. Moreover, the spectral features of the generated signal and idler photons have been analyzed as a function of the pump resonance mismatch for several Kerr coefficients and input visible “blue” pump powers. Cross correlation values around 2.3 ×104 at a biphoton flux of about 9×104 pairs/s and 2×103 at about 2.9×106 pairs/s for ring radius of 200 μm and 30 μm have been achieved, respectively, assuming a input pump power of 25 mW, while the signal is generated at wavelength of 369.5 nm and idler at 535.72 nm, for ring radius of 200 μm, and 369.5 and 457.45 nm for ring radius of 30 μm, respectively. These devices can be important for many applications, going from UV-visible spectroscopy to quantum sensing to image processing to nonlinear optics.

The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonics devices with low power consumption, such as optical switches and routers, reconfigurable meta-optics, displays, and photonic memories. However, conventional O-PCMs, such as VO2 and Ge2Sb2Te5, are inherently plagued by their excessive optical losses even in dielectric states, limiting their optical performance and hence application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel photonic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to LWIR. Capitalizing on the dramatically-enhanced optical performance, novel non-volatile, reconfigurable on-chip photonics devices and architectures are demonstrated. GSST-integrated Si photonics based on the material innovation and novel “non-perturbative” designs exhibit significantly improved switching performance over state-of-the-art GST-based approaches. The technology is further scalable to realize non-blocking matrix switches with arbitrary network complexity, paving the path towards high performance reconfigurable photonics chips.

Optical properties of germanium tin (Ge1−x Sn x ) alloys have been comprehensively studied with Sn compositions from 0 (Ge) to 12%. Raman spectra of the GeSn samples with various Sn compositions were measured. The room temperature photoluminescence (PL) spectra show a gradual shift of emission peaks towards longer wavelength as Sn composition increases. Temperature dependent PL shows the PL intensity variation along with the temperature change, which reveals the indirectness or directness of the bandgap of the material. As temperature decreases, the PL intensity decreases with Sn composition less than 8%, indicating the indirect bandgap Ge1−x Sn x ; while the PL intensity increases with Sn composition higher than 10%, implying the direct bandgap Ge1−x Sn x . Moreover, the PL study of n-doped samples shows bandgap narrowing compared to the unintentionally (Boron) doped thin film with similar Sn compositions due to the doping.

This paper reports theoretical designs and simulations of electrooptical 2 × 2 switches and 1 × 1 loss modulators based upon GST-embedded SOI channel waveguides. It is assumed that the amorphous and crystalline phases of GST can be triggered electrically by Joule heating current applied to a 10-nm GST film sandwiched between doped-Si waveguide strips. TEo and TMo mode effective indices are calculated over 1.3 to 2.1-μm wavelength range. For 2 × 2 Mach–Zehnder and directional coupler switches, low insertion loss, low crosstalk, and short device lengths are predicted for 2.1 μm, although a decreased performance is projected for 1.55 μm. For 1.3–2.1 μm, the 1 × 1 EO waveguide has application as a variable optical attenuator and as a digital modulator, albeit with ≦100-ns state-transition time. Because the active material has two “stable” phases, the device holds itself in either state, and voltage needs to be applied only during transition.

Two fundamental principles of the mode-matching method-mode orthogonality and tangential field continuity conditions have been revisited in depth. With a finite number of modes employed in the conventional method, the tangential field continuity condition at the waveguide-discontinuity interface fails leading to a field mismatch error. We propose an alternate, superior mode-matching method implemented by reconstruction of the auxiliary coefficient matrix, rather than by applying the abovementioned continuity and orthogonality. Detailed transfer-matrix equations have been derived for the finite-mode-number case. We showed that the improved mode-matching method yields a smaller field mismatch error under equal computational effort. Examples of bent and faceted waveguide structure have been investigated and the numerical simulation results demonstrated that the newly proposed method has the merits of simple implementation, high accuracy, and high computational efficiency for application in high-index-contrast photonic integrated circuits.

In this Letter, we propose a broadband, nonvolatile on-chip switch design in the telecommunication C-band with record low loss and crosstalk. The unprecedented device performance builds on: 1) a new optical phase change material (O-PCM) Ge2Sb2Se4Te1 (GSST), which exhibits significantly reduced optical attenuation compared to traditional O-PCMs, and 2) a nonperturbative design that enables low-loss device operation beyond the classical figure-of-merit (FOM) limit. We further demonstrate that the 1-by-2 and 2-by-2 switches can serve as basic building blocks to construct nonblocking and nonvolatile on-chip switching fabric supporting arbitrary numbers of input and output ports.

This theoretical modeling and simulation paper presents design and projected performance of an on-chip thermo-optical multi Sagnac loop Mach–Zehnder interferometer (MZI), operating at C-band and 3300 nm for silicon-on-insulator and germanium-on-silicon technological platforms, respectively. The MZI arms are comprised of an N -cascaded connection of Sagnac loop reflectors, each pair separated by a waveguide whose length is designed according to the wavelength-channel spacing requirements. N is chosen according to the Butterworth filter technique to provide one spectral response having maximal flatness within the desired bandwidth. Switched, spatial routing of odd and even channels is achieved by shifting the Through and Drop MZI spectra along the wavelength axis by means of a low-power thermo-optical heater stripe atop each loop-connector that changes its effective refractive index appropriately. We examined the SOI device performance for wavelength-division multiplexed wavelength (de)interleving. The analysis predicted good performance in terms of bandwidth, insertion loss, and channel isolation for 200, 50, and 25 GHz channel spacing. For the Ge-on-Si Sagnac MZI operating in the mid infrared, we showed that a comb filter is feasible whose lines exactly match the spectral signature of methane for trace-gas sensing applications.

We demonstrate an ultra-compact silicon polarization beam splitter with a coupling length of 0.768 μm. Lower than 2-dB insertion losses and over 10-dB extinction ratios are achieved over a wavelength range of 60 nm.

The characteristics Ge0.89Sn0.11 photodiodes were systematically investigated. A cutoff wavelength of 2.65 μm at 300 K and the peak detectivity of 4.3×109 Jones at 77 K were achieved. An infrared imaging of an object was demonstrated using the single Ge0.89Sn0.11 photodiode.

This theoretical modeling and simulation paper presents designs and projected performance of an on-chip digital Fourier transform spectrometer using a thermo-optical (TO) Michelson grating interferometer operating at ∼1550 and 2000 nm for silicon-on-insulator and for germanium-on-silicon technological platforms, respectively. The Michelson interferometer arms consist of two unbalanced tunable optical delay lines operating in the reflection mode. They are comprised of a cascade connection of waveguide Bragg grating resonators (WBGRs) separated by a piece of straight waveguide with lengths designed according to the spectrometer resolution requirements. The length of each WBGR is chosen according to the Butterworth filter technique to provide one resonant spectral profile with a bandwidth twice that of the spectrometer bandwidth. A selectable optical path difference (OPD) between the arms is obtained by shifting the notch in the reflectivity spectrum along the wavelength axis by means of a low-power TO heater stripe atop the WBGR, inducing an OPD that depends on the line position of the WBGR affected by TO switching. We examined the device performances in terms of signal recostruction in the radio-frequency (RF) spectrum analysis application at 1 GHz and at 1.5 GHz of spectrometer resolution. The investigation demonstrated that high-quality spectrum reconstruction is obtained for both Lorentzian and arbitrary input signals with a bandwidth up to 40 GHz. We also show that spectrum reconstruction of 100–200 GHz RF band input signals is feasible in the Ge-on-Si chips.

We presented optically pumped edge-emitting GeSn laser with 22.3% world-record maximum Sn content and 3 μm emission wavelength. Lasing threshold of 139 kW/cm2 at 77 K and maximum operating temperature of 150 K were achieved.

We experimentally demonstrate a two-bit thermal-optic ripple-carry full adder based on microdisk resonators in silicon photonics with the advantages of large bandwidth, low power consumption, and high scalability, paving the way to future optical computing.

We report on a three-waveguide electro-optic switch for compact photonic integrated circuits and data routing applications. The device features a plasmonic metal-oxide-semiconductor (MOS) mode for enhanced light-matter-interactions. The switching mechanism originates from a capacitor-like design where the refractive index of the active medium, indium-tin-oxide, is altered via shifting the plasma frequency due to carrier accumulation inside the waveguide-based MOS structure. This light manipulation mechanism controls the transmission direction of transverse magnetic polarized light into either a CROSS or BAR waveguide port. The extinction ratio of 18 (7) dB for the CROSS (BAR) state, respectively, is achieved via a gating voltage bias. The ultrafast broadband fJ/bit device allows for seamless integration with silicon-on-insulator platforms for low-cost manufacturing.

Germanium is becoming an important material for mid-infrared photonics, but the modulation mechanisms in Ge are not yet well understood. In this paper, we estimate the size of free-carrier electroabsorption and electrorefraction effects in germanium across the 2 to 16-μm wavelength range at 300 K. The predictions are based as much as possible upon experimental absorption data from the literature and are supported by extrapolations from experimental data using first-principle quantum theoretical modeling. We find that free-carrier absorption is substantially stronger in Ge than in Si.

Normal-incidence Ge1-xSnx photodiode detectors with Sn compositions of 7 and 10% have been demonstrated. Such detectors were based on Ge/Ge1-xSnx/Ge double heterostructures grown directly on a Si substrate via a chemical vapor deposition system. A temperature-dependence study of these detectors was conducted using both electrical and optical characterizations from 300 to 77 K. Spectral response up to 2.6 µm was achieved for a 10% Sn device at room temperature. The peak responsivity and specific detectivity (D*) were measured to be 0.3 A/W and 4 × 109 cmHz1/2W−1 at 1.55 µm, respectively. The spectral D* of a 7% Sn device at 77 K was only one order-of-magnitude lower than that of an extended-InGaAs photodiode operating in the same wavelength range, indicating the promising future of GeSn-based photodetectors.

We present a physical investigation on the generation of correlated photon pairs that are broadly spaced in the ultraviolet (UV) and visible spectrum on a AlGaN/AlN integrated photonic platform which is optically transparent at these wavelengths. Using spontaneous four wave mixing (SFWM) in an AlGaN microring resonator, we show design techniques to satisfy the phase matching condition between the optical pump, the signal, and idler photon pairs, a condition which is essential and is a key hurdle when operating at short wavelength due to the strong normal dispersion of the material. Such UV-visible photon pairs are quite beneficial for interaction with qubit ions that are mostly in this wavelength range, and will enable heralding the photon-ion interaction. As a target application example, we present the systematic AlGaN microresonator design for generating signal and idler photon pairs using a blue wavelength pump, while the signal appears at the transition of ytterbium ion (171Yb+, 369.5 nm) and the idler appears in the far blue or green range. The photon pairs have minimal crosstalk to the pump power due to their broad spacing in spectral wavelength, thereby relaxing the design of on-chip integrated filters for separating pump, signal and idler.

This paper reviews recent experimental and theoretical progress on 2 × 2 crossbar switches that operate within a narrow band of wavelengths (Δλ ∼ 0.5 nm) in a manner similar to that of 4-port reconfigurable add-drop multiplexers (ROADMs). The waveguided integrated-photonic devices discussed here can be actuated by thermo-optic (TO) or electro-optic (EO) means, the latter offering ultralow switching energy of 1 fJ/bit or less. The main switch architectures are the Mach-Zehnder interferometer (MZI) and the 2-waveguide (WG) contra-directional coupler with asymmetric WGs. Our 2 × 2 MZI's employ a pair of 1D photonic-crystal connecting arms — WGs with airhole or Bragg-grating lattices. Those WGs are (1) nanobeams that provide transmission over a Lorentzian resonance profile or (2) bandedge slow-light (SL) grating-WGs that give a step-like T/R spectrum with reflection at wavelengths below the edge and transmission above the edge. The grating-assisted asymmetric contra-directional coupler (ACDC) is resonant at the phase-matching wavelength between its two super modes. Reflection into the input is avoided using a A/4 phase shifting segment between two grating sections. This ACDC sends a reflected wave instead into the drop port. We discuss two NB devices, one SL device and three ACDC devices. In each case, the TO- or EO-induced wavelength shift of the resonance or step is Δλ s ∼ 0.8-nm, obtained by engineering the lattice and mode parameters. Our 2 × 2 s have great potential for creating N × N fabrics in WDM systems.